Effect of alkyl Chain of room temperature ionic liquid (RTILs) on the phase behavior of [C2mim][CnSO4]/TX-100/cyclohexane microemulsions: Solvent and rotational relaxation study

Surajit Ghosh, Chiranjib Banerjee, Sarthak Mandal, Vishal Govind Rao, Nilmoni Sarkar

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Abstract

In this investigation, we present microemulsions comprising a nonionic surfactant, Triton X-100 (TX-100), cyclohexane as nonpolar phase, and room temperature ionic liquids (RTILs) as a polar medium. To investigate the effect of alkyl chain length of ionic liquid on the physicochemical properties of microemulsions, we have used 1-ethyl-3-methylimidazolium n-butyl sulfate [C 2mim][C4SO4], 1-ethyl-3-methylimidazolium n-hexyl sulfate [C2mim][C6SO4], and 1-ethyl-3-methylimidazolium n-octyl sulfate [C2mim][C 8SO4] as polar media. The phase behavior of these ternary systems is investigated by direct observation of transition from clear transparent solution to turbid solution by using UV-vis spectrophotometer at 298 K. The single-phase region is found to increase with increase in chain length of RTIL anion. Dynamic light scattering (DLS) measurements revealed the formation of highly stable nano-sized RTIL-containing microemulsions. The size of the microemulsions increases with the addition of ionic liquid. The maximum increase in size is observed with the addition of [C2mim][C 4SO4]. It is proposed that the long octyl chain of octyl sulfate allows the anion to align itself along the TX-100 molecules which increases the rigidity of microemulsions, whereas in case of [C 2mim][C4SO4], the short butyl chain is apparently unable to do the same. The dynamics of solvent and rotational relaxation of coumarin 480 (C-480) has also been investigated in these ionic liquid containing microemulsions ([C2mim][C4SO 4]/TX-100/cyclohexane, [C2mim][C6SO 4]/TX-100/cyclohexane, and [C2mim][C8SO 4]/TX-100/cyclohexane) using picosecond time-resolved fluorescence spectroscopy. In RTIL microemulsions, solvent relaxation becomes retarded compared to neat RTIL. We have also shown that with increasing R value, the solvation dynamics becomes faster and the decrease in average solvation time is more pronounced in [C2mim][C4SO4]/TX-100/ cyclohexane compared to [C2mim][C6SO4]/TX-100/ cyclohexane and [C2mim][C8SO4]/TX-100/ cyclohexane microemulsions.

Original languageEnglish (US)
Pages (from-to)5886-5897
Number of pages12
JournalJournal of Physical Chemistry B
Volume117
Issue number19
DOIs
StatePublished - May 16 2013

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