Interactions between a 30 Charged Polyelectrolyte and an Anionic Surfactant in Bulk and at a Solid−Liquid Interface

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.

Static and Dynamic Forces between Adsorbed Polyelectrolyte Layers (Quaternized Poly-4-vinylpyridine)

“…Regarding the first point, it is known that the amount of adsorbed polyelectrolyte at low electrolyte concentration decreases with increasing charge density. 25, 44 Comparison of SFA studies of 1%, 14 10%, 13 and 30% 16 charged copolymer systems shows that the compressed film thickness (hard-wall) decreased from about 75 Å to 40 Å (for polyelectrolyte concentrations in the range 0.05 mg mL -1 to 0.2 mg mL -1 ), and for the corresponding fully charged polyelectrolytes 9,10,39 the hard-wall was found at a film thickness of only 10 Å (at concentrations from 9 0.01 mg mL -1 to 10 0.1 mg mL -1 ). In a study of 76% quaternized poly-2-vinylpyridine (concentration 0.1 mg mL -1 ), 20 a hard-wall separation of 23 Å was found at low pH, where also the nonquaternized segments are charged, as compared to 33 Å at high pH.…”

Coadsorption of Sodium Dodecyl Sulfate and a Polyanion onto Poly(ethylenimine) in Multilayered Thin Films

“…Van a 1:1 charge neutralization, precipitation of the PEI-SDS complex is often observed. 17,18 At SDS concentrations much greater than the critical micelle concentration (cmc), resolubilization in water occurs and is attributed to the interaction of micellar SDS with the complex. 16 Although cooperative hydrophobic interactions between neighboring alkyl chains on SDS may occur, PEI-SDS complexation is largely driven by electrostatic interactions.…”

Desorption of Low-Charge-Density Polyelectrolyte Adlayers in Aqueous Sodium n-Dodecyl Sulfate Solution

“…The first situation arises when both components (polymer and surfactant) are present in the bulk solution. In this case the main interest is to elucidate the surfactant effect on the adsorption process (concurrent adsorption) (19,(22)(23)(24)(25)(26). These systems have also become important in, for example, the construction of elaborate nanostructures comprising multiple associating molecules (27).…”