  We have established a comprehensive study of the molecular dynamics of the
menthol-thymol mixture, the prototype of the new class of type V deep eutectic
solvents. Dielectric spectroscopy and differential scanning calorimetry were
combined to assess the dipolar relaxation and glassy dynamics over an extended
range of timescales (10-6-10 2 s) and for eleven different compositions
including the two pure constituents. Positive deviations from ideal mixing
approximation were demonstrated for both the solvent dielectric strength and
the glass transition. They support the idea that preferential H-bond
interactions between unlike molecules induce structural rearrangements in the
DES mixtures. Excellent glassforming capability of the DES mixtures was
demonstrated for a broad range of compositions (xThymol = 0.4-0.7). In this
case, the dipolar dynamics could be assessed from the normal liquid to the
deeply supercooled state. Many salient parameters of the relaxation functions,
including fragility, non-Debye character and rotation-translation decoupling
point to the development of dynamic heterogeneities.

Soft Condensed Matter