The Effect of Different Substances Embedded in Fullerene Cavity on Surfactant Self-Assembly Behavior through Molecular Dynamics Simulation

Abstract

Fullerene-based amphiphiles are new types of monomers that form self-assemblies with profound applications. The conical fullerene amphiphiles (CFAs) have attracted attention for their uniquely self-assembled structures and have opened up a new field for amphiphile research. The CFAs and CFAs with different substances embedded in cavities are designed and their self-assembly behaviors are investigated using molecular dynamics (MD) simulations. The surface and internal structures of the micelles are analyzed from various perspectives, including micelle size, shape, and solvent-accessible surface area (SASA). The systems studied are all oblate micelles. In comparison, embedding Cl^- or embedding Na⁺ in the cavities results in larger micelles and a larger deviation from the spherical shape. Two typical configurations of fullerene surfactant micelles, quadrilateral plane and tetrahedral structure, are presented. The dipole moments of the fullerene molecules are also calculated, and the results show that the embedded negatively charged Cl^- leads to a decrease in the polarity of the pure fullerene molecules, while the embedded positively charged Na⁺ leads to an increase.

Keywords: fullerene; micelle; molecular dynamics simulations; self-assembled.

Figure 1

Molecular structure formulas of studied fullerene surfactants. To facilitate subsequent analysis, the R-including atoms were labeled sequentially as 1–13.

Figure 2

Probability of gauche defects as a function of carbon and nitrogen position.

Figure 3

Dipoles for all studied different fullerene surfactants.

Figure 4

Angle probability distribution.

Figure 5

The g(r)s of selected N atoms and Cl⁻ ions.

Figure 6

Hydration numbers of selected atoms. The inserted sketch map of the fullerene surfactant molecule describes the corresponding atom of each number, in which 2 and 6–8 are N atoms, and others are C atoms.

Figure 7

The g(r)s of the N7 (a) as well as N8 (b) atoms and Cl⁻ ions.

Figure 8

Time correlation function C_HB(t) for the hydrogen bonds between water and N6 atom, N7 atom, or N8 atom.

Figure 9

The distance between fullerene sphere COM and fullerene sphere COM in (a) CFA5, (b) CFA5-Cl, (c) CFA5-Na, (d) CFA5-H₂O, and (e) CFA5-Na-Cl. Different colors are used to distinguish different distances between two fullerene sphere COMs in each group.

Figure 10

Schematic of planar quadrilateral and tetrahedral for micelles.

Figure 11

Angle distribution of planar and tetrahedral structures in (a) CFA5, (b) CFA5-Cl, (c) CFA5-Na, (d) CFA5-H₂O, and (e) CFA5-Na-Cl.