Characterization of the adsorption of high molecular weight non-ionic and cationic polyacrylamide on glass from aqueous solutions using modified atomic force microscopy

High molecular weight, anionic, non-ionic and cationic polyacrylamide are used extensively in the oil industry in applications such as drilling, water shut-off, and enhanced oil recovery. They are also used as flocculants in water treatment processes. This study presents AFM measurements of the adsorption of high molecular weight, MW, non-ionic and cationic polyacrylamide from aqueous solvents on glass. The adsorption of the non-ionic polyacrylamide from 0.01 M NaCl solvent on glass was found to be weak and it took more than three days to attain full-surface coverage. In spite of the very high MW, weak adsorption and slow kinetics; the adsorbed layer thickness indicated a flat conformation of the adsorbed macromolecules, suggesting a low level of adsorption. The increase of the salt content of the solvent to 0.34 M NaCl resulted in faster kinetics and thinner layers, mainly due to the screening of the electrical double layer on the negatively charged glass surface. The adsorption of cationic polyacrylamide from both solvents was almost instantaneous due to the strong electrostatic attraction between the positively charged polymer and the negatively charged glass surface. Despite this strong attraction coupled with the MW being one third of the non-ionic polyacrylamide, the adsorbed layer thickness of the cationic polymer from both solvents were more than those formed using the non-ionic polymer. The increase in the salt content in the case of the cationic polyacrylamide adsorption on glass resulted in thicker adsorbed layer due to the charges of both the polymer and the surface being screened and hence more extended tails and loops of the adsorbed polymer molecules.