Probing the solubility of selected nanoscale building blocks using molecular simulation

Abstract

CHEMICAL ENGINEERING

PROBING THE SOLUBILITY OF SELECTED NANOSCALE BUILDING BLOCKS USING MOLECULAR SIMULATION Patrick Scott Redmill under the supervision of Peter T. Cummings and Clare McCabe

The solubility of a variety of nanoscale building blocks (C60, carbon nanotubes, and polyhedral oligomeric silsesquioxanes and their functionalized derivatives) have been determined using computational techniques. In particular, the Gibbs free energy of solvation () for fullerene particles of differing size and shape has been determined in octanol and water solvents using molecular dynamics simulations and thermodynamic integration. The fullerene molecules are all found to be strongly hydrophobic and organophilic, suggesting a strong preference for the organic phase. From a comparison of results for capped and uncapped carbon nanotubes we found that uncapped tubes exhibit significantly higher hydrophobicity than capped tubes. The use of the UNIFAC group-contribution method to predict infinite dilution activity coefficients () for selected nanoparticles in aqueous and organic solvents has also been evaluated. Ab initio calculations have been performed to determine the required binary energy parameters not available in the UNIFAC database. We find that UNIFAC can satisfactorily estimate the ratio of the activity coefficient of the particle in water versus the activity coefficient of the particle in octanol, which allows for estimation of the octanol-water partition coefficient (). Additionally, to gauge the propensity of the nanoparticles to cross a heterogeneous membrane, the Gibbs free energy of transfer () for each particle has been determined using molecular dynamics simulations and potential of mean force calculations performed across the axis normal to the bilayer surface. The studies show that C60 has a substantial energetic preference for the polar head region of the lipid bilayer system, whereas the POSS molecules studied show indicate an affinity for the water phase.