Molecular mobility in polymer thin films

被引:80
作者
Tseng, KC [1 ]
Turro, NJ [1 ]
Durning, CJ [1 ]
机构
[1] Columbia Univ, Dept Chem Engn & Appl Chem, New York, NY 10027 USA
来源
PHYSICAL REVIEW E | 2000年 / 61卷 / 02期
关键词
D O I
10.1103/PhysRevE.61.1800
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
Fluorescence recovery after photobleaching was used to measure in-plane dye-probe diffusion coefficients, D, in thin films of monodisperse polystyrene supported on fused quartz substrates. The substrates were prepared with a high density of surface hydroxyl groups which interact favorably with repeat units of the polymer. The effects of temperature and film thickness were investigated, at temperatures above the bulk glass transition of the polymer, T-g, and in the range of film thicknesses from 1-10(2) times the radius of gyration (R-g) of individual polymer molecules. As the film thickness decreases towards Rg the value of D increases above the bulk values, with significant effects first appearing in films similar or equal to 20R(g). In the thinnest films studied, about 4R(g), the values of D lie as much as two orders over bulk values. At the same time, the temperature dependence of D becomes much weaker than in hulk. Analysis by free volume theory indicates that apparent values of both T-g and the thermal expansion coefficient for liquid state, alpha(L), decrease as the film thickness decreases. The possible effects of surface segregation of the dye probe are discussed.
引用
收藏
页码:1800 / 1811
页数:12
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