Surface charge-induced EDL interaction on the contact angle of surface nanobubbles.
The contact angle (CA) of surface nanobubbles is believed to affect the stability of nanobubbles and fluid drag in micro/nanofluidic systems. The CA of nanobubbles is dependent on size and is believed to be affected by the surface charge-induced electrical double layer (EDL). However, neither of these of attributes are well understood. In this paper, by introducing an EDL-induced electrostatic wetting tension, a theoretical model is first established to study the effect of EDLs formed near the solid-liquid interface and the liquid-nanobubble interface on the gas phase CA of nanobubbles. The size-dependence of this EDL interaction is studied as well. Next, by using atomic force microscopy (AFM), the effect of the EDL on nanobubbles' gas phase CA is studied with variable electrical potential at the solid-liquid interface, which is adjusted by an applied voltage. Both the theoretical and the experimental results show that the EDLs formed near the solid-liquid interface and the liquid-nanobubble interface lead to a reduction of gas phase CA of the surface nanobubbles because of an electrostatic wetting tension on the nanobubble due to the attractive electrostatic interaction between the liquid and nanobubble within the EDL, which is in the nanobubbles' outward direction. An EDL with a larger zeta potential magnitude leads to a larger gas phase CA reduction. Furthermore, the effect of EDL on the nanobubbles' gas phase CA shows a significant size-dependence considering the size dependence of the electrostatic wetting tension. The gas phase CA reduction due to the EDL decreases with increasing nanobubble height and increases with the nanobubble's increasing curvature radius, indicating that a surface charge-induced EDL could possibly explain the size dependence of the gas phase CA of nanobubbles.
School of Mechanical Engineering, University of Shanghai for Science and Technology , Shanghai, 200093, China.
Dalei
D
Jing
School of Mechanical Engineering, Harbin Institute of Technology , Harbin, 150001, China.|School of Mechanical Engineering, Heilongjiang University of Science and Technology , Harbin 150022, China.
Dayong
D
Li
School of Mechanical Engineering, Harbin Institute of Technology , Harbin, 150001, China.
Yunlu
Y
Pan
School of Mechanical Engineering, Harbin Institute of Technology , Harbin, 150001, China.|Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics (NLB2), The Ohio State University , 201 West 19th Avenue, Columbus, Ohio 43210-1142, United States.
Bharat
B
Bhushan