Editing Flory-Huggins theory
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*Positive values of <math>\chi</math> necessarily lead to immiscibility for polymer mixtures of high molecular weight. | *Positive values of <math>\chi</math> necessarily lead to immiscibility for polymer mixtures of high molecular weight. | ||
*Polymer mixing always take place if the <math>\chi</math> parameter is negative. Miscible polymer mixtures with negative <math>\chi</math> exist due to specific interactions between given polymer segments. Miscibility or compatibility can be induced by several methods. For instance, introducing opposite charges in the different polymers or adding a copolymer containing A and B segments. | *Polymer mixing always take place if the <math>\chi</math> parameter is negative. Miscible polymer mixtures with negative <math>\chi</math> exist due to specific interactions between given polymer segments. Miscibility or compatibility can be induced by several methods. For instance, introducing opposite charges in the different polymers or adding a copolymer containing A and B segments. | ||
*For polymer solutions (whose sites have the volume of a solvent molecule, <math>n_A</math>=1), the critical Flory-Huggins parameter is close to <math>1/2</math>. The temperature corresponding to this value <math>\chi</math>=<math>1/2</math> would be the critical temperature if the polymer is infinitely long and defines the [[theta solvent | theta temperature]] of the polymer-solvent system | *For polymer solutions (whose sites have the volume of a solvent molecule, <math>n_A</math>=1), the critical Flory-Huggins parameter is close to <math>1/2</math>. The temperature corresponding to this value <math>\chi</math>=<math>1/2</math> would be the critical temperature if the polymer is infinitely long and defines the [[theta solvent | theta temperature]] of the polymer-solvent system. | ||
*For polymer mixtures, <math>\chi</math> should be referred to the arbitrarily chosen microscopic volume defined as a site, e.g. 100 Angstroms. | *For polymer mixtures, <math>\chi</math> should be referred to the arbitrarily chosen microscopic volume defined as a site, e.g. 100 Angstroms. Usual values are close to zero <ref>[ N. P. Balsara "Thermodynamics of Polymer Blends", in J. E. Mark, editor, “Physical Properties of Polymers Handbook” AIP Press, pp. 257-268, (1996) ISBN 1563962950] </ref> | ||
The <math>\chi</math> parameter is somewhat similar to a [[second virial coefficient]] expressing binary interactions between molecules and, therefore, it usually shows a linear dependence of <math>1/T</math> | The <math>\chi</math> parameter is somewhat similar to a [[second virial coefficient]] expressing binary interactions between molecules and, therefore, it usually shows a linear dependence of <math>1/T</math> |