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Sökning: L773:1873 4359 OR L773:0927 7757

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1.
  • Amenitsch, H, et al. (författare)
  • Bile salts form lyotropic liquid crystals
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757 .- 1873-4359. ; 213:1, s. 79-92
  • Tidskriftsartikel (refereegranskat)abstract
    • A reinvestigation of the phase diagrams relative to some conjugated and non-conjugated bile salts in water has demonstrated the formation of lyotropic liquid crystalline phases, in contradiction with generally accepted statements. The phase behaviour is complex and the phase diagrams are unusual, compared to most surfactants and lipids. In particular, coexistence of liquid crystalline phases with crystals has been obser ed. The formation of liquid crystalline phases requires very long equilibration times and the thermal stability of the lyotropic phases is moderate. The observed structure is tentatively assumed to be of the reverse hexagonal type. Structural relations with currently accepted models for the organisation of bile salts into micelles and solid form have been found. (C) 2002 Elsevier Science B.V. All rights reserved.
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2.
  • Groth, Cecilia, 1972, et al. (författare)
  • Diffusion of water in multilamellar vesicles of dialkyl and dialkyl ester ammonium surfactants
  • 2003
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 228:1-3, s. 64-73
  • Tidskriftsartikel (refereegranskat)abstract
    • The NMR self-diffusion technique is used for measuring diffusion of water in highly concentrated multilamellar vesicle solutions. The signal intensity of water, i.e. the water echo-decay, is monitored down to very small intensities thus providing an accurate measure of how water is diffusing in the solution. It is noted that a large curvature is dominating the functional form of the echo-decay indicating the presence of a large number of multilamellar vesicles. It is also concluded that in order to measure accurately the volume fraction of water inside and outside vesicles the experimental time scale can be changed. From a multiexponential fit to the echo-decay the fraction fast and the sum of all slow components can be extracted. When the apparent fraction "vesicle water", P-vw(app), is plotted versus the experimental time scale the graph produced is a good representation of the difference in how fast water diffuses over the different vesicle membranes. From an extrapolation to "zero time" the true fraction of trapped water can be extracted, i.e. a quantitative measure of the volume fraction of vesicles at a certain concentration of surfactant.
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3.
  • Wittung Stafshede, Pernilla, 1968, et al. (författare)
  • Detection of point mutations in DNA by PNA-based quartz-crystal biosensor
  • 2000
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 1873-4359 .- 0927-7757. ; 174:1-2, s. 269-273
  • Tidskriftsartikel (refereegranskat)abstract
    • Currently there is an extensive search for biosensors for detecting genetic defects by hybridisation to immobilised oligonucleotides. A concept able to detect a single mismatch in a 15mer single-strand target of the p53 tumor suppresser gene is presented (a mutation found in many types of cancer cells). In this method, the unique hybridisation properties of the DNA mimic peptide nucleic acid (PNA) are combined with electronically detected mass and shear dissipation at the surface of a quartz crystal. Cysteine-labeled PNA efficiently immobilises on crystal-gold surface at 20 degrees C. At 60 degrees C, addition of complementary DNA results in a signal response corresponding to hybridisation between DNA and the PNA-covered surface, whereas addition of DNA differing in only one of the 15 bases gives no response at all.
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4.
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5.
  • Gernandt, Renate, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 213:1, s. 15-25
  • Tidskriftsartikel (refereegranskat)abstract
    • Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, orders of mixing, salt concentrations and polymer concentrations. Initially the polymers were characterised by polyelectrolyte titration (charge), static light scattering (molecular weight, radius of gyration) and measurements with a scanning interferometric refractometer (refractive index). The complexes were characterised by ocular inspection and static light scattering in combination with a special evaluation algorithm allowing an estimation of the geometric form of the complexes. The results show that the initial complexes have a spherical form and that the size is fairly constant over a large range of charge ratios between the polymers, provided the complexes are formed in deionised water. When the charge mixing ratio exceeded neutrality a secondary agglomeration of the initially formed complexes occurred. The presence of salt during PEC formation caused a dependence of the level of aggregation on the mixing ratio, whereby small amounts of NaCl drastically lowered the particle mass at lower mixing ratios. Subsequent addition of salt to PECs formed in water led to a strong swelling of the complex particles and at a critical salt concentration to dissolution.
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6.
  • Gärdlund, Linda, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres II : Influence of complexes on wet and dry strength of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 218:1-3, s. 137-149
  • Tidskriftsartikel (refereegranskat)abstract
    • The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly (amide, amine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PEC�s were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%. Paper strength; Polyelectrolyte Complexes; PAE; CMC; Strength additive
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7.
  • Gärdlund, Linda, et al. (författare)
  • Polyelectrolyte complexes for surface modification of wood fibres II. Influence of complexes on wet and dry strength of paper
  • 2003
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 218:1-3, s. 137-149
  • Tidskriftsartikel (refereegranskat)abstract
    • The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly(amideamine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PECs were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%.
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8.
  • Norgren, Magnus, et al. (författare)
  • Aggregation of Kraft Lignin Derivatives under Conditions Relevant to the Process. Part I. Phase Behaviour
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 85-96
  • Tidskriftsartikel (refereegranskat)abstract
    • Aggregation of a commercial, polydisperse softwood kraft lignin (Indulin AT) in diluted aqueous alkaline solutions was investigated experimentally, by means of turbidity measurements. The influence of temperature, salt concentration and pOH and the role of a divalent counterion on the aggregation behaviour were studied. When the temperature was increased, an increased tendency of aggregation in samples containing high concentrations of sodium chloride was found. Phase separation could be detected even at pOH=2 at 175°C and the effect was pronounced when the concentration of hydroxide ions decreased. The phase transition from soluble to precipitated lignin was found to be irreversible concerning temperature change. Small amounts of calcium ions were seen to induce dramatic effects on the system stability, even at relatively high hydroxide concentrations (pOH 1-2). At a given temperature and pOH, the coagulation was found to appear at a certain critical coagulation concentration (CCC) of the added electrolyte. Furthermore, calculations were carried out to compare with the outcome of the experimental observations. A theoretical model, based on the DLVO theory, was found to predict the kraft lignin solution behaviour well.
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9.
  • Norgren, Magnus, et al. (författare)
  • Stabilisation of Kraft Lignin Solutions by Surfactant Additions
  • 2001
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 194:1-3, s. 239-248
  • Tidskriftsartikel (refereegranskat)abstract
    • The colloidal stability of kraft lignin (KL) and some various KL-surfactant mixtures in aqueous alkaline solutions, pH 10.0-11.50, was tuned and investigated at high ionic strengths, 0.5-1.1 M, and elevated temperatures, 70 and 150°C. The main techniques used were Quasi-Elastic Light-Scattering (QELS) and turbidity measurements, together with sample inspection by the naked eye. Samples without surfactant additions and samples containing various alkyl sulfonates showed a comparably low colloidal stability, whereas in mixtures containing sodium salts of bile acids, the stability was found greatly improved. The efficiency of different bile salts was investigated and it was found that the overall best solution stability is obtained in mixtures of KL and sodium taurodeoxycholate (STDC). STDC showed a relatively good stabilising effect also at very high temperatures (150°C). Furthermore, in already aggregated KL solutions, additions of STDC were found to cause 'de-aggregation' and the number of formed aggregates was dramatically decreased. From the outcome of the investigation, it can be concluded that by introducing surfactants, and maybe other designed additives too, new possibilities in controlling the colloidal stability of KL at rough solution conditions are given.
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10.
  • Rao, K. Hanumantha, et al. (författare)
  • Interfacial interactions and mechanical properties of mineral filled polymer composites : wollastonite in PMMA polymer matrix
  • 1998
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 133:1, s. 107-117
  • 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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11.
  • Ridell, Annika, et al. (författare)
  • On the water content of the solvent/monoolein/water sponge (L3) phase
  • 2003
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 228:1-3, s. 17-24
  • Tidskriftsartikel (refereegranskat)abstract
    • The water content of the solvent/monoolein/water sponge phase depends on the lipophilicity of the solvent used. The relatively lipophilic solvent 2-methyl-2,4-pentanediol (MPD) gives a sponge phase at about 60 wt.% water compared with 30 wt.% for the sponge phase formed with polyethylene glycol (Mw≈400, PEG 400). A reasonably good correlation is found between the water content of the sponge phase and the octanol/water partition coefficient for the solvent. The water content of the PEG 400 sponge phase increases considerably (to about 50 wt.%) by adding up to 3 wt.% of ionic compounds such as SDS, CTAB and salts of amphiphilic drugs. Nonionic detergents show less effect on increasing the water content, whereas membrane lipids such as lecithins and cholesterol show unchanged or even decreasing effect on the water content of the sponge phase.
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12.
  • Seppanen, R., et al. (författare)
  • Heteroflocculation of kaolin pre-treated with oppositely charged polyelectrolytes
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 164:2-3, s. 131-141
  • Tidskriftsartikel (refereegranskat)abstract
    • Heteroflocculation studies of kaolin particles have been carried out by mixing two kaolin suspensions; one stabilised by a cationic polymer and the other stabilised by a highly charged and low molecular weight anionic polymer. Molar mass and charge density of cationic polymer as well as the mixing ratio of oppositely charged suspensions were varied. Flee size and degradation during shearing were investigated by measuring hoc size using a light scattering/diffraction method at different flow rates. It was observed that floc size was small when subjected to a low flow rate and decreased with increasing how rate. Cationic polymers with high molar mass and low charge density produced flocs with high resistance towards flee degradation. Maximum flee size was obtained at a mixing ratio where the flocs became slightly negatively charged. Flee size and degradation were observed to be independent of primary kaolin particle size. Furthermore, floc size increased with increasing ionic strength. Scanning electron micrographs showed flocs with an open structure, which is expected to improve the optical properties of paper when using microflocs as a filler in paper production.
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13.
  • 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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14.
  • 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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15.
  • Solberg, D., et al. (författare)
  • Adsorption and flocculation behavior of cationic polyacrylamide and colloidal silica
  • 2003
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 219:03-jan, s. 161-172
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption of cationic polyacrylamide and silica nanoparticle systems onto a model surface has been compared with the adsorption and flocculation of a fiber suspension. An increase in ionic strength affects the polyelectrolyte adsorption in different ways in these two systems. With a silica surface, an increase in the ionic strength leads to a continuous increase in the adsorption. On a cellulose fiber, the adsorption increases at low ionic strength (1-10 mM NaCl) and then decreases at higher ionic strength (10-100 mM NaCl). When polyelectrolyte is added to the fiber suspension, flocculation occurs with an optimum around a polyelectrolyte addition of 0.4 mg g(-1). Above this addition level the flocculation effect is reduced and dispersion occurs when more than 1.2 mg g(-1) polyelectrolyte is added. This behavior suggests a bridging flocculation, the dispersion being explained by electrosteric stabilization of the suspension. Addition of silica nanoparticles to the fiber suspension leads to a greater degree of flocculation than in a single polyelectrolyte system. The adsorption of nanoparticles to a polyelectrolyte-covered silica surface increases both the adsorbed amount and the thickness of the adsorbed film. A more extended silica particle, giving a more extended polyelectrolyte-silica film, also results in a higher degree of fiber flocculation.
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16.
  • 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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17.
  • 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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18.
  • 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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19.
  • 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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20.
  • 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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21.
  • 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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22.
  • 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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23.
  • 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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24.
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25.
  • Andersson Trojer, Markus, 1981, et al. (författare)
  • 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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26.
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27.
  • 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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28.
  • 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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29.
  • 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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30.
  • Babakhani, Peyman, et al. (författare)
  • 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
  • Ingår i: Colloids and Surfaces A. - : ELSEVIER. - 0927-7757 .- 1873-4359. ; 582
  • 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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31.
  • Bai Palmkron, Shuai, et al. (författare)
  • Quantification of structures in freeze-dried materials using X-ray microtomography
  • 2023
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 658
  • 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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32.
  • Barrantes, Alejandro, et al. (författare)
  • Characteristics of saliva films adsorbed onto different dental materials studied by QCM-D
  • 2014
  • 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
  • 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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33.
  • Batili, Hazal, et al. (författare)
  • A comparative study on the surface chemistry and electronic transport properties of Bi2Te3 synthesized through hydrothermal and thermolysis routes
  • 2024
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 682
  • Tidskriftsartikel (refereegranskat)abstract
    • Bismuth telluride-Bi2Te3 is the most promising material for harvesting thermal energy near room temperature. There are numerous works on Bi2Te3 reporting significantly different transport properties, with no clear connection to the synthetic routes used and the resultant surface chemistry of the synthesized materials. It is of utmost importance to characterize the constituent particles’ surface and interfaces to get a better understanding of their influence on the transport properties, that will significantly improve the material design starting from the synthesis step. Electrophoretic deposition (EPD) is a promising technique, enabling the formation of thick films using colloidally stabilized suspensions of pre-made nanoparticles, which can enable the study of the effect of surface chemistry, in connection to the synthetic route, on the material's transport properties. In order to explore the differences in surface chemistry and the resultant transport properties in relation to the synthetic scheme used, here we report on Bi2Te3 synthesised through two wet-chemical routes in water (Hydro-) and oil (Thermo-) as the solvents. XRD analysis showed a high phase purity of the synthesized materials. SEM analysis revealed hexagonal platelet morphology of the synthesized materials, which were then used to fabricate EPD films. Characterization of the EPD films reveal significant differences between the Hydro- and Thermo-Bi2Te3 samples, leading to about 8 times better electrical conductivity values in the Thermo-Bi2Te3. XPS analysis revealed a higher metal oxides content in the Hydro-Bi2Te3 sample, contributing to the formation of a resistive layer, thus lowering the electrical conductivity. Arrhenius plots of electrical conductivity vs inverse temperature was used for the estimation of the activation energy for conduction, revealing a higher activation energy need for the Hydro-Bi2Te3 film, in agreement with the resistive barrier oxide content. Both the samples exhibited negative Seebeck coefficient (S) in the order of 160–170 mV/K. The small difference in S of Hydro- and Themo-Bi2Te3 films was explained by the effective medium theory, revealing that the magnitude of S is linearly correlated with the surface oxide content. Based on the findings, TE materials synthesized through thermolysis route is recommended for further studies using soft treatment/processing of pre-made TE materials. EPD platform presented here is shown to clearly expose the differences in the electronic transport in connection to nanoparticle surface chemistry, proving a promising methodology for the evaluation of morphology, size and surface chemistry dependence of electronic transport for a wide range of materials.
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34.
  • Batili, Hazal, et al. (författare)
  • On the electrophoretic deposition of Bi2Te3 nanoparticles through electrolyte optimization and substrate design
  • 2022
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 649, s. 129537-
  • Tidskriftsartikel (refereegranskat)abstract
    • Assembly of thermoelectric nanostructures with pre-defined morphology and surface chemistry on solid sub-strates has been one of the challenges for in-plane TE devices. Electrophoretic deposition (EPD) has the potential to be used for this purpose, where the use of non-conductive substrates is required to enable a reliable evaluation of the transport property of electrically active films. Bi2Te3 nanoparticles, which were synthesized using microwave-assisted hydrothermal route, were used for the EPD of thermoelectric films on glass substrates. A special substrate was fabricated using maskless photolithography, to evaluate the electronic transport properties of the TE films without the interference of the substrate. Electrolyte composition was optimized for high mobility of the suspended nanoparticles, and Bi2Te3 EPD films were fabricated with a high deposition rate, reaching 10 mu m/min. Initial EPD films showed high resistivity, ascribed to the surface oxide layer and capping ligands. The resistance was significantly reduced by the addition of a dithiol molecular linker, capable of interconnecting the Bi2Te3 nanoparticles through ligand-exchange. Seebeck coefficient in the range-150 to-180 mu V/K was measured, revealing the transport through the deposited films. Finally, a power factor of 169 nW/K-2.m was estimated, revealing the potential for the application of this technology to large area TE films as active coatings using the developed EPD process.
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35.
  • Bergek, Jonatan, 1984, et al. (författare)
  • Controlled release of microencapsulated 2-n-octyl-4-isothiazolin-3-one from coatings: Effect of microscopic and macroscopic pores
  • 2014
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 458:1, s. 155-167
  • Tidskriftsartikel (refereegranskat)abstract
    • To keep a painted facade protected from mold and algae, anti-growth agents are mixed in the coating. These biocides are small molecules with a high diffusivity inside the soft polymeric coating matrix resulting in a premature loss of protection. A promising improvement can be achieved by encapsulation of the biocide in micro-sized containers and thereby reducing the release rate from the coating. In this study, the biocide 2-n-octyl-4-isothiazolin-3-one (OIT) has been encapsulated by various formulation routes and the release has been studied with regard to different conditions. It was found that an exceptionally low interfacial tension between OIT and water practically prevents any formulation of core-shell particles. However, polymeric monoliths of OIT and poly(methyl methacrylate) could be formulated by the internal phase separation method. OIT release studies from these microspheres revealed formulation-dependent microscopic porosity where the chosen evaporation path of volatile solvent significantly alters the diffusion coefficient of the biocide in the microsphere. Dense microstructure with low diffusivity was given when the poly(methyl methacrylate) was provided time or heat for complete polymer relaxation. The microscopic porosity was evaluated within a framework of applied diffusion models to the experimental data. In an applied perspective, microspheres could offer a value for sustained release of OIT from coatings. In this work, we found a considerable decrease in release rate from dry-film coatings with encapsulated OIT compared to freely dispersed OIT. In addition, macroscopic porosity in the coating, i.e. the porosity in the binder material, was proven to be crucial for the diffusivity. It was shown that macroscopic porosity heavily depends on the drying time of the coating where longer drying times of several weeks gave a substantial decrease in macroscopic porosity and release rate of OIT.
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36.
  • Bergström, L. Magnus (författare)
  • Influence of bending energetics on the size, shape and polydispersity of droplet microemulsions
  • 2008
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 316:1-3, s. 15-26
  • Tidskriftsartikel (refereegranskat)abstract
    • A theory for ellipsoidal shape fluctuating droplet microemulsions in the presence of excess discrete phase (Winsor I and II) is expounded that combines bending energetics of the amphiphilic monolayer at the droplet interface with thermodynamics of self-assembling solute and amphiphilic molecules. The theory relates the three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant (k(c)) with interfacial tension, average size and shape and polydispersity of microemulsion droplets. It is demonstrated that the well-known conventional relations become modified as the entropy of self-assembling amphiphilic as well as solute molecules are taken into account, in particular at low values of the effective bending constant 2k(c) + (k) over bar (c). As a result, the average droplet radius (R) as well as the droplet polydispersity sigma(R)/< R > behave consistently in the limit 2k(c) + (k) over bar (c) -> 0 whereas the conventional expressions are recovered in the limit 2k(c) + (k) over bar (c) -> infinity. It is demonstrated that association entropy effects may be quantified by a parameter k(s) with same dimension and order of magnitude as k(c) and (k) over bar (c). k(s) is found to be always negative and tends to decrease (R) and to increase sigma(R)/< R. Moreover, the average axial ratio of an oblate/prolate fluctuating droplet is found to be a strong function of the bending rigidity (the droplets become increasingly non-spherical with decreasing k(c)) but is independent of (k) over bar (c), in contrast to previous investigations where association entropy effects were neglected.
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37.
  • Bergström, L (författare)
  • Shear thinning and shear thickening of concentrated ceramic suspensions
  • 1998
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 133, s. 151-155
  • Tidskriftsartikel (refereegranskat)abstract
    • The steady shear properties of two important ceramic systems; Si3N4 powder and the composite system SiC whiskers and A1203 particles, has been investigated. The concentrated, colloidally stable powder suspensions displayed a shear thinning behaviour with an approach to a plateau at high shear rates. The concentrated aqueous SiCw and composite suspensions showed a strong, sometimes discontinuous, shear thickening at some critical shear rate which was attributed to a possible order-disorder transition of the suspension structure. It was possible to fit the volume fraction dependence of the colloidally stable ceramic suspensions to a modified Krieger-Dougherty model which yields values of the maximum volume fraction; Φm. Large differences in Φm could be correlated to the differences in shape between the whiskers and powders. The viscosity of the composite suspensions were sucessfully predicted from the Farris theory using the rheological data for the separate components.
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38.
  • Blomberg, E, et al. (författare)
  • Surface interactions in emulsion and liposome solutions
  • 1999
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 159, s. 149-157
  • Tidskriftsartikel (refereegranskat)abstract
    • We have used two surface force techniques to investigate the interactions between hydrophilic and negatively charged mica and glass surfaces across concentrated and dilute oil-in-water emulsions, as well as across aqueous liposome solutions. It was observed with both the interferometric surface force apparatus, using mica surfaces, and with the non-interferometric MASIF technique, employing glass surfaces, that emulsion droplets adsorbed onto the surfaces. Under a high compressive force the adsorbed emulsion droplets were disintegrated and this resulted in a phase separation in the gap between the surfaces. The forces measured in the presence of the capillary condensate compared favourably with theoretical expectations. In contrast, no adsorption of large aggregates could be detected in the liposome solution. Instead it appears that upon adsorption the liposomes disintegrate and the surfaces become covered by a disordered layer of phospholipids. Measurements with the interferometric surface force apparatus, that allows absolute distances to be determined, allow us to draw the conclusion that some bilayer aggregates are adsorbed and that the inner layer consists of an intercalated monolayer.
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39.
  • Blute, Irena, et al. (författare)
  • Industrial manufactured silica nanoparticle sols. 2 : Surface tension, particle concentration, foam generation and stability
  • 2009
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 337:1-3, s. 127-135
  • Tidskriftsartikel (refereegranskat)abstract
    • Several earlier papers have revealed that several key parameters, such as hydrophobicity (contact angle), size, shape and degree of agglomeration, have an important influence on the behavior of particles at the air/water interface. However, the origin of foaming with particles is still not clear. In this article, we have tentatively related surface tension measurements and particle concentrations to the generation and stability of foam produced from industrial manufactured silica nanoparticle sols. Surprisingly, only slight reductions in surface tension were observed and the differences between the hydrophophilic and partially modified hydrophobic sols were small. However, in the case of the partially modified hydrophobic sol, the surface tension/concentration gradient was found to be pH and concentration responsive. Also, the greatest reduction in Surface tension was found to occur at low pH (in the region of the pH(pzc)) and could be related to the highest foamability (foam generation) as determined in our earlier publication [1. Blute, R.J. Pugh, J. van de Pas, I. Callaghan, Silica nanoparticle sols. 1. Surface chemical characterization and evaluation of the foam generation (foamability), J. Colloid Interface Sci. 313 (2007) 645-655]. Also, after centrifugation of the moderately hydrophobic modified concentrated sols, foaming tests carried out on the supernatant indicated that the particle concentration had a dominant influence on foamability and foam stability. Since only transient foams, with relatively short lifetimes, could be produced with these modified silica nanoparticles then (a) further surface modification or the reduction of pH to increase the Surface activity or (b) the addition of a cosurfactant Would be needed to increase the foamability and achieve foams with extended lifetimes.
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40.
  • Blute, I, et al. (författare)
  • Solution behavior of a surfactant aldehyde – the oxidation product of an alcohol ethoxylate
  • 1999
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 150, s. 105-113
  • Tidskriftsartikel (refereegranskat)abstract
    • It has previously been shown that alcohol ethoxylates readily undergo autoxidation and that one of the major oxidation products is the surfactant aldehyde, i.e. an ethoxylate carrying a –CH2CHO group at the terminal end of the polyoxyethylene chain. In this work the cloud point, phase behavior and aggregation characteristics of the surfactant aldehyde produced by oxidation of C12H25(OCH2CH2)50H(CI2E5) are determined and compared with the values obtained with the parent surfactant. It was found that the physico-chemical behavior of the two species was very similar, which indicates that a considerable portion of the aldehyde group is in hydrated state, i.e. the surfactant aldehyde consists of a mixture of aldehyde in carbonyl form and the corresponding geminal diol. The cloud point of the surfactant aldehyde decreased rapidly with time, even when it was stored at low temperature. Also the parent surfactant and its homologue C12E6 exhibited a decrease in cloud point during storage. For instance, a 1% aqueous solution of C12E6 showed a cloud point decrease from 62 to 32°C after 4 months storage at 40°C. Such a change in solution behavior can have important practical implications.
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41.
  • Blute, I, et al. (författare)
  • Solution behaviour of a formate capped surfactant - the oxidation product of an alcohol ethoxylate.
  • 1999
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 160, s. 229-236
  • Tidskriftsartikel (refereegranskat)abstract
    • The solution behaviour has been investigated for an alcohol ethoxylate terminated with a formic acid ester. This compound has previously been reported to be an important degradation product in the auto-oxidation of alcohol ethoxylates. In this work we have investigated the solution behaviour of the formic acid ester surfactant C12H25(OCH2CH2)4OCHO (C12E4-OCHO). The pure formate was found to be sparsely soluble in water with no clear point at 0.1%. The critical micelle concentration was found to be 129 µM at 35°C, compared to 50 µM for the parent surfactant C12H25(OCH2CH2)5OH (C12E5). To mimic the behaviour of the oxidised surfactant, the formate was mixed in different ratios with C12E5 and the cloud point, surface tension and critical micelle concentration of these mixtures were studied. The gradual increase of formate was found to shift the cloud point and isotropic regions to lower temperatures. The cmc of the mixture was found to be lower than for the pure surfactant. The favourable interaction was analysed according to the non-ideal model by Rubingh and the interaction parameter, b, was determined to be -4, which is unusually large for a mixture of two nonionic surfactants. These results indicate that the reduction of cloud point observed during oxidation of nonionic surfactants can in part be attributed to the formation of formate esters.
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42.
  • Bodvik, Rasmus, et al. (författare)
  • Aggregation and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions.
  • 2010
  • Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 354:1-3, s. 162-171
  • Tidskriftsartikel (refereegranskat)abstract
    • Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas for HPMC solutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed in MC solutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.
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43.
  • Boissier, Catherine, 1972, et al. (författare)
  • Interactions between polyvinylpyrrolidone, sodium dodecylsulfate and nonylphenol ethoxylate in solution and on polystyrene particles
  • 2007
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 301:1-3, s. 444-452
  • Tidskriftsartikel (refereegranskat)abstract
    • Mixtures of polyvinylpyrrolidone (PVP), nonylphenol ethoxylate with, on the average, 84 oxyethylene units (NP 100) and sodium dodecylsulfate (SDS) in solution and on polystyrene particles are discussed in terms of various types of interaction according to their mutual affinities. The mixtures in solution were analyzed by means of NMR and static surface tension, which showed that the combination of SDS with PVP agreed well with the classical model with surfactant aggregates along the polymer chain. In the mixture with the nonionic surfactant NP100 and the anionic surfactant SDS, mixed micelles were formed with a strong attraction parameter beta = -5. 1. Evidence of SDS encapsulation in the NP100 micelle was obtained from NMR diffusometry data where the long and short residence times of SDS in the mixed micelle were estimated to be iota(A) = 2.19 s and TB = 0. 15 s, respectively. No interaction was found in a mixture between NP100 and PVP in solution. Upon adsorption of these component mixtures to a polystyrene surface, it was shown that complexes formed in solution also dominated at the surface. This applied both for the mixtures of SDS-PVP and of SDS-NP100, with the exception that the mixed micelles of SDS-NP100 seemed to have higher affinity than PVP to the surface. This was considered a result of the nonylphenol group in NP100. For the mixture of NP100 and PVP, the NP100 had a higher affinity to the surface than PVP, though both components were able to co-exist on the surface. Finally, as SDS, NP100 and PVP were adsorbed simultaneously, all three components seemed to adsorb, with a surface complex including SDS with, probably, both NP100 and PVP. In this three-component mixture a preferential adsorption of SDS and NP100 seemed to exist.
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44.
  • Bondelind, Mia, 1980, et al. (författare)
  • Single- and two-phase numerical models of Dissolved Air Flotation: Comparison of 2D and 3D simulations
  • 2010
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 365:1-3, s. 137-144
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work single- and two-phase flow numerical models of a pilot DAF (Dissolved Air Flotation) tank are presented. In the latter framework, the mixture in the tank consists of water and air bubbles. The motion of air bubbles is resolved within the Lagrangian frame of reference. Interaction between bubbles is neglected in the present model. To account for turbulence in the tank, the realizable k– model is selected as a compromise between a need to correctly resolve the flow and the computational cost of the calculations. To validate the numerical simulations the results are compared with experimental results of an independent research group.The paper discusses the choice between performing two (2D)- or three-dimensional (3D) simulations of a flotation process. Our simulations show that a 3D hydrodynamic model of the flow pattern can well reproduce the single-phase flow in the pilot tank. Despite the major changes in the flow pattern that occur when the second phase (air bubbles) is introduced, the validated single-phase model provides a useful tool in the process of setting up the two-phase model. We show in the paper that a 2D two-phase model cannot resolve successfully the flow in the contact zone, whereas major flow characteristics in the separation zone can, to some extent, be described by a 2D approach (e.g. the stratification of the flow). In addition, two-phase simulations demonstrate that a 3D model is sensitive to the distribution of air and water from the needle valves, which, in turn, influences the stability of the solution obtained.
  •  
45.
  • Bordes, Romain, 1981, et al. (författare)
  • Physical chemical characteristics of dicarboxylic amino acid-based surfactants
  • 2011
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 391:1-3, s. 32-41
  • Tidskriftsartikel (refereegranskat)abstract
    • Three dicarboxylic amino acid-based surfactants, the disodium salts of dodecylaminomalonic acid, dodecylaspartic acid and dodecylglutamic acid, having one, two and three carbon atoms, respectively between the carboxyl groups, have been studied with respect to solution behavior and adsorption at the air-water interface, as well as on a number of solid surfaces. The dicarboxylic surfactants had 4-5 times higher CMC than the dodecylglycinate, which only has one carboxyl group. The role of the amide bond for the self-assembly process was assessed by comparing sodium dodecylglycinate with sodium dodecylsarcosinate. The former can build hydrogen bonds between adjacent molecules via the amide groups but the latter which has an N-methyl group, cannot, It was found that the ability to form intermolecular hydrogen bonds lead to tighter packing both at the air-water interface and in micelles. The CMC was not affected, however. Dodecylglutamate was found to be very calcium tolerant compared to the two other dicarboxylic surfactants. This was attributed to differences in chelating calcium. Whereas dodecylaminomalonate and dodecylaspartate can form intramolecular chelates with calcium ions, dodecylglutamate prefers to form an intermolecular complex. Formation of an intermolecular complex leads to tight packing at the air-water interface and to very low surface tension values. The ability to form intramolecular chelates is advantageous for adsorption at calcium-containing surfaces, however. Whereas dodecylaminomalonate and, in particular, dodecylaspartate adsorb strongly on hydroxyapatite, dodecylglutamate shows very weak adsorption. On other surfaces, where there exist no specific interactions involving the surfactant headgroup, the three surfactants gave similar adsorption behavior.
  •  
46.
  • Boschkova, K, et al. (författare)
  • Frictional properties of lyotropic liquid crystalline mesophases at surfaces
  • 2000
  • Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 166, s. 67-77
  • Tidskriftsartikel (refereegranskat)abstract
    • The lubricating effect of assemblies of amphiphiles at surfaces has been studied. Liquid crystalline mesophases were investigated in terms of frictional and wear properties in a pin on disc rig. It is shown that systems forming lamellar liquid crystals indeed serve as lubricating liquids, indicating that the lamellar liquid crystalline phase adsorb on the steel surface forming a lubricating tribofilm. Poor performance is obtained when the lubricating system is in a single phase, i.e. in this case a lamellar liquid crystalline region. However, good lubrication is found when the lamellar liquid crystalline phase is dispersed in the water. This is attributed to a low viscosity of the system rendering a fast relaxation of the system in order to form a new film after the disturbing action of the two sliding surfaces. The lamellar packing is altered by the addition of non-charged amphiphiles, such as short chain alcohols. Using different alcohols it was shown that aromatic short chain alcohols are detrimental to the wear. This was attributed to the Rebinder effect, i.e. a strong adsorption of the alcohol, which in turn facilitates crack formation and thus the wear. In systems with mixtures of cat- and anionic amphiphiles it was, not surprisingly found that the best lubrication is obtained with a slight excess of either surfactant.
  •  
47.
  •  
48.
  • Boulanger, Nicolas, et al. (författare)
  • High surface area activated carbon prepared from wood-based spent mushroom substrate for supercapacitors and water treatment
  • 2024
  • Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 680
  • Tidskriftsartikel (refereegranskat)abstract
    • Edible white-rot fungi are commonly cultivated on wood-based substrates and selectively degrade lignin to a larger extent during their growth. Spent mushroom substrate (SMS) is produced in huge amounts by the mushroom industry and today there is a lack of proven methods to valorize this kind of biomass waste, which in most cases is landfilled or used as fuel. This study demonstrates that birch wood-based SMS from the cultivation of oyster mushrooms can be converted into high-quality activated carbon (AC) with an extremely high surface area of about 3000 m2/g. These activated carbons showed good performance when used in electrodes for supercapacitors, with energy storage parameters nearly identical to AC produced from high-quality virgin birch wood. Moreover, AC produced from SMS showed high potential as an adsorbent for cleaning reactive orange-16 azo dye from aqueous solutions as well as contaminants from synthetic effluents and from real sewage water. The kinetics of adsorption were well represented by the Avrami fractional order model and isotherms of adsorption by the Liu model. The theoretical maximum reactive orange-16 adsorption capacities were approximately 519 mg/g (SMS-based carbon) and 553 mg/g (virgin birch-based carbon). The removal of contaminants from synthetic effluents made of different dyes and inorganic compounds was around 95% and 83% depending on the effluent composition. The removal of contaminants from raw sewage water was around 84%, and from treated sewage water was around 68%. Overall, the results showed that activated carbon prepared from waste generated during cultivation of white-rot fungi is as good as activated carbon prepared from high-quality virgin wood.
  •  
49.
  • Bysell, Helena, et al. (författare)
  • Effects of peptide cyclization on the interaction with oppositely charged microgels
  • 2011
  • Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 391:1-3, s. 62-68
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of peptide cyclization on the interaction between antimicrobial peptides and oppositely charged poly(acrylic acid-co-acrylamide) microgels of various charge density was investigated for linear and cyclic variants of peptide oligomers (C(ARKKAAKA)nC) (n = 1, 1.5, 2, 3). Through this, peptide length could be varied without substantially affecting peptide charge density and mean hydrophobicity. Furthermore, the peptides were demonstrated to display random coil conformation both in aqueous solution and when bound to oppositely charged microgels, allowing effects of cyclization to be monitored without interference from conformational transitions. With increasing peptide length, both cyclic and linear peptide variants displayed increased binding affinity to oppositely charged microgels. For all peptide lengths, however, the difference between cyclic and linear peptide variants was marginal at most, hence cyclization had little or no influence in peptide incorporation to oppositely charged microgels. In parallel, microgel deswelling increased with peptide length for both linear and cyclic peptide variants, while linear and cyclic peptide variants of the same length displayed very similar peptide-induced deswelling. Also electrolyte-induced peptide desorption from the microgels was similar for linear and cyclic peptide variants. Taken together, these findings demonstrate that end-to-end cyclization does not markedly affect peptide incorporation into, and release from, oppositely charged microgels. This opens up opportunities for the use of microgels as carriers for peptides which have been cyclized in order to improve their proteolytic and chemical stability, or in order to achieve other therapeutic advantages compared to the corresponding linear peptide variant.
  •  
50.
  • Cabaleiro-Lago, Celia, et al. (författare)
  • Spectrophotometric study of metal-ligand reactions in isooctane/Brij30/water nonionic microemulsions
  • 2007
  • Ingår i: Colloids and Surfaces A. - Univ Vigo, Dept Quim Fis, Fac Quim, Vigo 36310, Spain. Univ Santiago Compostela, Fac Chem, Dept Chem Phys, Santiago 15782, Spain. : ELSEVIER SCIENCE BV. - 0927-7757 .- 1873-4359. ; 295:1-3, s. 49-54
  • Tidskriftsartikel (refereegranskat)abstract
    • The complexation between Ni2+ and pyridine-2-azo-p-dimethylaniline (PADA) was studied in isooctane/polyoxyethylenglycol dodecyl ether (Brij30)/water microemulsions at 25 degrees C. The apparent complexation constant depends on microemulsion composition. The proposed model, which takes into account the heterogeneity of the system at the microscopic scale, allows us to determine the distribution constants of both reactants and the complexation constant at the interface. The complex is less stable in microemulsion than in water due to a more efficient hydration of the nickel hexahydrate coordination complex that arises from the interaction between the polar head group of the surfactant and the interfacial water. (c) 2006 Elsevier B.V. All rights reserved.
  •  
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