(574b) Determining Rate Constants for the Nucleation and Growth of Silver Nanowires Via the Polyol Method in a Batch and Millifluidic Reactor

Silver nanowires (AgNWs) have proven to be promising candidates as the conductive material in conductive inks due to unique properties such as high conductivity, transparency, and mechanical flexibility. These conductive inks can be implemented in printing processes to create conductive patterns for use in manufacturing transparent conductive films (TCF). When considering a colloidal process for synthesizing AgNWs, the polyol method is a popular option because it is reliable, easy, and inexpensive. Polyol syntheses involve using a glycol as the solvent and the reducing agent, a silver metal precursor, a salt mediator, and a capping agent. AgNWs can easily be synthesized using the polyol method in a batch process, but these syntheses face difficulties when considered for industrial scale up. The most common problems faced are producing undesired silver nanoparticles (AgNPs), reproducibility, separation methods, and large amounts of waste. To address the issues associated with batch reactors, a millifluidic reactor can be used. Millifluidic reactors are continuous flow reactors constructed from tubing with inner diameters on the milli- scale and have a uniform chemical and thermal environment promoted by a fixed reaction volume inside the tubing. The kinetic study and determining the rate constants for the polyol synthesis of AgNWs is crucial for industrial scale up as they provide the ability to produce AgNWs with certain lengths and diameters. In this study, a method by El-Ghamry and Frei is implemented to quantify the amount of silver ions present at different times during the polyol AgNW synthesis in batch and millifluidic reactors and to compare the rate constants between the two types of reactors. Rate constants are determined by applying the non-linear Finke-Watzky model.

To apply the El-Ghamry and Frei method for quantifying silver ions, a calibration curve is made using an acetate buffer, solutions of eosin-y and 1,10-phenanthroline (TBF-Phen), and known concentrations of silver nitrate, the metal precursor. When the above components are combined for each known concentration of Ag, silver ions in solution will form Ag-TBF-Phen complexes that can be detected by UV-Vis with a characteristic peak at 550 nm. Once the calibration curve is established, polyol AgNW reactions are conducted in both batch and millifluidic reactors. For the polyol method, ethylene glycol (EG), silver nitrate, copper chloride, and polyvinylpyrrolidone (PVP) are used as the solvent/reducing agent, metal precursor, salt mediator, and capping agent, respectively. At a specific time-interval, a sample is taken from the reactor, diluted, and combined with the TBF-Phen solutions in a cuvette, and an absorbance value is recorded at the 550 nm peak. Silver ion concentrations are calculated using the calibration curve equation. Three sets of data are taken for each batch and millifluidic reaction, and the non-linear Finke-Watzky method for determining rate constants is applied. Using non-linear regression, rate constants are quantified and compared for each reactor.

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