Okimichi Yano

Dielectric Relaxations in Various Crystal Modifications of Cyclohexanol and 2,3-Dimethylbutane

Abstract The dielectric constant and loss of crystalline cyclohexanol (CHOL) and 2,3-dimethylbutane (DMB) were measured from 4°K to the melting point, 299°K for CHOL and 145°K for DMB. The supercooled plastic crystal of CHOL above the glass temperature Tg exhibits a prominent relaxation (α) due to molecular rotation. The temperature dependence of therelaxation time was found to obey the Fogel-Tamman equation. A secondary relaxation (β) was observed below Tg , 149°K for CHOL and 76°K for DMB. The mechanism proposed for β is internal rotation; rotationof OH bond for CHOL and trans-gauche transformation for DMB. The β relaxation of DMB is well correlated with acoustic relaxation in the liquid state in the relaxation time versus timperature plot. Relaxations in the intermediate state, crystal III, of these two substances and the most stable state, crystal II of DMB were studied.

Dielectric loss of poly(vinylidene fluoride) at low temperatures and effect of poling on the low temperature loss

Abstract Dielectric constant and loss of poly(vinylidene fluoride) (PVDF) were measured at 20 Hz. 110 Hz and 1 kHz in the temperatures ranging from 4.2 K to 300 K. Dielectric loss peaks (1 kHz) were observed respectively at 75 K (δ peak) for melt-crystallized PVDF with form I1 crystals and at 18 K (e peak) for rolled PVDF with oriented form 1 crystals. Activation energies were evaluated to be 12.6 and 1.9 kJ/mol for δ and e respectively. The height of e loss peak is suppressed by poling the sample at a rather low poling field. suggesting that the dipolar orientation in the form I crystal accompanying reduction of crystal detects occurs at the early stage of poling process.