Size Effect on the Reaction Rate of Surface Nanodroplets

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 the chemical reaction rate under a given flow condition for the transport of the reactant and the product. We found that the overall kinetics increases rapidly with the decrease in droplet's 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 nonreactive compound was present 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.

Elucidating the Mechanism on the Transition-Metal Ion-Synergetic-Catalyzed Oxidation of SO2 with Implications for Sulfate Formation in Beijing Haze

“…Such results are consistent with that reported by Wang et al, who also found that the reaction rate of the manganese-catalyzed oxidation of SO 2 increased with a decreasing droplet diameter and an increasing S/V. The enhancing effect of bigger S/V on the reaction rate could be attributed to the stronger electric field on the surface, which can lower the activation energy of the reaction and enhance the mass transport of reagents and products through the aerosol/air interface. − …”

Growth Rates of Hydrogen Microbubbles in Reacting Femtoliter Droplets

“…Table 3 The enhanced reaction rate in smaller droplets was also found and quantitatively analyzed in our previous results. 30,35 The accelerated bubble kinetics in smaller droplets was attributed to the faster accumulation of the hydrogen product in smaller droplets with a higher surface-to-volume ratio.…”

“…The mass flux between the droplets into the surrounding phase also plays an important role in the droplet reaction kinetics. , In this regard, femtoliter droplets immobilized on a solid surface have been used as a model system for the quantitative study of droplet reaction rates. Because the three-phase contact line of surface droplets is pinned by the solid surface, these droplets are stable on the substrate as the reactant is supplied in a controlled flow. − The volume of surface droplets is conveniently controlled by the solvent exchange method .…”

Growth Rates of Hydrogen Microbubbles in Reacting Femtoliter Droplets

“…The enhanced reaction rate in smaller droplets was also found and quantitatively analyzed in our previous results. 28,36 The accelerated bubble kinetics in smaller droplets was attributed to the faster accumulation of the hydrogen product in smaller droplets with a higher surface-to-volume ratio.…”

“…The mass flux between the droplets to the surrounding phase also plays an important role in the droplet reaction kinetics. 27,28 In this regard, femtoliter droplets immobilized on a solid surface have been used as a model system for the quantitative study of droplet reaction rates. As the three-phase contact line of surface droplets is pinned by the solid surface, these droplets are stable on the substrate as the reactant is supplied in a controlled flow.…”