Biomedical subjects

Takeaki Araki

Publications and source records attributed to Takeaki Araki.

3 recordsLinked to original sources

PubMed2006

Colloidal aggregation in a nematic liquid crystal: topological arrest of particles by a single-stroke disclination line.

We numerically study many-body interactions among colloidal particles suspended in a nematic liquid crystal, using a fluid particle dynamics method, which properly incorporates dynamical coupling among particles, nematic orientation, and flow field. Based on simulation results, we propose a new type of interparticle interaction in addition to well-known quadrupolar interaction for particles accompanying Saturn-ring defects. This interaction is mediated by the defect of the nematic phase: upon nematic ordering, a closed disclination loop binds more than two particles to form a sheetlike dynamically arrested structure. The interaction depends upon the topology of a disclination loop binding particles, which is determined by aggregation history.

Biophysics↗

PubMed2006

Wetting-induced depletion interaction between particles in a phase-separating liquid mixture.

Inclusion of solid particles drastically affects the pattern evolution of phase separation of a binary fluid mixture, via preferential wetting of one of the phases to the particles. Here we study this problem by numerical simulation, which incorporates interparticle hydrodynamic interactions properly. When particles favor one of the components of a mixture, wetting layers are quickly formed on the particle surfaces and all particles are eventually included into the more wettable phase. For immobile particles, domains of the more wettable phase are pinned to the particles and the domain growth is thus suppressed. For this case, the domain size at a certain phase-separation time decreases monotonically with increasing the particle concentration. For mobile particles, on the other hand, the reentrant morphological transformation is observed as a function of the particle concentration: With an increase in the particle concentration, the domain morphology of the more wettable phase sequentially changes from network, droplet to network. We found that the final morphological transition is induced by wetting-induced depletion interaction: strong attractive interactions act among particles when the total volume of the more wettable phase is not enough to cover all the particles by wetting layers.

Journal Article↗

PubMed2005

Simple tools for complex phenomena: viscoelastic phase separation captured by disconnectable springs.

Viscoelastic phase separation is characterized by the formation of a transient gel upon phase separation. A transient gel state is widely observed in complex fluids including polymer solutions, colloidal suspensions, and protein solutions, but its physical description is quite difficult due to its intrinsically nonequilibrium nature. We have modeled this transient gel state using a type of Brownian dynamics simulation in which coarse-grained particles interacting with a Lennard-Jones potential are connected by elastic springs, which can be disconnected with the probability controlled by the ratio of the stored elastic energy to the thermal energy. The simulations well reproduce pattern evolution in a transient gel of a polymer solution. Our simulations indicate that domain morphology is controlled by two key physical factors: (i) the ratio between the nucleation and growth rates of domains of the less viscoelastic phase and (ii) the fragility of the transient gel.

Journal Article↗