| 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
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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)
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XPS imaging of surface diffusion of alkylketene dimer on paper surfaces
- 2003
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. ; 219:1-3, s. 35-43
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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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