Capturing the transient microstructure of poly(styrene)-poly(isoprene)-poly(styrene) gel subjected to temperature and large deformations

We present the real-time change in the microstructure of 10 and 20% (w/w) of poly(styrene)-poly(isoprene)-poly(styrene) [PS-PI-PS] gel in mineral oil, captured using small-angle X-ray scattering experiments and compared with shear rheology experiments. Here the polymer network consists of physically associated PS-blocks bridged by swollen PI-blocks. We capture the evolution of the network with temperature and relate it to the gelation mechanism. We probe the real-time change in microstructure at different temperatures during oscillatory shear and stress relaxation. At high oscillation amplitude, the microstructure splits into two arrangements after a particular strain, displaying circular and elliptical 2D-scattering patterns simultaneously. We characterize the split microstructure using a modified polydispersed core hard-sphere model. Our fitting results indicate a deviation in the stretch experienced by the PI-blocks than predicted by the affine deformation model. The orientation in the gel microstructure is quantified using the anisotropy factor. During relaxation, the anisotropy factor displays time-dependent decay, similar to the shear modulus. Using the stretched-exponential model, the microstructure restoration time and the stress-relaxation time are also compared.