Water, pure Terms Links

Solution Properties. Zwitterionic polymers show interesting aqueous solution behavior. As a general rule, they are insoluble in pure water due to the formation on intra- and interchain ion contacts resulting in an ionically cross-linked network-type structure. Polyampholytes and polybetaines which are not soluble become soluble upon the addition of low molecular weight electrolytes, such as NaCl (Fig. 51). This dissolution process can best be understood in terms of the low molecular weight electrolyte penetrating the ionically cross-linked network whereupon the ions screen the net attractive interactions between the polymer chains and hence promote solubility. The addition of the salt also results in an-tipolylelectrolyte behavior, ie chain expansion upon the addition of the salt. 

A study involving a multicomponent fibrous system can now be examined in terms of the above analysis. The tension required to maintain equilibrium between the crystalline and amorphous phases of cross-linked collagen has been deter-mined.(44) In these experiments the fiber is immersed either in a large excess of pure water or in an aqueous KCNS solution. The experiments were conducted over a wide temperature range. The equilibrium force at a given temperature was approximately independent of the total sample length and consequently the extent of the transformation. When the supernatant phase consists solely of pure water, the system is univariant and the aforementioned result is to be expected. However, the results obtained when the supernatant phase contains two components indicates that the single-liquid approximation is also valid in this particular case. 

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