Abstract
Abstract This paper introduces a droplet movement method on top of a surface prepared by gradient nano-scale self-assembled molecules on micro sized textures. Experimental results demonstrate the contact angles on hydrophobic surfaces without/with micro posts increase from 110□ to 143□, while on the hydrophilic surfaces decrease from 56.7□ to 12.4□. As a result, the droplet moving speed is increased around twice on the gradient SAM surface with micro structures than that with only SAM gradient or only micro textures. Droplet manipulation has been becoming an emerging alternative to continuous flow systems commonly employed in □TAS for its accurate dose control, less drag force from contact surface, and simpler flow system. Numerous approaches have been developed and tested to transport and manipulate □l-sized liquid droplets moving on the solid surface. The driving mechanisms for moving droplets on solid surfaces include electrostatic actuation, light-driven on photoisomerizable monolayer surface, the combination of Marogoni flow, capillary flow and phase change, and asymmetrically roughed surfaces, etc. All these driving forces are related to surface tension heterogeneity, and hysteresis of contact angles. This paper proposes another gentle approach, by employing surface hydrophobicity gradient with micro structured surfaces, to generate much larger surface tension gradient for droplet movement. Keywords: hydrophobicity gradient, Droplet movement, surface tension, thiol SAM’s, noano and micro Structures