| 1. |
- Buijs, Jos, et al.
(författare)
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Localized changes in the structural stability of myoglobin upon adsorption onto silica particles, as studied with hydrogen/deuterium exchange mass spectrometry
- 2003
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 263:2, s. 441-448
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Tidskriftsartikel (refereegranskat)abstract
- A new method is presented for monitoring the conformational stability of various parts of a protein that is physically adsorbed onto nanometer-sized silica particles. The method employs hydrogen/deuterium (H/D) exchange of amide hydrogens, a process that is extremely sensitive to structural features of proteins. The resulting mass increase is analyzed with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Higher structural specificity is obtained by enzymatically cleaving the adsorbed proteins prior to mass spectrometric analysis. The mass increases of four peptic fragments of myoglobin are followed as a function of the H/D exchange time. The four peptic fragments cover 90% of the myoglobin structure. Two of the peptic fragments, located in the middle of the myoglobin sequence and close to the heme group, do not show any adsorption-induced changes in their structural stability, whereas the more stable C- and N-terminal fragments are destabilized. Interestingly, for the N-terminal fragment, comprising residues 1–29, two distinct and equally large conformational populations are observed. One of these populations has a stability similar to that in solution (−23 kJ/mol), whereas the other population is highly destabilized upon adsorption (−11 kJ/mol).
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| 2. |
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| 3. |
- Lindman, Björn, et al.
(författare)
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Aggregation, aggregate composition, and dynamics in aqueous sodium cholate solutions
- 1980
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 73:2, s. 556-565
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Tidskriftsartikel (refereegranskat)abstract
- The translational mobility of aggregates formed in aqueous sodium cholate solutions was obtained from the self-diffusion coefficient of solubilized decanol, which was determined using the capillary tube method with radioactive labeling. Combining these results with the self-diffusion coefficients of cholate ions, sodium ions, and water molecules the following quantities were determined as a function of cholate concentration: the fraction of cholate aggregated, the ratio of counterions and cholate ions in the aggregates, and the hydration number of the aggregates. All the quantities considered differ in their concentration dependences from those of typical micelle forming long chain ionic surfactants. There seems to be no distinctly favored aggregate size but rather the aggregate radius and aggregation number increase progressively with increasing concentration. The aggregation number is much smaller than for typical surfactant micelles. The deduced fraction of aggregated cholate shows that association progresses continuously over a wide concentration range without a well-defined critical micelle concentration. Sodium ion binding to cholate aggregates is highly variable with a rapid increase taking place above 0.1 mole/kg, a conclusion which may also be drawn from 23Na chemical shift and relaxation data. The counterion binding is discussed in relation to the so-called ion condensation model, found to apply with good approximation for simple surfactant aggregates, and in relation to the progressive cholate aggregation. The aggregates are rather strongly hydrated and the hydration number shows a peculiar concentration dependence. Information on the orientation of cholate within the aggregates is deduced by combining deuterium NMR relaxation data of deuterated cholate with the diffusion results. The order parameter is rather insensitive to concentration and points to a packing of cholate in the aggregates which does not change appreciably with concentration and which corresponds to a marked mobility of cholate within the aggregates.
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| 4. |
- Tornberg, Eva, et al.
(författare)
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A study of the surface enlargement in the drop volume method and its relation to protein adsorption at A/W and O/W interfaces
- 1981
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 79:1, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- In the drop volume method the surface of the drop enlarges throughout the process of the interfacial tension decay. This surface expansion has been measured for drops of various sizes and shapes, where the interfacial tension depression was caused by different proteins such as lysozyme, β-lactoglobulin, bovine serum albumin, sodium caseinate, whey protein concentrate and soy protein isolate at different initial bulk-phase concentrations. The results showed that the surface enlargement could be as large as 33–34% in relation to the initial surface of the drop, and that this surface expansion was mainly dependent on the surface tension decay and the shape of the drop, irrespective of type of protein and protein concentration used. It was found within the limits of error that time of detachment for a drop was not influenced by its surface expansion. These findings make it possible to use the drop volume method for measuring protein adsorption at different interfaces, which has been shown for lysozyme adsorption at the soybean oil-water interface.
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| 5. |
- Tornberg, Eva
(författare)
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A Surface Tension Apparatus According to the Drop Volume Principle
- 1977
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 60:1, s. 50-53
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Tidskriftsartikel (refereegranskat)abstract
- A new construction of a drop volume apparatus has proved to be successful in determining the interfacial tension for a variety of pure liquids as well as for solutions having surface tensions, which come to equilibrium quickly. Temperature dependence of the surface tension can easily be recorded even at elevated temperatures, which has been shown for water.
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| 6. |
- Wahlgren, M, et al.
(författare)
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Adsorption of b-Lactoglobulin onto Silica, Methylated Silica and Polysulphone
- 1990
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 136:1, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- Milk and whey are widely processed by membrane filtration, often using polysulphone membranes. Adsorption of β-lactoglobulin onto polysulphone was studied at protein concn. of 0.1 and 1.0%, as well as 12% to represent concn. encountered during ultrafiltration. Adsorption onto silica and methylated silica surfaces (representing strongly hydrophilic and strongly hydrophobic surfaces resp.) was also studied. Protein was dissolved in 0.01 smallcap˜M phosphate buffer pH 7.0 containing 0.15 smallcap˜M NaC1 and adsorption/desorption was monitored in situ using a Rudolph Thin Film ellipsometer. Polysulphone surfaces adsorbed the greatest amount of β-lactoglobulin and silica the least; methylated silica was intermediate. Differences between methylated silica and polysulphone may reflect differences in surface roughness. Adsorption to polysulphone and methylated silica was not reversed on dilution, whereas adsorption to silica was partially reversible. Pretreatment of polysulphone and methylated silica surfaces with 0.1% β-lactoglobulin markedly reduced subsequent adsorption from 12% β-lactoglobulin (equivalent to adsorption from 0.1% solution alone); preadsorption to silica surfaces had much less effect on subsequent adsorption. Methylated silica was concluded to be a representative model for a polysulphone surface.
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| 7. |
- Wahlgren, Marie C, et al.
(författare)
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The concentration dependence of adsorption from a mixture of β-lactoglobulin and sodium dodecyl sulfate onto methylated silica surfaces
- 1992
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 148:1, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption from a mixture of SDS and β-Lactoglobulin, 1:5 (), onto a methylated silica surface was studied in situ by ellipsometry. The amounts adsorbed from different concentrations of the mixture, at pH 7, were compared with those adsorbed from the corresponding pure SDS and β-lactoglobulin solutions. At high concentrations of the mixture, where the CMC of SDS is approached or exceeded, the adsorbate was probably dominated by SDS, indicated by similar kinetics and amounts adsorbed as for SDS solution alone. The amount adsorbed increased, in this concentration range, when the system was rinsed with buffer solution. This was probably due to an exchange between SDS and β-lactoglobulin when the system was diluted. At intermediate concentrations of SDS and β-lactoglobulin, the amounts adsorbed from the mixtures increased and reached a maximum. This maximum was observed both before and after rinsing. Before rinsing the adsorbate might have been a mixture of SDS and β-lactoglobulin while after rinsing probably only β-lactoglobulin remained. At low concentrations, larger amounts were adsorbed from the mixture than from β-lactoglobulin solution alone. In this concentration range rinsing caused minor desorption, indicating that SDS is co-adsorbed with the protein, even in those cases were no adsorption from a pure SDS solution was seen. This indicated that the binding of SDS to β-lactoglobulin at low concentrations is stronger than to the silica surface and that this binding facilitated the adsorption of protein.
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| 8. |
- Bohlin, Leif, et al.
(författare)
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Cone-plate instrument for stress relaxation measurements
- 1980
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 73:1, s. 61-65
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Tidskriftsartikel (refereegranskat)abstract
- An instrument for the measurement of stress relaxation in shear is described. The force is detected by a sensitive piezoresistive pressure transducer. The requirement of constant strain can be fulfilled within less than 1%. Preset values of shear strain can be imposed on the sample within 0.1 sec. This instrument is suitable for soft solids and elastic liquids with a lower limit of ∼ 1 sec for the relaxation time. Results are given for wheat flour dough, a gelatinous deoxycholate complex and a gelatin gel. The instrument is simple, robust, and reliable, as well as inexpensive.
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| 9. |
- Bydén Sjöbom, Malin, et al.
(författare)
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Binary Phase Equilibria of Three alfa-Methylsubstituted Sodium Alkanoate Surfactant Systems.
- 2003
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797. ; 257:2, s. 333-336
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we continue our study of methyl -substituted surfactants and present the aqueous binary phase diagrams of racemic sodium 2-methyloctanoate, -nonanoate, and -dodecanoate, respectively. All systems have very low Krafft temperatures within the solution phase, between 1 and 4 degreesC. The phase sequences of the two shorter surfactants are very similar to those of the unsubstituted sodium octanoate, although with somewhat different range of existence for the phases formed. The sodium 2-methyldodecanoate system is different from the unsubstituted sodium dodecanoate system, as the former seems to lack a hexagonal phase. The surfactant systems were delineated using H-2 NMR splittings and crossed polarizers, and combined with SAXS for determination of phase structure.
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| 10. |
- Hermansson, Ann-Marie, et al.
(författare)
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Characterization of protein gels by scanning and transmission electron microscopy : A methodology study of soy protein gels
- 1981
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 81:2, s. 519-530
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Tidskriftsartikel (refereegranskat)abstract
- Different preparation techniques for scanning (SEM) and for transmission electron microscopy (TEM) were compared in order to characterize the structure of protein gels. SEM specimens were prepared by chemical fixation, dehydration, and critical-point drying. TEM specimens were prepared by using techniques of thin-sectioning and freeze-fracturing/etching. Thin sections were made after varying fixation and staining conditions. For freeze-fracturing/etching, the standard freezing procedure both using and omitting cryoprotectants (glycerol), as well as a particular modification of the "soil-emulsion" freezing technique without cryoprotective pretreatment were used. Finally, critical-point dried specimens (produced for SEM) were freeze-etched after infiltration with dioxane. The various techniques of preparation were applied to soy protein gels made in distilled water and in 0.2M NaCl under well defined conditions. The gel structures differed with regard to the state of aggregation which depended on the presence or absence of NaCl. The network structure was found to be of two levels. First, there was an orientation on the molecular level in the form of strands and fine ring structures. Second, there was a coarser network with voids of the magnitude of ?0.2 ?m. The pore size distribution of the latter network was found to be very sensitive to environmental factors such as low ionic strength and presence of cryoprotectants mainly due to swelling. The information obtained by the various techniques generally showed good agreement and were complementary. Distinct preparation artifacts caused by improper freezing or critical-point drying were also revealed. © 1981 Academic Press, Inc. All rights of reproduction in any form reserved.
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| 11. |
- Karlsson, L M, et al.
(författare)
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Penetration and loading of human serum albumin in porous silicon layers with different pore sizes and thicknesses
- 2003
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 266:1, s. 40-47
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Tidskriftsartikel (refereegranskat)abstract
- Human serum albumin was adsorbed into porous silicon layers with thickness up to 3 µm and with different mean pore radius in the range 4.5-10 nm. The adsorbed amount of protein was quantified by I125 radioactive labeling techniques and ellipsometry. The results show that albumin penetrated into the pores when the mean pore radius was larger than 5.5 nm, but could not totally occupy the available surface area when the layer thickness was larger than 1 µm. Loading of albumin both into porous layers and onto plane silicon as a function of albumin concentration was also investigated. These measurements show that loading of protein increased with protein concentration at least up to 10 mg/ml for porous silicon and up to 1 mg/ml for plane silicon. The maximum deposition into the type of porous layers used here was 28 µg/cm2, compared to 0.36 µg/cm2 for plane silicon. © 2003 Elsevier Inc. All rights reserved.
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| 12. |
- Otterstedt, J-E, et al.
(författare)
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Colloidal components in solutions of alkali silicates
- 1987
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 115:1, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- The particle size of colloidal silica in 1 to 5 M SiO2 solutions of lithium, sodium, potassium, and cesium silicates in the ratio range 1.5-20 moles of SiO2 per mole of M2O was determined by reaction with molybdic acid and by Sears titration. The particle size increased from 1.0 to 4.5 nm with increasing ratio but did not depend on the type of alkali-metal cation. The amount of monomeric silicate ions decreased sharply with increasing ratio from 35% for ratio 2 to 2% for ratio 15 in 5 M SiO2 solutions. The polymeric particles were extracted into tetrahydrofuran or tertiary butylalcohol at pH 2, without changing the particle size, in yields which increased to more than 95% for the highest ratios. Previous dilution caused the particle size to grow in high-ratio solutions but to decrease in low-ratio solutions.
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| 13. |
- Persson, C. M., et al.
(författare)
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Testing the Gouy-Chapman theory by means of surface tension measurements for SDS-NaCl-H2O mixtures
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 267:1, s. 151-154
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Tidskriftsartikel (refereegranskat)abstract
- Surface tension isotherms were measured for sodium dodecyl sulfate (SDS) at different concentrations of added salt (NaCl). The free energy of the surfactant monolayer was assessed by invoking the Gouy-Chapman theory for the charged head groups, the hydrophobic (Tanford) free energy of transfer of the hydrocarbon chain, and the hydrocarbon chain configurational free energy according to Gruen's calculations and finally macroscopic contact terms. In particular, the effect of an increased salt concentration in bulk was examined. Theoretical predictions compare well with the experimental findings, and good agreement was found with respect to both the variation of free energy of the monolayer and the surface pressure behavior. Thus, at least for a liquid-expanded monolayer of SDS, the Gouy-Chapman model yields a satisfactory account of the electrostatic contribution to the thermodynamic properties at different salt concentrations of NaCl.
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| 14. |
- Rao, K. Hanumantha, et al.
(författare)
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Mechanism of oleate interaction on salt-type minerals : IV. Adsorption, electrokinetic and diffuse reflectance FT-IR studies of natural fluorite in the presence of sodium oleate
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 145:2, s. 314-329
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of oleate interaction with fluorite is investigated through adsorption, electrokinetic, and diffuse reflectance FT-IR measurements coupled with theoretical thermodynamic chemical equilibrium calculations. The adsorption isotherms exhibit an infinite increase in the slope beyond an oleate density of 10 μmole m-2. This adsorption density corresponds to a bilayer formation of oleate by two-dimensional condensation with a reported molecular coverage area of 33Ao2 (liquid-crystal state). Comparison of the theoretical chemical equilibria with the experimental data shows that the infinite increase in the slope of the isotherms is due to the precipitation of calcium oleate. The solubility product of this three-dimensional phase is found to be in the pK range 14.4-14.5, and agrees with most of the values quoted in the literature. From IR studies, monocoordination of oleate through counter sodium and calcium ions is suggested for the monolayer filling. ζ potentials of fluorite are correlated to the adsorption of oleate up to bilayer formation, and formation on surface of calcium oleate (three-dimensional growth on substrate) at high oleate concentrations. Two-dimensional condensation of oleate on the fluorite surface followed by the association of hydrocarbon chains (tail-tail bond) for the second layer, prior to the precipitation of calcium oleate in the bulk solution, is proposed as the adsorption mechanism.
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| 15. |
- Rao, K. Hanumantha, et al.
(författare)
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Mechanism of oleate interaction on salt-type minerals. V : Adsorption and precipitation reactions in relation to the solid/liquid ratio in the synthetic fluorite-sodium oleate system
- 1991
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 145:2, s. 330-348
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of adsorption of oleate onto a synthetic fluorite sample at different solid/liquid ratios in alkaline solutions is elucidated through adsorption isotherms in conjunction with ζ-potential and diffuse reflectance Fourier transform-infrared spectroscopic studies. These studies show that the chemisorption of oleate on surface calcium species followed by the physical adsorption of hydrocarbon chains (bilayer formation) precede the precipitation of calcium oleate in bulk solution. With an increase in the solid/liquid ratio, the bulk precipitation of calcium oleate after bilayer formation is found to be reduced, and at a high solid concentration, the isotherm is seen to level off with bilayer formation. As the solid concentration increases, the concentration of calcium in bulk solution decreases because of its adsorption on the head group of the hydrophilic layer of oleate (bilayer), and hence the extent of bulk precipitation decreases. The adsorption density for a monolayer coverage corresponds to the condensed state of an alkyl chain with a cross-sectional area of 33Ao2 (liquid-crystal state). Application of the two-dimensional condensation model is considered and no evidence for the surface precipitation process is observed.
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| 16. |
- Rönngren, Lars, et al.
(författare)
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Surface reactions in aqueous metal sulfide systems : 2. Ion exchange and acid/base reactions at the ZnSH2O interface
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 145:2, s. 396-404
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Tidskriftsartikel (refereegranskat)abstract
- The amphoteric properties of hydrous ZnS surfaces as well as an ion exchange reaction between surface coordinated Zn2+ ions and H+ ions of the aqueous phase have been established. The measurements were performed as potentiometric titrations in 0.1 M NaClO4 medium at 25°C. Besides measuring -log[H+] by using a glass electrode, -log[S2-] was recorded (Ag/Ag2S selective electrode). In addition, the total concentrations of H+, Zn2+, and S were analyzed as a function of -log[H+] of the bulk solution. Synthetically prepared ZnS and the mineral sphalerite were studied. Bro¨nsted acidity constants pK1s = 6.91 and pK2s = 10.28 for synthetic ZnS, and pK1s = 7.14 and pK2s = 10.29 for sphalerite, were established, which implies -log[H+] of zero proton condition equal to 8.60 and 8.72, respectively. Furthermore, the ion exchange reaction ≡SZn + 2H+ ↔ ≡SH2 + Zn2+ was characterized within the range 4 ≤ -log[H+] ≤ 7, with log K = 9.59 and 9.65. Experimental data were evaluated on the basis of the constant capacitance model by using the computer program FITEQL. The "best" fit to experimental data was obtained by assuming no charge dependence of K1s and K2s.
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| 17. |
- Theander, Katarina, et al.
(författare)
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Synergism and Foaming Properties in Mixed Nonionic/Fatty Acid Surfactant Systems
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 267, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- The synergism and foaming behavior of a mixed surfactant system consisting of a nonionic surfactant (polyethoxylated alkyl ether CnEm) and a fatty acid soap (sodium oleate) were studied. The micellar interaction parameter (the beta-parameter) was determined from the cmc following the approach of Rubingh's regular solution theory. For both the C12E6/sodium oleate and the C14E6/sodium oleate mixtures, the results indicate a fairly strong attractive interaction (negative beta-values), which were in agreement with previous data reported for other nonionic/anionic surfactant systems. The characteristics of the foam produced from the surfactants were evaluated using a glass column equipped with a series of electrodes measuring the conductance of the foam, which enabled the water content of the foam to be determined. From these measurements. since the total foam volume was almost the same for all concentrations and surfactants, we compared the amount of liquid in the foam produced under dynamic foaming and the ability of the foam to entrain the liquid after the airflow was switched-off (static foam stability). The amount of liquid in the foam 100 s after the air was switched-off followed the order NaOl > C12E6 > C14E6. Also, the mixtures had the same foam volumes as the pure surfactants at the same concentration. However, both mixtures had higher concentrations of liquid in the foam when the mole fraction of the nonionic surfactant in the mixed surfactant system was greater than about >0.3 in the solution.
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| 18. |
- Uvdal, Kajsa, et al.
(författare)
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Tyrosine derivatives assembled on gold
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 260:2, s. 361-366
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Tidskriftsartikel (refereegranskat)abstract
- Two different tyrosine derivatives, one with the OH group free and one with the OH group phosphorylated, linked to 3-mercaptopropionic acid through an amide bond are adsorbed to gold surfaces. The adsorbates are studied by means of X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRAS). The techniques are used to investigate the coordination to the surface and the molecular orientation of adsorbates relative to the surface. Molecular surface interactions, causing chemical shifts in the core level XPS spectra of the adsorbates on gold, are investigated using multilayer films as references. Angle-dependent XPS, XPS(T), and IRAS are used to estimate molecular orientation relative to the surface. The tyrosine derivatives adsorb chemically to the surface through the sulfur atoms and highly organized monolayers are formed with the OH and the PO32- exposed to the air/vacuum interface. © 2003 Elsevier Science (USA). All rights reserved.
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| 19. |
- Wang, Xianghuai, et al.
(författare)
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EDTA-induced flotation of sulfide minerals
- 1990
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 140:1, s. 217-226
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Tidskriftsartikel (refereegranskat)abstract
- The native and induced floatabilities of pyrite, galena, arsenopyrite, and glaucodot were investigated by flotation tests in the absence and in the presence of EDTA. The dissolution and electrokinetic behavior of the minerals in EDTA solutions was studied as a function of pH and of EDTA concentration. It was found that the flotation and dissolution of these minerals in EDTA solutions depend strongly on the pH values and on EDTA concentration. At a moderate EDTA concentration, the floatabilities and the released metal concentration are low or absent at pH below 5 and above 10. In the range of pH 6–10, both the flotation recovery and the dissolution of these minerals exhibit a plateau. The amount of released metal species increases with increasing EDTA concentration. The floatabilities of these sulfides first increase with an increase in EDTA concentration. However, a further increase in EDTA concentration to above 10−3M leads to a significant decrease in flotation recovery. ζ-Potential measurements show that in the presence of EDTA the IEP of the sulfide minerals is shifted considerably to lower pH values. The principles underlying the phenomena are discussed in terms of the results obtained from electrochemical studies of these sulfides and the instabilities of iron hydroxides in EDTA solutions.
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| 20. |
- Wu, Liuming, et al.
(författare)
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Surface complexation of calcium minerals in aqueous solution : 1. Surface protonation at fluorapatite-water interfaces
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 147:1, s. 178-185
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Tidskriftsartikel (refereegranskat)abstract
- The amphoteric properties of hydrous fluorapatite surfaces have been investigated. The measurements were performed as potentiometric titrations in 0.1M NaCl medium at 25°C using a glass electrode. The experimental data could be explained by a model that assumes the surface equilibria equivalent P-O- + H+ = equivalent P-OH log β101s(int.) = 6.6 ± 0.1 (3σ) equivalent Ca-OH2+ - H+ = equivalent Ca-OH log β-110s(int.) = -9.7 ± 0.1 (3σ). The equilibrium constants were evaluated using the computer program FITEQL by Westall (Report 82-01, Department of Chemistry. Oregon State University, Corvallis, 1982), assuming a constant capacitance model for the electric double layer. The acidity constants result in a value of log [H+]pzc = -8.15, which shifts to log [H+]pzc = -7.13 upon exposure to atmospheric carbon dioxide
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| 21. |
- Abrahamsson, Christoffer, 1984, et al.
(författare)
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Magnetic orientation of nontronite clay in aqueous dispersions and its effect on water diffusion
- 2015
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 437, s. 205-210
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Tidskriftsartikel (refereegranskat)abstract
- The diffusion rate of water in dilute clay dispersions depends on particle concentration, size, shape, aggregation and water-particle interactions. As nontronite clay particles magnetically align parallel to the magnetic field, directional self-diffusion anisotropy can be created within such dispersion. Here we study water diffusion in exfoliated nontronite clay dispersions by diffusion NMR and time-dependant 1H-NMR-imaging profiles. The dispersion clay concentration was varied between 0.3 and 0.7 vol%. After magnetic alignment of the clay particles in these dispersions a maximum difference of 20% was measured between the parallel and perpendicular self-diffusion coefficients in the dispersion with 0.7 vol% clay. A method was developed to measure water diffusion within the dispersion in the absence of a magnetic field (random clay orientation) as this is not possible with standard diffusion NMR. However, no significant difference in self-diffusion coefficient between random and aligned dispersions could be observed.
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| 22. |
- Abreu, Barbara, et al.
(författare)
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Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes : Interplay of molecular parameters on nanotube dispersibility and debundling
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 547, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n-s-n gemini surfactants, varying n and s, the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials.
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| 23. |
- Afifi, Hala, et al.
(författare)
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Structural transitions in cholesterol-based wormlike micelles induced by encapsulating alkyl ester oils with varying architecture
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 378:1, s. 125-134
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Tidskriftsartikel (refereegranskat)abstract
- The effect of encapsulating oils on the phase behaviour and the microstructure of wormlike micelles formed by polyoxyethylene cholesteryl ether (ChEO10) and triethylene glycol monododecyl ether co-surfactant (C12EO3) was investigated using rheology, Cryo-TEM and small-angle neutron scattering measurements. Six alkyl ester oils bearing small, systematic variations in their molecular structure were encapsulated: ethyl butyrate (EB24), ethyl caproate (ECO26), ethyl caprylate (EC28), methyl enanthate (ME17), methyl caprylate (MC18) and butyl butyrate (BB44), where the subscripts refer to the length of the alkyl chain and fatty acid chain, respectively, on either sides of the ester link. The addition of alkyl ester oils to ChEO10/C12EO3 solutions promotes the longitudinal growth of the surfactant aggregates into wormlike micelles possessing an elliptical cross-section, with rminor 31 ± 2 Å and rmajor varying from 45 to 70 Å. At fixed alkyl chain length, oils with longer fatty acid chains were found to be more efficient in inducing wormlike micelle formation or their elongation, following the order: EC28 > ECO26 > EB24. Instead, at fixed fatty acid chain length, increasing the alkyl chain has a negative effect on the longitudinal micellar growth (MC18 > EC28 and EB24 > BB44). At high co-surfactant concentrations and in the presence of EB24, an unusual phase of ring-like micelles was detected. Overall, the orientation of the oil molecules within the micelles enables them to act as co-surfactants with a small head-group, decreasing the average cross-section area and promoting longitudinal growth of the micelles into worms.
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| 24. |
- Ahmad, SI, et al.
(författare)
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Microemulsions and phase equilibria
- 1974
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 47, s. 32-37
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Tidskriftsartikel (refereegranskat)
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| 25. |
- Ahualli, S., et al.
(författare)
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Use of a cell model for the evaluation of the dynamic mobility of spherical silica suspensions
- 2007
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 309:2, s. 342-349
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we evaluate the validity of a cell model for the calculation of the dynamic mobility of concentrated suspensions of spheres. The key point is the consideration of the boundary conditions (electrical and hydrodynamic) at the boundary of the fluid cell surrounding a single probe particle. The model proposed is based on a universal criterion for the averages of fluid velocity, electric potential, pressure field or electrochemical properties in the cell. The calculations are checked against a wide set of experimental data on the dynamic mobility of silica suspensions with two different radii, several ionic strengths, and two particle concentrations. The comparison reveals an excellent agreement between theory and experiment, and the model appears to be extremely suitable for correctly predicting the behavior of the dynamic mobility, including the changes in the zeta potential, ?, with ionic strength, the frequency and amplitude of the Maxwell-Wagner-O'Konski relaxation, and the inertial relaxation occurring at the top of the frequency range accessible to our experimental device. © 2007 Elsevier Inc. All rights reserved.
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| 26. |
- Alami, Eloi, et al.
(författare)
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A comparison between hydrophobically end-gapped poly(ethylene oxide) with ether and urethane bonds
- 1997
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Ingår i: JOURNAL OF COLLOID AND INTERFACE SCIENCE. - : ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS. - 0021-9797. ; 193:2, s. 152-162
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Tidskriftsartikel (refereegranskat)abstract
- Two models of HEUR (hydrophobically modified ethylene oxide urethane) associative polymers (AP) are compared. The two polymers are polyethyleneoxides simply end-capped with dodecyl groups, one through an ether bond H25C12-O-(CH2CH2O)(304)-C12H25 (AP14, M-
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| 27. |
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| 28. |
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| 29. |
- Altgärde, Noomi, 1983, et al.
(författare)
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Immobilization of chondroitin sulfate to lipid membranes and its interactions with ECM proteins
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 390:1, s. 528-266
-
Tidskriftsartikel (refereegranskat)abstract
- Glycosaminoglycans (GAGs) in the extracellular matrix (ECM) have multiple functions in tissues including providing support, mediating cell division and differentiation, and taking part in important interactions with proteins, e.g. growth factors. Studying GAG related interactions is inherently difficult and requires suit- able interaction platforms. We show two strategies to covalently couple the GAG chondroitin sulfate (CS) to supported lipid bilayers (SLBs), either by (a) activating carboxy-functionalized phospholipids in the lipid bilayer, followed by the addition of hydrazide-functionalized CS, or by (b) activating naturally occurring carboxyl groups on CS prior to addition to an amino-functionalized SLB. Bilayer formation and subsequent immobilization was followed in real-time using the Quartz Crystal Microbalance with Dissipation monitor- ing, a technique that provides unique information when studying highly hydrated molecular films. The two strategies yielded thin CS films (in the nanometer range) with similar viscoelastic properties. Fluidity of the lipid bilayer was retained when CS was coupled. The application of the CS interaction platform was exemplified for type I collagen and the bone inducing growth factor bone morphogenetic protein-2 (BMP-2). The addition of collagen to immoblized CS resulted in soft layers whereas layers formed by addition of BMP-2 were denser, independent on the immobilization strategy used.
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| 30. |
- Alves, Luis, et al.
(författare)
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On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants : Role of the surfactant architecture
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 513, s. 489-496
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis The rheological control of suspensions is of key interest in the formulation design. A chemically cross-linked hydrophobically modified poly(acrylic acid) (HMCL-PAA), used as rheology modifier, is pH sensitive and shows swelling behavior above a critical pH due to the ionization of the acrylic acid groups. At low pH, HMCL-PAA suspensions are liquid and turbid. The binding of surfactants to HMCL-PAA, at low pH conditions, can result in significant changes on rheology and transparency of the polymeric suspensions, due to the swelling of the microgel particles. Experiments The influence of surfactants addition on the rheological properties and transparency of HMCL-PAA suspensions was determined. A systematic study was performed using different types of surfactants (ionic, non-ionic and zwitterionic). Findings The gelation efficiency of HMCL-PAA suspensions at low pH is strongly dependent on surfactant architecture: ionic surfactants are found to be much more efficient than non-ionic or zwitterionic surfactants. Ionic surfactants lead to a liquid-to-gel transition accompanied by an increase of transparency of the suspensions. Among the ionic surfactants, anionics show stronger interactions with the polymer. Also the surfactant hydrophobicity is relevant; the more hydrophobic the surfactant, the stronger is the binding to the polymer and thus the larger the particle swelling.
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| 31. |
- An, Junxue, et al.
(författare)
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Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
- 2017
-
Ingår i: Journal of Colloid and Interface Science. - : Academic Press. - 0021-9797 .- 1095-7103. ; 487, s. 88-96
-
Tidskriftsartikel (refereegranskat)abstract
- Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40 °C. A local force minimum at short separation develops at 40 °C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25 °C are significantly lower after exposure to a temperature of 40 °C than prior to heating, which is due to higher polymer chain density on the surface after heating.
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| 32. |
- An, Junxue, et al.
(författare)
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Nanoscale characterization of PEGylated phospholipid coatings formed by spray drying on silica microparticles
- 2020
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 577, s. 92-100
-
Tidskriftsartikel (refereegranskat)abstract
- Phospholipids constitute biocompatible and safe excipients for pulmonary drug delivery. They can retard the drug release and, when PEGylated, also prolong the residence time in the lung. The aim of this work was to assess the structure and coherence of phospholipid coatings formed by spray drying on hydrophilic surfaces (silica microparticles) on the nanoscale and, in particular, the effect of addition of PEGylated lipids thereon. Scanning electron microscopy showed the presence of nanoparticles of varying sizes on the microparticles with different PEGylated lipid concentrations. Atomic force microscopy confirmed the presence of a lipid coating on the spray-dried microparticles. It also revealed that the lipid-coated microparticles without PEGylated lipids had a rather homogenous coating whereas those with PEGylated lipids had a very heterogeneous coating with defects, which was corroborated by confocal laser scanning microscopy. All coated microparticles had good dispersibility without agglomerate formation, as indicated by particle size measurements. This study has demonstrated that coherent coatings of phospholipids on hydrophilic surfaces can be obtained by spray drying. However, the incorporation of PEGylated lipids in a one-step spray-drying process to prepare lipid coated microparticles with both controlled-release and stealth properties is very challenging.
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| 33. |
- Andersson, Johanna, 1984, et al.
(författare)
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Stick–slip motion and controlled filling speed by the geometric design of soft micro-channels
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 524, s. 139-147
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis Liquid can move by capillary action through interconnected porous materials, as in fabric or paper towels. Today mass transport is controlled by chemical modification. It is, however, possible to direct mass transport by geometrical modifications. It is here proposed that it is possible to tailor capillary flow speed in a model system of micro-channels by the angle, size and position of attached side channels. Experiments A flexible, rapid, and cost-effective method is used to produce micro-channels in gels. It involves 3D-printed moulds in which gels are cast. Open channels of micrometre size with several side channels on either one or two sides are produced with tilting angles of 10 – 170°. On a horizontal plane the meniscus of water driven by surface tension is tracked in the main channel. Findings The presence of side channels on one side slowed down the speed of the meniscus in the main channel least. Channels having side channels on both sides with tilting angles of up to 30° indicated tremendously slower flow, and the liquid exhibited a stick-slip motion. Broader side channels decreased the speed more than thinner ones, as suggested by the hypothesis. Inertial forces are suggested to be important in branched channel systems studied here.
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| 34. |
- Andersson, KM, et al.
(författare)
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DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique
- 2002
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 246, s. 309-315
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the DLVO surface forces of oxidised tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray Photoelectron Spectroscopy (XPS), and electrokinetic measurements that this model system is representative for industrial WC and Co powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO3 and CoOOH. The repulsive electrostatic double layer forces between WO3 surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO3 and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.
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| 35. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Charged microcapsules for controlled release of hydrophobic actives Part II: Surface modification by LbL adsorption and lipid bilayer formation on properly anchored dispersant layers
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 409, s. 8-17
-
Tidskriftsartikel (refereegranskat)abstract
- Charge microcapsules with a dodecane core and a poly(methyl methacrylate) (PMMA) shell have been prepared via the internal phase separation method using ionic dispersants. The microcapsules have subsequently been surface modified with polyelectrolyte multilayers and lipid bilayers. Two types of ionic dispersant systems have been investigated: a small set of ionic amphiphilic block copolymers of poly(methyl methacrylate)-block-poly(sodium (meth)acrylate) type and an oil-soluble anionic surfactant, sodium 1,5-dioxo-1,5-bis(3,5,5-trimethylhexyloxy)-3((3,5,5trimethylhexyloxy)car bonyl)pentane-2-sulfonate, in combination with a water-soluble polycation, poly(diallyldimethylammonium chloride). The Layer-by-Layer adsorption of the polyelectrolyte pair poly(diallydimethylammonium chloride) (350,000 g/mol) and poly(sodium methacrylate) (15,000 g/mol) was successfully made on both microcapsule systems with the formation of very thin multilayers as indicated with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements on model surfaces. Formation of a lipid bilayer on the surface of the microcapsules from liposomes with a charge opposite that of the capsule surface was also proven to be successful as indicated by the C-potential of the microcapsules, the characteristic frequency shift as measured with QCM-D and fluorescence recovery after photobleaching (FRAP) on model systems. However, the proper anchorage of the dispersants in the underlying PMMA surface was key for the successful surface modification.
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| 36. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
-
Directed self-assembly of silica nanoparticles in ionic liquid-spun cellulose fibers
- 2019
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 553, s. 167-176
-
Tidskriftsartikel (refereegranskat)abstract
- The application range of man-made cellulosic fibers is limited by the absence of cost- and manufacturing-efficient strategies for anisotropic hierarchical functionalization. Overcoming these bottlenecks is therefore pivotal in the pursuit of a future bio-based economy. Here, we demonstrate that colloidal silica nanoparticles (NPs), which are cheap, biocompatible and easy to chemically modify, enable the control of the cross-sectional morphology and surface topography of ionic liquid-spun cellulose fibers. These properties are tailored by the silica NPs’ surface chemistry and their entry point during the wet-spinning process (dope solution DSiO2 or coagulation bath CSiO2). For CSiO2-modified fibers, the coagulation mitigator dimethylsulphoxide allows for controlling the surface topography and the amalgamation of the silica NPs into the fiber matrix. For dope-modified fibers, we hypothesize that cellulose chains act as seeds for directed silica NP self-assembly. This results for DSiO2 in discrete micron-sized rods, homogeneously distributed throughout the fiber and for glycidoxy-surface modified DSiO2@GLYEO in nano-sized surface aggregates and a cross-sectional core-shell fiber morphology. Furthermore, the dope-modified fibers display outstanding strength and toughness, which are both characteristic features of biological biocomposites.
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| 37. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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The effect of pH on charge, swelling and desorption of the dispersant poly(methacrylic acid) from poly(methyl methacrylate) microcapsules
- 2012
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 375:1, s. 213-215
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Tidskriftsartikel (refereegranskat)abstract
- Poly(methyl methacrylate) microcapsules have been prepared using the solvent evaporation technique with poly(methacrylic acid) (PMAA) as dispersant. The charge, swelling and desorption of PMAA from the microcapsules after treating the suspension with base have been followed using microelectrophoresis, X-ray photoelectron spectroscopy and quartz crystal microbalance with dissipation monitoring on model PMMA surfaces. Basic treatment of the microcapsule suspension leads to temporary colloidal stability through the introduction of charges on the PMAA chain. However, the increase in charge causes a continuous desorption of PMAA from the microcapsule surface, eventually leading to aggregation. If instead poly(diallyldimethylammonium chloride) is added to the base treated microcapsule suspension, good colloidal stability is obtained.
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| 38. |
- Ankerfors, Caroline, et al.
(författare)
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Use of polyelectrolyte complexes and multilayers from polymers and nanoparticles to create sacrificial bonds between surfaces
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 391, s. 28-35
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, particle polyelectrolyte complexes (PPECs) were formed by mixing cationic polyacrylamide (CPAM) and silica nanoparticles using the jet mixing technique. Within certain limits, the size of the formed PPECs could be controlled. The aim was to prepare PPECs with embedded sacrificial bonds, similar to those found in bones. Examination of PPEC adsorption to silica model surfaces indicated that,smaller PPECs adsorbed to a higher level than larger ones, due to the higher diffusion speed of smaller complexes. Adsorption studies of the same components as in the PPECs, but arranged in multilayers, that is, particle polyelectrolyte multilayers (PPEMs), indicated a stable, gradual build-up of material on the surface with smaller nanoparticles, whereas PPEMs comprising elongated nanoparticles appeared to be more loosely adsorbed onto the surface when the nanoparticles were in the outer layer, due to repulsive forces within the adsorbed layer. The AFM colloidal probe technique was used to study the interaction between surfaces treated with PPECs, multilayers, or polyelectrolyte complexes (PECs). The results showed that the expected long-range disentanglement could be achieved with PPECs but that the pull-off forces were generally low. Treatment with PPEMs comprising the same polymer and nanoparticle components produced higher pull-off values, together with disentanglement behaviour, possibly due to better contact between the surfaces. Adhesion experiments with polymer PECs showed significantly higher pull-off values than with the PPECs, probably due to polymer interdiffusion across the surface boundary.
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| 39. |
- Ankerfors, Caroline, et al.
(författare)
-
Using jet mixing to prepare polyelectrolyte complexes : Complex properties and their interaction with silicon oxide surfaces
- 2010
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 351:1, s. 88-95
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of mixing procedure on the properties of polyelectrolyte complexes (PECs) was investigated using two complexation techniques, polyelectrolyte titration and jet mixing, the latter being a new method for PEC preparation. For the low-molecular-weight polyelectrolytes polyacrylic acid (PAA) and polyallyl amine hydrochloride (PAH), shorter mixing times produced smaller PECs, whereas for higher molecular weights of the same polyelectrolytes, PEC size first decreased with decreasing mixing time to a certain level, after which it started increasing again. This pattern was likely due to the diffusion-controlled formation of "pre-complexes", which, in the case of low-molecular-weight polymers, occurs sufficiently quickly to form stable complexes; when polyelectrolytes are larger, however, non-equilibrium pre-complexes, more prone to aggregation, are formed. Comparing the techniques revealed that jet mixing produced smaller complexes, allowing PEC size to be controlled by mixing time, which was not the case with polyelectrolyte titration. Higher polyelectrolyte concentration during jet mixing led to the formation of larger PECs. It was also demonstrated that PEC size could be changed after preparation: increasing the pH of the PEC dispersion led to an irreversible increase in PEC size, whereas lowering the pH did not influence PEC size. The adsorption behavior of PECs formed from weak polyelectrolytes on model substrates was studied using QCM-D, SPAR, and AFM imaging; the results indicated that increasing the pH increased the amount of PECs adsorbed to model surfaces. However, the amount of PECs adsorbed to the model surfaces was low compared with other systems in all studied cases.
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| 40. |
- Aramaki, Kenji, et al.
(författare)
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Self-diffusion study of micelles in poly(oxyethylene)-polydimethylsiloxane diblock copolymer and poly(oxyethylene) alkyl ether systems
- 2006
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 300:1, s. 354-360
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Tidskriftsartikel (refereegranskat)abstract
- Self-diffusion constants of amphiphilic molecules in D2O solutions of mixed poly(oxyethylene)-polydimethylsiloxane diblock copolymer (POE-PDMS, SimC3EOn) and poly(oxyethylene) dodecyl ether (C12EOn) were measured by pulsed-field-gradient NMR method. In the D2O/Si25C3EO51.6/C12EO8 or D2O/Si52C3EO51.6/Cl2EO8 systems, small and large micelles coexist in a wide range of SimC3EO51.6 fraction in total amphiphiles, whereas such a coexisting phenomenon does not take place in the D2O/Si5.8C3EO51.6/Cl2EO8 system. The coexisting phenomenon also takes place in the D2O/Si25C3EO51.6/Cl2EO5 system although the range of mixing fraction is limited. By obtaining each contribution of surfactant and copolymer molecules to the attenuation decay of the echo signal from the proton of the poly(oxyethylene) chain, we could evaluate the composition of the mixed micelles in the D2O/Si25C3EO51.6/Cl2EO8 system. The copolymer content in the mixed micelle increases proportionally to the copolymer mole fraction in the aqueous solution. From the series of self-diffusion measurements, we can conclude that the miscibility Of SimC3EOn and C12EOn in aqueous micelles becomes poor and the coexisting phenomenon takes place when the PDMS chain becomes much longer than the dodecyl chain of C12EOn or the POE chain of C12EOn becomes long. Furthermore it is also revealed that very few silicone copolymer molecules can be incorporated in small surfactant micelles. (c) 2006 Elsevier Inc. All rights reserved.
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| 41. |
- Argyri, Smaragda Maria, 1994, et al.
(författare)
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Contact-free measurement of surface tension on single droplet using machine learning and acoustic levitation
- 2023
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 640, s. 637-646
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis Acoustic levitation provides the possibility to deform levitated droplets in a controllable, and quantifiable manner, thus offering a means to measure the surface tension of a liquid droplet based on its deviation from sphericity. However, for new generation of multi-source and highly stable acoustic levitators, no model relates the acoustic pressure field to the deformation and surface tension. Utilizing a machine learning algorithm is expected to identify correlations between the experimental data without any set preconditions. Experiments A series of aqueous surfactant solutions with a large range of surface tensions were prepared, and evaporated under levitation, while the acoustic pressure was varied. A dataset of over 50,000 images was used for the training and evaluation of the machine learning algorithm. Prior to that, the machine learning approach was validated on in silico data that also included artificial noise. Findings We achieved high accuracy in predicting the surface tension of single standing droplets (±0.88 mN/m), and we surpassed certain physical conditions related to the size, and shape of the suspended samples that simpler theoretical models are subject to.
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| 42. |
- Ashkarran, Ali Akbar, et al.
(författare)
-
Conformation- and phosphorylation-dependent electron tunnelling across self-assembled monolayers of tau peptides
- 2022
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 606, s. 2038-2050
-
Tidskriftsartikel (refereegranskat)abstract
- We report on charge transport across self-assembled monolayers (SAMs) of short tau peptides by probing the electron tunneling rates and quantum mechanical simulation. We measured the electron tunneling rates across SAMs of carboxyl-terminated linker molecules (C6H12O2S) and short cis-tau (CT) and trans-tau (TT) peptides, supported on template-stripped gold (AuTS) bottom electrode, with Eutectic Gallium-Indium (EGaIn)(EGaIn) top electrode. Measurements of the current density across thousands of AuTS/linker/tau//Ga2O3/EGaIn single-molecule junctions show that the tunneling current across CT peptide is one order of magnitude lower than that of TT peptide. Quantum mechanical simulation demonstrated a wider energy bandgap of the CT peptide, as compared to the TT peptide, which causes a reduction in its electron tunneling current. Our findings also revealed the critical role of phosphorylation in altering the charge transport characteristics of short peptides; more specifically, we found that the presence of phosphate groups can reduce the energy band gap in tau peptides and alter their electrical properties. Our results suggest that conformational and phosphorylation of short peptides (e.g., tau) can significantly change their charge transport characteristics and energy levels.
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| 43. |
- Atakan, Aylin, et al.
(författare)
-
Impact of the morphological and chemical properties of copper-zirconium-SBA-15 catalysts on the conversion and selectivity in carbon dioxide hydrogenation
- 2019
-
Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 546, s. 163-173
-
Tidskriftsartikel (refereegranskat)abstract
- A hybrid catalyst consisting of Zr-doped mesoporous silica (Zr-SBA-15) supports with intergrown Cu nanoparticles was used to study the effects of a catalysts chemical states on CO2 hydrogenation. The chemical state of the catalyst was altered by using tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS) as the silica precursor in the synthesis of the Zr-SBA-15 framework, and infiltration (Inf) or evaporation induced wetness impregnation (EIWI) as the Cu loading method. As a result, the silica precursor mainly affects the activity of the catalyst whereas the Cu loading method alters the selectivity of the products. TEOS materials exhibit a higher catalytic activity compared to SMS materials due to different Zr dispersion and bonding to the silica matrix. EIWI catalysts display selectivity for methanol formation, while the Inf ones enable methanol conversion to DME. This is correlated to a higher Zr content and lower Cu oxidation states of EIWI prepared catalysts. (C) 2019 Elsevier Inc. All rights reserved.
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| 44. |
- Attard, Phil, et al.
(författare)
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Effective spring description of a bubble or a droplet interacting with a particle
- 2002
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 247:1, s. 255-257
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- It is shown that the interaction of a particle with a liquid drop or a gas bubble may be quantitatively described over the whole distance regime by treating the fluid interface as a Hookean spring. An algorithm suitable for analyzing atomic force microscopy data suitable for a calculator or a spread-sheet is given and applied to data for oil drops. (C) 2002 Elsevier Science (USA).
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| 45. |
- Aulin, Christian, 1980-, et al.
(författare)
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Wetting kinetics of oil mixtures on fluorinated model cellulose surfaces
- 2008
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 317:2, s. 556-567
-
Tidskriftsartikel (refereegranskat)abstract
- The wetting of two different model cellulose surfaces has been studied; a regenerated cellulose (RG) surface prepared by spin-coating, and a novel multilayer film of poly(ethyleneimine) and a carboxymethylated microfibrillated cellulose (MFC). The cellulose films were characterized in detail using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM indicates smooth and continuous films on a nanometer scale and the RMS roughness of the RG cellulose and MFC surfaces was determined to be 3 and 6 nm, respectively. The cellulose films were modified by coating with various amounts of an anionic fluorosurfactant, perfluorooctadecanoic acid, or covalently modified with pentadecafluorooctanyl chloride. The fluorinated cellulose films were used to follow the spreading mechanisms of three different oil mixtures. The viscosity and surface tension of the oils were found to be essential parameters governing the spreading kinetics on these surfaces. XPS and dispersive surface energy measurements were made on the cellulose films coated with perfluorooctadecanoic acid. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the contact angle of castor oil on the surface. A dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (Ξe > 90 °) by castor oil.
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| 46. |
- Axe, Kristina, et al.
(författare)
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An ATR-FTIR spectroscopic study of the competitive adsorption between oxalate and malonate at the water-goethite interface.
- 2006
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 294:1, s. 31-7
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Tidskriftsartikel (refereegranskat)abstract
- The competitive adsorption between oxalate and malonate at the water-goethite interface was studied as a function of pH and total ligand concentrations by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results obtained show that ATR-FTIR spectroscopy resolves the individual spectroscopic features of oxalate and malonate when adsorbed simultaneously at the water-goethite interface. The characteristic peaks of all four types of predominating surface complexes existing in the single ligand systems were identified, namely one inner sphere and one outer sphere surface complex for each ligand. The quantitative adsorption data showed that oxalate partially out-competes malonate at the water-goethite interface. Evaluation of the peak area variations as a function of pH indicated that the stronger oxalate adsorption can be ascribed to the more stable inner sphere surface complex of oxalate, which in turn is related to the oxalate five-member chelate ring structure yielding a more stable complex compared to the six-member ring of malonate.
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| 47. |
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| 48. |
- Bahmanzadeh, Safiyeh, et al.
(författare)
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Proteolytic degradation of gelatin-tannic acid multilayers
- 2018
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 526, s. 244-252
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis Gelatin is one of the most popular constituents of biodegradable/edible films. Because of its poor mechanical properties, it typically needs to be cross-linked. In this regard, the use of tannic acid has attracted significant interest. Whereas the biodegradability of gelatin is well established, little is known on how different crosslinking methods affect biodegradability. In most cases, the ionic strength at which protein films are grown has a drastic effect on their structure. Thus, it is expected that by controlling the ionic strength during the growth of cross-linked gelatin films it should be possible to tune the access to relevant cleavage sites by proteases and, therefore, their biodegradability. Experiments Gelatin-tannic acid were grown at different ionic strengths by means of the layer-by-layer self-assembly method. The growth of these multilayers and their response to the presence of different proteases were monitored by means of Electrochemical Impedance Spectroscopy and Quartz Crystal Microbalance with Dissipation. Findings Gelatin-tannic acid multilayers grown at low ionic strength exhibited a swollen structure that allowed easy access to their cleavage sites by proteases. Multilayers formed at physiological ionic strength exhibited a compacter structure, which limited their proteolytic degradation.
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| 49. |
- Barrantes, Alejandro, et al.
(författare)
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Influence of pH on the build-up of poly-L-lysine/heparin multilayers
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 388:1, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- The effect of pH on the build-up-of polyelectrolyte multilayers, PEMs, composed by poly-L-lysine and heparin onto two different substrates, silica and gold, has been studied by means of ellispmetry and quartz crystal microbalance with dissipation, QCM-D. Ellipsometry results indicate that the dry mass grows exponentially with the number of layers, and that this amount is larger as the pH values are raised. From QCM-D data the viscoelastic properties of the multilayered structure have been obtained. These data reflect that PEMs become more viscoelastic as the pH values are increased for silica substrates, while for gold the highest viscoelastic behavior is obtained at neutral pH and the elastic behavior becomes dominant as the pH is further increased or decreased. By combining these two surface techniques it has been also possible to determine the solvent content in the multilayers and reach a deeper understanding of the internal structure.
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| 50. |
- Barrantes, Alejandro, et al.
(författare)
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Poly-L-lysine/heparin multilayer coatings prevent blood protein adsorption
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 485, s. 288-295
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of blood proteins, serum albumin (BSA), immunoglobulin G (IgG) and fibrinogen (FGN), onto model SiO2 planar surfaces coated with poly-L-lysine/heparin multilayers (PLL/HEP) has been investigated by means of ellipsometry and quartz crystal microbalance with dissipation. Aiming at the development of low fouling coatings, this study has been focused on the effects that the number of layers and the type of polyelectrolyte present on the topmost layer have on the adsorption of these proteins. The three proteins interact with PLL-ended coatings whereas HEP-ended coatings prevent the adsorption of both BSA and IgG and induce a decrease in the adsorbed amount of FGN, down to 0.4 mg/m(2) for three bilayers, as the number of PLL/HEP bilayers increases. These results suggest that heparin-ended multilayers prevent protein adsorption, which is an indicative of good blood compatibility. As a consequence we propose that PLL/HEP coatings could be used for the development of vascular medical devices. (C) 2016 Elsevier Inc. All rights reserved.
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