Patterning Silver Nanowires by Inducing Transient Concentration Gradients in Reaction Mixtures

Abstract

Patterning nanocrystals in polymer films is essential for the widespread use of nanocrystals in various fields from optics to electronics; therefore, the development of patterning methods for nanocrystals is an important task. Here, we report a unique approach for patterning silver nanowires (AgNWs) using a thermodynamic driving force induced by transient concentration gradients in reaction mixtures. The procedure starts with the preparation of a photocurable monomer solution containing homogeneously dispersed AgNWs. Ultraviolet illumination through a straight-line mask reduces the polymerization rate of monomers in the masked area, decreasing the polymer concentration in comparison with that in the unmasked area. Such transient polymer concentration gradients yield imbalances in the chemical potentials of AgNWs, inducing the migration of AgNWs to form a straight-line pattern of AgNWs. The pattern of AgNWs was visualized via photoluminescence imaging under a laser scanning confocal microscope and compared with the light patterns applied to the mixture. These observations revealed that the magnitude of the AgNW migration is enhanced as the transient concentration gradient increases by thickening the mask to decrease the intensity of light passing through the mask. The structural features of the AgNW pattern were reproduced using numerical simulations based on a set of reaction−diffusion equations, which suggested the key role of the polymerization kinetics characterized by the Trommsdorff−Norrish effect. Moreover, as the AgNW pattern becomes clearer, the electrical resistance along the patterns decreases and more complex patterns can be produced, indicating the potential of the method. Overall, the present patterning method constitutes a simple approach that only requires illumination through a mask to generate the AgNW pattern, which renders it a promising alternative for patterning nanocrystals in polymer films.

Patterning Perovskite Quantum Dots Using Photopolymerization

“…This observation indicated that CsPbBr 3 QDs migrate from the regions of strong light intensity to the regions of weak light intensity across the boundary line (in other words, CsPbBr 3 QDs migrate in a way to avoid exposure to strong light intensity). The migration direction coincided with the one observed previously for a different photocuring system, including silver nanowires and gold nanoparticles. , …”

“…A photosensitive film containing tetracene was used to image the light intensity, according to a previously reported procedure. , Specifically, the light intensity was calculated from the decreased amount of the fluorescence intensity (concentration) of tetracene in the film (tetracene moieties form dimers by light, and accordingly, the tetracene concentration in the film decreases and so does the fluorescence intensity). Briefly, polystyrene (1.7 g) and tetracene (5.0 mg) were dissolved in styrene as a solvent, and then, ∼5 μm thick tetracene–polystyrene film was formed using solvent casting.…”

“…The migration direction coincided with the one observed previously for a different photocuring system, including silver nanowires and gold nanoparticles. 44,45 To characterize the motion of CsPbBr 3 QDs, we introduced three types of parameters on I em ; integrated emission intensity S, peak emission intensity P, and emission peak width W. These parameters are shown in Figure 2d. The subscripts, L and H, attached to the parameters, respectively, refer to the portions that are lower and higher than the base emission intensity (red broken line).…”

“…An interesting diffusion phenomenon was observed during the formation of refractive index gratings via the photopolymerization of monomers. , Specifically, light-sensitive monomer-containing nanocrystals were irradiated with interference fringes obtained by two crossing laser beams, resulting in the diffusion of nanocrystals and the formation of the nanocrystal grating (refractive index grating). Separately, the long-range migration of nanocrystals was revealed in polymer films prepared by patterned light illumination using a tailor-made photomask. , In a typical procedure, a solution comprising the monomer, photoinitiator, and nanocrystal is illuminated through a special photomask, which allows a certain amount of light to pass through masked regions. Monomers in areas exposed to strong light intensity (unmasked areas) polymerize faster, and thus, a spatially inhomogeneous distribution in the polymer concentration is transiently formed over the mixture.…”

“…Separately, the long-range migration of nanocrystals was revealed in polymer films prepared by patterned light illumination using a tailormade photomask. 44,45 In a typical procedure, a solution comprising the monomer, photoinitiator, and nanocrystal is illuminated through a special photomask, which allows a certain amount of light to pass through masked regions. Monomers in areas exposed to strong light intensity (unmasked areas) polymerize faster, and thus, a spatially inhomogeneous distribution in the polymer concentration is transiently formed over the mixture.…”