Evaporation of Sessile Droplets of Polyelectrolyte/Surfactant Mixtures on Silicon Wafers

Andrew Akanno,Francisco Ortega,Manuel G. Velarde,Ramón G. Rubio,Lionel Perrin,Victor M. Starov,Sara Llamas,Eduardo Guzmán

doi:10.3390/colloids5010012

Abstract

The wetting and evaporation behavior of droplets of aqueous solutions of mixtures of poly(diallyldimethylammonium chloride) solution, PDADMAC, with two different anionic surfactants, sodium laureth sulfate, SLES, and sodium N-lauroyl N-methyl taurate, SLMT, were studied in terms of the changes of the contact angle θ and contact length L of sessile droplets of the mixtures on silicon wafers at a temperature of 25 °C and different relative humidities in the range of 30–90%. The advancing contact angle θa was found to depend on the surfactant concentration, independent of the relative humidity, with the mixtures containing SLES presenting improved wetting behaviors. Furthermore, a constant droplet contact angle was not observed during evaporation due to pinning of the droplet at the coffee-ring that was formed. The kinetics for the first evaporation stage of the mixture were independent of the relative humidity, with the evaporation behavior being well described in terms of the universal law for evaporation.

Highlights

IntroductionMany coupled factors dominate the evaporation process: heat and mass flows, thermocapillarity, substrate thermal conductivity and deformability, substrate patterning, surface curvature, and the formation of deposits
Association involving in Solution polyelectrolyte–surfactant mixtures requires a careful examination of the interactions occurring in solution between the polyThe analysis of any phenomena involving polyelectrolyte–surfactant mixtures reelectrolyte chains and the oppositely charged surfactant mixtures
These interactions, quires a careful examination of the interactions occurring in solution between the polycommonly driven by a combination of electrostatic and hydrophobic interactions, lead to electrolyte chains and the oppositely charged surfactant mixtures

Summary

Introduction

Many coupled factors dominate the evaporation process: heat and mass flows, thermocapillarity, substrate thermal conductivity and deformability, substrate patterning, surface curvature, and the formation of deposits. The decoupling of these processes is currently extremely difficult with current experimental and theoretical methods [8,9,10,11,12]. The situation is even more difficult when complex fluids—such as those frequently found in technological applications—are concerned because the prediction and control of the evaporation of fluid droplets becomes essential for the appropriate design of the abovementioned processes

Methods

Results

Conclusion