Evaporative Deposition on Superhydrophobic Surfaces

Sessile droplets containing colloidal suspensions of latex particles in water are evaporated on temperature‐controlled superhydrophobic surfaces of varying geometry. The transient droplet shape and wetting behavior under evaporation are analyzed as a function of surface temperature and morphology. Throughout the evaporation process, the solid‐liquid interface is characterized by a constant contact radius evaporation mode (CCR), a constant contact angle evaporation mode (CCA), or a mixed mode of both CCR and CCA. The total evaporation time can be significantly reduced via substrate heating as compared to diffusion‐limited evaporation at thermal equilibrium. To describe the spatial distribution of the particle residues left on the surfaces, qualitative and quantitative evaluations of the depositions are presented. The results show that droplet evaporation on superhydrophobic surfaces driven by either diffusion or substrate heating, suppresses particle deposition at the contact line ‐ the so‐called ‘coffee ring effect’ – and signifies the ability to control the location of solute deposits

Effect of Superhydrophobic Surface Morphology on Evaporative Deposition Patterns

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