Polymer Free Volume and Its Connection to the Glass Transition

In this Perspective we summarize the most widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volume and excess free volume

Ronald P. White; Jane E. G. Lipson

2016

Scholarcy highlights

  • In this Perspective we summarize the most widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volume and excess free volume
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  • We discuss the implications when alternative estimates for free volume are inserted into relationships that connect experimentally measured properties to free volume, such as those proposed by Doolittle, Fox and Flory, Simha and Boyer, Cohen and Turnbull, and Williams, Landel, and Ferry
  • Turning to the results of our own locally correlated lattice model, we demonstrate, by analyzing data for a set of over 50 polymers, that our calculations for total percent free volume lead to a predictive relationship with experimental glass transition temperatures and allow us to place the different definitions of free volume within a physical picture of what the proposed contributions represent
  • We find that melts go glassy upon reaching a “boundary” of minimum percent free volume that depends roughly linearly on temperature
  • Since the LCL model is a first-principles thermodynamic theory, we are able to link our free volume predictions to similar patterns that we find in the predicted entropy per theoretical segment
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