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Sökning: L773:1873 4359 OR L773:0927 7757 > (2000-2004)

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1.
  • Amenitsch, H, et al. (författare)
  • Bile salts form lyotropic liquid crystals
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757 .- 1873-4359. ; 213:1, s. 79-92
  • Tidskriftsartikel (refereegranskat)abstract
    • A reinvestigation of the phase diagrams relative to some conjugated and non-conjugated bile salts in water has demonstrated the formation of lyotropic liquid crystalline phases, in contradiction with generally accepted statements. The phase behaviour is complex and the phase diagrams are unusual, compared to most surfactants and lipids. In particular, coexistence of liquid crystalline phases with crystals has been obser ed. The formation of liquid crystalline phases requires very long equilibration times and the thermal stability of the lyotropic phases is moderate. The observed structure is tentatively assumed to be of the reverse hexagonal type. Structural relations with currently accepted models for the organisation of bile salts into micelles and solid form have been found. (C) 2002 Elsevier Science B.V. All rights reserved.
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2.
  • Groth, Cecilia, 1972, et al. (författare)
  • Diffusion of water in multilamellar vesicles of dialkyl and dialkyl ester ammonium surfactants
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 228:1-3, s. 64-73
  • Tidskriftsartikel (refereegranskat)abstract
    • The NMR self-diffusion technique is used for measuring diffusion of water in highly concentrated multilamellar vesicle solutions. The signal intensity of water, i.e. the water echo-decay, is monitored down to very small intensities thus providing an accurate measure of how water is diffusing in the solution. It is noted that a large curvature is dominating the functional form of the echo-decay indicating the presence of a large number of multilamellar vesicles. It is also concluded that in order to measure accurately the volume fraction of water inside and outside vesicles the experimental time scale can be changed. From a multiexponential fit to the echo-decay the fraction fast and the sum of all slow components can be extracted. When the apparent fraction "vesicle water", P-vw(app), is plotted versus the experimental time scale the graph produced is a good representation of the difference in how fast water diffuses over the different vesicle membranes. From an extrapolation to "zero time" the true fraction of trapped water can be extracted, i.e. a quantitative measure of the volume fraction of vesicles at a certain concentration of surfactant.
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3.
  • Wittung Stafshede, Pernilla, 1968, et al. (författare)
  • Detection of point mutations in DNA by PNA-based quartz-crystal biosensor
  • 2000
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 174:1-2, s. 269-273
  • Tidskriftsartikel (refereegranskat)abstract
    • Currently there is an extensive search for biosensors for detecting genetic defects by hybridisation to immobilised oligonucleotides. A concept able to detect a single mismatch in a 15mer single-strand target of the p53 tumor suppresser gene is presented (a mutation found in many types of cancer cells). In this method, the unique hybridisation properties of the DNA mimic peptide nucleic acid (PNA) are combined with electronically detected mass and shear dissipation at the surface of a quartz crystal. Cysteine-labeled PNA efficiently immobilises on crystal-gold surface at 20 degrees C. At 60 degrees C, addition of complementary DNA results in a signal response corresponding to hybridisation between DNA and the PNA-covered surface, whereas addition of DNA differing in only one of the 15 bases gives no response at all.
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4.
  • Gernandt, Renate, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 213:1, s. 15-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, orders of mixing, salt concentrations and polymer concentrations. Initially the polymers were characterised by polyelectrolyte titration (charge), static light scattering (molecular weight, radius of gyration) and measurements with a scanning interferometric refractometer (refractive index). The complexes were characterised by ocular inspection and static light scattering in combination with a special evaluation algorithm allowing an estimation of the geometric form of the complexes. The results show that the initial complexes have a spherical form and that the size is fairly constant over a large range of charge ratios between the polymers, provided the complexes are formed in deionised water. When the charge mixing ratio exceeded neutrality a secondary agglomeration of the initially formed complexes occurred. The presence of salt during PEC formation caused a dependence of the level of aggregation on the mixing ratio, whereby small amounts of NaCl drastically lowered the particle mass at lower mixing ratios. Subsequent addition of salt to PECs formed in water led to a strong swelling of the complex particles and at a critical salt concentration to dissolution.
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5.
  • Gärdlund, Linda, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres II : Influence of complexes on wet and dry strength of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 218:1-3, s. 137-149
  • Tidskriftsartikel (refereegranskat)abstract
    • The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly (amide, amine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PEC�s were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%. Paper strength; Polyelectrolyte Complexes; PAE; CMC; Strength additive
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6.
  • Gärdlund, Linda, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres II. Influence of complexes on wet and dry strength of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 218:1-3, s. 137-149
  • Tidskriftsartikel (refereegranskat)abstract
    • The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly(amideamine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PECs were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%.
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7.
  • Norgren, Magnus, et al. (författare)
  • Aggregation of Kraft Lignin Derivatives under Conditions Relevant to the Process. Part I. Phase Behaviour
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 85-96
  • Tidskriftsartikel (refereegranskat)abstract
    • Aggregation of a commercial, polydisperse softwood kraft lignin (Indulin AT) in diluted aqueous alkaline solutions was investigated experimentally, by means of turbidity measurements. The influence of temperature, salt concentration and pOH and the role of a divalent counterion on the aggregation behaviour were studied. When the temperature was increased, an increased tendency of aggregation in samples containing high concentrations of sodium chloride was found. Phase separation could be detected even at pOH=2 at 175°C and the effect was pronounced when the concentration of hydroxide ions decreased. The phase transition from soluble to precipitated lignin was found to be irreversible concerning temperature change. Small amounts of calcium ions were seen to induce dramatic effects on the system stability, even at relatively high hydroxide concentrations (pOH 1-2). At a given temperature and pOH, the coagulation was found to appear at a certain critical coagulation concentration (CCC) of the added electrolyte. Furthermore, calculations were carried out to compare with the outcome of the experimental observations. A theoretical model, based on the DLVO theory, was found to predict the kraft lignin solution behaviour well.
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8.
  • Norgren, Magnus, et al. (författare)
  • Stabilisation of Kraft Lignin Solutions by Surfactant Additions
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 239-248
  • Tidskriftsartikel (refereegranskat)abstract
    • The colloidal stability of kraft lignin (KL) and some various KL-surfactant mixtures in aqueous alkaline solutions, pH 10.0-11.50, was tuned and investigated at high ionic strengths, 0.5-1.1 M, and elevated temperatures, 70 and 150°C. The main techniques used were Quasi-Elastic Light-Scattering (QELS) and turbidity measurements, together with sample inspection by the naked eye. Samples without surfactant additions and samples containing various alkyl sulfonates showed a comparably low colloidal stability, whereas in mixtures containing sodium salts of bile acids, the stability was found greatly improved. The efficiency of different bile salts was investigated and it was found that the overall best solution stability is obtained in mixtures of KL and sodium taurodeoxycholate (STDC). STDC showed a relatively good stabilising effect also at very high temperatures (150°C). Furthermore, in already aggregated KL solutions, additions of STDC were found to cause 'de-aggregation' and the number of formed aggregates was dramatically decreased. From the outcome of the investigation, it can be concluded that by introducing surfactants, and maybe other designed additives too, new possibilities in controlling the colloidal stability of KL at rough solution conditions are given.
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9.
  • Ridell, Annika, et al. (författare)
  • On the water content of the solvent/monoolein/water sponge (L3) phase
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 228:1-3, s. 17-24
  • Tidskriftsartikel (refereegranskat)abstract
    • The water content of the solvent/monoolein/water sponge phase depends on the lipophilicity of the solvent used. The relatively lipophilic solvent 2-methyl-2,4-pentanediol (MPD) gives a sponge phase at about 60 wt.% water compared with 30 wt.% for the sponge phase formed with polyethylene glycol (Mw≈400, PEG 400). A reasonably good correlation is found between the water content of the sponge phase and the octanol/water partition coefficient for the solvent. The water content of the PEG 400 sponge phase increases considerably (to about 50 wt.%) by adding up to 3 wt.% of ionic compounds such as SDS, CTAB and salts of amphiphilic drugs. Nonionic detergents show less effect on increasing the water content, whereas membrane lipids such as lecithins and cholesterol show unchanged or even decreasing effect on the water content of the sponge phase.
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10.
  • Seppanen, R., et al. (författare)
  • Heteroflocculation of kaolin pre-treated with oppositely charged polyelectrolytes
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 164:2-3, s. 131-141
  • Tidskriftsartikel (refereegranskat)abstract
    • Heteroflocculation studies of kaolin particles have been carried out by mixing two kaolin suspensions; one stabilised by a cationic polymer and the other stabilised by a highly charged and low molecular weight anionic polymer. Molar mass and charge density of cationic polymer as well as the mixing ratio of oppositely charged suspensions were varied. Flee size and degradation during shearing were investigated by measuring hoc size using a light scattering/diffraction method at different flow rates. It was observed that floc size was small when subjected to a low flow rate and decreased with increasing how rate. Cationic polymers with high molar mass and low charge density produced flocs with high resistance towards flee degradation. Maximum flee size was obtained at a mixing ratio where the flocs became slightly negatively charged. Flee size and degradation were observed to be independent of primary kaolin particle size. Furthermore, floc size increased with increasing ionic strength. Scanning electron micrographs showed flocs with an open structure, which is expected to improve the optical properties of paper when using microflocs as a filler in paper production.
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11.
  • Shchukarev, Andrey, et al. (författare)
  • XPS imaging of surface diffusion of alkylketene dimer on paper surfaces
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. ; 219:1-3, s. 35-43
  • Tidskriftsartikel (refereegranskat)abstract
    • The alkylketene dimer (AKD) wax dispersion is introduced in the wet-end of a paper machine, and during drying it spreads and anchors to the fiber surface. Direct observation of the surface diffusion of the AKD wax at paper surfaces was obtained using X-ray photoelectron spectroscopy imaging technique. An AKD diffusion of approximately 400 μm was observed at a paper surface that was stored for 3 h at 80 °C. This gives a diffusion coefficient of approximately 10−11 m2 s−1. Storage for 1 week at room temperature also showed a remarkable spreading of AKD.
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12.
  • Shen, Huiting, et al. (författare)
  • Floatability, selectivity and flotation separation of plastics by using a surfactant
  • 2002
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 196:1, s. 63-70
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper, the floatability of seven plastics (POM. PVC, PET. PMMA, PC., PS and ABS) in the presence of alkyl ethoxylated nonionic surfactant (15-S-7) was investigated. It was found that the floatability of all the plastics decreases with the addition of the surfactant; but they are different in floatability and follow the order POM < PVC < PMMA < PET < PC < ABS < PS. From the separation test results of several plastic mixtures, it was shown that Gamma flotation method not only can be used to separate plastics mixture with different density, such as separation of POM and PVC from PC, POM and PVC from PS and ABS, PET and PMMA from PS and ABS, but also can be used to separate plastics mixture with similar density, such as separation of PMMA from PC. Products with grade higher than 99%. and recovery higher than 97% can be obtained for the separation of some plastic mixtures. Finally, surface chemical factors, such as wettability of plastics and surface tension of flotation medium, and gravity factors, such as particle density and shape, were studied, It was found that the depressing effect of surfactant 15-S-7 on the plastics is mainly due to the reduced liquid surface tension, and flotation selectivity for the plastics with identical particle size is dominated by contact angle, particle density and shape. (C) 2002 Elsevier Science B.V. All rights reserved.
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13.
  • Solberg, D., et al. (författare)
  • Adsorption and flocculation behavior of cationic polyacrylamide and colloidal silica
  • 2003
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 219:03-jan, s. 161-172
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption of cationic polyacrylamide and silica nanoparticle systems onto a model surface has been compared with the adsorption and flocculation of a fiber suspension. An increase in ionic strength affects the polyelectrolyte adsorption in different ways in these two systems. With a silica surface, an increase in the ionic strength leads to a continuous increase in the adsorption. On a cellulose fiber, the adsorption increases at low ionic strength (1-10 mM NaCl) and then decreases at higher ionic strength (10-100 mM NaCl). When polyelectrolyte is added to the fiber suspension, flocculation occurs with an optimum around a polyelectrolyte addition of 0.4 mg g(-1). Above this addition level the flocculation effect is reduced and dispersion occurs when more than 1.2 mg g(-1) polyelectrolyte is added. This behavior suggests a bridging flocculation, the dispersion being explained by electrosteric stabilization of the suspension. Addition of silica nanoparticles to the fiber suspension leads to a greater degree of flocculation than in a single polyelectrolyte system. The adsorption of nanoparticles to a polyelectrolyte-covered silica surface increases both the adsorbed amount and the thickness of the adsorbed film. A more extended silica particle, giving a more extended polyelectrolyte-silica film, also results in a higher degree of fiber flocculation.
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14.
  • Stén, Pekka, et al. (författare)
  • Precipitation of lead sulfide for surface chemical studies
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 172:1, s. 17-31
  • Tidskriftsartikel (refereegranskat)abstract
    • Although there seems to be a general agreement that the surface chemical properties of precipitated lead sulfide depend on the surface stoichiometry of the precipitate, the effect of the precipitation conditions on the surface stoichiometry has not been studied in detail. In this work, the precipitation procedure, per se, was studied by titrations with lead nitrate and sodium sulfide solutions. The titrations were controlled potentiometrically using glass, redox, and ion-selective (Pb2+, S2-) electrodes and supplemented by analyses of the precipitates. It was found that the titration speed exercised a major influence upon the results. When the titrations of lead nitrate solutions with sodium sulfide solutions were conducted slowly enough, two inflection points and slow achievement of equilibria at the titration points between them were obtained and were explained as being due to lead and sulfide ions adsorbing on the surfaces of the final crystals. Further, the position of the major inflection point was found to depend on the titration speed, which was explained by considering the coprecipitation of nitrate ions with lead sulfide. The coprecipitation was verified by analyzing the precipitates, which were shown to contain up to 3% nitrate. Due to these coprecipitation and adsorption phenomena, the addition of an equivalent amount of sulfide to a lead nitrate solution results in a lead sulfide suspension bearing an excess of sulfide on the surfaces. Both in situ monitoring of the precipitation by ion-selective electrodes and facilitated desorption of the excess adsorbed sulfide ions at a correctly adjusted pH are suggested as better methods for producing lead sulfide suspensions.
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15.
  • Vidyadhar, A., et al. (författare)
  • Mechanisms of amine–feldspar interaction in the absence and presence of alcohols studied by spectroscopic methods
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 214:1, s. 127-142
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption of long-chain primary amines on feldspars at neutral pH 6-7 was investigated using Hallimond flotation, zeta-potential, FT-IR and XPS studies. Two-dimensional (2D) followed by three-dimensional (3D) precipitation mechanism of amine adsorption on quartz reported earlier (Langmuir 16 (2000) 8071) was further substantiated. The orientation and packing of dodecyl- and hexadecylammonium acetate and chloride adsorbed on albite in the different regions of the adsorption isotherm were determined. It was shown that these characteristics depend strongly on the substrate. The influence of long-chain alcohols on the adsorption of amines in mixed amine/alcohol on feldspars, i.e. albite (NaAlSi3O8) and microcline (KAlSi3O8), was also examined. Coadsorption of the counterion was not revealed, but the counterion was found to affect indirectly the adsorption at concentrations above the concentration of the bulk amine precipitation. It was proved spectroscopically that co-adsorption of long-chain alcohols along with amine cations leads to formation of a closed packed surface layer as compared to the case of adsorption of pure amine alone at the same concentration. The highest order and packing at the surface were observed when the alkyl chain length of mixed amine and alcohol were the same. The condition of same chain length of amines and alcohols adsorbing at the surface corresponded to maximum flotation recovery. The results also confirmed the synergistic enhancement of amine adsorption in the presence of alcohols. A mechanism of mixed long-chain amine and alcohol adsorption onto silicates (albite and quartz) consistent with the primary adsorption species of alkylammonium-water-alcohol complex, where deprotonation of ammonium groups in the adsorbed layer leading to 2D precipitation of molecular amine was illustrated.
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16.
  • Wantke, K-D, et al. (författare)
  • Surface dilational properties of mixed sodium dodecyl sulfate/dodecanol solutions
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 221:1-3, s. 185-195
  • Tidskriftsartikel (refereegranskat)abstract
    • The surface dilatational properties of aqueous solutions of sodium dodecyl sulfate (SDS) and n-dodecanol areinvestigated in the frequency range 15/f5/500 Hz using the oscillating bubble method. The results demonstrate that apure dodecanol solution has an elastic surface without viscous effect whereas the surface of a SDS solution withoutadded dodecanol exhibits a strong viscoelastic behavior. Mixtures show graduated properties. The time behavior oftheir surface dilatational moduli demonstrates that dodecanol molecules drive the SDS molecules slowly out of thesurface. Therefore, the known one-component model describing the surface dilatational modulus can be used also forthese mixtures. A simple theoretical consideration explains this effect.
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17.
  • Boschkova, K, et al. (författare)
  • Frictional properties of lyotropic liquid crystalline mesophases at surfaces
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 166, s. 67-77
  • Tidskriftsartikel (refereegranskat)abstract
    • The lubricating effect of assemblies of amphiphiles at surfaces has been studied. Liquid crystalline mesophases were investigated in terms of frictional and wear properties in a pin on disc rig. It is shown that systems forming lamellar liquid crystals indeed serve as lubricating liquids, indicating that the lamellar liquid crystalline phase adsorb on the steel surface forming a lubricating tribofilm. Poor performance is obtained when the lubricating system is in a single phase, i.e. in this case a lamellar liquid crystalline region. However, good lubrication is found when the lamellar liquid crystalline phase is dispersed in the water. This is attributed to a low viscosity of the system rendering a fast relaxation of the system in order to form a new film after the disturbing action of the two sliding surfaces. The lamellar packing is altered by the addition of non-charged amphiphiles, such as short chain alcohols. Using different alcohols it was shown that aromatic short chain alcohols are detrimental to the wear. This was attributed to the Rebinder effect, i.e. a strong adsorption of the alcohol, which in turn facilitates crack formation and thus the wear. In systems with mixtures of cat- and anionic amphiphiles it was, not surprisingly found that the best lubrication is obtained with a slight excess of either surfactant.
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18.
  • Djuve, J, et al. (författare)
  • Foaming and dynamic surface tension of aqueous polymer/surfactants solutions 1: ethyl(hydroxyethyl) cellulose and sodium dodecyl sulphate
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 186, s. 189-202
  • Tidskriftsartikel (refereegranskat)abstract
    • Foaming (in a column) and dynamic surface tension behaviour of aqueous solutions of sodium dodecyl sulphate (SDS), and ethyl (hydroxy ethyl) cellulose/ sodium dodecyl sulphate (EHEC/SDS) mixtures was determined. The results indicated a synergism in foaming and surface activity for the EHEC/SDS mixtures over a specific concentration range. For the SDS solution, the maximum value in Marangoni Elasticity (EM max), as determined from dynamic surface tension data, was reached within a surface age of 0.05s and it could be suggested that in this case EM max was relevant to foam stability. However, for the EHEC (non-foaming solutions), EM max was reached after longer surface ageing periods (0.05-0.1 s). For the EHEC/SDS solutions, EM max occurred over a range of surface ageing periods depending on the polymer/surfactant ratio and no correlation was obtained between EM max and foaming. The EM max time lag for the polymer and polymer/surfactant mixtures was explained by the slower diffusion from solution to the new surface. For the EHEC/SDS, the enhanced the foaming behaviour was explained by the adsorption of surface active polymer/surfactant (clusters) species at the air/solution interface. It was suggested that this could lead to coherent (gelatinous) interfacial layers in the thin film lamella which reduce drainage from the central fluid.
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19.
  • Eriksson, JC, et al. (författare)
  • Entropy and droplet size distributions of Winsor I and II microemulsions
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 183-185, s. 347-360
  • Tidskriftsartikel (refereegranskat)abstract
    • A review is presented of some general notions underlying the current theory of Winsor I and II microemulsions where the exposition is based on a comparison between the droplet kind of approach with the corresponding multiple equilibrium treatment. We show that the droplet size distributions derived earlier, although put in different mathematical forms in the respective treatments, are in effect the same, of the type where the preexponential factor, S(R), is due to the fluctuations in size and shape of the droplets, and the droplet surface tension, s, is curvature-dependent in accordance with the Helfrich expression. Full consistency is demonstrated among the two approaches, at least insofar as surfactant density fluctuations are not explicity taken into account. Moreover, on the basis of the multiple equilibrium model we can actually estimate the length scale parameter l introduced earlier in the droplet kind of treatment to fully account for the entropy of dispersion, to be about 1 nm, in fair agreement with previous estimates
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20.
  • Ernstsson, Marie, et al. (författare)
  • A multianalytical approach to characterize acidic adsorption sites on a quartz powder
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 168, s. 215-230
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper three methods are described to estimate the number of adsorption sites and detect adsorption sites of differing nature on mineral surfaces. The methods are solution depletion adsorption isotherms, adsorption microcalorimetry, and desorption by solvent extraction followed by surface analysis using Electron Spectroscopy for Chemical Analysis (ESCA). The number of adsorption sites is obtained from the adsorbed amount of a test molecule on a mineral surface from the ESCA data using equations based on a substrate/overlayer model, and from the adsorption isotherms the number of sites available to accommodate a monolayer of test molecules is used. Information about whether the adsorption sites are of different or similar nature is provided by the desorption method using extraction in solvents of different polarities. More quantitative information concerning interactions between test molecules and adsorption sites, and possible interaction strength distribution due to sites of differing nature, is obtained from the adsorption enthalpies measured by microcalorimetry. The systems studied included strong basic test molecules (either a fatty diamine, octadecyl amine or pyridine) adsorbed on quartz powder from a nonpolar medium, n-octane. For the desorption study, subsequent extraction was carried out in pure n-octane, followed by ethanol. Adsorption/desorption of basic test molecules on quartz is important in applications of asphalt systems where fatty amines are often added to strengthen adhesion between bitumen and stone aggregates. The quartz powder studied here has acidic adsorption sites of differing nature on the surface. The strong interaction sites are consistent with iron oxide and/or oxohydroxide (strongest interactions with the fatty diamine where both nitrogen atoms can interact) and geminal hydroxyl groups. The weaker interaction sites are consistent with hydroxyl (silanol) groups forming hydrogen bonds with the basic test molecules.
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21.
  • Folmer, BM, et al. (författare)
  • The cross sectional headgroup area of nonionic surfactants; The influence of polydispersity
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 180, s. 187-191
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we have measured surface tension as a function of concentration of pure and technical nonionic ethoxylated surfactants. CMC values, surface tension at the CMC and the cross sectional headgroup areas are compared. It is shown that the CMC does not depend significantly on the polydispersity of the polyoxyethylene chain. However, the surfactant headgroup area, as determined from the surface tension plots, are much smaller for polydisperse surfactants than for homologue pure surfactants. This is due to the selective adsorption of the shorter polyoxyethylene species at the surface. For the same reason the surface tension at the CMC is lower for technical surfactants than for homologue pure species.
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22.
  • Hellebust, S, et al. (författare)
  • Associative and segregative phase behaviour of a mixed aqueous cationic surfactant and anionic hydrophilic polymer system
  • 2004
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 243, s. 133-138
  • Tidskriftsartikel (refereegranskat)abstract
    • The phase behaviour of a mixture of a highly charged hydrophilic polymer, dextran sulphate sodium salt, and a cationic surfactant, tetradecyltrimethylammonium bromide, was investigated in aqueous solution of different ionic strengths. The system has the interesting and novel property that at certain ionic strengths it displays both segregative and associative phase behaviour separated by a single-phase region within the same phase diagram. By increasing the ionic strength further the segregative area increases and the associative area disappears. In addition, the effect of cosolutes n-octane and 1-octanol on the above-mentioned phase behaviour has been studied. The effect of the former was to increase the miscibility and the latter to decrease the miscibility.
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23.
  • Häger, M, et al. (författare)
  • Oxidation of azo dyes in oil-in-water microemulsions catalyzed by metalloporphyrins in presence of lipophilic acids
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 183-185, s. 247-257
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrogen peroxide oxidation of two aqueous azo dyes, methyl orange and amaranth, catalyzed by manganese porphyrins, have been performed in an oil-in-water microemulsion based on a nonionic surfactant, C12E8. A lipophilic acid was used as cocatalyst in a variable amount. The oxidation was followed by UV spectroscopy. It was shown that the reactions performed in the microemulsion were rapid for both dyes and the reaction rate increased strongly with increasing amount of lipophilic acid added to the reaction mixture. As reference, the same reactions were performed in a two-phase system without surfactant. The reaction profiles in the two-phase system were similar to those in the microemulsion, but the rate was considerably lower. The effect of addition of small amounts of ionic surfactant was also investigated. Addition of anionic surfactant gave a pronounced decrease in reaction rate, whereas a cationic surfactant gave a small reduction in rate. We propose that the rate-limiting step is formation of a metallo-acylperoxy complex at the boundary between oil and water domains. The metallo-acylperoxy complex oxidizes the azo dye in a subsequent step.
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24.
  • Häger, M, et al. (författare)
  • Synthesis of an amphiphilic polymer performed in an oil-in-water microemulsion and in a liquid lamellar crystalline phase
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 189, s. 9-19
  • Tidskriftsartikel (refereegranskat)abstract
    • A nucleophilic addition reaction between a hydrophilic hydrazide, the hydrazide of polyethylene glycol with a molecular weight of 3400, and a hydrophobic aldehyde, has been performed in a microemulsion and a lamellar liquid crystalline phase of a ternary non-ionic surfactant-water-oil system. As a reference the same reaction was performed in a two-phase (water-oil) system, without any surfactant. The phase behavior of the microemulsion system in the presence and in the absence of the reactants, and the temperature effects on the phase behavior were investigated. Addition of the hydrophilic reactant, the PEG dihydrazide, to the aqueous component, as well as addition of the hydrophobic aldehyde to the oil, resulted in a reduction of the temperature range of the microemulsion which was interpreted as being due to a change of the spontaneous curvature of the surfactant monolayer in the direction of increased bending towards water. The reaction kinetics were investigated by 1H-NMR. It was shown that the reactions performed in the oil-in-water microemulsion and the liquid crystalline phase were very rapid with almost all of the starting materials being consumed after a 20-min reaction time. The reaction performed in the two-phase system was very slow and after 6 h only 10% of the starting material had reacted.
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25.
  • Johansson, B, et al. (författare)
  • Flotation de-inking studies using model hydrophobic particles and non-ionic dispersants
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 170, s. 217-229
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of non-ionic surfactants (alcohol ethoxylates, C10-14E6-8) with HLB within the range of 11.1 to 13.1 were used as dispersants during flotation of mondisperse hydrophobized silica particles (representing ink particles) in deinking formulations. Laboratory scale flotation experiments, contact angle, dynamic surface tension and thin film drainage experiments were carried out. These results indicated that the non-ionic surfactant with the highest CMC (C10E6) gave (a) the highest rate of adsorption at the air/solution interface (b) the lowest reduction in contact angle and (c) the lowest flotation efficiency at concentrations above the CMC. However, below the CMC for C10E6 the flotation efficiency was very high probably due to a low amount of adsorbed material at the particle/solution interface. It was also observed that flotation occurred, in spite of the fact that thin-film measurements indicated that the adsorption of non-ionic surfactants at the air/solution and silica/solution interfaces reduced the hydrophobicity of the particles, as indicated by an increase in stability of the aqueous thin film between the particle and air bubble. This result suggests that the bubble/ink particle capture mechanism (occurring through rupture of the thin aqueous film separating the interfaces) is not the only mechanism controlling the flotation efficiency and that other parameters (such as the kinetics of surfactant adsorption, foaming characteristics and bubble size) need to be taken into account. The kinetics is important with respect to the rate of adsorption of surfactant to both interfaces. Under equilibrium conditions, this may give rise to repulsive steric forces between the air bubble and the particles (stable aqueous thin film). However, at lower adsorption levels (caused by slow adsorption rates) the lower steric repulsion will allow effective collection of particles by the bubble. Also, it was suggested that the influence of alcohol ethoxylates on bubble size could effect the particle capture rate and mechanical entrainment of particles in the froth will also play a role in the flotation recovery.
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26.
  • Kapilashrami, A, et al. (författare)
  • Drying of oil-in-water emulsions on hydrophobic and hydrophilic substrates
  • 2004
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 233, s. 155-161
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the effect of the hydrophobic/hydrophilic character of the substrates on the drying behaviour of dilute silicone oil-in-water (o/w) emulsions by light microscopy and ellipsometry. The poly(dimethylsiloxane) (PDMS) emulsion droplets, which are stabilised by a triblock PEO/PPO/PEO copolymer, form a close-packed structure containing domains of hexagonally packed droplets on the hydrophilic substrate. We find that the hydrophilic substrate does not destabilise the emulsion droplets; the close-packed structures are very stable and coalesce very slowly only when most of the water has evaporated. This is supported by ellipsometry measurements, which showed that the emulsion droplets do not adsorb to the hydrophilic substrate. The hydrophobic substrate, on the other hand, destabilises the emulsion and we observed a significant increase in the coalescence rate. Ellipsometry measurements suggest that destabilisation is promoted by the strong interaction between the emulsion droplets and the hydrophobic substrate. We also find that the emulsion undergoes dewetting followed by a release of oil and rewetting of the substrate when the o/w emulsion film reaches a critical thickness on the hydrophobic substrate
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27.
  • Kapilashrami, A., et al. (författare)
  • Ellipsometric studies of nonionic copolymers adsorbed at the solid/water and oil/water interfaces
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 225, s. 181-192
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological properties of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers
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28.
  • Kugge, C, et al. (författare)
  • A scanning electron microscope study of the surface structure of model paper coatings
  • 2004
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 238, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the structure of model paper coating layers, composed of mineral pigments, latex binders and polymeric thickeners and dispersants, using Scanning Electron Microscopy (SEM). The main aim of the study is to identify how systematic variations in the composition of the coating, including pigment type (calcium carbonate, clay), the glass transition temperature of the binder, type (CMC, EHEC) and molecular weight of the polymeric thickener affect the surface features of the coating layer, including surface roughness and porosity and, consequently, gloss. The samples are investigated mainly in conventional high-vacuum SEM mode; however some studies are also performed with the environmental feature (ESEM mode) at higher pressures and humidities, in order to track dynamic changes drying and rewetting. The results are compared to those of recent measurements on the same systems obtained with Atomic Force Microscopy (AFM), where the local latex film formation process has been carefully studied
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29.
  • Larsson, A, et al. (författare)
  • 1H NMR of thermoreversible polymers in solution and at interfaces: The influence of charged groups on the phase transition
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 190, s. 185-192
  • Tidskriftsartikel (refereegranskat)abstract
    • The phase transition of thermoreversible polymers occurring at the lower critical solution temperature (LCST) is investigated by 1H NMR. Poly-N-isopropylacrylamide (PNIPAM) shows such a coil to globule transition at 32°C in aqueous solution. To study the effect of charged polymer segments on the phase transition, the temperature dependent properties of PNIPAM and of a charged PNIPAM-copolymer, containing 10% carboxylic groups, are investigated in solution. Experiments are performed by 1H spectra and PFG-NMR diffusion measurements at different polymer concentrations. The 1H liquid signal is sharply decreasing at the phase transition temperature. The transition is found to be equally sharp for the copolymer as for the homopolymer at concentrations below and around the overlap concentration, whereas the transition is broadened at higher concentrations. Diffusion measurements prove that the conformation of the polymer coils is maintained with increasing temperature until close to the phase transition, apart from a minor decrease of the hydrodynamic radius at about 2°C below the LCST. All data indicate identical phase transition properties of the copolymer as compared with the homopolymer. The introduction of charged groups (3% of monomers dissociated) has thus not altered the transition. Therefore, the copolymer is a suitable candidate for exhibiting a phase transition under electrostatic coupling conditions in layers. Both polymers are adsorbed to colloidal silica (Cab-O-Sil) and investigated by 1H NMR in order to monitor the phase transition in the restricted geometry of an adsorption layer. The liquid 1H intensities of both polymers are decreasing with temperature, this is interpreted as a phase transition of the loops and tails. The transition is substantially broader than in solution, especially at low surface coverage. Significant differences between the copolymer and the homopolymer are observed, since above the transition temperature a liquid signal from loops and tails of the copolymer is still observed. This is interpreted as a comparatively mobile arrangement of the copolymer layer, arising from electrostatic repulsion from the surface and between polymer segments, which is partly hindering globule formation.
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30.
  • Persson, Clas Marcus, et al. (författare)
  • Surface forces measured in sugar surfactant solutions between two hydrophobic thiolated silica spheres
  • 2004
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 233:1-3, s. 43-49
  • Tidskriftsartikel (refereegranskat)abstract
    • The force acting between two hydrophobic surfaces (hexadecyl-thiolated gold surfaces) across two different non-ionic sugar surfactant solutions above cmc was investigated. The two surfactants studied were n-decyl-beta-D-glucopyranoside (Glu) and n-decyl-beta-D-maltopyranoside (Mal). No long-range double-layer force was detected between the surfactant covered surfaces showing that they are non-ionic as expected. At distances from 20 nm down to a separation of 3 nm the ever-present van der Waals force creates a net attraction between the surfaces. At 3 nm the surfaces are in monolayer-monolayer contact and the system has a secondary force minimum. At shorter separations the surfactant monolayer starts to interact and a steric force develops counteracting the depletion of surfactants from the gap. As the compressive load reaches FIR approximate to 1.5 mN/m the surfaces are in hydrophobic-hydrophobic contact, where the system has its primary energy minimum. The nature of the pressure-induced depletion of surfactants from the contact zone showed a strong dependence on the approach velocity. This reveals that the time scale of the surfactants to reach their equilibrium situation under external compression is of several seconds. The surfactant with the glucoside head group offered a greater resistance against being forced out (15% higher). This was attributed to the larger adsorbed amount of Gin at the hydrophobic solid-liquid interface. It was further concluded that the forces generated from the surfactants were enough to prevent the system from coagulating but that flocculation will occur in the secondary force minimum (primary energy minimum). The hydrodynamic force was studied by changing the approach velocity of the surfaces. The position of the slipping plane coincided with the layer thickness of the adsorbed monolayer of surfactant at moderate approach velocities. The adhesion force increased with the time the surfaces were in contact and no limiting value was reached. This was attributed to surfactants remaining in the gap slowly being removed from the contact zone, thereby, increasing its hydrophobic character.
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31.
  • Persson, CM, et al. (författare)
  • Surface forces measured in sugar surfactant solutions between two hydrophobic thiolated silica spheres
  • 2004
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 233, s. 43-49
  • Tidskriftsartikel (refereegranskat)abstract
    • The force acting between two hydrophobic surfaces (hexadecyl-thiolated gold surfaces) across two different non-ionic sugar surfactant solutions above cmc was investigated. The two surfactants studied were n-decyl-ß-D-glucopyranoside (Glu) and n-decyl-ß-D-maltopyranoside (Mal). No long-range double-layer force was detected between the surfactant covered surfaces showing that they are non-ionic as expected. At distances from 20 nm down to a separation of 3 nm the ever-present van der Waals force creates a net attraction between the surfaces. At 3 nm the surfaces are in monolayer–monolayer contact and the system has a secondary force minimum. At shorter separations the surfactant monolayer starts to interact and a steric force develops counteracting the depletion of surfactants from the gap. As the compressive load reaches F/R≈1.5 mN/m the surfaces are in hydrophobic–hydrophobic contact, where the system has its primary energy minimum. The nature of the pressure-induced depletion of surfactants from the contact zone showed a strong dependence on the approach velocity. This reveals that the time scale of the surfactants to reach their equilibrium situation under external compression is of several seconds. The surfactant with the glucoside head group offered a greater resistance against being forced out (15% higher). This was attributed to the larger adsorbed amount of Glu at the hydrophobic solid–liquid interface. It was further concluded that the forces generated from the surfactants were enough to prevent the system from coagulating but that flocculation will occur in the secondary force minimum (primary energy minimum). The hydrodynamic force was studied by changing the approach velocity of the surfaces. The position of the slipping plane coincided with the layer thickness of the adsorbed monolayer of surfactant at moderate approach velocities. The adhesion force increased with the time the surfaces were in contact and no limiting value was reached. This was attributed to surfactants remaining in the gap slowly being removed from the contact zone, thereby, increasing its hydrophobic character.
  •  
32.
  • Rundlöf, M., et al. (författare)
  • Formation of multilayers on silica surfaces of a cationic polyelectrolyte and dissolved and colloidal substances originating from mechanical wood pulp-Adsorption and influence on adhesion
  • 2004
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 237:03-jan, s. 33-47
  • Tidskriftsartikel (refereegranskat)abstract
    • By measuring adsorption using a stagnation point reflectometer, it was shown that multilayers consisting of cationic polymers and dissolved and colloidal material released from wood fibres into process waters are formed on an anionic silica surface. The similarity of this experiment to the papermaking process was established. It was established using the JKR-method that this multilayer adsorption had a profound effect on the adhesion, in air, of an elastic polydimethyl siloxane (PDMS) probe to these surfaces. The adhesion of PDMS to a bare silica surface showed a large hysteresis, with a much stronger adhesion measured upon the separation of the two surfaces compared with the value obtained from gradually pressing them together. It was suggested that this hysteresis was due to specific interactions (hydrogen bonding) that develop over time. The first adsorbed layer, a cationic poly(dimethyldiallylammoniumchloride) (polyDMDAAC), decreased the magnitude of the hysteresis and gave a relatively low adhesion, which may be due to the fact that these specific interactions were blocked. The subsequent build up of layers of lipophilic wood extractives in the form of colloidal particles and cationic polymer increased the adhesion. This was interpreted as being due to the build up of a soft layer on the stiff mineral surface causing additional energy dissipation upon separation, even though the molecular adhesion was still decreased compared with the bare silica. This was supported by the fact that none of the individual components of the multilayer increased the adhesion when applied in a relatively thin layer on the silica, and by the fact that a thick deposition of cast coated wood extractives gave a very high adhesion. Stearic acid was chosen as a model substance for extractives and deposited onto silica from vapour phase. This resulted in a partial coverage of the surface where the stearic acid was present as patches of different size. This gave a significant reduction of the adhesion. The solid stearic acid melted and was redistributed when confined between the PDMS and the silica. This gave a thinner and more uniform layer. The application of a monolayer of C-18-tails covalently bound to the silica by siloxane links, gave a very significant reduction of the magnitude of the adhesion hystersis. It is concluded that the distribution of the contaminants over the surface is very significant for the adhesion properties. This is relevant to practical papermaking with respect to: (i) the build up of deposits on process equipment and its effect on adhesion to these surfaces; (ii) fibre-fibre adhesion and thereby paper strength, a phenomenon that can never be studied without directly measuring the adhesion, which makes specific solutions to the practical problems possible.
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33.
  • Shen, H, et al. (författare)
  • Flotability, selectivity and flotation separation of plastics by using a surfactant
  • 2002
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 196, s. 63-70
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the floatability of seven plastics (POM, PVC, PET, PMMA, PC, PS and ABS) in the presence of alkyl ethoxylated nonionic surfactant (15-S-7) was investigated. It was found that the floatability of all the plastics decreases with the addition of the surfactant; but they are different in floatability and follow the order POM
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34.
  • Theander, K, et al. (författare)
  • Surface chemicals concepts in flotation de-inking
  • 2004
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 240, s. 111-130
  • Tidskriftsartikel (refereegranskat)abstract
    • This review outlines the important parameters, which influence the flotation de-inking and discusses the surface chemical aspects of the process. Although, it has been established increasing temperature and pH facilitate the release of ink particles from the fibre during pulping (prior to flotation), it has not yet been completely established to what extent these parameters increase or decrease the efficiency of the primary flotation step. In fact, increasing temperature appears to decrease the flotation rate and also an increase in pH can retard the flotation due to a reduction in capture efficiency between the air bubbles and the ink particles decreasing the flotation in the cell. In addition, the size, shape and roughness of the ink particles influence this bubble/particle capture mechanism. Bubble frequency and bubble size is influenced by surface tension (type and concentration of frother) but X-ray studies also indicate that the fibre consistency can influence the bubble shape and flow patterns causing channelling and re-circulation of bubble flow in the cell. Tests with different gases (oxygen and nitrogen instead of air) show no significant gains in optical and mechanical properties of the fibre. Fatty acids with higher chain length and lower degree of saturation are less soluble and ensure lower carry-over but less foaming and also less fibre recovery. The primary mechanisms of fatty acid flotation involves precipitation of calcium soap, followed by micro-encapsulation of ink through a hetero-coagulation mechanism, followed by the bubble/ink particle capture step. In the use of nonionic surfactant, cloud point and HLB are important parameters, which influence brightness, washing and flotation efficiency. Optimum flotation occurs with slight excess of fatty acid to reduce surface tension and optimum calcium levels ensuring that most of the calcium is removed in the process. A lower calcium level gives lower stock loss but a high calcium has a detrimental effect, causing scaling and deposition. A critical nonionic/fatty acid balance is needed to minimize stock loss during the flotation. New chemicals need to be developed to increase selectivity, reduce entrainment and increase the process efficiency. Also, the underlying knowledge linking structural/function relationship for de-inking chemicals in relationship to the heterogenity at the pulps needs to be established. Further progress could help in the treatment of higher fibre content pulps, reducing water and chemical consumption and reducing redeposition of the ink on the fibre
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35.
  • von Bahr, M, et al. (författare)
  • Spreading dynamics of liquids and surfactant solutions on partially wettable hydrophobic substrates
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 193, s. 85-96
  • Tidskriftsartikel (refereegranskat)abstract
    • The drop spreading of water and aqueous solutions of ethanol and nonionic surfactant on hydrophobic substrates (alkylsilane treated glass) have been investigated. For the low viscous liquids and solutions, the spreading on the surface of hydrophobic glass rod was also studied and compared to the drop spreading experiment. In both experiments, care was taken to ensure a minimum impact of inertial forces. The results for the aqueous systems show rapid initial spreading processes that abruptly halts after less than 30 ms, as the interfacial tension forces are balanced. In the case of surfactants solutions, this is followed by slower adsorption driven drift towards equilibrium conditions. During the initial spreading phase, the wetting front exhibits ~t1/2 spreading law. Two more viscous liquids, ethylene glycol and glycerol, were also examined and found to show a weaker time-dependence in the whole spreading regime. An ~t1/10 scaling of the drop radius versus time was for these liquids observed in the asymptotic long-time regime. For the surfactant solution, a slow relaxation towards equilibrium was observed following the initial fast spreading phase. The rate-limiting process in this regimes was in the drop spreading experiment found to be surfactant adsorption from the bulk to the expanding liquid¯vapour interface, whereas surface diffusion at the liquid¯vapour interface appeared rate-determining in the rod experiment. The reason for this is the differences in aspect ratio between relative expansion of the liquid¯vapour and solid¯liquid interfaces during spreading in the two experiments. In the study of surfactant solution spreading, the importance of surface relaxation prior to contact of the solution and the solid was also pointed out.
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36.
  • Wallin, Mikaela, 1975, et al. (författare)
  • Preparation of Mn, Fe and Co based perovskite catalysts using microemulsions
  • 2004
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 238:1-3, s. 27-35
  • Tidskriftsartikel (refereegranskat)abstract
    • Mixed metal oxides with perovskite structure were prepared using microemulsions. The perovskite materials had the nominal composition La0.8Sr0.2M1-xRhxO3 (where M = Mn, Co, Fe and x = 0, 0.1). X-ray diffraction analysis showed that the perovskite phase was generally obtained at relatively low temperatures, ≤700C. When the calcination temperature was kept low, the surface areas were relatively high and the highest surface area (25m2/g) was observed for La0.8Sr0.2Mn0.9Rh0.1O3 after calcination at 500C. Microstructural analysis using TEM and SEM showed particles in the size range of microns consisting of smaller crystallites in the range of 3050 nm. The materials were tested as catalysts for the selective reduction of NOx with NH3 (NH3-SCR) and the activity varied between samples with different transition metal. However, potassium, which originated from the technical surfactant used in the microemulsion, was detected by XRF analysis in various amounts in the samples and it was therefore not possible to conclude if the differences in catalytic performance were due to the different transition metals or to the potassium in the samples. Characterisation showed that it was possible to incorporate rhodium in the perovskite materials, which generally resulted in enhanced catalytic activities for the reduction of NOx with NH3.
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37.
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38.
  • Zhmud, BV, et al. (författare)
  • Application of charge regulation model for evaluation of surface ionization parameters from atomic force microscopy (AFM) data
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 164, s. 3-7
  • Tidskriftsartikel (refereegranskat)abstract
    • The present state of affairs with calculation of electrostatic interaction between two charge regulated surfaces is briefly reviewed, placing a special emphasis on assumptions and limitations of underlying physical models. An application of the charge regulation model for evaluation of surface ionization parameters from the interaction force profile measured with an atomic force microscope in a symmetric silica¯silica system is demonstrated. The site density and the dissociation equilibrium constant of surface silanols are determined. As can be judged from the results obtained, surface silanols are considerably more acidic than it was considered before.
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39.
  • Antunes, Filipe, et al. (författare)
  • A rheological investigation of the association between a non-ionic microemulsion and hydrophobically modified PEG. Influence of polymer architecture
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 215:1-3, s. 87-100
  • Tidskriftsartikel (refereegranskat)abstract
    • ydrophobically modified polymers (HM-P) typically behave as thickeners in a wide range of systems. The thickening effect in an aqueous solution of this kind of polymer depends on intermolecular hydrophobic associations and also on chain entanglements if the polymer concentration is significantly above the overlap concentration. In the present investigation a rather short end-capped polymer has been investigated at concentrations that are significantly below the overlap concentration. Despite the rather low polymer concentration, polymer chains were connected into a three-dimensional network by using microemulsion droplets as cross-linking points. The simple structure of the solution simplifies interpretations of results since chain entanglements can be expected to be of low importance and only intermolecular hydrophobic associations have to be considered. In particular the rheological response is in most cases well characterized by one single relaxation time and, then, the solution can be rationalized withi the framework of the Maxwell model. We have found that the length of the polymer chain's hydrophobic end-groups, as well as the temperature, have a large influence on dynamics of the system, while the length of the hydrophilic mid-block has a relatively small significance. On the other hand, the connectivity in the system depends critically on the microemulsion concentration. Thus, a maximum was found in viscosity as a function of volume fraction, interpreted as being due to a decrease in crosslink lifetime. (C) 2002 Elsevier Science B.V. All rights reserved.
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40.
  • Francisco, J D, et al. (författare)
  • Liquid crystalline properties and extractability of monoolein-water systems by supercritical carbon dioxide
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 213:1, s. 69-78
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of phase structure on the extraction recovery of monoolein from monoolein-water systems by supercritical carbon dioxide was investigated. Two monoolein-water mi tures at concentrations of 9 wt% water and 18 wt% water, respectively, were studied. H-2-NMR was used to monitor changes of the phase structures in supercritical conditions. The results showed that the phase structure and the water-monoolein interactions play a role on the extraction yield. The monoolein recovery was higher in the 9 wt% water sample in which L-alpha phase was present compared to the 18 wt% water sample in which the L-alpha melted to yield a L-2 phase. When the phase structures were the same in both samples, the extraction recovery was determined by the solubility properties of the components of the system. The changes due to the presence of supercritical carbon dioxide were shown also to depend on the water concentration of the monoolein-water mixture besides the temperature. The 18 wt% mixture showed a L-2 phase structure in all the range of the temperature investigated while the 9 wt% water mixture showed phase changes from L-alpha phase to L-2 phase in the same temperature range. (C) 200 Elsevier Science B.V. All rights reserved.
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41.
  • Göransson, Anders, et al. (författare)
  • Mechanisms responsible for sub-micron particle deposition in a laminar wall jet
  • 2002
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 211:2-3, s. 133-144
  • Tidskriftsartikel (refereegranskat)abstract
    • An experimental study was performed to investigate the dependency of particle size on the deposition rate. Polystyrene latex particles of two radii (0.23 and 0.38 mum) were deposited onto a glass surface covered with indium-tin oxide. Reduced deposition efficiency was observed for the larger particles, although an increase in the deposition efficiency was seen as that the diffusion boundary layer became thicker. A critical degree of surface coverage, Brit, was defined as the fraction of surface coverage at which the linear variation of flux with time ended. When the two particle sizes were compared, it was found that the value of Brit depended only on the wall shear stress. This result indicates that surface shielding is an important factor in the decline in particle flux. The deposition process was divided into two separate processes, described by a mass-transfer coefficient and an adhesion rate coefficient. It was found that the process was governed by mass-transfer during the initial period, but for higher degrees of surface coverage adhesion became the rate-determining factor. (C) 2002 Elsevier Science B.V. All rights reserved.
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42.
  • Göransson, Anders, et al. (författare)
  • Modelling of sub-micron-sized particle deposition in a laminar wall jet - an investigation of the role of shielding
  • 2002
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 205:3, s. 149-159
  • Tidskriftsartikel (refereegranskat)abstract
    • The deposition of polystyrene latex particles (0.23 mum in radius) onto a glass surface, covered with indium-tin oxide, has been studied using a wall-jet cell. The particle deposition could be followed in a single experiment at several positions, exposed to a wide range of wall shear rates. A deposition model including a shielding function was applied in order to describe the process. Three shielding functions obtained from the literature, which assumed different shielded areas, were compared. The size of the excluded area was shown to be dependent on the wall shear rate: a higher shear rate resulted in a larger area being blocked by deposited particles, thus preventing non-deposited, free-flowing particles from reaching the surface. (C) 2002 Elsevier Science B.V. All rights reserved.
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43.
  • Karlson, L, et al. (författare)
  • Complex formed in the system hydrophobically modified polyethylene glycol/methylated alpha-cyclodextrin/water. An NMR diffusometry study
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 171-179
  • Tidskriftsartikel (refereegranskat)abstract
    • In aqueous solutions hydrophobically modified polyethylene glycol (HM-PEG) forms a transient polymer network held together by intermolecular hydrophobic associations. In the present investigation we have used NMR-diffusometry to study how the addition of methylated alpha-cyclodextrin (M-alpha-CD) influences the polymer network. The addit on of M-alpha-CD resulted in an increased mean self-diffusion of HM-PEG, DHM-PEG, which is referred to a degradation of the polymer network when hydrophobic associations are disrupted due to complex formation between the hydrophobic groups of HM-PEG and M-alpha-CD. Addition of small amounts of M-alpha-CD results in a dramatic increase in DHM-PEG. Upon further addition of M-a-CD the increase in DHM-PEG is less dramatic and at excess M-alpha-CD, DHM-PEG levels off and equals the mean self-diffusion coefficient for unmodified PEG with the same molecular weight. The suggested interpretation is that the addition of the first molecules of M-alpha-CD mainly reduces the probability for hydrophobic associations inter-connecting different clusters of polymer micelles whereas at higher M-alpha-CD concentrations a disengagement of the individual clusters into separate HM-PEG molecules becomes important. (C) 2003 Elsevier B.V. All rights reserved.
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44.
  • Oliviero, C, et al. (författare)
  • Dynamic phase diagram and onion formation in the system C10E3/D2O
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 85-90
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of the shear on the lamellar phase, L, of the system C10E3/D2O was studied along an isoplethal path (40 wt.% C10E3) in the temperature range 25-42degreesC. A dynamic phase diagram was determined by steady-state rheometry, where by shear action the lamellar phase was transformed into multilamellar vesicles (MLVs) ("onions"). The location of "onions" in the dynamic phase diagram, depends only on the temperature and the applied shear rate, and not on the shear history. The classical lamellar phase structure is stable at rest and at low shear rates. When exposed to higher shear rates, the lamellar structure is transformed into onions. The transition from lamellae to onions is shifted to higher shear rates with increasing temperature. In a range of shear rates in between the stable lamellae and stable onion structure, the transition is incomplete. The transformation of lamellae into onions appears to be governed by the imposed strain, in agreement with earlier studies. The effect of temperature can be understood from the general property of nonionic surfactants where the monolayer spontaneous curvature decreases with increasing temperature. (C) 2003 Published by Elsevier B.V.
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45.
  • Pacios, I E, et al. (författare)
  • Polymerization of N,N-dimethylacrylamide in Aerosol OT-water mixtures: from lamellae to segregation
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 218:1-3, s. 11-20
  • Tidskriftsartikel (refereegranskat)abstract
    • The polymerizable N,N-dimethylacrylamide (DMAA) is added to the lamellar liquid crystalline system formed by the anionic surfactant Aerosol OT and water. Small angle X-ray scattering, gives the same bilayer thickness and hydrophilic group cross-sectional area as without DMAA, and an environment sensitive fluorescent probe indicates that DMAA is likely to be in the water layers between the AOT bilayers. This shows that the structure of the AOT bilayer in the lamellar phase is not affected by DMAA. However, DMAA induces instability of the lamellar phase, and a second phase, an isotropic solution, appears for larger DMAA contents The effect of DMAA in stabilizing this phase with respect to lamellae is much larger than that expected from a simple dilution with water. Furthermore, there is a combined influence of temperature and DMAA concentration on the coexistence of the lamellar and the isotropic phases. When an initiator is added and the monomer polymerizes the tendency to phase separate increases strongly. The lamellar spacing after polymerization is below the value predicted by the global AOT/H2O ratio. This indicates that the polymer segregates from the AOT phase and that the lamellar phase is osmotically compressed by the polymer rich phase. (C) 2003 Elsevier Science B.V. All rights reserved.
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46.
  • Svensson, Anna, et al. (författare)
  • Phases and structures of a polyion-surfactant ion complex salt in aqueous mixtures: cationic hydroxyethyl cellulose with dodecylsulfate counterions
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 91-106
  • Tidskriftsartikel (refereegranskat)abstract
    • A polyion-surfactant ion complex salt, cat-HECDS, has been synthesised, consisting of cationic hydroxyethyl cellulose w th dodecylsulfate counterions. Ternary phase diagrams have been established for aqueous mixtures of cat-HECDS with either the conventional surfactant NaDS or the polyelectrolyte cat-HECCl. Such mixtures represent the simplest possible aqueous mixtures of oppositely charged polymer and surfactant where the proportions of polyion and surfactant ion may be varied. Phases and structures were investigated by visual inspection through crossed polarisers and by small-angle X-ray scattering (SAXS),The pure complex salt cat-HECDS was insoluble in water, but it could absorb up to 60 wt.% water. No crystalline order was detected at any water content. Dissolution of the complex salt in water occurred if sufficient amounts of either surfactant or polyelectrolyte was added. A smaller excess of surfactant (50% by charge) than polyelectrolyte (100% by charge) was needed to dissolve the complex salt in the dilute region. The efficiency of excess NaDS to dissolve the complex salt was attributed to hydrophobic interactions be ween the surfactant and the cat-HEC backbone. The free surfactant concentration at the onset of dissolution was in good agreement with the critical association concentration observed in previous gel experiments.The investigated phase diagrams were dominated by a large isotropic phase containing micellar surfactant aggregates without long-range order. The micellar aggregation number varied from similar to20 for aqueous cat-HECDS to similar to80 for mixtures rich in NaDS. A small fraction of added complex salt was enough to destroy the hexagonal phase formed in binary mixtures of NaDS and water. The absence of liquid crystalline phases containing significant amounts of complex salt was attributed to the stiff character of the polyion and its low charge density. In a ternary complex salt-surfactant-water system studied previously, where the complex salt contained a flexible polyion with a high charge density, liquid crystalline phases were found at all proportions of complex salt. (C) 2003 Elsevier B.V. All ri hts reserved.
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47.
  • Thuresson, Krister, et al. (författare)
  • Clouding of a cationic hydrophobically associating comb polymer
  • 2002
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 201:1-3, s. 9-15
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel cationic hydrophobically associating comb polymer, containing poly(oxyethylene) chains in the back-bone, is described and investigated with respect to the aqueous solubility by cloud point measurements. Cloud points were investigated as a function of polymer charge, poly(oxyethylene) chain length and concentrations of added NaCl and could be interpreted in terms of the aqueous behavior of poly(oxyethylene) chains, general electrostatic effects, salting-out effects for nonionic polymer chains and polymer association. (C) 2002 Elsevier Science B.V. All rights reserved.
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48.
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49.
  • Almgren, M, et al. (författare)
  • Cryo transmission electron microscopy of liposomes and related structures
  • 2000
  • Ingår i: COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS. - : ELSEVIER SCIENCE BV. - 0927-7757. ; 174:1-2, s. 3-21
  • Tidskriftsartikel (refereegranskat)abstract
    • Cryo-transmission electron microscopy, c-TEM, has during the last 10 years contributed significantly to the understanding of the numerous, and often complex, structures formed by amphiphilic molecules in dilute aqueous solutions. In particular, the method
  •  
50.
  • Angelescu, Daniel, et al. (författare)
  • Some observations on the effect of the trivalent counterion Al3+ to the self-assembly of sodium dodecyl sulphate in water
  • 2004
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 245:1-3, s. 49-60
  • Tidskriftsartikel (refereegranskat)abstract
    • The phase behavior and phase structure of the SDS (sodium dodecyl sulfate)-Al(NO3)(3)-H2O system have been studied by combined NMR, SAXS, cryo-TEM and optical polarization microscopy methods at 298 K (25 degreesC) and 311 K (38 degreesC). At 298 K, the micellar solution phase of the binary system SDS-water is not capable of solubilising substantial amount of Al(NO3)(3) salt, and at a certain substoichiometric molar ratio Al(NO3)(3)/SDS. the solution phase coexists with a precipitate. When the concentration of the salt exceeds 5 wt.%, the precipitate is completely solubilised giving rise to a concentrated micellar phase that dominates the phase diagram. At high concentration of Al(NO3)(3) (30-40 wt.%), a vesicle phase is formed at low (maximum 10 wt.%) SDS content. On warming to 311 K, the vesicle region expanded, by converting the hydrated surfactant crystals to a lamellar liquid crystalline phase, around the concentrated micellar phase, with a narrow width towards the SDS-H2O axis (up to 43.5 wt.% SDS and 3 wt.% Al(NO3)(3)). The lamellar phase coexists with both hexagonal and micellar phases with appropriate multiphase regions. The optical- and cryo-transmission electron microscopy images show the presence of unilamellar vesicles and the liquid crystalline phases are characterized by H-2 NMR quadrupolar splitting and following the liquid crystalline texture by optical microscopy techniques. The NMR self-diffusion measurements, together with the cryo-TEM micrographs, identified the long worm-like micelles in the redissolution area. (C) 2004 Elsevier B.V. All rights reserved.
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