Spreading of completely wetting, non-Newtonian fluids with non-power-law rheology

Spreading non-Newtonian liquids with non-power-law rheology on completely wetting surfaces are seldom investigated. This study assessed the wetting behavior of polydimethylsiloxane (PDMS), a Newtonian fluid, two carboxymethylcellulose (CMC) sodium solutions, a PDMS + 2% w/w silica nanoparticle suspension and three polyethylene glycol (PEG400) + 5–10% w/w silica nanoparticle suspensions (non-power-law fluids) on a mica surface. The θD–U and R–t data for spreading drops of the six tested, non-power-law fluids can be described by power-law wetting models. We propose that this behavior is attributable to a uniform shear rate (a few tens to a few hundreds of s−1) distributed over the thin-film regime that controls spreading dynamics. Estimated film thickness was below the resolution of an optical microscope for direct observation. Approximating a general non-Newtonian fluid spreading as a power-law fluid greatly simplifies theoretical analysis and data interpretation.

Graphical abstractSpreading exponents of complete wetting, non-Newtonian fluids of non-power-law rheology with power-law model.Figure optionsDownload full-size imageDownload high-quality image (56 K)Download as PowerPoint slide