Physics

Small-angle X-ray scattering

Polystyrene

Mathematics

Optics

RADIUS

Composite material

Radius of gyration

Scattering

Materials science

Geometry

Condensed matter physics

Gyration

Computer science

Molecular physics

Compressibility

Computer security

Polymer

Thermodynamics

Physical Review Letters

Changes to the structure of polystyrene melt films as measured through the spectrum of density fluctuations have been observed as a function of film thickness down to the polymer radius of gyration (${R}_{g}$). Films thicker than $4{R}_{g}$ show bulklike density fluctuations. Thinner films exhibit a peak in $S(q)$ near $q=0$ which grows with decreasing thickness. This peak is attributed to a decreased interpenetration of chains resulting in an enhanced compressibility. Measurements were made using small angle x-ray scattering in a standing wave geometry designed to enhance scattering from the interior of the film compared to interface scattering.

Thickness Induced Structural Changes in Polystyrene Films