@article{KyriakosPhilippLinetal.2016, author = {Kyriakos, Konstantinos and Philipp, Martine and Lin, Che-Hung and Dyakonova, Margarita and Vishnevetskaya, Natalya and Grillo, Isabelle and Zaccone, Alessio and Miasnikova, Anna and Laschewsky, Andre and M{\"u}ller-Buschbaum, Peter and Papadakis, Christine M.}, title = {Quantifying the Interactions in the Aggregation of Thermoresponsive Polymers: The Effect of Cononsolvency}, series = {Macromolecular rapid communications}, volume = {37}, journal = {Macromolecular rapid communications}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1336}, doi = {10.1002/marc.201500583}, pages = {420 -- 425}, year = {2016}, abstract = {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.}, 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} }