Dynamic wetting characteristics of submicron‐structured injection molded parts

Abstract

The generation of submicron structures on plastic part surfaces can be used to modify their wetting properties allowing the creation of superhydrophobic surfaces. The modified wetting behavior can allow functionalities such as fluid collection or transport, which are critical for microfluidics. Consistent manufacturing is achieved through surface replication and process characterization. In this work, submicron structures were generated on steel mold inserts using ultrafast femtosecond laser and then replicated by micro injection molding on polypropylene and polylactic acid. Samples with Laser-Induced Periodic Surface Structures (LIPSS) were fabricated using a femtosecond laser and characterized to investigate the effects of mold temperature, texture orientation, and material selection on the dynamic contact angle. The dynamic wetting functionality of the surfaces was investigated by analysis of the advancing and receding contact angles. The hysteresis obtained from the dynamic measurements provides information about the fluid/texture interaction dynamics. The experimental results show that the effects of mold temperature and drop orientation are only significant for the advancing contact angles. The large contact angle hysteresis suggests a parahydrophobic wetting behavior for the manufactured plastic parts.

Wetting Characteristics of Laser-Ablated Hierarchical Textures Replicated by Micro Injection Molding

“…According to other research [50,51], pure Wenzel and Cassie-Baxter wetting states rarely occur. The intermediate state, which is called composite or mixed wetting state, was observed by many other researchers [4,52,53]. In this state, the water droplet partially penetrates the valleys and comes in contact with the rough solid surfaces, while part of the water droplet sits on the air pocket between the bottom of the liquid surface and the base of the solid features.…”

“…The measurements were repeated three times on each sample without disrupting the sample's position or the platform height, so as to ensure consistency. The measurements were conducted in parallel and orthogonal directions for textures with trencheslike features [4]. The AFM scan on insert A is demonstrated in Figure 4.…”

“…The modification and creation of functional plastic surfaces have been the topic of research and industrial production over the last 20 years. Wettability is one of the most important properties of solid surfaces [3][4][5]. The contact angle has been commonly used to represent surface wettability.…”

Editorial for the Special Issue on Advances in Micro and Nano Manufacturing: Process Modeling and Applications, Volume II

“…Different hierarchical texture geometries were obtained using direct laser ablation to generate micro-scale features; then, the ultrashort pulsed laser was used to create laser-induced periodic surface structures (LIPSSs). The hierarchical texture designs were selected to achieve wetting functionalization while keeping a low aspect ratio for easier replication during molding [ 8 ]. Indeed, the aspect ratio is the main factor limiting the replication of textured mold surfaces [ 9 ].…”