Sessile drop evaporation and condensation on slippery
liquid-infused
porous surfaces (SLIPS) is crucial for many applications. However,
its modeling is complex since the infused lubricant forms a wetting
ridge around the drop close to the contact line, which partially blocks
the free surface area and decreases the drop evaporation rate. Although
a good model was available after 2015, the effects of initial lubricant
heights (hoil)iabove the pattern,
and the corresponding initial ridge heights (hr)i, lubricant viscosity, and solid pattern type
were not well studied. This work fills this gap where water drop evaporations
from SLIPS, which are obtained by infusing silicone oils (20 and 350
cSt) onto hydrophobized Si wafer micropatterns having both cylindrical
and square prism pillars, are investigated under constant relative
humidity and temperature conditions. With the increase of (hoil)i, the corresponding (hr)iincreased almost linearly on
lower parts of the drops for all SLIPS samples, resulting in slower
drop evaporation rates. A novel diffusion-limited evaporation equation
from SLIPS is derived depending on the available free liquid–air
interfacial area,ALV, which represents
the unblocked part of the total drop surface. The calculation of the
diffusion constant,D, of water vapor in air from
(dALV/dt) values obtained
by drop evaporation was successful up to a threshold value of (hoil)i= 8 μm within ±7%,
and large deviations (13–27%) were obtained when (hoil)i> 8 μm, possibly due to the
formation
of thin silicone oil cloaking layers on drop surfaces, which partially
blocked evaporation. The increase of infused silicone oil viscosity
caused only a slight increase (12–17%) in drop lifetimes. The
effects of the geometry and size of the pillars on the drop evaporation
rates were minimal. These findings may help optimize the lubricant
oil layer thickness and viscosity used for SLIPS to achieve low operational
costs in the future.