Understanding the wettability of a hairy surface: effect of hair rigidity and topology

Abstract

We present a computer simulation study on the wettability of a hairy surface with different topological structures such as single hairs, hair bundles and network structure. Superficially, for end-tethered rigid hairs or flexible hairs, the nonwettability of the substrate should be analyzed in completely different ways. For rigid hairs, the contact angle is dominantly dependent on the top layer density of hairs. A larger top layer density leads to a larger interaction between droplet and surface, as well as a lower contact angle. For flexible hairs, the nonwettability is determined by the typical properties of hairs right below the droplet, e.g., the chemistry of the surface, the topography and strength of the hair bundle/network or nonwetted area below the projection of the droplet. Nevertheless, it is also possible to generalize these aspects into a uniform procedure, which implies an intrinsic consistent mechanism of the dewetting behavior for droplets on such hairy surfaces. Counterintuitively, we also suggest that the surface which can strongly resist the transition to the Wenzel state does not necessarily lead to a large contact angle, especially in a system where the droplet is treated as liquid bulk. This study helps to build up guidelines for the design of nonwetting surface materials.

Process-morphology scaling relations quantify self-organization in capillary densified nanofiber arrays

“…Investigation of CNT cell aspect ratio and circularity shows no statistically significant difference between c-CNTs and nc-CNTs, illustrating that further work building on recent advances in two-dimensional meso-scale simulation of self-organization of such nanosystems due to capillary forces is needed. [67][68][69] Additionally, since cementation modifies the cellular pattern formation by altering the CNT substrate adhesion force (F a ), but data that could allow the characterization and modeling of the physics and/or chemical mechanisms that gives rise to the observed enhancement in F a (e.g. CNT-CNT, CNT-catalyst, catalyst-substrate or combination thereof) is not currently available, additional work is required to quantify and predict how F a scales with processing conditions.…”

Study of the Friction Behavior of Embedded Fibers in YG8 Surface Grooves

“…At room temperature (25 °C), when the droplet viscosity was constant, the contact angle between the oil and SS surface was the largest and the contact angle between the oil and FS was the smallest. Within 1–2 s of droplet contact, the contact angles of both GS and FS produced a large decrease, which was due to the pressure difference between the inside and outside of the groove [ 35 ]. As time increased, GS spread at a relatively stable rate.…”

Assessment of a Bionic Broach Implanted with Nylon Fibers

“…After 1 s, the contact angle of the oil droplet on the surface of the FB broach decreases rapidly to zero. The reason for this phenomenon is that when the droplet enters the fluff, due to the capillary effect between the fluff, the droplet quickly diffuses between the fluff, which follows the Wenzel state, so that the contact angle of the droplet decreases rapidly [33]. The spreading experiment of castor oil on the rake face was implemented.…”

“…Wenzel et al [32] proposed a method for the evaluation of the wetting behavior of material surfaces. Pei et al [33] also conducted a simulation study of the wetting of hair surfaces with different topologies. Therefore, modeling is widely used to assist in guiding the dynamics of materials.…”