Patterning Silver Nanowires by Inducing Transient Concentration Gradients in Reaction Mixtures

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.