Explanation of Various Properties

Explanation of Various Properties. The postulate of a network with cross-links which can be dissociated by raising the temperature, whether they are single or multiple, is useful in interpreting many of the properties of gelatin gels described above. 

Melting Point. The melting point corresponds to a concentration of cross-links just sufficient to form an incipient network. Qualitatively, for a dimerization equilibrium, this should depend upon concentration in the manner observed. Although Equation 2 could be formally applied to a quantitative calculation, the error introduced in applying it to a diluted system is uncertain, so no attempt will be made to do so at the present time. The meager influence of pH and simple salts at moderate concentrations on melting points indicates that coulomb forces are unimportant in the association equilibrium. 

In this case, the rigidity should be proportional to the concentration 

Another possibility which cannot be present be eliminated is that the rigidity is proportional to the square of the concentration of cross-links (due to a stiff strutted structure rather than rubberlike elasticity), and the latter is proportional to the first power of the total concentration. The latter assumption would correspond to a very peculiar sort of association such as that recently postulated by Doty, Wagner, and Singer (1947) in dilute solutions of synthetic polymers. 

A decrease in rigidity with decreasing molecular weight, as observed, is inherent in several of the reservations associated with Equation 5. The effects of pH and neutral salt on rigidity are explained in the same way as their effects on melting point. 

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