Numerical Simulation Study Of The Solvation Effect On The Kinetic Behavior Of Au Nanoparticles

Nanoparticle self-assembly,as a new nanotechnology,spontaneously forms structurally stable and high performance aggregates through non-covalent bonding interactions,which not only has enhanced integration properties among multiple monomers,but also can be easily and artificially regulated.Most of the colloidal self-assembly process occurs in the solvent,but due to the presence of various effects in solution,such as dipole,dissipation,polarization and hydrogen bonding networks,and the solvent molecules at the interface exhibit different structural and energetic changes from the bulk phase.However,experimental methods are very difficult to observe and identify small amounts of localized water molecules at the liquid/particle interface,especially at sub-nanometer separation distances,so scholars have focused on the selection of various dispersants,modification of the particle surface and the application of electrical/magnetic fields to regulate self-assembly,while ignoring the kinetic effects of metal interface solventization on the particles during self-assembly.In this work,This work adoptes all-atom molecular dynamics simulations to establish the diffusion model of single gold particles with three different particle sizes in water and the spontaneous aggregation model of multiple 1 nm in water model using all-atom simulations,respectively.The EAM and TIP3P force field potentials are used to describe the interaction between gold atoms and water molecules,and the LB mixing law is used to calculate the potential energy of the LJ interaction between gold atoms and water molecules.To describe the stability of the system was assessed by monitoring the temperature and total energy during the relaxation state of the model,and the translational diffusion coefficient and kinetic viscosity of water molecules were calculated,and the results differed by 5%and 15%compared with the theoretical simulation,which verified the accuracy of the model.Based on the established model,the free diffusion of a single particle in the water model was firstly investigated,and the Brownian trajectory showed continuous everywhere but non-conducting everywhere.The motion of the particles was decoupled into translational and rotational diffusion for analysis,and it was found that when the diameter of the particles increased,the translational diffusion ability of the particles would be cut down.The translational diffusion coefficients of the particles with 1 nm diameter were compared with 2nm and 3 nm,and the translational diffusion coefficients were 1.5 times and 4.8 times,while the rotational diffusion coefficients were 8 times and 29 times,respectively.The main reason is that the flat-rotation friction coefficient is proportional to the third power of radius and radius,respectively.The adsorption of local water molecules on gold particles of different particle sizes showed a structured phenomenon,and the adsorption capacity weakened with the increase of particle size.Next,the free diffusion to spontaneous aggregation process of the two particles in the water model was investigated,and the trajectories were divided into Brownian motion phase,relaxation phase and aggregation phase on the time scale and space scale.An umbrella sampling method was used to calculate the process of self-assembly of the two particles and quantify the free energy potential of the transition at different stages,and it was found that a free energy potential of 22 k J/mol(8.90 k _BT)needs to be crossed from the Brownian motion stage to the polymerization stage.Then the number density distribution of localized water molecules in the dynamic region was calculated,and the water molecules move violently in the localized region.The diffusion coefficients in the three dimensions were quantified,and it was found that the diffusion coefficients in the Z-direction are five times higher than those in the bulk phase.It was found that the local water molecules were connected by hydrogen bonds to form a skeletal structure of hydrogen bonding network to resist the self-assembly process of the two particles,and the survival time of the skeletal structure was quantified by the hydrogen bonding lifetime.