Quantifying cononsolvent-mediated interactions in the aggregation of thermoresponsive polymers

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 cononsolvents methanol or ethanol at mole fractions of 5 -% is investigated during a temperature jump across the respective cloud point. At the cloud point, aggregates are formed, and their growth is followed with time-resolved smallangle neutron scattering. Using the reversible association model, we determine the interaction potential between the aggregates from their growth rate in dependence on the cononsolvent. We attribute the effect of the cononsolvent on the interaction potential to the fact that the structured layer of hydration water around the aggregates is perturbed by the cononsolvent, which reduces the repulsive hydration force between the aggregates. The effect is the more pronounced, the larger the molar volume of the cononsolvent. PACS numbers: 82.35.Jk Copolymers, phase transitions, structure. 61.25.he Polymer solutions. 61.05.fg Neutron scattering (including small-angle scattering) ∗Electronic address: [email protected]