Networks of gel-forming triblock copolymer solutions: In situ SANS and rheological measurements

Triblock copolymers in a solvent, selective for their middle blocks provide the basis for the formation of novel physical networks where cross-links are formed by self-assembled domains of the end-blocks. Triblock copolymers of poly(styrene)-poly(ethylene,butylene)-poly(styrene) (SEBS) dissolved in a mixture of aliphatic and alicyclic compounds constitute such a network system. Using a Rheometrics RSA-2 instrument modified for in situ measurements of small-angle neutron scattering and rheology provides a unique possibility for detailed understanding thermodynamics of such a gel. The self-association of the PS-blocks do not only promote formation of highly inter-connected end-block domains, but within a narrow temperature range these domains furthermore constitute a network with body-centered cubic (BCC) microstructure. Upon large amplitude oscillating shear the polycrystalline soft gel can be aligned into a twinned BCC monodomain.