Liquid mixtures of polymers and surfactants are complex molecular systems, from the viewpoint of physical chemistry and molecular physics. Such solutions have tremendous importance in various applications as paints, cosmetics, detergents, pharmaceuticals, in enhanced oil recovery, emulsion stabilization and flocculation among others. The current understanding of the role of molecular interactions in liquid dispersions consisting of polymers and surfactants, especially in non-ionic solutions, is limited. The focus of this thesis is on intermolecular interactions and their role in determining structure and molecular thermodynamics of polymer-surfactant complexes as well as interacting aggregates of surfactants. We have studied non-ionic as well as ionic systems involving weak poly-acid poly(acrylic acid) PAA with non-ionic as well as ionic surfactants in aqueous solution. All-atom (Atomistic) MD simulations in explicit solvent were carried out for aqueous solution consisting of poly(acrylic acid) PAA and various non-ionic surfactants of the Cn(E)m type, C8E5, C12E6 and C10E8, across a wide range of surfactant concentration and aggregation numbers of surfactant micelles. Spherical micelles and polymer-surfactants are formed at low concentration while lamellar aggregates are formed at higher concentration. The formation of lamellar aggregates in such systems and the critical transition from spherical to lamellar micelle regimes, T1 , were captured for the first time by a computational study. In PAA-C10E8-water ternary solution a new conformational transition of the polymer adsorbed on the micelle is identified that occurs at the aggregation number commensurate with the transition from spherical micelle to anisotropic lamellar aggregate. Solvation enthalpy values indicate strong favorable interaction between surfactant and water in the concentration range investigated, with the attractive interactions being more favorable in ternary solution as compared to binary. The formation of lamellar aggregates is favored over spherical micelles at higher aggregation numbers. The ability of surfactant molecules to aggregate increases with tail length of the surfactant in agreement with experimental results. An increase in the HLB number of the surfactant results in a decrease in solvation enthalpy and increase in the number of hydrogen bonds between PAA and nonionic surfactant. The ionic system Na+-PAA-DTAB (anionic-cationic) in water was studied under the condition of strong electrostatics and fully ionized condition. Strong electrostatic interactions between carboxylate ions of PAA chain and quaternary ammonium ion head groups of surfactant favor adsorption and conformational structure of PAA on the micelle surface. The size and sphericity of the micelles increases with the aggregation number of micelle. In order to develop new models for study of high molecular weight polymers in solution, we have investigated the capability of well-known implicit-solvent models that have been utilized for biomolecular systems such as proteins and polypeptides, to the prediction of conformational and thermodynamic properties of synthetic polar polymers in water for the first time. Investigation of conformation of higher molecular weight polymers (M = 106 Da and above) in very dilute solution using explicit solvent or coarse-grained solvent simulations is computationally intensive and beyond the scope of present day computational resources. A recently refined GB model was adapted to study chain dimensions and solvation free-energy of uncharged polar polymer chains (DP or N = 20 to 500) of different polarity and stereo-chemistry in aqueous solution. The scaling of aRgn with N obtained from our simulations are in good agreement with results of fully-atomistic simulations in a limited range of molecular weights as well as well-established scaling in good solvents from experiments and theory in literature for high molecular weight. The solvation free-energy values indicate that PAA is more hydrophilic and more soluble in water as compared to PMA as would be qualitatively expected. Such models would be useful for simulating mixtures consisting of high molecular weight polymers and surfactants in solution.​