Liquid Repellence of Phobic Fiber Networks

Abstract

The wetting behavior of fiber networks, which are central to many research and industrial applications, can be difficult to predict accurately owing to their complex, heterogeneous structure. The cylindrical pore model, widely used to interpret and predict the forced wetting of hydrophobic porous materials, often does not yield correct results when working with fibrous networks like paper substrates and non-woven fabrics. This is because these materials exhibit variation in pore size, fiber length, and fiber diameter, as well as a reentrant pore geometry. Quantitative prediction of the critical wetting resistance of hydrophobized papers to arbitrary entrant liquids requires a more sophisticated analytical approach that considers this unique fibrous structure and the effect of stochastic variations within the pore matrix. In this work, we directly measure the critical breakthrough pressure for different porous substrates across various wetting entrant liquids. To isolate the effects of the structure and stochastics on critical wetting behavior of fibrous networks, we analyze additional materials strategically chosen for their subsets of structural features. Ultimately, we formulate a method that demonstrates physical reasonableness, numerical accuracy, and the ability to elucidate the effects of pore size, pore size distribution, fiber diameter, fiber diameter distribution, surface wettability, and liquid surface tension on critical breakthrough pressure of liquids through hydrophobic fibrous networks.

Theoretical Investigation of Wenzel and Cassie Wetting States on Porous Films and Fiber Meshes

“…The transition from the hydrophobic Cassie state to Wenzel state, i.e., penetration of liquid across a porous film is resisted by an energy barrier when the porous film is hydrophobic. To overcome the energy barrier, applying pressure is needed, and the minimum pressure necessary for overcoming the energy barrier is called the critical pressure , or critical breakthrough pressure. , Within the classical equilibrium theory, the critical breakthrough pressure P can be approximately evaluated as follows (refer to section S3): P = − σ γ GL ⁡ cos ⁡ θ 1 ε v where ε v denotes the volume porosity of the porous film and cos θ 1 is assumed to be negative. When the porous medium comprises capillary tubes with a uniform round cross-section with radius a ′ , P becomes P = − 2 γ GL ⁡ cos ⁡ θ 1 a ′ which corresponds to the capillary pressure of a single capillary tube.…”

“…To overcome the energy barrier, applying pressure is needed, and the minimum pressure necessary for overcoming the energy barrier is called the critical pressure 13,28 or critical breakthrough pressure. 29,33 Within the classical equilibrium theory, the critical breakthrough pressure P can be approximately evaluated as follows (refer to section S3):…”

Experimental study on the optimum number of layers of fiber mats for gas-liquid coalescer

“…The filter material was smoothed by placing it on the surface of 400-grit and 800-grit sandpaper before the filter preparation process was completed (Figure 2(g)-(h)). The transport of aerosols and liquids during the experiment can weaken the water-soluble binder in the filter media [19]. To address this issue, the pressure drop curve was recorded for each newly made filter media.…”

Instability enhanced dewatering during mechanical pressing of elastic porous media

“…These include membranes (Deng et al 2013;Gabelman and Hwan 1999;Su et al 2017), microfluidic labs-on-chip Raj et al 2019;Yetisen et al 2013), enhanced oil recovery systems (Mulligan et al 2001), medical devices (Davies 2009), and liquid-liquid separators (Kim et al 2018;Voulgaropoulos et al 2019), to name a few. Therefore, great effort has been expended to develop new methods to control the behavior of fluids in porous media, especially in situations where unidirectional flow is desired (Dudick et al 2022). Invoking the oft-used analogy of fluid flow with current in electrical circuits, materials that permit unidirectional flow are sometimes referred to as liquid diodes (Li et al 2017;Panter et al 2020) Some of the tools previously developed to promote unidirectional flow include Janus membranes (Li et al 2016;Zhou & Guo 2019;Zhou et al 2013), passive liquid diodes (Tesla valves) (de Vries et al 2017;Hong et al 2004), bio-inspired channels (Comanns et al 2015), and variable-porosity materials .…”