LAMELLAR DIBLOCK COPOLYMER GRAIN-BOUNDARY MORPHOLOGY .4. TILT BOUNDARIES

Tilt grain boundaries in poly(styrene-b-butadiene)lamellar diblock cop olymers were characterized using transmission electron microscopy (TEM ). Three distinct tilt grain boundary morphologies were observed: the chevron, the omega boundary, and the T-junction. All three boundary ty pes are found to have intermaterial dividing surfaces, separating the polystyrene and polybutadiene microphases, that approximate surfaces o f constant mean curvature. The chevron and omega morphologies are obse rved for symmetric tilt boundaries, and a transition occurs from the c hevron to the omega as tilt is increased at constant boundary width. A transition from either the chevron or the omega boundary to the T-jun ction occurs as the boundary becomes more asymmetric. Analyses of both of these transitions using geometrical arguments are in agreement wit h experimental observations.