Conformation of Polystyrene Chain in Ultrathin Films Obtained by Spin Coating

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 M w, 230 000 and 660 000, are confined in layers of thickness equal to either 1000 Å, thus greater than their unperturbed radii of gyration R g, or 100 Å, thus smaller than R g . 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 Å films, the chain has the same Gaussian conformation as in the bulk. In the films of 100 Å, the persistence length of the chain is increased (compared to 9.2 Å the value in the bulk) up to 45 Å, for both M w values. However, the corresponding scattering intensity is higher than expected for such an extended chain.