Surfactant induced autophobing

Abstract

Surfactant adsorption in a three-phase system and its influence on wetting properties are relevant in various applications. Here, we report a hitherto not observed phenomenon, namely the retraction of an aqueous drop on hydrophilic solid substrates (which we refer to as 'autophobing') in ambient oil containing water-insoluble fatty acids, caused by the deposition of these fatty acids from the ambient oil onto the solid substrate. AFM measurements confirm that the surfactant is deposited on the solid by the moving contact line. This leads to a more hydrophobic substrate, the retraction of the contact line and a concomitant increase in the contact angle. The deposition process is enabled by the formation of a reaction product between deprotonated fatty acids and Ca(2+) ions at the oil/water interface. We investigate how the transition to a new equilibrium depends on the concentrations of the fatty acids, the aqueous solute, the chain lengths of the fatty acid, and the types of alkane solvent and silica or mica substrates. This phenomenon is observed on both substrates and for all explored combinations of fatty acids and solvents and thus appears to be generic. In order to capture the evolution of the contact angle, we develop a theoretical model in which the rate of adsorption at the oil-water interface governs the overall kinetics of autophobing, and transfer to the solid is determined by a mass flux balance (similar to a Langmuir Blodgett transfer).

Equilibrium Contact Angle and Adsorption Layer Properties with Surfactants

“…where we used [Υ ∂xh ξ δh(x)] ∞ 0 = 0. Based on (12), the free surface profile is given by the Euler-Lagrange equation…”

“…Besides the modified Tanner law, the interplay between surfactant dynamics and free surface thin film flows leads to a variety of intriguing phenomena, such as surfactant induced fingering of spreading droplets [2][3][4][5][6][7], superspreading of aqueous droplets on hydrophobic surfaces [8,9], or autophobing of aqueous drops on hydrophilic * u.thiele@uni-muenster.de substrates [10][11][12]. In addition to creating Marangonistresses at the free interface, several other properties of surfactants enrich the spectrum of dynamical behaviors observed.…”

“…The recent formulation of the dynamic equations in arXiv:1802.04042v1 [physics.flu-dyn] 12 Feb 2018 terms of a thermodynamically consistent gradient dynamics [13,14] sheds some light on a more rigorous approach to model surfactant driven thin film flows using an energy functional. Following the approach from Refs.…”

Salinity-Dependent Contact Angle Alteration in Oil/Brine/Silicate Systems: the Critical Role of Divalent Cations

“…These imperfections are ascribed to heterogeneities in the deposited layer; from previous studies of brine droplets under oil with stearic acid 26 and on exposure of dried Langmuir–Blodgett layers to brine, 27 it is known that inhomogeneous patterns are formed. To obtain the best representative contact angle, we measured the droplet/muscovite interfacial area using the bottom-view camera.…”

Combined microfluidics–confocal Raman microscopy platform for studying enhanced oil recovery mechanisms

“…Such mechanisms should therefore be discarded from macroscopic models for core flood experiments or reservoir models. Recent years have seen multiple improvements of existing techniques and the development of novel ones to characterize recovery systems in more detail, including atomic force microscopy (AFM), contact angle goniometry, X‐ray tomography, zeta potential analysis, mass spectrometry, quartz crystal microbalance, and optical and fluorescence microscope that provide access to various complementary properties. One particularly important aspect, however, that cannot be addressed using these tools is to provide a detailed map of the distribution of chemical species and its evolution in the course of a water flooding experiment.…”