| 1. |
- Amenitsch, H, et al.
(författare)
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Bile salts form lyotropic liquid crystals
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757 .- 1873-4359. ; 213:1, s. 79-92
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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. |
- Antunes, Filipe, et al.
(författare)
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A rheological investigation of the association between a non-ionic microemulsion and hydrophobically modified PEG. Influence of polymer architecture
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 215:1-3, s. 87-100
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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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| 3. |
- Francisco, J D, et al.
(författare)
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Liquid crystalline properties and extractability of monoolein-water systems by supercritical carbon dioxide
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 213:1, s. 69-78
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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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| 4. |
- Groth, Cecilia, 1972, et al.
(författare)
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Diffusion of water in multilamellar vesicles of dialkyl and dialkyl ester ammonium surfactants
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 228:1-3, s. 64-73
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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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| 5. |
- Göransson, Anders, et al.
(författare)
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Mechanisms responsible for sub-micron particle deposition in a laminar wall jet
- 2002
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 211:2-3, s. 133-144
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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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| 6. |
- Göransson, Anders, et al.
(författare)
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Modelling of sub-micron-sized particle deposition in a laminar wall jet - an investigation of the role of shielding
- 2002
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 205:3, s. 149-159
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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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| 7. |
- Karlson, L, et al.
(författare)
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Complex formed in the system hydrophobically modified polyethylene glycol/methylated alpha-cyclodextrin/water. An NMR diffusometry study
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 171-179
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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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| 8. |
- Oliviero, C, et al.
(författare)
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Dynamic phase diagram and onion formation in the system C10E3/D2O
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 85-90
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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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| 9. |
- Pacios, I E, et al.
(författare)
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Polymerization of N,N-dimethylacrylamide in Aerosol OT-water mixtures: from lamellae to segregation
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 218:1-3, s. 11-20
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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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| 10. |
- Svensson, Anna, et al.
(författare)
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Phases and structures of a polyion-surfactant ion complex salt in aqueous mixtures: cationic hydroxyethyl cellulose with dodecylsulfate counterions
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 91-106
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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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| 11. |
- Thuresson, Krister, et al.
(författare)
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Clouding of a cationic hydrophobically associating comb polymer
- 2002
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 201:1-3, s. 9-15
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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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| 12. |
- Wahlgren, Marie C, et al.
(författare)
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Adsorption of globular model proteins to silica and methylated silica surfaces and their elutability by dodecyltrimethylammonium bromide
- 1993
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 70:2, s. 139-149
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a cationic surfactant (dodecyltrimethylammonium bromide) and six model proteins adsorbed on to methylated silica and silica surfaces was investigated. The proteins were bovine serum albumin, cytochrome c, β-lactoglobulin, α-lactalbumin, lysozyme and ovalbumin. The adsorption of the proteins at pH 7 and their subsequent removal by surfactant were studied by in situ ellipsometry. The degree of desorption upon dilution and the degree of elutability were compared and no relationship between these parameters could be found, which indicates that the mechanisms behind the two ways of protein removal are quite different. Further, the degree of elutability by surfactant was related to the physicochemical properties of the proteins. It was found that the size, charge, temperature of denaturation and adiabatic compressibility influenced the degree of elutability at the hydrophilic negatively charged silica surfaces for those of the model proteins that were still adsorbed after buffer rinsing. Negatively charged proteins with high denaturation temperatures, indicating high structural stability, did not adsorb on to this surface (ovalbumin) or adsorbed to a very low degree and were desorbed upon rinsing with buffer (β-lactoglobulin). All proteins adsorbed on to the hydrophobic methylated silica and the parameters that seemed to influence the degree of elutability were size and shell hydrophobicity of the proteins.
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| 13. |
- Wahlgren, M, et al.
(författare)
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The Elutability of Fibrinogen by Sodium Dodecyl Sulphate and Akyltrimethylammonium Bromides.
- 1993
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 70:2, s. 151-158
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Tidskriftsartikel (refereegranskat)abstract
- The elutability of adsorbed fibrinogen by cationic surfactants of different chain lengths (dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide), and an anionic surfactant (sodium dodecyl sulphate (SDS)) was studied using in situ ellipsometry. The concentrations of the surfactants were twice the CMC in water and for fibrinogen, 0.4 mg ml−1. The investigation was carried out for two model surfaces: methylated silica (hydrophobic) and silica (hydrophilic and negatively charged, at pH 7). As a complement, a surface with a gradient in surface hydrophobicity was used. The end points of the gradient are similar to the methylated silica and silica surfaces with respect to hydrophobicity. All the surfactants adsorbed on the methylated silica surfaces, whereas only the cationic surfactants adsorbed on the silica surface. The adsorption of fibrinogen was 0.64 ± 0.03 μg cm−1 and 0.35 ± 0.03 μg cm−2 on the methylated silica and silica surfaces, respectively. Addition of surfactant led to a decrease in the amount of fibrinogen adsorbed on the methylated silica surface for all the surfactants, but only SDS affected the amounts adsorbed on the silica surfaces to any great extent. Despite the fact that the cationic surfactants adsorbed onto the silica surface, they did not affect the amount of fibrinogen adsorbed. The removal of protein decreased for the alkyltrimethylammonium bromides with increasing hydrophilicity of the gradient surfaces, and the amount of fibrinogen remaining after surfactant treatment decreased slightly for SDS. The effect of the chain length of the surfactant on elutability was small. The rate of removal of fibrinogen by the surfactants was found to be slower for SDS compared with the alkyltrimethylammonium bromides at the methylated silica surface, and at the hydrophobic end and in the intermediate part of the gradient.Adsorption from mixtures of surfactant and fibrinogen was also studied and the effects of cationic and anionic surfactants were quite different. The adsorption of fibrinogen was increased in the presence of the cationic surfactants, especially on the silica surface, but decreased in the presence of SDS. As surfactant adsorption onto clean surfaces is reversible with respect to dilution it might be assumed that the adsorbate mainly consists of fibrinogen. A trend was observed for the amounts of fibrinogen remaining after rinsing with buffer; the amounts increased with decreasing length of the surfactant hydrocarbon chain.
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| 14. |
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| 15. |
- Wittung Stafshede, Pernilla, 1968, et al.
(författare)
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Detection of point mutations in DNA by PNA-based quartz-crystal biosensor
- 2000
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 174:1-2, s. 269-273
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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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| 16. |
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| 17. |
- Gernandt, Renate, et al.
(författare)
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Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper
- 2003
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 213:1, s. 15-25
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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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| 18. |
- Gärdlund, Linda, et al.
(författare)
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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
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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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| 19. |
- Gärdlund, Linda, et al.
(författare)
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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
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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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| 20. |
- Norgren, Magnus, et al.
(författare)
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Aggregation of Kraft Lignin Derivatives under Conditions Relevant to the Process. Part I. Phase Behaviour
- 2001
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 85-96
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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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| 21. |
- Norgren, Magnus, et al.
(författare)
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Stabilisation of Kraft Lignin Solutions by Surfactant Additions
- 2001
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 239-248
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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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| 22. |
- Rao, K. Hanumantha, et al.
(författare)
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Interfacial interactions and mechanical properties of mineral filled polymer composites : wollastonite in PMMA polymer matrix
- 1998
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 133:1, s. 107-117
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Tidskriftsartikel (refereegranskat)abstract
- The nature of stearic acid and polymethylmethacrylate (PMMA) adsorption onto wollastonite has been studied from basic, neutral and acidic organic solvents by infrared (IR) spectroscopy. The roles of acid-base interactions on adsorption and wollastonite dispersion in polymer matrix have been discussed with the determined mechanical properties of surface-treated (stearic acid) and untreated wollastonite-filled PMMA polymer composites. Maximum adsorption of either stearic acid or PMMA occurs from a nonpolar solvent, and the adsorption is found to decrease with increasing acidity or basicity of the solvents. The adsorption corresponds to two geometrical layers either from nonpolar (carbon tetrachloride) or from slightly basic (benzene) and acidic (methylene dichloride) solvents. Increased acidity (chloroform) or basicity (tetrahydrofuran) of solvents led to a monolayer or a fraction of the monolayer coverage. The primary adsorption of stearic acid is thought to be the formation of hydrogen bonds between surface hydroxyl groups and carboxylic acid groups. The tensile and impact strength properties of the composites that are filled with stearic acid-treated wollastonite are improved when compared to the untreated filled composite. The results suggest a stronger interfacial bonding between stearic acid and filler than that of polymer to the filler. Thus, the application of stearic acid for surface modification of acidic fillers such as wollastonite is emphasized.
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| 23. |
- Ridell, Annika, et al.
(författare)
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On the water content of the solvent/monoolein/water sponge (L3) phase
- 2003
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 228:1-3, s. 17-24
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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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| 24. |
- Seppanen, R., et al.
(författare)
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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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| 25. |
- 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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| 26. |
- 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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| 27. |
- Solberg, D., et al.
(författare)
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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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| 28. |
- 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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| 29. |
- 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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| 30. |
- Wang, Yanmin, et al.
(författare)
-
Influence of interparticle surface forces on the coagulation of weakly magnetic mineral ultrafines in a magnetic field
- 1994
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 90:2, s. 117-133
-
Tidskriftsartikel (refereegranskat)abstract
- The paper demonstrates that the coagulation of dispersions of weakly magnetic mineral ultrafines in an external magnetic field can be described theoretically by invoking interparticle forces. This was done with the use of experimental results that relate the coagulation process to particle size, slurry pH and the external magnetic field. Coagulation were seen to occur either on the primary minimum or secondary minimum depending on the exerted magnetic force.
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| 31. |
- 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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| 32. |
- Abbas, Zareen, 1962, et al.
(författare)
-
Synthesis, characterization and particle size distribution of TiO2 colloidal nanoparticles
- 2011
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 384:1-3, s. 254-261
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of controlled size, well defined shape, pure phase and of clean surfaces are ideal model systems to investigate surface/interfacial reactions. In this study we have explored the possibility of synthesizing TiO2 nanoparticles in the size range of 7–20 nm under well controlled experimental conditions. A simple method based on the hydrolysis of TiCl4 was used to obtain particles having surfaces free from organics. Stable dispersions of TiO2 nanoparticles of various sizes were obtained by optimizing the reaction/dialysis time and temperature. The synthesized TiO2 particles were found to be predominantly of anatase phase and narrow particle size distributions were obtained. The TiO2 particles were characterized with respect to their phase, size and shape by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Particle size distribution in a colloidal dispersion was obtained by the electrospray scanning mobility particle sizer (ES-SMPS) method and compared with an average particle size determined from dynamic light scattering (DLS). The average particle sizes obtained by the DLS and ES-SMPS methods were in good agreement, while a primary particle size of 4 nm was found in X-ray diffraction irrespective of the particle size in solution. Early stages of the nucleation process were monitored by the ES-SMPS method. These results show that small particles of 4–5 nm are initially formed and it is highly likely that large particles are formed due to aggregation of primary particles.
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| 33. |
- Al-Tikriti, Yassir, et al.
(författare)
-
A small-angle X-ray scattering study of amphiphilic drug self-assemblies in polyacrylate microgels
- 2024
-
Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 686
-
Tidskriftsartikel (refereegranskat)abstract
- Common ionisable amphiphilic drug molecules form micelles in aqueous solution. Loaded onto oppositely charged polyelectrolyte microgels they associate with the network chains to form dense complex phases. The self-assembling properties control the loading and release properties in drug delivery applications of microgel systems but little is known about the nature of the aggregates and the phase structure. In this paper, we investigated the size and organization of the self-assemblies formed by the hydrochloride salts of amitriptyline (AMT), chlorpromazine (CPZ), and doxepin (DXP) in sodium polyacrylate microgels. Small-angle X-ray scattering (SAXS) was used to determine the microstructure of drug loaded microgels in aqueous environment at ionic strengths relevant for drug loading (0.01 M) and release (0.15 M). The composition of drug loaded microgels was determined by means of a purpose built microscopy cell and UV spectroscopy measurements. Upon drug loading the microgels formed complex phases of low water content. SAXS experiments showed that the drugs formed oblate shaped or spherical micelles displaying local ordering but without long-range ordering even at very high micelle volume fractions. The local ordering resembled the packing of randomly packed hard oblates and spheres. The aggregation number of AMT varied between 10 and 49 depending on the composition. Incorporation of the uncharged base form of the drug caused a transformation of oblate shaped (aspect ratio ∼ 0.4) to spherical micelles, accompanied by an abrupt increase of the aggregation number. Variation of the ionic strength had minor effects on the aggregation number. CPZ formed oblate shape micelles (aspect ratios 0.3–0.4) with aggregation number between 9 and 30. DXP formed oblate shape micelles (aspect ratios 0.3–0.4) with aggregation numbers 10 − 11 at all studied compositions. The results provide a structural basis for, and justification of, previously assumed microstructures underlying mechanistic models of drug-microgel interactions and drug release.
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| 34. |
- Alexandrova, L, et al.
(författare)
-
The influence of mixed cationic-anionic surfactants on the three-phase contact parameters in silica-solution systems
- 2011
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 373, s. 145-151
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C14TAB) and (b) surfactant mixture of the cationic C14TAB with the anionic sodium alkyl- (straight chain C12-, C14- and C16-) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C14TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.
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| 35. |
- Alexandrova, L, et al.
(författare)
-
Three-phase contact parameters measurements for silica-mixed cationic-anionic surfactant systems
- 2009
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 348:1-3, s. 228-233
-
Tidskriftsartikel (refereegranskat)abstract
- The stability and interactions in thin wetting films between the silica surface and air bubble containing (a) straight chain C10 amine and (b) cationic/anionic surfactant mixture of a straight chain C10 amine with sodium C8, C10 and (straight chain) C12 sulfonates, were studied using the microscopic thin wetting film method developed by Platikanov [D. Platikanov, J. Phys. Chem. 68 (1964) 3619]. Film lifetimes, three-phase contact (TPC) expansion rate, receding contact angles and surface tension were measured. The presence of the mixed cationic/anionic surfactants was found to lessen contact angles and suppresses the thin aqueous film rupture, thus inducing longer film lifetime, as compared to the pure amine system. In the case of mixed surfactants heterocoagulation could arise through the formation of positively charged interfacial complexes. Mixed solution of cationic and anionic surfactants shows synergistic lowering in surface tension. The formation of the interfacial complex at the air/solution interface was confirmed by surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants system controls the strength of the interfacial complex. The observed phenomena were discussed in terms of the electrostatic heterocoagulation theory, where the interactions can be attractive or repulsive depending on the different surface activity and charge of the respective surfactants at the two interfaces.
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| 36. |
- 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
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| 37. |
- Alves, Luis, et al.
(författare)
-
On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions
- 2015
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 483, s. 257-263
-
Tidskriftsartikel (refereegranskat)abstract
- The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved.
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| 38. |
- Andersson, I. M., et al.
(författare)
-
Impact of protein surface coverage and layer thickness on rehydration characteristics of milk serum protein/lactose powder particles
- 2019
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 561, s. 395-404
-
Tidskriftsartikel (refereegranskat)abstract
- Spray-dried powders were produced from milk serum protein concentrate and lactose in varying ratios, and the rehydration characteristics of the powders were evaluated. The dissolution rate was estimated with a flow-cell based technique, and the external and internal distribution of the powder components were evaluated with X-ray photoelectron spectroscopy and confocal Raman microscopy, respectively. The surface of the powder particles is more or less covered by a thin protein layer. A phase segregation between protein and lactose is observed in the interior of the particle resulting in a protein rich layer in the vicinity of the surface. However, the protein layer in the vicinity of the particle surface tends to become thinner as the bulk protein concentration increases in the powders (from 10 to 60% w/w). The time for the spontaneous imbibition to occur show a linear correlation with the protein surface coverage. The dissolution rate of powders containing 0.1% w/w protein is around 60 times faster than for a powder containing 1% w/w protein but the dissolution rate of powders containing 1% and 100% w/w differ only by a factor of 2. Thus, it is suggested that the outer protein layer becomes denser at the interface as the protein content increases in the powders, thereby causing poorer rehydration characteristics of the powders (especially for low protein concentrations 0.1–1% w/w). This insight has relevance for the formulation of whey protein powders with improved rehydration characteristics. © 2018 Elsevier B.V.
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| 39. |
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| 40. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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A highly hydrophobic anionic surfactant at oil-water, water-polymer and oil-polymer interfaces: Implications for spreading coefficients, polymer interactions and microencapsulation via internal phase separation
- 2013
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 436, s. 1048-1059
-
Tidskriftsartikel (refereegranskat)abstract
- Multicore-shell particles consisting of a poly(methyl methacrylate) shell and multiple dodecane cores have been prepared via the internal phase separation method using the oil-soluble anionic surfactant sodium 1,5-dioxo-1,5-bis(3,5,5-trimethylhexylocy)-3-((3,5,5 trimethylhexyloxy)carbonyl)pentane-2-sulfonate (TC4) and the water-soluble polycation poly(diallyldimethylammonium chloride) (PDADMAC) in combination as a dispersant pair. The multicore-shell particles have been investigated using SEM, light microscopy and microelectrophoresis. The detailed influence of TC4 on the oil-water, water-polymer and oil-polymer interfaces and its interaction with PDADMAC have been investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) and different optical tensiometry methods. TC4 stabilizes in particular the polymer-water interface in the presence of PDADMAC instead of the oil-water interface in contrast to water-soluble surfactants. In addition, the oil-polymer interface is stabilized by TC4 which prevents coalescence of the oil droplets and leads to multicore-shell morphology rather than single core-shell.
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| 41. |
- 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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| 42. |
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| 43. |
- Arnold, Celine, et al.
(författare)
-
Surfactant distribution in waterborne acrylic films. 2 Surface Investigation
- 2011
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 374:1-3, s. 58-68
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results on sodium dodecyl sulfate (SDS) enrichment at the surface of pure acrylic or acrylic/laponite composite latex films. Surface concentrations were measured by Confocal Raman Spectroscopy leading to higher values than the nominal concentration of 6 wt%. X-ray Photoelectron Spectroscopy (XPS) analyses showed uppermost surface layers saturated with SDS in most cases. High resolution Atomic Force Microscopy (AFM) revealed a variety of morphologies for these surfactant top layers, highlighting the occurrence of SDS bilayers in different configurations. In an attempt to check for a correlation between the surface concentration of the surfactant in dry films and the concentration of free surfactant in water in the initial latex, this latter concentration was determined from the level of the plateau in adsorption isotherms. Adsorption studies by conductimetry showed an unexpected increase of the amount of adsorbed SDS with pH. The proposed interpretation is that, upon acrylic acid neutralization, the chains at the surface become more hydrophilic and spread out in water, revealing more sites for SDS to adsorb on. No correlation between free surfactant and surface enrichment could be established, indicating that the enrichment process is more complex than expected.
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| 44. |
- Arumughan, Vishnu, 1994, et al.
(författare)
-
Specific ion effects in the adsorption of carboxymethyl cellulose on cellulose: The influence of industrially relevant divalent cations
- 2021
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 626
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.
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| 45. |
- Asaro, Fioretta, et al.
(författare)
-
Micellar crowding and branching in a versatile catanionic system
- 2016
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 506, s. 202-209
-
Tidskriftsartikel (refereegranskat)abstract
- The catanionic system didodecyldimethylammonium bromide (DDAB)-sodium taurodeoxycholate (STDC)-D2O is characterized by an exceptionally extended L1 region. The comparison of self-diffusion coefficient of the solvent and the DDAB embedded in the micelles provided information about hydration of the aggregates. Moreover, correlating self-diffusion and 14N NMR relaxation measurements new insight could be obtained regarding the translational and rotational micellar motions in the crowded solutions of systems with 0.2 DDAB-STDC molar ratio. 1H 2D NMR spectra gave some hints about the mutual arrangement of DDAB and STDC within the aggregates. For samples with 1.8 and 2.6 DDAB/STD molar ratios the 14N data were in agreement with the presence of somewhat branched, interconnected micelles. 23Na and 81Br dynamic parameters resulted particularly sensitive to the surrounding environment. The peculiar rheological behaviour of the, highly concentrated, branched micelles samples, namely the steady oscillations in the step tests, was found to be an example of instability originated by the combined effect of material elasticity and slippage at the fixed wall.
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| 46. |
- Ata, S., et al.
(författare)
-
The influence of interfacial ageing and temperature on the coalescence of oil droplets in water
- 2011
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 374:1-3, s. 96-101
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the coalescence behaviour of two single droplets of industrial kerosene oil is an important precursor for predicting the stability of a concentrated kerosene emulsion system. In taking such an approach, distinct differences in the dynamic coalescence of fresh and aged binary droplets of analytical and technical grade kerosene was observed which we believe to be important with regard to the stability of concentrated systems. It was shown from induction time measurements (the time from first contact to rupture of the thin film separating the droplets) that the analytical grade kerosene binary droplets are considerable more stable than the technical grade at higher temperature (up to 65 degrees C) but the analytical grade shows a gradual decrease in stability up to 65 degrees C. At 75 degrees C, both grades of kerosene droplets remained stable to coalescence. After this initial rupture, coalescence proceeded as a series of dynamic oscillations and further insight into the fusion behaviour could be obtained by analysis of the change in the surface area of the aggregated droplets as a function of time. The longer induction times correlated with the more vigorous post rupture oscillations (less damping resulting from an increase in interfacial elasticity) which were recorded during the drop fusion. These experiments reveal preliminary steps in the coalescence of oil droplets where measurements from first contact to final damped equilibrium are quantified. This aspect of coalescence has not been well represented in the earlier literature. (C) 2010 Elsevier B.V. All rights reserved.
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| 47. |
- Babakhani, Peyman, et al.
(författare)
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Comparison of a new mass-concentration, chain-reaction model with the population-balance model for early- and late-stage aggregation of shattered graphene oxide nanoparticles
- 2019
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Ingår i: Colloids and Surfaces A. - : ELSEVIER. - 0927-7757 .- 1873-4359. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation as an essential mechanism impacting nanoparticle (NP) functionality, fate, and transport in the environment is currently modelled using population-balance equation (PBE) models which are computationally expensive when combined with other continuum-scale reactive transport models. We propose a new simple mass-concentration-based, chain-reaction modelling (CRM) framework to alleviate computational expenses of PBE and potentially to facilitate combination with other fate, transport, and reaction models. Model performance is compared with analytical PBE solution and a standard numerical PBE technique (fixed pivot, FP) by fitting against experimental data (i.e., hydrodynamic diameter and derived count rate of dynamic light scattering used as a representative of mass concentration) for early- and late-stage, aggregation of shattered graphene oxide (SGO) NP across a broad range of solution chemistries. In general, the CRM approach demonstrates a better match with the experimental data with a mean Nash-Sutcliffe model efficiency (NSE) coefficient of 0.345 than the FP model with a mean NSE of 0.29. Comparing model parameters (aggregation rate constant and fractal dimension) obtained from fitting CRM and FP to the experimental data, similar trends or ranges are obtained between the two approaches. Computationally, the modified CRM is an order-of-magnitude faster than the FP technique, suggesting that it can be a promising modelling framework for efficient and accurate modelling of NP aggregation. However, in the scope of this study, reaction rate coefficients of the CRM have been linked to collision frequencies based on simplified and empirical relationships which need improvement in future studies.
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| 48. |
- Backfolk, K, et al.
(författare)
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Study by isothermal calorimetry and electrophoresis of the interaction between latices and cellulose derivatives
- 2006
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 276:1-3, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the latex surface chemistry on the association of latices with different cellulose derivatives has been investigated by means of isothermal calorimetry and electrophoresis. The chemistries of three grades of coating latices differed with regard to the type and amount of vinylic monomer and the level of carboxylation. In addition, a styrene/butadiene latex substantially free from surfactant was used to establish the influence of physically pre-adsorbed surfactants on the association with the cellulose derivatives sodium carboxymethylcellulose (NaCMC), hydroxyethyl cellulose (HEC) and ethyl(hydroxyethyl)cellulose (EHEC). The results show that the latex chemistry, in terms of hydrophilic character originating from carboxylic acid groups, significantly affects the adsorption of the non-ionic HEC and EHEC. A higher degree of carboxylation or a more polar latex, such as vinyl acetate/acrylate, reduces the association with non-ionic cellulose derivatives. The addition of anionic sodium dodecylbenzene sulphonate or non-ionic fatty alcohol ethoxylate surfactants to the surfactant-free styrene/butadiene latex emulsion did not significantly change the association behaviour with EHEC, although it was evident that, for example, a sodium dodecyl sulphonate type of surfactant participated significantly in the adsorption process. Even if the surface polarity of the latex governs the association characteristics at the interface, the solubility properties of the cellulose derivatives Must be considered, meaning that the hydrophobic character plays an important role in the associative interaction between the latex and cellulose derivatives in aqueous media. (c) 2005 Elsevier B.V. All rights reserved.
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| 49. |
- Bai Palmkron, Shuai, et al.
(författare)
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Quantification of structures in freeze-dried materials using X-ray microtomography
- 2023
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 658
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Tidskriftsartikel (refereegranskat)abstract
- The structure of a freeze-dried material is essential for its ability to preserve and protect biologics such as proteins, cells and other sensitive structures. The structure of a typical freeze-dried matrix can be described as pores surrounded by thin walls where the walls are the encapsulating material (for e.g. cells). The objective of this investigation is to evaluate X-ray microtomography (µCT) as a characterization method to quantifying the matrix of a freeze dried material, and compare it to scanning electron microscopy (SEM). The material consists of maltodextrin, freeze-dried below or above the glass transition temperature of the maximal freeze concentration (Tg′) and after applying annealing. The SEM images have high resolution and provide an excellent view of the sample. However, it is challenging to perform any image analysis and to ensure that a representative section is presented. The µCT images provide a rather uniform contrast between material and void, allowing for a simple grey-level thresholding when separating structure from the background. A robust image analysis procedure allows the results extracted from a representative sample volume to be evaluated. Further image analysis has been focused on understanding the thickness of the encapsulating structures by estimations of volume-weighted averages of inscribed spheres within the walls. The results show two types of structures: A large pore structure of around 20–100 µm separated by thin walls around 2–3 µm thick, and a finer structure consisting of smaller pockets of air (< 10 µm) packed in a honeycomb like structure. The structures of the samples dried below and above Tg′ have smaller and thinner structures, while material dried after annealing has larger and thicker structures. The structures display comparably small differences between the different drying protocols despite the quite different drying conditions.
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| 50. |
- Barrantes, Alejandro, et al.
(författare)
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Characteristics of saliva films adsorbed onto different dental materials studied by QCM-D
- 2014
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 442:Special issue: Selected papers from the 26th European Colloid and Interface Society conference (26th ECIS 2012), s. 56-62
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Tidskriftsartikel (refereegranskat)abstract
- The formation of salivary films onto different surfaces relevant in dental research like titania, hydroxyapatite, gold, zirconia, silica, and hydrophobized silica has been studied by means of QCM-D. Human whole saliva (HWS), and sterile filtered HWS (sHWS) both diluted in water to a final concentration of 25% (v/v) were used. Main differences between the salivary films formed from the two saliva types were observed with the help of ΔD vs Δf plots where sHWS samples showed an almost linear adsorption regime for most of the surfaces whereas most of the HWS samples had a marked multi-regime nature indicating that the former ones are homogenous and the later are heterogeneous supporting previous data on a multi-phase adsorption process. The films with highest shear elastic modulus, μ > 105 N m−2, shear viscosity, η ∼ 3 × 10−3 N s m−2, and lowest thickness (∼10 nm) were formed for both types of saliva onto hydroxyapatite and for sHWS on titania. Furthermore, the ratio between the loss, G″, and the storage modulus, G′, indicates that these films have a solid-like behavior (G″/G′ ≤ 0.5). In contrast, for the remaining surfaces the adsorbed films show higher d values and are also characterized by low μ ∼ 104 N m−2, η ∼ 10−3 N s m−2, and by high ratios, G″/G′ > 2, that indicate a fluid like behavior. These observations might be expected to have influence on the lubricating properties of the salivary films. The SDS induced elutability also indicates a different interaction strength and composition of the adsorbed films and is likely associated with the ease by which these surfaces can be cleaned. Our results suggest that, among the relevant materials, zirconia and titania would yield the more lubricious films whereas hydroxyapatite will be the most easily cleaned.
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