Chain conformation in ultrathin polymer films

Polymer thin films are used in a variety of technological applications—for example, as paints, lubricants and adhesives. Theories that predict the properties of molten polymers in confined geometries (as in a thin film) generally start from the premise that the chains maintain their unperturbed gaussian conformation in the direction parallel to the surface. This assumption has been questioned, however, by recent experiments. Here we use small-angle neutron scattering to characterize the chain structure and conformation in ultrathin (less than 100 nm) polymer films. The conformation can be deduced directly from the scattering from mixtures of protonated and perdeuterated polystyrenes. We find that the gaussian conformation is retained parallel to the surfaces in all cases. Chain sizes equal the bulk value, within experimental uncertainty, although there is a systematic trend towards chain swelling in the thinnest films.

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