Affiliation:
1. Laboratory of Technical Physics, University of Liverpool, Brownlow Hill, Liverpool L69 3GH, UK
Abstract
The onset and early stages of dynamic wetting on different hydrophobic surfaces is investigated experimentally for aqueous solutions of two commercial trisiloxane surfacants of similar chemical structure, one of which exhibits superspreading behaviour, in order to investigate the spreading dynamics independently of the surface activity. Superspreading, or the ability of a surfactant solution to spread on a surface beyond the state determined by thermodynamic equilibrium, has been investigated for more than 30 years however its physical mechanism remains poorly understood to date despite its important applications in the formulation of agrochemicals. Surfactant solutions were prepared by dissolving S233 and S240 surfactants (Evonik Industries AG, Essen, Germany) into de-ionised water at a weight concentration of 0.1%. Drops of surfactant solutions and pure water were deposited on three horizontal substrates with different wettability (equilibrium contact angle of water ranging between 55∘ and 100∘), and observed from below with a high-frame rate camera to visualise the advancing contact line. The spreading ratio of drops as a function of time was extracted from high-speed videos by digital image processing. Results reveal that the superspreading solution exhibits an intermittent spreading rate, as well as peculiar features of the contact line, which are not observed for the non-superspreading solution, and confirm the superspreading effect becomes less significant when the surface energy of the substrate is decreased.
Subject
Colloid and Surface Chemistry,Chemistry (miscellaneous)
Reference28 articles.
1. Humble, G., Simpelkamp, J., and Kennedy, M. (2004). Use of Non-Spreading Silicone Surfactants in Agrochemical Compositions. (No. AU 2002301504 B2), U.S. Patent.
2. A study of the solution, interfacial and wetting properties of silicone surfactants;Ananthapadmanabhan;Colloids Surf.,1990
3. Superspreading;Hill;Curr. Opin. Colloid Interface Sci.,1998
4. Superspreading—20 years of physicochemical research;Venzmer;Curr. Opin. Colloid Interface Sci.,2011
5. Brutin, D. (2015). Droplet Wetting and Evaporation, Academic Press.