Enhanced high-frequency molecular dynamics in the near-surface region of polystyrene thin films observed with ß-NMR.
Soft Matter
; 11(9): 1755-61, 2015 Mar 07.
Article
em En
| MEDLINE
| ID: mdl-25605007
ABSTRACT
ß-detected nuclear spin relaxation of (8)Li(+) has been used to probe the depth dependence of molecular dynamics in high- and low-molecular-weight deuterated polystyrene. The average nuclear spin-lattice relaxation rate, 1/T(avg)(1), is a measure of the spectral density of the polymer motion at the Larmor frequency (41 MHz at 6.55 T). In both samples, 1/T(avg)(1) is depth independent below â¼200 K but above this temperature it decreases approximately exponentially with distance from the free surface, returning to bulk behavior for depths greater than â¼10 nm. This is direct evidence for a region near the free surface with enhanced molecular dynamics compared with the bulk. The effective thickness of the surface region increases with increasing temperature and is finite even above the glass transition. These results present challenges for the current understanding of dynamics near the surface of polymer glasses.
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1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Soft Matter
Ano de publicação:
2015
Tipo de documento:
Article
País de afiliação:
Canadá