The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review

Abstract

SummaryThe drag of fluid flow at the solid–liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found.

Electroviscous effect and convective heat transfer of pressure-driven flow through microtubes with surface charge-dependent slip

“…Furthermore, they established a mathematic model to describe this negative dependence. In addition, Jing and Bhushan [12] and Pan et al [19] experimentally studied the surface charge-dependent slip based on the atomic force microscope technique and found similar relationship between surface charge and slip as the work of Joly et al [23].…”

“…Usually, no-slip boundary condition at the solid-liquid interface, that is, there is no relative motion between the solid and liquid at the interface is valid in macroscale. However, in the micro/nanoscale, the boundary slip, indicating a status of relative motion between the solid and liquid, at some solid-liquid interfaces cannot been neglected when analyzing the fluidic behavior [12,[17][18][19]. Considering the convective heat transfer of the fluid flow is related to the fluidic behavior, thus, the existence of surface charge and boundary slip inevitably affect the convective heat transfer of fluid flow in a micro/nanofluidic system by affecting the fluidic behavior.…”

Simulation of Effective Slip and Drag in Pressure-Driven Flow on Superhydrophobic Surfaces

“…wherê0 is the pressure at the outside of the fluid field near inlet or outlet,̂0 ≥ in at the inlet, and̂0 ≤ out at the outlet; t is the tangential vector to the wall. In many previous publications about pressure-driven microchannel flow [15,35,36], the pressure gradient is assumed / = −1 × 10 −6 N/m 3 . With reference to this, in this model, in is set a variable parameter ranging from 6 to 600 Pa with the step length of 6 Pa, while out = 0; in which case, / ranges from −1 × 10 5 to −1 × 10 7 N/m 3 with the step length −1 × 10 5 N/m 3 .…”

“…Researches have shown that flat, smooth, and chemically homogenous hydrophilic surfaces exhibit no or less slip [10,11]. However, if the surface is hydrophobic, there can be slip with the magnitude up to tens of nanometers [6,[12][13][14][15]. In the meanwhile, superhydrophobic surfaces, on which the contact angle exceeds 150 ∘ and the contact angle hysteresis is less than 5 ∘ , have been proved to be able to significantly amplify the magnitude of slip.…”

Measurement and Quantification of Effective Slip Length at Solid–Liquid Interface of Roughness-Induced Surfaces with Oleophobicity

“…, where b is the slip length, v is the tangential velocity, and y is the axis perpendicular to the wall. At the micro or nano scale, slip lengths of various surfaces immersed in liquid have been investigated in theoretical and experimental studies [7][8][9][10][11][12][13][14][15][16][17]. For the measurement technique, Appl.…”