Forces between surfaces in the presence of a cationic polyelectrolyte and an anionic surfactant (original) (raw)
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Langmuir, 2002
The interactions between silica and R-alumina surfaces with and without polyelectrolyte and combinations of both polyelectrolyte (sodium poly(styrene sulfonate) or PSS) and surfactant (cetyltrimethylammonium bromide or CTAB) have been measured using the atomic force microscope (AFM) colloid probe technique. In this case, silica particles were glued to the AFM cantilever to give a surface of known geometry. The forces between silica and R-alumina in electrolyte only were well described by the Derjaguin-Landau-Verwey-Overbeek theory at all separation distances. However, introduction of a solution of negatively charged PSS and mixtures of PSS and a positively charged surfactant, CTAB, at the point of zero charge of R-alumina, modified the interaction forces, introducing short-range steric interactions superimposed onto electrostatic interactions. Thus, the adsorption of strongly charged polyelectrolytes onto net neutral surfaces resulted in a flat conformation with few loops and tails. When PSS and CTAB were added sequentially, the interaction forces were further modified, resulting in weak electrostatic interactions and the presence of attractive van der Waals or bridging forces between the surfaces. The sign of the surfaces was altered from negative to positive in this case. Increasing the concentration of the added CTAB resulted in swelling of the adsorbed layer and an increase in the effective surface potential fitted to the data.
The Journal of Physical Chemistry B, 1998
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. S1089-5647(97)03216-1 CCC: $15.00
Langmuir, 2001
Silica surfaces were premodified by the saturated adsorption of the cationic polyelectrolyte of poly(2vinyl-1-methyl-pyridinium bromide), P2VP, in water. The interaction forces between and the zeta potential of the silica surfaces were then measured in water and in ethanol solutions of perfluorinated anionic surfactants as a function of their chain length and concentration using the AFM surface force and electrophoresis methods. In water, the electrostatic repulsive forces between P2VP-modified silica surfaces in CF3CF2COONa, CF3(CF2)6COONa, and CF3(CF2)7SO3Li solutions of 0.1 mM were identical to the force curve in 0.1 mM NaNO3 but greatly decreased in 0.1 mM CF3(CF2)9COOLi (critical micelle concentration (cmc), 0.39 mM). The concentration increase of CF3(CF2)7SO3Li (cmc, 6.3 mM) from 0.1 to 1.0 mM caused the repulsive force curves to weaken and then to strengthen after passing through a zero repulsive force. The surface potentials obtained by the best curve fitting of the force curves agreed well with the zeta potentials, which indicated a surface charge reversal from positive to negative for a high concentration of CF3(CF2)7SO3Li. These observations were explained by the formation of a Stern layer due to specific counterion binding of the surfactant anions, which increased with the surfactant chain length and concentration. In ethanol, CF3(CF2)7SO3Li always showed strong repulsive force curves, when CF3(CF2)7-SO3Li concentrations that were adjusted to give identical Debye lengths as those in water were used and the surface charge of P2VP-modified silica was the same as that in water. The surface potential obtained by the best curve fitting coincided with the zeta potential of positive sign, confirming no charge reversal. This suggested no obviously firm formation of a Stern layer by the surfactant ions. This was not always the case for shorter carbon-chain surfactants, since CF3(CF2)6COONa revealed a much weaker repulsive force curve than CF3(CF2)7SO3Li for concentrations of identical Debye lengths. This was explained in terms of an increased surfactant binding, due to the polarity difference between the solvent and surfactant molecules.
Polyelectrolyte-surfactant association at solid surfaces
Berichte der Bunsengesellschaft für physikalische Chemie, 1996
The interferometric surface force technique has been utilized for studying the interaction between negatively charged surfaces coated with a cationic polyelectrolyte across solutions of anionic surfactant, sodium dodecyl sulphate (SDS). The polyelectrolyte used was poly ([2-(propionyloxy)ethyl]trimethylammonium chloride), PCMA, which has one positive charge per segment. At low ionic strength the polyelectrolyte adsorbs in a flat conformation and neutralizes the negative mica surface charge. The interaction forces between the polyelectrolyte-coated surfaces are dominated by a strongly attractive force at distances shorter than about 150 A.
Adhesive forces between adsorbed anionic polyelectrolyte layers in high ionic strength solutions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004
Direct interaction forces between a hematite surface and a silica sphere in the presence of high-molecular weight anionic polyelectrolytes, sodium polyacrylate (NaPAA), an acrylamide/acrylate copolymer, an hydroxamate copolymer and starch have been measured using the atomic force microscope (AFM). In aqueous solution at high pH, the interaction between the bare oxide surfaces is well described by DLVO theory and is dominated by a repulsive electrostatic force. Addition of a high-molecular weight polyelectrolyte did not significantly alter the forces on approach. There was no sign of steric repulsion prior to the distance of closest approach. Therefore, it appears that these molecules are adsorbed to the surface in a flat conformation. On separation, the adhesive force between the surfaces was observed to change in magnitude as a function of polyelectrolyte type and concentration. Elastic minima that were found to extend to large surface separations were observed to occur on separation of the surfaces for all polyelectrolytes studied. At high-polyelectrolyte concentration, the interaction on both approach and separation of the surfaces was repulsive. Specific interaction of the functional groups with the metal ion of the oxide surface appears to be responsible for the differences in the adhesive force. Hydroxamate and starch molecules were found to produce the strongest and most extended adhesive forces.
Interactions between Two Polyelectrolyte Multilayers Investigated by the Surface Force Apparatus
Langmuir, 2004
The distance-dependent interaction between multilayers of alternating polycation (poly-L-lysine) and polyanion (poly-L-glutamic acid) deposited onto mica surfaces in aqueous solution is investigated with the surface force apparatus. At large separations, a long-range, weak attraction is observed. The interaction turns into repulsion as opposite multilayers overlap when the surface separation is reduced. The initially observed exponential force-distance law is ultimately overcome by a steep steric interaction at full compression of the films. The evolution of the force profiles as a function of time and upon subsequent unload-load sequences is monitored. The origin of the different interaction regimes arises from osmotic pressure and the formation of complexes between the oppositely charged chains.
Interfacial Properties of Aggregates Formed by Cationic Polyelectrolyte and Anionic Surfactant
Langmuir, 2000
Interactions between mica surfaces across aqueous solutions containing mixtures of a highly positively charged polyelectrolyte and an anionic surfactant were studied by use of a surface force apparatus. The investigation was carried out with a constant polyelectrolyte concentration (20 ppm) and a wide range of surfactant concentrations [0-1 times the critical micelle concentration (cmc)]. The chemical composition of the adsorbed polyelectrolyte-surfactant layers was analyzed by x-ray photoelectron spectroscopy (XPS). The properties of polyelectrolyte-surfactant aggregates formed in bulk were studied by measurements of turbidity and electrophoretic mobility. The aggregates formed at low surfactant concentrations (<0.04 times cmc) were positively charged, whereas at higher surfactant concentrations the aggregates carried a net negative charge. It was shown that polyelectrolyte-surfactant aggregates rapidly adsorb on negatively charged mica surfaces regardless of the sign of their charge. At surfactant concentrations up to 0.01 times cmc, the polyelectrolytes adsorb on mica surfaces with loops and tails stretching out into solution and repulsive steric forces are generated. The thickness of the layer decreases with time and we suggest that this conformational change is accompanied by some expulsion of surfactant from the adsorbed layers. Thick adsorbed layers were formed in the surfactant concentration range 0.02-0.1 times cmc. In this concentration regime the measurement of equilibrium forces was inaccessible due to a very slow layer relaxation. During compression the forces were repulsive and during separation an attraction developed. We attribute this to formation of interlayer surfactant bridges. Finally, at high surfactant concentrations (g0.4 times cmc) highly negatively charged aggregates adsorb on the surfaces in rather thin layers, resulting in purely repulsive forces of mixed electrostatic and steric origin.
Langmuir : the ACS journal of surfaces and colloids, 2005
Forces have been measured between silica surfaces with adsorbed surfactants by means of a bimorph surface force apparatus. The surfactants used are the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) and the nonionic surfactant hexakis(ethylene glycol) mono-n-tetradecyl ether (C(14)E(6)) as well as mixtures of these two surfactants. The measurements were made at elevated pH, and the effect of salt was studied. At high pH the glass surface is highly charged, which increases the adsorption of TTAB. Despite the low adsorption generally seen for nonionic surfactants on silica at high pH, addition of C(14)E(6) has a considerable effect on the surface forces between two glass surfaces in a TTAB solution. The barrier force is hardly affected, but the adhesion is reduced remarkably. Also, addition of salt decreases the adhesion, but increases the barrier force. In the presence of salt, addition of C(14)E(6) also increases the thickness of the adsorbed layer. The force barrier...
Langmuir, 1997
An atomic force microscope has been used to study the forces between a silica sphere in the colloidal size range and silica or mica flat surfaces as a function of distance of separation. At low ionic strength, independent electrokinetic measurements ( potentials) of both the spheres (by electrophoresis) and flat surfaces (by streaming potential) under the same conditions show excellent agreement with the diffuse double layer potentials derived from the force data using conventional DLVO theory. At higher ionic strength, the electrokinetically derived potentials were found to deviate from those derived from the fitted atomic force microscopy data, and a short range steric type repulsion was observed between the surfaces, the magnitude of which increased with decreasing pH.