A stable nanoemulsion consisting of nanometer-sized oil droplets in water having a self-standing capability was prepared by high-pressure emulsification. Rheological measurements show that the nanoemulsion has a yield stress. Small-angle neutron scattering (SANS) revealed the presence of an ordered crystal-like lattice structure in addition to spherical domains with a radius of 17 nm.
A mixed solution of 2-hydroxyethyl cellulose and dilution of the nanoemulsion has shear-thickening behavior (shear-induced gelation). Real-time SANS measurements with a Couette geometry as a function of shear rate showed an increase in the scattering intensity exclusively at low scattering angle region. However, neither aggregation nor deformation of droplet was detected and the SANS patterns remained isotropic irrespective of shear rate. A possible mechanism of gelation is proposed from the viewpoint of shear-induced percolation transition.
Crystal growth behaviors and thermodynamical properties were investigated for the two polytypic structures of n-alkanes. The solution crystallization of n-hexatriacontane (n-C36H74) were followed by oblique transmission micro-FTIR spectroscopy, which showed that a polytypic transformation took place during the crystallization. A single crystal appeared as single-layer polytype Mon and then a domain of double-layer polytype Orth II was generated heterogeneously. The crystal transformed gradually to a single crystal of Orth II through a solution-mediated phase transition. Inelastic neutron scattering measurements showed that the driving force of this transformation came from the difference in the vibrational density of state. From the frequency of methyl torsional mode, it is suggested that the cohesive force at the lamellar interface is stronger in Mon than in Orth II.
Neutron scattering measurements are known to be powerful tools for condensed matter physics. Single crystals are better but restrict materials. We can investigate magnetism of several quantum spin systems using neutron scattering measurements on powder samples. We determined a spin system in Cu2CdB2O6 or β-AgCuPO4 from data of powder samples.
We have experienced essential importance of neutron scattering in our recent materials research, i.e. iron pnictide superconductor and RT stable electride C12A7:e-. The neuron scattering provided more direct and unique information that cannot be obtained by other method. I describe two events experienced associated with neutron scattering and requests viewed from a materials scientist.
A 36 meter small-angle neutron scattering (SANS) spectrometer in Serpong, Indonesia is the one of the largest SANS spectrometers nowadays in the Asia-Oceania region. The spectrometer has been revitalized, developed, and improved both on the instrumentation and experimental method, and then utilized for inter-laboratory comparison and basic research purposes. Liquid, gel, powder, solid-state thin film, metal plate and amorphous samples have been performed for structural and self-assembly mechanism studies. The morphological changes of micelles in micellar solutions were the most interesting research works in the last several years. Detailed structure studies on core-shell micelle were succeeded by applying a contrast variation method, i.e. H2O/D2O mixture solution. Diluted nanoparticle and ordered systems from solution, powder and solid-state samples which correspond to form and structure factors have been investigated. The fractals structures of disordered system from aggregation of ferrofluids nanoparticles and aerogels have been accomplished directly through a “power-law” scattering approximation. Magnetic structure from metal-alloys, showing anisotropic magnetic scattering structure properties up to 1 tesla of external magnetic field was also accomplished confirming the crystalline and magnetic domain sizes. Recently, most of experiments on biological materials were performed for investigating the structure and dynamics of protein and virus in solutions.
We highlight that polymer systems provide extremely good model systems for basic researches on soft-matter physical science. Their inherently large characteristic space-time scale enables us to elucidate the space-time organization of self-assembling processes via phase transitions in such a level that cannot be easily attained by small-molecule systems having small space-time scales. We emphasize also the fact that SANS studies are crucial in elucidating a whole spectrum of hierarchical structures of soft-matters and their responses to external stimuli. As an example, we reviewed some experimental results on space-time organization of phase-separating structures during spinodal decomposition of dynamically symmetric molecular mixtures and discussed universality in this context between polymers and small molecules.
To utilize high neutrons up to eV region with a low background noise, a T0 chopper rotating at 100 Hz with a phase control accuracy of ±5 μs was designed and assembled. We investigated properties of this T0 chopper. Based on the development, actual machines were produced for some neutron beamlines at J-PARC.
Effects of pressure on the physical properties are very important for understanding highly correlated electron systems, in which pressure-induced attractive phenomena such as superconductivity have been observed. In this article, the characteristic features of various materials and pressure transmitting media for use of piston-cylinder type clamp cells are reported. Both CuBe and hybrid CuBe/NiCrAl piston-cylinder-type high-pressure clamp cells were designed for low-temperature neutron diffraction measurements. We also introduce, as the application of the cells, the results of the neutron diffraction under pressure on pressure induced superconductors of UGe2 and CeRhIn5.
It is well known that neutron diffraction method enables us to measure residual stresses inside materials. It can also evaluate deformation behaviors and phase transformation of materials under loading at various environments such as high or low temperature and also evaluate microstructural factors such as dislocation density, cell size and texture by analyzing diffraction profile. This article reviews some topics of structural materials evaluation using neutron diffraction.
Neutron spin echo studies on polymer systems are reviewed, including polymer motions in solutions and melts, collective dynamics in polymer gels and polymer micelles, and slow dynamics in glass-forming polymers.
Aqueous solutions of synthesized phospholipids have been well investigated as model biomembranes. These lipids usually self-assemble into regular stacks of bilayers with a characteristic repeat distance on the order of nm, whereas real biomembranes exist as single bilayers. The key phenomenon in understanding the formation of single isolated bilayers is "unbinding" of lipid bilayers, in which the inter-bilayer distance of lipid bilayers diverges by the steric interaction due to the membrane undulation. In this paper, we show some results of neutron spin-echo (NSE) experiments to investigate the effect of the steric interaction on unbinding and related phenomena.