2010 Volume 76 Issue 772 Pages 2135-2142
A new method to actuate a small droplet on a plate was proposed. In order to reduce the resistance to the droplet movement, which is typically represented by the resultant of surface tension acting on the three-phase contact line, i.e., σ (cos θ_R-cos θ_A) (σ: liquid surface tension, θ_R, θ_A: receding and advancing contact angles), a supersonic oscillation was imposed on the plate to suppress the contact angle hysteresis (θ_R-θ_A). The experimental results using SAMs (Self-Assembled Monolayers) plates showed that the resistance was reduced by 80% due to the oscillation having the frequency of 28kHz and the amplitude of few micrometers. Then the Laser beam was directed to one end of the droplet. The contact angle was remarkably decreased due to the local heating of SAMs plate and the droplet moved to the end of the Laser beam, since the tangential component of surface tension at the heated end overcomes that on the other. The droplet can be actuated by about 0.6mm/s by the method combining the oscillation and the local heating by the Laser beam.