Impact of dispersed particles on the structure and shear alignment of block copolymer soft solids

At high concentrations, solvent-selective block copolymer molecules self-assemble into concentrated micellar solutions that form highly ordered, nanostructured, soft solids. Solvent stable nanoparticles dispersed in these soft solids will sample the solvent-swollen, continuous structure, providing a method to template, store, and define the environment of nanoparticulate material. Globular proteins are used as nanoparticulate material and dispersed into two different block copolymer solutions (Pluronic® P123 and P103) that differ slightly in block length but not chemistry or architecture. We characterize the impact of added nanoparticles on the local micelle packing, flow mechanism, and overall structure of the soft solid. Small angle neutron scattering with contrast variation and rheology are used to characterize the structure and mechanical behavior of the system. In the P123 soft solid, added nanoparticles change the local order of the cubic and cylindrical phases. In the P103 soft solid, added nanoparticles change the phase behavior of the cubic phase and orientation of the micelles in the cylindrical phase. Even though these two block copolymer systems are quite similar, added nanoparticles impact the local structure, shear alignment, and polycrystallinity in a complicated way, important to the processing of nanocomposite materials.