Electrowetting actuation of gold nanofluid droplets: a physics dissertation defense by Crismar Patacsil

ateneophysicsnews_crismar_patacsil_dissertation_defense_20170408 (2)
The Department of Physics of Ateneo de Manila University cordially invites you to a Physics Dissertation Defense:

  • Dissertation title: ELECTROWETTING ACTUATION OF GOLD NANOFLUID DROPLETS
  • PhD candidate: Crismar P. Patacsil
  • Date and Venue: April 8, 2017, 1:00 PM at Faura Hall F-106

Panel members:

  • Raphael A. Guerrero, Ph.D., Dissertation Supervisor
  • Benjamin O. Chan, Ph.D., Dissertation Examiner
  • Gil Nonato C. Santos, Ph.D., Dissertation Examiner
  • Erwin P. Enriquez, Ph.D., Dissertation Reader
  • Joel T. Maquiling, Ph.D., Dissertation Reader

Abstract:
Nanoparticles exhibit completely different properties (physical, chemical, electronic, magnetic and optical) from their bulk material counterparts. This study explores the interaction of gold nanoparticle (AuNP) suspensions in a liquid droplet with an applied electric field. A basic planar electrowetting set-up is employed, consisting of a bottom copper electrode coated with a thin insulating layer of uncured polydimethysiloxane (PDMS) silicone oil mounted on an adjustable stage and a platinum wire upper electrode in contact with the sessile gold nanofluid droplet sitting on the dielectric layer. A voltage source is connected across the top and bottom electrodes. Changes in the contact angle of the droplet, as voltage is varied, is captured using a USB microscope camera. The contact angles of the images are determined using ImageJ software. The electrowetting on dielectric (EWOD) experiment is done with varying concentrations (in µM) of gold nanofluid (deionized water containing gold nanoparticles with an average size of 10 nm): 0.5, 0.33, 0.25, 0.05 and deionized water (no gold nanoparticles) as a control fluid. Results show a different electrowetting response for each concentration. The contact angle is found to decrease with increasing nanoparticle concentration, indicating a decrease in the liquid-gas surface tension as concentration increases. Increasing the nanoparticle content also lowers the required voltage for effective actuation. Contact angle saturation is observed with nanofluid droplets, with the threshold voltage decreasing as nanoparticle concentration rises. Maximum droplet actuation before contact angle saturation is achieved at only 10 V for a concentration of 0.5 μM. To explain the mechanism for the observed enhanced electrowetting actuation, the specific capacitance C is calculated from the voltage versus contact angle data for each concentration. For the control fluid, the calculated specific capacitance is 0.0012 F/m^2. Specific capacitances are C = 0.0097 F/m^2, C = 0.0049 F/m^2, and C = 0.0015 F/m^2 for 0.5µM, 0.33µM, and 0.05µM gold nanofluid concentrations, respectively. The presence of gold nanoparticles affects electrowetting response by increasing the capacitance with increasing concentration of the nanoparticles. Higher specific capacitance results in increased induced charges at the solid-liquid interface which would result in increased electro-mechanical force on the droplet as voltage is applied.

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