Morphology of a hydrogen-bond mediated self-assembling small molecule in a polycarbonate matrix

Abstract

Dispersing functional small molecules in a polymer matrix is a well-known method of device fabrication for optoelectronic applications. Normally, no specific interactions such as hydrogen bonding occur between the polymer and the small molecule. The latter does not belong to the category of “self-assembling” molecules. When phase separation occurs, the small molecule would diffuse to the surface and crystallize. In this paper, we describe a very different morphological behaviour of hydrogen-bond mediated self-assembling molecules in a polycarbonate matrix. We used a series of biscarbamates with two hydrogen-bonding motifs and alkyl side chain lengths symmetrically varying from C4 to C18. We infer that the rate of self-assembly is faster than the diffusion of the small molecule to the surface. As a result, crystallization of the small molecule occurs predominantly in the bulk, i.e., sub surface, and not on the surface of the polymer film.Key words: self-assembly, crystallization, diffusion, phase separation.