Takushi Sugino

Electrolytes in porous electrodes: Effects of the pore size and the dielectric constant of the medium

Monte Carlo simulations in the constant voltage ensemble were performed for electrolytes in porous electrodes. It was found that the electrical and mechanical properties in porous electrodes dramatically change depending on the pore size and the dielectric constant of the medium. For a low dielectric constant of the medium, the capacitance of porous electrodes tends to increase as the pore size decreases and the pressure in the porous electrodes is positive or negative depending on the pore size. For a high dielectric constant of the medium, on the contrary, the capacitance tends to decrease as the pore size decreases and the pressure is positive for all the conditions studied here. Such pore size dependencies are explained in terms of the balance between the electrostatic interaction and the volume exclusion interaction in the porous electrode.

Ionic electroactive polymer artificial muscles in space applications

A large-scale effort was carried out to test the performance of seven types of ionic electroactive polymer (IEAP) actuators in space-hazardous environmental factors in laboratory conditions. The results substantiate that the IEAP materials are tolerant to long-term freezing and vacuum environments as well as ionizing Gamma-, X-ray, and UV radiation at the levels corresponding to low Earth orbit (LEO) conditions. The main aim of this material behaviour investigation is to understand and predict device service time for prolonged exposure to space environment.

Phase transition in porous electrodes

It is shown by Monte Carlo simulation that electrochemical thermodynamics of electrolytes in a porous electrode is qualitatively different from that in the bulk with a planar electrode. In particular, first order phase transitions occur in porous electrodes when the pore size is comparable to the ion size of the electrolytes: as the voltage is increased from zero, the surface charge density and the ion density in the porous electrodes discontinuously change at a specific voltage. The critical points for those phase transitions are identified.

Expansion and contraction of polymer electrodes under applied voltage

The authors developed a scheme for characterizing the expansion and contraction of polymer electrodes when voltage is applied by coupling a symmetry analysis, the elasticity theory, and the experimental measurements. This scheme was applied to the bucky-gel electrodes and the expansion and contraction rates for the cathode and the anode were determined separately. For the case of the bucky-gel electrodes, it was found that the cathode expands and the anode contracts as voltage is applied. The stress exerted inside the electrode layers was also determined and the mechanical efficiency of the actuator composed of the bucky-gel electrodes is discussed.The authors developed a scheme for characterizing the expansion and contraction of polymer electrodes when voltage is applied by coupling a symmetry analysis, the elasticity theory, and the experimental measurements. This scheme was applied to the bucky-gel electrodes and the expansion and contraction rates for the cathode and the anode were determined separately. For the case of the bucky-gel electrodes, it was found that the cathode expands and the anode contracts as voltage is applied. The stress exerted inside the electrode layers was also determined and the mechanical efficiency of the actuator composed of the bucky-gel electrodes is discussed.

FEMTOSECOND OPTICAL KERR STUDY OF HEAVY-ATOM EFFECTS ON THE THIRD-ORDER OPTICAL NON-LINEARITY OF THIOPHENE HOMOLOGUES : ELECTRONIC HYPERPOLARIZABILITY OF TELLUROPHENE

Abstract Second hyperpolarizability γ of tellurophene (C 4 H 4 Te), a tellurium-containing homologue of thiophene, was measured by optically heterodyne-detected optical Kerr effect (OHD–OKE) experiments. We found that the γ of tellurophene was +6.3×10 −36 esu and was larger than twice of that for selenophene and almost three times that for thiophene. The large γ for tellurophene as the homologue was discussed in terms of the symmetry species of the two lowest excited states and their transition energies from the ground state under the 3-state approximation. Low-lying excited A 1 state is presented as the plausible cause of the large γ .

Mechanical behaviour of bending bucky-gel actuators and its representation

Bucky-gel actuators are ionic electromechanically active materials that bend in response to a low-voltage excitation. While bending actuators may offer new approaches in engineering solutions, the characterization of bending poses many challenges in comparison to conventional rotary motion. It is often desired to reduce the bending behaviour to a single parameter, which may lead to the loss of accuracy in modelling. A high-speed laser profilometer is utilized to characterize the bending response of different bucky-gel actuators at their full length and to critically compare the applicability of existing representation tools for bending. The best analytical representation of the bending of a bucky-gel actuator is found to be in the form of a power function. It is also observed that, along the length of the actuator, sections closer to the electrical input clamp exhibit back-relaxation (a common drawback for bending ionic actuators) already when the far end of the bending strip is still in forward motion.

Electrochemistry of Carbon Nanotubes: Reactive Processes, Dual Sensing–Actuating Properties and Devices

Single-walled carbon nanotubes (SWCNT) embedded in a non-electroactive polymer are electrochemically characterized. The increasing voltammetric maximums obtained with rising temperature or electrolyte concentration point to a chemical nature of the processes. The chemical kinetic control of the processes is corroborated by its empirical chemical kinetics: the initial reaction rates are obtained from the chronoamperometric responses to potential steps. The activation energy of the reaction includes information about the structural state of the SWCNT before the potential step. Under constant current the potential evolution (chronopotentiometric response) and consumed electrical energy at any time change as a function of (are sensors of) the experimental temperature or the electrolyte concentration. The reactive material, or any device based on this material, senses these working variables, and shows dual and simultaneous actuating-sensing properties.

Alignment behaviour of the discotic nematic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene on polyimide and cetyltrimethylammonium bromide coated substrates

The orientational behaviour of the nematic discotic phase of 2,3,6,7,10,11-hexa(4-n-octyloxybenzoyloxy)triphenylene (C8OBT) on substrates coated with a polyimide or cetyltrimethylammonium bromide (CTAB) was investigated by polarizing optical microscopy. The averaged order parameters and directions of the triphenylene core and the carbonyl groups of C8OBT were evaluated by an infrared dichroic method. The discotic nematic (ND) phase of C8OBT exhibits a homeotropic alignment on a polyimide film, a typical nematic schlieren texture on a glass substrate, and a tilted or planar homogeneous alignment on a CTAB-coated substrate. The order parameter of the triphenylene core is higher on a polyimide film (S = 0.6) than on a CTAB-coated substrate (S = 0.2), whereas that of the carbonyl groups remains roughly constant at 0.2 to 0.3 independent of the substrate for the ND phase.

Phase transition in porous electrodes. II. Effect of asymmetry in the ion size

The electrochemical thermodynamics of electrolytes in porous electrodes is qualitatively different from that in the bulk with planar electrodes when the pore size is comparable to the size of the electrolyte ions. In this study, the effect of the ion size asymmetry on the thermodynamics in porous electrodes was studied by using Monte Carlo simulation. We used the electrolyte ions for which the size of the cations and that of anions is different. Due to the asymmetry in the ion size, the ionic structure and the way the surface charge is distributed on the electrode surfaces were found to be qualitatively different in the cathode and in the anode. In particular, for some ranges of applied voltage, the distribution of the surface charge induced on the electrode planes shows inhomogeneity, which is not intrinsic to the structure of the porous electrodes. The transition from the homogeneous to the inhomogeneous distribution of surface charge on changing the voltage is a second order phase transition.

Photopolymerization and Molecular Orientational Order of the Discotic Nematic Phase in 2,3,6,7,10,11-Hexakis(4-(8-acryloyloxyoctyloxy)benzoyloxy)triphenylene

A triphenylene-based discotic liquid crystal, 2,3,6,7,10,11-hexakis(4-(8-acryloyloxyoctyloxy)benzoyloxy)triphenylene (6ABTP) was investigated on the behavior of local order parameters for the discotic nematic (N D ) phase from the viewpoint of change of the molecular orientational order by photopolymerization. The local order parameters of the aromatic C = C, C-H and two C = O bonds of the acryloyl and benzoyl C = O groups were evaluated by an infrared dichroic method of Vij et al. It was found that 6ABTP tends to show a homeotropic alignement in the N D phase on a polyimide film spin-coated on BaF 2 and the triphenylene core shows a large order parameter (ca. 0.4-1.0), while the C = O moieties have a quite lower one (< 0.3). In order to investigate the disordering of molecular alignement due to crosslinking by photopolymerization, the behavior of local order parameters in photopolymerization was also evaluated. It was found that the order parameter of the aromatic core in the N D phase remarkably decreases at the early stage of photopolymerization, but only about 20% of decrease in the order parameter could be attained at the end of polymerization.