We present the first computational (molecular level) study of aggregation in a chemically real polymer-non-ionic surfactant-water system. Previous related studies have looked at surfactant self-assembly in aqueous solution. Atomistic MD simulations were carried out to study intermolecular strucutre and thermodynamics of solvation in an aqueous solution containing C8E5 and C10E8 separately with uncharged poly(acrylic acid) PAA.The concentration of surfactant (Cs) was varied in the range 0.01–0.3 M (dilute to concentrated) while polymer concentration (Cp) was kept in the dilute condition (i.e. Cp= 0.01 M). The binary (surfactant, water) and ternary (polymer, surfactant, water) systems show random non-unifom (RNU) micellar-like aggregates at low Cs and lamellar aggregates at high Cs. The transition from RNU micelle phase to lamellar phase in the ternary system occurs at lower Cs for C10E8 as compared to C8E5, whereas this transition in the binary systems occurs at lower Cs for C8E5 than C10E8. The interaction and binding between PAA and surfactants takes place at low Cs suggesting strong intermolecular interaction, in agreement with experimental data [1]. For lamellar aggregates the adsorption of PAA chain on to the aggregate shows favorable interaction between -COOH groups of PAA and -C-O- groups of the surfactant. PAA absorbs as a coiled chain at low Cs (RNU micelle) and as a stretched chain at high Cs (lamellar phase). In the C10E8 binary systems micelles form at lower values of Cs indicating a decrease in CMC with increase in hydrophobic tail length, in good agreement with experimental data. Symmetric lamellar aggregates are formed in the C8E5 system at higher Cs and are absent in the C10E8 system. The RNU micelles formed in both surfactant systems were approximately spherical. SASA of the aggregates was high in binary systems as compared to the respective ternary systems, for both surfactants, which indicates polymer chain absorbed on the surface of the aggregate instead of penetrating the hydrophobic core. These results were analyzed using radial distribution functions (RDF). Solvation enthalpy of binary and ternary systems becomes more exothermic with increase in Cs indicating a strong favorable interaction between surfactant and polymer. Detailed analysis of hydrogen bonding and atom density profiles was carried out and results will be presented.

Structure and dynamics of aqueous solutions containing poly-(acrylic acid) and non-ionic surfactant: A comparative study between pentaethylene glycol n-octyl ether (C8E5) and octaethylene glycol n-decyl ether (C10E8)

256th National Meeting (2018)

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