Fabricating patterned microstructures by embedded droplet printing on immiscible deformable surfaces

The deposition of droplets inside the deformable surfaces has attracted researchers for decades due to its application in direct-writing microporous polymer architectures, printing embedded flexible wires, patterning functional nanoparticles, etc. Herein, a patterned microstructure method based on droplets, named as the embedded droplet printing (EDP), is proposed. The experiments were conducted at a Weber number of 5.49–17.7 to explore the impact outcome, spreading laws and embedded morphology of the droplets. The rebound of droplets impacting the viscous surface was suppressed under appropriate conditions. The spreading factor of the droplet impacting on the high viscous surface followed the power law d*∝ t α. However, the exponent α was observed to be in the range 0.042–0.031, much smaller than the reported values (0.1–1), which could be explained by the Oh number. The diameters of droplets wrapped with viscous PDMS were only about 1/6th as compared to the spreading on the surface of PDMS precured for 30 min. In particular, a domain map was plotted in which patterns of solid bracts, plates and coffee rings were printed. Overall, EDP is a promising candidate to tailor the size, depth and morphology of droplets for preparing the patterned microstructures inside the soft materials.