Dynamical Behavior of Hydration Water Molecules between Phospholipid Membranes

The dynamical behavior of hydration water sandwiched between 1,2-dimyristyl-<i>sn</i>-glycero-3-phosphocholine (DMPC) bilayers was investigated by quasi-elastic neutron scattering (QENS) in the range between 275 and 316 K, where the main transition temperature of DMPC is interposed. The results revealed that the hydration water could be categorized into three types of water: (1) free water, whose dynamical behavior is slightly different from that of bulk water; (2) loosely bound water, whose dynamical behavior is 1 order of magnitude slower than that of the free water; and (3) tightly bound water, whose dynamical behavior is comparable with that of DMPC molecules. The number of loosely bound and tightly bound water molecules per DMPC molecule monotonically decreased and increased with decreasing temperature, respectively, and the sum of these water molecules remained constant. The number of free water molecules per DMPC molecule was constant in the measured temperature range

Formation of a Multiscale Aggregate Structure through Spontaneous Blebbing of an Interface

The motion of an oil–water interface that mimics biological motility was investigated in a Hele–Shaw-like cell where elastic surfactant aggregates were formed at the oil–water interface. With the interfacial motion, millimeter-scale pillar structures composed of the aggregates were formed. The pillars grew downward in the aqueous phase, and the separations between pillars were roughly equal. Small-angle X-ray scattering using a microbeam X-ray revealed that these aggregates had nanometer-scale lamellar structures whose orientation correlated well with their location in the pillar structure. It is suggested that these hierarchical spatial structures are tailored by the spontaneous interfacial motion

Structure and Mechanical Properties of Polybutadiene Thin Films Bound to Surface-Modified Carbon Interface

The structure and mechanical properties of polybutadiene (PB) films on bare and surface-modified carbon films were examined. There was an interfacial layer of PB near the carbon layer whose density was higher (lower) than that of the bulk material on the hydrophobic (hydrophilic) carbon surface. To glean information about the structure and mechanical properties of PB at the carbon interface, a residual layer (RL) adhering to the carbon surface, which was considered to be a model of “bound rubber layer”, was obtained by rinsing the PB film with toluene. The density and thickness of the RLs were identical to those of the interfacial layer of the PB film. In accordance with the change in the density, normal stress of the RLs evaluated by atomic force microscopy was also dependent on the surface free energy: the RLs on the hydrophobic carbon were hard like glass, whereas those on the hydrophilic carbon were soft like rubber. Similarly, the wear test revealed that the RLs on the hydrophilic carbon could be peeled off by scratching under a certain stress, whereas the RLs on the hydrophobic carbons were resistant to scratching

Mechanism of Spontaneous Blebbing Motion of an Oil–Water Interface: Elastic Stress Generated by a Lamellar–Lamellar Transition

A quaternary system composed of surfactant, cosurfactant, oil, and water showing spontaneous motion of the oil–water interface under far-from-equilibrium condition is studied in order to understand nanometer-scale structures and their roles in spontaneous motion. The interfacial motion is characterized by the repetitive extension and retraction of spherical protrusions at the interface, i.e, blebbing motion. During the blebbing motion, elastic aggregates are accumulated, which were characterized as surfactant lamellar structures with mean repeat distances <i>d</i> of 25 to 40 nm. Still unclear is the relationship between the structure formation and the dynamics of the interfacial motion. In the present study, we find that a new lamellar structure with <i>d</i> larger than 80 nm is formed at the blebbing oil–water interface, while the resultant elastic aggregates, which are the one reported before, have a lamellar structure with smaller <i>d</i> (25 to 40 nm). Such transition of lamellar structures from the larger <i>d</i> to smaller <i>d</i> is induced by a penetration of surfactants from an aqueous phase into the aggregates. We propose a model in which elastic stress generated by the transition drives the blebbing motion at the interface. The present results explain the link between nanometer-scale transition of lamellar structure and millimeter-scale dynamics at an oil–water interface