Single-chain polystyrene particles adsorbed on the silicon surface: A molecular dynamics simulation

Molecular dynamics simulations of a single-chain polystyrene particle adsor bed on the substrate surface of silicon were investigated. The particles, w ith various molecular weights, were prepared from the initial conformation of a Flory state coil after a 1000 ps dynamics run at 300 K. The morphology of the single-chain particles on the surface and the process from the Flor y state to the collapse regime in vacuum were examined. It was found that t he height of the particles depends weakly on molecular weight, and the part icles have an irregular shape, findings which are in good agreement with ex periment observations. A simulated heating process for a polystyrene partic le of 100 repeat units adsorbed on the surface was performed from 320 up to 460 K with a heating rate of 20 K/ns for 8 ns. When the temperature is low er than 400 K, the particle shape tends to round with time. The results cor respond to the AFM observation of single-chain PMMA particles with a long p eriod of standing at room temperature. When the temperature is higher than 400 K, it is found that the particle tends to spread on the surface with a heat release of about 400 kJ/mol chain.