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• 1. Bostrom, M.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
The influence of Lifshitz forces and gas on premelting of ice within porous materials2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 115, no 1, article id 13001Article in journal (Refereed)

Premelting of ice within pores in earth materials is shown to depend on the presence of vapor layers. For thick vapor layers between ice and pore surfaces, a nanosized water sheet can be formed due to repulsive Lifshitz forces. In the absence of vapor layers, ice is inhibited from melting near pore surfaces. In between these limits, we find an enhancement of the water film thickness in silica and alumina pores. In the presence of metallic surface patches in the pore, the Lifshitz forces can dramatically widen the water film thickness, with potential complete melting of the ice surface.

• 2. Bostrom, Mathias
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
Lifshitz interaction can promote ice growth at water-silica interfaces2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 15, article id 155422-1Article in journal (Refereed)

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.

• 3. Boström, M.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Non-perturbative theory of dispersion interactions2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 3, article id 035405Article in journal (Refereed)

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.

• 4. Boström, Mathias
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 7, article id 075403Article in journal (Refereed)

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).

• 5. Fiedler, Johannes
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. University of Oslo, Norway. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
Effective Polarizability Models2017In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 121, no 51, p. 9742-9751Article in journal (Refereed)

Theories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and-cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir-Polder interaction with an interface.

• 6. Malyi, Oleksandr I.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Univ Oslo, Ctr Mat Sci & Nanotechnol, Norway.
Volume dependence of the dielectric properties of amorphous SiO22016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 10, p. 7483-7489Article in journal (Refereed)

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.

• 7.
KTH, School of Industrial Engineering and Management (ITM).
A study of finite-size and non-perturbative effects on the van der Waals and the Casimir-Polder forces2016Licentiate thesis, comprehensive summary (Other academic)

This licentiate thesis addresses two important aspects of the van der Waals and the Casimir-Polder ground-state and excited-state (resonance) interactions between two atoms or molecules. The first is the finite-size effect and the second is the non-perturbative effect. Going beyond the usual assumption of atoms and molecules as point particles and adopting a description of finite size, the divergence inherent in such interaction energies in the limit of zero separation distance between the two interacting atoms or molecules is removed. The attainment of finite interaction energy at such close separation distance facilitates the estimation of van der Waals force contribution to the binding energy of the molecules, and towards surfaces. This is particularly important for noble atoms. We investigate in detail for a pair of helium (He) atoms and krypton (Kr) atoms, and for a pair of methane (CH4) molecules considering its environmental importance. The application of finite size further leads to finite self energies of the atoms. The expression of the interaction energy, as is discussed in detail in this thesis, typically contains a logarithmic factor of the form ln(1-x). Formerly, in evaluating the interaction energies, this factor is customarily series-expanded and truncated in the leading order with certain assumptions. This thesis explores the effect of using the full expression, which we refer to as the non-perturbative (or, the non-expanded) theory, analytically wherever possible as well as numerically. The combined application of the finite-size theory and the non-perturbative theory results in as much as 100% correction in the self energy of atoms in vacuum. This may give rise to significant physical consequences, for example, in the permeabilities of atoms across dielectric membranes. The non-perturbative theory, in addition, exhibits interesting behaviour in the retarded resonance interaction.

• 8.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
A study of finite-size, non-perturbative and anisotropic effects on the Lifshitz-van der Waals forces and torque with material dielectric responses from first-principles calculations2018Doctoral thesis, comprehensive summary (Other academic)

The van der Waals and the Casimir-Lifshitz forces are forces of attraction that exist between neutral polarizable bodies due to quantum fluctuations. They can be repulsive depending on the material properties and the geometry of the system. Since they are pervasive in nature, they encompass a great deal of relevance in the study of interaction between bodies in several different scenarios and background geometrical settings.

This doctoral thesis first addresses the important aspects of finite-size and the non-perturbative effects of the van der Waals interactions between two atoms or molecules. Going beyond the usual assumption of atoms and molecules as point particles and adopting a description of finite size, the divergence inherent in such interaction energies in the limit of zero separation distance between the two interacting atoms or molecules is removed. The attainment of finite interaction energy at such close separation distance facilitates the estimation of van der Waals force contribution to the binding energy of the molecules, and towards surfaces. This is particularly important for noble atoms. The interaction between a pair of helium (He) atoms and krypton (Kr) atoms, and between a pair of methane (CH$_4$) molecules considering its environmental relevance, is investigated in detail. The application of finite size further leads to finite self energies of the atoms. The full expression of the interaction energy, as is discussed in detail in this thesis, typically contains a logarithmic factor of the form $\ln(1 \pm x)$. Formerly, in evaluating the interaction energies, this factor is customarily series-expanded and truncated in the leading order with certain assumptions. This thesis explores the effect of using the full expression, which is referred herein as the non-perturbative (or, the non-expanded) theory, analytically wherever possible as well as numerically. The combined application of the finite-size theory and the non-perturbative theory results in as much as 100\,\% correction in the self energy of atoms in vacuum. This may give rise to significant physical consequences, for example, in the permeabilities of atoms across dielectric membranes.

The thesis next addresses the aspect of anisotropy in the Casimir-Polder interaction between a completely polarizable molecule and a dielectric slab polarizable in the normal direction. The formalism is applied to the study of preferential adsorption in the specific case of carbon dioxide (CO$_2$) and methane (CH$_4$) molecules interacting with amorphous silica slabs and thin gold films. Owing to its greater polarizability, the linearly polarizable CO$_2$ molecule is found to attract more towards the surfaces than the isotropically polarizable CH$_4$ molecule. In addition, the stable orientation of the CO$_2$ molecule with respect to the surface is determined to be the one in which the long, linear axis of the molecule is perpendicular to the surface. Further, the feature of Casimir torque which is a consequence of anisotropy in the interacting dielectric slabs is explored in the case of biaxial materials, in particular the bulk black phosphorus and its novel 2D counterpart phosphorene. The torque between a pair of phosphorus slabs, one face rotated with respect to the other, is observed to change sign at a particular separation distance which is determined by the crossing frequency of its planar dielectric components. This distance-dependent reversal of the sign of torque has never been observed before. The observation is verified with several other biaxial materials. This finding will help assist in the experimental detection of the Casimir torque, and can potentially be exploited in the future for designing nanodevices.

Another remarkable effect that is uncovered is the submersion of ice microcrystals under water governed by the balance of repulsive Lifshitz force from the vapor-water interface and the buoyant force of water. The repulsive effect is found to be enhanced by the presence of salt ions in the system. An exclusion zone ranging from 2 nm to 1 ${\mu}$m devoid of small ice particles is formed below the water surface. As the ice sphere grows in size, the buoyant force overcomes the Lifshitz force, and the ice sphere starts to float with a fraction of its volume above the water surface in accordance with the classical Archimedes principle. The combined impact of Lifshitz forces and double-layer interactions is further investigated in ice-water-CO$_2$ and vapor-water-CO$_2$ systems  employing different models of effective polarizability for ions, {\it viz.} the hardsphere model and Onsager's model. The CO$_2$ bubble is found to be repelled by the vapor-water interface and attracted towards the ice-water interface. The equilibrium thin film of water formed between vapor and ice surfaces varies in thickness depending on the model of effective polarizability and the type of salt present in the system. Further studies of the interaction energy in geometries comprising two molecules near an interface and molecule in a three-layer geometry are conducted which may be relevant for potential energy storage applications. The density functional theory (DFT) is employed to generate the frequency-dependent dielectric functions required for Lifshitz energy and force calculations.

Summing up, in the numerous contexts outlined above, the importance of the van der Waals and Lifshitz forces has been demonstrated. The studies in this thesis enable significant predictions related to these forces which may be verifiable by experiments.

• 9.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
Distance-Dependent Sign Reversal in the Casimir-Lifshitz Torque2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 131601Article in journal (Refereed)
• 10.
KTH, School of Industrial Engineering and Management (ITM).
Ice particles sink below the water surface due to a balance of salt, van der Waals and buoyancy forcesManuscript (preprint) (Other academic)
• 11.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
Finite-size-dependent dispersion potentials between atoms and ions dissolved in water2014In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 106, no 5, p. 53002-Article in journal (Refereed)

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.

• 12.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15311-15317Article in journal (Refereed)

According to the classical Archimedes' principle, ice floats in water and has a fraction of its volume above the water surface. However, for very small ice particles, other competing forces such as van der Waals forces due to fluctuating charge distributions and ionic forces due to salt ions and charge on the ice surface also contribute to the force balance. The latter crucially depends on both the pH of the water and the salt concentration. We show that a bulge in the air-water interface due to interaction of surface tension with the rising ice particle becomes significant when the particle radius is greater than 50-100 mu m. The role of these forces in governing the initial stages of ice condensation has never been considered. Here, we show that small ice particles can only form below an exclusion zone, from 2 nm (in high salt concentrations) up to 1 mu m (in pure water at pH 7) thick, under the water surface. This distance is defined by an equilibrium of upward buoyancy forces and repulsive van der Waals forces. Ionic forces due to salt and ice surface charge push this zone further down. Only after growing to a radius larger than 10 pm, will the ice particles eventually float toward the water surface in agreement with the simple intuition based on Archimedes' principle. Our result is the first prediction of observable repulsive van der Waals forces between ice particles and the water surface outside a laboratory setting. We posit that it has consequences on the biology of ice water as we predict an exclusion zone free of ice particles near the water surface which is sufficient to support the presence of bacteria.

• 13.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
Effects of van der Waals forces and salt ions on the growth of water films on ice and the detachment of CO2 bubbles2016In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 113, no 4, article id 43002Article in journal (Refereed)

We study the effect of salts on the thickness of wetting films on melting ice and interactions acting on CO2 bubble near ice-water and vapor-water interfaces. Governing mechanisms are the Lifshitz and the double-layer interactions in the respective three-layer geometries. We demonstrate that the latter depend on the Casimir-Polder interaction of the salt ions dissolved in water with the respective ice, vapor and CO2 interfaces, as calculated using different models for their effective polarizability in water. Significant variation in the predicted thickness of the equilibrium water film is observed for different salt ions and when using different models for the ions' polarizabilities. We find that CO2 bubbles are attracted towards the ice-water interface and repelled from the vapor-water interface.

• 14.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
Effective lennard-jones parameters for CO2-CO2 dispersion interactions in water and near amorphous silica-water interfaces2015Conference paper (Refereed)

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.

• 15.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM). University of Oslo, Norway.
Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 5, article id 052704Article in journal (Refereed)

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.

• 16.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM).
Nonperturbative theory for the dispersion self-energy of atoms2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 5, p. 054502-Article in journal (Refereed)

We go beyond the approximate series expansions used in the dispersion theory of finite-size atoms. We demonstrate that a correct, and nonperturbative, theory dramatically alters the dispersion self-energies of atoms. The nonperturbed theory gives as much as 100% corrections compared to the traditional series-expanded theory for the smaller noble gas atoms.

• 17.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway . KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. College of Physical Science and Technology, China .
Trends of CO2 adsorption on cellulose due to van der Waals forces2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 470, p. 316-321Article in journal (Refereed)

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.

• 18.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
Intermolecular Casimir-Polder forces in water and near surfaces2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 90, no 3, p. 032122-Article in journal (Refereed)

The Casimir-Polder force is an important long-range interaction involved in adsorption and desorption of molecules in fluids. We explore Casimir-Polder interactions between methane molecules in water, and between a molecule in water near SiO2 and hexane surfaces. Inclusion of the finite molecular size in the expression for the Casimir-Polder energy leads to estimates of the dispersion contribution to the binding energies between molecules and between one molecule and a planar surface.

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