Influence of a block copolymer on flow-induced phase-inverted morphology of an immiscible blend

The Row-induced morphology of ternary blends containing poly(styrene-ro-acr ylonitrile) (SAN) random copolymer as major phase. polystyrene (PS) as mino r phase, and poly(styrene-b-methylmethacrylate) (PS-b-PMMA) block copolymer as emulsifier is investigated as a function of the acrylonitrile content o f the SAN copolymer. In this way. the degree of exothermic interaction and swelling power between SAN and PMMA block is varied systematically. Consist ent with previous work, a well-emulsified morphology is produced when the s welling tendency of the block segment in the major phase (S-out) is compara ble to that in the minor phase (S-int) (0.4 less than or equal to Sout/Sint less than or equal to 2.5). Outside this window, emulsification failure oc curs. We further investigate the influence of S-out/S-int on the formation of phase-inverted (PIN) morphology, induced by lowering the viscosity of th e disperse phase. We demonstrate that a decrease in swelling power assists the tendency of the minor phase to be continuous, i.e. the formation of PIN structure is possible at a lower weight fraction of the minor component. ( C) 2001 Elsevier Science Ltd. All rights reserved.