| 1. |
- Apostolopoulou-Kalkavoura, Varvara, 1988-, et al.
(författare)
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Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams
- 2021
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Ingår i: Matter. - : Elsevier BV. - 2590-2393 .- 2590-2385. ; 4:1, s. 276-289
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.
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| 2. |
- Carlborg, Carl Fredrik, et al.
(författare)
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Thermal boundary resistance between single-walled carbon nanotubes and surrounding matrices
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:20, s. 205406-
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Tidskriftsartikel (refereegranskat)abstract
- Thermal boundary resistance (TBR) between a single-walled carbon nanotube (SWNT) and matrices of solid and liquid argon was investigated by performing classical molecular-dynamics simulations. Thermal boundary conductance (TBC), i.e., inverse of TBR, was quantified for a range of nanotube lengths by applying a picosecond heat pulse to the SWNT and observing the relaxation. The SWNT-length effect on the TBC was confirmed to be absent for SWNT lengths from 20 to 500 A. The heat transfer mechanism was studied in detail and phonon spectrum analysis provided evidence that the resonant coupling between the low-frequency modes of the SWNT and the argon matrix is present both in solid and liquid argon cases. The heat transfer mechanism was qualitatively analyzed by calculating the spectral temperature of the SWNT in different frequency regimes. It was found that the low-frequency modes that are resonantly coupled to the argon matrix relaxes roughly ten times faster than the overall TBC time scale, depending on the surrounding matrix. However, such resonant coupling was found to transfer little energy despite a popular picture of the linear transfer path. The analysis suggests that intrananotube energy transfer from high-frequency modes to low-frequency ones is slower than the interfacial heat transfer to the argon matrix.
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| 3. |
- Do-Quang, Minh, et al.
(författare)
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When and how surface structure determines the dynamics of partial wetting
- 2015
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 110:4
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Tidskriftsartikel (refereegranskat)abstract
- The motion of a three phase contact line, as in a droplet spreading over a dry surface, is ubiquitous in nature and common in technology, but is still not well understood. As has been recently shown, line friction may play an important role in rapid dynamic wetting. Recognizing this as a sometimes dominating factor, we identify the possible scenarios for dynamic wetting of a partially wetting fluid, given the fluid and substrate properties. In doing so, we also reconcile the seemingly different interpretations of dynamic wetting that have been put forward in the recent literature. Copyright (C) EPLA, 2015
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| 4. |
- Lee, Yaerim, et al.
(författare)
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Revealing How Topography of Surface Microstructures Alters Capillary Spreading
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Wetting phenomena, i.e. the spreading of a liquid over a dry solid surface, are important for understanding how plants and insects imbibe water and moisture and for miniaturization in chemistry and biotechnology, among other examples. They pose fundamental challenges and possibilities, especially in dynamic situations. The surface chemistry and micro-scale roughness may determine the macroscopic spreading flow. The question here is how dynamic wetting depends on the topography of the substrate, i.e. the actual geometry of the roughness elements. To this end, we have formulated a toy model that accounts for the roughness shape, which is tested against a series of spreading experiments made on asymmetric sawtooth surface structures. The spreading speed in different directions relative to the surface pattern is found to be well described by the toy model. The toy model also shows the mechanism by which the shape of the roughness together with the line friction determines the observed slowing down of the spreading.
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| 5. |
- Lee, Yaerim, et al.
(författare)
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Vibration sorting of small droplets on hydrophilic surface by asymmetric contact-line friction
- 2022
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Ingår i: PNAS Nexus. - : National Academy of Sciences. - 2752-6542. ; 1:2
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Tidskriftsartikel (refereegranskat)abstract
- Droplet spreading and transport phenomenon is ubiquitous and has been studied by engineered surfaces with a variety of topographic features. To obtain a directional bias in dynamic wetting, hydrophobic surfaces with a geometrical asymmetry are generally used, attributing the directionality to one-sided pinning. Although the pinning may be useful for directional wetting, it usually limits the droplet mobility, especially for small volumes and over wettable surfaces. Here, we demonstrate a pinning-less approach to rapidly transport millimeter sized droplets on a partially wetting surface. Placing droplets on an asymmetrically structured surfaces with micron-scale roughness and applying symmetric horizontal vibration, they travel rapidly in one direction without pinning. The key, here, is to generate capillary-driven rapid contact-line motion within the time-scale of period of vibration. At the right regime where a friction factor local at the contact line dominates the rapid capillary motion, the asymmetric surface geometry can induce smooth and continuous contact-line movement back and forth at different speed, realizing directional motion of droplets even with small volumes over the wettable surface. We found that the translational speed is selective and strongly dependent on the droplet volume, oscillation frequency, and surface pattern properties, and thus droplets with a specific volume can be efficiently sorted out.
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| 6. |
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| 7. |
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| 8. |
- Lin, Yuan, et al.
(författare)
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Dielectric relaxation of water inside a single-walled carbon nanotube
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:4
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Tidskriftsartikel (refereegranskat)abstract
- We report a molecular dynamics study of anisotropic dynamics and dielectric properties of water confined inside a single-walled carbon nanotube (SWNT) at room temperature. The model includes dynamics of an SWNT described by a realistic potential function. A comparison with simulations assuming a rigid nanotube demonstrates that the popular assumption severely overestimates the dielectric constant for small diameter SWNTs. Simulations of water inside flexible SWNTs with various diameters reveal strong directional dependence of the dynamic and dielectric properties due to the confinement effect. The obtained dielectric permittivity spectra (DPS) identify two different dipolar relaxation frequencies corresponding to the axial and the cross-sectional directions, which are significantly smaller and larger than the single relaxation frequency of bulk water, respectively. The frequency variation increases as the SWNT diameter decreases. The results suggest that DPS can be used as a fingerprint of water inside SWNTs to monitor the water intrusion into SWNTs.
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| 9. |
- Lin, Yuan, et al.
(författare)
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Electrothermal flow in dielectrophoresis of single-walled carbon nanotubes
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:4, s. 045419-1-045419-5
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically investigate the impact of the electrothermal flow on the dielectrophoretic separation of single-walled carbon nanotubes (SWNTs). The electrothermal flow is observed to control the motions of semiconducting SWNTs in a sizable domain near the electrodes under typical experimental conditions, therefore helping the dielectrophoretic force to attract semiconducting SWNTs in a broader range. Moreover, with the increase of the surfactant concentration, the electrothermal flow effect is enhanced, and with the change of frequency, the pattern of the electrothermal flow changes. It is shown that under some typical experimental conditions of dielectrophoretic separation of SWNTs, the electrothermal flow is a dominating factor in determining the motion of SWNTs.
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| 10. |
- Lin, Yuan, et al.
(författare)
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Numerical calculation of the dielectrophoretic force on a slender body
- 2009
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 30:5, s. 831-838
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a model is proposed to numerically calculate the dielectrophoretic (DEP) force acting on a straight slender body in a non-uniform electric field. The induced charges are assumed to be located along the centerline of the slender body. By enforcing the boundary conditions at the interfaces of the two dielectrics, an integral equations system is obtained with the induced charge densities as unknowns. Based on the calculated induced charge densities, expressions to calculate the DEP force and torque are obtained. The calculated induced charge density of a prolate ellipsoid under a uniform electric field is compared with the analytic solution and an excellent agreement is achieved. The smaller the slenderness (the ratio of maximum radius to length of the slender body), the smaller the error is. The DEP force that a prolate ellipsoid experiences in a general electric field is numerically calculated and compared with the results obtained by the commonly accepted effective dipole moment method. The current model is expected to possess higher accuracy than the effective dipole moment method and to demand less calculation work than the Maxwell stress tensor method.
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