| 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. |
- 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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| 3. |
- 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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| 4. |
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| 5. |
- 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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| 6. |
- 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
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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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| 7. |
- 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
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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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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