Iwao Seo

Large Dielectric Relaxations in an Alternate Copolymer of Vinylidene Cyanide and Vinyl Acetate

An alternate copolymer of vinylidene cyanide and vinyl acetate has been investigated dielectrically at temperatures above Tg ~170°C. A remarkable relaxation was observed in the 1 Hz to 10 kHz frequency range due to a separation from coexisting contributions as a result of the dc conductivity. The relaxation time depends upon the temperature in the WLF according to the characteristics of the micro-Brownian motions of molecular segments. The relaxation strength was found to reach 125, resulting in an unusually high dielectric constant. Such a large relaxation strength is an indication of some cooperative effects in relation to dipolar motions. Cooling to below Tg in the presence of a high electric field creates a large remanent polarization which is consistent with the strong piezoelectric activity reported for this copolymer.

Nonlinear Dielectric Relaxations in a Vinylidene Cyanide / Vinyl Acetate Copolymer

The third-order nonlinear permittivity has been measured as a function of the frequency for an alternate copolymer of vinylidene cyanide and vinyl acetate at temperatures above Tg~170degC. The observed frequency spectra were found to be fitted by a function Δe3/(1+(i ωτ3)β3 )3 with negative Δe3. Its real part changes sign from positive to negative with decreasing frequency. A negative Δe3 implies that the polarization tends to be saturated as the field is increased. Combined knowledge about linear and nonlinear dielectric increments allows an estimate of the size of equivalent dipoles, which explains the unusually large permittivity of this copolymer.

13C n.m.r. studies on the microstructure of poly(vinylidene cyanide/vinyl benzoate) and poly(vinylidene cyanide/styrene)

Abstract The microstructure of vinylidene cyanide-vinyl benzoate and vinylidene cyanide-styrene copolymers, both of which were prepared by radical copolymerization, were studied by 125 MHz 13 C n.m.r. spectroscopy. The former shows high piezoelectricity, while the latter has low piezoelectricity. It was found that the compositional sequence distribution and tacticity of both copolymers were not largely different from each other, namely, both were highly alternating copolymers with a non-stereoregular structure. Possible origins of piezoelectricity were suggested for vinylidene cyanide copolymers.

Electrochromic display device of tungsten trioxide and prussian blue films using polymer gel electrolyte of methacrylate

Abstract The electrochemical redox behaviors and electrochromic characteristics of tungsten trioxide (WO 3 ) and Prussian Blue (PB) thin films have been examined in two- and three-electrode systems using polymer gel electrolyte ( pge ), which is based on composites of copolymer of 2-hydroxyethylmethacrylate and neopentylglycoldimethacrylate containing lithium perchlorate in the mixture solution of butylene carbonate and propylene carbonate. The conductivity of the pge prepared was ca . 10 −3 S cm −1 at 30 °C. A reversible color change between blue and colorless was observed when an appropriate potential was applied repeatedly to the WO 3 - and PB-based electrochromic device ( ecd ). With the potential cycling more than 10 5 times less than 10% of the electrochromic characteristics were lost. The response time of the bleaching process of ecd using pge is higher than that using a solution electrolyte and the response time of coloration using pge is analogous to that using a solution electrolyte. The ecd properties characterized provide the optimum feature of the practical device.

13C n.m.r. studies on the microstructure of piezoelectric copolymers of vinylidene cyanide

The microstructure of vinylidene cyanide-vinyl pivalate, vinylidene cyanide-isopropenyl acetate and vinylidene cyanide-α-methyl styrene copolymers, which were prepared by radical copolymerization, was studied by 125 MHz 13C nuclear magnetic resonance spectroscopy. The first copolymer shows high piezoelectricity. For the last two, piezoelectricity could not be measured because their films were too brittle. The copolymers were not found to differ greatly from each other: they were highly alternating copolymers with a non-stereoregular structure.

Microstructure of vinylidene cyanide copolymers with linear-chain fatty acid vinyl esters

Abstract The microstructure of vinylidene cyanide (VDCN) copolymers with linear-chain fatty acid vinyl esters, vinyl propionate, vinyl butyrate and vinyl hexanoate, was studied by 67.9 MHz 13 C n.m.r. spectroscopy. It was found that the compositional sequence distributions obtained from the analysis of the cyanide carbon (VDCN-centred) pentad and the methine carbon (comonomer-centred) triad resonances of all copolymers were highly alternative. Tactic structures in the alternating sequence were almost completely atactic. The microstructures of all copolymers were not largely different from each other. So, we suppose that possible origins of piezoelectricity observed for vinylidene cyanide copolymers should be found in other factors than the microstructure.

Enhanced second-harmonic generation with Cerenkov radiation scheme in organic film slab-guide at IR lines

Second-harmonic generation is enhanced with both symmetric and asymmetric slab-guides composed of vinylidene cyanide/vinyl acetate copolymer film and a fused silica in the Cerenkov radiation scheme at Nd:YAG 1.06 mu m and Er:YAG 2.94 mu m laser lines. At 1.06 mu m wavelength an enhancement factor of about five in comparison with a bulk scheme has been obtained with the symmetrical Cerenkovian configuration having the film thickness d approximately=5 mu m. Extending the theory to the experimental model presented, the results are well explained theoretically, and an enhancement of the SHG power by a factor of 50 can be expected if d approximately=0.5 mu m. >

Anomaly in dielectric relaxation in alternating copolymers of vinylidene cyanide and fatty acid vinyl ester

Abstract Dielectric relaxation spectra at 10 Hz to 1 MHz for five vinylidene cyanide-vinyl ester copolymers were studied as functions of temperature and length of aliphatic side-chain in the comonomer unit. Three unusual phenomena in their dielectric behaviours were found: (1) extremely large dielectric relaxation strength; (2) dielectric transition phenomena whose strength changed suddenly at a critical temperature; and (3) unusual temperature dependence of the strength above the transition temperature. The dielectric transition temperature depends upon length of the side-chain and corresponds well with enthalpy peak temperature in the differential scanning calorimetry study. It was also found that the thermal history strongly affects the dielectric behaviours.

Second-harmonic generation in amorphous vinylidene cyanide/vinyl acetate copolymer using a pulsed Nd:YAG laser

Second-harmonic generation was recently observed in an amorphous vinylidene cyanide/vinyl acetate copolymer film by using a pulsed Nd:YAG 1.06-microm laser.

Enhanced SHG power using periodic poling of and vinylidene cyanide/vinyl acetate copolymer

Embedding poling-inverted corrugation of the optical nonlinear susceptibility into vinylidene cyanide/vinyl acetate organic copolymer, the second-harmonic (SH) power has been enhanced at pulsed Nd:YAG 1.06 /spl mu/m and Er:YAG 2.94 /spl mu/m laser lines by quasi-phase matching (QPM) the interaction between the fundamental and SH waves. Using a sample with a corrugation period of 120 /spl mu/m with poling corrugated by an interdigital electrode, an enhancement factor of about 94 and /spl sim/3 was obtained at 1.06 /spl mu/m and 2.94 /spl mu/m, respectively, in comparison with a bulk sample having uniform poling. Taking the first-order QPM, the maximum conversion efficiency was also about 0.001 percent at the wavelength /spl lambda//sub /spl omega//=1.06 /spl mu/m, with the fundamental peak power P/sub /spl omega// of 2.5 W, and the extinction coefficients of /spl alpha//sub /spl omega//=/spl alpha//sub 2/spl omega//=0.7 mm/sup -1/ in the film having a path length of 2.4 mm, while /spl sim/0.03 percent at /spl lambda//sub /spl omega//=2.94 /spl mu/m with P/sub /spl omega//=200 W, and /spl alpha//sub /spl omega//=1.4 mm/sup -1/ and /spl alpha//sub 2/spl omega//=0.7 mm/sup -1/ for the same film. >