Polymers in inorganic scale control: Molecular dynamics study of edge-active polymers

Abstract

Scale formation from aqueous solution is a significant problem in many industrial processes, impairing efficiency and necessitating costly shut-downs in processes as diverse as sugar milling and seawater desalination. For many years low molecular-weight polyelectrolytes have been used to inhibit scale formation in aqueous solution. Experimental work in our group on poly(acrylic acid) scale inhibitors of known molecular weight and end-group functionality has shown that the extent of inhibition of bulk crystallization by poly(acrylic acid) can be increased by incorporating end-groups of moderate hydrophobicity. We have found dramatic effects on inhibition time, crystal morphology and speciation, and the balance between heterogeneous and homogeneous nucleation. <br/> Under conditions where different charge densities are exhibited by different crystal surfaces, we have hypothesized that polymers with structure encouraging them to be ‘edge-active’ are most effective in inhibiting scale formation. This presentation will survey the molecular dynamics modelling we utilize to determine the specificity of polymer adsorption/desorption behavior onto crystal faces under the same conditions employed experimentally. By first quantifying the charge distribution at the junction of crystal faces exposed to solvent in the presence of various ion ratios and concentrations, then modelling the statistically favoured positioning of polymers in relation to the surface and edges of these crystal faces, we aim to develop a quantitative model to explain experimental results in terms of disproportionately selective adsorption behavior by edge-active polymers.