| 1. |
- Cervin, Nicholas, et al.
(författare)
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Lightweight and strong cellulose materials made from aqueous foams stabilized by NanoFibrillated Cellulose (NFC)
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A novel, lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified NanoFibrillated Cellulose (NFC). This material differs from other particle stabilized foams in that we use renewable cellulose as stabilizing particle. Confocal microscopy and high speed video imaging show that the long-term stability of the wet foams can be attributed to the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface which prevent the air bubbles from collapsing or coalescing. This can be achieved at solids content around 1 % by weight. Careful removal of the water results in a cellulose-based material with a porosity of 98 % and a density of 30 mg cm-3. These porous cellulose materials have a higher Young’s modulus than other cellulose materials made by freeze drying and a compressive energy absorption of 56 kJ m-3 at 80 % strain. Measurement with the aid of an autoporosimeter revealed that most pores are in the range of 300 to 500 μm.
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| 2. |
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| 3. |
- Olin, Pontus, et al.
(författare)
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Development of a Semicontinuous Spray Process for the Production of Superhydrophobic Coatings from Supercritical Carbon Dioxide Solutions
- 2015
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 54:3, s. 1059-1067
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Tidskriftsartikel (refereegranskat)abstract
- Superhydrophobic surfaces have been fabricated in a continuous spray process, where an alkyl ketene dimer (AKD) wax is dissolved in supercritical carbon dioxide (scCO(2)) and sprayed onto the substrate. The mass of extracted AKD from scCO2 has been investigated as well as the pressure, temperature, and flow of CO2 at the steady-state spray conditions. Several different substrates such as glass, aluminum, paper, poly(ethylene terephthalate) (PET), and polytetrafluoroethylene (PTFE) have been successfully coated, and the superhydrophobic properties have been evaluated by measurement of water contact angle, water drop friction, scanning electron microscopy (SEM), and surface topography. The most efficient spray process, considering surface properties and mass of extracted AKD, is obtained at the lowest temperature investigated, 67 degrees C, and the highest pressure evaluated in this study, 25 MPa. We also show that the influence of preexpansion conditions (p, T) on the surface temperature at the selected spray distance (3 cm) is negligible by measurement with an infrared camera during spraying.
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| 4. |
- Olin, Pontus, 1979-
(författare)
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Fundamentals of Wetting and Mechanical Durability of Superhydrophobic Coatings
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In paper I the friction between three different superhydrophobic surfaces and water drops were investigated using high‑speed video. The surfaces were two based on a hydrophobic wax and the third was the leaf of a Lotus (Nelumbo Nucifera). The acceleration of water drops was measured as a function of drop size and surface inclination. For small capillary numbers it was shown that the dissipation was dominated by pinning‑depinning transitions along the trailing contact line. A parameter called the superhydrophobic sliding resistance bsh has been introduced. The motion of drops on superhydrophobic surfaces of a general macroscopic topography can be predicted provided that bsh and the drop size are known. This theory also infers the existence of an equilibrium sliding angle, beq, at which the drop acceleration is zero.The effect of line‑shaped defects on the motion of water drops on superhydrophobic surfaces were also investigated using high‑speed video in paper II. It was shown that the motion of the drop in the vicinity of the defect can be approximated by a damped harmonic oscillator. Whether a drop got trapped or not while traversing the defect was determined by the incident speed and the characteristics of the oscillator. In systems with low viscous dissipation it is possible to predict the trapping speed as well as the exit speed using a simple work‑energy consideration.The resistance of wax based superhydrophobic coatings subjected to different types of mechanical damage were investigated in paper III. Scratch tests were performed using atomic force microscopy (AFM) and rubbing with an index finger. Coatings were also subjected to compression with a silicone rubber stamp. The effect of impacting water drops was also investigated. A load of 12 nN was enough to remove the coating from the substrate. The coatings remained superhydrophobic at compression pressures up to 59 kPa but the superhydrophobic properties were lost after only one stroke with a finger. The coatings resisted at least 200 000 impacts of falling water drops without losing their superhydrophobic properties.In paper IV superhydrophobic coatings were fabricated in a semi‑continuous process, where an alkyl ketene dimer (AKD) was dissolved in supercritical carbon dioxide (scCO2) and sprayed onto the substrate. Several different substrates such as: glass, aluminium, paper, poly (ethylene terephthalate) (PET) and poly (tetrafluoroethylene) (PTFE) were successfully coated. The most efficient spray process, considering surface properties and mass of extracted AKD, was obtained at the lowest temperature investigated, 67 °C, and the highest pressure evaluated in this study, 25 MPa. The influence of the pre‑expansion conditions (p, T) on the surface temperature (at a spray distance of 3 cm) was also shown to be negligible.
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| 5. |
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| 6. |
- Olin, Pontus, 1979-, et al.
(författare)
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Trapping of Water Drops by Defects on Superhydrophobic Surfaces
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this work the effect of line‑shaped defects on the motion of water drops on superhydrophobic surfaces have been investigated using high‑speed video. The defects were introduced on superhydrophobic wax surfaces by a simple scratching method. It is shown that the motion of the drop in the vicinity of the defect can be approximated by a damped harmonic oscillator. Whether a drop gets trapped or not while traversing the defect is determined by the incident speed and the characteristics of the oscillator, more specifically by the damping ratio z and the nondimensional forcing constant â. We also show that it is possible to predict the trapping speed as well as the exit speed using a simple work‑energy consideration in systems with negligible viscous dissipation.
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| 7. |
- Olin, Pontus, et al.
(författare)
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Trapping of Water Drops by Line-Shaped Defects on Superhydrophobic Surfaces
- 2015
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:23, s. 6367-6374
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effect of line-shaped topographical defects on the motion of water drops across superhydrophobic wax surfaces using a high-speed video camera. The defects are introduced onto the superhydrophobic wax surfaces by a scratching procedure. It is demonstrated that the motion of a drop interacting with the defect can be approximated by a damped harmonic oscillator. Whether a drop passes or gets trapped by the defect is determined by the incident speed and the properties of the oscillator, specifically by the damping ratio and a nondimensional forcing constant representing the effects of gravity and pinning forces. We also show that it is possible to predict a critical trapping speed as well as an exit speed in systems with negligible viscous dissipation using a simple work energy consideration.
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| 8. |
- Olin, Pontus, et al.
(författare)
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Water Drop Friction on Superhydrophobic Surfaces
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:29, s. 9079-9089
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Tidskriftsartikel (refereegranskat)abstract
- To investigate water drop friction on superhydrophobic surfaces, the motion of water drops on three different superhydrophobic surfaces has been studied by allowing drops to slide down an incline and capturing their motion using high-speed video. Two surfaces were prepared using crystallization of an alkyl ketene dimer (AKD) wax, and the third surface was the leaf of a Lotus (Nelumbo Nucifera). The acceleration of the water droplets on these superhydrophobic surfaces was measured as a function of droplet size and inclination of the surface. For small capillary numbers, we propose that the energy dissipation is dominated by intermittent pinning-depinning transitions at microscopic pinning sites along the trailing contact line of the drop, while at capillary numbers exceeding a critical value, energy dissipation is dominated by circulatory flow in the vicinity of the contacting disc between the droplet and the surface. By combining the results of the droplet acceleration with a theoretical model based on energy dissipation, we have introduced a material-specific coefficient called the superhydrophobic sliding resistance, b(sh). Once determined, this parameter is sufficient for predicting the motion of water drops on superhydrophobic surfaces of a general macroscopic topography. This theory also infers the existence of an equilibrium sliding angle, beta(eq), at which the drop acceleration is zero. This angle is decreasing with the radius of the drop and is in quantitative agreement with the measured tilt angles required for a stationary drop to start sliding down an incline.
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| 9. |
- Ovaskainen, Louise, et al.
(författare)
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The effect of different wear on superhydrophobic wax coatings
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 32:2, s. 195-203
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Tidskriftsartikel (refereegranskat)abstract
- Wear resistance of superhydrophobic coatings made by spraying a crystallizing wax from supercritical carbon dioxide solutions was evaluated using several methods. Scratch tests were performed using a tip in contact with the surface using atomic force microscope (AFM). Compression tests were performed by applying different loads on a rubber stamp placed on the surface. Frictional wear was evaluated by stroking an index finger over the surfaces while measuring applied load and friction. The wetting properties of the coatings were subsequently evaluated as advancing and receding water contact angles, superhydrophobic sliding resistance according to a recently developed method and surface roughness, coating morphology was studied using scanning electron microscopy and optical profilometry. Scratching with tip of an AFM cantilever with a force of 12 nN removed major fraction of the wax coating from underlying silica substrate whereas subjecting the surfaces to a compressive load up to 59 kPa did not significantly influence the superhydrophobicity of the coatings. Frictional wear measurements indicate that superhydrophobic properties were immediately lost after pressing and moving a finger over the coating, as movement of the finger destroyed the fine surface structure. Nevertheless, the surfaces could withstand up to 200000 falling water drops without losing their superhydrophobicity. © 2017 De Gruyter Open Ltd. All rights reserved.
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