Experimental evidence of nonlocal hydrodynamic influence on the dynamic contact angle

Abstract

The dynamic contact angle formed when a liquid curtain impinges onto a moving solid is measured for aqueous glycerol solutions in different flow regimes. It is usually assumed that the dynamic contact angle is simply a function of the contact-line speed and the material properties of the contacting media. The new results show that this is not the case. For a given gas/liquid/solid combination and a given contact-line speed, the dynamic contact angle can be varied by varying the flow rate of the liquid and/or the curtain height, that is by varying the flow field near the contact line. The possibility of attributing this effect merely to free-surface bending and interpreting the results in terms of the so-called ''apparent'' contact angle is discussed and ruled out on the basis of some general qualitative arguments and analysis of the characteristic length scales involved. A probable connection between the observed effect and the physical mechanism of interface disappearance and formation incorporated in a recently developed theory of wetting is discussed.

Flow Patterns in the Vicinity of Triple Line Dynamics Arising from a Local Surface Tension Model

“…We have discretized and implemented macroscopic part of the Shikhmurzaev model, [10], [2], using an ALE formulation and a finite element scheme. Also, a connection with Qian-Wang-Sheng's results, [11], is presented.…”

“…The "implicit" model does not impose the contact line velocity and the wetting angle but consider them as a response of the model. This model is based on the Shikhmurzaev's theory, [10], [2], which makes introduce the generalized Navier slip condition (3) and the condition (2). These conditions are local since the extra terms g and h vanish except in a vicinity of the triple point.…”

“…The most frequent contact line model is an explicit mobility relation giving the contact line velocity in function of the wetting angle value at any time (Tanner type laws). Nevertheless, it has been showed, [2], that the dynamic wetting angle cannot be determined inherently by such a mobility relation.…”

“…In the present paper, we consider an "implicit" model based on the Shikhmurzaev theory, [10], [2]. This model lead to generalized Navier slip type boundary conditions with local surface tension gradient terms.…”

Wetting front dynamics in an isotropic porous medium

“…As shown by experiments on dynamic wetting, in a general case θ d depends on, and hence should be regarded as a functional of, the flow field in the vicinity of the moving contact line (Blake et al 1999;Clarke & Stattersfield 2006). For flow in a porous medium, the contact angle's dependence on the flow field reduces to its dependence only on the contact-line speed u 1 , which is the leading factor determining the flow field in the vicinity of the contact line.…”