Icephobic Properties of Slippery Liquid Infused Porous Surfaces

Abstract

Coatings that can repel water and ice will have substantial positive effects on multiple industrial operators working in cold atmospheres. Especially ice accumulation hinders many activities in marine, transportation, energy and aviation industries by increasing energy consumption. Thus, the utilization of passive coating technologies could enable and enhance safe activities regardless freezing rain or ice accumulation as the coating would be shedding any impacting droplets from the surface prior icing. One of such surface designs incorporates a porous solid material with a lubricating liquid to form slippery liquid infused porous surfaces, SLIPS.

This work aims in investigating the SLIPS surface design performance in terms of water and ice repellency. The experiments have been conducted at freezing temperatures to mimic the cold atmospheres and the environmental stresses commonly encountered by the industries on cold regions. Various SLIPS options were evaluated to understand and reveal performance differences and to estimate which would be suitable requirements for icephobic SLIPS. Additionally, while examining and developing best optimal icephobic SLIPS, sustainable options were reviewed throughout the studies. With the tightening plastic regulations and recycling possibilities, novel surface engineering should consider the utilization of recyclable and environmentally friendly material usage in coating development. Here, a proof-of-concept was provided to acknowledge recyclable porous solid materials and vegetable oil for compiling a SLIPS design with icephobic performance.

Throughout the work the wettability analyses were examined via various of methods to cover broader understanding of the SLIPS hydrophobic behaviour. Droplet-based analyses were conducted to review the static and the dynamic wetting states and droplet mobility. In addition to this, these surfaces were studied under multiple wetting events with force tensiometer which allowed the SLIPS to be evaluated not only for the wetting endurance but also for the lubricant depletion under forced wetting. For the ice adhesion evaluation, specific ice type was accreted by impacting supercooled water droplets in icing wind tunnel. This was followed by ice adhesion strength determination by centrifugal shear force, providing experimental information to evaluate the surfaces to be icephobic. Furthermore, the surfaces were characterized with confocal and electron microscope techniques to learn how structural differences affect the performance but also to see how the porous solid deforms after conducted environmental stress tests.

Overall, the SLIPS surface design reached extremely low ice adhesion values when compared to other materials and surface modifications. Additionally, based on the learnings gained through the experimental analysis, a transparent Meso-SLIPS was fabricated from silica with extremely prominent properties to endure wetting, freezing and ultimately showing remarkably low ice adhesion strength. When reflecting these results with high droplet mobility and freeze resistance data, the SLIPS examined in this work can be stated to possess icephobic characteristics. This icephobic behaviour endured cyclic testing procedures, however, the lubricant depletion was observed from the SLIPS structure. This indicates the porous solid materials can be further engineered to obtain stronger capillary effects to enable longevity for slippery surfaces. Based on the research conducted, the SLIPS can function as icephobic solution in applications where extremely low ice adhesion is desired for a given number of times. Still, the possibilities to develop SLIPS designs in terms of circular economy should be one of the focus points for the future endeavours.