@article{CommingesFrascaSuetterlinetal.2014, author = {Comminges, Clement and Frasca, Stefano and Suetterlin, Martin and Wischerhoff, Erik and Laschewsky, Andr{\´e} and Wollenberger, Ursula}, title = {Surface modification with thermoresponsive polymer brushes for a switchable electrochemical sensor}, series = {RSC Advances}, volume = {4}, journal = {RSC Advances}, number = {81}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2046-2069}, doi = {10.1039/c4ra07190e}, pages = {43092 -- 43097}, year = {2014}, abstract = {Elaboration of switchable surfaces represents an interesting way for the development of a new generation of electrochemical sensors. In this paper, a method for growing thermoresponsive polymer brushes from a gold surface pre-modified with polyethyleneimine (PEI), subsequent layer-by-layer polyelectrolyte assembly and adsorption of a charged macroinitiator is described. We propose an easy method for monitoring the coil-to-globule phase transition of the polymer brush using an electrochemical quartz crystal microbalance with dissipation (E-QCM-D). The surface of these polymer modified electrodes shows reversible switching from the swollen to the collapsed state with temperature. As demonstrated from E-QCM-D measurements using an original signal processing method, the switch is operating in three reversible steps related to different interfacial viscosities. Moreover, it is shown that the one electron oxidation of ferrocene carboxylic acid is dramatically affected by the change from the swollen to the collapsed state of the polymer brush, showing a spectacular 86\% decrease of the charge transfer resistance between the two states.}, language = {en} } @misc{CommingesFrascaSuetterlinetal.2014, author = {Comminges, Cl{\´e}ment and Frasca, Stefano and S{\"u}tterlin, Martin and Wischerhoff, Erik and Laschewsky, Andr{\´e} and Wollenberger, Ursula}, title = {Surface modification with thermoresponsive polymer brushes for a switchable electrochemical sensor}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-99471}, year = {2014}, abstract = {Elaboration of switchable surfaces represents an interesting way for the development of a new generation of electrochemical sensors. In this paper, a method for growing thermoresponsive polymer brushes from a gold surface pre-modified with polyethyleneimine (PEI), subsequent layer-by-layer polyelectrolyte assembly and adsorption of a charged macroinitiator is described. We propose an easy method for monitoring the coil-to-globule phase transition of the polymer brush using an electrochemical quartz crystal microbalance with dissipation (E-QCM-D). The surface of these polymer modified electrodes shows reversible switching from the swollen to the collapsed state with temperature. As demonstrated from E-QCM-D measurements using an original signal processing method, the switch is operating in three reversible steps related to different interfacial viscosities. Moreover, it is shown that the one electron oxidation of ferrocene carboxylic acid is dramatically affected by the change from the swollen to the collapsed state of the polymer brush, showing a spectacular 86\% decrease of the charge transfer resistance between the two states.}, language = {en} } @article{HildebrandLaschewskyZehm2014, author = {Hildebrand, Viet and Laschewsky, Andr{\´e} and Zehm, Daniel}, title = {On the hydrophilicity of polyzwitterion poly (N, N-dimethyl-N(3-(methacrylamido)propyl)ammoniopropane sulfonate) in water, deuterated water, and aqueous salt solutions}, series = {Journal of biomaterials science : Polymer edition}, volume = {25}, journal = {Journal of biomaterials science : Polymer edition}, number = {14-15}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0920-5063}, doi = {10.1080/09205063.2014.939918}, pages = {1602 -- 1618}, year = {2014}, language = {en} } @article{KopecLapokLaschewskyetal.2014, author = {Kopec, Maciej and Lapok, Lukasz and Laschewsky, Andr{\´e} and Zapotoczny, Szczepan and Nowakowska, Maria}, title = {Polyelectrolyte multilayers with perfluorinated phthalocyanine selectively entrapped inside the perfluorinated nanocompartments}, series = {Soft matter}, volume = {10}, journal = {Soft matter}, number = {10}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26938d}, pages = {1481 -- 1488}, year = {2014}, abstract = {A novel perfluorinated magnesium phthalocyanine (MgPcF64) was synthesized and employed to probe nanodomains in hydrophobically modified, amphiphilic cationic polyelectrolytes bearing alkyl and/or fluoroalkyl side chains. MgPcF64 was found to be solubilized exclusively in the aqueous solutions of the fluorocarbon modified polycations, occupying the perfluorinated nanocompartments provided, while analogous polyelectrolytes with alkyl side chains forming hydrocarbon nanocompartments could not host the MgPcF64 dye. Multilayer films were fabricated by means of the layer-by-layer (LbL) deposition method using sodium poly(styrene sulfonate) as a polyanion. Linear multilayer growth was confirmed by UV-Vis spectroscopy and spectroscopic ellipsometry. Atomic force microscopy studies indicated that the micellar conformation of the polycations is preserved in the multilayer films. Fluorescence spectroscopy measurements confirmed that MgPcF64 stays embedded inside the fluorocarbon domains after the deposition process. This facile way of selectively incorporating water-insoluble, photoactive molecules into the structure of polyelectrolyte multilayers may be utilized for nanoengineering of ultrathin film-based optoelectronic devices.}, language = {en} } @article{KopecNiemiecLaschewskyetal.2014, author = {Kopec, Maciej and Niemiec, Wiktor and Laschewsky, Andr{\´e} and Nowakowska, Maria and Zapotoczny, Szczepan}, title = {Photoinduced energy and electron transfer in micellar multilayer films}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {118}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {4}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/jp410808z}, pages = {2215 -- 2221}, year = {2014}, abstract = {Micellar multilayer films were prepared from an amphiphilic comb-like polycation ("polysoap") and the polyanion poly(styrene sulfonate) (PSS) using alternate polyelectrolyte layer-by-layer (LbL) self-assembly. Linear growth of the film thickness was evidenced by UV-vis spectroscopy and spectroscopic ellipsometry. Imaging by atomic force microscopy (AFM) indicated that the micellar conformation adopted by the polycation in solutions was preserved in the films. Thus, hydrophobic photoactive molecules, which were solubilized by the hydrophobic nanodomains of the micellar polymer prior to deposition, could be transferred into the films. Photoinduced energy transfer was observed in the nanostructured multilayers between naphthalene (donor) and perylene (acceptor) molecules embedded inside the polymer micelles. The efficiency of the energy transfer process can be controlled to some extent by introducing spacer layers between the layers containing the donor or acceptor, revealing partial stratification of the micellar LbL films. Also, photoinduced electron transfer was evidenced between perylene (donor) and butyl viologen (acceptor) molecules embedded inside the multilayers by steady-state fluorescence spectroscopy. The obtained photoactive nanostructures are promising candidates for solar-to-chemical energy conversion systems.}, 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} } @misc{Laschewsky2014, author = {Laschewsky, Andr{\´e}}, title = {Structures and synthesis of zwitterionic polymers}, series = {Polymers}, volume = {6}, journal = {Polymers}, number = {5}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym6051544}, pages = {1544 -- 1601}, year = {2014}, abstract = {The structures and synthesis of polyzwitterions ("polybetaines") are reviewed, emphasizing the literature of the past decade. Particular attention is given to the general challenges faced, and to successful strategies to obtain polymers with a true balance of permanent cationic and anionic groups, thus resulting in an overall zero charge. Also, the progress due to applying new methodologies from general polymer synthesis, such as controlled polymerization methods or the use of "click" chemical reactions is presented. Furthermore, the emerging topic of responsive ("smart") polyzwitterions is addressed. The considerations and critical discussions are illustrated by typical examples.}, language = {en} } @misc{Laschewsky2014, author = {Laschewsky, Andr{\´e}}, title = {Structures and synthesis of zwitterionic polymers}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1043}, issn = {1866-8372}, doi = {10.25932/publishup-47616}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-476167}, pages = {60}, year = {2014}, abstract = {The structures and synthesis of polyzwitterions ("polybetaines") are reviewed, emphasizing the literature of the past decade. Particular attention is given to the general challenges faced, and to successful strategies to obtain polymers with a true balance of permanent cationic and anionic groups, thus resulting in an overall zero charge. Also, the progress due to applying new methodologies from general polymer synthesis, such as controlled polymerization methods or the use of "click" chemical reactions is presented. Furthermore, the emerging topic of responsive ("smart") polyzwitterions is addressed. The considerations and critical discussions are illustrated by typical examples.}, language = {en} } @article{OrtmannAhrensMilewskietal.2014, author = {Ortmann, Thomas and Ahrens, Heiko and Milewski, Sven and Lawrenz, Frank and Groening, Andreas and Laschewsky, Andr{\´e} and Garnier, Sebastien and Helm, Christiane A.}, title = {Lipid monolayers with adsorbed oppositely charged polyelectrolytes: Influence of reduced charge densities}, series = {Polymers}, volume = {6}, journal = {Polymers}, number = {7}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym6071999}, pages = {1999 -- 2017}, year = {2014}, abstract = {Polyelectrolytes in dilute solutions (0.01 mmol/L) adsorb in a two-dimensional lamellar phase to oppositely charged lipid monolayers at the air/water interface. The interchain separation is monitored by Grazing Incidence X-ray Diffraction. On monolayer compression, the interchain separation decreases to a factor of two. To investigate the influence of the electrostatic interaction, either the line charge density of the polymer is reduced (a statistic copolymer with 90\% and 50\% charged monomers) or mixtures between charged and uncharged lipids are used (dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB)) On decrease of the surface charge density, the interchain separation increases, while on decrease of the linear charge density, the interchain separation decreases. The ratio between charged monomers and charged lipid molecules is fairly constant; it decreases up to 30\% when the lipids are in the fluid phase. With decreasing surface charge or linear charge density, the correlation length of the lamellar order decreases.}, language = {en} }