Assembly by Solvent Evaporation: Free Energy, Role of Solvent and the Equilibrium State

Many ordered nanostructure assemblies with crystalline and quasi-crystalline order have been experimentally realized via solvent evaporation, where the presumably equilibrium state is free of solvent. Understanding the equilibrium structure and thermodynamic stability of these realized nanoparticle (NP) systems requires precise free energy and internal energy calculations. In this talk, I will systematically discuss two aspects of nanoparticle assembly by solvent evaporation. First, I will discuss the factors that control the accuracy calculations via molecular dynamics simulations for free energies in the dry state to 1 kBT precision, such as timestep, thermostat type, drag coefficient, and the parameter of the harmonic bias potential, ultimately providing optimal parameter values and precise calculations of free energies and internal energies. Second, I will discuss the process of solvent evaporation in a superlattice and compare the results against the predictions from a mean field molecular theory (MOLT). Application of both MD and MOLT computations allows for efficient calculation of various thermodynamic and dynamical quantities of a given nanoparticle system, allowing a detailed understanding of nanoparticle assembly via solvent evaporation.