| 1. |
- Abitbol, Tiffany, et al.
(författare)
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Nanocellulose-Based Hybrid Materials for UV Blocking and Mechanically Robust Barriers
- 2020
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Ingår i: ACS Applied Bio Materials. - : American Chemical Society (ACS). - 2576-6422. ; 3:4, s. 2245-2254
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Tidskriftsartikel (refereegranskat)abstract
- Nanocellulose (NC)-based hybrid coatings and films containing CeO2 and SiO2 nanoparticles (NPs) to impart UV screening and hardness properties, respectively, were prepared by solvent casting. The NC film-forming component (75 wt % of the overall solids) was composed entirely of cellulose nanocrystals (CNCs) or of CNCs combined with cellulose nanofibrils (CNFs). Zeta potential measurements indicated that the four NP types (CNC, CNF, CeO2, and SiO2) were stably dispersed in water and negatively charged at pH values between 6 and 9. The combination of NPs within this pH range ensured uniform formulations and homogeneous coatings and films, which blocked UV light, the extent of which depended on film thickness and CeO2 NP content, while maintaining good transparency in the visible spectrum (∼80%). The addition of a low amount of CNFs (1%) reduced the film hardness, but this effect was compensated by the addition of SiO2 NPs. Chiral nematic self-assembly was observed in the mixed NC film; however, this ordering was disrupted by the addition of the oxide NPs. The roughness of the hybrid coatings was reduced by the inclusion of oxide NPs into the NC matrix perhaps because the spherical oxide NPs were able to pack into the spaces between cellulose fibrils. We envision these hybrid coatings and films in barrier applications, photovoltaics, cosmetic formulations, such as sunscreens, and for the care and maintenance of wood and glass surfaces, or other surfaces that require a smooth, hard, and transparent finish and protection from UV damage.
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| 2. |
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| 3. |
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| 4. |
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| 5. |
- Brandner, Birgit D., et al.
(författare)
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Solvent segregation and capillary evaporation at a superhydrophobic surface investigated by confocal Raman microscopy and force measurements
- 2011
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Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 7:3, s. 1045-1052
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Tidskriftsartikel (refereegranskat)abstract
- Wetting of water, a 1 : 1 water/ethanol mixture and an aqueous dodecylbenzene sulfonic acid surfactant solution on hydrophobic and superhydrophobic surfaces were studied using confocal Raman microscopy. The superhydrophobic surfaces were prepared by immersion of a glass substrate in a silica particle/fluoropolymer formulation followed by silanization. Preparation of hydrophobic surfaces was done in the same way with the exception that the silica particles were excluded from the formulation. The hydrophobic and superhydrophobic surfaces were characterized with respect to surface roughness using AFM, and by contact angle measurements using different liquids. Confocal Raman microscopy measurements in a 1 : 1 water/ethanol mixture showed an enrichment of ethanol close to the superhydrophobic surface, which could not be observed for the hydrophobic surface. Unexpectedly, the Raman spectrum of a pure water film in close proximity to the superhydrophobic surface displayed some differences compared to that of bulk water and indicated a stronger hydrogen-bonding close to the superhydrophobic surface. Evidence for capillary evaporation next to the superhydrophobic surface was also found, and this results in very long-range capillary attraction between one superhydrophobic surface and a hydrophobic colloidal probe as shown by AFM colloidal probe force measurements. Addition of a surfactant or ethanol suppresses capillary evaporation.
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| 6. |
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| 7. |
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| 8. |
- Charlène, Reverdy, et al.
(författare)
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Superhydrophobic surfaces manufacturing with nanocellulose
- 2016
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Ingår i: N.I.C.E. 2016 - The 3rd International Conference on Bioinspired and Biobased Chemistry & Materials.
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Konferensbidrag (refereegranskat)abstract
- Researchers in natural fibers see opportunities in superhydrophobicity for fabrics or paper. The first challenge with natural fiber is their high hydrophilicity when the second is the perpetual search for water born coating in papermaking. These challenges were overcome by a one pot formulation comprising a latex binder, precipitated calcium carbonate and fatty acids to give their hydrophobicity to pigments 1. In this study, we want to go further by replacing the petro-sourced latex with a new kind of fibers that are cellulose nanofibers (CNF).Inspired by the Lotus leaf, superhydrophobic surfaces have been a center of interest in the last decade because of their high potential in industry for a variety of applications. It is seen as the next generation of surface for anti-fouling and corrosive retardant in navy industry but also in general anti corrosive materials industry. Now widely studied , mechanisms for manufacturing superhydrophobicity are well understood. Born from the alliance of low surface energy chemistry and physical structuration of surface, superhydrophobic materials give a water contact angle above 150° and a slidding angle below 10°.
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| 9. |
- Chernyy, Sergey, et al.
(författare)
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Superhydrophilic Polyelectrolyte Brush Layers with Imparted Anti-Icing Properties : Effect of Counter ions
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:9, s. 6487-6496
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates the feasibility of superhydrophilic polyelectrolyte brush coatings for anti-icing applications. Five different types of ionic and nonionic polymer brush coatings of 25-100 nm thickness were formed on glass substrates using silane chemistry for surface premodification followed by polymerization via the SI-ATRP route. The cationic [2-(methacryloyloxy)ethyl]trimethylammonium chloride] and the anionic [poly(3-sulfopropyl methacrylate), poly(sodium methacrylate)] polyelectrolyte brushes were further exchanged with H+, Li+, Na+, K+, Ag+, Ca2+, La3+, C16N+, F-, Cl-, BF4-, SO42-, and C12SO3- ions. By consecutive measurements of the strength of ice adhesion toward ion-incorporated polymer brushes on glass it was found that Li+ ions reduce ice adhesion by 40% at 18 degrees C and 70% at 10 degrees C. Ag+ ions reduce ice adhesion by 80% at -10 degrees C relative to unmodified glass. In general, superhydrophilic polyelectrolyte brushes exhibit better anti-icing property at -10 degrees C compared to partially hydrophobic brushes such as poly(methyl methacrylate) and surfactant exchanged polyelectrolyte brushes. The data are interpreted using the concept of a quasi liquid layer (QLL) that is enhanced in the presence of highly hydrated ions at the interface. It is suggested that the ability of ions to coordinate water is directly related to the efficiency of a given anti-icing coating based on the polyelectrolyte brush concept.
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| 10. |
- Ejenstam, Lina, 1985-, et al.
(författare)
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Corrosion protection by hydrophobic silica particle-polydimethylsiloxane composite coatings
- 2015
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Ingår i: Corrosion Science. - : Elsevier. - 0010-938X .- 1879-0496. ; 99, s. 89-97
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the time-dependent corrosion protection ability of 10-15. μm thin polydimethylsiloxane-nanoparticle composite coatings was evaluated using mainly open circuit potential and electrochemical impedance spectroscopy measurements. The best result was obtained for the coating containing 20. wt% hydrophobic silica nanoparticles, where it was possible to achieve protection for almost 80 days in 3. wt% NaCl solution. The protective properties offered by this coating are suggested to be due to a synergistic effect of the hydrophobicity of the polydimethylsiloxane matrix and the prolonged diffusion path caused by addition of hydrophobic silica particles.
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| 11. |
- Ejenstam, Lina, 1985-
(författare)
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Hydrophobic and superhydrophobic coatings for corrosion protection of steel
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since metals in general, and steels in particular, are vital construction materials in our modern society, the corrosion protection of said materials is of great importance, both to ensure safety and to reduce costs associated to corrosion. Previously, chromium (VI) and other harmful substances were effectively used to provide corrosion protection to steel, but since their use was heavily regulated around year 2000, no coating has yet been developed that, in a fully satisfactory manner, replaces their corrosion protective properties.In this thesis, the use of hydrophobic and superhydrophobic surface coatings as part of corrosion protective coating systems has been studied. Since the corrosion mechanism relies on the presence of water to take place, the use of a superhydrophobic coating to retard the penetration of water to an underlying metal surface is intuitive. The evaluation of corrosion protective properties of the hydrophobic and superhydrophobic surfaces was performed using mainly contact angle measurements and electrochemical measurements in severely corrosive 3 wt% NaCl water solution.First, the differences in corrosion protection achieved when employing different hydrophobic wetting states were investigated using a model alkyl ketene dimer wax system. It was found that superhydrophobicity in the Lotus state is superior to the other states, when considering fairly short immersion times of less than ten days. This is due to the continuous air film that can form between such a superhydrophobic surface and the electrolyte, which can retard the transport of electrolyte containing corrosive ions to the metal surface to the point where the electrical circuit is broken. Since corrosion cannot occur unless an electrical current is flowing, this is a very efficient way of suppressing corrosion.An air layer on an immersed superhydrophobic surface is, however, not stable over long time, and to investigate long-term corrosion protection using hydrophobic coatings a polydimethylsiloxane formulation containing hydrophobic silica nanoparticles was developed. This system showed enhancement in corrosion protective properties with increasing particles loads, up until the point where the particle load instead causes the coating to crack (at 40 wt%). The conclusion is that the hydrophobicity of the matrix and filler, in combination with the elongatedivdiffusion path supplied by the addition of particles, enhanced the corrosion protection of the underlying substrate.To further understand how hydrophobicity and particle addition affect the corrosion protective properties of a coating a three layer composite coating system was developed. Using this coating system, consisting of a polyester acrylate base coating, covered by TiO2 particles (with diameter < 100 nm) and finally coated with a thin hexamethyl disiloxane coating, it was found that both hydrophobicity and particles are needed to reach a great enhancement in corrosion protective properties also for this system.
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| 12. |
- Ejenstam, Lina, 1985-, et al.
(författare)
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Long-term corrosion protection by a thin nano-composite coating
- 2015
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Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 357:Part B, s. 2333-2342
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Tidskriftsartikel (refereegranskat)abstract
- We report and discuss the corrosion protective properties of a thin nano-composite coating system consisting of an 11μm thick polyester acrylate (PEA) basecoat, covered by an approximately 1-2μm thick layer of TiO2 nanoparticles carrying a 0.05μm thick hexamethyl disiloxane (HMDSO) top coat. The corrosion protective properties were evaluated on carbon steel substrates immersed in 3wt% NaCl solution by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The protective properties of each layer, and of each pair of layers, were also evaluated to gain further understanding of the long-term protective properties offered by the nano-composite coating. The full coating system showed excellent corrosion protective properties in the corrosive environment of 3wt% NaCl-solution for an extended period of 100 days, during which the coating impedance, at the lower frequency limit (0.01Hz), remained above 108 Ωcm2. We suggest that the excellent corrosion protective properties of the complete coating system is due to a combination of (i) good adhesion and stability of the PEA basecoat, (ii) the surface roughness and the elongated diffusion path provided by the addition of TiO2 nanoparticles, and (iii) the low surface energy provided by the HMDSO top coat.
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| 13. |
- Ejenstam, Lina, et al.
(författare)
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The effect of superhydrophobic wetting state on corrosion protection : The AKD example
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 412, s. 56-64
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion is of considerable concern whenever metal is used as construction material. In this study we address whether superhydrophobic coatings could be used as part of an environmentally friendly corrosion-protective system, and specific focus is put on how the wetting regime of a superhydrophobic coating affects corrosion inhibition. Superhydrophobic alkyl ketene dimer (AKD) wax coatings were produced, using different methods resulting in hierarchical structures, where the coatings exhibit the same surface chemistry but different wetting regimes. Contact angle measurements, ESEM, confocal Raman microscopy, open circuit potential and electrochemical impedance spectroscopy were used to evaluate the surfaces. Remarkably high impedance values of 1010Ωcm2 (at 10-2Hz) were reached for the sample showing superhydrophobic lotus-like wetting. Simultaneous open circuit potential measurements suggest that the circuit is broken, most likely due to the formation of a thin air layer at the coating-water interface that inhibits ion transport from the electrolyte to the metal substrate. The remaining samples, showing superhydrophobic wetting in the rose state and hydrophobic Wenzel-like wetting, showed less promising corrosion-protective properties. Due to the absence of air films on these surfaces the coatings were penetrated by the electrolyte, which allowed the corrosion reaction to proceed.
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| 14. |
- Ejenstam, Lina, 1985-, et al.
(författare)
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Towards superhydrophobic polydimethylsiloxane-silica particle coatings
- 2016
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Ingår i: Journal of Dispersion Science and Technology. - : Taylor & Francis. - 0193-2691 .- 1532-2351. ; 37:9, s. 1375-1383
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Tidskriftsartikel (refereegranskat)abstract
- Hydrophobized silica nanoparticles of different sizes, from 16 to 500 nm, were used to impart roughness to a hydrophobic polydimethylsiloxane (PDMS) coating with the aim of obtaining superhydrophobic properties. The particle silanization process and the curing process of the PDMS coating were optimized to increase the contact angle of the particle containing coating. The evaluation of the coatings, by means of water contact angle measurements and scanning electron microscopy imaging, show that superhydrophobicity in the adhesive rose state was achieved using combinations of two differently sized particles, with an excess of the small 16 nm ones. Superhydrophobicity in the Lotus state was obtained when the filler concentration of 16 nm particles was 40 wt%, but under such conditions the coating was found to partially crack, which is detrimental in barrier applications. The preference for the rose wetting state can be explained by the round shape of the particles, which promotes the superhydrophobic rose wetting state over that of the superhydrophobic Lotus state.
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| 15. |
- Eriksson, Mimmi, et al.
(författare)
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Direct Observation of Gas Meniscus Formation on a Superhydrophobic Surface
- 2019
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 13:2, s. 2246-2252
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Tidskriftsartikel (refereegranskat)abstract
- The formation of a bridging gas meniscus via cavitation or nanobubbles is considered the most likely origin of the submicrometer long-range attractive forces measured between hydrophobic surfaces in aqueous solution. However, the dynamics of the formation and evolution of the gas meniscus is still under debate, in particular, in the presence of a thin air layer on a superhydrophobic surface. On superhydrophobic surfaces the range can even exceed 10 μm. Here, we report microscopic images of the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. This is achieved by combining laser scanning confocal microscopy and colloidal probe atomic force microscopy. The configuration allows determination of the volume and shape of the meniscus, together with direct calculation of the Young-Laplace capillary pressure. The long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.
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| 16. |
- Eriksson, Mimmi, et al.
(författare)
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Effects of Gas Layer Thickness on Capillary Interactions at Superhydrophobic Surfaces
- 2024
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 40:9, s. 4801-4810
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Tidskriftsartikel (refereegranskat)abstract
- Strongly attractive forces act between superhydrophobic surfaces across water due to the formation of a bridging gas capillary. Upon separation, the attraction can range up to tens of micrometers as the gas capillary grows, while gas molecules accumulate in the capillary. We argue that most of these molecules come from the pre-existing gaseous layer found at and within the superhydrophobic coating. In this study, we investigate how the capillary size and the resulting capillary forces are affected by the thickness of the gaseous layer. To this end, we prepared superhydrophobic coatings with different thicknesses by utilizing different numbers of coating cycles of a liquid flame spraying technique. Laser scanning confocal microscopy confirmed an increase in gas layer thickness with an increasing number of coating cycles. Force measurements between such coatings and a hydrophobic colloidal probe revealed attractive forces caused by bridging gas capillaries, and both the capillary size and the range of attraction increased with increasing thickness of the pre-existing gas layer. Hence, our data suggest that the amount of available gas at and in the superhydrophobic coating determines the force range and capillary growth.
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| 17. |
- Eriksson, Mimmi, et al.
(författare)
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Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m−1), ethylene glycol (48 mN m−1) and hexadecane (27 mN m−1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient.
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| 18. |
- Eriksson, Mimmi, et al.
(författare)
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Forces at superhydrophobic and superamphiphobic surfaces
- 2020
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier Ltd. - 1359-0294 .- 1879-0399. ; 47, s. 46-57
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Tidskriftsartikel (refereegranskat)abstract
- Forces exerted at surfaces and interphases due to formation of gaseous (air or vapor) bridges describe the extreme liquid repellence in superhydrophobicity (SH) and amphiphobicity. The neighboring research areas of liquid capillary bridges and that of interactions between hydrophobic surfaces are highly valuable reference systems. We review recent findings with particular focus on the three-phase contact line and surface forces. Although macroscopic contact angles (>150°), low contact angle hysteresis (<10°, but can be high; parahydrophobic or petal type) and low roll-off angle (≤5–10°) are adequate criteria for SH and superamphiphobicity (SA) for most studies, a detailed understanding requires a view related to mechanisms. Experimental studies of liquid drop–substrate and particle–substrate adhesion in hydrophobic, SH, and SA systems are summarized by relating measured forces to the wetting tension, γcosθ. A low wetting tension value is a necessary but not sufficient criterion for SH and SA systems. The picture emerging from detailed force distance studies is that extreme liquid repellence in SH and SA systems is a progression of liquid repellence due to hydrophobicity, in which force curves can be explained by capillary forces of constant volume of the gaseous capillary. In SH and SA, neither the capillary force equation assuming constant volume nor constant pressure of the gaseous capillary explains experimental force measurements as the capillary increases in both volume and pressure. In recent experimental studies, a transition is observed into nonconstant volume and pressure which suggests an SH and SA wetting transition from constant volume or pressure to a capillary growth as driven by the γA and the PV works but also by forces at the three-phase contact SLV (solid-liquid-vapor) line, viz. pinning forces, Fpin and Fdepin, and line energy, (τL)SLV, terms. Supported by calculations of the different contributions, we suggest this transition being an appropriate definition for the onset of (appreciable) SH and SA. © 2019 The Author(s)
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| 19. |
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| 20. |
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| 21. |
- Eriksson, Mimmi, 1986-
(författare)
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Super liquid-repellent surfaces - interactions and gas capillaries
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Super liquid-repellent surfaces have attracted a lot of interest in recent years. In addition to the large scientific interest there are many potential technological applications ranging from self-cleaning materials to microfluidic devices. In this thesis, interactions between liquid-repellent surfaces in liquids were studied, with the aim to investigate the detailed mechanisms of super liquid-repellence, such as superhydrophobicity and superamphiphobicity. An atomic force microscope (AFM) was used to measure the interaction forces between super liquid-repellent surfaces and a microsphere in different liquids. Additionally, a setup combining AFM with laser scanning confocal microscopy (LSCM) was used, which enabled simultaneous imaging in order to capture the microscopic events between the sphere and the surface during a force measurement. The confocal images successfully visualized how the strongly attractive forces measured between liquid-repellent surfaces are due to the formation of a gaseous capillary bridge between the two surfaces. Similar long-ranged forces with capillary formation and growth were observed both in water and in lower surface tension liquids. Additionally, the confocal images enabled determination of the capillary shape and volume, and the data showed an increase of the capillary volume during the major part of the process of separating the surfaces. A gaseous layer underneath the liquid at super liquid-repellent surfaces was also visualized with LSCM, and it was concluded that this gaseous layer is responsible for the formation and growth of large gas capillaries. It was found that an increased amount of available gas in the gaseous layer influenced the interactions and allowed the capillary to grow larger during separation. Further, theoretical calculations based on the size and shape of the capillary suggested that a small under pressure in the capillary drives the gas to flow from the gaseous surface layer into the capillary, facilitating growth during separation.
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| 22. |
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| 23. |
- Eriksson, Mimmi, et al.
(författare)
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Wetting Transition on Liquid-Repellent Surfaces Probed by Surface Force Measurements and Confocal Imaging
- 2019
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Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 35:41, s. 13275-13285
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Tidskriftsartikel (refereegranskat)abstract
- Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.
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| 24. |
- Fuaad, P. A., et al.
(författare)
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Simulation of slot-coating of nanocellulosic material subject to a wall-stress dependent slip-velocity at die-walls
- 2022
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Ingår i: JCT Research. - : Springer Nature. - 1547-0091 .- 2168-8028. ; 19:1, s. 111-120
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Tidskriftsartikel (refereegranskat)abstract
- Bio-based nanocellulosic materials are non-toxic, renewable, exhibit excellent barrier properties, and are suitable candidates for sustainable food packaging applications. Sizing and designing coating parameters for slot-coating process using nanocellulose suspensions is challenging due to complex shear-thinning rheology and the presence of a water-rich boundary layer, effecting significant apparent slip at the wall. Previous studies have shown that the flow inside the coating bead can be complex, with occasional stagnation regions and a rheological model incorporating yield stress which should be considered while analyzing slot coating of nanocellulosic flows. This work extends earlier investigations by including the effects of the particle depleted water-rich boundary layer. The suspension is modeled as a Casson fluid with a shear-thinning viscosity, and the particle depletion at the wall is represented by an infinitely thin layer modeled as a local shear-dependent nonlinear slip law. The resulting two-phase flow equations are solved using a Finite Volume Method (FVM) coupled with the Volume of Fluid (VoF) method for tracking the free surface interface. It is observed that slip alters the flow’s dynamics in the coating bead, and the effect of slip cannot be ignored, especially at high shear rates. For thin films, the presence of slip enhances the flow, leading to more material coated on the substrate. In contrast, for thicker coatings, apparent slip leads to an augmentation in stagnant, non-yielded regions, potentially generating uneven surfaces.
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| 25. |
- Hansson, Petra M., et al.
(författare)
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Effect of surface depressions on wetting and interactions between hydrophobic pore array surfaces
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:30, s. 11121-11130
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Tidskriftsartikel (refereegranskat)abstract
- The surface structure is known to significantly affect the long-range capillary forces between hydrophobic surfaces in aqueous solutions. It is, however, not clear how small depressions in the surface will affect the interaction. To clarify this, we have used the AFM colloidal probe technique to measure interactions between hydrophobic microstructured pore array surfaces and a hydrophobic colloidal probe. The pore array surfaces were designed to display two different pore spacings, 1.4 and 4.0 ÎŒm, each with four different pore depths ranging from 0.2 to 12.0 ÎŒm. Water contact angles measured on the pore array surfaces are lower than expected from the Cassie-Baxter and Wenzel models and not affected by the pore depth. This suggests that the position of the three-phase contact line, and not the interactions underneath the droplet, determines the contact angle. Confocal Raman microscopy was used to investigate whether water penetrates into the pores. This is of importance for capillary forces where both the movement of the three-phase contact line and the situation at the solid/liquid interface influence the stability of bridging cavities. By analyzing the shape of the force curves, we distinguish whether the cavity between the probe and the surfaces was formed on a flat part of the surface or in close proximity to a pore. The pore depth and pore spacing were both found to statistically influence the distance at which cavities form as surfaces approach each other and the distance at which cavities rupture during retraction.
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| 26. |
- Hansson, Petra M., et al.
(författare)
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Frictional forces between hydrophilic and hydrophobic particle coated nanostructured surfaces
- 2013
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 15:41, s. 17893-17902
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Tidskriftsartikel (refereegranskat)abstract
- Friction forces have long been associated with the famous Amontons' rule that states that the friction force is linearly dependent on the applied normal load, with the proportionality constant being known as the friction coefficient. Amontons' rule is however purely phenomenological and does not in itself provide any information on why the friction coefficient is different for different material combinations. In this study, friction forces between a colloidal probe and nanostructured particle coated surfaces in an aqueous environment exhibiting different roughness length scales were measured by utilizing the atomic force microscope (AFM). The chemistry of the surfaces and the probe was varied between hydrophilic silica and hydrophobized silica. For hydrophilic silica surfaces, the friction coefficient was significantly higher for the particle coated surfaces than on the flat reference surface. All the particle coated surfaces exhibited similar friction coefficients, from which it may be concluded that the surface geometry, and not the roughness amplitude per se, influenced the measured friction. During measurements with hydrophobic surfaces, strong adhesive forces related to the formation of a bridging air cavity were evident from both normal force and friction force measurements. In contrast to the frictional forces between the hydrophilic surfaces, the friction coefficient for hydrophobic surfaces was found to depend on the surface structure and we believe that this dependence is related to the restricted movement of the three-phase line of the bridging air cavity. For measurements using a hydrophobic surface and a hydrophilic probe, the friction coefficient was significantly smaller compared to the two homogeneous systems. A layer of air or air bubbles on the hydrophobic surface working as a lubricating layer is a possible mechanism behind this observation.
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| 27. |
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| 28. |
- Hansson, Petra M., 1983-, et al.
(författare)
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Hydrophobic pore array surfaces : Wetting and interaction forces in water/ethanol mixtures
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 396, s. 278-286
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between and wetting behavior of structured hydrophobic surfaces using different concentrations of water/ethanol mixtures have been investigated. Silica surfaces consisting of pore arrays with different pore spacings and pore depths were made hydrophobic by silanization. Their static and dynamic contact angles were found to be independent of the pore depth while fewer pores on the surface, i.e. a closer resemblance to a flat surface, gave a lower contact angle. As expected, a higher amount of ethanol facilitated wetting on all the surfaces tested. Confocal Raman microscopy measurements proved both water and ethanol to penetrate into the pores. AFM colloidal probe force measurements clearly showed that formation of air cavitation was hindered between the hydrophobic surfaces in presence of ethanol, and an increase in ethanol concentration was followed by a smaller jump-in distance and a weaker adhesion force. On separation, an immediate jump-out of contact occurred. The measured forces were interpreted as being due to capillary condensation of ethanol between the surfaces giving rise to very unstable cavities immediately rupturing on surface separation.
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| 29. |
- Hansson, Petra M, 1983-
(författare)
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Hydrophobic surfaces: Effect of surface structure on wetting and interaction forces
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of hydrophobic surfaces is important for many processes both in nature and industry. Interactions between hydrophobic species play a key role in industrial applications such as water-cleaning procedures and pitch control during papermaking but they also give information on how to design surfaces like hydrophobic mineral pigments.In this thesis, the influence of surface properties on wetting and interaction forces has been studied. Surfaces with close-packed particles, pore arrays, randomly deposited nanoparticles as well as reference surfaces were prepared. The atomic force microscope (AFM) was utilized for force and friction measurements while contact angles and confocal Raman microscopy experiments were mainly used for wetting studies.The deposition of silica particles in the size range of nano- to micrometers using the Langmuir-Blodgett (LB) technique resulted in particle coated surfaces exhibiting hexagonal close-packing and close to Wenzel state wetting after hydrophobization. Force measurements displayed long-range interaction forces assigned to be a consequence of air cavitation. Smaller roughness features provided larger forces and interaction distances interpreted as being due to fewer restrictions of capillary growth. Friction measurements proved both the surface structure and chemistry to be important for the observed forces.On hydrophobic pore array surfaces, the three-phase contact line of water droplets avoided the pores which created a jagged interface. The influence of the pores was evident in the force curves, both in terms of the shape, in which the three-phase contact line movements around the pores could be detected, as well as the depth of the pores providing different access and amount of air. When water/ethanol mixtures were used, the interactions were concluded to be due to ethanol condensation.Confocal Raman microscopy experiments with water and water/ethanol mixtures on superhydrophobic surfaces gave evidence for water depletion and ethanol/air accumulation close to the surface. Force measurements using superhydrophobic surfaces showed extremely long-range interaction distances.This work has provided evidence for air cavitation between hydrophobic surfaces in aqueous solution. It was also shown that the range and magnitude of interaction forces could, to some extent, be predicted by looking at certain surface features like structure,roughness and the overall length scales.
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| 30. |
- Hansson, Petra M., et al.
(författare)
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Influence of Surface Topography on the Interactions between Nanostructured Hydrophobic Surfaces
- 2012
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:21, s. 8026-8034
-
Tidskriftsartikel (refereegranskat)abstract
- Nanostructured particle coated surfaces, with hydrophobized particles arranged in close to hexagonal order and of specific diameters ranging from 30 nm up to 800 nm, were prepared by Langmuir-Blodgett deposition followed by silanization. These surfaces have been used to study interactions between hydrophobic surfaces and a hydrophobic probe using the AFM colloidal probe technique. The different particle coated surfaces exhibit similar water contact angles, independent of particle size, which facilitates studies of how the roughness length scale affects capillary forces (previously often referred to as "hydrophobic interactions") in aqueous solutions. For surfaces with smaller particles (diameter < 200 nm), an increase in roughness length scale is accompanied by a decrease in adhesion force and bubble rupture distance. It is suggested that this is caused by energy barriers that prevent the motion of the three-phase (vapor/liquid/solid) line over the surface features, which counteracts capillary growth. Some of the measured force curves display extremely long-range interaction behavior with rupture distances of several micrometers and capillary growth with an increase in volume during retraction. This is thought to be a consequence of nanobubbles resting on top of the surface features and an influx of air from the crevices between the particles on the surface.
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| 31. |
- Hansson, Petra M., et al.
(författare)
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Robust Hydrophobic Surfaces Displaying Different Surface Roughness Scales While Maintaining the Same Wettability
- 2011
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:13, s. 8153-8159
-
Tidskriftsartikel (refereegranskat)abstract
- A range of surfaces coated with spherical silica particles, covering the size range from nanometer to micrometer, have been produced using Langmuir-Blodgett (LB) deposition. The particles were characterized both in suspension and in the Langmuir trough to optimize the surface preparation procedure. By limiting the particle aggregation and surface layer failures during the preparation steps, well-defined monolayers with a close-packed structure have been obtained for all particle sizes. Thus, this procedure led to structured surfaces with a characteristic variation in the amplitude and spatial roughness parameters. In order to obtain robust surfaces, a sintering protocol and an AFM-based wear test to determine the stability of the deposited surface layer were employed. Hydrophobization of the LB films followed by water contact angle measurements showed, for all tested particle sizes, the same increase in contact angle compared to the contact angle of a flat hydrophobic surface. This indicates nearly hexagonal packing and gives evidence for nearly, complete surface wetting of the surface features.
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| 32. |
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| 33. |
- Johansson, Kenth S., et al.
(författare)
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Surface modification of wheat gluten films for improved water resistance
- 2010
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Ingår i: Abstracts of Papers of the American Chemical Society. - : American Chemical Society (ACS). - 0065-7727. ; 240
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Renewable packaging materials are of interest for a more sustainable environment, and wheat gluten (WG) is one of the most interesting candidates to replace petroleum-based oxygen-barrier polymers for packaging applications. This is due to its attractive combination of flexibility and strength, high gas (especially O2) barrier properties under low humidity conditions and renewability. The main drawback of WG, as with most biopolymers, is its water and moisture sensitivity. The aim of this study was therefore to improve the hydrophobicity of WG films by means of surface modification while maintaining the excellent O2 barrier properties. The surface modification work included a combination of electrospinning of WG fibers and different plasma surface modifications. The latter involved He plasma treatment for crosslinking the WG film prior to the deposition of electrospun WG fibers, O2/Ar plasma etching of the WG films with and without electrospun WG fibers for increasing the surface roughness, and plasma polymerization of hexamethyldisiloxane (HMDSO) and other hydrophobic precursors for hydrophobicity. The plasma polymerization trials were performed both at reduced and atmospheric pressure conditions. The aim of the combined work was to maximize the hydrophobicity by combining a suitable nano-microstructure of the WG fibers with the hydrophobicity of the plasma-deposited coatings. The surface modification work was mainly evaluated by means of water contact angle measurements (hydrophobicity), Scanning Electron Microscopy (surface structures), Water Vapor Transmission Rate (WVTR) (moisture barrier) and Oxygen Transmission Rate (OTR) measurements (oxygen barrier). The surface modification work resulted in significantly improved hydrophobic properties of the WG films. The initial water contact angle increased from 65 to 110-130 degrees, depending on the combinations of electrospinning and plasma modification conditions. The plasma coatings prepared at ambient conditions resulted in slightly lower contact angles compared the plasma coating prepared at reduced pressure. The WVTR and OTR measurements are still in progress and will be reported at the meeting.
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| 34. |
- Koppolu, R., et al.
(författare)
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Continuous Processing of Nanocellulose and Polylactic Acid into Multilayer Barrier Coatings
- 2019
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:12, s. 11920-11927
-
Tidskriftsartikel (refereegranskat)abstract
- Recent years have seen an increased interest toward utilizing biobased and biodegradable materials for barrier packaging applications. Most of the abovementioned materials usually have certain shortcomings that discourage their adoption as a preferred material of choice. Nanocellulose falls into such a category. It has excellent barrier against grease, mineral oils, and oxygen but poor tolerance against water vapor, which makes it unsuitable to be used at high humidity. In addition, nanocellulose suspensions' high viscosity and yield stress already at low solid content and poor adhesion to substrates create additional challenges for high-speed processing. Polylactic acid (PLA) is another potential candidate that has reasonably high tolerance against water vapor but rather a poor barrier against oxygen. The current work explores the possibility of combining both these materials into thin multilayer coatings onto a paperboard. A custom-built slot-die was used to coat either microfibrillated cellulose or cellulose nanocrystals onto a pigment-coated baseboard in a continuous process. These were subsequently coated with PLA using a pilot-scale extrusion coater. Low-density polyethylene was used as for reference extrusion coating. Cationic starch precoating and corona treatment improved the adhesion at nanocellulose/baseboard and nanocellulose/PLA interfaces, respectively. The water vapor transmission rate for nanocellulose + PLA coatings remained lower than that of the control PLA coating, even at a high relative humidity of 90% (38 °C). The multilayer coating had 98% lower oxygen transmission rate compared to just the PLA-coated baseboard, and the heptane vapor transmission rate reduced by 99% in comparison to the baseboard. The grease barrier for nanocellulose + PLA coatings increased 5-fold compared to nanocellulose alone and 2-fold compared to PLA alone. This approach of processing nanocellulose and PLA into multiple layers utilizing slot-die and extrusion coating in tandem has the potential to produce a barrier packaging paper that is both 100% biobased and biodegradable.
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| 35. |
- Koppolu, Rajesh, et al.
(författare)
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Continuous roll-to-roll coating of cellulose nanocrystals onto paperboard
- 2018
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 25:10, s. 6055-6069
-
Tidskriftsartikel (refereegranskat)abstract
- There is an increased interest in the use of cellulose nanocrystal (CNC) films and coatings for a range of functional applications in the fields of material science, biomedical engineering, and pharmaceutical sciences. Most of these applications have been demonstrated on films and coatings produced using laboratory-scale batch processes, such as solvent casting, dip coating, or spin coating. For successful coating application of CNC suspensions using a high throughput process, several challenges need to be addressed: relatively high viscosity at low solids content, coating brittleness, and potentially poor adhesion to the substrate. This work aims to address these problems. The impact of plasticizer on suspension rheology, coating adhesion, and barrier properties was quantified, and the effect of different pre-coatings on the wettability and adhesion of CNC coatings to paperboard substrates was explored. CNC suspensions were coated onto pre-coated paperboard in a roll-to-roll process using a custom-built slot die. The addition of sorbitol reduced the brittleness of the CNC coatings, and a thin cationic starch pre-coating improved their adhesion to the paperboard. The final coat weight, dry coating thickness, and coating line speed were varied between 1–11 g/m2, 900 nm–7 µm, and 2.5–10 m/min, respectively. The barrier properties, adhesive strength, coating coverage, and smoothness of the CNC coatings were characterized. SEM images show full coating coverage at coat weights as low as 1.5 g/m2. With sorbitol as plasticizer and at coat weights above 3.5 g/m2, heptane vapor and water vapor transmission rates were reduced by as much as 99% and 75% respectively. Compared to other film casting techniques, the process employed in this work deposits a relatively thick coating in significantly less time, and may therefore pave the way toward various functional applications based on CNCs.
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| 36. |
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| 37. |
- Kutty, F. P. A., et al.
(författare)
-
Numerical analysis of slot die coating of nanocellulosic materials
- 2020
-
Ingår i: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 19:11, s. 575-582
-
Tidskriftsartikel (refereegranskat)abstract
- Nanocellulosic coatings as a food packaging material are of commercial interest due to their nontox-ic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computational fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot die coater, where the model parameters are established from existing slot rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot die operated in an unconventional metering mode. Results with the Casson model predict the presence of unyielded regions in the flow, which was not captured using the power law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to poten-tial defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear rates, is also highlighted. Application: This work identifies and clarifies the challenges to be addressed when considering industrial scale nanocellulose coating of paperboard.
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| 38. |
- Kutty, F. P. A., et al.
(författare)
-
Numerical analysis of slot die coating of nanocellulosic materials
- 2021
-
Ingår i: TAPPICon LIVE 2021. - : TAPPI Press. - 9781713848370 ; , s. 63-73
-
Konferensbidrag (refereegranskat)abstract
- Nanocellulosic coatings as a food-packaging material are of commercial interest due to their non-toxic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computation fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot-die coater, where the model parameters are established from existing slot-rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot-die operated in an unconventional metering mode. Results with the Casson model predicts the presence of unyielded regions in the flow, which was not captured using the power-law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to potential defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear-rates, is also highlighted.
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| 39. |
- Lindström, Tom, et al.
(författare)
-
On The Mechanical and Chemical Factors Governing Retention and Formation of a Fine Paper Stock : The Case of Headbox Elongational Shear
- 2015
-
Ingår i: Journal of Science & Technology for Forest Products and Processes. - : Pulp and Paper Technical Association of Canada. - 1927-6311 .- 1927-632X. ; 5:4, s. 30-37
-
Tidskriftsartikel (refereegranskat)abstract
- The relation between formation and retention is of key importance in papermaking. This paper deals with how various variables (mix-to-wire speed difference, softwood/hardwood ratio, pulp consistency, headbox contraction, and various amounts of added two-component retention aid) affect the forming of paper and in turn retention and paper formation. The experiments were conducted using the EuroFEX paper machine at Innventia, which can be operated under steady-state conditions of the white water system. It was found that formation is worst when the mix-to-wire speed difference is close to zero or when the oriented shear is lowest. Retention, on the other hand, is to a large extent independent of mix-to-wire speed. Higher consistency during forming is generally associated with an enhanced susceptibility of fibres to flocculate, but a higher consistency in the headbox is, in this study, also associated with increased headbox contraction, which increases elongational shear. The higher the headbox consistency, the higher will be the first-pass retention because of the closer proximity of particles, which is beneficial for bridging flocculation. It is known that elongational shear is in general more beneficial to fibre dispersion than transverse shear and also that for weaker fibre flocs (higher hardwood pulp content), the effect of high headbox contraction (higher consistency) actually reverses the effect of consistency on sheet formation because elongational shear overcomes the effects of fibre crowding at high headbox consistency on sheet formation. In conclusion, we show how the effects of mix-to-wire speed difference, softwood/hardwood ratio, headbox consistency, headbox contraction, and amount of retention aid added (cationic polyacrylamide and colloidal silica) affect retention and formation of paper.
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| 40. |
- Lindström, Tom, et al.
(författare)
-
On the mechanical and chemical factors governing retention and formation of a fine paper stock : The case of headbox elongational shear
- 2016
-
Ingår i: Journal of Science & Technology for Forest Products and Processes. - : Walter de Gruyter. - 1927-6311 .- 1927-632X. ; 5:4, s. 30-37
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The relation between formation and retention is of key importance in papermaking. This paper deals with how various variables (mix-to-wire speed difference, softwood/hardwood ratio, pulp consistency, headbox contraction, and various amounts of added two-component retention aid) affect the forming of paper and in turn retention and paper formation. The experiments were conducted using the EuroFEX paper machine at Innventia, which can be operated under steady-state conditions of the white water system.It was found that formation is worst when the mix-to-wire speed difference is close to zero or when the oriented shear is lowest. Retention, on the other hand, is to a large extent independent of mix-to-wire speed. Higher consistency during forming is generally associated with an enhanced susceptibility of fibres to flocculate, but a higher consistency in the headbox is, in this study, also associated with increased headbox contraction, which increases elongational shear. The higher the headbox consistency, the higher will be the first-pass retention because of the closer proximity of particles, which is beneficial for bridging flocculation. It is known that elongational shear is in general more beneficial to fibre dispersion than transverse shear and also that for weaker fibre flocs (higher hardwood pulp content), the effect of high headbox contraction (higher consistency) actually reverses the effect of consistency on sheet formation because elongational shear overcomes the effects of fibre crowding at high headbox consistency on sheet formation.In conclusion, we show how the effects of mix-to-wire speed difference, softwood/hardwood ratio, headbox consistency, headbox contraction, and amount of retention aid added (cationic polyacrylamide and colloidal silica) affect retention and formation of paper.
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| 41. |
- MacKenzie, Jordan, et al.
(författare)
-
Turbulent stress measurements of fiber suspensions in a straight pipe with MRV
- 2016
-
Ingår i: Paper Conference and Trade Show, PaperCon 2016. ; , s. 1024-1031
-
Konferensbidrag (refereegranskat)abstract
- The focus of the present work is an experimental study of the behaviour of semi-dilute, opaque fibre suspensions in fully developed cylindrical pipe flows. Measurements of the normal and turbulent shear stress components and the mean flow were acquired using phase-contrast magnetic resonance velocimetry. Two fibre types, namely, pulp fibre and nylon fibre, were considered in this work and are known to differ in elastic modulus. In total, three different mass concentrations and seven Reynolds numbers were tested to investigate the effects of fibre interactions during the transition from the plug flow to fully turbulent flow. It was found that in fully turbulent flows of nylon fibres, the normal, uzuz+, and shear, uzur+ (note that · is the temporal average, u is the fluctuating velocity, z is the axial or streamwise component, and r is the radial direction), turbulent stresses increased with Reynolds number regardless of the crowding number (a concentration measure). For pulp fibre, the turbulent stresses increased with Reynolds number when a fibre plug was present in the flow and were spatially similar in magnitude when no fibre plug was present. Pressure spectra revealed that the stiff, nylon fibre reduced the energy in the inertial-subrange with an increasing Reynolds and crowding number, whereas the less stiff pulp fibre effectively cuts the energy cascade prematurely when the network was fully dispersed.
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| 42. |
- MacKenzie, Jordan, et al.
(författare)
-
Turbulent stress measurements of fibre suspensions in a straight pipe
- 2018
-
Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 30:2
-
Tidskriftsartikel (refereegranskat)abstract
- The focus of the present work is an experimental study of the behaviour of semi-dilute, opaque fibre suspensions in fully developed cylindrical pipe flows. Measurements of the normal and turbulent shear stress components and the mean flow were acquired using phase-contrast magnetic resonance velocimetry. Two fibre types, namely, pulp fibre and nylon fibre, were considered in this work and are known to differ in elastic modulus. In total, three different mass concentrations and seven Reynolds numbers were tested to investigate the effects of fibre interactions during the transition from the plug flow to fully turbulent flow. It was found that in fully turbulent flows of nylon fibres, the normal, uzuz+, and shear, uzur+ (note that · is the temporal average, u is the fluctuating velocity, z is the axial or streamwise component, and r is the radial direction), turbulent stresses increased with Reynolds number regardless of the crowding number (a concentration measure). For pulp fibre, the turbulent stresses increased with Reynolds number when a fibre plug was present in the flow and were spatially similar in magnitude when no fibre plug was present. Pressure spectra revealed that the stiff, nylon fibre reduced the energy in the inertial-subrange with an increasing Reynolds and crowding number, whereas the less stiff pulp fibre effectively cuts the energy cascade prematurely when the network was fully dispersed.
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| 43. |
- MacKenzie, Jordan, et al.
(författare)
-
Turbulent stress measurements with phase-contrast magnetic resonance through tilted slices
- 2017
-
Ingår i: Experiments in Fluids. - : Springer Verlag. - 0723-4864 .- 1432-1114. ; 58
-
Tidskriftsartikel (refereegranskat)abstract
- Aiming at turbulent measurements in opaque suspensions, a simplistic methodology for measuring the turbulent stresses with phase-contrast magnetic resonance velocimetry is described. The method relies on flow-compensated and flow-encoding protocols with the flow encoding gradient normal to the slice. The experimental data is compared with direct numerical simulations (DNS), both directly but also, more importantly, after spatial averaging of the DNS data that resembles the measurement and data treatment of the experimental data. The results show that the most important MRI data (streamwise velocity, streamwise variance and Reynolds shear stress) is reliable up to at least r¯=0.75'>r¯=0.75r¯=0.75 without any correction, paving the way for dearly needed turbulence and stress measurements in opaque suspensions.
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| 44. |
- Montibon, Elson, 1979-
(författare)
-
Preparation of Electroconductive Paper by Deposition of Conducting Polymer
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis describes an investigation into the interaction between the conducting polymer and cellulosic materials, and the preparation of electroconductive paper. The adsorption behavior of the conducting polymer onto cellulosic materials was characterized. Poly(3,4-ethylenedioxythiophene) doped with poly(4-styrene sulfonate) (PEDOT:PSS) was used as conducting polymer because of its attractive properties in terms of conductivity, water solubility, and environmental stability. The model substrate used for adsorption was microcrystalline cellulose (MCC). Various pH levels and salt concentrations were explored to completely understand the adsorption behavior of PEDOT:PSS. The variation in surface charge characteristics when the pH and salt concentration were changed was monitored by polyelectrolyte titration and zeta potential measurement. The adsorption isotherm showed a broad molecular distribution of the conducting polymer and considerable interaction between the polymer and MCC. As the pH of the solution was increased, the adsorbed amount decreased. With varying salt concentrations, the adsorption passed through a maximum. The extent of deposition of PEDOT:PSS on the surface of cellulosic fibers was investigated using X-ray Photoelectron Spectroscopy (XPS) with a commercial base paper as substrate. XPS analysis of dip-coated paper samples showed PEDOT enrichment on the surface. The degree of washing the dip-coated paper with acidic water did not significantly affect the PEDOT enrichment on the surface. A base paper was coated with PEDOT:PSS blends to produce electroconductive papers. The bulk conductivities (σdc) of the coated papers were measured using a four-probe technique and impedance spectroscopy. One-side and two-side coating gave comparable conductivity levels. Various organic solvents added to the PEDOT:PSS dispersion at different concentrations showed various effects on the bulk conductivity of the coated paper. Blends containing sorbitol and isopropanol did not enhance the bulk conductivity of the coated paper, and at high concentrations these organic solvents lowered the conductivity. Paper samples coated with a PEDOT:PSS blend containing N-methylpyrrolidinone (NMP) and dimethyl sulfoxide (DMSO) exhibited a higher conductivity than when coated with pure PEDOT:PSS, due to conformational changes and their plasticizing effect. The effect of calendering was investigated and only the sample subjected to 174 kN/m line load after coating showed significant conductivity enhancement. The addition of TiO2 pigment lowered the bulk conductivity of the paper. Contact angle measurements were made to monitor the effect of coating the paper with PEDOT:PSS blends on the hydrophilicity of the paper samples. The amount of PEDOT:PSS deposited in the fiber network was determined using total sulfur analysis. Thus, this study makes use of conventional paper surface treatment as method for achieving bulk conductivity of paper in the semi-conductor range without significantly decreasing the paper strength.
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| 45. |
- Niga, Petru, et al.
(författare)
-
Interactions between model cell membranes and the neuroactive drug propofol
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 526, s. 230-243
-
Tidskriftsartikel (refereegranskat)abstract
- phospholipid, NR data reveal that propofol is located exclusively in the head group region, which is rationalized in the context of previous studies. The results imply a non-homogeneous distribution of propofol in the plane of real cell membranes, which is an inference that requires urgent testing and may help to explain why such low concentration of the drug are required to induce general anaesthesia.
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| 46. |
- Niga, Petru, et al.
(författare)
-
Propofol adsorption at the air/water interface : a combined vibrational sum frequency spectroscopy, nuclear magnetic resonance and neutron reflectometry study
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Propofol interaction with cell membrane has remarkable influence on neuronal function, yet data regarding its behaviour at an interface is still scarce. Here we present the results of propofol adsorption at the air/water interface studied by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS was utilized to elucidate the orientation change of propofol at the surface as a function of concentration, and the water of hydration was studied by probing the OH vibrational region of the spectrum in two different polarisation combinations. Data show that propofol adsorbs at the air/water interface in an ordered fashion showing strong interactions with the water of hydration, as well as weak interactions with water in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied (0 – 0.89 mM) there is almost no change in the orientation adopted at the interface. NR shows that propofol forms a dense monolayer with a thickness of 4.8 Å, and this result is consistent with a limiting area per molecule equivalent to a close-packed monolayer as demonstrated by surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded. Additionally, the ability of propofol to form associations/multimeric structures in water was studied using nuclear magnetic resonance (NMR). The 1H NMR chemical shifts recorded indicate that propofol does not form dimers or multimers in bulk water (D2O).
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| 47. |
- Niga, Petru, et al.
(författare)
-
Propofol adsorption at the air/water interface : a combined vibrational sum frequency spectroscopy, nuclear magnetic resonance and neutron reflectometry study
- 2019
-
Ingår i: Soft Matter. - : ROYAL SOC CHEMISTRY. - 1744-683X .- 1744-6848. ; 15:1, s. 38-46
-
Tidskriftsartikel (refereegranskat)abstract
- Propofol is an amphiphilic small molecule that strongly influences the function of cell membranes, yet data regarding interfacial properties of propofol remain scarce. Here we consider propofol adsorption at the air/water interface as elucidated by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS data show that propofol adsorbed at the air/ water interface interacts with water strongly in terms of hydrogen bonding and weakly in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied there is almost no change in the orientation adopted at the interface. Data from NR show that propofol forms a dense monolayer with a thickness of 8.4 angstrom and a limiting area per molecule of 40 angstrom(2), close to the value extracted from surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded as long as the solubility limit is not exceeded. Additionally, measurements of the 1H NMR chemical shifts demonstrate that propofol does not form dimers or multimers in bulk water up to the solubility limit.
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| 48. |
- Niga, Petru, et al.
(författare)
-
Propofol adsorption at the air/water interface : a combined vibrational sum frequency spectroscopy, nuclear magnetic resonance and neutron reflectometry study
- 2019
-
Ingår i: Soft Matter. - 1744-683X .- 1744-6848. ; 15:1, s. 38-46
-
Tidskriftsartikel (refereegranskat)abstract
- Propofol is an amphiphilic small molecule that strongly influences the function of cell membranes, yet data regarding interfacial properties of propofol remain scarce. Here we consider propofol adsorption at the air/water interface as elucidated by means of vibrational sum frequency spectroscopy (VSFS), neutron reflectometry (NR), and surface tensiometry. VSFS data show that propofol adsorbed at the air/water interface interacts with water strongly in terms of hydrogen bonding and weakly in the proximity of the hydrocarbon parts of the molecule. In the concentration range studied there is almost no change in the orientation adopted at the interface. Data from NR show that propofol forms a dense monolayer with a thickness of 8.4 Å and a limiting area per molecule of 40 Å2, close to the value extracted from surface tensiometry. The possibility that islands or multilayers of propofol form at the air/water interface is therefore excluded as long as the solubility limit is not exceeded. Additionally, measurements of the 1H NMR chemical shifts demonstrate that propofol does not form dimers or multimers in bulk water up to the solubility limit.
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| 49. |
- Oko, Asaf, et al.
(författare)
-
Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper
- 2014
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 456, s. 92-99
-
Tidskriftsartikel (refereegranskat)abstract
- Papers coated with salts containing divalent cations exhibit superior inkjet print quality, which has been suggested to be due to fast aggregation of the colorant pigments close to, or even on, the surface of the paper. In this work we show the pivotal role of the carboxylic acid containing dispersing polymer. We report a series of aggregation and sedimentation experiments with commercial inks, generic ink formulations and specific ingredients comprising these formulations, and find differences in their response to the presence of MgCl2 or CaCl2. In particular, flocs and sediments formed in the presence of MgCl2 are denser than those formed in the presence of CaCl2. These differences are not predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We suggest that ion specific interactions occurring between Mg2+ or Ca2+, and charged carboxylate groups residing on the dispersing polymers, provoke the observed behavior.
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| 50. |
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