Microgel particle-laden drop impact on a nanofiber material with varying wettability: Effect of liquid impalement

This study deals with the impact of a microgel particle-laden drop of the water–agar solution onto nanofiber mats of different wettability at Weber numbers in the range of 14–502 and initial velocities in the range of 0.32–1.83 m/s. We examined the effects of inertia and the competition between the wetting and antiwetting pressures within the liquid impalement on the hydrodynamic behavior of drops in the spreading and contraction phases. Hydrophilic mat representing a full water absorption coating is manufactured by electrospinning from a mixture of polycaprolactone and polyvinylpyrrolidone; hydrophobic—from polytetrafluoroethylene. The micro- and nanoscale characteristics of nanofiber mats are analyzed by scanning electron microscopy and atomic force microscopy, respectively. A physical model of liquid flow under an impacting microgel particle-laden drop along and inside the micro- and nanostructures of nanofiber mats is proposed. Empirical expressions for the prediction of drop impact hydrodynamics are derived. By introducing the impalement factor, which is physically close to the Euler number, they take into account the difference between wetting and anti-wetting pressures in addition to inertia. Microgel particle-laden drop deposition accounting for the effect of liquid impalement inside nanofiber materials with different wettability is expected to enhance the efficiency of bioprinting polymer layers in tissue engineering.