3D Confocal Scanning Laser Microscopy to Quantify Contact Angles in Natural Oil-Water Mixtures

A Salim,J Sausse,J Pironon,C Le Carlier De Veslud,M Fourar

doi:10.2516/ogst:2008011

Abstract

The contact angle of a liquid drop on a solid surface is one of the most simple, useful and sensitive parameters in the hydraulic sciences to quantify and to qualify the wettability and the surface energy of different materials. In this paper, a confocal scanning laser microscope (CSLM) has been used to quantify contact angle and then the wettability. This technique uses a laser scan and allows series of 2-D images of a fluorescent liquid droplet set on various solid surfaces to be recorded. The generation of 3-D images is carried out with the summation of several images acquired with a regular step along the CSLM z-axis. The results obtained are compared and discussed with those obtained with a conventional goniometric technique for different solid-liquid-air systems. CSLM results show that similar values are obtained with both methods. Thus, this technique shows that the length interval of sampling between the solid contact and the curvature rupture of the drop seems to be essential to correctly estimate the contact angles. This method allows the study of the local contact angle along the periphery of the drop, and the deformation of the drop shape. Construction of 3-D images shows that drops are characterized by complex morphologies and that the local contact angles can be modified by chemical heterogeneities in the fluids.

Highlights

The concept of contact angle has been widely used in studies involving characterization of solid-fluid1-fluid2 interfacial interactions
On the contrary, when the liquid is characterized by higher surface tension and the solid by lower surface energy, the contact angle becomes nonzero, even larger than 90°, at which the liquid on the solid surface is considered as non-wetting
Sequences of 2D images are obtained by confocal scanning laser microscope (CSLM) (G2R laboratory, University of Nancy, France) and 3D models of the liquid droplets are constructed with the gOcad 3D modeler (Earth Decision SciencesTM, ParadigmTM; Mallet, 2002)

Summary

Introduction

The concept of contact angle has been widely used in studies involving characterization of solid-fluid1-fluid interfacial interactions. A liquid characterized by a low surface tension set on a smooth solid with a high surface energy produces a small contact angle (θ) between the two phases. When θ is equal to zero, the liquid spreads along the solid and the droplet becomes a liquid film. On the contrary, when the liquid is characterized by higher surface tension and the solid by lower surface energy, the contact angle becomes nonzero, even larger than 90°, at which the liquid on the solid surface is considered as non-wetting. Contact angle measurement is a key parameter to determine the solid wettability which characterizes the tendency of a fluid to spread along a solid surface in the presence of another (Crocker and Marchin, 1988). The wettability has a crucial impact on flow during oil recovery and upon the volume and distribution of the residual oil (Craig, 1971; Samathiel, 1973; Morrow et al, 1986; Anderson, 1987; Morrow, 1991; Jadhunandan and Morrow, 1995)

Methods

Results

Discussion

Conclusion