Formulation of pyridinium based RTIL-in-cyclohexane microemulsions: Investigations on size, conductivity and molecular interactions

• Published in: Journal of molecular liquids 2016-06, Vol.218, p.586-594
• Main Authors: Bharatiya, B., Hassan, P.A., Sastry, N.V.
• Format: Article
• Language: English
• Subjects: DLS; Hydrogen bonding; Microemulsion; Percolation; RTIL
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2016.03.013

Room-temperature ionic liquids (RTILs) based on alkyl pyridinium (py) and alkyl picolinium (pic) based structure are synthesized in combination with tetrafluoroborate (BF4−) anion [CnH2n+1py/pic][BF4], and further dispersed in cyclohexane using Triton X-100 (nonionic surfactant) as the emulsifier. The phase boundaries of the ternary system RTIL/TX-100/cyclohexane are investigated and microstructures in different regions of the phase diagram are identified by electrical conductivity measurements. At the onset corresponding to formation of RTIL-in-cyclohexane microemulsions, the required weight fraction of cyclohexane is higher for octyl substituted cations compared to their butyl counterpart. The electrical conductivity of the formed microemulsion increases gradually with a corresponding increase in temperature. Microemulsion of RTILs bearing butyl chain showed higher electrical conductivity compared to octyl substituted structures. The size and size distribution of the droplets in microemulsion were measured by dynamic light scattering (DLS), which revealed gradual increase in the droplet size with a corresponding increase in the RTIL/TX-100 mole ratio (R). The FTIR measurements confirmed strong H-bond formation between the pyridine hydrogen and oxyethylene (OE) groups in TX-100, which provides structural stability to the formed microemulsion. [Display omitted] •Pyridinium (py) and picolinium (pic) based RTIL-in-cyclohexane microemulsion are synthesized using TX-100 as stabilizer.•The size of formed RTIL droplet in cyclohexane is higher for pic based RTILs compared to py based cation structures.•Size of RTIL-in-cyclohexane emulsion droplet increases linearly with corresponding increase in RTIL/TX-100 mole ratio (R).•H-bonding between py ring hydrogen and OE unit in TX-100 provides structural stability to RTIL nano droplets in cyclohexane.•Low toxic pyridinium based cation structure is expected to undergo faster degradation in presence of octyl substitution.