Ordered Packing of Emulsion Droplets toward the Preparation of Adjustable Photomasks

Abstract

Monodisperse emulsion droplets with a high volume fraction form crystalline phases that can potentially serve as adjustable photomasks in photolithography. Such photomasks were prepared using a microfluidic device in which a flow-focusing junction, side channels, and a reservoir were connected in series. Transparent oil droplets were generated in a dye-containing continuous water phase at the flow-focusing junction. The droplets were then concentrated through the selective removal of the continuous phase using the side channels. This process led to the formation of a regular array of droplets in the reservoir with a configuration that depended on the relative height of the reservoir to the droplet diameter. The configurations could be selected among a single-layered hexagonal array, a bilayered square array, and a bilayered hexagonal array. The droplet arrays were used as a photomask to create hexagonal or square arrays of microdots. The transmittance profile of the ultraviolet (UV) light from each droplet was parabolic, which enabled the dot size to be tuned by controlling the UV irradiation time. This mask effect is otherwise difficult to achieve using conventional photomasks. The dot size and array periodicity could be adjusted by the in-situ control of the droplet size at the flow-focusing droplet maker. The combination of droplet size adjustments and the UV irradiation time provided independent control over the dot size and array periodicity to enable the preparation of a series of hexagonal microarrays with a wide spectrum of array parameters using a single microfluidic device.

Droplet-based electro-coalescence for probing threshold disjoining pressure

“…The coalescence of droplets driven by an applied electric field is termed electrocoalescence. [21][22][23][24][25][26][27][28][29][31][32][33] Surprisingly, the value of the critical voltage U c for droplet electro-coalescence is not constant as reported previously. 28,29 Instead, U c changes and depends crucially on the scanning rate of the applied voltage.…”

“…Knowledge of the threshold disjoining pressure Π threshold can help to predict the emulsion stability, which is especially crucial to the design of emulsion-based formulations 2 and the manipulation of droplets in emulsion-based techniques. [19][20][21][22][23] The traditional method to measure the disjoining pressure isotherm usually utilizes the porous-plate technique, 24 which probes the ΠIJh) through hydrostatic pressure when the film is in an equilibrium state. However, the threshold value of the disjoining pressure is much more rarely measured.…”

Microfluidic Lithography of Bioinspired Helical Micromotors

“…In particular, with the integration of projection photolithography techniques into microfluidic systems, polymeric microparticles with specific geometrical shapes can be achieved. These microfluidic‐generated materials have found many important applications in different areas . However, due to the limitation of the flow forms in the microfluidic lithography channel, which were usually with dispersed emulsions or continuous co‐flow, the recent microfluidic lithography approaches cannot generate complex 3D microparticles, especially those with helical structures.…”

Microfluidic Lithography of Bioinspired Helical Micromotors

“…[21][22][23] It has created exciting avenues of scientific and engineering research into continuous fabrication of functional materials with different morphologies,s uch as spherical microparticles and linear microfibers. [32][33][34][35][36][37][38][39] However, due to the limitation of the flow forms in the microfluidic lithography channel, which were usually with dispersed emulsions or continuous co-flow,the recent microfluidic lithography approaches cannot generate complex 3D microparticles,e specially those with helical structures.F urthermore,t he potential value of the microfluidically generated microparticles as bioinspired micromotors remains unexplored. These microfluidic-generated materials have found many important applications in different areas.…”

“…These microfluidic-generated materials have found many important applications in different areas. [32][33][34][35][36][37][38][39] However, due to the limitation of the flow forms in the microfluidic lithography channel, which were usually with dispersed emulsions or continuous co-flow,the recent microfluidic lithography approaches cannot generate complex 3D microparticles,e specially those with helical structures.F urthermore,t he potential value of the microfluidically generated microparticles as bioinspired micromotors remains unexplored.…”