Interactions between Adsorbed Layers of a Low Charge Density Cationic Polyelectrolyte on Mica in the Absence and Presence of Anionic Surfactant

✍ Scribed by U.R.Mikael Kjellin; Per M. Claesson; Roland Audebert

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 166 KB
• Volume: 190
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1997.4906

✦ Synopsis

changing the surface properties of colloids, such as surface Interactions between two negatively charged mica surfaces charge or wettability, and/or to modify the rheology of soluacross aqueous solutions containing various amounts of a 10% tions. In particular, cationic polyelectrolytes are used in the charged cationic polyelectrolyte have been studied. It is found that industry because of their ability to interact with and condithe mica surface charge is neutralized when the polyelectrolyte is tion negatively charged surfaces. The effect of the polyelecadsorbed from a 10-50 ppm aqueous solution. Consequently no trolyte depends on many variables such as polyelectrolyte electrostatic double-layer force is observed. Instead an attractive charge density, flexibility and molecular weight, surface force acts between the surfaces in the distance regime 250-100 A ˚. charge density, and the ionic strength of the solution.

We suggest that this attraction is caused by bridging. Additional

Polyelectrolyte adsorption has been studied in several inadsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion devel-vestigations, both theoretical and experimental. Adsorption ops. This repulsive force is both of electrostatic and steric origin. measurements of various cationic polyelectrolytes on silica The polyelectrolyte layer adsorbed from a 50 ppm solution does and Na-montmorillonite particles have demonstrated that the not desorb when the polyelectrolyte solution is replaced with an adsorbed amount at the plateau level increases when the aqueous polyelectrolyte-free solution. Injection of sodium dodecyl charge density of the polyelectrolyte decreases (2, 3). An sulfate (SDS) into the measuring chamber to a concentration of important reason for this is that for lower polyelectrolyte about 0.01 CMC (8.3 1 10 05 M) does not affect the adsorbed layers charge densities a larger mass of polyelectrolytes is needed or the interaction forces. However, when the SDS concentration is to neutralize the particle charge. However, at very low catincreased to 0.02 CMC (0.166 mM) the adsorbed layer expands ionicities the adsorbed amount may decrease again due to a dramatically due to adsorption of SDS to the polyelectrolyte reduced affinity between the polyelectrolyte and the surface chains. The sudden swelling suggests a cooperative adsorption of (2, 3). It has also been shown that silica and clay suspen-SDS to the preadsorbed polyelectrolyte layer and that the critical sions are most efficiently flocculated by polyelectrolytes aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the when the zeta-potential is close to zero (3-5). Less efficient polyelectrolyte in solution upon addition of SDS was also examflocculation is obtained at lower polyelectrolyte concentrained. It was found that 0.16-0.32 mol SDS/mol charged segments tions (negative zeta-potential) and higher polyelectrolyte on the polyelectrolyte is enough to make the solution slightly turconcentrations (positive zeta-potential). Results from theobid. ᭧ 1997 Academic Press retical investigations based on lattice mean field calculations Key Words: polyelectrolyte-surfactant association; surface (6-8) are consistent with the results mentioned above. They forces; polyelectrolyte adsorption. also show that the number and length of tails and loops increase as the linear charge density of the polyelectrolyte decreases (6). In addition, as long as electrostatic forces