Control of Molecular and Microdomain Orientation in a Semicrystalline Block Copolymer Thin Film by Epitaxy

Epitaxial crystallization is utilized to control both molecular chain orientation and microdomain structure in a thin film of a semicrystalline triblock copolymer, composed of crystallizable polyethylene (PE) end blocks and an amorphous ethylene- alt -propylene (PEP) midblock where the microphase separation is driven by crystallization from a homogeneous melt, characterized by small-angle and wide-angle X-ray diffraction. Surface interaction due to a crystallographic matching of unit cells between the crystalline PE block and benzoic acid (BA) substrate induces high orientation of the crystalline PE block, resulting in a well-ordered parallel lamellar microphase-separated structure. The excellent orientation induced by the surface interaction is evidenced by the selected area electron diffraction (SAD) pattern and bright-field (phase contrast) and dark-field (diffraction contrast) transmission electron microscope (TEM) images of the block copolymer thin film. The data clearly show that the chain axis ( ĉ ) of PE is parallel to the normal ( n̂ ) of the microphase-separated lamellar surfaces.