Swelling general theory

We have considered above the predictions of the general theory of the swelling and collapse of charged networks which contain both positive and negative charges. These predictions were first checked in Ref. [15]. The objects of the investigation were the copolymers of AA with SMA and 2-methyl-5-vinyl-pyridine, quatemized by dimethyl sulfate (MVPQ), crosslinked with BAA. The solvents were mixtures of water with ethanol. 

The first quantitative theory of the reentrant collapse was developed in Ref. [49], The theory explained the phenomenon of the simple reentrant collapse which was observed in Refs. [14, 41]. A more general theory of swelling and collapse of charged networks in the binary solvent was developed in Ref. [31] and described in Sect. 2.4.1. We have seen that one of the most essential features of the swelling behavior in mixed solvents is a redistribution of solvent molecules within the network giving a different solvent composition in the gel and the external solution. This redistribution is more pronounced for the collapsed gel, because the probability of contacts of the molecules of the solvent with polymer links in the collapsed gel is higher than in the swollen gel. 

The general theory of swelling assumes that the free energy of mixing and the elastic free energy in a swollen network are additive. The chemical potential difference between gel and solvent is given by the equation ... 

For convenience and simplicity, polymers have generally been considered to be isotropic in which the principle force is shear stress. While such assumptions are acceptable for polymers at low shear rates, they fail to account for stresses perpendicular to the plane of the shear stress, which are encountered at high shear rates. For example, an extrudate such as the formation of a pipe or filament expands when it emerges from the die in what is called the Barus or Weissenberg effect or die swell. This behavior is not explained by simple flow theories. 

First, we will describe briefly the biology of secretory cells in general and goblet cells in particular. Next, we will outline our earlier studies on the conformation of mudn networks using dynamic laser scattering. Short discussions on the Donnan swelling properties of the mucin network will bring us to the application of the theory of polymer gel phase transition to explain condensation and decondensation in secretion. 

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