Haruhiko Yao

Nonadiabatic scanning calorimeter

A high-resolution computerized calorimeter capable of fully automatic operation in either ac or relaxation modes is described. Emphasis is given to a new version of the relaxation technique in which the heater power is ramped linearly in time. This improvement results in superior performance and convenience in studying both first- and second-order phase transitions and allows quantitative evaluation of latent heats as well as pretransitional heat capacity variations. Examples are given for the use of this calorimeter in the study of liquid crystal phase transitions.

Some aspects of recent improvements of temperature-modulated calorimeter

Abstract Some aspects of recent improvements in temperature modulated calorimeter have been described. The contents are: (1) a low-frequency AC calorimeter with an improved resolution; δC p C p ≅ 0.010% , δT ∼ 7 mK; (2) an ultra-low frequency fully automated multifrequency AC calorimeter operated down to 0.5 mHz; and (3) a calorimeter with a capability of both AC-mode and relaxation-mode operations.

Heat Capacity in α-β Phase Transition of Quartz

The heat capacity ( C p ) of quartz was measured by AC calorimetry near the α-β phase transition temperature. The existence of the intermediate phase (IP) was confirmed. A sharp increase of C p was observed at T C , the lower transition temperature. The value of T C in heating runs (HR) was higher than that in cooling runs (CR) by about 0.9 K. A hump of C p was clearly observed at T Q , the higher transition temperature in CR and also in HR of a special heating cycle without passing through T C . It was obscure, however, in the ordinary HR because of the hysteresis. The temperature range of IP was 1.15±0.05 K in CR, which is significantly narrower than the range where the X-ray satellite reflections are observable.

Phase transitions of quartz studied by a.c. calorimetry

Abstract An a.c. calorimetric heat capacity measurement has been performed on high-quality synthetic quartz. It was found that at the incommensurate (IC)-β-phase transition, the heat capacity C p of as-grown samples show critical behavior, i.e. there is a sharp peak at the IC-β transition. The shapes of the C p are almost identical in both heating and cooling runs. However, when as-grown samples were annealed in the α-phase just below the α-IC transition, the C p peak became considerably rounded and, at the same time, the transition temperature slightly increased. The shapes of the C p peaks on heating and cooling became dissimilar for the annealed samples.

Anomalous behaviours of the heat capacity in a liquid crystal showing a re-entrant isotropic phase

High resolution a.c. calorimetric measurements have been carried out on a liquid crystal 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-{4-[(S)-2-fluoro-2-methyldecanoyloxy]phenyl}pyrimidine (RSFPPY), determined the present measurement revealed precise temperature dependence of the heat capacity over a wide temperature range including the phase transition temperatures. The isotropic-chiral smectic C transition was anomalous in that it showed quite different behaviours depending on whether the measurement was made on heating or cooling; that is attributed to the relaxational character of the transition. A new non-transitional feature in the isotropic phase was found, corresponding to a very broad heat capacity peak over a 30 K temperature range. This indicates an existence of a new phase, possibly some kind of blue phase, at the lower temperature side of the isotropic phase. (RSFPPY), determined the present measurement revealed precise temperature dependence of

HIGH-RESOLUTION AC CALORIMETER FOR MEASURING THE HEAT CAPACITY OF SMALL AMOUNTS OF LIQUID SAMPLES

A high-resolution AC microcalorimeter has been developed to measure the heat capacity of liquid samples. A very stable AC heat flux is supplied to a sample by applying an AC electric current to a tubelike sample cell made of metal. The fluctuation of the AC temperature of the cell caused by heat leakage from the cell to the surroundings is corrected using the phase of the AC temperature together with its amplitude. Consequently, heat capacity can be measured with a precision of ±0.01%.

Local Orientational Analysis of Helical Filaments and Nematic Director in a Nanoscale Phase Separation Composed of Rod-Like and Bent-Core Liquid Crystals Using Small- and Wide-Angle X-ray Microbeam Scattering

We analyzed the local nanostructure in binary mixtures of rod- and bent-shaped molecules, n-pentyl-4-cyanobiphenyl (5CB) and 1,3-phenylene bis[4-(4-n-octyloxyphenyliminomethyl) benzoates] (P-8-OPIMB), respectively, using small- and wide-angle X-ray microbeam and macrobeam scattering. From the orientational X-ray scattering patterns, we concluded that the nematic director of 5CB is almost parallel to the smectic layers dominated by bent-core molecules in Bx. Moreover, we observed oriented small-angle diffraction peaks (about 300 Å), which is close to the spacing of 5-7 layers, and also consistent with the width of a helical nanofilament textures as observed by freeze-fracture transmission electron microscopy. The kinetics in B4 was also discussed based on the contact experimental method.

Slow relaxation process in the main transition of phosphatidylcholines studied with heat capacity spectroscopy. I. Multilamellar vesicles.

Extremely slow relaxation processes have been examined near the main transition of multilamellar vesicle samples of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) with a heat capacity spectroscopic technique. The dynamic heat capacity showed a significant frequency dependence in the studied frequency region of 0.5 mHz to 50 mHz. The relaxation observed here has been analyzed with the Cole-Cole equation. The mean relaxation times were 120 s in DMPC, and 260 s in DPPC. The relaxation showed a polydispersive character. The parameter beta was around 0.5 in both DMPC and DPPC.

ac nanocalorimeter for measuring heat capacity of biological macromolecules in solution

A precise calorimeter has been developed to measure the heat capacity of a small amount of liquid using a novel ac calorimetric method in which the effect of heat loss from a sample cell is corrected using the phase of the ac temperature. The sample cell is made of a fine glass tube, whose outer surface is plated with a nickel film as an ac heater. The ac temperature of the sample is detected precisely with a microbead thermistor attached to the middle of the tube. The resistance of the thermistor is measured with an ac Wheatstone bridge which is composed of resistors with a low temperature coefficient of ±1 ppm/K. The unbalance ac signal of the bridge is measured with a lock-in amplifier. To reduce the drift of measured values caused by the variation of room temperature, the amplifier and measuring instruments with temperature coefficients of >1 ppm/K are kept at constant temperature. Moreover, the gain of the amplifier is calibrated at every measuring point. Consequently, the heat capacity of 10 μl liqu...

An ac Microcalorimetric Method for Precise Heat Capacity Measurement in a Small Amount of Liquid

Making the most of light-irradiation-type ac calorimetry, a microcalorimeter is designed for measuring the heat capacity of a 1- µl liquid sample. The heat capacity can be determined within an accuracy of 1%.