| 1. |
- Claesson, PM, et al.
(författare)
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Interactions between a 30% charged polyelectrolyte and an anionic surfactant in bulk and at a solid-liquid interface
- 1998
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Ingår i: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 102, s. 1270-1278
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Tidskriftsartikel (refereegranskat)abstract
- The association between a 30% charged cationic polyelectrolyte and an anionic surfactant, sodium dodecyl sulfate (SDS), in 10 mM 1:1 electrolyte was investigated using surface force measurements and dynamic light scattering. The polyelectrolyte employed was a random copolymer of the neutral acrylamide and cationic [3-(2-methylpropionamide)propyl]trimethylammonium chloride (AM-MAPTAC-31). Light scattering measurements show that upon progressive addition of SDS to an AM-MAPTAC-31 solution the single coil size decreases until precipitation occurs at an SDS/MAPTAC ratio of just above 0.4. At SDS/MAPTAC ratios at or above 2, redispersion of the aggregates takes place. The interfacial behavior of AM-MAPTAC-31/SDS complexes was investigated in two ways. In one set of experiments a droplet containing a mixture of SDS and AM-MAPTAC-31 was placed between the surfaces and adsorption was allowed to occur from the aqueous mixture. It was found that the range of the steric force decreased when the SDS/MAPTAC ratio was increased from 0 to 0.4, indicating adsorption in a less extended conformation due to a decreased repulsion between the polyelectrolyte segments. At a ratio of 0.6 a compact interfacial complex was formed and the measured force was attractive over a small distance regime. A further increase in SDS/MAPTAC ratio resulted in precipitation of large aggregates at the surface, and reproducible force data could not be obtained. At an even higher SDS/AM-MAPTAC ratio of 4, individual aggregates were once again adsorbed at the surface. Hence, we find a good correspondence between association in bulk and at the solid surface. In another set of experiments the polyelectrolyte was first preadsorbed to mica surfaces and then SDS was added to the polyelectrolyte-free solution surrounding the surfaces. In this way precipitation of large SDS-polyelectrolyte aggregates onto the surfaces was avoided. Addition of SDS up to a concentration of 0.1 mM hardly affected the long-range interaction but gave an increased compressed layer thickness. A further increase in SDS concentrations to 1 mM results in a dramatic increase in the range of the force, suggesting formation of strongly negatively charged polyelectrolyte-surfactant complexes.
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| 2. |
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| 3. |
- Fielden, ML, et al.
(författare)
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A comparison of three methods for the convenient determination of SDS in aqueous solutions
- 1998
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 198, s. 261-265
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Tidskriftsartikel (refereegranskat)abstract
- Three methods for determining the concentration of sodium dodecyl sulfate (SDS) in aqueous solutions have been investigated. The first was to titrate SDS by cetyltrimethylammonium bromide (CTAB), where the endpoint (corresponding to 1:1 neutralization) was determined by measuring the potential drop between a surfactant ion selective electrode and a silver/silver chloride reference electrode. The second was to measure the endpoint of an analogous titration by following the formation of the insoluble CTAB/SDS complex with turbidimetry. The third was to measure the turbidity of a solution as a function of SDS concentration in the presence of myristyltrimethylammonium bromide (MTAB). Of these methods, which all provide a reasonable assessment of the SDS concentration, the last was certainly the fastest and most convenient, particularly for large numbers of samples.
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| 4. |
- Fielden, ML, et al.
(författare)
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Investigating the adsorption of the gemini surfactant "12-2-12" onto mica using atomic force microscopy and surface force apparatus measurements
- 1999
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 3924-3934
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of the cationic gemini surfactant 1,2-bis(n-dodecyldimethylammonium)ethane dibromide on mica was followed by measuring forces between mica surfaces and by atomic force microscopy (AFM) imaging. The surface charge was found to be neutralized at total surfactant concentrations between 8 ? 10-7 and 5 ? 10-6 M, depending on equilibration time, as judged by the elimination of the repulsive electrostatic double-layer force. At around this concentration, monolayer aggregates of the surfactant started to form on the surface, varying in size between 8 and 130 nm across and between 0.5 and 0.6 nm high. The coverage rapidly increased with a small increase in surfactant concentration, as seen by AFM images. In the concentration range (5 ? 10-6)-(1 ? 10-4) M the surfactant continued to adsorb steadily as judged by the increase in the double-layer repulsion between surfaces. The hydrophobicity of the surfaces was confirmed by the magnitude of the force required to separate the surfaces, which increased from 20 mN/m in pure water to 120 mN/m at 4.6 ? 10-6 M, up to 270 mN/m at 9.0 ? 10-6 M; it then stayed virtually constant. AFM imaging showed that, in this range, a significant amount of the surfactant adsorbed on top of the monolayer, although neither technique suggested that the adsorbing material aggregated into bilayer patches. At 1.8 ? 10-4 M, a full bilayer formed on each surface, causing an increase in the compressed layer thickness from 1 to 4 nm, and a reduction in pull-off force to 5-10 mN/m. In this concentration range, the nucleation and growth of the complete bilayer was directly observed with AFM. It appeared to occur as isotactic growth of patches, which were initially around 70 nm in size and evenly distributed. These patches grew and joined together to form a flat bilayer over a time scale of around 2 h. Between 1.8 ? 10-4 and 7.6 ? 10-4 M, a non-DLVO (Derjaguin-Landau-Verwey-Overbeek) force was observed between 12 and 7 nm, followed by an attractive force which pulled the surfaces into bilayer-bilayer contact. The extra repulsive force, which has not been observed previously with cationic surfactant bilayers, was probably due to additional surfactant adsorbed outside the bilayer. AFM imaging confirmed that an extra layer was present above the critical micellar concentration (cmc), as indicated by a significant increase in surface roughness from 0.5 nm to 7-8 nm.
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| 5. |
- Fielden, ML, et al.
(författare)
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Investigation of a 31% charged cationic polyelectrolyte interacting with sodium dodecyl sulfate in bulk solution and as a preadsorbed layer on mica. Low ionic strength
- 1998
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 14, s. 5366-5375
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of mixtures of a cationic polyelectrolyte of intermediate charge density (31%) and anionic surfactant both in bulk and at a negatively charged solid surface has been investigated. The polyelectrolyte employed was a random copolymer of the neutral acrylamide and cationic [3-(2-methylpropionamido)propyl]trimethylammonium chloride, and the surfactant was sodium dodecyl sulfate (SDS). Measurements of flocculation and electrophoretic mobility in bulk solution clearly showed a phase separation with a maximum in turbidity corresponding roughly to charge neutralization of the polyelectrolyte/surfactant complex. Conductivity measured at low SDS concentrations showed a strong uptake of ions by the polyelectrolyte at a critical SDS concentration. The interferometric surface force apparatus was used to measure forces between muscovite mica surfaces onto which the polyelectrolyte was adsorbed from a 20 ppm, 10-4 M KBr solution. After the polymer solution was replaced with polymer-free 10-4 M KBr solution, a weak long range double-layer repulsion was observed between approaching surfaces, with a bridging attraction dominating at smaller separations. A weak adhesion was observed upon separating the surfaces. Addition of 4.2 ? 10-4 M SDS caused a large swelling of the preadsorbed polymer layer due to formation of an associative complex between the polymer and surfactant. Further increasing the SDS concentration decreased the force and layer thickness due to screening of the electrostatic repulsion within the layers and some desorption of polymer molecules. That a slight desorption did occur was supported by electron spectroscopy for chemical analysis measurements. The results broaden the understanding of the effect of polyelectrolyte charge density on the interaction of preadsorbed polyelectrolyte layers with oppositely charged surfactants.
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