The equilibrium swelling ratios of temperature sensitive polymer gels have been studied as a function of the initial monomer concentration at preparation in both the swollen and the shrunken states. The linear swelling ratio, d/d0, was independent of the initial monomer concentration of N-isopropylacrylamide, C0, where d and d0 are the diameters of gels at observation and at preparation, respectively. On the other hand, d/d0 was proportional to C0 in the shrunken state. The swelling curves of gels with different C0's were successfully reproduced with a modified Flory-Rehner equation, where the effective cross-link density was modified to be proportional to C0 by taking account of the contribution of "excess cross-linking" by entanglement. Scaling rules for the polymer fractions were derived for both the swollen and the shrunken states; i.e., φsw ∼ C0 1 and φsh ∼ C0 0 , where φsw and φsh are the equilibrium volume fractions of the network at the swollen and shrunken phases, respectively.
The dynamic light scattering study has been carried out on swollen and reactor-batch gels of poly(N-isopropylacrylamide) (NIPA) in water as a function of polymer volume fraction, φ. The scattered intensity from these gels showed strong intensity fluctuations dependent on the sample position. The ensemble (i.e., position) average scattered intensity, 〈I〉E, increased by swelling for all gels prepared at different initial monomer concentrations, indicating an increase of the static inhomogeneities by swelling. On the other hand, the dynamic component, e.g., the intensity component of the thermal fluctuations, IF, decreased by swelling. The collective diffusion coefficient, D, increased with increasing φ and by swelling. The physical meaning of the static inhomogeneities and the dynamics of gels are discussed. Furthermore, the concentration dependence of the diffusion coefficient is discussed as a function of φ.
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