Adsorption Kinetics of Cationic Polyelectrolytes Studied with Stagnation Point Adsorption Reflectometry and Quartz Crystal Microgravimetry

Abstract

The effects of charge density, pH, and salt concentration on polyelectrolyte adsorption onto the oxidized surface of silicon wafers were studied using stagnation point adsorption reflectometry and quartz crystal microgravimetry. Five different polyelectrolytescationic polyacrylamides of four charge densities and one cationic dextranwere examined. The adsorption kinetics was characterized using each technique, and the adsorption kinetics observed was in line with the impinging jet theory and the theory for one-dimensional diffusion, respectively. The polyelectrolyte adsorption increased with pH as an effect of the increased silica surface charge. A maximum in the saturation adsorption for both types of polyelectrolytes was found at 10 mM NaCl concentration. A significant adsorption also occurred at 1 M NaCl, which indicated a significant nonionic contribution to the adsorption mechanism. The fraction of solvent in the adsorbed layer was determined to be 70-80% by combining the two analysis techniques. This indicated a loose structure of the adsorbed layer and an extended conformation at the surface, favoring loops and tails. However, considering the solution structure with a hydrodynamic diameter larger than 100 nm for the CPAM and a thickness of the adsorbed layer on the order of 10 nm, the results showed that the adsorption is accompanied by a drastic change in polymer conformation. Furthermore, this conformation change takes place on a time scale far shorter than seconds.

Using jet mixing to prepare polyelectrolyte complexes: Complex properties and their interaction with silicon oxide surfaces

“…However, the dissipation signal is lower than would be expected with other systems, for example, the adsorption of a polyelectrolyte monolayer [18,27]. As previously mentioned, low dissipation is an indication of a rigid film, tightly adsorbed to the surface of the substrate.…”

“…Fig. 7 shows that dissipation increased as pH increased; it must be stressed, however, that these dissipation values are still very low compared, for example, with the corresponding values for high-molecular-weight polyacrylamides adsorbed to silicon oxide surfaces [18].…”

“…The adsorption of cationic complexes to silicon oxide substrates stops at a low level, compared with the adsorption of free polyelectrolytes such as PAH [21] or cationic polyacrylamide [18].…”

Polyelectrolyte Adsorption on Solid Surfaces: Theoretical Predictions and Experimental Measurements

“…The practical relevance of polyion adsorption has generated substantial theoretical [6][7][8][9][10][11][12][13][14][15][16][17][18][19] and experimental 6,16,[20][21][22][23][24][25][26][27][28][29][30][31][32] efforts. As mentioned above, surface interactions in polyelectrolyte solutions can often be regulated by increasing or decreasing the addition of simple salt.…”

Effect of cationic polyacrylamide on the processing and properties of nanocellulose films

“…If the MFC specific surface area is 35 m 2 /g, then the maximum CPAM surface coverage is 0.22 mg/m 2 and 0.14 mg/m 2 for the CPAM of 10% and 50% charge density, respectively. CPAM of charge density ranging from 1.25meq/g to 2.75meq/g are reported to adsorb from 0 to 0.5 mg/m 2 on silica [37]. In general, polyelectrolyte adsorb from 0.1 to 2 mg/m 2 [38].…”