Micro‐/Nanofluidics for Liquid‐Mediated Patterning of Hybrid‐Scale Material Structures

Abstract

Various materials are fabricated to form specific structures/patterns at the micro‐/nanoscale, which exhibit additional functions and performance. Recent liquid‐mediated fabrication methods utilizing bottom‐up approaches benefit from micro‐/nanofluidic technologies that provide a high controllability for manipulating fluids containing various solutes, suspensions, and building blocks at the microscale and/or nanoscale. Here, the state‐of‐the‐art micro‐/nanofluidic approaches are discussed, which facilitate the liquid‐mediated patterning of various hybrid‐scale material structures, thereby showing many additional advantages in cost, labor, resolution, and throughput. Such systems are categorized here according to three representative forms defined by the degree of the free‐fluid–fluid interface: free, semiconfined, and fully confined forms. The micro‐/nanofluidic methods for each form are discussed, followed by recent examples of their applications. To close, the remaining issues and potential applications are summarized.

Reversible Doping and Photo Patterning of Polymer Nanowires

“…The use of microfluidic forces or mechanical strain can be used to align or order the nanoparticles during transfer fabrication to achieve ordered patterns, aligned Ag nanowires (1-100 nm) within patterned circuits (0.1-10 μm), or heirarchical order. [14,17] For all of the listed printing methods, there is a tradeoff between printing speed and print resolution; thus, the task of achieving sub-μm features over large areas (in the order of ≈m 2 ) remains a significant challenge. All of the listed printing techniques have been used to fabricate transparent conducting layers, in devices such as OPVs, OLEDs, organic TFTs, waveguides, lasers, touch panels, and strain sensors.…”

“…[ 11 ] Inclusion of nanoparticles into ink solutions, selective dissolution, substrate patterning, and the intelligent use of microfluidic forces at interfaces enable the formation of highly organized substructures that constitute patterning order that is much smaller than the minimum feature size that can be achieved directly through coating techniques. [ 14 ]…”

“…The use of microfluidic forces or mechanical strain can be used to align or order the nanoparticles during transfer fabrication to achieve ordered patterns, aligned Ag nanowires (1–100 nm) within patterned circuits (0.1–10 μm), or heirarchical order. [ 14,17 ]…”

Controlled open-cell two-dimensional liquid foam generation for micro- and nanoscale patterning of materials

“…However, the state-of-the-art methods require expensive preparation steps for templates 15 ; otherwise, the spatial control of the liquid is low-resolution 11 . Microstructured templates, which provide a compromise between the cost and controllability issues 19 , are also limited in that it is only possible to produce simple unidirectional one-dimensional (1D) structures 12 .…”

“…First and most importantly, the topology of liquid foam spontaneously varies in a complex and restricted manner during evaporative change of the liquid volume fraction, due to combination of Plateau’s law and Ostwald ripening 23,24 . Second, control of liquid morphologies with free surfaces remains difficult 19 , because of the dynamic fluidity (e.g., capillary action and Marangoni effect) associated with interfacial forces 25 and the scaling law 26 . With regard to these two issues, Huang et al recently suggested the use of a post array for modulating the direction of the Ostwald ripening, demonstrating a controllable and designable liquid film network 22 .…”