| 1. |
- Zhang, Renyun, et al.
(författare)
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Soap-film coating : High-speed deposition of multilayer nanofilms
- 2013
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Ingår i: Scientific Reports. - Nature Publishing Group : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. Art. no. 1477-
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Tidskriftsartikel (refereegranskat)abstract
- The coating of thin films is applied in numerous fields and many methods are employed for the deposition of these films. Some coating techniques may deposit films at high speed; for example, ordinary printing paper is coated with micrometre-thick layers of clay at a speed of tens of meters per second. However, to coat nanometre thin films at high speed, vacuum techniques are typically required, which increases the complexity of the process. Here, we report a simple wet chemical method for the high-speed coating of films with thicknesses at the nanometre level. This soap-film coating technique is based on forcing a substrate through a soap film that contains nanomaterials. Molecules and nanomaterials can be deposited at a thickness ranging from less than a monolayer to several layers at speeds up to meters per second. We believe that the soap-film coating method is potentially important for industrial-scale nanotechnology.
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| 2. |
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| 3. |
- Costa, Carolina
(författare)
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Cellulose Dissolution and Amphiphilicity : Insights on the Emulsion Formation and Stabilization
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An amphiphilic polymer is expected to adsorb at the oil-water interface and be capable of stabilizing emulsions. Cellulose derivatives, cellulose nanoparticles and regenerated cellulose particles show an intrinsic amphiphilic character by self-assembling at oil-water interfaces and stabilizing emulsions without the aid of surfactants or any other co-stabilizers. In its polymeric form, the native cellulose chains could be expected to share similar emulsifying abilities. However, cellulose dissolution is the main issue when it comes to its direct application in emulsion technology and, therefore, there is a lack of knowledge when it comes to this type of approach on making emulsions. Cellulose does not dissolve in either oil or water, but it can be dissolved in water based-solvents at extreme pH's. In this thesis, the interfacial behaviour of cellulose was studied at oil-water interfaces by having cellulose dissolved in aqueous solutions of H3PO4 (very low pH) and NaOH/NaOH-urea and TBAH (very high pH). In its dissolved state, cellulose was seen to substantially decrease the interfacial tension (IFT) between the oil phase and the aqueous media, which was a consequence of the adsorption of cellulose at oil-water interfaces. The extent of the IFT reduction was shown to be dependent on the solvent quality. The optimal solvency conditions for cellulose were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favourable conditions for adsorption of an amphiphilic polymer. However, in stabilizing oil-in-water emulsions (O/W), to achieve long-term stability and prevent oil separation from the emulsions, further reduction in cellulose's solvency was needed. This was achieved by a change in the pH of the emulsions that induced the regeneration of cellulose on the surface of the oil droplets (in-situ regeneration) in the form of a continuous film, which was revealed by cryogenic scanning electron microscopy (cryo-SEM). The topography of the droplets surface was found to be very different from what has been reported for cellulose Pickering emulsions. Upon in-situ regeneration, the rate of droplets coalescence was dramatically reduced and emulsions showed a remarkable stability against oil-separation. Finally, the combination of cellulose with lignin as an amphiphilic natural co-stabilizer was studied regarding their compatibility in solution. Lignin was found to improve cellulose dissolution in NaOH (aq.) and delay the gelation kinetics upon ageing or temperature increase in the solutions. Data suggests lignin as an amphiphilic additive able to weaken the hydrophobic interactions among cellulose molecules.
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| 4. |
- Costa, Carolina, et al.
(författare)
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Emulsion Formation and Stabilization by Biomolecules : The Leading Role of Cellulose.
- 2019
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).
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| 5. |
- Costa, Carolina, et al.
(författare)
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Interfacial activity and emulsion stabilization of dissolved cellulose
- 2019
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Ingår i: Journal of Molecular Liquids. - : Elsevier B.V.. - 0167-7322 .- 1873-3166. ; 292
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Tidskriftsartikel (refereegranskat)abstract
- Some aspects of the interfacial behavior of cellulose dissolved in an aqueous solvent were investigated. Cellulose was found to significantly decrease the interfacial tension (IFT) between paraffin oil and 85 wt% phosphoric acid aqueous solutions. This decrease was similar in magnitude to that displayed by non-ionic cellulose derivatives. Cellulose's interfacial activity indicated a significant amphiphilic character and that the interfacial activity of cellulose derivatives is not only related to the derivatization but inherent in the cellulose backbone. This finding suggests that cellulose would have the ability of stabilizing dispersions, like oil-in-water emulsions in a similar way as a large number of cellulose derivatives. In its molecularly dissolved state, cellulose proved to be able to stabilize emulsions of paraffin in the polar solvent on a short-term. However, long-term stability against drop-coalescence was possible to achieve by a slight change in the amphiphilicity of cellulose, effected by a slight increase in pH. These emulsions exhibited excellent stability against coalescence/oiling-off over a period of one year. Ageing of the cellulose solution before emulsification (resulting in molecular weight reduction) was found to favour the creation of smaller droplets.
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| 6. |
- Costa, Carolina, et al.
(författare)
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Lignin enhances cellulose dissolution in cold alkali
- 2021
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 274
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.
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| 7. |
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| 8. |
- Costa, Carolina, et al.
(författare)
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On the formation and stability of cellulose-based emulsions in alkaline systems : Effect of the solvent quality
- 2022
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 286
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Tidskriftsartikel (refereegranskat)abstract
- With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).
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| 9. |
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| 10. |
- Edlund, Håkan, 1966-, et al.
(författare)
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Formation of a Liquid Crystalline Phase in the Sodium Taurodeoxycholate-Water System
- 1998
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Ingår i: Langmuir. - Washington DC : ACS Publications. - 0743-7463 .- 1520-5827. ; 14, s. 3691-3697
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Tidskriftsartikel (refereegranskat)abstract
- The binary phase equilibria for the system sodium taurodeoxycholate-water have been studied. The system forms a liquid crystalline phase in addition to the previously known isotropic solution phase at 22 °C. 2H (water) NMR quadrupole splitting, SAXS data in combination with the polarizing microscopic texture observed for the liquid crystal indicate that the liquid crystalline phase consists of a hexagonal-type aggregate structure. A metastable liquid crystal, probably with lamellar-type structure, also appears to exist prior to the formation of the stable hexagonal phase. A micellar growth is measured with the NMR self-diffusion method for the isotropic solution phase. Electrical conductance experiments are used to determine the liquid crystal-solution thermal transition.
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