Dielectric and\nShear-Mechanical “Humps”\nin the Nonlinear Response of Polar Glassformers

Many glassformers display electrorheological\neffects\nand a pronounced\nmaximum in their frequency dependent nonlinear dielectric response.\nThe latter so-called “hump” feature was often linked\nto correlated-particle motions and, so far, was not explored in the\nlarge-perturbation mechanical response of viscous liquids. To first\nclarify the electro-viscoelastic coupling in the linear domain, using\nthe modified Gemant, DiMarzio, and Bishop model, it is demonstrated\nhow the small-amplitude shear mechanical response of <i>S</i>-methoxy-PC, a derivative of propylene carbonate, can be related\nto its complex dielectric permittivity. Then, in the nonlinear regime,\na “hump” feature is identified in the rheological third-order\nshear modulus of <i>S</i>-methoxy-PC and of another polar\nglassformer, propylene glycol. Thus, the observation of a “hump”\nin the cubic response of viscous liquids does not necessarily rely\non the application of electrical fields.