Freezing delay, frost accumulation and droplets condensation properties of micro- or hierarchically-structured silicon surfaces

The processes of single droplet freezing, frost accumulation and droplets flooding during condensation were analyzed and compared for surfaces of different morphologies. Four samples were first fabricated - a micro-cubes silicon, a micro-cylinders silicon, a hierarchically-structured silicon and a smooth silicon. After measuring the static contact angles and roll angles, the sessile water droplet freezing and frost accumulation under a series of surface temperature were studied. The droplets condensation processes were for the first time compared through environmental scanning electron microscopy (ESEM). The results showed that the droplet freezing time on hierarchically-structured silicon was 4 times longer than that of uncoated silicon. Micro-pillared and hierarchically-structured silicons could minimize the frost thickness only in the initial stage of frost formation and had quite different frost growth patterns. The ESEM images can facilitate explain the different patterns of freezing and frosting on micro-pillared and hierarchically-structured samples.