In search of the Griffiths shield region |
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Authors: | I -Chien Wei Robert L. Scott |
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Affiliation: | (1) Department of Chemistry and Biochemistry, University of California, 90024 Los Angeles, California;(2) Present address: Department of Chemistry, Wright State University, 45435 Dayton, Ohio |
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Abstract: | The van der Waals equation of state for binary mixtures has been used to determine the location and shape of the Griffiths shield region (where three tricritical lines intersect). If one takes the geometric mean fora12, the arithmetic mean forb12, and the configurational free energy as ideal, the center of the Griffiths shield region is found only when the ratio of molecular sizes is infinite. When the Flory equation for the configurational free energy for mixtures of chain molecules is substituted for the ideal form, the results appear to be somewhat different. However, for all the cases studied, with systems which approach geometric mean behavior one finds the shield region only when the ratio of molecular size is very large and when the internal pressure of the small molecule is very much greater than that of the long-chain molecule.This paper is dedicated to our colleague Howard Reiss on the occasion of his 66th birthday. |
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Keywords: | Tricritical lines Griffiths shield region binary mixtures molecular size differences van der Waals equation of state Flory configurational free energy |
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