| 1. |
- Buehler, Stefan, et al.
(författare)
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A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:S2, s. 109-128
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Tidskriftsartikel (refereegranskat)abstract
- A passive satellite radiometer operating at submillimetre wavelengths can measure cloud ice water path (IWP), ice particle size, and cloud altitude. The paper first discusses the scientific background for such measurements. Formal scientific mission requirements are derived, based on this background and earlier assessments. The paper then presents a comprehensive prototype instrument and mission concept, and demonstrates that it meets the requirements. The instrument is a conically scanning 12-channel radiometer with channels between 183 and 664 GHz, proposed to fly in tandem with one of the Metop satellites. It can measure IWP with a relative accuracy of approximately 20% and a detection threshold of approximately 2 g m−2. The median mass equivalent sphere diameter of the ice particles can be measured with an accuracy of approximately 30 µm, and the median IWP cloud altitude can be measured with an accuracy of approximately 300 m. All the above accuracies are median absolute error values; root mean square error values are approximately twice as high, due to rare outliers.
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| 2. |
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| 3. |
- Bain, C. D., et al.
(författare)
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Complexes of surfactants with oppositely charged polymers at surfaces and in bulk
- 2010
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 155:1-2, s. 32-49
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Tidskriftsartikel (refereegranskat)abstract
- Addition of surfactants to aqueous solutions of polyelectrolytes carrying an opposite charge causes the spontaneous formation of complexes in the bulk phase in certain concentration ranges. Under some conditions, compact monodisperse multichain complexes are obtained in the bulk. The size of these complexes depends on the mixing procedure and it can be varied in a controlled way from nanometers up to micrometers. The complexes exhibit microstructures analoguous to those of the precipitates formed at higher concentrations. In other cases, however, the bulk complexes are large, soft and polydisperse. In most cases, the dispersions are only kinetically stable and exhibit pronounced non-equilibrium features. Association at air-water interfaces readily occurs, even at very small concentrations. When the surfactant concentration is small, the surface complexes are usually made of a surfactant monolayer to which the polymer binds and adsorbs in a flat-like configuration. However, under some conditions, thicker layers can be found, with bulk complexes sticking to the surface. The association at solid-water interfaces is more complex and depends on the specific interactions between surfactants, polymers and the surface. However, the behaviour can be understood if distinctions between hydrophilic surfaces and hydrophobic surfaces are made. Note that the behaviour at air-water interfaces is closer to that of hydrophobic than that of hydrophilic solid surfaces. The relation between bulk and surface complexation will be discussed in this review. The emphasis will be given to the results obtained by the teams of the EC-funded Marie Curie RTN "SOCON".
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| 4. |
- Stubenrauch, C., et al.
(författare)
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Mixtures of n-dodecyl-beta-D-maltoside and hexaoxyethylene dodecyl ether : Surface properties, bulk properties, foam films, and foams
- 2010
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 155:1-2, s. 5-18
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of the two non-ionic surfactants hexaoxyethylene dodecyl ether (C12E6) and n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) were studied with regard to surface properties, bulk properties, foam films, and foams. The reason for studying a mixture of an ethylene oxide (CiEj) and a sugar (C(n)G(m),) based surfactant is that despite being non-ionic, these two surfactants behave quite differently. Firstly, the physico-chemical properties of aqueous solutions of C(n)G(m) surfactants are less temperature-sensitive than those of CiEj solutions. Secondly, the surface charge density q(0) of foam films stabilized by C(n)G(m) surfactants is pH insensitive down to the so-called isoelectric point, while that of foam films stabilized by CiEj surfactants changes linearly with the pH. The third difference is related to interaction forces between solid surfaces. Under equilibrium conditions very high forces are needed to expel beta-C(12)G(2) from between thiolated gold surfaces, while for C12E6 low loads are sufficient. Fourthly, the adsorption of C12E6 and beta-C(12)G(2) on hydrophilic silica and titania, respectively, is inverted. While the surface excess of C12E6 is large on silica and negligible on titania, beta-C(12)G(2) adsorbs very little on silica but has a large surface excess on titania. What is the reason for this different behaviour? Under similar conditions and for comparable head group sizes, it was found that the hydration of CiEj surfactants is one order of magnitude higher but on average much weaker than that of C(n)G(m) surfactants. Moreover, C(n)G(m) surfactants possess a rigid maltoside unit, while CiEj surfactants have a very flexible hydrophilic part. Indeed, most of the different properties mentioned above can be explained by the different hydration and the head group flexibilities. The intriguing question of how mixtures of CiEj and C(n)G(m) surfactants would behave arises organically. Thus various properties of C12E6 + beta-C(12)G(2) mixtures in aqueous solution have been studied with a focus on the 1:1 mixture. The results are compared with those of the single surfactants and are discussed accordingly.
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| 5. |
- Rojas, OJ, et al.
(författare)
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Interactions between non-polar surfaces coated with the non-ionic surfactant n-dodecyl-β-D-maltoside β-C12G2
- 2005
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 21, s. 11836-11843
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Tidskriftsartikel (refereegranskat)abstract
- The forces acting between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-β-D-maltoside (β-C12G2) were investigated at concentrations below and above the critical micelle concentration. The long-range and adhesive forces were measured with a bimorph surface force apparatus (MASIF). It was found that the effect of hydrodynamic interactions had to be taken into account for an accurate determination of the short-range static interactions. The results were compared with disjoining pressure versus thickness curves that were obtained earlier with a thin film pressure balance (TFPB). This comparison led to the conclusion that the charges observed at the air-water interface are not due to charged species present in the surfactant sample. In addition, it was observed that the stability of thin liquid films crucially depends on the surfactant's bulk concentration (c) and thus on the packing density in the adsorbed layer. The force barrier preventing removal of the surfactant layer from between two solid-liquid interfaces increases with increasing c, while for foam films it is the stability of the Newton black film that increases with c. Finally, the results obtained for β-C12G2 were compared with those obtained for the homologue n-decyl-β-D-maltoside (β-C12G2) as well as with those obtained for nonionic surfactants with polyoxyethylene moieties as polar groups
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| 6. |
- Rojas, O. J., et al.
(författare)
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Interactions between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-beta-D-maltoside
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:25, s. 11836-11843
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Tidskriftsartikel (refereegranskat)abstract
- The forces acting between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) were investigated at concentrations below and above the critical micelle concentration. The long-range and adhesive forces were measured with a bimorph surface force apparatus (MASIF), It was found that the effect of hydrodynamic interactions had to be taken into account for an accurate determination of the short-range static interactions. The results were compared with disjoining pressure versus thickness curves that were obtained earlier with a thin film pressure balance (TFPB). This comparison led to the conclusion that the charges observed at the air-water interface are not due to charged species present in the surfactant sample. In addition, it was observed that the stability of thin liquid films crucially depends on the surfactant's bulk concentration
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| 7. |
- Stubenrauch, C, et al.
(författare)
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Aqueous foams stabilized by n-dodecyl-β-D-maltoside, hexaethyleneglycol monododecyl ether, and their 1 : 1 mixture
- 2009
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 5:16, s. 3070-3080
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous foams stabilized by the non-ionic surfactants n-dodecyl-β-D-maltoside (β-C12G2) and hexaethyleneglycol monododecyl ether (C12E2) as well as by their 1 : 1 mixture were studied as a function of the total surfactant concentration from 0.1 to 10 cmc. Foamability and foam stability were measured with home-built winding equipment, the commercially available FoamScan, and a home-built foam conductivity apparatus (FCA), respectively. It was found that the foamability increases with increasing surfactant concentration for both the single and the mixed surfactant systems. On the other hand, at a fixed relative surfactant concentration (c/cmc) the foamability of β-C12G2 solutions was found to be much higher than that of C12E6 solutions, while the 1 : 1 mixture behaves like the pure C12E6.Measurements at different gas (N2) flow rates have shown that the foamability decreases non-linearly with decreasing N2 flow rate, which shows that foam generation and foam breakdown occur simultaneously. Regarding foam stability it was found that it also increases with increasing surfactant concentration. As was the case for the foamability, the stability of foams stabilized by β-C12G2 was much higher than that of foams stabilized by C12E6, while the foam stability of the 1 : 1 mixture was comparable to that of the pure C12E6. The foam results are discussed in the light of static surface tensions, dynamic surface tensions, and surface elasticities, which were measured for the single and the mixed surfactant systems.
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| 8. |
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| 9. |
- Stubenrauch, C., et al.
(författare)
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Comparison between interaction forces at air/liquid interfaces in the presence of non-ionic surfactants
- 2004
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Ingår i: Tenside Surfactants Detergents. - : Walter de Gruyter GmbH. - 0932-3414 .- 2195-8564. ; 41:4, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- Interactions in thin liquid foam films and between solid/liquid surfaces coated with the non-ionic surfactant hexaoxyethylene dodecylether (C12E6) were investigated with TFPB (thin film pressure balance) and the MASIF (Measurement and Analysis of Surface Interaction Forces) technique, respectively. For foam films the formation of common black films (CBF) and Newton black films (NBF) was observed depending on the surfactant concentration and the applied pressure. With increasing surfactant concentration and increasing pressure the CBF is destablized, whereas a stabilization of the NBF is observed. In addition, MASIF measurements with two different hydrophobic surfaces were made. In one case silanated glass surfaces and in the other case thiolated gold surfaces were used. Differences and similarities of the interactions between these two surfaces are shown and discussed. Furthermore, the results of the MASIF measurements are compared with the ones of the thin films pressure balance measurements and the influence of the surfactant concentration on the interactions is discussed.
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| 10. |
- Stubenrauch, C., et al.
(författare)
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Interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl Ether C12E6 and the origin of surface charges at the air/water interface
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:12, s. 4977-4988
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.
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