Size Effect on Reaction Rate of Surface Nanodroplets

TL;DR

This study investigates how the size of surface nanodroplets influences chemical reaction rates, revealing that smaller droplets significantly accelerate reactions due to increased concentration effects and surface interactions.

Contribution

It provides quantitative analysis of size-dependent reaction kinetics in nanodroplets, demonstrating the rapid increase in reaction rate as droplet size decreases, which was not previously characterized.

Findings

Reaction rate increases rapidly as droplet radius decreases

Smaller droplets enhance product concentration and reaction kinetics

Droplet size critically influences chemical reaction efficiency

Abstract

Compartmentalizing reagents within small droplets is promising for highly efficient conversion and simplified procedures in many biphasic chemical reactions. In this work, surface nanodroplets (i.e., less than 100 nm in their maximal height) were employed to quantitatively understand the size effect on the chemical reaction rate of droplets. In our systems, a surface-active reactant in pure or binary nanodroplets reacted with the reactant in the bulk flow. Meanwhile, the product was removed from the droplet surface. The shrinkage rate of the nanodroplets was characterized by analyzing the lateral size as a function of time, where the droplet size was solely determined by chemical reaction rate at a given flow condition for the transport of the reactant and the product. We found that the overall kinetics increases rapidly with the decrease of droplets lateral radius R, as dR/dt ~ R^(-2). The faster increase in the concentration of the product in smaller droplets contributes to accelerating reaction kinetics. The enhancement of reaction rates from small droplet sizes was further confirmed when a non-reactive compound presented inside the droplets without reducing the concentrations of the reactant and the product on the droplet surface. The results of our study improve the understanding of chemical kinetics with droplets. Our findings highlight the effectiveness of small droplets for the design and control of enhanced chemical reactions in a broad range of applications.