On the measurement of slip length for liquid flow over super-hydrophobic surface

2009 ◽  
Vol 54 (24) ◽  
pp. 4560-4565 ◽  
Author(s):  
Jian Li ◽  
Ming Zhou ◽  
Lan Cai ◽  
Xia Ye ◽  
Run Yuan
Keyword(s):  
Liquid Flow ◽  
Slip Length ◽  
Hydrophobic Surface

scholarly journals ESTIMATION OF THE SLIP LENGTH IN THE FLOW OF LIQUID IN MICRO-CHANNELS

2018 ◽  
Vol 40 (2) ◽  
pp. 12-19
Author(s):  
Y.Y. Kovetska
Keyword(s):  
Slip Length ◽  
Slip Flow ◽  
Gas Bubbles ◽  
Hydrophobic Surface ◽  
Dissipative Heating ◽  
Research Review ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Lower Viscosity ◽  
Micro Channels

Research review of phenomenon for slip flow in micro and nanocannels is presented in the paper. The analysis of theoretical and experimental data characterizing the slip length is carried out. In slip flow in microchannels the slip length is affected by the contact angle of the liquid with the surface, shear stress, pressure, dissipative heating, the amount and nature of the dissolved gas in the liquid, electrical characteristics, surface roughness. Studies of flow in microchannels with hydrophobic walls, which are based on molecular dynamics, showed that the slip length has order of 20 nm. This is much less than the values observed in the experiment. The introduction of an effective (apparent) slip length suggests the existence of a thin layer of gas bubbles near the hydrophobic surface or liquid layer with low value of viscosity and density. Since the idealized model for the total coverage of a hydrophobic surface by gas bubbles gives, as a rule, overestimated values of the slip length in comparison with experimental ones, some researchers consider the inhomogeneous coating of the wall by gas bubbles. In this case, the effect of a layer with a lower viscosity on the slip length turns out to be weaker.

scholarly journals A novel physical mechanism of liquid flow slippage on a solid surface

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz0504 ◽  
Author(s):  
Yuji Kurotani ◽  
Hajime Tanaka
Keyword(s):  
Liquid Flow ◽  
Density Fluctuation ◽  
Physical Mechanism ◽  
Slip Length ◽  
Quiescent State ◽  
Physical Explanation ◽  
Liquid Transport ◽  
Viscous Liquids ◽  
Gas Layer ◽  
Solid Walls

Viscous liquids often exhibit flow slippage on solid walls. The occurrence of flow slippage has a large impact on the liquid transport and the resulting energy dissipation, which are crucial for many applications. It is natural to expect that slippage takes place to reduce the dissipation. However, (i) how the density fluctuation is affected by the presence of the wall and (ii) how slippage takes place through forming a gas layer remained elusive. Here, we report possible answers to these fundamental questions: (i) Density fluctuation is intrinsically enhanced near the wall even in a quiescent state irrespective of the property of wall, and (ii) it is the density dependence of the viscosity that destabilizes the system toward gas-layer formation under shear flow. Our scenario of shear-induced gas-phase formation provides a natural physical explanation for wall slippage of liquid flow, covering the slip length ranging from a microscopic (nanometers) to macroscopic (micrometers) scale.

scholarly journals Role of Solid Wall Properties in the Interface Slip of Liquid in Nanochannels

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 663 ◽  
Author(s):  
Wei Gao ◽  
Xuan Zhang ◽  
Xiaotian Han ◽  
Chaoqun Shen
Keyword(s):  
Liquid Flow ◽  
Coupling Strength ◽  
Solid Wall ◽  
Slip Length ◽  
Boundary Slip ◽  
Near Surface ◽  
Wall Properties ◽  
Fluid Coupling ◽  
Interface Slip

A two-dimensional molecular dynamics model of the liquid flow inside rough nanochannels is developed to investigate the effect of a solid wall on the interface slip of liquid in nanochannels with a surface roughness constructed by rectangular protrusions. The liquid structure, velocity profile, and confined scale on the boundary slip in a rough nanochannel are investigated, and the comparison of those with a smooth nanochannel are presented. The influence of solid wall properties, including the solid wall density, wall-fluid coupling strength, roughness height and spacing, on the interfacial velocity slip are all analyzed and discussed. It is indicated that the rough surface induces a smaller magnitude of the density oscillations and extra energy losses compared with the smooth solid surface, which reduce the interfacial slip of liquid in a nanochannel. In addition, once the roughness spacing is very small, the near-surface liquid flow dominates the momentum transfer at the interface between liquid and solid wall, causing the role of both the corrugation of wall potential and wall-fluid coupling strength to be less obvious. In particular, the slip length increases with increasing confined scales and shows no dependence on the confined scale once the confined scale reaches a critical value. The critical confined scale for the rough channel is larger than that of the smooth scale.

Nanobubble Formation at the Solid-Liquid Interface Studied by Atomic Force Microscopy

2005 ◽  
Vol 899 ◽  
Author(s):  
Abhinandan Agrawal ◽  
Gareth H. McKinley
Keyword(s):  
Atomic Force Microscopy ◽  
Solid Surface ◽  
Silicon Oxide ◽  
Slip Length ◽  
Hydrophobic Surface ◽  
Force Microscopy ◽  
Atomic Force ◽  
Experimental Values ◽  
Solid Liquid ◽  
Wafer Surfaces

AbstractThe formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase. While nanobubbles do not form on flat hydrophilic (silicon oxide wafer) surfaces immersed in water, they appear spontaneously at the interface of water against smooth, hydrophobic (silanized wafer) surfaces. From the experimental observations we draw the conclusion that the features observed in the AFM images are deformable, air-filled bubbles. In addition to the hydrophobicity of the solid surface, differences in solubility of air between two miscible fluids can also lead to formation of nanobubbles. We observe that nanobubbles appear at the interface of water against hydrophilic silicon oxide surfaces after in-situ mixing of ethanol and water in the fluid-cell.The shapes of the nanobubbles are well approximated by spherical caps, with width much larger than the height of the caps. We quantify the morphological distribution of nanobubbles by evaluating several important bubble parameters including surface coverage and radii of curvature. In conjunction, with an analytical model available in the literature, we use this information to estimate that the present nanobubble morphology may give rise to slip lengths ∼1–2 µm in pressure driven flows for water flowing over the hydrophobic surface. The consistency of the calculated slip length with the experimental values reported in the literature, suggests that the apparent fluid slip observed experimentally at hydrophobic surfaces may arise from the presence of nanobubbles.

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

2014 ◽  
Vol 5 ◽  
pp. 1042-1065 ◽  
Author(s):  
Yunlu Pan ◽  
Bharat Bhushan ◽  
Xuezeng Zhao
Keyword(s):  
Contact Angle ◽  
Fluid Flow ◽  
Charge Density ◽  
Surface Charge ◽  
Liquid Flow ◽  
Applied Voltage ◽  
Surface Charge Density ◽  
Slip Length ◽  
Surface Wetting ◽  
Boundary Slip

The 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.

Energy dissipation and the contact-line region of a spreading bridge

2012 ◽  
Vol 703 ◽  
pp. 111-141 ◽  
Author(s):  
H. B. van Lengerich ◽  
P. H. Steen
Keyword(s):  
Energy Dissipation ◽  
Flow Field ◽  
Contact Line ◽  
Sliding Friction ◽  
Slip Length ◽  
Cox Model ◽  
Hydrophobic Surface ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Line Region

AbstractA drop on a circular support spontaneously spreads upon contact with a substrate. The motion is driven by a loss of surface energy. The loss of recoverable energy can be expressed alternatively as work done at the liquid–gas interface or dissipation through viscosity and sliding friction. In this paper we require consistency with the energy lost by dissipation in order to infer details of the contact-line region through simulations. Simulations with the boundary integral method are used to compute the flow field of a corresponding experiment where polydimethylsiloxane spreads on a relatively hydrophobic surface. The flow field is used to calculate the energy dissipation, from which slip lengths for local slip and Navier slip boundary conditions are found. Velocities, shear rates and pressures along the interface as well as interface shapes in the microscopic region of the contact line are also reported. Angles, slip length and viscous bending length scale allow a test of the Voinov–Hocking–Cox model without free parameters.

Effect of the Surface Tension of Liquid-Solid Interface on Liquid Flow in Parallel-Plate Sub-Micron Channels Using Multi-Body Dissipative Particle Dynamics

2013 ◽  
Author(s):  
Toru Yamada ◽  
Yutaka Asako ◽  
Mohammad Faghri ◽  
Bengt Sundén
Keyword(s):  
Surface Tension ◽  
Liquid Flow ◽  
Parallel Plate ◽  
Slip Length ◽  
Flow Direction ◽  
Dissipative Particle Dynamics ◽  
Particle Dynamics ◽  
Wall Surface ◽  
Multi Body ◽  
Solid Walls

The liquid flow in sub-micron channels is simulated using multi-body dissipative particle dynamics (MDPD) to study the effect of the surface tension between liquid and wall surface on the flow in sub-micon scale. The solution domain is considered to be two-dimensional, where DPD particles are randomly distributed. Periodic boundary condition is employed in the flow direction and the solid walls are created by distributing DPD particles in the additional layers on the top and bottom of the domain. The different surface tensions between liquid and wall surface are obtained by changing the interaction parameters between the liquid and wall DPD particles. The ratio of Capillary number (Ca) to Reynolds number (Re) is used to relate the DPD units to the physical units. The results are shown in the form of slip length and the effect of the surface tension on the liquid flow in sub-micron channels is discussed.

On the Measurement of Slip Length for Liquid on Super-Hydrophobic Surface

2009 ◽  
pp. 697-698
Author(s):  
Li Jian ◽  
Zhou Ming ◽  
Cai Lan ◽  
Yang Haifeng ◽  
Ye Xia
Keyword(s):  
Slip Length ◽  
Hydrophobic Surface

A New Slip Boundary Model of Liquid Flows

2012 ◽  
Vol 629 ◽  
pp. 611-616 ◽  
Author(s):  
Fu Quan Song ◽  
Xiao Xing Chen
Keyword(s):  
Shear Rate ◽  
External Force ◽  
Liquid Flow ◽  
Slip Length ◽  
Power Law Model ◽  
Independent Variables ◽  
Slip Boundary ◽  
Boundary Model ◽  
Non Equilibrium Molecular Dynamics ◽  
Liquid Flows

With the development of Micro Electro Mechanism System, the linear slip boundary of liquid flow has been often used. In this paper, some flows in different wettability boundaries were researched by Non-Equilibrium Molecular Dynamics (NEMD) simulation, and the characteristics of the slip length were discussed. The results show that: when liquid flow on the hydrophobic boundary, the slip length decreases with the external force increasing and the shear rate increasing near boundaries, the width of channel and the external force are not independent variables of the slip length, and the shear rate and the surface wettability are independent variables of the slip length. The slip length can be reduced by increasing the driving force for liquid flow in a channel. Finally, a new power law model of the slip boundary of liquid flow was derived.

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