The spreading of surfactant on substrates with higher surface tension is practically important such as in painting and printing. Ionic liquids (ILs) are organic electrolytes that are liquids at room temperature. From the viewpoint of interfacial chemistry, almost all ionic liquids, especially those with long hydrocarbon chains, have amphiphilic structures. Thus, like surfactants, they modify the surface tension of water when they are adsorbed on an air/water interface. In this study, we investigated spreading of three imidazolium-based ILs with different alkyl chain length: 1-buthyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), on a thick aqueous substrate (thickness: 5 mm). Because of the presence of the hydrophobic anion [PF6]-, [BMIM][PF6] is water insoluble, and [HMIM][PF6] and [OMIM][PF6] are water immiscible. The spreading was observed by depositing of a droplet of each IL on the aqueous surface where mica powder was sprinkled.The spreading advanced in a circle whose radius increased with time as At-a. The exponent a was ~0.5 and tended to decrease with alkyl chain length. While, the prefactor A increased with increase in alkyl chain length or with decrease in the surface tension of the IL. As the spreading progressed, the periphery of the spreading area became instable and had an unevenness. The instability increased with time. In the IL with longer alkyl chain, the unevenness was more regular and had a shape of gear. The number of the tooth of the gear tended to decrease with time and increase with increase in alkyl chain length. The spreading instability is explained in mathematical analogy to radial fingering in Hele-Shaw cells1 by taking spreading kinetics of liquids on thick liquid layers2into consideration.1. Peterson, L. J. Fluid Mech. 1981 , 113, 513.2. Joos, P.; Pintens, J. J. Colloid Interface Sci. 1977  , 60, 507.

Spreading of ionic liquids on aqueous surface

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.