Flory equation terms Links

The structure of hydrogels that do not contain ionic moieties can be analyzed by the Flory Rehner theory (Flory and Rehner 1943a). This combination of thermodynamic and elasticity theories states that a cross-linked polymer gel which is immersed in a fluid and allowed to reach equilibrium with its surroundings is subject only to two opposing forces, the thermodynamic force of mixing and the retractive force of the polymer chains. At equilibrium, these two forces are equal. Equation (1) describes the physical situation in terms of the Gibbs free energy. 

The condition of swelling equilibrium can be calculated by means of two theoretical approaches. It is assumed that the chemical potential of mixing for a network is the same as the chemical potential of mixing an uncross-linked polymer of high molecular weight and of the same structure as the network polymer. The mixing term can be described by means of the Flory-Huggins (FH) equation. The calculation of the elastic deformation term is based on the rubber elasticity theory (RET). 

Equation (5.14) represents the link between the specific retention volumes 7 , calculated from chromatographic data, and the thermodynamic interaction parameter, as defined by the Flory-Huggins approach. This parameter depends on the polymer concentration, as has been proved experimentally [12, 13]. Orofino and Flory [14] have shown that the term Xi2 92 iu eqn (5.8) represents an incomplete expression for the non-configurational contribution to the activity, this must be written as a series of powers in terms of the volume fraction, the first term being Xi2[Pg.131]

Since model networks have known values of Me, they are also extremely useful for clarifying aspects of the equilibrium swelling of elastomers The interpretation of such results utilizes the very recent theory of Flory in which the extent to which the deformation is non-affine depends on the looseness with which the cross-links are embedded in the network structure. This depends in turn on both the structure of the network and its degree of equilibrium swelling. In this case, comparisons between theory and experiment are most conveniently carried out in terms of the equation ... 

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