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Coexisting hydration and gelation

In some aqueous polymer solutions, hydration is noncompetitive with association. For instance, in solutions of telechelic polymers, main chain hydration only indirectly affects the end-chain association. There is interference only in the region very close to the chain end. Dehydration and chain collapse start near the core of the flower micelles in the form of heterogeneous nucleation. The solutions with such coexisting hydration and association turn into gels on cooling (low-temperature gelation), while they phase separate at high temperatures. [Pg.352]

In the solutions of homopolymers, the onset temperature of phase separation coincides with the coil-globule transition temperature. In contrast, telechelic PNIPAM solutions have a cloud-point temperature that is several degrees lower than the collapse temperature. The solution becomes turbid by the scattering of the light due to the formation of aggregates (of flower micelles) whose size is comparable to the wavelength of the light. Thus, the LCST splits from the collapse transition temperature. [Pg.352]

Let us consider a model solution consisting of N telechelic polymer chains (main chain of DP=n) carrying two end groups of DP n. The total DP of the polymer chains is = n+2n. The chains are mixed with a number A o of water molecules. To describe [Pg.353]

In the postgel regime where hydrated gel networks exist, one needs consider the number N i) of polymer chains of type I involved in the network. Their number density is given by (i) = (i) / S2, and their volume fraction by (i) = n (i) (i). [Pg.354]

In particular, the number of polymer chains of hydration type i that remain unassociated in solution is given by A (jo mo(i)). Similarly, the number of bound water molecules is [Pg.355]


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Hydration and gelation

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