Effect of superhydrophobic surface morphology on evaporative deposition patterns

Abstract

Prediction and active control of the spatial distribution of particulate deposits obtained from sessile droplet evaporation are vital in printing, nanostructure assembly, biotechnology, and other applications that require localized deposits. This Letter presents surface wettability-based localization of evaporation-driven particulate deposition and the effect of superhydrophobic surface morphology on the distribution of deposits. Sessile water droplets containing suspended latex particles are evaporated on non-wetting textured surfaces with varying microstructure geometry at ambient conditions. The droplets are visualized throughout the evaporation process to track the temporal evolution of contact radius and apparent contact angle. The resulting particle deposits on the substrates are quantitatively characterized. The experimental results show that superhydrophobic surfaces suppress contact-line deposition during droplet evaporation, thereby providing an effective means of localizing the deposition of suspended particles. A correlation between deposit size and surface morphology, explained in terms of the interface pressure balance at the transition between wetting states, reveals an optimum surface morphology for minimizing the deposit coverage area.

Buoyancy-induced on-the-spot mixing in droplets evaporating on nonwetting surfaces

“…The rate of evaporation increases with substrate temperature, thereby increasing the extent of evaporative cooling, and the resulting temperature difference T across the droplet. The recirculating flow behavior inside the droplet during evaporation on hydrophobic and superhydrophobic surfaces in conjunction with the sliding droplet contact line explains the localized evaporative deposition of particulate inclusions on such surfaces [28,30].…”

“…Extreme particulate localization can be achieved during evaporation on hydrophobic and superhydrophobic surfaces for biosensing [6] and self-assembly [29] applications. Localized deposition was reported during evaporation on superhydrophobic surfaces [30]; tuning of the surface geometry achieved a deposit size as small in area as 0.9% of the initial droplet base [30]. A quantitative estimate of the internal flow characteristics, and identification of the governing mechanism that establishes the flow field inside droplets evaporating on nonwetting surfaces, are needed to understand their relationship with the localized deposition pattern realized.…”

Spatiotemporal infrared measurement of interface temperatures during water droplet evaporation on a nonwetting substrate

“…7 In these applications, an understanding of the thermal and species transport characteristics is critical for controlling the droplet evaporation behavior and deposition of suspended particulates. The inspection of interface temperatures is crucial to understanding and controlling the thermal and evaporative behavior of droplets for various droplet-based manufacturing and testing applications.…”

Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

“…[1][2][3][4][5] There has been considerable focus on understanding their wettability 6,7 and developing them for a wide range of applications including droplet impact resistance, [8][9][10][11][12][13] anti-icing, [14][15][16][17][18][19] dropwise condensation, [20][21][22][23][24] electro-wetting, 25,26 drag reduction, [27][28][29][30][31][32] evaporation, 33,34 and anti-corrosion. [35][36][37][38] An important challenge for broad applicability of these hydrophobic materials is their limited robustness.…”