STRESS-RELAXATION IN THE LAMELLAR COPOLYMER MESOPHASE

When diblock copolymers organize into a lamellar mesophase, the interpénétration between like blocks from opposing interfaces is inhibited at high molecular weight. For layers of height h and polymerization index iV we show that interpénétration is confined to distances ξ of order (h/N2),113, which becomes much smaller than h itself. We show by self-consistent field methods that the concentration of penetrating monomers falls off with penetration depth y as exp(-Cy/£)3/2). We argue that the relaxation time for sliding stress grows exponentially as a fractional power of the molecular weight because of this small interpénétration. A numerical example calculation suggests that interpénétration is significantly inhibited in real copolymers and that the predicted slow-relaxation regime should be accessible. © 1990, American Chemical Society. All rights reserved.