MULTIBLOCK COPOLYMERS AND COLLOIDAL STABILITY

Block copolymers that have both adsorbing and nonadsorbing blocks can be used to stabilize colloidal dispersions. However, they can also ind uce an attraction between two particles by forming bridges between the surfaces. In this paper we investigate when such an attraction occurs and how its magnitude depends on the relevant system parameters. Most attention is paid to end-adsorbed triblock (A-B-A) copolymers and a f ew calculations are presented for polymers consisting of a larger numb er of blocks ((A-B)n-A with n > 1). Adsorbed layers of triblock copoly mers with identical adsorbing groups always cause an attractive part i n the two-particle interaction curves. Adsorbed layers of multiblock ( n > 1) copolymers with long blocks behave similar to triblock copolyme rs. When their blocks become very short, these multiblock copolymers r esemble homopolymers whose interaction parameters have some average va lue of those for both types of blocks. (C) 1994 Academic Press, Inc.