Non-Perturbative Theory of Dispersion Interactions

Some open questions exist with fluctuation-induced forces between extended dipoles. Conventional intuition derives from large-separation perturbative approximations to dispersion force theory. Here we present a full non-perturbative theory. In addition we discuss how one can take into account finite dipole size corrections. It is of fundamental value to investigate the limits of validity of the perturbative dispersion force theory.Comment: 9 pages, no figure

Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface

We consider theoretically the retarded van der Waals interaction of a small gas bubble in water with a porous SiO2 surface. We predict a possible transition from repulsion to attraction as the surface is made more porous. It highlights that bubbles will interact differently with surface regions with different porosity (i.e., with different optical properties)

Effect of excess charge carriers and fluid medium on the magnitude and the sign of the Casimir-Lifshitz torqueP. Thiyam

Last year, we reported a perturbative theory of the Casimir-Lifshitz torque between planar biaxially anisotropic materials in the retarded limit [Phys. Rev. Lett. {\bf 120}, 131601 (2018)], which is applied here to study the change of sign and magnitude of the torque with separation distance in biaxial black phosphorus having excess charge carriers. The study is carried out both in vacuum as well as in a background fluid medium. The presence of extra charge carriers and that of an intervening fluid medium are both found to promote enhancement of the magnitude of the torque between identical slabs. The degree of enhancement of the magnitude of torque increases not only with an increased carrier concentration but also with separation distance. In the non-identical case when different planes of anisotropic black phosphorus face each other, owing to the non-monotonic characteristic of the sign-reversal effect of the torque, the enhancement by carrier addition and intervening medium also becomes non-monotonic with distance. In the presence of a background medium, the non-monotonic degree of enhancement of the torque with distance is observed even between identical slabs

Effective Lennard-Jones parameters for CO2-CO2 dispersion interactions in water and near amorphous silica-water interfaces

Different models for effective polarizability in water and the corresponding dispersion forces between dissolved molecules are explored in bulk water and near interfaces. We demonstrate that the attractive part of the Lennard-Jones parameters, i.e., the van der Waals parameter C6 (UvdW ≈ -C6/ρ6), is strongly modified when two carbon dioxide (CO2) molecules are near an amorphous silica-water and near a vapor-water interface. Standard simulation parameters for near-surface modeling are based on intermolecular forces in bulk media

Lifshitz interaction can promote ice growth at water-silica interfaces

At air-water interfaces, the Lifshitz interaction by itself does not promote ice growth. On the contrary, we find that the Lifshitz force promotes the growth of an ice film, up to 1–8 nm thickness, near silica-water interfaces at the triple point of water. This is achieved in a system where the combined effect of the retardation and the zero frequency mode influences the short-range interactions at low temperatures, contrary to common understanding. Cancellation between the positive and negative contributions in the Lifshitz spectral function is reversed in silica with high porosity. Our results provide a model for how water freezes on glass and other surfaces

Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films

In order to understand why carbon dioxide (CO2) and methane (CH4) molecules interact differently with surfaces, we investigate the Casimir-Polder energy of a linearly polarizable CO2 molecule and an isotropically polarizable CH4 molecule in front of an atomically thin gold film and an amorphous silica slab. We quantitatively analyze how the anisotropy in the polarizability of the molecule influences the van der Waals contribution to the binding energy of the molecule

Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface

We consider theoretically the retarded van der Waals interaction of a small gas bubble in water with a porous SiO 2 surface. We predict a possible transition from repulsion to attraction as the surface is made more porous. It highlights that bubbles will interact differently with surface regions with different porosity (i.e., with different optical properties)

Trends of CO2 adsorption on cellulose due to van der Waals forces

The non-retarded van der Waals and Casimir-Polder forces on a CO2 molecule in water near a single surface and between surfaces are explored. We observe preferential adsorption and desorption of CO2 molecules depending on the material of the surfaces. We also find a potential mechanism of capture and storage of CO2 molecules in a geometry consisting of a cellulose surface coated by a thin film of water and then by air

Volume dependence of the dielectric properties of amorphous SiO2

Using first principles calculations, the analysis of the dielectric properties of amorphous SiO2 (am-SiO2) was performed. We found that the am-SiO2 properties are volume dependent, and the dependence is mainly induced by the variation of nanoporosity at the atomic scale. In particular, both ionic and electronic contributions to the static dielectric constants are functions of volume with clear trends. Moreover, using the unique parameterization of the dielectric function provided in this work, we predict dielectric functions at imaginary frequencies of different SiO2 polymorphs having similar band gap energies

Finite-size-dependent dispersion potentials between atoms and ions dissolved in water

A non-expanded theory is used for dispersion potentials between atoms and ions dissolved in a medium. The first-order dispersion interaction between two atoms in an excited state must account for the fact that the two atoms are coupled via the electromagnetic field and must include effects from background media, retardation and finite size. We show that finite-size corrections when two particles are close change the dispersion interactions in water by several orders of magnitude. We consider as four illustrative examples helium atoms, krypton atoms, phosphate ions, and iodide ions. We demonstrate that, due to large cancellation effects, retardation dominates the interaction for helium atom pairs in an isotropic excited state down to the very small atom-atom separations where finite-size corrections are also important