Cooperative hydration in solutions of temperature-responsive polymers

Cooperative hydration in solutions of temperature-responsive polymers 

In contrast to PEO, other water-soluble polymers, such as poly(Al-isopropylacrylamide) (PNIPAM), show very flat LCST, whose cloud-point lines and spinodal lines are horizontal up to 20 wt% of polymer concentration and almost independent of the molecular weight [49-54]. The phase separation region takes a shape like the bottom part of a square, so that in what follows we refer to it as the miscibility square. Obviously, the miscibility square cannot be explained by random adsorption of water molecules. But, 

The coupled equations (6.81) and (6.82) should be solved for x and y to find the cluster distribution function in terms of the polymer volume fraction and the temperature. Upon eliminating x, the second equation is transformed to 

The total number of free water molecules and associated complex is given by 

For random hydration, /f(j) should be replaced by Km = -Vmln)nCm All results reduce to random hydration, as studied in the previous section. 

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