Swelling curve salt effect

It is now possible to classify the salt effects on the swelling curve. Till now four types of salt effects have been found and these are summarized in Fig. 28. These results suggest that two parameters, contact free energy and the S value in... 

Fig. 28. Classification of salt effects on the swelling curve. Until now four types of effect have been observed, each of which has different combination of increment or decrement of the transition temperature, induction or reduction of the transition discontinuity, and their combinations...

Figure 5 shows the swelling behavior of the model acrylic latexes as determined by photon correlation spectroscopy. Changes in particle diameter are shown instead of radius as in Figures 3 and 4. The diameter, d, at each pH was divided by the initial diameter, d0, determined at pH = 5 (unexpanded). In general shape, the curves are similar to those determined by sedimentation and viscometry. The initial points occurred at a higher pH due to the much lower particle concentration. No effort was made to lower the initial pH with acid consequently, the undesirable salt effect was avoided. 

Figure 5. Effect of network ionization on temperature-induced collapse of NIPA gel. Swelling measurements performed in aqueous solution (no added salt). Calculated swelling curves are predictions based on parameters obtained for uncharged NIPA gel in water. (Reproduced with permission from [13]).

The influence of neutral salts as well as of acids and bases on the swelling of gelatine which we have seen can be attributed to an apparent change in the solvation of the gel fibrils and may be interpreted in the light of Donnan s theory of the effect of a non-diffusible ion on the osmotic pressure differences between the two phases, is likewise to be noted in the alteration of the viscosity and alcohol precipitation values of protein solutions. From the considerations already advanced there should exist two well-defined maxima in the viscosity and alcohol precipitation curves when these properties are plotted as functions of the Ph, the maxima coinciding with the points of maximum dissociation of the salts... 

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