Free Energy Contributions to the Template-Assisted Self-Assembly of Nanoparticles Using Steered Molecular Dynamics Simulations: Implications for Molecular-Specific Imaging and Sensing

Directed self-assembly of nanoparticles (DSA-n) over a templated surface is of wide interest in many technological applications such as semiconducting, plasmonic, and photovoltaic devices and, in particular, molecular-specific imaging and sensing. Understanding the complex energetics of nanoparticle deposition will aid in improving the yield and scalability of DSA-n. In this study, we report steered molecular dynamics (SMD) simulations to predict the free-energy contribution to DSA-n over a templated surface. We utilize many-body dissipative particle dynamics along with Jarzynski’s equality for both stagnant and receding liquid film, as a nonequilibrium system, for DSA-n. We apply the harmonic spring approximation in SMD simulations and calculate the average work, internal energy, entropy, and free energy for various nanoparticle densities in the liquid film. The results of SMD simulations in the stagnant and receding liquid film suggest that the free energy is a concave function of the nanoparticle density. The simulation results also indicate that the impact of the receding liquid film on the free energy associated with DSA of a nanoparticle is similar to that of the stagnant liquid film. The understanding gained from this study will shed some light on the mechanism of DSA-n, and the ways to increase the yield and decrease the defect density.