Repulsive Casimir and Casimir–Polder forces

Milton, Kimball A.; Abalo, E. K.; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen Å.

doi:10.1088/1751-8113/45/37/374006

Cited by 51 publications

(32 citation statements)

References 92 publications

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“…[65,67] Recent studies on the interactions of two materials, including NWs, separated by a thin film of fluid have shown that the Casimir[68, 69] interaction energies can be either repulsive or attractive depending on 6 the permittivities of the materials (NWs and fluids). [70][71][72] They also reported that, due to retardation effects, the separation of the two materials has a very strong influence on the permittivities,[71] which could transform the Casimir interaction energy from attractive to repulsive at intermediate separations ( 10 nm).…”

Section: Discussionmentioning

confidence: 99%

“…[65] This regime is known as the relativistic retarded regime, [65] where the finite speed of light leads to significant attenuation of the dispersion interactions, [64] and the resulting fluctuations in dipole moments lead to forces known as the Casimir forces. [65,67] Recent studies on the interactions of two materials, including NWs, separated by a thin film of fluid have shown that the Casimir [68,69] interaction energies can be either repulsive or attractive depending on the permittivities of the materials (NWs and fluids). [70][71][72] They also reported that, due to retardation effects, the separation of the two materials has a very strong influence on the permittivities, [71] which could transform the Casimir interaction energy from attractive to repulsive at intermediate separations ( 10 nm).…”

Section: Discussionmentioning

confidence: 99%

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Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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Here we present a study on the presence of physisorbed water on the surface of aligned carbon nanotubes (CNTs) in ambient conditions, where the wet CNT array mass can be more than 200% larger than that of dry CNTs, and modeling indicates that a water layer > 5 nm thick can be present on the outer CNT surface. The experimentally observed non-linear and non-monotonic dependence of the mass of adsorbed water on the CNT packing (volume fraction) originates from two competing modes. Physisorbed water cannot be neglected in the design and fabrication of materials and devices using nanowires/nanofibers, especially CNTs, and further experimental and ab initio studies on the influence of defects on the surface energies of CNTs, and nanowires/nanofibers in general, are necessary to understand the underlying physics and chemistry that govern this system.One dimensional nanoscale systems, such as nanowires, nanofibers, and nanotubes, are well known for their phenomenal electrical, [1][2][3][4] thermal, [5][6][7][8] and mechanical properties, [9][10][11] which could enable the design and manufacture of next-generation materials with unprecedented properties. [12][13][14][15][16][17][18] However, while many studies have previously explored the synthesis of new architectures and devices using one dimensional nanomaterials, specifically carbon nanotubes (CNTs), the properties they reported were far lower than the properties of predicted using current theory.[12] Some of the main reasons why existing models cannot accurately predict the behavior of CNTs in scalable architectures, such as aligned CNT arrays, are the various CNT morphology and proximity effects, [13][14][15]19] which can strongly impact properties, but are not well understood and cannot be properly integrated into theoretical frameworks. Here we report the presence of a commonly neglected morphological effect, an unexpectedly large (compared to the CNT mass) amount of moisture located on the surface of CNTs in aligned CNT (A-CNT) arrays at ambient conditions; show the non-linear and non-monotonic dependence of this effect on array porosity, which suggests two competing mechanisms; and discuss the strong impact such an effect can have on the structure and properties of nanocomposite architectures composed of A-CNTs.Previous studies on how water interacts with the outer surface of a CNT illustrated that the water molecules form a layer-like shell surrounding the CNTs, [20][21][22][23] and that the water layer density varies greatly and non- * wardle@mit.edu.monotonically with its thickness. [21,22] A recent study on the physisorption of water onto the external surface of a suspended ∼ 1.1 − 1.2 nm diameter single walled CNT showed that more than one layer of water is present on the CNT surface in water vapor, and that water molecules more easily adsorb onto larger diameter CNTs.[24] However, this study was limited to isolated and defect-free CNTs, [24,25] meaning that the interaction of moisture present in ambient air with multiwalled CNTs, which normally have nativ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

et al. 2014

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“…In order to obtain a more treatable analytical solution for such a problem, we compute the non-retarded dispersion force (van der Waals force) between a quantum particle and a perfectly conducting toroid with the quantum particle lying in the symmetry axis of the toroid. Though the perfectly conducting hypothesis and short-distance regime are conflicting assumptions, this choice was made for the following reasons: (i) it will work for molecules whose dominant transition wavelengths allow the existence of a window of distances to the conducting surface that are far enough so that the surface can be considered in a first approximation as perfectly conducting but not too far away so that the retardation effects can be neglected; (ii) we expect that some important features of the interaction, like the attractive/repulsive character of the force will be essentially the same, as it occurs in the atom-plane with a hole system (this can be checked by comparing qualitatively the analytical results obtained in Ref(s) [41][42][43][44] with the exact numerical solution presented in [39]). Indeed, we show that for appropriate values of the two radii of the toroid the dispersive force on the quantum particle is repulsive.…”

Section: Introductionmentioning

confidence: 91%

Repulsive van der Waals interaction between a quantum particle and a conducting toroid

et al. 2018

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We calculate the non-retarded dispersion force exerted on an electrically polarizable quantum particle by a perfectly conducting toroid, which is one of the most common objects exhibiting a nontrivial topology. We employ a convenient method developed by Eberlein and Zietal that essentially relates the quantum problem of calculating dispersion forces between a quantum particle and a perfectly conducting surface of arbitrary shape to a corresponding classical problem of electrostatics.Considering the quantum particle in the symmetry axis of the toroid, we use this method to find an exact analytical result for the van der Waals interaction between the quantum particle and the conducting toroid. Surprisingly, we show that for appropriate values of the two radii of the toroid the dispersive force on the quantum particle is repulsive. This is a remarkable result since repulsion in dispersive interactions involving only electric objects (and particles) in vacuum is rarely reported in the literature. Final comments are made about particular limiting cases as for instance the quantum particle-nanoring system. *

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“…It has been found that the Casimir force does depend on the topology as well as on the peculiar geometry of the boundaries [3,4].…”

Section: Introductionmentioning

confidence: 99%

Casimir energy in Kerr space-time

Sorge¹

2014

Phys. Rev. D

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We investigate the vacuum energy of a scalar massless field confined in a Casimir cavity moving in a circular equatorial orbit in the exact Kerr space-time geometry. We find that both the orbital motion of the cavity and the underlying space-time geometry conspire in lowering the absolute value of the (renormalized) Casimir energy hϵ vac i ren , as measured by a comoving observer, with respect to whom the cavity is at rest. This, in turn, causes a weakening in the attractive force between the Casimir plates. In particular, we show that the vacuum energy density hϵ vac i ren → 0 when the orbital path of the Casimir cavity comes close to the corotating or counter-rotating circular null orbits (possibly geodesic) allowed by the Kerr geometry. Such an effect could be of some astrophysical interest on relevant orbits, such as the Kerr innermost stable circular orbits, being potentially related to particle confinement (as in some interquark models). The present work generalizes previous results obtained by several authors in the weak field approximation.

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Repulsive Casimir and Casimir–Polder forces

Cited by 51 publications

References 92 publications

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Exohedral Physisorption of Ambient Moisture Scales Non-monotonically with Fiber Proximity in Aligned Carbon Nanotube Arrays

Repulsive van der Waals interaction between a quantum particle and a conducting toroid

Casimir energy in Kerr space-time

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