Structure study of self-assemblies with ionic liquid

Abstract

Self-assemblies were made with an Ionic Liquid (IL), 1-tetradecyl-3-methylimidazolium chloride ($[C_{14}MIM]Cl$). Crystal structure was formed in alkane solvents by addition of octanol. Crystals grew 1-dimensional rod shape. The growing rate is 7.0 $\pm$ $1.4 day^{-1}$. Crystal growth was maximized in the octane solvent by matching alkyl chain length. Though the length was matched, formation of crystal was failed in an irregular shape solvent, 2-methyloctane. For further analysis, we experimented by varying the $[C_{14}MIM]Cl$ /octanol ratio. And we characterized the crystal structure by indexing the X-Ray Diffraction (XRD). One lattice parameter, $25 {AA}$, consists with the length of $[C_{14}MIM]Cl$. It is interpreted the interdigitated chains between adjacent layers. The lattice parameter to the normal direction of imidazolium ring plane was increased $4 {AA}$ against the one of $[C_{14}MIM]Cl$ powder. It is explained with the interspaced octanol molecule. When we increase amount of water, crystal wasn’t formed. In specific water amount, clear solution was found. The solution was optically transparent and thermodynamically stable during several months. We used Small Angle Neutron Scattering (SANS) technique to investigate the structure of the solution. By fitting data with a Guinier plot in the low q region, the radius of gyration of a microemulsion droplet is $20 {AA}$. In the high q region, scattering intensity falls off slowly than that of sphere. Since the solution is expected to be a w/o (water in oil) microemulsion, scattering intensity can be analyzed by fitting with core-shell model. We have estimated the composition of the core and shell of a microemulsion droplet by measuring the value of Scattering Length Density (SLD) by a contrast matching method to reduce the number of fitting parameters. We discussed the SANS data with the core-shell model of three shapes: sphere, oblate and prolate. SANS intensity was also analyzed with different division of the interior droplet. In prolate case, the exterior size and shape resulted is independent of the way how to divide the interior of microemulsion droplet. We did additional SANS experiments in terms of water. An aspect of microemulsion with change of the water amount is reported. And we tried to match contrast between core and shell by combination of $D_2O$ and $H_2O$.