DETERMINATION OF MOLECULAR ORIENTATIONAL DISTRIBUTION USING SURFACE 2ND-HARMONIC GENERATION ANALYZED BY 5-LAYER MODEL AND MAXIMUM-ENTROPY METHOD

A novel analytical method to determine molecular orientational distrib ution functions (ODFs) at interfaces has been developed to apply to po lymer film possessing second-harmonic generation (SHG) active side cha ins with C-infinity v symmetry. This method treats SHG in five layers, i.e., air, an upper SHG-active layer, an SHG-inactive polymer bulk, a lower SHG-active layer and a substrate (five-layer model). We first o btain tentative ODFs of the side chains at two SHG-active layers by th e assumption of two undetermined multipliers in the maximum-entropy me thod. These ODFs give the order parameters of the side chains and in t urn the dielectric constants of the SHG-active layers. Achieving the b est fit of the theoretical SHG intensity to the experimental results o btained in four different geometries, we succeeded in obtaining unbias ed ODFs together with the dielectric constants of the SHG-active layer s. (C) 1998 American Institute of Physics. [S0021-8979(98)03620-2].