Abstract
The freezing process is significantly influenced by environmental factors and surface morphologies. At atmospheric pressure, a surface below the dew and freezing point temperature for a given relative humidity nucleates water droplets heterogeneously on the surface and then freezes. This paper examines the effect of nanostructured surfaces on the nucleation, growth, and subsequent freezing processes. Microsphere Photolithography (MPL) is used to pattern arrays of silica nanopillars. This technique uses a self-assembled lattice of microspheres to focus UV radiation to an array of photonic jets in photoresist. Silica is deposited using e-beam evaporation and lift-off. The samples were placed on a freezing stage at an atmospheric temperature of 22±0.5°C and relative humidities of 40% or 60%. The nanopillar surfaces had a significant effect on droplet dynamics and freezing behavior with freezing accelerated by an order of magnitude compared to a plain hydrophilic surface at 60% RH where the ice bridges need to cover a larger void for the propagation of the freezing front within the growing droplets. By pinning droplets, coalescence is suppressed for the nanopillared surface, altering the size distribution of droplets and accelerating the freezing process. The main mechanism affecting freezing characteristics was the pinning behavior of the nanopillared surface.
Highlights
Condensate freezing or frost is formed when a surface is cooled below the dew point and freezing temperature
Condensate freezing is of significant importance for applications such as aviation, satellites, power transmission, refrigeration, food preservation, and air conditioning
Engineered surfaces have the ability to control the droplet dynamics and freezing propagation. Engineered surfaces such as hydrophobic, superhydrophobic, and biphilic surfaces have been previously tested as a method to delay or prevent freezing.[3,4,5,6,7,8,9,10,11,12,13,14,15]
Summary
Condensate freezing or frost is formed when a surface is cooled below the dew point and freezing temperature. For an © injected droplet, the apparent advancing and receding contact angle on plain and Teflon coated surface was measured by tilt table method using goniometer (see supplementary material, Sec. I). At 40% RH the nanopillared droplet dynamics and freezing are notably different compared to the plain surface, as shown in Fig. 2 (see supplementary material, Sec. V).
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