Thermodynamic Investigation of the Stability of Copolymer Grafted Bentonite Nanoclays in an High Salinity Electrolyte

Stability of clays is one of the most important characteristics of these colloidal systems and its degree can be determined by the balance of attractive and repulsive forces acting between the colloidal particles. In this work, the stability of grafted bentonite nanoclays by different copolymers including poly (1-vinyl pyrrolidone-co-styrene) (PVP), poly(methyl methacrylate -co-methacrylic acid) (PMMA) and poly (acrylamide-co-diallyl dimethyl ammonium chloride) (PDADMAC) in a high salinity polyelectrolyte solution containing partially hydrolyzed polyacrylamide (PHPA) was investigated. Adsorption of PHPA chains onto the modified bentonite-nanoclay surfaces, according to the Langmuir isotherm mechanism, led to the stabilization of the nanoclay particles in the polyelectrolyte medium. The thermodynamic parameters including enthalpy (ΔH), entropy (ΔS), free energy (ΔG) and adsorption constant (Kn) of the interactions of organic-organic-inorganic hybrids in the nano-clay suspensions were determined by Langmuir equation using a spectrophotometer analyzer. The stability and thermodynamic studies indicated that modified PVP-nanoclay had the longest stability among the un-modified and modified nanoclays in the prepared suspensions.

Keywords:

Thermodynamic , Polyelectrolyte , Modified-nanoclay , Enhanced oil recovery (EOR