Pattern Transfer and Characterization of Biomimetic Micro-Structured Surfaces for Hydrophobic and Icephobic Applications
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Using both artificial and natural templates, biomimetic micro-structures are fabricated on conventional coating materials (epoxy and silicone elastomers) to mimic both artificial and natural templates through effective pattern transfer processes. The pattern transfer processes use a soft-polymer negative stamp, where the flexibility of the stamp allows for easy conformation to both flat and curved surfaces. Patterns have been successfully transferred as a rigid epoxy to complex surfaces or as a soft elastomer replica of a hydrophobic Trembling Aspen leaf. The hydrophobicity and friction behaviour of the resulting micro-patterned surfaces are systematically investigated, showing that surface patterning can be used as an effective way to improve hydrophobicity while reducing the surface adhesion and friction without a loss of the structural integrity or rigidity typical of epoxy coatings. The relative strength of the micro-pattern was determined through indentation testing in order to support the claim of a robust pattern on the micro-scale that is able to withstand the harsh environment of industrial application or weather exposure. With the well characterized patterned epoxy material fabricated and able to be transferred to many different surfaces, the potential for the patterned surface to act as an icephobic coating was pursued. The robustness of the epoxy material with the unique ability to coat surfaces that are typically unable to possess a micro-structure makes this coating an ideal candidate for large-scale icephobic application. The potential use of a micro-patterned epoxy coating is investigated against comparable surface coatings within an innovative experimental set-up to measure the relative ice-adhesion strength of different substrates. In characterizing the relative shear-force required to remove frozen water droplets from the coating surface at the interface, several variables and factors were explored. The addition of a surface pattern was found to impact the icephobic ability of several materials, where different materials with the same pattern were compared to identify that the surface energy of the substrate influences the icephobic nature of a surface. Moreover, previous studies that relate the water contact angle or hysteresis to ice-adhesion strength are questioned through a preliminary qualitative analysis of ice adhesion strength data. This work demonstrates a potential process for the utilization of biomimetic epoxy micro-patterns as an enhanced hydrophobic and icephobic option for large scale protective coatings.