Isochronal superposition and density scaling of the intermolecular dynamics in glass-forming liquids with varying hydrogen bonding propensity

We have tested the idea of thermodynamic scaling T-1 rho(gamma) and isochronal superposition in glass-forming liquids with varying propensity to form hydrogen bonds. The samples under investigation were dimeric rich ketoprofen and it is incapable of forming local hydrogen bonding structures, methylated derivative. We find that both features of viscous liquid dynamics hold better for the methylated sample and include the entire pressure-sensitive dynamics. We also show that it is possible to scale simultaneously the alpha- and secondary relaxation times in terms of T-1 rho(-gamma) approach using the same value of the gamma exponent. This is the first such clear observation reported for supercooled liquids to date. The removal of the hydrogen bonds enables these effects to be clearly identified experimentally.