Self-Assembly of Cations in Aqueous Solutions of Hydroxyl-Functionalized Ionic Liquids: Molecular Dynamics Studies

A Thermal Thickening System Based on the Self-Assembly of a Zwitterionic Hydrophobic Association Polymer and Surfactant

The zwitterionic monomer, 1-(2-hydroxypropyl-sulfo)-acrylamide ethyl-N,N-dimethyl ammonium chloride (MeSA) was copolymerised with acrylamide (AM), acrylic acid (AA), and a hydrophobic monomer N,N-diallyl oleamide (DNDA) to obtain the zwitterionic hydrophobic association polymer AM/AA/DNDA/MeSA. The structure of the hydrophobic association polymer was characterised by 1H NMR, FT-IR, and intrinsic viscosity studies. The self-assembly system of the polymer and the surfactant Tween-40 was then formed, and the rheological properties and adsorptive performance of the self-assembly system were investigated. The result showed that the polymer–surfactant self-assembly system had good properties such as thickening, temperature resistance, salt resistance, and shear resistance. It is shown that the thermal thickening phenomenon, which allows the system to be used as a good petrochemical product in a high-temperature environment, provides a vital research foundation for the future application of this kind of self-assembly system.

Aqueous solutions of hydroxyl-functionalized ionic liquids: Molecular dynamics studies

A series of aqueous solutions of 1-(n-hydroxyalkyl)-3-(n-hydroxyalkyl) imidazolium bromide ([HOC_nC_mOHIm][Br], with n and m = 2, 6,10 and 14) were studied by atomistic molecular dynamics simulations. Structural properties were characterized by the radial distribution functions between different pairs, angular distributions and aggregation numbers. Dynamics of the system has been investigated by computing the diffusion of the ions and molecules. Structures of the aggregates formed depend upon the length of the hydroxyalkyl chains. The long-distance spatial correlations observed in solutions with cations having long chain substituent are arising due to the formation of intercalated structures. A thin film like structure is formed in solutions having longer hydroxyalkyl chains, with the structure stabilized by the dispersion interactions between the interdigitated alkyl chains and the hydrogen bond formation between the hydroxyl group of a cation with head group of a different cation. Anions are dispersed near the surface of the film.

Molecular Dynamics Study of the Effect of Water on Hydrophilic and Hydrophobic Ionic Liquids

We performed molecular dynamics (MD) simulations of ionic liquid (IL)-water mixtures to investigate the effects of water addition. The IL cation 1-butyl-3-methylimidazolium ([C₄mim]) and the four anions, nitrate (NO₃), tetrafluoroborate (BF₄), hexafluorophosphate (PF₆), and bis(trifluoromethanesulfonyl)imide (NTf₂), were used to examine the effects of differences in hydrophobicity and anion size. The radial distribution functions of water-water have two different water content dependences. In NO₃ and BF₄ systems, the effect of water-anion-water structures connected by hydrogen bonds due to the strong interaction of anion-water is large. The growth of water clusters changes the peak heights of the radial distribution functions in PF₆ and NTf₂ systems. The increase in the diffusion constant is small in the NO₃ system but is not small in the other systems. The relaxation time of the anion-water hydrogen bonds in the NO₃ system is much longer than those in the other systems. It is the reason for the low water content dependency of the diffusion constants of the NO₃ system. The water constant dependences of structures in NO₃ and BF₄ systems are similar, but that in the diffusion constant is not. The BF₄ system shows hydrophilic features in the structural change and hydrophobic features in the water content dependences of the diffusion constant. The addition of water molecules provides various hydrophobicity/hydrophilicity of anions.