TY  - JOUR
A1  - Bivigou Koumba, Achille Mayelle
A1  - Kristen, Juliane
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Synthesis of symmetrical triblock copolymers of styrene and N-isopropylacrylamide using bifunctional bis(trithiocarbonate)s as RAFT agents
N2  - 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.
Y1  - 2009
UR  - http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291521-3935
U6  - https://doi.org/10.1002/macp.200800575
SN  - 1022-1352
ER  - 
TY  - JOUR
A1  - Adelsberger, Joseph
A1  - Kulkarni, Amit
A1  - Jain, Abhinav
A1  - Wang, Weinan
A1  - Bivigou Koumba, Achille Mayelle
A1  - Busch, Peter
A1  - Pipich, Vitaliy
A1  - Holderer, Olaf
A1  - Hellweg, Thomas
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Thermoresponsive PS-b-PNIPAM-b-PS micelles : aggregation behavior, segmental dynamics, and thermal response
N2  - 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.
Y1  - 2010
UR  - http://pubs.acs.org/journal/mamobx
U6  - https://doi.org/10.1021/Ma902714p
SN  - 0024-9297
ER  - 
TY  - JOUR
A1  - Bivigou Koumba, Achille Mayelle
A1  - Goernitz, Eckhard
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N- isopropylacrylamide) : synthesis, self-organization, and hydrogel formation
N2  - 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.
Y1  - 2010
UR  - http://www.springerlink.com/content/101551
U6  - https://doi.org/10.1007/s00396-009-2179-9
SN  - 0303-402X
ER  - 
TY  - JOUR
A1  - Adelsberger, Joseph
A1  - Meier-Koll, Andreas
A1  - Bivigou Koumba, Achille Mayelle
A1  - Busch, Peter
A1  - Holderer, Olaf
A1  - Hellweg, Thomas
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - The collapse transition and the segmental dynamics in concentrated micellar solutions of P(S-b-NIPAM) diblock copolymers
JF  - Colloid and polymer science : official journal of the Kolloid-Gesellschaft
N2  - 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).
KW  - Block copolymers
KW  - Responsive polymers
KW  - Small-angle neutron scattering
KW  - Neutron spin-echo spectroscopy
Y1  - 2011
U6  - https://doi.org/10.1007/s00396-011-2382-3
SN  - 0303-402X
VL  - 289
IS  - 5-6
SP  - 711
EP  - 720
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Miasnikova, Anna
A1  - Laschewsky, André
A1  - De Paoli, Gabriele
A1  - Papadakis, Christine M.
A1  - Müller-Buschbaum, Peter
A1  - Funari, Sergio S.
T1  - Thermoresponsive Hydrogels from Symmetrical Triblock Copolymers Poly(styrene-block-(methoxy diethylene glycol acrylate)-block-styrene)
JF  - Langmuir
N2  - 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.
Y1  - 2012
U6  - https://doi.org/10.1021/la204665q
SN  - 0743-7463
VL  - 28
IS  - 9
SP  - 4479
EP  - 4490
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Kaune, Gunar
A1  - Rawolle, Monika
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Müller-Buschbaum, Peter
T1  - Switching kinetics of thin thermo-responsive hydrogel films of poly(monomethoxy-diethyleneglycol-acrylate) probed with in situ neutron reflectivity
JF  - Soft matter
N2  - 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.
Y1  - 2012
U6  - https://doi.org/10.1039/c2sm25401h
SN  - 1744-683X
VL  - 8
IS  - 19
SP  - 5241
EP  - 5249
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Adelsberger, Joseph
A1  - Metwalli, Ezzeldin
A1  - Diethert, Alexander
A1  - Grillo, Isabelle
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Kinetics of collapse transition and cluster formation in a thermoresponsive micellar solution of P(S-b-NIPAM-b-S) induced by a temperature jump
JF  - Macromolecular rapid communications
N2  - 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.
KW  - polymer physics
KW  - thermoresponsive polymers
KW  - small-angle neutron scattering
KW  - time-resolved measurements
Y1  - 2012
U6  - https://doi.org/10.1002/marc.201100631
SN  - 1022-1336
VL  - 33
IS  - 3
SP  - 254
EP  - 259
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Adelsberger, Joseph
A1  - Grillo, Isabelle
A1  - Kulkarni, Amit
A1  - Sharp, Melissa
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Kinetics of aggregation in micellar solutions of thermoresponsive triblock copolymers - influence of concentration, start and target temperatures
JF  - Soft matter
N2  - 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.
Y1  - 2013
U6  - https://doi.org/10.1039/c2sm27152d
SN  - 1744-683X
VL  - 9
IS  - 5
SP  - 1685
EP  - 1699
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Adelsberger, Joseph
A1  - Niedermeier, M. A.
A1  - Golosova, Anastasi
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Funari, S. S.
A1  - Papadakis, Christine M.
A1  - Müller-Buschbaum, Peter
T1  - The influence of selective solvents on the transition behavior of poly(styrene-b-monomethoxydiethylenglycol-acrylate-b-styrene) thick films
JF  - Colloid and polymer science : official journal of the Kolloid-Gesellschaft
N2  - 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.
KW  - Hydrogel
KW  - Thin film
KW  - Thermo-responsive
KW  - LCST behavior
KW  - SAXS
Y1  - 2013
U6  - https://doi.org/10.1007/s00396-012-2879-4
SN  - 0303-402X
VL  - 291
IS  - 6
SP  - 1439
EP  - 1451
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Rawolle, Monika
A1  - Kaune, Gunar
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Müller-Buschbaum, Peter
T1  - Structure and Thermal Response of Thin Thermoresponsive Polystyrene-block-poly(methoxydiethylene glycol acrylate)-block-polystyrene Films
JF  - Macromolecules : a publication of the American Chemical Society
N2  - 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.
Y1  - 2013
U6  - https://doi.org/10.1021/ma400627u
SN  - 0024-9297
VL  - 46
IS  - 10
SP  - 4069
EP  - 4080
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kyriakos, Konstantinos
A1  - Aravopoulou, Dionysia
A1  - Augsbach, Lukas
A1  - Sapper, Josef
A1  - Ottinger, Sarah
A1  - Psylla, Christina
A1  - Rafat, Ali Aghebat
A1  - Benitez-Montoya, Carlos Adrian
A1  - Miasnikova, Anna
A1  - Di, Zhenyu
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Kyritsis, Apostolos
A1  - Papadakis, Christine M.
T1  - Novel thermoresponsive block copolymers having different architectures-structural, rheological, thermal, and dielectric investigations
JF  - Colloid and polymer science : official journal of the Kolloid-Gesellschaft
N2  - 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.
KW  - Block copolymers
KW  - Thermoresponsive
KW  - Structural investigations
KW  - Mechanical properties
KW  - Thermal behavior
KW  - Dielectric properties
Y1  - 2014
U6  - https://doi.org/10.1007/s00396-014-3282-0
SN  - 0303-402X
SN  - 1435-1536
VL  - 292
IS  - 8
SP  - 1757
EP  - 1774
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Kyriakos, Konstantinos
A1  - Philipp, Martine
A1  - Adelsberger, Joseph
A1  - Jaksch, Sebastian
A1  - Berezkin, Anatoly V.
A1  - Lugo, Dersy M.
A1  - Richtering, Walter
A1  - Grillo, Isabelle
A1  - Miasnikova, Anna
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Cononsolvency of water/methanol mixtures for PNIPAM and PS-b-PNIPAM: pathway of aggregate formation investigated using time-resolved SANS
JF  - Macromolecules : a publication of the American Chemical Society
N2  - 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
Y1  - 2014
U6  - https://doi.org/10.1021/ma501434e
SN  - 0024-9297
SN  - 1520-5835
VL  - 47
IS  - 19
SP  - 6867
EP  - 6879
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Adelsberger, Joseph
A1  - Bivigou Koumba, Achille Mayelle
A1  - Miasnikova, Anna
A1  - Busch, Peter
A1  - Laschewsky, André
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Polystyrene-block-poly (methoxy diethylene glycol acrylate)-block-polystyrene triblock copolymers in aqueous solution-a SANS study of the temperature-induced switching behavior
JF  - Colloid and polymer science : official journal of the Kolloid-Gesellschaft
N2  - 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.
KW  - Hydrogel
KW  - Thermoresponsive
KW  - LCST behavior
KW  - SANS
Y1  - 2015
U6  - https://doi.org/10.1007/s00396-015-3535-6
SN  - 0303-402X
SN  - 1435-1536
VL  - 293
IS  - 5
SP  - 1515
EP  - 1523
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Rawolle, Monika
A1  - Kaune, Gunar
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, André
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Müller-Buschbaum, Peter
T1  - Rehydration of Thermoresponsive Poly(monomethoxydiethylene glycol acrylate) Films Probed in Situ by Real-Time Neutron Reflectivity
JF  - Macromolecules : a publication of the American Chemical Society
N2  - 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.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.macromol.5b00645
SN  - 0024-9297
SN  - 1520-5835
VL  - 48
IS  - 11
SP  - 3604
EP  - 3612
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Vishnevetskaya, Natalya S.
A1  - Hildebrand, Viet
A1  - Niebuur, Bart-Jan
A1  - Grillo, Isabelle
A1  - Filippov, Sergey K.
A1  - Laschewsky, Andre
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Aggregation Behavior of Doubly Thermoresponsive Polysulfobetaine-b-poly(N-isopropylacrylamide) Diblock Copolymers
JF  - Macromolecules : a publication of the American Chemical Society
N2  - 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.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.macromol.6b01186
SN  - 0024-9297
SN  - 1520-5835
VL  - 49
SP  - 6655
EP  - 6668
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kyriakos, Konstantinos
A1  - Philipp, Martine
A1  - Lin, Che-Hung
A1  - Dyakonova, Margarita
A1  - Vishnevetskaya, Natalya
A1  - Grillo, Isabelle
A1  - Zaccone, Alessio
A1  - Miasnikova, Anna
A1  - Laschewsky, Andre
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency
JF  - Macromolecular rapid communications
N2  - The aggregation kinetics of thermoresponsive core-shell micelles with a poly(N-isopropyl acrylamide) shell in pure water or in mixtures of water with the cosolvents methanol or ethanol at mole fractions of 5% is investigated during a temperature jump across the respective cloud point. Characteristically, these mixtures give rise to cononsolvency behavior. At the cloud point, aggregates are formed, and their growth is followed with time-resolved small-angle neutron scattering. Using the reversible association model, the interaction potential between the aggregates is determined from their growth rate in dependence on the cosolvents. The effect of the cosolvent is attributed to the interaction potential on the structured layer of hydration water around the aggregates. It is surmised that the latter is perturbed by the cosolvent and thus the residual repulsive hydration force between the aggregates is reduced. The larger the molar volume of the cosolvent, the more pronounced is the effect. This framework provides a molecular-level understanding of solvent-mediated effective interactions in polymer solutions and new opportunities for the rational control of self-assembly in complex soft matter systems.
KW  - colloidal aggregation
KW  - cononsolvency
KW  - interaction potential
KW  - polymer solutions
KW  - self-assembled micelles
KW  - thermoresponsive polymers
Y1  - 2016
U6  - https://doi.org/10.1002/marc.201500583
SN  - 1022-1336
SN  - 1521-3927
VL  - 37
SP  - 420
EP  - 425
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Rawolle, Monika
A1  - Kaune, Gunar
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, Andre
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Wang, Jiping
A1  - Müller-Buschbaum, Peter
T1  - Influence of Hydrophobic Polystyrene Blocks on the Rehydration of Polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene Films Investigated by in Situ Neutron Reflectivity
JF  - Macromolecules : a publication of the American Chemical Society
N2  - The rehydration of thermoresponsive polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene (PS-b-PMDEGA-b-PS) films forming a lamellar microphase-separated structure is investigated by in situ neutron reflectivity in a D2O vapor atmosphere. The rehydration of collapsed PS-b-PMDEGA-b-PS films is realized by a temperature change from 45 to 23 degrees C and comprises (1) condensation and absorption of D2O, (2) evaporation of D2O, and (3) reswelling of the film due to internal rearrangement. The hydrophobic PS layers hinder the absorption of condensed D2O, and a redistribution of embedded D2O between the hydrophobic PS layers and the hydrophilic PMDEGA layers is observed. In contrast, the rehydration of semiswollen PS-b-PMDEGA-b-PS films (temperature change from 35 to 23 degrees C) shows two prominent differences: A thicker D2O layer condenses on the surface, causing a more enhanced evaporation of D2O. The rehydrated films differ in film thickness and volume fraction of D2O, which is due to the different thermal protocols, although the final temperature is identical.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.macromol.5b02279
SN  - 0024-9297
SN  - 1520-5835
VL  - 49
SP  - 317
EP  - 326
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Hildebrand, Viet
A1  - Laschewsky, Andre
A1  - Päch, Michael
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)
JF  - Polymer Chemistry
N2  - 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.
Y1  - 2016
U6  - https://doi.org/10.1039/c6py01220e
SN  - 1759-9954
SN  - 1759-9962
VL  - 8
SP  - 310
EP  - 322
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Zhong, Qi
A1  - Metwalli, Ezzeldin
A1  - Rawolle, Monika
A1  - Kaune, Gunar
A1  - Bivigou Koumba, Achille Mayelle
A1  - Laschewsky, Andre
A1  - Papadakis, Christine M.
A1  - Cubitt, Robert
A1  - Wang, Jiping
A1  - Müller-Buschbaum, Peter
T1  - Vacuum induced dehydration of swollen poly(methoxy diethylene glycol acrylate) and polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene films probed by in-situ neutron reflectivity
JF  - Polymer : the international journal for the science and technology of polymers
N2  - The isothermal vacuum-induced dehydration of thin films made of poly(methoxy diethylene glycol acrylate) (PMDEGA), which were swollen under ambient conditions, is studied. The dehydration behavior of the homopolymer film as well as of a nanostructured film of the amphiphilic triblock copolymer polystyrene-block-poly(methoxy diethylene glycol acrylate)-block-polystyrene, abbreviated as PS-b-PMDEGA-b-PS, are probed, and compared to the thermally induced dehydration behavior of such thin thermo-responsive films when they pass through their LCST-type coil-to globule collapse transition. The dehydration kinetics is followed by in-situ neutron reflectivity measurements. Contrast results from the use of deuterated water. Water content and film thickness are significantly reduced during the process, which can be explained by Schott second order kinetics theory for both films. The water content of the dehydrated equilibrium state from this model is very close to the residual water content obtained from the final static measurements, indicating that residual water still remains in the film even after prolonged exposure to the vacuum. In the PS-b-PMDEGA-b-PS film that shows micro-phase separation, the hydrophobic PS domains modify the dehydration process by hindering the water removal, and thus retarding dehydration by about 30%. Whereas residual water remains tightly bound in the PMDEGA domains, water is completely removed from the PS domains of the block copolymer film. (C) 2017 Elsevier Ltd. All rights reserved.
KW  - Dehydration
KW  - Vacuum drying
KW  - In-situ neutron reflectivity
Y1  - 2017
U6  - https://doi.org/10.1016/j.polymer.2017.07.066
SN  - 0032-3861
SN  - 1873-2291
VL  - 124
SP  - 263
EP  - 273
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Vishnevetskaya, Natalya S.
A1  - Hildebrand, Viet
A1  - Niebuur, Bart-Jan
A1  - Grillo, Isabelle
A1  - Filippov, Sergey K.
A1  - Laschewsky, Andre
A1  - Müller-Buschbaum, Peter
A1  - Papadakis, Christine M.
T1  - "Schizophrenic" Micelles from Doubly Thermoresponsive Polysulfobetaine-b-poly(N-isopropylmethacrylamide) Diblock Copolymers
JF  - Macromolecules : a publication of the American Chemical Society
Y1  - 2017
U6  - https://doi.org/10.1021/acs.macromol.7b00356
SN  - 0024-9297
SN  - 1520-5835
VL  - 50
SP  - 3985
EP  - 3999
PB  - American Chemical Society
CY  - Washington
ER  -