Molecular Motion in Free-Standing Thin Films of Poly (methyl methacrylate), Poly (4-tert-butylstyrene), Poly (α-methylstyrene), and Poly (2-vinylpyridine)

TitleMolecular Motion in Free-Standing Thin Films of Poly (methyl methacrylate), Poly (4-tert-butylstyrene), Poly (α-methylstyrene), and Poly (2-vinylpyridine)
Publication TypeJournal Article
Year of Publication2011
AuthorsPaeng, K., and M. D. Ediger
JournalMacromolecules
Volume44
Start Page7034
ISBN Number0024-9297
Accession NumberWOS:000294585600048
KeywordsBEHAVIOR, DYNAMICS, GLASS-TRANSITION TEMPERATURE, LENGTH, METHACRYLATE)S, MOBILITY, NANOSCALE CONFINEMENT, POLY(N-ALKYL, POLYSTYRENE FILMS, SURFACE, THICKNESS, ULTRATHIN POLYMER-FILMS
Abstract

A photobleaching technique has been used to measure the reorientation of dilute fluorescent probes in free-standing polymer films from 7 nm to 20 mu m thick. Similar to our previous report on free-standing polystyrene films, two subsets of probes with distinct dynamics were observed in free-standing poly(methyl methacrylate) films. The more mobile subset of probes is consistently interpreted in terms of a surface layer, and the thickness of the mobile surface layer is shown to increase with temperature. Poly(methyl methacrylate) has a mobile surface layer thickness of 4 nm at the bulk T-g. Similar measurements on freestanding poly(2-vinylpyridine) and poly(4-tert-butylstyrene) films indicate mobile surface layer thicknesses from 7 to 10 nm at their bulk T-g values, similar to the 7 nm value previously reported for polystyrene. In contrast to the other four polymers, free-standing poly(alpha-methylstyrene) films show no evidence of a mobile surface layer. We interpret these results in terms of contributions from a bulk correlation length and specific surface effects.

DOI10.1021/ma201266r