Influence of Drop Volume and Surfactant Concentration on the Marangoni Flow and Contact Line Instabilities during the Spreading of Surfactant Solutions on Hydrophilic Surface

Abstract

The dynamics of drop spreading of glycerol-water mixtures in the presence of a nonionic surfactant on hydrophilic glass surfaces has been investigated. The influence of drop volume and alkyl (8)-(16) glucoside (Plantacare 2000) surfactant concentration on the number and the nature of the spreading regimes is systematically investigated. For each regime, the radius can be expressed by a power law of the form R˭Ktn. The number and the nature of the regimes are strongly affected by the drop volume. An analysis of contact line instabilities is presented. The occurrence of instabilities and the characteristics of the instability pattern are controlled by the drop volume and the surfactant concentration. For drop volumes less than or equal to 15 µL, no contact line instability is evident. A succession of two different regimes occurs in the following order: a molecular-kinetic regime followed by a hydrodynamic regime regardless of the surfactant concentration. For drop volumes larger than 15 µL, the spreading process goes through a combination of three different regimes. The succession of a hydrodynamic regime, followed by a Marangoni regime and lastly a gravity regime is demonstrated. In the second regime, the spreading is controlled by the Marangoni effect. Instabilities develop at the contact line for surfactant concentrations higher than the critical micelle concentration.