Dudowicz Jacek, Freed Karl F, Douglas Jack F
The James Franck Institute and Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
J Phys Chem B. 2005 Nov 17;109(45):21350-6. doi: 10.1021/jp053693k.
The fragility of polymeric glass-forming liquids is calculated as a function of molecular structural parameters from a generalized entropy theory of polymer glass-formation that combines the Adam-Gibbs (AG) model for the rate of structural relaxation with the lattice cluster theory (LCT) for polymer melt thermodynamics. Our generalized entropy theory predicts the existence of distinct high and low temperature regimes of glass-formation that are separated by a thermodynamically well-defined crossover temperature T(I) at which the product of the configurational entropy and the temperature has an inflection point. Since the predicted temperature dependence of the configurational entropy and structural relaxation time are quite different in these temperature regimes, we introduce separate definitions of fragility for each regime. Experimentally established trends in the fragility of polymer melts with respect to variations in polymer microstructure and pressure are interpreted within our theory in terms of the accompanying changes in the chain packing efficiency.
聚合物玻璃形成液体的脆性是根据分子结构参数计算得出的，该计算基于聚合物玻璃形成的广义熵理论，该理论将用于结构弛豫速率的亚当 - 吉布斯（AG）模型与用于聚合物熔体热力学的晶格簇理论（LCT）相结合。我们的广义熵理论预测了玻璃形成存在明显的高温和低温区域，这两个区域由一个热力学上定义明确的交叉温度T(I)分隔开，在该温度下，构型熵与温度的乘积有一个拐点。由于在这些温度区域中预测的构型熵和结构弛豫时间的温度依赖性有很大不同，我们为每个区域引入了单独的脆性定义。在我们的理论中，根据链堆积效率的伴随变化，解释了聚合物熔体脆性随聚合物微观结构和压力变化的实验确定趋势。
