Assembly of Conductive Polyaniline Microstructures by a Laser-Induced Microbubble

Abstract

Micropatterns of conductive polymers are key for various applications in the fields of flexible electronics and sensing. A bottom-up method that allows high-resolution printing without additives is still lacking. Here, such a method is presented based on microprinting by the laser-induced microbubble technique (LIMBT). Continuous micropatterning of polyaniline (PANI) was achieved from a dispersion of the emeraldine base form of PANI (EB-PANI) in n-methyl-2-pyrrolidone (NMP). A focused laser beam is absorbed by the EB-PANI nanoparticles and leads to formation of a microbubble, followed by convection currents, which rapidly pin EB-PANI nanoparticles to the bubble/substrate interface. Micro-Raman spectra confirmed that the printed patterns preserve the molecular structure of EB-PANI. A simple transformation of the printed lines to the conducting emeraldine salt form of PANI (ES-PANI) was achieved by doping with various acid solutions. The hypothesized deposition mechanism was verified, and the resulting structures were characterized by microscopic methods. The microstructures displayed conductivities of 3.8 × 10–1 S/cm upon HCl doping and 1.5 × 10–1 S/cm upon H2SO4 doping, on par with state-of-the-art patterning methods. High fidelity control over the width of the printed lines down to ∼650 nm was accomplished by varying the laser power and microscope stage velocity. This straightforward bottom-up method using low-power lasers offers an alternative to current microfabrication techniques.

Laser‐Based Printing: From Liquids to Microstructures

“…[ 77 ] and Edri et al. [ 70 ] (Figure 4h), a non‐continuous deposition is formed. However, it was shown [ 69,79,84 ] that modulations of the laser enable the formation of continuous patterns (Figure 4i).…”

“…A micro-printed structure can be formed by repeating this process. In many cases, excluding Roy et al [77] and Edri et al [70] (Figure 4h), a non-continuous deposition is formed. However, it was shown [69,79,84] that modulations of the laser enable the formation of continuous patterns (Figure 4i).…”

“…(h) Reproduced with permission. [ 70 ] Copyright 2020, American Chemical Society. (j) Reproduced with permission.…”

“…manner of material fixation to the substrate, which makes it appealing for the assembly of a wide range of materials. It was referred to in the literature by many names: bubble printing, [32,68] laser-induced microbubble technique (LIMBT), [69,70] hapticinterfaced bubble printing, [71] bubble pen lithography, [72] laserinduced micro-nano bubble, [73] continuous-wave laser-induced vapor bubble, [74] optothermally generated surface bubble, [75,76] thermo-optically manipulated laser-induced microbubbles, [77,78] and optothermal-surface bubble-assisted printing. [79] Mechanism: Thermal heating arises from a CW laser beam that is absorbed by the preformed dispersed particles or a light absorbing substrate.…”

“…[76] Products: Microbubble assisted printing was used for depositing various material families. Specific examples include Ag NPs, [69] Cu NPs, [69] Pd/Ni NPs, [84] quantum dots (QDs), [68,[71][72][73] polystyrene, [72,74] polyaniline (PANI), [70] soft oxometalate nanotubes (SOMs), [77] glycine, [77] paracetamol, [77] CNTs, [77] and Si-Au core-shell NPs. [79] The minimal deposited feature size is affected mainly by the size of the microbubble, as the deposition occurs at its contact area with the substrate.…”