Simple and fast fluorimetric determination of the critical gel concentration of soft nanomaterials.

Soft materials or gels are new interesting materials resulting from the combination of carbon nanotubes with ionic liquids. However, it should be noted that not all ionic liquid/carbon nanotubes combinations lead to the formation of gels. In fact, this requires using an optimum concentration of CNTs known as "critical gel concentration" (CGC) in the mixture. Up to now, this critical concentration has been determined by means of rheological measurements or by observing a change of a physical property in the new material such as density. On the basis of the high stability of gels in solvents, owing to the presence of carbon nanotubes, this paper reports for the first time a simple and fast method to determine the critical gel concentration for the formation of soft materials by means of fluorescence measurements. We have determined the critical gel concentration of four gels obtained by the combination of three different types of multi walled carbon nanotubes and one single walled carbon nanotubes with the ionic liquid 1-hexyl 3-methylimidazolium hexafluorophosphate. The main characteristics of carbon nanotubes and gels resulting of them were established by Raman spectroscopy. The proposed methodology is presented as an alternative to traditional complex rheological measurements.