Intramolecular and Intermolecular Rearrangements in Nanoconfined Polystyrene

Vacuum ultraviolet spectroscopy reveals an intramolecular rearrangement involving a change in "physical dimers" of adjacent pendant benzene rings of atactic polystyrene (aPS) from "oblique" to "head-to-tail" (ht) configuration in aPS films spin coated on fused quartz, as film thickness R goes below 4R g (R g = unperturbed polystyrene gyration radius ≈ 20.4 nm). Simultaneously, transverse layering of molecular "gyration spheres", for film thickness R ≤ 4R g, causes an increase in free energy (reduction in cohesion) that follows a (R g/R) h dependence with b ≈ 3, a clear deviation from planar confinement. The variation of in-plane and outof-plane cohesive energy over a film of a given thickness is explained by invoking a fixed-range, repulsive, modified Pöschl-Teller intermolecular potential, with the strength of this potential decreasing with increase in R. Possible reduction of "dimer" dipole moment due to ht configuration is consistent with reduction of cohesion between aPS molecular gyration spheres.