Thickness/morphology of functional material patterned by topographical discontinuous dewetting

Abstract

Topographical discontinuous dewetting (TDD) patterning is a nascent 2D printing technique explored for high‐throughput nanoscale patterning of functional material inks. However, variables affecting the z thickness and morphology of the deposited functional materials inside the patterned microchannels remain unexplored. We developed a theoretical model that can determine the thickness of the deposited functional material layers using the TDD patterning technique. We then confirmed the model with experimental data by depositing colloidal dispersions into microchannels using TDD patterning to systematically study the effects of different processing variables. The contribution of evaporation‐driven flow to the deposited layer thickness was significant, with the relationship of thickness to inking speed different to that previously determined for thin film blade coating of colloidal dispersions in the evaporative regime. Additionally, a viscosity dampening effect was observed, unique to TDD of microchannels, which slowed the evaporation‐driven flow due to local viscosity increase in the microchannels. Channel dimensions and ink dispersion concentration affected thickness as hypothesized. Internal flows in the microchannels normal to the sidewalls and perpendicular to the microchannel length (“coffee ring” effect capillary flow/Marangoni flow) were found to contribute significantly to the final morphology/thickness of the deposited layers for the systems/dispersions experimentally measured.

High-Resolution R2R-Compatible Printing of Carbon Nanotube Conductive Patterns Enabled by Cellulose Nanocrystals

“…The ethanol/water binary solvent system can also allow control of the deposition rate of the dispersed functional materials in the patterned cavities as increasing ethanol proportion will increase the evaporation rate of the dispersion, increasing the evaporation-driven flow of the ink dispersion into the patterned cavities. 15 The dispersibility of the different nanomaterials in aqueous/ polar solvents depends on the shape of the nanomaterial particles and the polarity of their surface. Nanocellulose in the form of CNCs and CNFs can be very stable as an aqueous dispersion due to the abundance of negatively charged sulfate and carboxylic acid functional groups on the surface of the particles.…”

“…10, 13 Increasing the ethanol proportion of the binary solvent system can decrease the RCA of the dispersion on the PDMS substrate during patterning, while also increasing the deposition rate of nanocellulose in the patterned cavities due to increased evaporation-driven flow. 15 We prepared nanocellulose (CNC and CNF) dispersions with various ethanol proportions and used them for TDD patterning of the nanocellulose within patterned rectangular microchannel cavities on PDMS substrates at various inking speeds. Attempts to pattern CNF dispersions through TDD resulted in non-uniform CNF deposition within the microchannels or CNF deposition in the non-patterned, non-cavity substrate areas, regardless of the patterning parameters trialed (Figure S2).…”

“…Decreasing inking speed can result in a thicker deposited layer due to increased deposition from the evaporation-driven flow. 15 Patterned Deposition of Conductive CNT Layers on CNC Layers via TDD. Following deposition of the preliminary CNC layer, we deposited conductive CNTs via TDD patterning on the CNC layer in the patterned cavities of the PDMS substrate to form the conductive patterns (Figure 5A,B).…”

“…Again, generally decreasing inking speeds result in thicker deposited layers due to increased deposition from the evaporation-driven flow. 15 Increasing the CNT layer thickness will clearly decrease the resistance of any patterns. The presence of CNTs deposited in the patterned cavities as a uniform film was confirmed through Raman spectra maps of the patterned cavities, which display the signal of the integral over the peak of interest.…”

“…11−14,17−25 Recent research by our group has successfully extended this technique to pattern dispersions of larger, higher-aspect ratio particles like CNTs through (a) the necessary use of preliminary wetting layers in the patterned cavities and (b) enhancing the evaporation-driven flow of the functional particles in the patterned cavities. 10,15 We previously used a preliminary wetting/structural layer of Nafion polymer to facilitate uniform, high-density deposition of CNTs in the patterned cavities. However, the use of the Nafion polymer has environmental concerns as it is a fluoropolymer that can release hazardous per-and polyfluoroalkyl substances into the environment during their production or while breaking down in the environment.…”