Stiffening of double-shelled fullerene molecules under uniaxial strains.

Onion-like fullerenes (OLFs) have spherical and tunable shell structures that make them perfect solid lubricants, but their molecular mechanical properties are largely unknown as they are extremely difficult to measure. In this computational study, double-shelled OLFs C₆₀@C₁₈₀, C₈₀@C₁₈₀, C₆₀@C₂₄₀ and C₈₀@C₂₄₀ are subject to uniaxial elastic strains to obtain their mechanical response. Compressive and tensile elastic moduli are calculated using density functional theory with van der Waals correction. We found that the tensile elastic moduli of the single- and double-shelled fullerenes are always larger than the compressive ones by about 50% to 100%. Inserting C₈₀ into C₁₈₀ causes an increase in compressive elastic modulus from 96.8 GPa to 178.6 GPa, while inserting C₆₀ into C₂₄₀ cause much smaller increases. The key factor that determines the stiffening effects is the relative sizes of the inner and outer shells. [ABSTRACT FROM AUTHOR]