Takeshi Kawai

Fourier transform infrared study on the phase transitions of an octadecyltrimethylammonium chloride-water system

Abstract Fourier transform infrared spectroscopy has been used to study thermotropic phase transitions of a 20 g% water-octadecyltrimethylammonium chloride (ODAC) system. In this system, there appear three successive phases of coagel, gel, and liquid crystal with increasing temperature. In the coagel phase, the methylene chains take the trans-zigzag conformation packed in parallel with each other. The hydrophilic part of ODAC is in a fixed state, and the presence of bound water is evident. In the gel phase, the rotational motion of the methylene chain around the chain axis occurs in the hexagonal lattice. The hydrophilic part is in a fused state. The water spectrum becomes similar to that of liquid water. In the liquid crystalline phase, both hydrophobic and hydrophilic parts of ODAC are in fused states. The water spectrum also resembles that of liquid water.

Non-resonance Raman studies on spread monolayers of stearic acid-d35 and cadmium stearate-d35 on water surfaces and thin LB films

Abstract Non-resonance Raman spectra in the CD stretching region of spread monolayers of stearic acid- d 35 and cadmium stearate- d 35 on water surfaces and of their thin LB films were measured by combining a CCD detector with the total reflection technique. From an analysis of the linewidth of the symmetric CD 2 stretching band, we discuss changes in the lateral packing and conformational disorder of the carbon chains during the process of monolayer compression on the water surface and of monolayer transfer from the water surface to a solid substrate.

Orientation evaluation of polyion complex Langmuir-Blodgett films by Fourier transform IR transmission and reflection-absorption spectroscopy

Quantitative evaluation of molecular orientation in Langmuir-Blodgett (LB) films of polyion complexes between two azobenzene-containing fatty acids with different chain lengths (the C12 and C8 tail with the common C5 spacer) and two polycations were performed by comparing the absorption intensities of the Fourier transform IR transmission and reflection-absorption spectra. The results obtained were discussed in connection with the UV absorption peak maxima of the azobenzene chromophores and the limiting areas of the surface pressure-area isotherms of the spread monolayers on the water surface. For LB films of polyion complexes of the fatty acid with the C12 tail, the self-association forces are so strong that the degree of perpendicular orientation of the molecular chain and the stacking aggregation of the azobenzene chromophores remain high and unchanged from those for its barium salt. The polymer chain is considered to be twisted or folded to fit with the compact cross-section of the fatty acid. For LB films of polyion complexes of the fatty acid with the C8 tail, however, the degree of orientation and aggregation are degraded from those of its barium salt, the polymer chain being highly extended.

Cold Neutron Interferometry Using Multilayer Mirrors

Abstract Cold neutron interferometry using multilayer mirrors is discussed. The interferometry includes two kinds of multilayer interferometers, which are analogous optically to the Mach-Zehnder and the Jamin interferometer in classical optics. The Mach-Zehnder multilayer interferometer has been installed at JRR-3M reactor of JAERI. We describe the conditions required for the Mach-Zehnder multilayer interferometer and the characteristics of the interferometer. The Jamin multilayer interferometer, called a phase echo interferometer, shows a phase echo effect analogous functionally to the spin echo principle. We describe briefly the first successful performance tests. We propose a phase echo spin interferometer using multilayer spin splitters, based on the phase echo principle and the coherent superposition of the spin eigenstates.

An improvement of the detection efficiency of a solid state UCN detector with a 6Li/Ti multilayer neutron converter working at liquid helium temperature

Abstract The detection efficiency of a solid state ultracold neutron (UCN) detector which works at liquid helium temperature has been improved. The neutron converter was a 6Li/Ti multilayer evaporated onto the surface of a commercial silicon-surface-barrier detector for the charged particles. The advantage of a 6Li/Ti multilayer is that the positive optical potential of 6Li is compensated by the negative potential of Ti. UCNs can therefore penetrate into the neutron converter which transforms neutrons to charged particles. The surface of the neutron converter was coated by a 1800 A thick Ti layer which prevents lithium from reacting with oxygen in the atmosphere. Ti easily absorbs oxygen during evaporation so that the effect of the Ti negative potential was diminished in our previous detector due to the positive potential of oxygen. The main improvement now is that the 6Li/Ti multilayer and a protective Ti layer were evaporated in one order of magnitude higher vacuum than in the previous case. As a result, the neutron reflectivity of a 6Li/Ti multilayer mirror, which was made in the same evaporation as the solid state UCN detector, has been decreased at wavelengths longer than 800 A compared with the previous case and is 0.6 at 1500 A. This implies that even UCN of 1500 A can penetrate into the 6Li/Ti multilayer and could be detected with a high detection efficiency by the solid-state UCN detector with a 6Li/Ti multilayer neutron converter.

Development of a solid-state detector with a 6Li/Ti multilayer converter for ultracold neutrons

A new type of solid-state detector for ultracold neutrons has been developed and confirmed to be applicable at 4.2 K. 6Li/Ti multilayers, in which the effective potential is compensated, were formed as a neutron converter by vacuum evaporation on the surface of a silicon-surface-barrier detector. The detector was tested using a cold-neutron beam, and the reaction products in 6+Li+n → α + t were clearly observed in the pulse-height spectrum with a detection efficiency of 0.28% for 4A neutrons. This is consistent with the estimated value, and implies that ultracold neutrons can be detected with an efficiency of greater than 60%. The detector enables us to study the characteristics of ultracold neutrons in liquid helium, which is necessary to discuss the feasibility of an intense ultracold neutron source based on the superthermal method.

Fourier Transform Infrared Study on the Phase Transitions of a Water-Dioctadecyldimethylammonium Chloride System

Abstract Fourier transform infrared spectroscopy have been applied to study thermotropic phase transitions of the 21 g% water-dioctadecyldimethylammonium chloride (DODAC) system, in which three successive phases of coagel, gel, and liquid crystal appear with increasing temperature. In the coagel phase, the methylene chains take the (rara-zigzag conformation packed in parallel with each other. The hydrophilic part of DODAC in this phase is in a fixed state, and the presence of the bound water is evident. In the gel phase, the rotational motion of the methylene chain around the chain axis occurs in the hexagonal lattice. There exists more bound water in this phase than in the coagel phase, and the hydrophilic part in a rather fixed state. These findings are in conflict with the generally accepted concept of the gel state by x-ray studies. It is found molecular-spectroscopically that there exists an intermediate state between the coagel and gel phases, which is associated with the cooperative rearrangement o...

Resonance Raman study of spread monolayers of cetyl orange on water and thin LB films

Abstract Resonance Raman spectra (RRS) of a spread monolayer of cetyl orange on the water surface at pH 2.6 have been recorded in situ at various stages of monolayer compression. The results indicate that the molecules are in an equilibrium between the azo and hydrazone forms of the azobenzene moiety. Upon monolayer compression, the equilibrium shifts towards the azo form which is originally in a more condensed state than the hydrazone form. The same study upon monolayer transfer to a quartz plate has also been examined and is discussed in terms of the surface acidity of the quartz plate. Time dependences of the equilibrium shift in the LB film after film fabrication are compared between dry and moist atmospheres.

Self-regulating characteristics of a cold neutron source with a cylindrical-annulus moderator cell

The conditions, under which a cold neutron source of the ORPHEE type with a cylindrical-annulus moderator cell could have a self-regulating characteristics, were obtained through thermodynamic considerations. From an engineering viewpoint, it is not easy to establish these conditions because three parameters are involved even in an idealized system, without the effect of the mass transfer through the moderator transfer tube between the condenser and the moderator cell. The inner shell of the ORPHEE moderator cell is open at the bottom, but it is expected that only hydrogen vapor is contained in the inner shell and liquid hydrogen in the outer shell. Thermodynamic considerations show that such a state is maintained only when the liquefaction capacity of the condenser is large compared to the heat load and three parameters should be adjusted with well balance. We have proposed another type of a moderator cell which has an inner cylindrical cavity with no hole at the bottom but a vapor inlet opening at its uppermost part. In this structure, a self-regulating characteristic is easily established and the liquid level in the outer shell is maintained almost constant against thermal disturbances.

Multilayer mirror interferometer for very cold neutrons

Abstract The feasibility of a very cold neutron interferometer using multilayer mirrors is discussed. This device is a kind of Mach-Zehnder interferometer known in classical optics, using multilayer neutron monochromator mirror as optical elements. These mirrors consist of thin layers deposited on a very flat silicon multilayer substrate. Spacings of the multilayer are available in the range from 80 to 500 A. We discuss the characteristics of the mirror, the accuracy with which the mirror positions must be adjusted to their position and the perfection of the mirror including the present status of our development. Applications to physics are listed.