Effect of interlamellar interactions on shear induced multilamellar vesicle formation.

Shear-induced multilamellar vesicle (MLV) formation has been studied by coupling the small-angle neutron scattering (SANS) technique with neutron spin echo (NSE) spectroscopy. A 10% mass fraction of the nonionic surfactant pentaethylene glycol dodecyl ether (C12E5) in water was selected as a model system for studying weak inter-lamellar interactions. These interactions are controlled either by adding an anionic surfactant, sodium dodecyl sulfate, or an antagonistic salt, rubidium tetraphenylborate. Increasing the charge density in the bilayer induces an enhanced ordering of the lamellar structure. The charge density dependence of the membrane bending modulus was determined by NSE and showed an increasing trend with charge. This behavior is well explained by a classical theoretical model. By considering the Caillé parameters calculated from the SANS data, the layer compressibility modulus B¯ is estimated and the nature of the dominant inter-lamellar interaction is determined. Shear flow induces MLV formation around a shear rate of 10 s-1, when a small amount of charge is included in the membrane. The flow-induced layer undulations are in-phase between neighboring layers when the inter-lamellar interaction is sufficiently strong. Under these conditions, MLV formation can occur without significantly changing the inter-lamellar spacing. On the other hand, in the case of weak inter-lamellar interactions, the flow-induced undulations are not in-phase, and greater steric repulsion leads to an increase in the inter-lamellar spacing with shear rate. In this case, MLV formation occurs as the amplitude of the undulations gets larger and the steric interaction leads to in-phase undulations between neighboring membranes.

Effect of interfacial structure on bioinert properties of poly(2-methoxyethyl acrylate)/poly(methyl methacrylate) blend films in water.

In this study, we found that the surface made of a mixture of poly(2-methoxyethyl acrylate) (PMEA) and poly(methyl methacrylate) (PMMA) exhibited excellent blood compatibility by inhibiting platelet adhesion. To obtain a better understanding of this bioinertness, the polymer/water interface was characterized by neutron reflectivity measurements and sum frequency generation spectroscopy, in conjunction with bubble contact angle measurements. Based on the results, we can say that the outermost region of the blend film was reorganized in water. When the orientation of PMEA segments at the water interface became random with increasing immersion time, the fractional amount of lower-coordinated water molecules increased at the interface. Such an interfacial structure caused the suppression of platelet adhesion.

Influence of solution- and thermal-annealing processes on the sub-nanometer-ordered organic-organic interface structure of organic light-emitting devices.

Solution- and thermal-annealing processed organic-organic interface structures were investigated by neutron reflectometry. We revealed the true picture of interfaces, a polymer hole-transporting layer - a small molecule light-emitting layer - a small molecule electron-transporting layer, and discussed influences of those interface structures on organic light-emitting devices.

Highly reversible capacity at the surface of a lithium-rich manganese oxide: a model study using an epitaxial film system.

Epitaxial films of Li2MnO3 were synthesized using pulsed laser deposition. A 12.6 nm film exhibited a high discharge capacity of over 300 mA h g(-1) following its fiftieth cycle and better stability than 29.8 and 47.8 nm films. The surfaces of such films are intrinsically active at the electrochemical interface.

Morphological development of multilamellar phospholipid film depending on drying kinetics.

The mechanism for the formation of solid-supported phospholipid membranes during a drying process was investigated. Terracelike multilamellar structures were found to develop from a micellar solution with either spinodal decompositionlike process or nucleation growth, depending on the evaporation rate of an organic solvent. In contrast to the well-known kinetics of phase separation, fast drying induces nucleation while slow drying induces spinodal decompositionlike lipid-film formation. The existing models for the interpretation of phase separation are not sufficient to understand this unexpected kinetics. We suggest a schematic model with which this kinetic feature can be interpreted in terms of a self-assembly pathway in a three-component phase diagram for a phospholipid, organic solvent, and water.

Bending modulus of lipid bilayers in a liquid-crystalline phase including an anomalous swelling regime estimated by neutron spin echo experiments.

Membrane fluctuations of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) were investigated by neutron spin echo spectroscopy. The intermediate structure factor was analyzed in terms of the model proposed by Zilman and Granek (Phys. Rev. Lett. 77, 4788 (1996)), and the bending modulus of lipid bilayers was derived. The hardening of a lipid bilayer upon approaching the main transition point in the anomalous swelling regime was observed, which naturally connects the bending modulus in the gel phase below the main transition temperature.

Temperature and pressure effects on the bending modulus of monolayers in a ternary microemulsion.

We performed small-angle neutron scattering and neutron spin echo experiments on a ternary microemulsion composed of ionic surfactant AOT, water, and decane. Thermal fluctuations of monolayers have been investigated as a function of temperature and pressure. The amphiphilic monolayers become more flexible with increasing temperature and more rigid with increasing pressure. These results are consistent with the microscopic picture that the head-head repulsion of the AOT molecules is enhanced at high temperature while an attractive interaction between the hydrophobic tails of the AOT molecules increases at high pressure.