Drop Impact, Spreading, Splashing, and Penetration into Electrospun Nanofiber Mats

Abstract

Experiments were conducted to study peculiarities of drop impact onto electrospun polymer nanofiber mats. The nanofiber cross-sectional diameters were of the order of several hundred nanometers, the pore sizes in the mats of about several micrometers, and the mat thicknesses of the order of 200 microm. Polyacrylonitrile (PAN), a polymer which is partially wettable by water, was used to electrospin nanofiber mats. The experiments revealed that drop impact onto nanotextured surfaces of nanofiber mats produce spreading similar to that on the impermeable surfaces. However, at the end of the spreading stage, the contact line is pinned and drop receding is prevented. At higher impact velocities, prompt splashing events with formation of tiny drops were observed. It was shown that the splash parameter K(d) = We(1/2) Re(1/4) (with We and Re being the Weber and Reynolds numbers, respectively) previously used to characterize the experiments with drop impact onto smooth impermeable dry substrates can be also used to describe the onset of splash on substrates coated by nanofiber mats. However its threshold value K(ds) (in particular, corresponding to the minimal impact velocity leading to generation of secondary droplets) for the nanotextured surfaces is higher than that for dry flat substrates. In addition, water penetration and spreading inside wettable nanofiber mats after drop impact was elucidated and quantified. The hydrodynamics of drop impact onto nanofiber mats is important for understanding effective spray cooling through nanofiber mats, recently introduced by the same group of authors.

Experimental investigation into the impact of a liquid droplet onto a granular bed using three-dimensional, time-resolved, particle tracking

“…The higher the splashing parameter is, the greater the propensity for droplet breakup. The threshold between splashing and nonsplashing (K d ) has been reported to vary according the surface: For a smooth surface K d = 57.7 [25], for a bed of 5-μm fibers K d = 87 [27], and for a bed of 81-μm glass spheres K d = 120 [12]. The impacting droplet in this work has a splashing parameter K = 556, a value far exceeding these thresholds, indicating its propensity to splash.…”

Nonisothermal drop impact and evaporation on polymer nanofiber mats

“…A novel approach in drop and spray cooling of microelectronic devices employs coating of hot surfaces with electrospun non-woven polymer nanofiber mats [8,9]. Electrospun nanofiber mats are nano-textured permeable materials comprising of individual polymer nanofibers (with diameter of about several hundred nanometers) which are randomly orientated in the mat plane.…”

Hydrodynamics of Drop Impact and Spray Cooling through Nanofiber Mats

“…Application of a nanofiber mat coating to a surface has been shown to promote droplet spreading and adhesion. 2 It also has been proposed and shown that if a metal surface is coated with polymer nanofiber mat, the mass loss can be minimized to a great amount 3 and ameliorate our capability to remove heat through spray cooling economically and effectively. The thermal and structural properties of four different polymer nanofiber mats were measured.…”