Adsorption behavior of isotactic Poly(acrylic acid) (i-PAA) and isotactic Poly(methacrylic acid) (i-PMA) at CCL4-H2O interface was studied by all-atom molecular dynamics simulations with varying charge density f and concentration of the polyelectrolyte. i-PAA as well as i-PMA chains exist a planar extended conformation at the interface shows a different from its coiled conformation in bulk water. Orientation distribution of carbonyl and hydroxyl groups show characteristic aspects specific to these groups. Adsorption occurs only for low values of degree of ionization (f &lt; 0.2) in agreement with experimental observations. Uncharged i-PAA and i-PMA, and charged i-PMA chains undergo structural change from extended planar conformation to random coiled conformation with increase in interface concentration. This conformational change is reflected in torsion angle distribution of backbone dihedrals and orientation distribution side groups. The preferential orientation of backbone and side groups disappear with increase in interface concentration. The morphological properties of adsorbed film such as film thickness and interface coverage were calculated. i-PMA exists in an extended and ordered conformation at interface as compared to the random coil conformation in bulk water. The analysis of the distributions of orientation of carbonyl, methyl, hydroxyl groups with respect to the interface-normal, showed characteristic orientations for f = 0, which disappear at higher f . Although such conformational changes are expected from interpretation of pressure-area isotherms, MD simulations add strength to these arguments along with providing additional molecular level information. Interface pressure-area isotherms obtained from out simulations were compared with limited available experimental data in literature for PMA at low pH. The structural changes associated with increase in interface concentration are reflected in conformational properties. 90% of COOH groups are involved in the formation of a single H-bond between hydrogen of O-H group and water and 50-60% of these groups also form H-bond with oxygen of the C=O groups. Along with the detailed structural analysis, the solvation behavior of COOH groups in water as characterized by hydrogen bonding interactions will be presented.

Effect of polymer charge and interface concentration on structure of isotactic poly(acrylic acid) PAA and isotactic poly(methacrylic acid) PMA at oil-water interface

2019 Fall National Meeting

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