  Shear-mechanical and dielectric measurements on the two monohydroxy
(mono-alcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to
the glass transition temperature are presented. The shear-mechanical data are
obtained using the piezoelectric shear-modulus gauge method covering
frequencies from 1mHz to 10kHz. The shear-mechanical relaxation spectra show
two processes, which follow the typical scenario of a structural (alpha)
relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric
relaxation spectra are dominated by a Debye-type peak with an additional
non-Debye peak visible. This Debye-type relaxation is a common feature peculiar
to mono-alcohols. The time scale of the non-Debye dielectric relaxation process
is shown to correspond to the mechanical structural (alpha) relaxation.
Glass-transition temperatures and fragilities are reported based on the
mechanical alpha relaxation and the dielectric Debye-type process, showing that
the two glass-transition temperatures differ by approximately 10K and that the
fragility based on the Debye-type process is a factor of two smaller than the
structural fragility. If a mechanical signature of the Debye-type relaxation
exists in these liquids, its relaxation strength is at most 1% and 3% of the
full relaxation strength of 2-butanol and 2-ethyl-1-hexanol respectively. These
findings support the notion that it is the non-Debye dielectric relaxation
process that corresponds to the structural alpha relaxation in the liquid.
