New Perspectives on van der Waals - London Interactions of Materials. From Planar Interfaces to Carbon Nanotubes

The drive towards nanoscale assembly necessitates an accurate understanding of all the fundamental forces present in a given system to ensure the greatest chance of success. The van der Waals London dispersion (vdW-Ld) interaction is the universal, long range, interaction that is present in all materials systems. However, scientists and engineers often either ignore or crudely approximate the vdW-Ld interactions because the calculations often appear impractical due to the 1) lack of the required full spectra optical properties and 2) lack of the proper geometrical formulation to give meaningful results. These two barriers are being actively eliminated by the introduction of robust ab initio codes that can calculate anisotropic full spectral optical properties and by proper extensions to the Lifshitz vdW-Ld formulation that take into account anisotropic spectral optical properties as well as novel geometries. These new capabilities are of broad utility, especially in the biological community, because of the difficulty in experimental determination of full spectral optical properties of nanoscale, liquid phase biomolecules. Here we compare 3 levels of complexity of vdW-Ld interactions (optically isotropic planar, optically anisotropic planar, and optically anisotropic solid cylinder) as well as calculate and compare a variety of Hamaker coefficients relevant to these systems. For the latter two, more complex, cases, we use the ab initio optical properties of single wall carbon nanotubes (SWCNTs). Our results show the effects of strong optical anisotropy upon the overall vdW-Ld interaction strength as well as the presence of strong dispersion-driven torques in both anisotropic cases, which can play a role in CNT alignment with other CNTs and also preferred CNT alignment directions with optically anisotropic substrates[1, 2].