Self-assembly and complex manipulation of colloidal mesoscopic particles by active thermocapillary stress

We demonstrate that the active thermocapillary stresses induced by multiple microbubbles offer simple routes to directed self-assembly and complex but controllable micromanipulation of mesoscopic colloidal particles embedded in a liquid.

Effect of thermocapillary stress on slip length for a channel textured with parallel ridges

We compute the apparent hydrodynamic slip length for (laminar and fully developed) Poiseuille flow of liquid through a heated parallel-plate channel. One side of the channel is textured with parallel (streamwise) ridges and the opposite one is smooth. On the textured side of the channel, the liquid is in the Cassie state. No-slip and constant heat flux boundary conditions are imposed at the solid–liquid interfaces along the tips of the ridges, and the menisci between ridges are considered to be flat and adiabatic. The smooth side of the channel is subjected to no-slip and adiabatic boundary conditions. We account for the streamwise and transverse thermocapillary stresses along menisci. When the latter is sufficiently small, Stokes flow may be assumed. Then, our solution is based upon a conformal map. When, additionally, the ratio of channel height to half of the ridge pitch is of order 1 or larger, an accurate but less cumbersome solution follows from a matched asymptotic expansion. When inertial effects are relevant, the slip length is numerically computed. Setting the thermocapillary stress equal to zero yields the slip length for an adiabatic flow.

Study on Lubricant Depletion Induced by Laser Heating in Thermally Assisted Magnetic Recording Systems: Effect of Lubricant Thickness

In this study, fundamental research on lubricant depletion due to laser heating in thermally assisted magnetic recording was conducted. In particular, the effect of lubricant film thickness on lubricant depletion was investigated. The conventional lubricant Zdol2000 was used. As a result, it was found that the lubricant depletion characteristics due to laser heating depend largely on the lubricant film thickness. In addition, it was suggested that the lubricant depletion mechanism involves the evaporation of the mobile lubricant molecules, when the maximum attained temperature is not very high. Another suggested lubricant depletion mechanism involves the thermocapillary stress effect induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.

Molecular Tagging Fluorescence Velocimetry (MTFV) to Measure Meso- to Micro-Scale Thermal Flow Fields

The development of a molecular tagging fluorescence velocimetry (MTFV) system is discussed and measurement results are presented for a meso-scale flow field of thermally driven capillary pore of 5-mm inner diameter that is tilted 5° from the horizon. The developed technique uses caged Dextran conjugates of caged fluorescene dyes of less than 10 nm in size for tracers. The frequency-tripled UV band (λ = 355 nm) of a pulsed Nd:YAG laser uncages the molecules by photo-cleaving that is decomposition of a caging chemical group and a fluorescence chemical group. Then a CW blue Argon-ion laser (λ = 488 nm) pumps the fluorescence of only those uncaged molecules, whose emmission band is centered at λ = 518 nm, and a sequential recording of the fluorescence images are digitally recorded and analyzed for Lagrangian velocity field mapping. The use of the technique allows detailed measurements of the thermally driven three-dimensional flow inside a heated capillary pore. The measurement shows that the meniscus surface flow is mainly driven by the thermocapillary stress field, occurring due to the surface temperature gradient, while the bulk flow inside the pore is driven largely by the natural convection buoyancy. The whole capillary flow is made by a combination of these two different flow effects. As to the heater position, above or below the interface, the three dimensional flow patterns are measured totally in the opposite way.