Wetting phenomena observed in evaporating droplets on structured surfaces

摘要

A study was undertaken of ethanol droplet evaporation on structured surfaces of pillars (square pillars of variable dimensions and spacing of order microns, and cylindrical of various spacings). On seasoned perflourodecyltrichlorosilane surfaces, significant films were observed extending far beyond the initial contact line for pure ethanol droplets, most prominently for 4 microlitre droplets. On parylene coated surfaces, similar imbibed films were seen for 1.5 microlitre droplets of 50% by volume ethanol-water mixture. This film acts as an additional surface for evaporation and it appears that the droplet then serves as a reservoir for feeding the film until the evaporation process is completed, rather than evaporation being governed by evaporation at the contact line. The droplets with films show higher evaporation rates.