Joint Simulations of Confined Diffusion Inside Nanotubules

Confined diffusion of active biological agents consisting of macromolecules inside nano-tubules is simulated with two differing approaches: a semi-continuum approach and a stochastic Langevin approach. In the first approach, the Virtual Identity Particles model (VIP) is developed to efficiently simulate the interactions between macromolecules and fluid. The effects of confinement and different surface charges are investigated in both approaches via parametric studies in an attempt to explain the sustained release experiments with clay nanotubes of 15 nm interior diameter. These halloysite clay nanotubes, loaded with macromolecules of 1∼3 nm in diameter (proteins, drugs, anticorrosion inhibitors), typically provide slow release about 5∼10 hours. Simulation results are compared with relevant established diffusion coefficients and the release rates are discussed. Results indicate that the confined diffusion coefficient in nanotubules is one to two orders smaller than that of free diffusion.