Y. Kawabata

Neutron spin–echo investigations of membrane undulations in complex fluids involving amphiphiles

Abstract The intermediate functions I ( Q , t ) obtained from neutron spin–echo (NSE) experiments were well fitted to I(Q,t)=I(Q,0) exp [−(Γt) 2/3 ] for the bicontinuous microemulsion and the lamellar phases of the C 12 E 5 / n -octane/water system and also for the lamellar phase of the DPPC/water/CaCl 2 system. The relaxation rate Γ increased as Q 3 . These results support the theory presented by Zilman and Granek [Phys. Rev. Lett. 77 (1996) 4788]. Bending modulus of the membrane ϰ was estimated in the C 12 E 5 / n -octane/water system and in the DPPC/water/CaCl 2 system using their theory.

Pressure and temperature effects on the phase transition from a dense droplet to a lamellar structure in a ternary microemulsion

A small-angle x-ray scattering (SAXS) study of a ternary microemulsion composed of AOT [sodium bis(2-ethylhexyl) sulfosuccinate], water and n-decane was undertaken in order to clarify the phase behavior and the feature of the corresponding structural transition from a dense droplet to a lamellar structure with increasing pressure and temperature. The volume fractions of water and decane were fixed to be equal and the volume fraction of AOT against the whole volume (φs) was selected to be 0.209 and 0.230 in order to compare results with those obtained by small-angle neutron scattering (SANS). The pressure was varied between 1 and 800 bar under controlled temperature at 20, 25, 29, or 33u200a°C. Under all conditions applied, the phase transition from the droplet structure to the lamellar structure was observed. The results of analysis of the SAXS profiles indicated that the short-range adhesive potential between droplets becomes more intense with increasing pressure.

Effects of temperature and pressure on phase transitions in a ternary microemulsion system

Temperature variation experiments of small angle neutron scattering (SANS) and neutron spin echo (NSE) were carried out in order to compare effects of temperature and pressure on a structural formation in a ternary microemulsion system composed of AOT (Aerosol-OT; dioctyl sulfosuccinate sodium salt), D2O, and n-decane. From SANS measurements, a phase transition from one-phase dense water-in-oil droplet to two-phase coexistence with a lamellar and a disordered structure was observed with increasing temperature, similar to the case of pressure variation. Another phase transition was observed at a higher temperature above the lamellar phase, although such a subsequent phase transition has not been observed at higher pressure. The characteristic features of structural phase transitions by temperature and by pressure were compared by introducing a reduced temperature and pressure. The dynamical property observed from the NSE measurement was different between the high-temperature phase and the high-pressure pha...

Pressure-induced structural phase transition of dense droplet microemulsions studied by small-angle x-ray scattering

A small-angle x-ray scattering (SAXS) study of dense water-in-oil droplet microemulsions composed of water, decane, and AOT [sodium bis(2-ethylhexyl) sulfosuccinate] was performed in order to clarify phase behavior with applied pressure and the corresponding structural phase transitions. SAXS spectra were collected for pressures between ambient pressure (0.1 MPa) and 80 MPa and droplet volume fraction, φ, from 0.40 to 0.70. With increasing φ, the mean radius of droplets decreased slightly and polydispersity increased. With increasing pressure, the droplet structure transformed to a two-phase system with coexistence of lamellar and droplet structures, independent of the droplet volume fraction. These results suggest that, with increasing pressure, the increasing inter-droplet attractive force controls the pressure variation of the structure.

Temperature- and Pressure-dependences of Shape Fluctuations in a Ternary Microemulsion System

Shape fluctuations in a microemulsion system composed of Aerosol-OT (AOT), D 2 O and deuterated decane were investigated by means of neutron spin echo. In this system, a water-in-oil droplet structure at ambient temperature and pressure decomposes into two-phases, both with increasing temperature and pressure. However, its dynamical behavior was different. The observed effective diffusion constant of the droplet shape fluctuation increased with increasing temperature, while it decreased with increasing pressure. Temperature- and pressure-dependences of a bending modulus of AOT monolayers were estimated, and it was confirmed that AOT monolayers become floppy with increasing temperature and stiff with increasing pressure.

Temperature and pressure effects on structural formations in a ternary microemulsion

Small angle neutron scattering experiments were conducted on a temperature-induced phase transition in a ternary microemulsion composed of AOT (dioctyl sulfosuccinate sodium salt), D2 O and n-decane and the results were compared with those of pressure-induced one. Although the static features of both the temperature- and the pressure-induced phase behaviour were similar, a temperature dependence of its characteristic repeat distance at high temperature was quite different from a pressure dependence of that at high pressure. Neutron spin echo experiments were also performed on both the phase transitions. The dynamics of the high temperature phase was different from that of the high pressure phase. These results indicated that the effect of pressure on the structural formation was different from that of temperature.

Improvement of neutron spin echo spectrometer at C2-2 of JRR3M

Abstract We have improved a neutron spin echo spectrometer at the C2-2 port of JRR-3M, JAERI. The new double reflection supermirror monochromators with the wavelength λ =5.9xa0A (Δ λ / λ =15%) and λ =7.14xa0A (Δ λ / λ =18%) increased the polarized neutron flux at the sample position about three times more than the old monochromator. The deflection angle 2 θ M at C2-2 port increased up to 7.00° using double reflection, which reduced the disturbance from the iron cover of C2 guide for C2-3 port. In order to gain more neutron intensity, we replaced the spiral coils with a wider one and installed a new detector system with an assembly of eight one-dimensional PSDs.

COLLECTIVE MOTIONS OF A NETWORK OF WORMLIKE MICELLES

Abstract Aqueous solutions of non-ionic amphiphile C 16 E 7 (ue605C 16 H 33 (OC 2 H 4 ) 7 OH) are known to form “wormlike micelles”, whose static properties are analogously understood as chain-like polymers. However, their dynamical properties are different from those of polymers because the micelles not only entangle but also fuse each other. In order to clarify collective motions of the wormlike micelles, neutron spin echo measurements were carried out. Observed correlation functions were explained by a stretched exponential function with an index of 3/4. The obtained relaxation rates obeyed Q 8/3 as Zilman and Granek (Phys. Rev. Lett. 77 (1996) 4788) expected for the one-dimensional polymer-like model.

Neutron Spin Echo Studies on Poly(Vinyl Alcohol) Gel in a Mixture of Dimethyl Sulfoxide and Water

Dynamics of poly(vinyl alcohol) (PVA) gel have been investigated using a neutron spin echo technique. The intermediate scattering function I ( Q , t ) of the gel shows a very rapid decay and a non-decaying component in time ranges shorter and longer than about 3 ns, respectively, in the Q range of 0.03-0.1 A m 1. This Q range corresponds to the so-called Porods region, suggesting that we are seeing the dynamics of cross-linking points of the gel. We therefore analyzed the data assuming that the cross-linking point performs a random motion in a restricted region around its quasi-equilibrium position.

Detector Area Expansion at iNSE Neutron Spin Echo Spectrometer

A 2D-detector and an analyzer had been installed on iNSE neutron spin echo spectrometer for wide-area data acquisition. Since the areas of the 2nd π/2 spin flipper and the last Fresnel coil were not wide enough for a full area measurement, only the center area of the detector had been used. In 2006, we renewed the spin flipper and the Fresnel coils to expand the detection area. To improve the efficiency of the data acquisition, we proposed a novel method for phase correction of NSE signals. Finally, the efficiency of the NSE measurement increased by approximately one order of magnitude.