Antisurfactant (Autophobic) Behavior of Superspreader Surfactant Solutions

Abstract

Surfactants are often added to water to increase the wetting of hydrophobic surfaces. We previously showed that most surfactant solutions behave identically to simple liquids with the same surface tension, indicating that the surfactants do not change the wettability of the solid surface itself. Here, we show that the superspreading surfactant Silwet results in a systematically higher contact angle on a hydrophobic surface than other surfactant solutions of comparable liquid−vapor surface tension. We also experimentally observe this "antisurfactant" behavior for CTAB on hydrophilic substrates. Supported by sum-frequency generation spectroscopy results, we suggest that this effect is due to chargebinding of the surfactant with the substrate.

Adsorption of CTAB on Sapphire-c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation

“…Surfactant adsorption on mineral surfaces is of great interest in many areas, from fundamental surface science to applications where flotation, wetting, or stabilization of dispersions is important. − It is also important in heterogeneous ice nucleation in the atmosphere, where marine aerosol particles may be coated by surfactants. , When surfactants adsorb on solid surfaces in contact with an electrolyte, the common view is that the exposed surface will preferably attract the hydrophilic part of the surfactant. Macroscopic adsorption isotherms of surfactants at oxide surfaces show distinct concentration regimes, where different configurations of the adsorbed surfactants can exist as was summarized by Tyrode et al One adsorption geometry that is often proposed at low surface coverage involves flat lying and isolated surfactants with their symmetry axis parallel to the surface plane.…”

Tuning Contact Angles of Aqueous Droplets on Hydrophilic and Hydrophobic Surfaces by Surfactants

“…When the surfactant is introduced into the droplet, it adsorbs to both interfaces, solid–water and water–vapor, thereby reducing their surface tensions, which become dependent on the surfactant concentration (i.e., γ sw (c 0 ) and γ­(c 0 )). In principle, less-soluble surfactants can also adsorb at the solid–vapor interface, which does, however, not occur in our case (see Section S7 of the Supporting Information). Consequently, the solid–vapor surface tension, γ sv , remains unaffected.…”

“… 29 , 30 In recent years, we have witnessed an enormous interest in surfactant-containing droplets, where the surfactant’s adsorption to the solid–water and air–water interfaces can render wetting in a nontrivial way. 31 − 39 …”

“…An important effect of adsorbed molecules is that they reduce the surface tension of the interface to which they adsorb, , which is why surfactants are often used to enhance the wetting ability of aqueous solutions and to suppress hydrophobic cavitation. , Surface-active molecules can dramatically alter the substrate wettability, thereby leading to phenomena such as superspreading or autophobing (spontaneous retraction of a drop after initial spreading). , Determining the relationship between the surface tension and the structures of surfactant additives at different temperatures, pressures, salinities, and pH regimes is critical for the design in many industry sectors, ranging from consumer chemicals to oil and gas extraction. , In recent years, we have witnessed an enormous interest in surfactant-containing droplets, where the surfactant’s adsorption to the solid–water and air–water interfaces can render wetting in a nontrivial way. − …”

Synthesis and surface activity of novel amino acid surfactants

“…Wettability is one of the important indexes to evaluate surfactants (Bera et al, 2021; Meng et al, 2021). Directional adsorption of surfactants on the interface affects the wettability of solids by changing the interfacial tension.…”