Confinement effects on the chain conformation in thin polymer films

The chain conformation of thin polymer films was investigated via diffuse neutron scattering. The samples consist of blend films of protonated and deuterated polystyrene spin coated onto glass substrates. A variation of the thickness of the blend films in a range of about 41 down to 0.66 times the radius of gyration R_g of the chains in the bulk enables the determination of film thickness and confinement effects. With diffuse neutron scattering in a reflection geometry the chain conformation in thin polymer films with film thicknesses less than 20 nanometers could be investigated. With decreasing film thickness d below approximately 6 R_g the in-plane dimension of the chains starts to increase which is caused by distortion of the chain conformation along the direction parallel and perpendicular to the surface of the film. This increase is quite significant below d < R_g and can be compared to theoretical predictions and simulations.