Takahiko Ban

Oil droplets loaded with surfactant propel themselves with a velocity up to 6 mm s(-1) when they are placed in an aqueous phase of NaOH solution or buffer solution. The required driving force for such motion is generated on the interface of the droplets by the change in interfacial tension, due to deprotonation of the surfactant. This force induces Marangoni convection, which gives rise to a circulating flow inside the droplets. The droplets begin to move when the axis of this circulation deviat

Chemical potential gradient in a multicomponent fluid system undergoing phase separation acts as a driving force for transporting a fluid. We have experimentally shown the self-propelled motion of the droplet undergoing phase separation and its shape changes using the aqueous two-phase system. The droplet behavior depended on the composition of the continuous phase. For higher concentrations of the continuous phase than the equilibrium concentration, a droplet moved unidirectionally even in a ho

We have developed self-propelled droplets having the abilities to detect a chemical gradient, to move toward a higher concentration of a specific metal ion (particularly the dysprosium ion), and to extract it. Such abilities rely on the high surface activity of di(2-ethylhexyl) phosphoric acid (DEHPA) in response to pH and the affinity of DEHPA for the dysprosium ion. We used two external stimuli as chemical signals to control droplet motion: a pH signal to induce motility and metal ions to indu

Abstract Phase-separating droplets exhibit self-generated motion depending on the composition of the constituent solution of a biocompatible material, aqueous two phase system. For higher concentrations than the equilibrium concentration, a droplet moved unidirectionally even in a homogeneous concentration field. For lower concentrations, the droplets hardly moved. The translational motion we observed is an effect of convection caused by Korteweg force.

Chemically driven self-propulsion of soft matter is useful for various applications because it can move toward a desired location, without external power fields, in response to chemical signals in environmental media. We have developed a suitable steering mechanism to maintain the orientation of self-propelled droplets loaded with surfactant in fluidic environments. A spatial gradient of alkaline-earth metal ions induces directional sensing. These metal ions can be arranged in descending order o

This study describes the development of self-propelled vesicles using transient interfacial energy in an aqueous two-phase system composed of polyethylene glycol (PEG), dextran (DEX), and water. The transient interfacial energy was generated at the mixing boundary between the PEG and DEX solutions when the two miscible liquids were in contact with each other far from equilibrium. Vesicles encapsulating 20 wt % DEX solution traveled spontaneously when the PEG concentration in the environmental me

Cortico-cortical connections from the prefrontal cortex to the superior temporal sulcal cortex (STs area) were studied in the monkey by means of retrograde axonal transport of horseradish peroxidase (HRP). After injections of 0.15-0.6 microliter of 50% HRP into the STs area, labeled cells were found in various cortical regions. In the prefrontal-STs projections, main features of topographic correlation were revealed; the posterior part of the STs area receives fibers from the superior frontal co

We develop coupled evolution equations for viscous fingering (VF) and phase separation in partially miscible systems by combining a simple double-well thermodynamic free energy and Korteweg force with a classical miscible VF model for a binary system. The VF pattern transition into a droplet formation pattern by the spinodal decomposition effect is demonstrated, and the simultaneous increases in the depth of the energy minimum, in the difference in the equilibrium concentrations, and in the Kort

Abstract Autonomous motions of an oil/water interface can be controlled by hydrophobicity of an anion and its chemical reaction with a cationic surfactant. Hydrophobic anions generate a rhythmical motion of the contact line, and hydrophilic anions induce the Marangoni instability. A cooperative effect of them causes an outstanding motion of the interface.

When inherently immobile solid particles collectively form precipitates in a reaction-diffusion system involving a redissolution reaction, a propagation phenomenon may occur in which a dynamic pattern of precipitation bands forms. This propagating precipitation phenomenon has been studied by many researchers. However, two completely different processes-i.e., the reaction-diffusion of reactants and the crystal growth of products-progress simultaneously in the system, thereby rendering the phenome

This work focuses on the relationship between surface activities of extractants and drop coalescence and breakage. Drop size distribution and Sauter mean diameter have been measured in one stage of a mixer-settler extraction column for three different liquid−liquid systems as functions of flow rate of dispersed phase, agitation speed, and concentration of extractants. Effects of drop coalescence on drop size have been investigated for three different types of extractants. The results show that t

Abstract We demonstrate that an aqueous droplet containing calcium ions undergoes rhythmical oscillation in an organic phase containing a surfactant of phosphate group. The same oil/water interface exhibited the self-pulsing of the electrical potential. The patterns for the rhythmical oscillation and the self-pulsing were dramatically affected by the cation species.

We studied dissipative structures in the pattern formation of self-organized flow inside a droplet and spontaneous motion of the droplet when two driving forces, mass transfer of a solute from the droplet to surrounding media and continuous supply of solution to the droplet, were applied. When solute concentration increases beyond a critical value, a jetlike flow erupts out of the droplet (eruption). A similar flow simultaneously enters the droplet (irruption), producing internal flow. The resul