2-DIMENSIONAL SELF-ASSEMBLY OF POLYSTYRENE-B-POLY (BUTYL-METHACRYLATE) DIBLOCK COPOLYMERS

We report a study of the two-dimensional self assembly of polystyrene- poly(n-butyl methacrylate) and polystyrenepoly(t-butylmethacrylate) no nionic diblock copolymers at the air-water interface. Langmuir film ba lance experiments, transmission electron microscopy and atomic force m icroscopy show that both of these diblocks form surface micelles. Star fish, rod and planar morphologies are observed, similar to those forme d by copolymers where one block is ionic. The boundaries between the v arious morphologies in he nonionic systems occur at lower PS (polystyr ene) content than in the ionic system. A plateau, indicative of a phas e transition, is seen in isotherms when the PBMA block exceeds a certa in length. The temperature dependence allows us to estimate the entrop y change associated with the transition. Hysteresis effects are seen o n cycling the compression and expansion of the films, and the phase tr ansition is shown to be reversible. We suggest that the transition is associated with a pressure-induced reorientation of the ester side cha ins. These studies further establish the broad generality of the surfa ce micellization phenomenon and assist us in our understanding the rel ationships between polymer conformations, polymer surface properties a nd the self-assembly properties of polymeric surfactants. (C) 1998 Els evier Science B.V.