Molecular Dynamics Simulation of C60 Encapsulation into Single-Walled Carbon Nanotube in Solvent Conditions

In this work, molecular dynamics simulations were performed to study the process and mechanism of fullerene (C-60) encapsulation into single-walled carbon nanotube (SWNT) in three kinds of solvents: supercritical CO2 (scCO(2)), CS2 and water. It was demonstrated that a C-60 molecule could spontaneously insert into the SWNT in scCO(2), which is in good agreement with the experimental observation. However, no encapsulation of C-60 was observed in CS, and water during the simulation period. We also, for the first time, simulated the PMF (potential of mean force) profile along the C-60 inserting path. The occurring free energy barrier near the entrance of the SWNT could hinder the insertion of C-60, which is determined by the interaction strength between solvent and C-60, as well as the solvation structures around C-60. The C-60-SWNT interaction provides the driving force in the filling, whereas the solvent-induced force instead offers an obstructing effect. It is revealed that both the solvent-induced free energy barrier and the change of free energy cooperatively determine whether C-60 can fill a SWNT. Our simulation result provides an insightful understanding of the role of solvents on the encapsulation of molecules into SWNTs, which is important for further development of low-temperature nanotube filling techniques.