Conformation of polystyrene chain in ultrathin films obtained by spin coating

This article reports a study of the chain conformation in thin films of amo rphous polymer prepared by spin coating. Polystyrene chains of two molecula r weights M-w, 230 000 and 660 000, are confined in layers of thickness equ al to either 1000 Angstrom, thus greater than their unperturbed radii of gy ration R-g, or 100 Angstrom, thus smaller than R-g. The form factor of the chain inside the layer is measured by small-angle neutron scattering. Chang es of the scattering are observed as a function of the film thickness in th e intermediate scattering vector range. We analyze the data in the frame of the wormlike model. In the 1000 Angstrom films, the chain has the same Gau ssian conformation as in the bulk. In the films of 100 Angstrom, the persis tence length of the chain is increased (compared to 9.2 Angstrom the value in the bulk) up to 45 Angstrom, for both M-w values. However, the correspon ding scattering intensity is higher than expected for such an extended chai n.