Dynamical behavior of unfreezable molecules restricted in a frozen matrix

Broadband dielectric spectroscopy measurements performed around the freezing temperature showed two different dynamical behaviors for various mixtures of poly(vinyl pyrrolidone) (PVP)/water, poly(vinyl acetate)(PVAc)/benzene, PVP/poly(ethylene glycol) (PEG), and 4,4′-n-pentylcyanobiphenyl (5CB)/benzene. A discontinuous behavior of the temperature dependence of the relaxation time around the freezing temperature was observed for the processes due to water in PVP/water, PVP in PVP/PEG, and 5CB in 5CB/benzene mixtures, and a continuous behavior was observed for PVAc in PVAc/benzene and PEG in PVP/PEG mixtures. These behaviors are explained by a large volume effect from the large motional unit. PVP/n-alcohol mixtures support that the high hydrogen-bonding ability of water brings about the large volume effect also in PVP/water mixture.