Wetting kinetics of water nano-droplet containing non-surfactant nanoparticles: A molecular dynamics study

Abstract

In this Letter, dynamic wetting of water nano-droplets containing non-surfactant gold nanoparticles on a gold substrate is examined via molecular dynamics simulations. The results show that the addition of non-surfactant nanoparticles hinders the nano-second droplet wetting process, attributed to the increases in both surface tension of the nanofluid and friction between nanofluid and substrate. The droplet wetting kinetics decreases with increasing nanoparticle loading and water-particle interaction energy. The observed wetting suppression and the absence of nanoparticle ordering near the contact line of nano-sized droplets differ from the wetting behaviors reported from nanofluid droplets of micron size or larger. V

Dynamical Density Functional Theory for the Evaporation of Droplets of Nanoparticle Suspension

“…66. To describe the non-equilibrium dynamics of such systems, one should simply insert the given approximation for the equilibrium Helmholtz free energy into the generalisation of the DDFT equations (20) and (21) that also include additional terms related to rotational diffusion. 67 The main direction where the present approach should be extended is to incorporate the advective hydrodynamics of the solvent liquid.…”

“…The average densities of the liquid and nanoparticles at site i, ρ l i and ρ n i , respectively, are now both functions of time t. Note that since the system we consider here is a lattice model, the ∇ operators in Eqs. (20) and (21) are implicitly the finite difference approximations. For more details on this, see Ref.…”

“…The divergence and gradients in Eqs. (20) and (21) are performed using nearest neighbour finite difference approximations. Care in how these are done is needed to prevent numerical instabilities.…”

“…Fully microscopic models based on molecular dynamics (MD) computer simulations, such as those described in Refs. [19][20][21][22], do of course describe every aspect of the structure and dynamics in the droplet. However, these approaches are limited in the size of droplet that can be modelled.…”

Modelling the evaporation of nanoparticle suspensions from heterogeneous surfaces

“…This does not allow a description of the variations in the nanoparticles density distribution in the direction perpendicular to the surface. A fully microscopic approach, such as molecular dynamics (MD) does include every aspect of the motion of the particles and can be used to describe small liquid drops on a surface [8][9][10][11]. Generally MD is computationally infeasible even for moderate system sizes due to the long time scales over which the evaporative drying occurs.…”