Ionic liquid gels and antioxidant carbon nanotubes: Hybrid soft materials with improved radical scavenging activity

Hypothesis: Performances of materials are frequently affected by the action of radicals that can induce their degradation. To overcome the above issue, natural antioxidants (AOs) can be added during manufacturing. Considering the high instability of AOs, they have been adsorbed on carbon nanomaterials surface. However, the inclusion of functionalized carbon nanomaterials into gel matrix could enhance the antioxidant efficiency and represent an easy way to disperse and handle the active species. Experiments: Carboxypropyl functionalized carbon nanotubes (f-CNT), pure or with physically adsorbed a-tocopherol (f-CNT-VE) and quercetin (f-CNT-Q), were incorporated in some ionic liquid gels (ILGs) formed by 1,3-didodecylimidazolium-based salts. Temperature of gel-sol transition, morphology, response to external stimuli and rheology of hybrid ILGs (HILGs) were investigated before their use as radical scavengers. To this purpose a free radical test was performed on gels. Findings: The properties of HILGs significantly differ from the ones of pure ILGs, as CNTs appreciably improved gel rheological response. Besides, the gel network is able to enhance radical scavenging activity of both natural AOs and f-CNTs, achieving a complete radical reduction in less than 1 h. Furthermore, the activity is also preserved in thin films obtained from HILGs, opening the way to the application of these systems as material coatings.