(200f) The Continuous Millifluidic Surface Modification of Silver Nanowires By Palladium Via Galvanic Replacement Reaction

With the scarcity and cost of manufacturing indium tin oxide going up, industry is looking towards other materials to be the conductive medium in conductive inks for use in manufacturing transparent conductive films (TCFs). Silver nanowires (AgNWs) are promising candidates due to unique properties such as high transparency, conductivity, and mechanical flexibility. The cost associated with the raw material production for this application is among the most important factors in material selection. The polyol method is a reliable, easy, and inexpensive wet chemical technique to synthesize AgNWs. A batch reactor is typically used for AgNW syntheses, but batch polyol AgNW syntheses face difficulties for industrial scale up such as producing silver nanoparticles (AgNPs), reproducibility, separation methods to remove AgNPs, and large amounts of waste. A millifluidic reactor can be used to address the problems faced with AgNW batch reactions because they have a uniform chemical and thermal environment promoted by a fixed reaction volume inside the tubing. Although AgNWs are easily synthesized and possess desirable properties for industrial application, they are prone to oxidation. Oxidation on AgNWs can not only weaken mechanical stability but also increase the sheet resistance of TCFs. To mitigate the oxidation concern, the surface of AgNWs can be alloyed with noble metals such as palladium via a galvanic replacement reaction. The formation of high reduction potential alloys on the surface of AgNWs has been shown to improve the performance and stability of AgNW-based TCFs.

In this study, the Minitab software is used to create a Design of Experiments (DoE) aimed to optimize the AgNW polyol reaction conditions to produce 100% AgNWs with high aspect ratios in a millifluidic reactor. Once the optimized reaction conditions are established, AgNWs are synthesized and prepared for surface modification reactions. A galvanic replacement reaction is used to modify the surface of the synthesized AgNWs. A palladium chloride (PdCl₂) precursor is dissolved in hydrochloric acid (HCl) and then diluted to different concentrations (10µM to 100 µM). The differing concentrations of the PdCl₂/HCl solutions are prepped and various amounts of synthesized AgNWs are introduced. The process will be conducted in batch, semi batch, semi-continuous, and fully continuous reactors. Once the Pd surface modification conditions are finalized in the continuous reactor, the outlet tubing from the AgNW reactor is connected to the tubing of the Pd surface modification reactor via a t-joint. The PdCl₂/HCl solution will be introduced perpendicularly in the t-joint. Reagents for both AgNW synthesis and Pd surface modification are added via syringe pump. After completion of the galvanic replacement reaction, the Pd treated AgNWs are washed and separated and redispersed in deionized water for further x-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and inductively coupled plasma - optical emission spectrometry (ICP-OES) characterizations. Treated AgNWs will be introduced into differing concentrations of hydrogen peroxide to test resistance to oxidation. Further SEM characterization will be conducted to confirm the analysis.

This work is supported by the National Science Foundation (NSF) under grant number 1939018.