AGGREGATION STRUCTURE OF A 2-DIMENSIONAL ULTRATHIN POLYSTYRENE FILM PREPARED BY THE WATER CASTING METHOD

A two-dimensional ultrathin film was defined as a film with a dimension thinner than that of an unperturbed chain. The aggregation structure of the two-dimensional ultrathin polystyrene (PS) film prepared by the water casting method was examined. The radius of gyration of a PS chain in the two-dimensional ultrathin film was evaluated from small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) measurements. The radius of gyration along the direction parallel to the film surface was found to be larger than the radius of gyration of an unperturbed chain. The apparent occupied volume for a corresponding chain, which consists of overlapping of a noticed chain and surrounding chains, was calculated from the radius of gyration and film thickness. The apparent volume in the two-dimensional ultrathin film was found to be smaller than that in the three-dimensional solid film, indicating that the amount of interpenetration of surrounding chains is small; that is, the degree of entanglement among chains is low. A PS chain with a low degree of entanglement in the two-dimensional ultrathin film was expanded along the direction parallel to the film surface owing to unequilibrium characteristics of the film formation process. The radial distribution function (RDF) in the two-dimensional ultrathin film was also obtained from the Fourier transform of the wide angle X-ray scattering profile. The shape of the peak corresponding to intermolecular distance in the two-dimensional ultrathin film was broadened toward the long distance side, indicating that the packing of PS chains in the two-dimensional ultrathin film was looser than that in the three-dimensional solid film.