Thermochemical control of oil droplet motion on a solid substrate

2012

Biomicrofluidics

We conduct a numerical investigation and analytical analysis of the effect of slippage on the thermocapillary migration of a small liquid droplet on a horizontal solid surface. The finite element method is employed to solve the Navier-Stokes equations coupled with the energy equation. The effect of the slip behavior on the droplet migration is determined by using the Navier slip condition at the solid-liquid boundary. The results indicate that the dynamic contact angles and the contact angle hysteresis of the droplet are strictly correlated to the slip coefficient. The enhancement of the slip length leads to an increase in the droplet migration velocity due to the enhancement of the net momentum of thermocapillary convection vortices inside the droplet. A larger contact angle leads to an increase in the migration velocity which in turn enlarges the rate of the droplet migration velocity to the slip length. There is good agreement between the analytical and the numerical results when the dynamic contact angle utilizes in the analytical approach obtained from the results of the numerical computation, and the static contact angle is smaller than 50°.

Section: Introductionmentioning

confidence: 99%

“…[24][25][26][27][28][29][30][31][32][33] The main objective of the theoretical studies has been to predict the steady migration velocity of the droplet. Lubrication approximation has been employed for this purpose in several works.…”

Section: Introductionmentioning

confidence: 99%

Effect of slippage on the thermocapillary migration of a small droplet

Nguyen

2012

Biomicrofluidics

“…Smith 8 showed that the thermocapillary cell inside the droplet distorts the free surface and changes the dynamic contact angles. Song et al 11 employed a chemical gradient coating and local laser heating to manipulate the migration of a droplet. They pointed out that the direction of motion is closely related to the change in the contact angle.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of a droplet migration induced by combined thermocapillary-buoyancy convection

Nguyen

2010

Physics of Fluids

Numerical computations have been performed to study the effects of thermocapillary convection and buoyancy convection, and free surface deformation induced by gravity on the migration behavior of a liquid droplet on a horizontal solid surface subjected to a uniform temperature gradient. Investigations are carried out by solving the Navier-Stokes equations coupled with the energy equation through the finite element method. The combined thermocapillary and buoyancy force driven convection produces complex dynamic behavior of fluid motion inside the droplet. The net momentum generated by a pair of asymmetric thermocapillary convection vortices inside the droplet drives the droplet to move in both small and middle droplet sized regimes. In the small sized regime, the quasisteady migration speed of the droplet is mostly linearly proportional to its size because of the stronger net thermocapillary momentum. When the droplet is in the middle sized regime, its quasisteady migration speed reaches a maximum, but this is gradually reduced as the droplet size increases due to the suppression of the net thermocapillary momentum by the buoyancy force. In the large droplet sized regime, two pairs of convection vortices exist inside the droplet as a result of the appearance of the buoyancy-driven convection accompanying the thermocapillary convection. The quasisteady migration speed quickly diminishes mainly due to the reduction of the net thermocapillary momentum from the stronger buoyancy convection.

“…This technique has been applied to change in size of droplets by voltage. [21][22][23][24] The voltage-dependency of the size means that the curvature radius of the sessile drop can be controlled with the voltage. Then the drop may work as a focal length-adjustable lens.…”

mentioning

confidence: 99%

Electrochemically Focus-Tunable Convex Lenses by Oil-Sessile Drop

ECS Electrochemistry Letters

Nishiumi

et al. 2014

A sessile drop of nitrobenzene (NB) mounted on the transparent electrode immersed in the aqueous solution works as an optical lens of which focus can be controlled by electrode potential when the solution includes K3Fe(CN)6 and tetrapentylammonium (TPA+) chloride. K3Fe(CN)6 functions as a redox species, whereas TPACl does as supporting electrolyte as well as a surfactant. The focal length decreases in the reduction potential domain. The switching between the long and the short focuses is almost reversible for 1 h by the potential control, synchronized with voltammograms. The size of a real image of an object varies with the potential