Drop impacts on electrospun nanofiber membranes

R P Sahu,B Pourdeyhimi,A L Yarin,S Sinha-Ray

doi:10.1039/c2sm06744g

R P Sahu, B Pourdeyhimi + Show 2 more

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https://doi.org/10.1039/c2sm06744g

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Abstract

This work reports a systematic study of drop impacts of polar and non-polar liquids onto different electrospun nanofiber membranes (of 8–10 μm thickness and pore sizes of 3–6 μm) with an increasing degree of hydrophobicity. The liquids studied were water, FC 7500 (Fluorinert fluid) and hexane. The nanofibers used were electrospun from polyacrylonitrile (PAN), nylon 6/6, polycaprolactone (PCL) and Teflon. It was found that for any liquid/fiber pair there exists a threshold impact velocity (∼1.5 to 3 m s−1) above which water penetrates membranes irrespective of their hydrophobicity. The other liquids (FC 7500 and hexane) penetrate the membranes even more easily. The low surface tension liquid, FC 7500, left the rear side of sufficiently thin membranes as a millipede-like system of tiny jets protruding through a number of pores. For such a high surface tension liquid as water, jets immediately merged into a single bigger jet, which formed secondary spherical drops due to capillary instability. No mechanical damage to the nanofiber mats after liquid perforation was observed. A theoretical estimate of the critical membrane thickness sufficient for complete viscous dissipation of the kinetic energy of penetrating liquid is given and corroborated by the experimental data.

Highlights

Questions on penetration of liquid drops into porous media arise in relation to filtration through porous nonwoven membranes, coalescence filters and ordered fibrous media with fiber diameters from several tens of micron down to electrospun nanofibers[1,2,3,4,5,6,7,8,9]
Drop impacts on porous nonwovens are characteristic of coalescence filtration and of protective clothes used as a barrier for warfare liquid aerosols, e.g. such nerve agents as VX13
When the drop impact velocity was increased above 2 m/s, visible penetration of water through bare Nylon grids was observed (Fig. 3)

Summary

Introduction

Questions on penetration of liquid drops into porous media arise in relation to filtration through porous nonwoven membranes, coalescence filters and ordered fibrous media with fiber diameters from several tens of micron down to electrospun nanofibers[1,2,3,4,5,6,7,8,9]. Single collector capture mechanisms intercept a single drop per event, at one point on a fiber or at the pore surface. Various physical mechanisms of drop interception and drainage are discussed in the above-mentioned references. Drop impacts on porous nonwovens are characteristic of coalescence filtration and of protective clothes used as a barrier for warfare liquid aerosols, e.g. such nerve agents as VX13

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