Spreading of Completely Wetting or Partially Wetting Power-Law Fluid on Solid Surface

Abstract

This study investigated the drop-spreading dynamics of pseudo-plastic and dilatant fluids. Experimental results indicated that the spreading law for both fluids is related to rheological characteristics or power exponent n. For the completely wetting system, the evolution of the wetting radius over time can be expressed by the power law R = atm, where the spreading exponent m of the dilatant fluids is >0.1 and the spreading exponent m of pseudo-plastic fluids is <0.1. The strength of non-Newtonian effects is positively correlated to the extent of deviation from the theoretical value 0.1 of m for Newtonian fluids. For the partially wetting system, the power law on the time dependence of the wetting radius no longer holds; therefore, an exponential power law, R = Req(1-exp(-at(m)/Req)), is proposed, where Req denotes the equilibrium radius of drop and a is a coefficient. Comparing experimental data with the exponential power law revealed that both are in good agreement.

Molecular dynamics simulations on dissolutive wetting of Al–Ni alloy droplets on NiAl substrate

“…The increased liquid volume owing to substrate dissolution into the droplet was proposed to be responsible to the noted faster wetting kinetics [28] . However, since the large droplet volume had been confirmed not being able to accelerate the spreading in either capillary or gravitational spreading regime [1,44,45] , the increased droplet volume is unlikely the main driving force for the faster wetting on relaxed substrates than on rigid substrates.…”

Does macroscopic flow geometry influence wetting dynamic?

“…Most of the experimental data reviewed by Kistler involved completely wetting, and all the fluids were Newtonian fluids. Although there have been some theoretical and experimental studies of non-Newtonian fluids [19][20][21][22][23][24], none have mentioned the flow geometry effect. There is limited experimental data for a fixed the fluid-solid system with different experimental methods and different wetting systems for analyzing the macroscopic flow geometry effect.…”

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

“…Film thickness can be more accurately estimated using correlations developed using power-law fluid [14]. However, Eq.…”

“…The dynamic wetting process of Newtonian fluids has been examined using a hydrodynamic model, molecular model and combined model [1][2][3][4][5][6]. A few theoretical and experimental studies explored how non-Newtonian fluids spread over solid substrates [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Liang et al [21] reviewed the development of theoretical models that consider power-law fluid spreading.…”

“…Wang et al [14] also examined droplet shape near a contact line as an unknown free surface, and adopted lubrication theory for a traveling wave form. Wang et al obtained a dynamic wetting model for completely wetting fluids,…”