Molecular dynamics simulation on spreading of mixture nanodroplets on a smooth and homogeneous surface

Jiawei Di,Zhen Yang,Yuanyuan Duan

doi:10.1063/5.0043039

Abstract

The dynamic wetting of mixture droplets on the solid surface is important for various industrial technologies and applications, such as evaporation, microfluidics, surface self-cleaning, and power cycling. Due to the influence of different components, the dynamic wetting process of mixture droplets is quite different from that of pure fluids. Currently, the understanding of the spreading mechanism of mixture droplets is lacking. In this paper, molecular dynamics simulation is used to study the dynamic spreading process of ethanol/water and difluoromethane (R32)/2,3,3,3-tetrafluoroprop-1-ene (R1234yf) mixture droplets on a smooth and homogeneous surface. The droplets have different component mole fractions and various diameters of 9.4–12.8 nm. The influences of the component mole fraction on the spreading radius and dynamic contact angle are analyzed and compared with molecular kinetic theory. It is found that for the R32/R1234yf mixture droplets, the component mole fractions in the bulk and at the interface of the droplet are close and the dynamic spreading process is similar to that of pure fluids. However, for the ethanol/water mixture droplets, the mole fraction of ethanol is higher at the vapor–liquid and solid–liquid interfaces than in the bulk, and the spreading is faster than that of pure fluids. The mole fraction and the physical properties in the triple contact region are analyzed, and an improved prediction is proposed for the moving velocity of the triple contact line and the spreading process of the mixture droplet.

Highlights

The dynamic wetting of mixture droplets on solid surfaces is important for various industrial technologies and applications, such as evaporation,1 microfluidics,2–6 surface self-cleaning,7,8 and power cycling
The Extended Single Point Charge (SPC/E) model39 is applied for water molecules, and the Optimized Potentials for Liquid Simulations-All Atoms (OPLS-AA) model40,41 is applied for ethanol molecules
The relative spreading radius is defined as R′ = R/R0, where R is the spreading radius of the droplet given by circular fitting mentioned before during the dynamic spreading process and R0 is the radius of the spherical droplet before spreading

Summary

INTRODUCTION

The dynamic wetting of mixture droplets on solid surfaces is important for various industrial technologies and applications, such as evaporation, microfluidics, surface self-cleaning, and power cycling. Zhang et al and Daub et al investigated the wetting of water/salt droplets spreading on solid surfaces.28,29 Their works pointed out that the component with a lower intermolecular interaction, such as alcohols, short-chain polymers, or salt ions, tends to be distributed at the solid–liquid and vapor–liquid interfaces, while the other component is more concentrated in the bulk.. The movement of atoms and molecules in the liquid and solid phases and interaction among them can be clearly obtained, especially for the migration of different components in the liquid and vapor phases and the influence of the solid surface In this way, a further understanding of the dynamic wetting of mixture droplets on solid surfaces may be obtained. Scitation.org/journal/adv elucidate a further understanding of the spreading mechanism of mixture droplets

Simulation model

Calculation method of the spreading radius and dynamic contact angle

Effect of droplet size

Component distribution of mixture droplets

CONCLUSION