(222g) Probing the Structure and Aggregation Features of 1-N-alkyl-3-Methyl Imidazolium Octylsulfate Ionic Liquid Homologous Series Using Molecular Dynamics Simulations

Authors: 
Kapoor, U., Oklahoma State University
Shah, J. K., Oklahoma State University
Ionic liquids (ILs) are novel chemical substances composed entirely of ions and are attractive candidates for replacement of volatile organic compounds used in chemical industry. One of the widely research topics in the field of IL is their ability to absorb polar substances such as water, CO2 and SO2 owing to their ionic nature. At the same time, conventional ILs exhibit rather poor solubility for nonpolar substances such as alkanes commonly obtained from crude oil. One strategy, to enhance the solubility of nonpolar compounds, is to increase the nonpolar content, for example, by increasing the alkyl chain length, in either the cation or the anion. It has been established that such changes induce structural heterogeneities resulting in the formation of nanodomains composed of polar and nonpolar regions in which alkanes can be dissolved. It is believed that the origin of such molecular level segregation is due to the competition between the electrostatic interactions of the ionic moieties in ILs and short-range attractive interactions between the nonpolar regions. An increasing amount of research studies are being carried out by carefully selecting alkyl chain lengths either on cation or anion to tune the size and shape of these domains. In this study, mesoscopic segregation of ILs containing long alkyl chains on both the ions is probed with molecular dynamic simulations. The ionic liquids studied here belong to the 1-n-alkyl-3-methyl-Imidazolium [Cnmim] (n=1,2,4,6,8,10,12) family with octylsulfate [C8SO4] as the anion. The results of total static structure factors and radial distribution functions will be presented in an effort to interpret the morphology of polar and non-polar domains. Further, the nonpolar region will be characterized in terms of aggregate size and shape using domain analysis.