Superspreading performance of branched ionic trimethylsilyl surfactant Mg(AOTSiC)2

Nina M Kovalchuk,Masanobu Sagisaka,Suzuna Osaki,Mark J.H Simmons

doi:10.1016/j.colsurfa.2020.125277

Abstract

The spreading performance of aqueous solutions containing a novel branched trimethylsilyl hedgehog ionic surfactant, Mg(AOTSiC)2, was compared with that of trisiloxane superspreaders on a hydrophobic polyvinylidenefluoride substrate. The work shows that Mg(AOTSiC)2 is a superspreader with spreading kinetics similar to trisiloxane surfactants, demonstrating that a hammer-like molecular architecture is not a necessary requirement for superspreading. The aqueous solutions of Mg(AOTSiC)2 are much more stable than trisiloxane solutions and retain the same spreading performance for at least 45 days. Comparison of the spreading kinetics with dynamic surface tension revealed that Mg(AOTSiC)2 requires a 10 fold faster equilibration rate at the air/water interface to demonstrate the same spreading kinetics as trisiloxane superspreaders. Addition of 20 % glycerol to the Mg(AOTSiC)2 solutions suppressed superspreading by slowing down surfactant diffusion; then only surfactant enhanced spreading with a time dependence of spread area S ∼ t0.8 was observed.

Highlights

The work shows that Mg(AOTSiC)2 is a superspreader with spreading kinetics similar to trisiloxane surfactants, demonstrating that a hammer-like molecular architecture is not a necessary requirement for superspreading
Comparison of the spreading kinetics with dynamic surface tension revealed that Mg(AOTSiC)2 requires a 10 fold faster equilibration rate at the air/ water interface to demonstrate the same spreading kinetics as trisiloxane superspreaders
Addition of 20 % glycerol to the Mg(AOTSiC)2 solutions suppressed superspreading by slowing down surfactant diffusion; only surfactant enhanced spreading with a time dependence of spread area S ∼ t0.8 was observed

Summary

Introduction

The spreading of liquids over solid surfaces is an ubiquitous component of many natural phenomena, for example the wetting of soil by rain and of industrial processes including painting, printing, enhanced oil recovery, foliar application of pesticides and fertilisers in agriculture. Temporal and spatial variations in the local concentration of surfactant over the surface of spreading drop will cause surface tension gradients (and Marangoni flows) which will change the value of spreading exponent This can strongly influence the spreading kinetics and numerous experimental studies show that when a surfactant is added to an aqueous formulation, kinetics become much faster than for pure liquids. Numerical studies in [25] show that spreading accelerates in the presence of a surfactant as a result of surfactant depletion at the liquid/air interface and formation of strong gradients of surface tension in the vicinity of the TPCL. Assuming that the characteristic length over which the concentration gradient is formed remains constant, the maximum gradient appears when the surface tension near the drop centre is close to the equilibrium value, whereas that in the vicinity of the TPCL is equal to pure water. Whilst such an increase in viscosity has a negligible effect on the spreading kinetics in the case of pure liquids [34], it results in a diffusion coefficient of surfactant which is approximately half that for pure water

Experimental

Properties of surfactant solutions

Declaration of Competing Interest