Editing Flory-Huggins theory
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where <math>a</math> and <math>b</math> are assumed to be constants, but can actually depend on density, | where <math>a</math> and <math>b</math> are assumed to be constants, but can actually depend on density, | ||
concentration, molecular weight, etc. A usual interpretation is that <math>a</math> represents an [[enthalpy |enthalpic]] quantity and <math>b</math> an [[entropy | entropic]] contribution, although both <math>a</math> and <math>b</math> are actually empirical parameters. According to this description, the systems should show an upper critical temperature. Many polymer | concentration, molecular weight, etc. A usual interpretation is that <math>a</math> represents an [[enthalpy |enthalpic]] quantity and <math>b</math> an [[entropy | entropic]] contribution, although both <math>a</math> and <math>b</math> are actually empirical parameters. According to this description, the systems should show an upper critical temperature. Many polymer systems and solutions, however, show an increase of <math>\chi</math> for increasing temperatures (negative entropic contribution) what implies the existence of a lower critical temperature. | ||