@article{AdelsbergerBivigouKoumbaMiasnikovaetal.2015, author = {Adelsberger, Joseph and Bivigou Koumba, Achille Mayelle and Miasnikova, Anna and Busch, Peter and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Polystyrene-block-poly (methoxy diethylene glycol acrylate)-block-polystyrene triblock copolymers in aqueous solution-a SANS study of the temperature-induced switching behavior}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {293}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {5}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-015-3535-6}, pages = {1515 -- 1523}, year = {2015}, abstract = {A concentrated solution of a symmetric triblock copolymer with a thermoresponsive poly(methoxy diethylene glycol acrylate) (PMDEGA) middle block and short hydrophobic, fully deuterated polystyrene end blocks is investigated in D2O where it undergoes a lower critical solution temperature-type phase transition at ca. 36 A degrees C. Small-angle neutron scattering (SANS) in a wide temperature range (15-50 A degrees C) is used to characterize the size and inner structure of the micelles as well as the correlation between the micelles and the formation of aggregates by the micelles above the cloud point (CP). A model featuring spherical core-shell micelles, which are correlated by a hard-sphere potential or a sticky hard-sphere potential together with a Guinier form factor describing aggregates formed by the micelles above the CP, fits the SANS curves well in the entire temperature range. The thickness of the thermoresponsive micellar PMDEGA shell as well as the hard-sphere radius increase slightly already below the cloud point. Whereas the thickness of the thermoresponsive micellar shell hardly shrinks when heating through the CP and up to 50 A degrees C, the hard-sphere radius decreases within 3.5 K at the CP. The volume fraction decreases already significantly below the CP, which may be at the origin of the previously observed gel-sol transition far below the CP (Miasnikova et al., Langmuir 28: 4479-4490, 2012). Above the CP, small, and at higher temperatures, large aggregates are formed by the micelles.}, language = {en} } @article{AdelsbergerGrilloKulkarnietal.2013, author = {Adelsberger, Joseph and Grillo, Isabelle and Kulkarni, Amit and Sharp, Melissa and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Kinetics of aggregation in micellar solutions of thermoresponsive triblock copolymers - influence of concentration, start and target temperatures}, series = {Soft matter}, volume = {9}, journal = {Soft matter}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm27152d}, pages = {1685 -- 1699}, year = {2013}, abstract = {In aqueous solution, symmetric triblock copolymers with a thermoresponsive middle block and hydrophobic end blocks form flower-like core-shell micelles which collapse and aggregate upon heating through the cloud point (CP). The collapse of the micellar shell and the intermicellar aggregation are followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while heating micellar solutions of a poly((styrene-d(8))-b-(N-isopropyl acrylamide)-b-(styrene-d(8))) triblock copolymer in D2O rapidly through their CP. The influence of polymer concentration as well as of the start and target temperatures is addressed. In all cases, the micellar collapse is very fast. The collapsed micelles immediately form small clusters which contain voids. They densify which slows down or even stops their growth. For low concentrations and target temperatures just above the CP, i.e. shallow temperature jumps, the subsequent growth of the clusters is described by diffusion-limited aggregation. In contrast, for higher concentrations and/or higher target temperatures, i.e. deep temperature jumps, intermicellar bridges dominate the growth. Eventually, in all cases, the clusters coagulate which results in macroscopic phase separation. For shallow temperature jumps, the cluster surfaces stay rough; whereas for deep temperature jumps, a concentration gradient develops at late stages. These results are important for the development of conditions for thermal switching in applications, e.g. for the use of thermoresponsive micellar systems for transport and delivery purposes.}, language = {en} } @article{AdelsbergerKulkarniJainetal.2010, author = {Adelsberger, Joseph and Kulkarni, Amit and Jain, Abhinav and Wang, Weinan and Bivigou Koumba, Achille Mayelle and Busch, Peter and Pipich, Vitaliy and Holderer, Olaf and Hellweg, Thomas and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Thermoresponsive PS-b-PNIPAM-b-PS micelles : aggregation behavior, segmental dynamics, and thermal response}, issn = {0024-9297}, doi = {10.1021/Ma902714p}, year = {2010}, abstract = {We have studied I lie thermal behavior of amphiphilic, symmetric triblock copolymers having short, deuterated polystyrene (PS) end blocks and a large poly(N-isopropylacrylarnicle) (PNIPAM) middle block exhibiting a lower critical solution temperature (LCST) in aqueous solution. A wide range of concentrations (0.1-300 mg/mL) is investigated using it number of analytical methods such as fluorescence correlation spectroscopy (FCS), turbidimetry, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and neutron spin-echo spectroscopy (NSE). The critical micelle concentration is determined using FCS to be 1 mu M or less. The collapse of the micelles at the LCST is investigated using turbidimetry and DLS and shows a weak dependence on the degree of polymerization of the PNIPAM block. SANS with contrast matching allows its to reveal the core-shell Structure of the micelles as well as their correlation as a function of temperature. The segmental dynamics of the PNIPAM shell are studied as a function of temperature and arc found to be faster in the collapsed state than in the swollen state. The mode detected has a linear dispersion in q(2) and is found to be faster in the collapsed state as compared to the swollen state. We attribute this result to the averaging over mobile and immobilized segments.}, language = {en} } @article{AdelsbergerMeierKollBivigouKoumbaetal.2011, author = {Adelsberger, Joseph and Meier-Koll, Andreas and Bivigou Koumba, Achille Mayelle and Busch, Peter and Holderer, Olaf and Hellweg, Thomas and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {The collapse transition and the segmental dynamics in concentrated micellar solutions of P(S-b-NIPAM) diblock copolymers}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {289}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {5-6}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-011-2382-3}, pages = {711 -- 720}, year = {2011}, abstract = {We investigate concentrated solutions of poly(styrene-b-N-isopropyl acrylamide) (P(S-b-NIPAM)) diblock copolymers in deuterated water (D2O). Both structural changes and the changes of the segmental dynamics occurring upon heating through the lower critical solution temperature (LCST) of PNIPAM are studied using small-angle neutron scattering and neutron spin-echo spectroscopy. The collapse of the micellar shell and the cluster formation of collapsed micelles at the LCST as well as an increase of the segmental diffusion coefficient after crossing the LCST are detected. Comparing to our recent results on a triblock copolymer P(S-b-NIPAM-b-S) [25], we observe that the collapse transition of P(S-b-NIPAM) is more complex and that the PNIPAM segmental dynamics are faster than in P(S-b-NIPAM-b-S).}, language = {en} } @article{AdelsbergerMetwalliDiethertetal.2012, author = {Adelsberger, Joseph and Metwalli, Ezzeldin and Diethert, Alexander and Grillo, Isabelle and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Kinetics of collapse transition and cluster formation in a thermoresponsive micellar solution of P(S-b-NIPAM-b-S) induced by a temperature jump}, series = {Macromolecular rapid communications}, volume = {33}, journal = {Macromolecular rapid communications}, number = {3}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {1022-1336}, doi = {10.1002/marc.201100631}, pages = {254 -- 259}, year = {2012}, abstract = {Structural changes at the intra- as well as intermicellar level were induced by the LCST-type collapse transition of poly(N-isopropyl acrylamide) in ABA triblock copolymer micelles in water. The distinct process kinetics was followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while a micellar solution of a triblock copolymer, consisting of two short deuterated polystyrene endblocks and a long thermoresponsive poly(N-isopropyl acrylamide) middle block, was heated rapidly above its cloud point. A very fast collapse together with a multistep aggregation behavior is observed. The findings of the transition occurring at several size and time levels may have implications for the design and application of such thermoresponsive self-assembled systems.}, language = {en} } @article{BivigouKoumbaGoernitzLaschewskyetal.2010, author = {Bivigou Koumba, Achille Mayelle and Goernitz, Eckhard and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N- isopropylacrylamide) : synthesis, self-organization, and hydrogel formation}, issn = {0303-402X}, doi = {10.1007/s00396-009-2179-9}, year = {2010}, abstract = {Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30-35 wt.\%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 A degrees C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations.}, language = {en} } @article{BivigouKoumbaKristenLaschewskyetal.2009, author = {Bivigou Koumba, Achille Mayelle and Kristen, Juliane and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Synthesis of symmetrical triblock copolymers of styrene and N-isopropylacrylamide using bifunctional bis(trithiocarbonate)s as RAFT agents}, issn = {1022-1352}, doi = {10.1002/macp.200800575}, year = {2009}, abstract = {Six new bifunctional bis(trithiocarbonate)s were explored as RAFT agents for synthesizing amphiphilic triblock copolymers ABA and BAB, with hydrophilic "A" blocks made from N-isopropylacrylamide and hydrophobic "B" blocks made from styrene. Whereas the extension of poly(N-isopropylacrylamide) by styrene was not effective, polystyrene macroRAFT agents provided the block copolymers efficiently. End group analysis by H-1 NMR spectroscopy supported molar mass analysis and revealed an unexpected side reaction for certain bis(trithiocarbonate)s, namely a fragmentation to simple trithiocarbonates while extruding ethylene-trithiocarbonate. The amphiphilic block copolymers with short polystyrene blocks are directly soluble in water and self-organize into thermo-responsive micellar aggregates.}, language = {en} } @article{GeigerReitenbachHenscheletal.2021, author = {Geiger, Christina and Reitenbach, Julija and Henschel, Cristiane and Kreuzer, Lucas and Widmann, Tobias and Wang, Peixi and Mangiapia, Gaetano and Moulin, Jean-Fran{\c{c}}ois and Papadakis, Christine M. and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter}, title = {Ternary nanoswitches realized with multiresponsive PMMA-b-PNIPMAM films in mixed water/acetone vapor atmospheres}, series = {Advanced engineering materials}, volume = {23}, journal = {Advanced engineering materials}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1438-1656}, doi = {10.1002/adem.202100191}, pages = {12}, year = {2021}, abstract = {To systematically add functionality to nanoscale polymer switches, an understanding of their responsive behavior is crucial. Herein, solvent vapor stimuli are applied to thin films of a diblock copolymer consisting of a short poly(methyl methacrylate) (PMMA) block and a long poly(N-isopropylmethacrylamide) (PNIPMAM) block for realizing ternary nanoswitches. Three significantly distinct film states are successfully implemented by the combination of amphiphilicity and co-nonsolvency effect. The exposure of the thin films to nitrogen, pure water vapor, and mixed water/acetone (90 vol\%/10 vol\%) vapor switches the films from a dried to a hydrated (solvated and swollen) and a water/acetone-exchanged (solvated and contracted) equilibrium state. These three states have distinctly different film thicknesses and solvent contents, which act as switch positions "off," "on," and "standby." For understanding the switching process, time-of-flight neutron reflectometry (ToF-NR) and spectral reflectance (SR) studies of the swelling and dehydration process are complemented by information on the local solvation of functional groups probed with Fourier-transform infrared (FTIR) spectroscopy. An accelerated responsive behavior beyond a minimum hydration/solvation level is attributed to the fast build-up and depletion of the hydration shell of PNIPMAM, caused by its hydrophobic moieties promoting a cooperative hydration character.}, language = {en} } @article{HarmsRaetzkeFaupeletal.2010, author = {Harms, Stephan and Raetzke, Klaus and Faupel, Franz and Egger, Werner and Ravello, Lori Boyd de and Laschewsky, Andr{\´e} and Wang, Weinan and M{\"u}ller-Buschbaum, Peter}, title = {Free volume and swelling in thin films of poly(n-isopropylacrylamide) end-capped with n-butyltrithiocarbonate}, issn = {1022-1336}, doi = {10.1002/marc.201000067}, year = {2010}, abstract = {The free volume in thin films of poly(N-isopropylacrylamid) end-capped with n-butyltrio-carbonate (nbc-PNIPAM) is probed with positron annihilation lifetime spectroscopy (PALS). The PALS measurements are performed as function of energy to obtain depth profiles of the free volume of nbc-PNIPAM films. The range of nbc-PNIPAM films with thicknesses from 40 to 200 nm is focused. With decreasing film thickness the free volume increases in good agreement with an increase in the maximum swelling capability of the nbc-PNIPAM films. Thus in thin hydrogel films the sorption and swelling behavior is governed by free volume.}, language = {en} } @article{HildebrandLaschewskyPaechetal.2017, author = {Hildebrand, Viet and Laschewsky, Andre and P{\"a}ch, Michael and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)}, series = {Polymer Chemistry}, volume = {8}, journal = {Polymer Chemistry}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1759-9954}, doi = {10.1039/c6py01220e}, pages = {310 -- 322}, year = {2017}, abstract = {A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents of the zwitterionic group. Radical polymerisation via the RAFT (reversible addition-fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and was well controlled, yielding polymers with predictable molar masses. Molar mass analysis and control of the end-group fidelity were facilitated by end-group labeling with a fluorescent dye. The polymers showed distinct thermo-responsive behaviour of the UCST (upper critical solution temperature) type in an aqueous solution, which could not be simply correlated to their molecular structure via an incremental analysis of the hydrophilic and hydrophobic elements incorporated within them. Increasing the spacer length separating the ammonium and the sulfonate groups of the zwitterion moiety from three to four carbons increased the phase transition temperatures markedly, whereas increasing the length of the spacer separating the ammonium group and the carboxylate ester group on the backbone from two to three carbons provoked the opposite effect. Moreover, the phase transition temperatures of the analogous polyzwitterions decreased in the order dimethylammonio > morpholinio > piperidinio alkanesulfonates. In addition to the basic effect of the polymers' precise molecular structure, the concentration and the molar mass dependence of the phase transition temperatures were studied. Furthermore, we investigated the influence of added low molar mass salts on the aqueous-phase behaviour for sodium chloride and sodium bromide as well as sodium and ammonium sulfate. The strong effects evolved in a complex way with the salt concentration. The strength of these effects depended on the nature of the anion added, increasing in the order sulfate < chloride < bromide, thus following the empirical Hofmeister series. In contrast, no significant differences were observed when changing the cation, i.e. when adding sodium or ammonium sulfate.}, language = {en} } @misc{HildebrandLaschewskyPaechetal.2016, author = {Hildebrand, Viet and Laschewsky, Andr{\´e} and P{\"a}ch, Michael and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102028}, pages = {13}, year = {2016}, abstract = {A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents of the zwitterionic group. Radical polymerisation via the RAFT (reversible addition-fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and was well controlled, yielding polymers with predictable molar masses. Molar mass analysis and control of the end-group fidelity were facilitated by end-group labeling with a fluorescent dye. The polymers showed distinct thermo-responsive behaviour of the UCST (upper critical solution temperature) type in an aqueous solution, which could not be simply correlated to their molecular structure via an incremental analysis of the hydrophilic and hydrophobic elements incorporated within them. Increasing the spacer length separating the ammonium and the sulfonate groups of the zwitterion moiety from three to four carbons increased the phase transition temperatures markedly, whereas increasing the length of the spacer separating the ammonium group and the carboxylate ester group on the backbone from two to three carbons provoked the opposite effect. Moreover, the phase transition temperatures of the analogous polyzwitterions decreased in the order dimethylammonio > morpholinio > piperidinio alkanesulfonates. In addition to the basic effect of the polymers' precise molecular structure, the concentration and the molar mass dependence of the phase transition temperatures were studied. Furthermore, we investigated the influence of added low molar mass salts on the aqueous-phase behaviour for sodium chloride and sodium bromide as well as sodium and ammonium sulfate. The strong effects evolved in a complex way with the salt concentration. The strength of these effects depended on the nature of the anion added, increasing in the order sulfate < chloride < bromide, thus following the empirical Hofmeister series. In contrast, no significant differences were observed when changing the cation, i.e. when adding sodium or ammonium sulfate.}, language = {en} } @article{HuLinMetwallietal.2023, author = {Hu, Neng and Lin, Li and Metwalli, Ezzeldin and Bießmann, Lorenz and Philipp, Martine and Hildebrand, Viet and Laschewsky, Andr{\´e} and Papadakis, Christine M. and Cubitt, Robert and Zhong, Qi and M{\"u}ller-Buschbaum, Peter}, title = {Kinetics of water transfer between the LCST and UCST thermoresponsive blocks in diblock copolymer thin films monitored by in situ neutron reflectivity}, series = {Advanced materials interfaces}, volume = {10}, journal = {Advanced materials interfaces}, number = {3}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2196-7350}, doi = {10.1002/admi.202201913}, pages = {11}, year = {2023}, abstract = {The kinetics of water transfer between the lower critical solution temperature (LCST) and upper critical solution temperature (UCST) thermoresponsive blocks in about 10 nm thin films of a diblock copolymer is monitored by in situ neutron reflectivity. The UCST-exhibiting block in the copolymer consists of the zwitterionic poly(4((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate), abbreviated as PSBP. The LCST-exhibiting block consists of the nonionic poly(N-isopropylacrylamide), abbreviated as PNIPAM. The as-prepared PSBP80-b-PNIPAM(400) films feature a three-layer structure, i.e., PNIPAM, mixed PNIPAM and PSBP, and PSBP. Both blocks have similar transition temperatures (TTs), namely around 32 degrees C for PNIPAM, and around 35 degrees C for PSBP, and with a two-step heating protocol (20 degrees C to 40 degrees C and 40 degrees C to 80 degrees C), both TTs are passed. The response to such a thermal stimulus turns out to be complex. Besides a three-step process (shrinkage, rearrangement, and reswelling), a continuous transfer of D2O from the PNIPAM to the PSBP block is observed. Due to the existence of both, LCST and UCST blocks in the PSBP80-b-PNIPAM(400 )film, the water transfer from the contracting PNIPAM, and mixed layers to the expanding PSBP layer occurs. Thus, the hydration kinetics and thermal response differ markedly from a thermoresponsive polymer film with a single LCST transition.}, language = {en} } @article{KreuzerLindenmeirGeigeretal.2021, author = {Kreuzer, Lucas and Lindenmeir, Christoph and Geiger, Christina and Widmann, Tobias and Hildebrand, Viet and Laschewsky, Andr{\´e} and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {Poly(sulfobetaine) versus poly(N-isopropylmethacrylamide)}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {54}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {3}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.0c02281}, pages = {1548 -- 1556}, year = {2021}, abstract = {The swelling and co-nonsolvency behaviors in pure H2O and in a mixed H2O/CH3OH vapor atmosphere of two different polar, water-soluble polymers in thin film geometry are studied in situ. Films of a zwitterionic poly(sulfobetaine), namely, poly[3-((2-(methacryloyloxy)ethyl)dimethylammonio) propane-1-sulfonate] (PSPE), and a polar nonionic polymer, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), are investigated in real time by spectral reflectance (SR) measurements and Fourier transform infrared (FTIR) spectroscopy. Whereas PSPE is insoluble in methanol, PNIPMAM is soluble but exhibits cononsolvency behavior in water/methanol mixtures. First, the swelling of PSPE and PNIPMAM thin films in H2O vapor is followed. Subsequently, CH3OH is added to the vapor atmosphere, and its contracting effect on the water-swollen films is monitored, revealing a co-nonsolvency-type behavior for PNIPMAM and PSPE. SR measurements indicate that PSPE and PNIPMAM behave significantly different during the H2O swelling and subsequent exposure to CH3OH, not only with respect to the amounts of absorbed water and CH3OH, but also to the cosolvent-induced contraction mechanisms. While PSPE thin films exhibit an abrupt one-step contraction, the contraction of PNIPMAM thin films occurs in two steps. FTIR studies corroborate these findings on a molecular scale and reveal the role of the specific functional groups, both during the swelling and the cosolvent-induced switching of the solvation state.}, language = {en} } @article{KreuzerWidmannGeigeretal.2021, author = {Kreuzer, Lucas and Widmann, Tobias and Geiger, Christina and Wang, Peixi and Vagias, Apostolos N. and Heger, Julian Eliah and Haese, Martin and Hildebrand, Viet and Laschewsky, Andr{\´e} and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {Salt-dependent phase transition behavior of doubly thermoresponsive poly(sulfobetaine)-based diblock copolymer thin films}, series = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, volume = {37}, journal = {Langmuir : the ACS journal of surfaces and colloids / American Chemical Society}, number = {30}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.1c01342}, pages = {9179 -- 9191}, year = {2021}, abstract = {The water vapor-induced swelling, as well as subsequent phase-transition kinetics, of thin films of a diblock copolymer (DBC) loaded with different amounts of the salt NaBr, is investigated in situ. In dilute aqueous solution, the DBC features an orthogonally thermoresponsive behavior. It consists of a zwitterionic poly(sulfobetaine) block, namely, poly(4-(N-(3'-methacrylamidopropyl)-N, N-dimethylammonio) butane-1-sulfonate) (PSBP), showing an upper critical solution temperature, and a nonionic block, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), exhibiting a lower critical solution temperature. The swelling kinetics in D2O vapor at 15 degrees C and the phase transition kinetics upon heating the swollen film to 60 degrees C and cooling back to 15 degrees C are followed with simultaneous time-of-flight neutron reflectometry and spectral reflectance measurements. These are complemented by Fourier transform infrared spectroscopy. The collapse temperature of PNIPMAM and the swelling temperature of PSBP are found at lower temperatures than in aqueous solution, which is attributed to the high polymer concentration in the thin-film geometry. Upon inclusion of sub-stoichiometric amounts (relative to the monomer units) of NaBr in the films, the water incorporation is significantly increased. This increase is mainly attributed to a salting-in effect on the zwitterionic PSBP block. Whereas the addition of NaBr notably shifts the swelling temperature of PSBP to lower temperatures, the collapse temperature of PNIPMAM remains unaffected by the presence of salt in the films.}, language = {en} } @article{KreuzerWidmannHohnetal.2019, author = {Kreuzer, Lucas and Widmann, Tobias and Hohn, Nuri and Wang, Kun and Biessmann, Lorenz and Peis, Leander and Moulin, Jean-Francois and Hildebrand, Viet and Laschewsky, Andr{\´e} and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {Swelling and exchange behavior of poly(sulfobetaine)-based block copolymer thin films}, series = {Macromolecules : web edition}, volume = {52}, journal = {Macromolecules : web edition}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.9b00443}, pages = {3486 -- 3498}, year = {2019}, abstract = {The humidity-induced swelling and exchange behavior of a block copolymer thin film, which consists of a zwitterionic poly(sulfobetaine) [poly(N,N-dimethyl-N-(3-(methacrylamido)propyl)ammoniopropanesulfonate) (PSPP)] block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block, are investigated by time-of-flight neutron reflectometry (TOF-NR). We monitor in situ the swelling in the H2O atmosphere, followed by an exchange with D2O. In the reverse experiment, swelling in the D2O atmosphere and the subsequent exchange with H2O are studied. Both, static and kinetic TOF-NR measurements indicate significant differences in the interactions between the PSPP80-b-PNIPAM(130) thin film and H2O or D2O, which we attribute to the different H- and D-bonds between water and the polymer. Changes in the chain conformation and hydrogen bonding are probed with Fourier transform infrared spectroscopy during the kinetics of the swelling and exchange processes, which reveals the key roles of the ionic SO3- group in the PSPP block and of the polar amide groups of both blocks during water uptake and exchange.}, language = {en} } @article{KyriakosAravopoulouAugsbachetal.2014, author = {Kyriakos, Konstantinos and Aravopoulou, Dionysia and Augsbach, Lukas and Sapper, Josef and Ottinger, Sarah and Psylla, Christina and Rafat, Ali Aghebat and Benitez-Montoya, Carlos Adrian and Miasnikova, Anna and Di, Zhenyu and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Kyritsis, Apostolos and Papadakis, Christine M.}, title = {Novel thermoresponsive block copolymers having different architectures-structural, rheological, thermal, and dielectric investigations}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {292}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {8}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-014-3282-0}, pages = {1757 -- 1774}, year = {2014}, abstract = {Thermoresponsive block copolymers comprising long, hydrophilic, nonionic poly(methoxy diethylene glycol acrylate) (PMDEGA) blocks and short hydrophobic polystyrene (PS) blocks are investigated in aqueous solution. Various architectures, namely diblock, triblock, and starblock copolymers are studied as well as a PMDEGA homopolymer as reference, over a wide concentration range. For specific characterization methods, polymers were labeled, either by partial deuteration (for neutron scattering studies) or by fluorophores. Using fluorescence correlation spectroscopy, critical micellization concentrations are identified and the hydrodynamic radii of the micelles, r (h) (mic) , are determined. Using dynamic light scattering, the behavior of r (h) (mic) in dependence on temperature and the cloud points are measured. Small-angle neutron scattering enabled the detailed structural investigation of the micelles and their aggregates below and above the cloud point. Viscosity measurements are carried out to determine the activation energies in dependence on the molecular architecture. Differential scanning calorimetry at high polymer concentration reveals the glass transition of the polymers, the fraction of uncrystallized water and effects of the phase transition at the cloud point. Dielectric relaxation spectroscopy shows that the polarization changes reversibly at the cloud point, which reflects the formation of large aggregates upon heating through the cloud point and their redissolution upon cooling.}, language = {en} } @article{KyriakosPhilippAdelsbergeretal.2014, author = {Kyriakos, Konstantinos and Philipp, Martine and Adelsberger, Joseph and Jaksch, Sebastian and Berezkin, Anatoly V. and Lugo, Dersy M. and Richtering, Walter and Grillo, Isabelle and Miasnikova, Anna and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Cononsolvency of water/methanol mixtures for PNIPAM and PS-b-PNIPAM: pathway of aggregate formation investigated using time-resolved SANS}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {47}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {19}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/ma501434e}, pages = {6867 -- 6879}, year = {2014}, abstract = {We investigate the cononsolvency effect of poly(N-isopropylacrylamide) (PNIPAM) in mixtures of water and methanol. Two systems are studied: micellar solutions of polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers and, as a reference, solutions of PNIPAM homopolymers, both at a concentration of 20 mg/mL in DO. Using a stopped-flow instrument, fully deuterated methanol was rapidly added to these solutions at volume fractions between 10 and 20\%. Time-resolved turbidimetry revealed aggregate formation within 10-100 s. The structural changes on mesoscopic length scales were followed by time-resolved small-angle neutron scattering (TR-SANS) with a time resolution of 0.1 s. In both systems, the pathway of the aggregation depends on the content of deuterated methanol; however, it is fundamentally different for homopolymer and diblock copolymer solutions: In the former, very large aggregates (>150 nm) are formed within the dead time of the setup, gradient appears at their surface in the late stages. In contrast, the growth of the aggregates in the latter system features different regimes, and the final aggregate size is 50 nm, thus much smaller than for the homopolymer. For the diblock copolymer, the time dependence of the aggregate radius can be described by two models: In the initial stage, the diffusion-limited coalescence model describes the data well; however, the resulting coalescence time is unreasonably high. In the late stage, a logarithmic coalescence model based on an energy barrier which is proportional to the aggregate radius is successfully applied. and a concentration}, language = {en} } @article{MiasnikovaLaschewskyDePaolietal.2012, author = {Miasnikova, Anna and Laschewsky, Andr{\´e} and De Paoli, Gabriele and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter and Funari, Sergio S.}, title = {Thermoresponsive Hydrogels from Symmetrical Triblock Copolymers Poly(styrene-block-(methoxy diethylene glycol acrylate)-block-styrene)}, series = {Langmuir}, volume = {28}, journal = {Langmuir}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/la204665q}, pages = {4479 -- 4490}, year = {2012}, abstract = {A series of symmetrical, thermo-responsive triblock copolymers was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization, and studied in aqueous solution with respect to their ability to form hydrogels. Triblock copolymers were composed of two identical, permanently hydrophobic outer blocks, made of low molar mass polystyrene, and of a hydrophilic inner block of variable length, consisting of poly(methoxy diethylene glycol acrylate) PMDEGA. The polymers exhibited a LCST-type phase transition in the range of 20-40 degrees C, which markedly depended on molar mass and concentration. Accordingly, the triblock copolymers behaved as amphiphiles at low temperatures, but became water-insoluble at high temperatures. The temperature dependent self-assembly of the amphiphilic block copolymers in aqueous solution was studied by turbidimetry and rheology at concentrations up to 30 wt \%, to elucidate the impact of the inner thermoresponsive block on the gel properties. Additionally, small-angle X-ray scattering (SAXS) was performed to access the structural changes in the gel with temperature. For all polymers a gel phase was obtained at low temperatures, which underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurred. With increasing length of the PMDEGA inner block, the gel-sol transition shifts to markedly lower concentrations, as well as to higher transition temperatures. For the longest PMDEGA block studied (DPn about 450), gels had already formed at 3.5 wt \% at low temperatures. The gel-sol transition of the hydrogels and the LCST-type phase transition of the hydrophilic inner block were found to be independent of each other.}, language = {en} } @article{NiebuurPuchmayrHeroldetal.2018, author = {Niebuur, Bart-Jan and Puchmayr, Jonas and Herold, Christian and Kreuzer, Lucas and Hildebrand, Viet and M{\"u}ller-Buschbaum, Peter and Laschewsky, Andre and Papadakis, Christine M.}, title = {Polysulfobetaines in aqueous solution and in thin film geometry}, series = {Materials}, volume = {11}, journal = {Materials}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {1996-1944}, doi = {10.3390/ma11050850}, pages = {11}, year = {2018}, abstract = {Polysulfobetaines in aqueous solution show upper critical solution temperature (UCST) behavior. We investigate here the representative of this class of materials, poly (N,N-dimethyl-N-(3-methacrylamidopropyl) ammonio propane sulfonate) (PSPP), with respect to: (i) the dynamics in aqueous solution above the cloud point as function of NaBr concentration; and (ii) the swelling behavior of thin films in water vapor as function of the initial film thickness. For PSPP solutions with a concentration of 5 wt.\%, the temperature dependence of the intensity autocorrelation functions is measured with dynamic light scattering as function of molar mass and NaBr concentration (0-8 mM). We found a scaling of behavior for the scattered intensity and dynamic correlation length. The resulting spinodal temperatures showed a maximum at a certain (small) NaBr concentration, which is similar to the behavior of the cloud points measured previously by turbidimetry. The critical exponent of susceptibility depends on NaBr concentration, with a minimum value where the spinodal temperature is maximum and a trend towards the mean-field value of unity with increasing NaBr concentration. In contrast, the critical exponent of the correlation length does not depend on NaBr concentration and is lower than the value of 0.5 predicted by mean-field theory. For PSPP thin films, the swelling behavior was found to depend on film thickness. A film thickness of about 100 nm turns out to be the optimum thickness needed to obtain fast hydration with H2O.}, language = {en} } @misc{NiebuurPuchmayrHeroldetal.2018, author = {Niebuur, Bart-Jan and Puchmayr, Jonas and Herold, Christian and Kreuzer, Lucas and Hildebrand, Viet and M{\"u}ller-Buschbaum, Peter and Laschewsky, Andr{\´e} and Papadakis, Christine M.}, title = {Polysulfobetaines in aqueous solution and in thin film geometry}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {713}, issn = {1866-8372}, doi = {10.25932/publishup-42736}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-427363}, pages = {11}, year = {2018}, abstract = {Polysulfobetaines in aqueous solution show upper critical solution temperature (UCST) behavior. We investigate here the representative of this class of materials, poly (N,N-dimethyl-N-(3-methacrylamidopropyl) ammonio propane sulfonate) (PSPP), with respect to: (i) the dynamics in aqueous solution above the cloud point as function of NaBr concentration; and (ii) the swelling behavior of thin films in water vapor as function of the initial film thickness. For PSPP solutions with a concentration of 5 wt.\%, the temperature dependence of the intensity autocorrelation functions is measured with dynamic light scattering as function of molar mass and NaBr concentration (0-8 mM). We found a scaling of behavior for the scattered intensity and dynamic correlation length. The resulting spinodal temperatures showed a maximum at a certain (small) NaBr concentration, which is similar to the behavior of the cloud points measured previously by turbidimetry. The critical exponent of susceptibility depends on NaBr concentration, with a minimum value where the spinodal temperature is maximum and a trend towards the mean-field value of unity with increasing NaBr concentration. In contrast, the critical exponent of the correlation length does not depend on NaBr concentration and is lower than the value of 0.5 predicted by mean-field theory. For PSPP thin films, the swelling behavior was found to depend on film thickness. A film thickness of about 100 nm turns out to be the optimum thickness needed to obtain fast hydration with H 2 O.}, language = {en} } @article{NieuwenhuisZhongMetwallietal.2019, author = {Nieuwenhuis, Sophie and Zhong, Qi and Metwalli, Ezzeldin and Biessmann, Lorenz and Philipp, Martine and Miasnikova, Anna and Laschewsky, Andre and Papadakis, Christine M. and Cubitt, Robert and Wang, Jiping and M{\"u}ller-Buschbaum, Peter}, title = {Hydration and Dehydration Kinetics: Comparison between Poly(N-isopropyl methacrylamide) and Poly(methoxy diethylene glycol acrylate) Films}, series = {Langmuir}, volume = {35}, journal = {Langmuir}, number = {24}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.9b00535}, pages = {7691 -- 7702}, year = {2019}, abstract = {Thermoresponsive films of poly(N-isopropyl methacrylamide) (PNIPMAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) are compared with respect to their hydration and dehydration kinetics using in situ neutron reflectivity. Both as-prepared films present a homogeneous single-layer structure and have similar transition temperatures of the lower critical solution temperature type (TT, PNIPMAM 38 degrees C and PMDEGA 41 degrees C). After hydration in unsaturated D2O vapor at 23 degrees C, a D2O enrichment layer is observed in PNIPMAM films adjacent to the Si substrate. In contrast, two enrichment layers are present in PMDEGA films (close to the vapor interface and the Si substrate). PNIPMAM films exhibit a higher hydration capability, ascribed to having both donor (N-H) and acceptor (C=O) units for hydrogen bonds. "While the swelling of the PMDEGA films is mainly caused by the increase of the enrichment layers, the thickness of the entire PNIPMAM films increases with time. The observed longer relaxation time for swelling of PNIPMAM films is attributed to the much higher glass transition temperature of PNIPMAM. When dehydrating both films by increasing the temperature above the TT, they react with a complex response consisting of three stages (shrinkage, rearrangement, and reswelling). PNIPMAM films respond faster than PMDEGA films. After dehydration, both films still contain a large amount of D2O, and no completely dry film state is reached for a temperature above their TTs.}, language = {en} } @article{PapadakisMuellerBuschbaumLaschewsky2019, author = {Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter and Laschewsky, Andre}, title = {Switch It Inside-Out: "Schizophrenic" Behavior of All Thermoresponsive UCST-LCST Diblock Copolymers}, series = {Langmuir}, volume = {35}, journal = {Langmuir}, number = {30}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.9b01444}, pages = {9660 -- 9676}, year = {2019}, abstract = {This feature article reviews our recent advancements on the synthesis, phase behavior, and micellar structures of diblock copolymers consisting of oppositely thermoresponsive blocks in aqueous environments. These copolymers combine a nonionic block, which shows lower critical solution temperature (LCST) behavior, with a zwitterionic block that exhibits an upper critical solution temperature (UCST). The transition temperature of the latter class of polymers is strongly controlled by its molar mass and by the salt concentration, in contrast to the rather invariant transition of nonionic polymers with type II LCST behavior such as poly(N-isopropylacrylamide) or poly(N-isopropyl methacrylamide). This allows for implementing the sequence of the UCST and LCST transitions of the polymers at will by adjusting either molecular or, alternatively, physical parameters. Depending on the location of the transition temperatures of both blocks, different switching scenarios are realized from micelles to inverse micelles, namely via the molecularly dissolved state, the aggregated state, or directly. In addition to studies of (semi)dilute aqueous solutions, highly concentrated systems have also been explored, namely water-swollen thin films. Concerning applications, we discuss the possible use of the diblock copolymers as "smart" nanocarriers.}, language = {en} } @misc{TrollKulkarniWangetal.2011, author = {Troll, K. and Kulkarni, Amit and Wang, W. and Darko, C. and Koumba, A. M. Bivigou and Laschewsky, Andr{\´e} and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {The collapse transition of poly(styrene-b-(N-isopropyl acrylamide)) diblock copolymers in aqueous solution and in thin films}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {289}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-010-2344-1}, pages = {227 -- 227}, year = {2011}, language = {en} } @article{VishnevetskayaHildebrandDyakonovaetal.2018, author = {Vishnevetskaya, Natalya S. and Hildebrand, Viet and Dyakonova, Margarita A. and Niebuur, Bart-Jan and Kyriakos, Konstantinos and Raftopoulos, Konstantinos N. and Di, Zhenyu and M{\"u}ller-Buschbaum, Peter and Laschewsky, Andre and Papadakis, Christine M.}, title = {Dual orthogonal switching of the "Schizophrenic" self-assembly of diblock copolymers}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {51}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {7}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.8b00096}, pages = {2604 -- 2614}, year = {2018}, abstract = {Based on diblock copolymers, a pair of "schizophrenic" micellar systems is designed by combining a nonionic and thermoresponsive block with a zwitterionic block, which is thermoresponsive and salt-sensitive. The nonionic block is poly(N-isopropylacrylamide) (PNIPAM) or poly(N-isopropylmethacrylamide) (PNIPMAM) and exhibits a lower critical solution temperature (LCST) behavior in aqueous solution. The zwitterionic block is a polysulfobetaine, i.e., poly(4((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate) (PSBP), and has an upper critical solution temperature (UCST) behavior with the clearing point decreasing with increasing salt concentration. The PSBP-b-PNIPAM and PSBP-b-PNIPMAM diblock copolymers are prepared by successive reversible addition-fragmentation chain transfer (RAFT) polymerizations. The PSBP block is chosen such that the clearing point of the homopolymer is significantly higher in pure water than the cloud point of PNIPAM or PNIPMAM. Using turbidimetry, H-1 NMR, and small-angle neutron scattering, we investigate the overall phase behavior as well as the structure and interaction between the micelles and the intermediate phase, both in salt-free D2O and in 0.004 M NaBr in D2O in a wide temperature range. We find that PSBP-b-PNIPAM at 50 g L-1 in salt-free D2O is turbid in the entire temperature range. It forms spherical micelles below the cloud point of PNIPAM and cylindrical micelles above. Similar behavior is observed for PSBP-b-PNIPMAM at 50 g L-1 in salt-free D2O with a slight and smooth increase of the light transmission below the cloud point of PNIPMAM and an abrupt decrease above. Upon addition of 0.004 M NaBr, the UCST-type cloud point of the PSBP-block is notably decreased, and an intermediate regime is encountered below the cloud point of PNIPMAM, where the light transmission is slightly enhanced. In this regime, the polymer solution exhibits behavior typical for polyelectrolyte solutions. Thus, double thermosensitive and salt-sensitive behavior with "schizophrenic" micelle formation is found, and the width of the intermediate regime, where both blocks are hydrophilic, can be tuned by the addition of electrolyte.}, language = {en} } @article{VishnevetskayaHildebrandNiebuuretal.2016, author = {Vishnevetskaya, Natalya S. and Hildebrand, Viet and Niebuur, Bart-Jan and Grillo, Isabelle and Filippov, Sergey K. and Laschewsky, Andre and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Aggregation Behavior of Doubly Thermoresponsive Polysulfobetaine-b-poly(N-isopropylacrylamide) Diblock Copolymers}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {49}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.6b01186}, pages = {6655 -- 6668}, year = {2016}, abstract = {A 2-fold thermoresponsive diblock copolymer PSPP430-b-PNIPAM(200) consisting of a zwitterionic polysulfobetaine (PSPP) block and a nonionic poly(N-isopropylacrylamide) (PNIPAM) block is prepared by successive RAFT polymerizations. In aqueous solution, the corresponding homopolymers PSPP and PNIPAM feature both upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The diblock copolymer exhibits thermally induced "schizophrenic" aggregation behavior in aqueous solutions. Moreover, the ion sensitivity of the, cloud point of the zwitterionic PSPP block to both the ionic strength and the nature of the salt offers the possibility to create switchable systems which respond sensitively to changes of the temperature and of the electrolyte type and concentration. The diblock copolymer solutions in D2O are investigated by means of turbidimetry and small-angle neutron scattering (SANS) with respect to the phase behavior and the self-assembled structures in dependence on temperature and electrolyte content. Marked, differences of the aggregation below the UCST-type and above the LCST-type transition are observed. The addition of a small amount of NaBr (0.004 M) does not affect the overall behavior, and only the UCST-type transition and aggregate structures are slightly altered, reflecting the well-known ion sensitivity of the zwitterionic PSPP block.}, language = {en} } @article{VishnevetskayaHildebrandNizardoetal.2019, author = {Vishnevetskaya, Natalya S. and Hildebrand, Viet and Nizardo, Noverra Mardhatillah and Ko, Chia-Hsin and Di, Zhenyu and Radulescu, Aurel and Barnsley, Lester C. and M{\"u}ller-Buschbaum, Peter and Laschewsky, Andr{\´e} and Papadakis, Christine M.}, title = {All-in-One "Schizophrenic" self-assembly of orthogonally tuned thermoresponsive diblock copolymers}, series = {Langmuir}, volume = {35}, journal = {Langmuir}, number = {19}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.9b00241}, pages = {6441 -- 6452}, year = {2019}, abstract = {Smart, fully orthogonal switching was realized in a highly biocompatible diblock copolymer system with variable trigger-induced aqueous self-assembly. The polymers are composed of nonionic and zwitterionic blocks featuring lower and upper critical solution temperatures (LCSTs and UCSTs). In the system investigated, diblock copolymers from poly(N-isopropyl methacrylamide) (PNIPMAM) and a poly(sulfobetaine methacrylamide), systematic variation of the molar mass of the latter block allowed for shifting the UCST of the latter above the LCST of the PNIPMAM block in a salt-free condition. Thus, successive thermal switching results in "schizophrenic" micellization, in which the roles of the hydrophobic core block and the hydrophilic shell block are interchanged depending on the temperature. Furthermore, by virtue of the strong electrolyte-sensitivity of the zwitterionic polysulfobetaine block, we succeeded to shift its UCST below the LCST of the PNIPMAM block by adding small amounts of an electrolyte, thus inverting the pathway of switching. This superimposed orthogonal switching by electrolyte addition enabled us to control the switching scenarios between the two types of micelles (i) via an insoluble state, if the LCST-type cloud point is below the UCST-type cloud point, which is the case at low salt concentrations or (ii) via a molecularly dissolved state, if the LCST-type cloud point is above the UCST-type cloud point, which is the case at high salt concentrations. Systematic variation of the block lengths allowed for verifying the anticipated behavior and identifying the molecular architecture needed. The versatile and tunable self-assembly offers manifold opportunities, for example, for smart emulsifiers or for sophisticated carrier systems.}, language = {en} } @article{WangGeigerKreuzeretal.2022, author = {Wang, Peixi and Geiger, Christina and Kreuzer, Lucas and Widmann, Tobias and Reitenbach, Julija and Liang, Suzhe and Cubitt, Robert and Henschel, Cristiane and Laschewsky, Andr{\´e} and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {Poly(sulfobetaine)-based diblock copolymer thin films in water/acetone atmosphere: modulation of water hydration and co-nonsolvency-triggered film contraction}, series = {Langmuir : the ACS journal of surfaces and colloids}, volume = {38}, journal = {Langmuir : the ACS journal of surfaces and colloids}, number = {22}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.2c00451}, pages = {6934 -- 6948}, year = {2022}, abstract = {The water swelling and subsequent solvent exchange including co-nonsolvency behavior of thin films of a doubly thermo-responsive diblock copolymer (DBC) are studied viaspectral reflectance, time-of-flight neutron reflectometry, and Fourier transform infrared spectroscopy. The DBC consists of a thermo-responsive zwitterionic (poly(4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate)) (PSBP) block, featuring an upper critical solution temperature transition in aqueous media but being insoluble in acetone, and a nonionic poly(N-isopropylmethacrylamide) (PNIPMAM) block, featuring a lower critical solution temperature transition in water, while being soluble in acetone. Homogeneous DBC films of 50-100 nm thickness are first swollen in saturated water vapor (H2OorD2O), before they are subjected to a contraction process by exposure to mixed saturated water/acetone vapor (H2OorD2O/acetone-d6 = 9:1 v/v). The affinity of the DBC film toward H2O is stronger than for D2O, as inferred from the higher film thickness in the swollen state and the higher absorbed water content, thus revealing a pronounced isotope sensitivity. During the co-solvent-induced switching by mixed water/acetone vapor, a two-step film contraction is observed, which is attributed to the delayed expulsion of water molecules and uptake of acetone molecules. The swelling kinetics are compared for both mixed vapors (H2O/acetone-d6 and D2O/acetone-d6) and with those of the related homopolymer films. Moreover, the concomitant variations of the local environment around the hydrophilic groups located in the PSBP and PNIPMAM blocks are followed. The first contraction step turns out to be dominated by the behavior of the PSBP block, where as the second one is dominated by the PNIPMAM block. The unusual swelling and contraction behavior of the latter block is attributed to its co-nonsolvency behavior. Furthermore, we observe cooperative hydration effects in the DBC films, that is, both polymer blocks influence each other's solvation behavior.}, language = {en} } @article{WangKaunePerlichetal.2010, author = {Wang, Weijia and Kaune, Gunar and Perlich, Jan and Paradakis, Christine M. and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and Schlage, K. and R{\"o}hlsberger, Ralf and Roth, Stephan V. and Cubitt, Robert and M{\"u}ller-Buschbaum, Peter}, title = {Swelling and switching kinetics of gold coated end-capped poly(N-isopropylacrylamide) thin films}, issn = {0024-9297}, doi = {10.1021/Ma902637a}, year = {2010}, abstract = {Thin thermoresponsive hydrogel films of poly(N-isopropylacrylamide) end-capped with n-butyltrithiocarbonate(nbc- PNIPAM) oil si I icon supports with a gold layer on top, causing an asymmetric confinement, are investigated. For two different gold layer thicknesses (nominally 0.4 and 5 rim), the swelling and switching kinetics are probed with in situ neutron reflectivity. With a temperature jump from 23 to 40 degrees C the film is switched from a swollen into a collapsed state. For the thin gold layer this switching is faster as compared to the thick gold layer. The switching is a two-step process of water release and a subsequent structural relaxation. fit swelling and deswelling cycles, aging of the films is probed. After five cycles, the film exhibits enhanced water storage capacity. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that these gold coated nbc-PNIPAM films do not age with respect to the inner structure but slightly roughen at the gold surface. As revealed by atomic force microscopy, the morphology of the gold layer is changed by the water uptake and release.}, language = {en} } @article{ZhongAdelsbergerNiedermeieretal.2013, author = {Zhong, Qi and Adelsberger, Joseph and Niedermeier, M. A. and Golosova, Anastasi and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and Funari, S. S. and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {The influence of selective solvents on the transition behavior of poly(styrene-b-monomethoxydiethylenglycol-acrylate-b-styrene) thick films}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {291}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {6}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-012-2879-4}, pages = {1439 -- 1451}, year = {2013}, abstract = {Thick poly(styrene-b-monomethoxydiethylenglycol-acrylate-b-styrene) [P(S-b-MDEGA-b-S)] films (thickness 5 mu m) are prepared from different solvents on flexible substrates by solution casting and investigated with small-angle X-ray scattering. As the solvents are either PS- or PMDEGA-selective, micelles with different core-shell micellar structures are formed. In PMDEGA-selective solvents, the PS block is the core and PMDEGA is the shell, whereas in PS-selective solvents, the order is reversed. After exposing the films to liquid D2O, the micellar structure inside the films prepared from PMDEGA-selective solvents remains unchanged and only the PMDEGA (shell part) swells. On the contrary, in the films prepared from PS-selective solvents, the micelles revert the core and the shell. This reversal causes more entanglements of the PMDEGA chains between the micelles. Moreover, the thermal collapse transition of the PMDEGA block in liquid D2O is significantly broadened. Irrespective of the solvent used for film preparation, the swollen PMDEGA shell does not show a prominent shrinkage when passing the phase transition, and the transition process occurs via compaction. The collapsed micelles have a tendency to densely pack above the transition temperature.}, language = {en} } @article{ZhongMetwalliKauneetal.2012, author = {Zhong, Qi and Metwalli, Ezzeldin and Kaune, Gunar and Rawolle, Monika and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and Papadakis, Christine M. and Cubitt, Robert and M{\"u}ller-Buschbaum, Peter}, title = {Switching kinetics of thin thermo-responsive hydrogel films of poly(monomethoxy-diethyleneglycol-acrylate) probed with in situ neutron reflectivity}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {19}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm25401h}, pages = {5241 -- 5249}, year = {2012}, abstract = {The switching kinetics of thin thermo-responsive hydrogel films of poly(monomethoxy-diethyleneglycol-acrylate) (PMDEGA) are investigated. Homogeneous and smooth PMDEGA films with a thickness of 35.9 nm are prepared on silicon substrates by spin coating. As probed with white light interferometry, PMDEGA films with a thickness of 35.9 nm exhibit a phase transition temperature of the lower critical solution temperature (LCST) type of 40 degrees C. In situ neutron reflectivity is performed to investigate the thermo-responsive behavior of these PMDEGA hydrogel films in response to a sudden thermal stimulus in deuterated water vapor atmosphere. The collapse transition proceeds in a complex way which can be seen as three steps. The first step is the shrinkage of the initially swollen film by a release of water. In the second step the thickness remains constant with water molecules embedded in the film. In the third step, perhaps due to a conformational rearrangement of the collapsed PMDEGA chains, water is reabsorbed from the vapor atmosphere, thereby giving rise to a relaxation process. Both the shrinkage and relaxation processes can be described by a simple model of hydrogel deswelling.}, language = {en} } @article{ZhongMetwalliRawolleetal.2015, author = {Zhong, Qi and Metwalli, Ezzeldin and Rawolle, Monika and Kaune, Gunar and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and Papadakis, Christine M. and Cubitt, Robert and M{\"u}ller-Buschbaum, Peter}, title = {Rehydration of Thermoresponsive Poly(monomethoxydiethylene glycol acrylate) Films Probed in Situ by Real-Time Neutron Reflectivity}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {48}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {11}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b00645}, pages = {3604 -- 3612}, year = {2015}, abstract = {The rehydration of thermoresponsive poly(monomethoxydiethylene glycol acrylate) (PMDEGA) films exhibiting a lower critical solution temperature (LCST) type demixing phase transition in aqueous environments, induced by a decrease in temperature, is investigated in situ with real-time neutron reflectivity. Two different starting conditions (collapsed versus partially swollen chain conformation) are compared. In one experiment, the temperature is reduced from above the demixing temperature to well below the demixing temperature. In a second experiment, the starting temperature is below the demixing temperature, but within the transition regime, and reduced to the same final temperature. In both cases, the observed rehydration process can be divided into three stages: first condensation of water from the surrounding atmosphere, then absorption of water by the PMDEGA film and evaporation of excess water, and finally, rearrangement of the PMDEGA chains. The final rehydrated film is thicker and contains more absorbed water as compared with the initially swollen film at the same temperature well below the demixing temperature.}, language = {en} } @article{ZhongMetwalliRawolleetal.2013, author = {Zhong, Qi and Metwalli, Ezzeldin and Rawolle, Monika and Kaune, Gunar and Bivigou Koumba, Achille Mayelle and Laschewsky, Andr{\´e} and Papadakis, Christine M. and Cubitt, Robert and M{\"u}ller-Buschbaum, Peter}, title = {Structure and Thermal Response of Thin Thermoresponsive Polystyrene-block-poly(methoxydiethylene glycol acrylate)-block-polystyrene Films}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {46}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/ma400627u}, pages = {4069 -- 4080}, year = {2013}, abstract = {Thin thermoresponsive films of the triblock copolymer polystyrene-block-poly(methoxydiethylene glycol acrylate)-block-polystyrene (P(S-b-MDEGA-b-S)) are investigated on silicon substrates. By spin coating, homogeneous and smooth films are prepared for a range of film thicknesses from 6 to 82 nm. Films are stable with respect to dewetting as investigated with optical microscopy and atomic force microscopy. P(S-b-MDEGA-b-S) films with a thickness of 39 nm exhibit a phase transition of the lower critical solution temperature (LCST) type at 36.5 degrees C. The swelling and the thermoresponsive behavior of the films with respect to a sudden thermal stimulus are probed with in-situ neutron reflectivity. In undersaturated water vapor swelling proceeds without thickness increase. The thermoresponse proceeds in three steps: First, the film rejects water as the temperature is above LCST. Next, it stays constant for 600 s, before the collapsed film takes up water again. With ATR-FTIR measurements, changes of bound water in the film caused by different thermal stimuli are studied. Hydrogen bonds only form between C=O and water in the swollen film. Above the LCST most hydrogen bonds with water are broken, but some amount of bound water remains inside the film in agreement with the neutron reflectivity data. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that the inner lateral structure is not significantly influenced by the different thermal stimuli.}, language = {en} } @article{ZhongMiMetwallietal.2018, author = {Zhong, Qi and Mi, Lei and Metwalli, Ezzeldin and Biessmann, Lorenz and Philipp, Martine and Miasnikova, Anna and Laschewsky, Andre and Papadakis, Christine M. and Cubitt, Robert and Schwartzkopf, Matthias and Roth, Stephan V. and Wang, Jiping and M{\"u}ller-Buschbaum, Peter}, title = {Effect of chain architecture on the swelling and thermal response of star-shaped thermo-responsive (poly(methoxy diethylene glycol acrylate)-block-polystyrene)(3) block copolymer films}, series = {Soft matter}, volume = {14}, journal = {Soft matter}, number = {31}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c8sm00965a}, pages = {6582 -- 6594}, year = {2018}, abstract = {The effect of chain architecture on the swelling and thermal response of thin films obtained from an amphiphilic three-arm star-shaped thermo-responsive block copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene ((PMDEGA-b-PS)(3)) is investigated by in situ neutron reflectivity (NR) measurements. The PMDEGA and PS blocks are micro-phase separated with randomly distributed PS nanodomains. The (PMDEGA-b-PS)(3) films show a transition temperature (TT) at 33 degrees C in white light interferometry. The swelling capability of the (PMDEGA-b-PS)(3) films in a D2O vapor atmosphere is better than that of films from linear PS-b-PMDEGA-b-PS triblock copolymers, which can be attributed to the hydrophilic end groups and limited size of the PS blocks in (PMDEGA-b-PS)(3). However, the swelling kinetics of the as-prepared (PMDEGA-b-PS)(3) films and the response of the swollen film to a temperature change above the TT are significantly slower than that in the PS-b-PMDEGA-b-PS films, which may be related to the conformation restriction by the star-shape. Unlike in the PS-b-PMDEGA-b-PS films, the amount of residual D2O in the collapsed (PMDEGA-b-PS)(3) films depends on the final temperature. It decreases from (9.7 +/- 0.3)\% to (7.0 +/- 0.3)\% or (6.0 +/- 0.3)\% when the final temperatures are set to 35 degrees C, 45 degrees C and 50 degrees C, respectively. This temperature-dependent reduction of embedded D2O originates from the hindrance of chain conformation from the star-shaped chain architecture.}, language = {en} } @article{ZhongWangAdelsbergeretal.2011, author = {Zhong, Qi and Wang, Weinan and Adelsberger, Joseph and Golosova, Anastasia and Koumba, Achille M. Bivigou and Laschewsky, Andr{\´e} and Funari, Sergio S. and Perlich, Jan and Roth, Stephan V. and Papadakis, Christine M. and M{\"u}ller-Buschbaum, Peter}, title = {Collapse transition in thin films of poly(methoxydiethylenglycol acrylate)}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {289}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {5-6}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-011-2384-1}, pages = {569 -- 581}, year = {2011}, abstract = {The thermal behavior of poly(methoxydiethylenglycol acrylate) (PMDEGA) is studied in thin hydrogel films on solid supports and is compared with the behavior in aqueous solution. The PMDEGA hydrogel film thickness is varied from 2 to 422 nm. Initially, these films are homogenous, as measured with optical microscopy, atomic force microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering (GISAXS). However, they tend to de-wet when stored under ambient conditions. Along the surface normal, no long-ranged correlations between substrate and film surface are detected with GISAXS, due to the high mobility of the polymer at room temperature. The swelling of the hydrogel films as a function of the water vapor pressure and the temperature are probed for saturated water vapor pressures between 2,380 and 3,170 Pa. While the swelling capability is found to increase with water vapor pressure, swelling in dependence on the temperature revealed a collapse phase transition of a lower critical solution temperature type. The transition temperature decreases from 40.6 A degrees C to 36.6 A degrees C with increasing film thickness, but is independent of the thickness for very thin films below a thickness of 40 nm. The observed transition temperature range compares well with the cloud points observed in dilute (0.1 wt.\%) and semi-dilute (5 wt.\%) solution which decrease from 45 A degrees C to 39 A degrees C with increasing concentration.}, language = {en} }