Free-radical precipitation polymerization was used to make non-ionic poly(N-isopropylacrylamide) (PNIPAM) microgel particles. On the synthesized PNIPAM microgel particles, a dynamic light scattering experiment was performed, and hydrodynamic radii were determined to be roughly 240 and 125 nm for temperatures of 298 and 313 K, respectively. Dielectric experiments were carried out on a 10 wt % PNIPAM microgel aqueous suspension at temperatures extending from 288 to 323 K, including volume phase transition temperature (VPTT) at 305 K in the frequency range of 40 Hz to 50 GHz. At frequencies of about 3−5 MHz and 16−18 GHz, two distinct relaxation processes were detected, in addition to electrode polarization and the contribution of dc conductivity. The local chain motion of PNIPAM (p-process) and the average relaxation mode of water located at the bulk solution and also within the microgel (w-process) are assumed to be the origins of the two relaxation processes. Furthermore, based on the idea of two kinds of water models, contributions of each of the two kinds of water, both free water outside the microgel (w1, with its relaxation time of τ w1 ) and confined water within the microgel (w2, with its relaxation time of τ w2 ), to the high-frequency relaxation spectrum were evaluated. The τ w2 is only 2−2.7 times larger than τ w1 above VPTT. This means that rotational motion of water molecules is not significantly constrained inside the microgel particle even above VPTT. The NMR rotational correlation time τ c , which is comparable to the dielectric relaxation time, was estimated using Bloembergen−Purcell−Pound (BPP) theory. The 3τ c value for the microgel suspension obeys BPP theory only up to VPTT; above that, due to anisotropy and/or loss of translational mobility of water induced by microgel shrinkage, precondition of BPP theory is broken. Furthermore, we obtained the concentration of PNIPAM in microgel particles using both the relaxation times and relaxation strengths of w1 and w2 above and below VPTT. Below VPTT, the p-process locates at the MHz region, and it shifts toward the lower-frequency side above VPTT due to the hindrance by microgel structural changes. The dynamics of the polymer and water inside and outside microgel particles in the solution bulk are observed simultaneously by the same physical quantities through the volume phase transition.

This study investigates the cooperative molecular dynamics of poly­(vinyl methyl ether) (PVME) at temperatures above and below the glass transition temperature, T g, using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The DSC measurements of PVME aged at temperatures below T g revealed the aging-time-dependent enthalpy relaxation. The BDS measurements revealed the structural α-relaxation process that originated from segmental chain motion at temperatures above T g. Both the enthalpy and dielectric relaxation are described via a stretched exponential function, exp­(−(t/τ)βK ), and the relaxation time, τ, and the stretching index, βK, are obtained. τ and βK of the enthalpy relaxation obtained via DSC measurements are compatible with those of the structural α-relaxation obtained via BDS measurements. This similarity indicates that the molecular origin of the enthalpy relaxation is the same as that of the dielectric α-relaxation process of the polymer, i.e., its segmental chain motion.

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Electrical stimulation is one of the candidates for elongation-driven regeneration of damaged peripheral nerves. Different organs and tissues have an inherent cell structure and size. This leads to variation in the tissue-specific electrical properties of the frequency of interfacial polarization. Although nervous tissues have a membrane potential, the electrical reaction inside these tissues following electrical stimulation from outside remains unexplored. Furthermore, the pathophysiological reaction of an injured nerve is unclear. Here, we investigated the electrical reaction of injured and non-injured rat sciatic nerves via broadband dielectric spectroscopy. Crush injured and non-injured sciatic nerves of six 12-week-old male Lewis rats were used, 6 days after infliction of the injury. Both sides of the nerves (with and without injury) were exposed, and impedance measurements were performed at room temperature (approximately 25°C) at frequencies ranging from 100 mHz to 5.5 MHz and electric potential ranging from 0.100 to 1.00 V. The measured interfacial polarization potentially originated from the polarization by ion transport around nerve membranes at frequencies between 3.2 kHz and 1.6 MHz. The polarization strength of the injured nerves was smaller than that of non-injured nerves. However, the difference in polarization between injured and non-injured nerves might be caused by inflammation and edema. The suitable frequency range of the interfacial polarization can be expected to be critical for electrical stimulation of injured peripheral nerves.

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