Chain conformation in ultrathin polymer films

Using Small Angle Neutron Scattering (SANS), we present the first quantitative measurements of the 3-dimensional conformation of macromolecules in thin polymer films of D < RG,Bulk, where D is the film thickness and RG,Bulk is the bulk radius of gyration. For D approximately equals 0.5 RG,Bulk, the molecular size along the film normal is less than 0.5 RG,Bulk, while relatively small changes are observed parallel to the surface. The observed changes in molecular size agree with predictions of molecular dynamics simulations of polymers confined in thin films, resulting from increased molecular orientation rather than chain distortion. Segregation of molecular centers of mass to the film center facilitates molecular packing while minimizing chain distortion. Estimates of length scales relating to the onset of chain distortion and chain orientation in thin film resists are D approximately equals 0.1 RG,Bulk and D approximately equals N(sigma ) respectively, where D is the film thickness, N is the number of chain segments, and (sigma) is the persistence length.

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