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A01 KITA, Rio |Proposed Research Projects (2014-2015)

Paper | Original Paper

2016

Yasutaka Ohnishi, Rio Kita, Kazuyoshi Tsuchiya and *Satoru Iwamori,
Optical characteristics of poly(tetrafluoroethylene) thin film prepared by a vacuum evaporation,
Japanese Journal of Applied Physics 55, 02BB04/1-5 (2016).

[Summary] Poly(tetrafluoroethylene) (PTFE) thin films were deposited onto a glass slide substrate by a heat-resistance type vacuum evaporation apparatus due to changing the evaporation conditions. Transparency of the PTFE thin films prepared by the vacuum evaporation depended on the deposition conditions, i.e., temperatures of the basket, and distance between the evaporation source and substrate. To elucidate relationship between the molecular structure and transparency of the PTFE thin film prepared by the vacuum evaporation, chemical structures, crystallinity and thermophysical property were investigated. The chemical bonding state of the PTFE thin film prepared by the vacuum evaporation was almost the same as that of the pristine PTFE, however, the crystalinity was different. Although the pristine PTFE was crystal structure, the transparent evaporated thin film was estimated to be microcrystal structure. In addition, endothermic peaks in a differential scanning calorimeter (DSC) spectrum of the PTFE thin film were different from that of the pristine PTFE. These endothermic peaks of the PTFE thin film prepared by the vacuum evaporation shifted lower temperature compared to the pristine PTFE, which suggests that molecular weight of the PTFE thin film prepared by the vacuum evaporation decreased compared with that of the pristine PTFE.

2015

Kousaku Maeda, Naoki Shinyashiki, Shin Yagihara, Simone Wiegand, and *Rio Kita,
Ludwig-Soret effect of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol: Temperature, molecular weight, and hydrogen bond effect,
Journal of Chemical Physics 143, 124504/1-7 (2015).

[Summary] The thermal diffusion, also called the Ludwig-Soret effect, of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol is investigated as a function of temperature by thermal diffusion forced Rayleigh scattering. The Soret coefficient, S_T, and the thermal diffusion coefficient, D_T, show a linear temperature dependence for all studied compounds in the investigated temperature range. The magnitudes and the slopes of S_T and D_T vary with the chemical structure of the solute molecules. All studied molecules contain ether and/or hydroxyl groups, which can act as acceptor or donor to form hydrogen bonds, respectively. By introducing the number of donor and acceptor sites of each solute molecule, we can express their hydrogen bond capability. S_T and D_T can be described by an empirical equation depending on the difference of donor minus acceptor sites and the molecular weight of the solute molecule.

S. K. Kundu, S. Choe, K. Sasaki, Rio Kita, N. Shinyashiki, and *S. Yagihara,
Relaxation dynamics of liposomes in an aqueous solution,
Physical Chemistry Chemical Physics 17, 18449-18455 (2015).

[Summary] The gel–liquid crystal phase transition has been studied by the temperature and frequency dependent dielectric relaxation behavior of liposomes in an aqueous solution (40 g L^{-1} DPPC–water mixture). Four relaxation processes were observed in the frequency range from 40 Hz to 30 GHz which were ascribed to different molecular mechanisms, related to the structural units of the system. The gel–liquid crystal phase transition was also described very accurately from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions obtained from the fitting procedure. Relaxation process 3, obtained from the dielectric fitting procedure, was confirmed by dielectric modulus analysis. A comparison of the lipid membrane with non-biological systems like liquid crystals was performed. It was determined that the lipid membrane has a ferroelectric liquid crystal like behavior. Process 3 is comparable to the soft mode relaxation process observed in ferroelectric liquid crystals which was detected close to the smectic-C*–smectic-A phase transition. Differential scanning calorimetry was also used to confirm the gel–liquid crystal phase transition of this mixture.

2014

Kousaku Maeda, Naoki Shinyashiki, Shin Yagihara, Simone Wiegand, *Rio Kita,
How does thermodiffusion of aqueous solutions depend on concentration and hydrophobicity?,
European Physical Journal E 37, 94(6pages) (2014).

[Summary] The thermal diffusion of aqueous solutions of mono-, di-ethylene glycols, poly(ethylene glycol), methanol, and glycerol is investigated systematically as a function of concentration using the Thermal Diffusion Forced Rayleigh Scattering (TDFRS). For all investigated binary mixtures, the Soret coefficient, ST , decays with increasing concentration of the non-aqueous component showing two regions. For aqueous solution of ethylene glycol, at a very low solute content the decay is steep, while it becomes less steep for higher solute concentration. All mixtures show a sign change of ST with concentration. The sign change concentration is discussed with respect to chemical structures of solute molecules and the partition coefficient, log p . It turns out that the number of hydroxyl groups plays an important role. For the investigated aqueous mixtures, we find empirical linear relations between the sign change concentration and the ratio of the number of hydroxyl groups to the number of carbon atoms as well as the partition coefficient, log p.