Reinosuke Hayakawa’s research while affiliated with The University of Tokyo and other places

Mechanical and dielectric relaxations in crystalline phase (crystalline relaxation), glassy phase (local mode relaxation), and paracrystalline phase (paracrystalline relaxation) are interpreted in terms of torsional motion of chains in respective phases. A theory is developed on the relaxation strength, and a satisfactory agreement is found between theory and experiment for mechanical crystalline relaxations in normal paraffins. Dielectric crystalline relaxations in oxidized paraffins, poly(vinyl alcohol), and polyoxymethylene, dielectric paracrystalline relaxation in polyacrylonitrile, and local mode relaxations in several polymers are studied both experimentally and theoretically.

Without Abstract

In terms of power series expansion, we calculated the nonlinear after-effect and response function from the general time-evolution equation. From the result, we theoretically elucidated the connection between TEB and FEB. Also we clarified that the dc component of the electric birefringence relaxation yielded the information similar to that from the dielectric relaxation. We confirmed that our theoretical treatment agreed with the experimental results of NaPSS by two-dimensional electric birefringence relaxation spectroscopy. Further, we measured the FEB spectrum of conducting polymer solution. As a result, we detected the rod-coil transition directly by the FEB method. In addition, we clarified the two kinds of intra-molecular carrier transport mechanisms, that is, the carrier diffusion within the contour length and the diffusion within the more local range between the defects.

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

We study the dielectric response in lyotropic lamellar and sponge phases made up of a binary mixture of a nonionic surfactant and water. A single relaxation is observed in both phases within the measured frequency range of 10-10(7) Hz. This relaxation originates from the obstruction of electric current by insulating membranes. In the sponge phase, it depends on surfactant concentration and conductivity of solvent. The observed dependence is well-described quantitatively by the equivalent electric circuit of the sponge structure, including the effect of accumulation of ions at the interface between water and membrane. In the lamellar phase, there is little dependence of dielectric relaxation on surfactant concentration. This is presumably due to the fact that submicrometer-sized defects play a more important role in the electrical property in this phase than the lamellar structure in smaller length scales does. Our results offer some basic information to study more complicated systems composed of charged membranes in aqueous solution.

Nonlinear dielectric response of antiferroelectric liquid crystals has been studied in the smectic C(alpha)* (SmC(alpha)*) phase. The linear dielectric spectrum shows a single relaxation of Debye type and its relaxation frequency is as high as one hundred kHz. The profile of the third-order nonlinear dielectric spectrum varies in complex fashion with temperature. In the vicinity of the SmA-SmC(alpha)* phase transition, experimentally obtained nonlinear spectra are well described by those calculated with phenomenological theory of Landau type. The soft mode of the SmC(alpha)* phase shows critical slowing-down near the transition temperature. In the lower-temperature region of the SmC(alpha)* phase, the contribution from the soft mode of the SmC(alpha)* phase reduces and the other relaxation mode with Debye-type spectrum appears at several hundred Hz in the nonlinear spectrum. The appearance of this low-frequency mode suggests that the cooperative fluctuation of directors over long range exists in the SmC(alpha)* phase.

We study the nonlinear permittivity of chiral liquid crystals in the smectic-A (Sm-A) phase near the ferroelectric smectic-C* (Sm-C*) phase and the smectic-C(*)(alpha) (Sm-C(*)(alpha)) phase theoretically and experimentally. The third-order nonlinear permittivity epsilon(3) shows the critical behavior with the exponent of four near the Sm-C* phase and its sign depends on the order of the phase transition. In the case of the Sm-A-Sm-C(*)(alpha) phase transition, the sign inversion of epsilon(3), presumably due to the large fluctuation of order parameter, is observed near the transition temperature.

We measure the nonlinear dielectric response of antiferroelectric liquid crystals in the SmC A * and SmC f * phase. In the SmC A * phase, the spectrum of the third-order nonlinear permittivity l 3 * shows a Debye-type relaxation and is ascribed to the deformation of helical structure due to the coupling between dielectric anisotropy and electric field. In the SmC f * phase, the spectrum of l 3 * shows a complicated form and is explained by the Landau-type phenomenological free-energy which is composed of the ferroelectric and the antiferroelectric order parameter.

We measured the complex electrophoretic mobility mu(*)(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, and observed two relaxation processes corresponding to the two characteristic lengths of lamellar structure. Faster relaxation is caused by the distortion field of lamellar phase induced by the colloidal particles, and slower relaxation is presumably due to the defects in lamellar structure. Since the dynamic transport property is strongly influenced by the microscopic circumstances as shown in this paper, this method is referred to as electrophoretic microrheology.

We prepared salt-free polystyrenesulfonate (PSS) solutions with various ratios alpha of univalent and divalent counterions, i.e., X0.5alphaNa1-alphaPSS (X=Mg,Ca), and investigated them in the dilute region by means of the electrostatic birefringence spectroscopy that detects the rotational relaxations of polyelectrolyte chains. The obtained relaxation spectra show that, with replacing univalent counterions by divalent ones, the relaxation strengths decrease and the relaxation times gradually shift to higher values. From the rotational relaxation times, the electrostatic persistence length Lp for 0