Deeply supercooled aqueous LiCl solution studied by frequency-resolved shear rheology

Abstract

To characterize the structural relaxation of an aqueous solution of LiCl, frequency-dependent shear rheological experiments are carried out near its glass transition. Analyzed within the fluidity representation, the generic spectral shape that was previously found for a range of different kinds of glass formers is confirmed for the currently studied hydrogen-bonded fluid as well. Furthermore, the validity of the rheological equivalent of the Barton-Nakajima-Namikawa relation is demonstrated for the aqueous LiCl solution. Its mechanical response is compared with that obtained using dielectric spectroscopy, a technique which is sensitive to both the reorientational dynamics of the water molecules and the translational dynamics of the ionic species. The extent to which these electrical polarization processes are coupled to those governing the viscoelastic response is discussed, also in comparison with the behavior of other ion conducting liquids.

Translational and reorientational dynamics in deep eutectic solvents

“…13, it was shown that the dielectric response of ethaline cannot be fitted by the RBM alone, 46 while for several other glass formers, this approach was found to be applicable. 55 As discussed in Sec. I, the RBM was not conceived to describe spectra FIG.…”

“…We ascribe these to spurious contributions in J ′ (ν) due to the low-torque limitations of the rheometer. 48,49,55,61 To a lesser extent, they also affect the glyceline spectra [cf. the two highest temperatures in Fig.…”

“…12 it was shown that the dielectric response of ethaline cannot be fitted by the RBM alone, 37 while for several other glass formers this approach was found applicable. 46 As discussed in section I, the RBM was not conceived to describe spectra of materials with pronounced relaxation shoulders on their '() responses, arising from reorientational motions. Showing the 221 K spectra as an example, Fig.…”

Ionic conductivity and relaxation dynamics in plastic crystals with nearly globular molecules

“…Another interesting possibility is the relaxation-like process, sometimes assumed to universally occur in dielectric permittivity spectra due to ionic diffusion. 60,61,62,63,64 A prominent example is a small relaxation process found in ' measurements of the ionic-melt glass former [Ca(NO 3 ) 2 ] 0.4 [KNO 3 ] 0.6 (CKN), which does not contain any dipolar molecules or ions. 60,65 Within the modulus fomalism for the description of ionic conductors, its occurrence is rationalized by a distribution of conductivity-relaxation times.…”

Spectral shape simplicity of viscous materials

“…16,17 The former two electrolytes behave as "simple" liquids, the latter two display clear evidence of chain dynamics at frequencies below wa. The type V materials are linear polymers with different chain lengths, 18,19 whereas a water solution of lithium chloride 21 is considered as type VIcorresponding to aqueous systems.…”