We applied a time-resolved small-angle neutron scattering technique to the vesicle system of dimyristoylphosphatidylcholine for the first time to determine lipid kinetics. The observed kinetics could be explicitly represented by a simple model that includes two independent kinetic parameters, i.e., the rates of transbilayer and interbilayer exchange. This technique is perfectly suited for the determination of lipid exchange kinetics in equilibrium and applicable to evaluation of the activity of the factors relevant to lipid migration, such as translocase and lipid transfer proteins.

Nanodiscs are phospholipid-protein complexes which are relevant to nascent high-density lipoprotein and are applicable as a drug carrier and a tool to immobilize membrane proteins. We evaluated the structure and dynamics of the nanoparticles consisting of dimyristoylphosphatidylcholine (DMPC) and apolipoprotein A-I (apoA-I) with small-angle neutron scattering (SANS) and fluorescence methods and compared them with static/dynamic properties for large unilamellar vesicles. SANS revealed that the nanodisc includes a lipid bilayer with a thickness of 44 A and a radius of 37 A, in which each lipid occupies a smaller area than the reported molecular area of DMPC in vesicles. Fluorescence measurements suggested that DMPC possesses a lower entropy in nanodiscs than in vesicles, because apoA-I molecules, which surround the bilayer, force closer lipid packing, but allow water penetration to the acyl chain ends. Time-resolved SANS experiments revealed that nanodiscs represent a 20-fold higher lipid transfer via an entropically favorable process. The results put forward a conjunction of static/dynamic properties of nanodiscs, where the entropic constraints are responsible for the accelerated desorption of lipids.

Vulcanization is the most important and conventional process in preparing rubber products. Network structure in the vulcanizates has been assumed to dominantly determine their physical properties together with network-chain density. Therefore, control of network structure in the vulcanizates is of at most importance for a fundamental design of rubber products. However, inhomogeneity of the network structure has not been much elucidated in spite of the long history of vulcanization since 1839, due to the complicated reactions among rubber and cross-linking reagents. Here, we look more closely at vulcanization and show its new role to control the network inhomogeneity on the basis of small-angle neutron scattering analysis of vulcanized rubbers. Combination and composition of the cross-linking reagents, especially those of zinc oxide with the other reagents, were found to be crucial for the control. A characteristic feature of strain-induced crystallization of the vulcanizates is also accounted for by the notion of network inhomogeneity. These results will be useful for further enhancing the technological potential of the traditional yet indispensable vulcanization.

The gelation mechanism of poly(N-isopropylacrylamide)-clay nanocomposite gels (NC gel) was investigated by dynamic light scattering (DLS) and contrast variation small-angle neutron scattering (SANS). It was found that the gelation mechanism of NC gels is similar to that of conventional gels made with organic cross-linker (OR gels). Namely, time-resolved DLS measurements captured all of the characteristic features of gelation at the threshold. This indicates that the gelation of NC gels is also classified to an ergode-nonergode transition. However, the size of the clusters at the gelation threshold is much larger than that of OR gels. This results in a significant depression of optical transmittance exclusively at the gelation threshold for NC gels. Partial scattering functions, i.e., two self-terms S PP (q) and S CC (q) and the corresponding cross-term S CP (q), were obtained by contrast-variation SANS, where P and C denote polymer and clay, respectively, and q is the magnitude of the scattering vector. The detailed analysis of S PP (q), S CC (q), and S CP (q) indicates that (i) each clay platelet is surrounded by polymer layers, (ii) the volume fraction of the polymer layer per clay platelet is independent of the concentrations, and (iii) the correlation length of the network polymer decreases with increasing clay concentration. These results confirm that the screening length of the system is influenced by the concentrations of clay platelets as well as of polymer chains, and the local structures of polymers near clay platelets are similar between in a sol state near the gelation threshold and in bulk NC gels.