Are Superhydrophobic Surfaces Best for Icephobicity?

Abstract

Ice formation can have catastrophic consequences for human activity on the ground and in the air. Here we investigate water freezing delays on untreated and coated surfaces ranging from hydrophilic to superhydrophobic and use these delays to evaluate icephobicity. Supercooled water microdroplets are inkjet-deposited and coalesce until spontaneous freezing of the accumulated mass occurs. Surfaces with nanometer-scale roughness and higher wettability display unexpectedly long freezing delays, at least 1 order of magnitude longer than typical superhydrophobic surfaces with larger hierarchical roughness and low wettability. Directly related to the main focus on heterogeneous nucleation and freezing delay of supercooled water droplets, the observed ensuing crystallization process consisted of two distinct phases: one very rapid recalescent partial solidification phase and a subsequent slower phase. Observations of the droplet collision process employed for the continuous liquid mass accumulation up to the point of ice formation reveal a previously unseen atmospheric-pressure, subfreezing-temperature regime for liquid-on-liquid bounce. On the basis of the entropy reduction of water near a solid surface, we formulate a modification to the classical heterogeneous nucleation theory, which predicts the observed freezing delay trends. Our results bring to question recent emphasis on super water-repellent surface formulations for ice formation retardation and suggest that anti-icing design must optimize the competing influences of both wettability and roughness.

The icephobic performance of alkyl-grafted aluminum surfaces

“…Significantly delayed ice formation [3,10,12,13,15,16,23,26] and reduced ice adhesion or accumulation [3,10,[15][16][17]19,21,25] have been reported for various SHSs. Theoretical models have also been developed, demonstrating how SHSs can delay ice formation from impinging water droplets [9,11,13], which is in good agreement with experimental work [3,14,25,26].…”

“…Therefore, the prevention and control of ice accretion is of high potential in all these fields of human activity. The design and use of surfaces/coatings with minimum ice adherence and reduced ice accumulation is still actively considered as the most appealing and universal approach to the problem [3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Most of the existing studies on anti-ice surfaces are focused on the reduction of ice adhesion strength [1,[5][6][7][8]10,[19][20][21][22][23][24] or delayed ice nucleation/formation [3,9,12,13,23,25,26].…”

“…Most of the existing studies on anti-ice surfaces are focused on the reduction of ice adhesion strength [1,[5][6][7][8]10,[19][20][21][22][23][24] or delayed ice nucleation/formation [3,9,12,13,23,25,26]. Therefore lately the research in this area has been chiefly focused on the use and development of superhydrophobic surfaces (SHSs) for preventing ice formation and accumulation [4,[9][10][11][13][14][15][16][17][18][19][20][21][22][23][25][26][27][28][29]. Significantly delayed ice formation [3,10,12,13,15,16,23,26] and reduced ice adhesion or accumulation [3,…”

“…At the same time, several recent reports have raised doubts about SHSs as universal and durable anti-ice materials with long-term service and high efficiency under different conditions [1,[13][14][15][16]22,27,[29][30][31].…”

“…so-called lubricant-impregnated surfaces (having rough surfaces infused with water-immiscible liquid). Furthermore, Jung and coworkers investigated the water freezing delay of supercooled microdroplets on untreated and coated surfaces ranging from hydrophilic to superhydrophobic and used the delay values to evaluate the materials' icephobicity [14]. Certain surfaces with nanometer-scale roughness and higher wettability were found to display unexpectedly long freezing delays, at least one order of magnitude longer than typical SHSs with larger hierarchical roughness and low wettability [14].…”