Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

Abstract

Water droplet mobility on a hydrophobic surface cannot be guaranteed even when the droplet exhibits a high contact angle (CA) with the surface. In fact, droplet mobility on a surface, especially a fibrous surface, has remained an unsolved empirical problem. This paper is a combined experimental-computational study focused on droplet mobility on a fibrous surface. Electrospun polystyrene (PS) coatings were used in this work for their ability to exhibit high CAs simultaneously with low droplet mobility. To simplify this otherwise complicated problem and better isolate droplet-fiber interactions, the orientation of the fibers in the coatings was limited to the x and y directions. As the earth gravity was not strong enough to mobilize small droplets on PS coatings, experiments were conducted using ferrofluid droplets, and a magnet was used to make them move on the surface. Experimentally validated numerical simulations were used to enhance our understanding of the forces acting on a droplet before moving on the surface. Effects of Young-Laplace CA and fiber-fiber spacing on droplet mobility were investigated. In particular, it was found that droplet mobility depends strongly on the balance of forces exerted on the droplet by the fibers on the receding and advancing sides.

Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

“…The mobility of the surface droplets mainly depends on the force applied by the fiber to the droplet. [174] The mobility of droplet on the fabric surface depends mainly on the force on the fabric. In the experiment of studying the dynamics of flexible SHS, Kim et al [175] sprayed the commercial superhydrophobic coating with smooth polydimethylsiloxane as the substrate.…”

Numerical Simulation and Experimental Validation of Liquid Metal Droplet Formation in a Co-Flowing Capillary Microfluidic Device

“…That means the produced droplet at larger contact angle has better monodispersity compared with the smaller one. It could be worth noting that the micro-needle inside the capillary had a better wettability performance with a larger contact angle, which is good for droplet movement and adsorption on the microfiber [37,49,50]. Therefore, the flow stability of droplet formation was affected at a lower contact angle and a droplet diameter with a better distribution could be obtained with a relatively large contact angle.…”

A micro-needle induced strategy for preparation of monodisperse liquid metal droplets in glass capillary microfluidics

“…3d, f), it can be clearly seen that the droplets produced with the metal needle have much better uniformity. Since Galinstan liquid metal has more similar material properties with the metallic micro-needle than the glass, which may give better wettability performance for droplet movement and adsorption on a microfiber media (Fang et al 2015;Jamali et al 2018;Manzo et al 2016). Therefore, it can be probably attributed to the better wettability between the liquid metal and the metallic micro-needle than with the glass capillary, which greatly affects the stability of droplet formation.…”