Conformation of Polystyrene Chain in Ultrathin Films Obtained by Spin Coating

Abstract

This article reports a study of the chain conformation in thin films of amorphous polymer prepared by spin coating. Polystyrene chains of two molecular weights Mw, 230 000 and 660 000, are confined in layers of thickness equal to either 1000 A, thus greater than their unperturbed radii of gyration Rg, or 100 A, thus smaller than Rg. The form factor of the chain inside the layer is measured by small-angle neutron scattering. Changes of the scattering are observed as a function of the film thickness in the intermediate scattering vector range. We analyze the data in the frame of the wormlike model. In the 1000 A films, the chain has the same Gaussian conformation as in the bulk. In the films of 100 A, the persistence length of the chain is increased (compared to 9.2 A the value in the bulk) up to 45 A, for both Mw values. However, the corresponding scattering intensity is higher than expected for such an extended chain.