Thermoreversible viscoelastic to weak gel transition in a micellar ionic liquid with salt

Rheological measurements as a function of temperature have been carried out on a micellar-ionic liquid (4.45 wt% sodium dodecylsulfate (SOS) in 1-butyl-3-methylimidazolium chloride (BmimCl)) with 18.7 wt% lithium chloride (LiCl). We report here for the first time, the formation of a "weak gel" state at high temperatures (>80 degrees C) based on elastic and loss moduli behavior and yield stress measurements. Below 80 degrees C. the sample is identified to be in a viscoelastic liquid state. The transition from viscoelastic liquid to weak gel state is found to be thermoreversible. From the theological evolutions, small angle neutron scattering measurements and turbidity measurements, we argue that the weak gel state arises due to the winning of the micellar network structures over the association structure of BmimCl in the presence of lithium chloride and is responsible for the viscoelastic liquid to weak gel transformation observed in the micellar-ionic liquid. (C) 2012 Elsevier B.V. All rights reserved.