1. Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, USA

Correspondence to: Darsh T. Wasan Correspondence and requests for materials should be addressed to D.T.W. (Email: wasan@iit.edu).

Abstract

Suspensions of nanometre-sized particles (nanofluids) are used in a variety of technological contexts. For example, their spreading and adhesion behaviour on solid surfaces can yield materials with desirable structural and optical properties¹. Similarly, the spreading behaviour of nanofluids containing surfactant micelles has implications for soil remediation, oily soil removal, lubrication and enhanced oil recovery. But the well-established concepts of spreading and adhesion of simple liquids do not apply to nanofluids^{2, 3, 4, 5, 6, 7}. Theoretical investigations have suggested that a solid-like ordering of suspended spheres will occur in the confined three-phase contact region at the edge of the spreading fluid, becoming more disordered and fluid-like towards the bulk phase^{8, 9}. Calculations have also suggested that the pressure arising from such colloidal ordering in the confined region will enhance the spreading behaviour of nanofluids^{10, 11}. Here we use video microscopy to demonstrate both the two-dimensional crystal-like ordering of charged nanometre-sized polystyrene spheres in water, and the enhanced spreading dynamics of a micellar fluid, at the three-phase contact region. Our findings suggest a new mechanism for oily soil removal—detergency.

1. Department of Chemical and Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, USA

Correspondence to: Darsh T. Wasan Correspondence and requests for materials should be addressed to D.T.W. (Email: wasan@iit.edu).