| 1. |
- Heydari, Golrokh, et al.
(författare)
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Wetting hysteresis induced by temperature changes : supercooled water onhydrophobic surfaces
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The state and stability of supercooled water on (super)hydrophobic surfaces is crucial for low temperature applications and for obtaining anti-icing and de-icing properties. Surface characteristics such as topography and chemistry are expected to affect wetting hysteresis during temperature cycling experiments, and also the freezing delay of supercooled water. We utilized stochastically rough wood surfaces that were further modified to render them hydrophobic or superhydrophobic. Liquid flame spraying (LFS) was utilized to create a multi-scale roughness by depositing titaniumdioxide nanoparticles. The coating was subsequently made non-polar by applying a thin plasma polymer layer. As flat reference samples modified silica surfaces with similar chemistries were utilized. With these sets of surfaces we test the hypothesis that superhydrophobic surfaces also should retard ice formation. Wetting hysteresis was evaluated using contact angle measurements during a freeze-thaw cycle from room temperature to freezing occurrence at -7 °C, and then back to room temperature. Further, the delay in freezing of supercooled water droplets was studied at temperatures of -4 °C and -7 °C. The hysteresis in contact angle observed during a cooling-heating cycle is found to be small on flat hydrophobic surfaces. However, significant changes in contact angles during a cooling-heating cycle are observed on the rough surfaces, with a higher contact angle observed on cooling compared to during the subsequent heating. This hysteresis is lower for hydrophobic wood samples with multi-scale roughness compared to those with predominantly micro-scale features. Condensation and subsequent frost formation at sub-zero temperatures induce the hysteresis. The freezing delay data suggests that the multi-scale roughness reduces the penetration of supercooled water into surface depressions, and enhances the freezing delay at low degrees of supercooling. However, the flat surface is even more efficient in enhancing the freezing delay than the rougher surfaces, which can be rationalized considering heterogeneous nucleation theory. Thus, our data suggests that molecular flat surfaces, rather than rough superhydrophobic surfaces, are beneficial for retarding ice formation under conditions that allow condensation and frost formation to occur.
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| 2. |
- Sedighi Moghaddam, Maziar, 1981-, et al.
(författare)
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Microstructure of chemically modified wood using X-ray computedtomography scanning in relation to wetting properties
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- X-ray computed tomography was utilized to visualize and quantify the 2D and 3D microstructure of acetylated and furfurylated southern yellow pine (SYP) and maple samples. The total porosity and the porosity of different anatomical components, the cell wall thickness and the maximum opening of tracheid lumens were evaluated. The wetting properties (swelling and capillary uptake) were related to these microstructural characteristics. Our data show significant changes in the wood structure for furfurylated sapwood samples, including a change in tracheid shape and filling of tracheids by furan polymer. In contrast, no such changes were noted for acetylated samples at the resolution of the measurement (0.8 μm). The images obtained for furfurylated maple samples demonstrated that all ray cells and some vessel elements were filled with furan polymer while the fibres largely remained unchanged. Furfurylation significantly decreased the porosity of the sample, and this was observed in both earlywood and latewood regions in southern yellow pine softwood samples. In contrast, the total porosity of this softwood sample was hardly affected by acetylation. These findings are in line with wetting results demonstrating that furfurylation reduces both swelling and capillary uptake in contrast to acetylation which reduces mostly swelling. Cell wall thickness measurements revealed a significant increase after chemical modification especially at higher levels of furfurylation.
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| 3. |
- Sedighi Moghaddam, Maziar, 1981-, et al.
(författare)
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Wettability and swelling of acetylated and furfurylated wood analyzed by multicycle Wilhelmy plate method
- 2016
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Ingår i: Holzforschung. - : De Gruyter. - 0018-3830 .- 1437-434X. ; 70:1, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- The wetting, dimensional stability and sorption properties of a range of modified wood samples obtained either by acetylation or furfurylation were compared with those of unmodified samples of the same wood species via a multicycle Wilhelmy plate method. Wettability measurements were performed with water and octane as the swelling and non-swelling liquids, respectively. It was found that acetylation reduces water uptake mainly by reducing the swelling. In comparison, furfurylation reduces both swelling and the void volume in the sample. To quantify the effect of the modification process of the wood properties, the parameters “liquid up-take reduction” and the “perimeter change reduction” were introduced, which were determined from multicycle Wilhelmy plate measurements. Compared with the acetylated wood, the furfurylated wood with a higher level of weight percent gain exhibited larger property changes on the surface and in terms of swelling and sorption properties.
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| 4. |
- Sedighi Moghaddam, Maziar, 1981-
(författare)
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Wettability of modified wood
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite many excellent properties of wood which make it suitable for many applications, it suffers from a number of disadvantages limiting its use. For instance, modification is needed to reduce water sorption and to improve decay resistance, dimensional stability and weathering performance. In addition, wood/liquid interaction such as water wettability on wood plays an important role in design and characteristics of many processes and phenomena such as adhesion, coating, waterproofing, wood chemical modification, and weathering. This thesis focuses on enhancing the understanding of wetting of wood, with emphasis on modified wood. The influence of surface chemical composition of wood and its microstructural characteristics on wetting and swelling properties has also been studied.A multicycle Wilhelmy plate technique has been developed to evaluate wetting properties of porous materials, such as wood, in which the samples were subjected to repeated immersions and withdrawals in a swelling liquid (water) and in a non-swelling liquid (octane). This method was utilized to dynamically investigate contact angle, sorption and swelling properties, as well as dimensional stability of unmodified, chemically and surface modified wood samples. Scots pine sapwood and heartwood samples were utilized to establish the principles of the technique. Acetylated and furfurylated wood samples with different level of modification were thereafter examined utilizing the developed technique for wetting measurements. A perimeter model based on a linear combination of the measured force and final change in sample perimeter was suggested to evaluate the dynamic dimensional stability of wood veneers. The feasibility of this method for studying dynamic wettability was investigated by measuring the changes of advancing and receding contact angles over repeated cycles on surface modified wood samples, created by combining liquid flame spray and plasma polymerisation methods. X-ray photoelectron spectroscopy (XPS) and X-ray computed tomography (XCT) were employed to study the surface chemical composition and microstructural properties of the samples, respectively.Three different kinetic regimes were observed in the wetting measurements: i) fast wetting and spreading of the liquid on the wood surface, ii) void filling and wicking and iii) swelling, which was the slowest of the three. The multicycle Wilhelmy plate method was found to be suitable for studying liquid penetration, sorption, and dimensional stability of swelling materials. The results demonstrate that the wetting properties of wood are highly affected by surface chemistry and microstructure. It was shown that using both swelling and non-swelling liquids in wetting measurements allow to distinguish between capillary liquid uptake and swelling. Based on this, for chemically modified samples, it was demonstrated that acetylation mostly reduces swelling, while furfurylation reduces both swelling and capillary uptake. This is in line with the microstructural study with X-ray computed tomography where a significant change in the porosity was found as a result of furfurylation, conversely acetylation left the total porosity values unchanged. Wetting results for hydrophobised wood samples demonstrate that the multi-scale roughness obtained by combination of nanoparticle coating and plasma polymerization increased both the hydrophobicity and the forced wetting durability compared to the micro-scale roughness found on wood modified with plasma polymerisation alone.
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| 5. |
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| 6. |
- Yin, Haiyan, et al.
(författare)
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Non-fluorine surface modification of acetylated birch for improved water repellence
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this work, a non-fluorinatedsurface treatment, i.e.,hydrophobized silicone nanofilaments,wasapplied onboth birchandacetylatedbirchwoodsamplesviaa gas-phase based reaction.A superhydrophobic behavior was observedon both the surface-modified samplesas revealed by thestatic water contact angles greater than 160°, also valid for samples prepared withthe shortestreaction timeof 1 h. The dynamic wettability behavior of the samples was studied by a multicycle Wilhelmy plate method.The surface-modified acetylatedbirchexhibited a pronounced enhancedwater resistance,resultingin very low water uptake of 3 ±1 wt% after 100 cycles,which was about 29, 5 and 3 times lower than that of the birch, acetylated birch and surface-modified birch, respectively.Moreover,the aesthetic appearance of the acetylated wood was maintained asthe surfacemodification only resulted in a small color change.This work shows the potential of preparing superwater-repellent wood by non-fluorinated surface modification
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| 7. |
- Yin, Haiyan, et al.
(författare)
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Susceptibility of surface-modified superhydrophobic wood and acetylated wood to mold and blue stain fungi
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The susceptibility of surface-modified wood, surface-modified acetylated wood and acetylated wood to mold and blue stain fungi was investigated. The surface modifications were based on fluorinated and non-fluorinated silicone nanofilaments for increased hydrophobicity. Results showed an increased mold resistance of the surface-modified superhydrophobic wood with mold appearing later or with less intensity on the modified surfaces than on the untreated wood in accelerated mold chamber tests due to the increased water resistance of the samples. All acetylated wood samples exhibited good mold resistance as the available water in acetylated wood was reduced. The surface modifications on acetylated wood had a slightly negative effect on mold resistance due to side effects from the modification. The surface-modified wood showed high blue stain fungi coverage, whereas almost no blue stain fungi were observed on the acetylated wood and surface-modified acetylated wood. The surface-modified superhydrophobic wood showed high mold coverage after conditioning in a high-humidity environment or after exposure to UV irradiation. Meanwhile, the acetylated wood and surface-modified superhydrophobic acetylated wood showed a small amount of mold coverage in these conditions.
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