Mechanically tuning of the shape and controlling the motion of the droplet on a patterned elastic surface

A patterned surface with stimuli responsive properties attracts considerable interest for its importance in advanced engineering, partly due to its reversibility, easy design and control, good compatibility and responsive behavior to external stimuli. In this research, we have designed and fabricated a bilayer structure with a patterned surface which is capable of a dynamic on/off switching of a pattern responsive to the external compressive/tensile strain. A deformation map for describing the on/off switching of the void has been generated as a function of voids geometries (diameter, depth, density) and the applied strain. The critical strains have been determined for the extreme closure state of the void at a strain of 0.4 - 0.6. The dynamic deformation and possible local strain concentration have been investigated under fluorescence microscope and Laser Scanning Confocal Microscopy (LSCM). Furthermore, we characterize the corresponding changes in the static and dynamic contact angles. Depending on the external mechanical inputs, we show that it is possible to control the droplet shape, its critical sliding angle, as well as its dynamics. The control kinetics will be discussed by considering the surface condition and system variables. The results provide a strategic solution on how to mimic the preferred pattern on a soft surface and to apply it in a microfluid environment, indicating a potential application as a liquid optical switch in a microfluidic device.