Spreading of fluids on solids under pressure: Slip and stick effects

Spreading of different types of fluid on solids under an impressed force is an interesting problem. Here we study spreading of four fluids, having different hydrophilicity and viscosity on two substrates – glass and perspex, under an external force. The area of contact of fluid and solid is video-photographed and its increase with time is measured. The results for different external forces can be scaled onto a common curve. We try to explain the nature of this curve on the basis of existing theoretical treatment where either the no-slip condition is used or slip between fluid and substrate is introduced. We find that of the eight cases under study, in five cases quantitative agreement is obtained using a positive slip coefficient. The remaining three can be explained with a negative slip coefficient, equivalent to a sticking effect.

Fluids with different viscosity and hydrophilicity spread differently on substrates, when forced by an external load. To explain the curves, viscous dissipation with slip/stick is necessary.Figure optionsDownload high-quality image (41 K)Download as PowerPoint slideResearch Highlights
► We study contact area for different fluid–solid combinations under load.
► Normally low-spreading pairs spread more under loading and vice-versa.
► Viscous dissipation with slip or stick can explain the area vs. time curves.