Micellar Solutions of PMMA-b-PNIPAM in Water/Methanol Mixtures: Effect of Temperature on the Micellar Size, Core-shell Structure, and Interaction

In aqueous solution, diblock copolymers PMMA-b-PNIPAM having a short PMMA block and a long PNIPAM block form micelles with a PMMA core and a PNIPAM-rich shell. The same holds true for solutions in water containing small amounts of methanol. Here, we address the micellar structures for 10 g L^-1 solutions of PMMA₂₁-b-PNIPAM₂₈₃ in 90:10 and 80:20 v/v water/methanol in wide temperature ranges across the respective cloud point temperature. Dynamic light scattering and synchrotron small-angle X-ray scattering reveal that the content of methanol strongly influences the temperature behavior of the overall micellar size upon heating to the cloud point temperature, the aggregation number of the micelles, their shell thickness, and their interactions. While the behavior in the 90:10 mixture is similar to that in neat water, in the 80:20 mixture, the micelles are significantly smaller and form clusters already below the cloud point temperature in water. Thus, by variation of the methanol content, the structure and interactions of the micelles can be controlled.