arXiv subjects

H. Seto

Publications and source records attributed to H. Seto.

5 recordsLinked to original sources

arXiv2025

Molecular dynamics of $cis$-polybutadiene across the glass transition revealed by muonated-radical spin relaxation

The local molecular motion of $cis$-polybutadiene, a typical polymeric material exhibiting a glass transition ($T_{\rm g}=168$ K), is investigated by the spin relaxation of muonated radicals, where the relaxation is induced by the fluctuation of hyperfine (HF) fields exerted from an unpaired electron to a nearby muon and surrounding protons. The relaxation rate $1/T_\mu$ measured under various longitudinal magnetic fields is analyzed using the recently developed theory of spin relaxation to consider the coexistence of quasistatic and fluctuating HF fields, where the fluctuation frequency for the latter $\nu$ is evaluated over a temperature $T$ range of 5-320 K. The obtained $\nu(T)$ is found to be well reproduced by the Arrhenius relation, and the activation energy and preexponential factor are in good agreement with those for the "elemental process" revealed by quasielastic neutron scattering and attributed to a fluctuation across three carbon-carbon bonds. This result demonstrates that muonated-radical spin relaxation is a promising approach for direct access to local molecular motions in the sub-nanosecond range and for their detailed modeling at the atomic scale.

cond-mat.mtrl-sci↗

arXiv2006

Unbinding Transition Induced by Osmotic Pressure in Relation to Unilamellar Vesicle Formation

Small-angle X-ray scattering and phase-contrast microscopy experiments were performed to investigate the effect of the osmotic pressure on vesicle formation in a dioleoylphosphatidylcholine (DOPC)/water/NaI system. Multi-lamellar vesicles were formed when a pure lipid film was hydrated with an aqueous solution of NaI. On the other hand, uni-lamellar vesicles (ULVs) were formed when a lipid film mixed with an enough amount of NaI was hydrated. To confirm the effect of the osmotic pressure due to NaI, a free-energy calculation was performed. This result showed that the osmotic pressure induced an unbinding transition on the hydration process, which resulted in ULV formation.

cond-mat.soft↗

arXiv2006

Hydration process of multi-stacked phospholipid bilayers to form giant vesicles

The hydration process of multi-stacked phospholipid bilayers to form giant vesicles was investigated by time-resolved small angle X-ray scattering. The hydration of lipids in the liquid-crystalline phase was found to proceed in two stages. In the early stage, until about 100 s after hydration, lipid bilayers on a solid substrate swell about 12 $\rmÅ$ and reach a quasi-stable state. In the late stage, after several hundreds of seconds, lipid bilayers gradually peel off from the stack. On the other hand, in the case of a lipid in the gel phase, only the early stage is observed. These behaviors correspond to the capacity for the giant vesicle formation depending on the lipid phases. The kinetics of the peeling-off process is discussed in terms of Kramers' formulas.

physics.chem-ph↗

arXiv2006

A swollen phase observed between the liquid-crystalline phase and the interdigitated phase induced by pressure and/or adding ethanol in DPPC aqueous solution

A swollen phase, in which the mean repeat distance of lipid bilayers is larger than the other phases, is found between the liquid-crystalline phase and the interdigitated gel phase in DPPC aqueous solution. Temperature, pressure and ethanol concentration dependences of the structure were investigated by small-angle neutron scattering, and a bending rigidity of lipid bilayers was by neutron spin echo. The nature of the swollen phase is similar to the anomalous swelling reported previously. However, the temperature dependence of the mean repeat distance and the bending rigidity of lipid bilayers are different. This phase could be a precursor to the interdigitated gel phase induced by pressure and/or adding ethanol.

cond-mat.soft↗

arXiv1998

Raman Scattering in the Inorganic Spin-Peierls System alpha'-Na_{1-delta}V_2O_5

We have studied the spin-Peierls (SP) transition in alpha'-Na_{1-delta}V_2O_5 (delta = 0, 0.01 and 0.1) by means of Raman scattering. At room temperature, we observe six A_1 and three A_2 phonon modes and a broad Raman band. Below T_{SP}several new peaks and a new broad band appear. The new peak at 62 cm^{-1} originates from the SP-gap excitation. The new peak at 128 cm^{-1} and the new broad band between 130 and 400 cm^{-1} come from two magnetic excitations. The new peaks at 102, 646 and 944 cm^{-1} are assigned to the folded phonon modes and their Na^+-ion deficiency dependence shows that the defect of Na^+ ion suppresses the SPtransition. The polarized Raman spectra below T_{SP} suggest that the possible crystal symmetry is C_s^2(Pn) or C_1^1(P1). The asymmetric lineshape of the 531-cm^{-1} peak superimposed on the electronic Raman band from the d-d transition around 600 cm^{-1} is interpreted in terms of the Fano resonance between the electronic continuous band and the phonon with a finite lifetime. The defects of the Na^+ ions reduce the Fano effect because the life time of the phonon and the phonon-continuum interaction are decreased.

cond-mat.str-el↗