Adsorption of polyacrylamide on gold and iron from acidic aqueous solutions

✍ Scribed by T. Grchev; M. Cvetkovska; T. Stafilov; J.W. Schultze

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 845 KB
• Volume: 36
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(91)80011-v

✦ Synopsis

The adsorption behaviour of polyacrylamide (PAA) on gold, and mild steel from sulphuric and hydrochloridic acid was studied using cyclic voltammetry with simultaneous monitoring of the double layer capacity. Adsorption isotherms, obtained by capacity measurements (using the two-condenser model), and corresponding thermodynamic parameters of the adsorption processes strongly depend upon the molecular mass of the polymer, electrode potential and temperature. In all cases the experimentally-obtained results show the best fit with Frumkin's isotherm (Langmuir and Flory-Huggins isotherms were tested as well).

It was found that nearly complete coverage (fl = 1) can be reached at extremely low polymer concentrations in the solution (lO-8-lO-7 m) which can be explained by a significant participation of the directly attached segments of the polymer molecules (trains) at the metallic surface and weak lateral interactions. This conclusion was proved by comparison of the polymer adsorption with the adsorption behaviour of the monomer itself.

Capacity measurements predict flat orientation of the polymer molecules at the metal/solution interface with an average thickness of the adsorbed layer of about 0.8 nm.

Thermodynamic parameters of the polymer adsorption on gold, at low anodic potentials, are comparable with those obtained from corrosion measurements on iron and mild steel. At high anodic potentials adsorption of PAA on gold is an endothermic process which can be explained by a substitutional adsorption (Polym,,, + xH,O,, = Polym,, + xH,O& and conformation changes of the adsorbed polymer molecule. Thus, the calculated values of AHI$, and ASL, correspond to the whole process; adsorption of polymer molecules and desorption of x-water molecules per polymer molecule.