Mechanical spectroscopy study of ionic liquids with quaternary cations: Effect of conformational flexibility

Understanding the effects of targeted modifications on the 1 : 2 Choline And GEranate structure

“…It should be noted here that the stress applied by this method is not a pure shear stress; instead, the mechanical modulus presently measured is a combination of both the shear and the bulk modulus. [32][33][34][35]…”

“…Dynamic mechanical analysis (DMA) is a technique used to study the thermomechanical properties of different kinds of systems. 32,33,[50][51][52] In particular, it has been successfully used for ILs [32][33][34][35]52 since it allows the measurement of their mechanical modulus and its variation during phase transitions, in both the liquid and the solid states.…”

Dynamics in Quaternary Ionic Liquids with Non-Flexible Anions: Insights from Mechanical Spectroscopy

“…The influence aggregates have on ion dynamics has also been reported by recent Dynamical Mechanical Analysis (DMA) measurements on several ILs composed of quaternary cations and two anions with different conformational flexibility [ 12 ]. These measurements showed the presence of a relaxation process in the liquid phase of the ILs with the flexible [NTf 2 ] − anion, which was related to the ion hopping between non-equivalent configurations; on the contrary, for other ILs with rigid ions, a fast dynamic at the local level in the liquid phase was rarely observed because a partial transition to a solid state is favored.…”

“…In particular, the conformational flexibility of anions is a key parameter to obtain lower values for viscosities and thermal transition temperatures and, at the same time, faster transport properties. Moreover, anion conformational flexibility is involved in the dynamics occurring within the ILs, and it has also been hypothesized that anion conformational relaxation correlates with translational diffusion [ 9 , 10 , 11 , 12 ].…”

“…These measurements showed the presence of a relaxation process in the liquid phase of the ILs with the flexible [NTf 2 ] − anion, which was related to the ion hopping between non-equivalent configurations; on the contrary, for other ILs with rigid ions, a fast dynamic at the local level in the liquid phase was rarely observed because a partial transition to a solid state is favored. Indeed, tetraalkylphosphonium cations give rise to ionic interactions between the oppositely charged ions, which can induce strong structural correlations, thus promoting the occurrence of nanoscale structural heterogeneities [ 12 , 28 ]. The presence of these aggregates, for which the organization can result in domain formation, hinders the observation of any relaxation in the liquid state and assists the occurrence of at least partial solidification [ 12 , 29 ].…”