Comparison of Dielectric Relaxations of Water Mixtures of Poly(vinylpyrrolidone) and 1-Vinyl-2-pyrrolidinone

Microwave dielectric studies on the dynamics of water in poly(vinylpyrrolidone) (PVP)−water mixtures and 1-vinyl-2-pyrrolidinone (VP)−water mixtures were performed to compare the relaxation processes of water in polymer−water and monomeric compound−water mixtures. For the PVP−water mixtures, a relaxation peak for water was observed and the shape of the absorption curve was symmetrical about the logalism of frequency, which the Cole−Cole equation describes well. In this case, the polymer behaves as a geometric constraint for rotational motion of water molecules, and a variation of the local structure of water yields the symmetrical relaxation curve. On the other hand, one relaxation peak due to the rotational motion of the dipoles of water and VP molecules was also observed for VP−water mixtures. However, the shape of the absorption curve is asymmetric and is described well by the KWW function. Cooperative motion of water and VP molecules resulted in a variation of local structure which is observed as an asymmetric relaxation curve.