Study of glass transition phenomena in the supercooled liquid phase of methocarbamol, acetaminophen and mephenesin

We studied the thermochemical behaviour of five commonly used drugs namely naproxen, atenolol, methocarbamol (ML), acetaminophen and mephenesin (MP) using dielectric spectroscopy (10−3 Hz-1 MHz) and differential scanning calorimeter (DSC) down to liquid nitrogen temperature. The first two samples quickly crystallize during cooling, and we are able to study the glass transition phenomena in the latter three drugs only. The dielectric spectroscopy of the supercooled liquids of the latter three sample reveals the glass transition process as a pronounced relaxation process identifiable with so called primary relaxation process, or α-process, which is non-Debye in nature, and can be described well using Hevriliak-Negami (HN) equation. One sub-Tg process much smaller in magnitude is found in temperature range of 150 K-250 K that is arrhenius in its temperature dependence, which does not appear to be inter-molecular in nature.