Small-angle neutron scattering of poly(styrene)/poly(acrylic acid-ethyl acrylate) copolymers: The effect of the degree of hydrolysis of the poly(acrylic acid-ethyl acrylate) block

We report the results of systems based on polystyrene-poly(ethyl acrylate) (PEA) diblocks, which self-assemble in aqueous solutions to form spherical micelles. Previous work has shown that the rheological properties of these solutions, in particular the gel-liquid transition, can be tuned through the use of a simple hydrolysis reaction to convert PEA to poly (acrylic acid) (PAA). We studied the effect of the extent of hydrolysis on the self-assembly and micellar interactions. Small-angle neutron scattering (SANS) spectra were fit with a variety of models to determine the micelle structure. As more PEA was converted to PAA (i.e., as the corona became more charged and more hydrophilic), the micellar aggregation number decreased, analogous to observations of other polymeric micelles. This effect could impact the gel-liquid transition and rheology in this system and in similar micellar block copolymer gels. Finally, our SANS spectra qualitatively agreed with predictions for attractive colloidal glasses, confirming the idea that the elasticity of these gels arises from the jamming of micelles.