期刊
MACROMOLECULES
卷 45, 期 4, 页码 1913-1923出版社
AMER CHEMICAL SOC
DOI: 10.1021/ma2023292
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资金
- Deutscher Akademischer Austauschdienst (DAAD) [PKZ: A/07/80278]
The film formation of poly(vinyl alcohol) of different molecular weights from concentrated solution has been, observed in real time by means of low-field nuclear magnetic resonance (NMR) methods. The drying of films was followed with a depth resolution of 50 mu m up to the formation of the final film of typically 300 mu m thickness, and the molecular mobility was determined with spatial resolution by analyzing the NMR relaxation times (T-2, T-1) behavior. A gradient in the molecular dynamics was observed from T-1 data during evaporation process up to an intermediate time when the film shrinkage rate decreases significantly; T-2 indicates dynamical heterogeneity as well, persisting up to complete removal of water. The relaxation times suggest an increase of local molecular order which is more pronounced toward the air/film interface. Wide-angle X-ray diffraction confirms the formation of an ordered region at this interface with a crystallinity higher-depending on molecular weight-than at the bottom side of the film.
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