Self-Assembly and Digital Memory Characteristics of an Oxadiazole-Containing Brush Polymer in Nanoscale Thin Films

Abstract

The self-assembly characteristics in nanoscale thin films and digital memory behaviors of poly(5-phenyl-1,3,4-oxadiazol-2-yl-[1,1'-biphenyl]carboxyloxy-n-nonyl acrylate), a well-defined brush polymer bearing oxadiazole moieties, were investigated. The synchrotron grazing incidence X-ray scattering analysis found that the brush polymer molecules in thin films always formed a multibilayer structure consisting of fully extended backbone and bristle conformations. In the structure, the bristles were interdigitated in part; In particular, the oxadiazole containing mesogens were fully interdigitated via the pi-pi interaction of the biphenyl linkers. The multibilayer structured film undergoes three phase transitions (glass, melting, and liquid crystal-to-isotropic transitions) below the degradation temperature of 350 degrees C. The film's overall crystallinity, as well as the orientation of the multibilayer structure was found to depend on the film formation process conditions. While the as-cast films had a relatively low crystallinity and formed a vertical multibilayer structure with a broad orientation distribution, the thermally annealed films had a high crystallinity and formed an almost perfect horizontally oriented multibilayer structure. These different morphologies led different digital memory modes in devices; the as-cast films revealed volatile memory behavior, whereas the thermally annealed films showed permanent memory characteristics. These memory modes originated from the oxadiazole moieties in the two different film morphologies. The memory modes were demonstrated for the polymer films in the thickness range 5-50 nm.