MORPHOLOGY OF BLOCK COPOLYMERS AND MIXTURES OF BLOCK COPOLYMERS AT FREE SURFACES

The microdomain morphology of block copolymers at the free surfaces of solution-cast films was investigated by means of transmission electron microscopy and ultramicrotomy. The free surfaces of block copolymers consisting of amorphous components obey the thermodynamic requirements, i.e. the constituent block chains with lower critical surface tension always cover the free surface even for block copolymer films in which the component with higher critical surface tension forms the matrix. On the other hand, the free surfaces of block copolymers with crystalline components are governed by the crystallization kinetics, and their morphology depends on the orientation of the crystalline lamellae near or at the free surface. Therefore, the surface composition may vary with the method of preparation, and both amorphous and crystalline components can have a chance to be exposed to the free surface.