(318f) The Effect of Dispersed Nanoparticles on the Mechanics and Flow Behavior of Block Copolymer Soft Solids

Nanoparticulate material can be spatially organized when introduced into structured soft solids. This allows soft solids to be considered for applications such as nanoparticle storage and aggregation prevention. However, development of these applications requires understanding of the impact of dispersed nanoparticles on the structure, rheology and phase transitions of soft solids. Nonionic amphiphilic triblock copolymers self-assemble into micelles in aqueous solution.  These systems undergo a thermoreversible phase transition from a disordered polymer solution to a lyotropic block copolymer soft solid. We characterize the impact of nanoparticles (3wt% bovine serum albumin (BSA)) on a thermoreversible soft solid (30wt% Pluronic^® P103) under large amplitude oscillatory shear.   Rheology provides a sensitive test of the phase behavior of the system, particularly the disorder-order transition (ODT) and the order-order transition (OOT) and hysteresis in transitions between these phases. The OOT and the hysteresis occur at lower temperatures with the addition of nanoparticles. The inclusion of particles also increases the time required for the relaxation modulus and structure to reach steady state. Finally, small angle neutron scattering (SANS) was used to examine the nanoscale structure of the block copolymer.  For the SANS experiment, the scattering from the polymer was isolated by contrast matching the solvent to the nanoparticles. The anisotropy observed in the two-dimensional scattering patterns was analyzed and showed that the addition of nanoparticles changed the alignment of the micelles while the system is under shear.