Multi-height structures in injection molded polymer

Abstract

We present the fabrication process for injection molded multi-height surface structures for studies of wetting behavior. We adapt the design of super hydrophobic structures to the fabrication constrictions imposed by industrial injection molding. This is important since many super hydrophobic surfaces are challenging to realize by injection molding due to overhanging structures and very high aspect ratios. In the fabrication process, we introduce several unconventional steps for producing the desired shapes, using a completely random mask pattern, exploiting the diffusion limited growth rates of different geometries, and electroforming a nickel mold from a polymer foil. The injection-molded samples are characterized by contact angle hysteresis obtained by the tilting method. We find that the receding contact angle depends on the surface coverage of the random surface structure, while the advancing contact angle is practically independent of the structure. Moreover, we argue that the increase in contact angle hysteresis correlates with the concentration of pinning sites among the random surface structures.

Drop shape analysis for determination of dynamic contact angles by double sided elliptical fitting method

“…In order to evaluate the performance of real images of drops we have captured drop profiles of seven sample drops shown in Figure 4. The structured surfaces for drops (3), (4), (6), and (7) in Figure 4., are: (3) randomly structured PP substrate, [14] (4) FDTS coated Si substrate fabricated by same method as in Søgard et al [15] but with hierarchical pillar structures with 2% resulting surface coverage, (6) same substrate as (3), and (7) same substrate as (4). These images are chosen to test a wide range of contact angles and some have been tilted in order to measure contact angle hysteresis.…”

Replication of micro-sized pillars in polypropylene using the extrusion coating process

“…The details of the shim fabrication are given in references [9][10][11] , but in short, 100 mm Si wafers were spin coated (SSE Spinner, Maximus 804) with positive tone resist (AZ512E), and patterned by photolithography (SUSS Mask Aligner MA6) using a mask of 10µm diameter spots and developed for 60 s (AZ 351B developer). The patterns were then etched using DRIE (Pegasus DRIE, STS.…”

Advances in the Fabrication of Superhydrophobic Polymeric Surfaces by Polymer Molding Processes

“…On the other hand, low aspect ratio structures normally lead to an easy transition from a Cassie− Baxter regime to a Wenzel regime. Andersen and Taboryski 38 figured out how to introduce random multiple heights (7 different height levels) to overcome the latter problem (Figure 4b). The surface coverage by microstructures was a determining factor of the CAH.…”

“…37 However, the production of high aspect ratio structures is limited due to processing constraints. 38 Moreover, high aspect ratio structures are prone to faster wear and bending by mechanical forces. 33 The introduction of nanostructures to create hierarchical micronanostructures can improve the performance of the produced surfaces in terms of wettability.…”