Predicting Dielectric and Shear-Rheology Properties of Glass-Forming Pharmaceutical Liquids from Each Other: Applications and Limitations

Acetaminophen, nicotine, and lidocaine hydro-chloride were investigated in their deeply supercooled liquid states using oscillatory shear rheology. The mechanical spectra of thesedrugs are presented in modulus, compliance, as well asfluidityformats. Their frequency profiles can be described via modelsadapted from thefield of charge transport. Inspired by the successof this approach, the Barton-Nakajima-Namikawa relation, bestknown from the samefield, was also tested. When adapted torheology, this approach interrelates static and dynamic character-istics of viscousflow and was found to work excellently. Thetemperature dependence of the characteristic shear frequencies waschecked against the shoving model, which relates them to thetemperature-dependent instantaneous shear modulus and accept-able agreement was found. Combined with shear mechanical literature data on ibuprofen and indomethacin, a modified version ofthe phenomenological model by Gemant, DiMarzio, and Bishop (GDB) was employed to successfully predict the shape andamplitude of the dielectric spectra for all studied liquids, except for lidocaine hydrochloride. For the latter, the modified GDB modelis suggested to aid in mapping out the reorientational part of the dielectric response, while the experimental results are stronglysuperimposed by ionic conduction phenomena. The reverse transformation, the calculation of rheological spectra based on dielectricones, is also successfully demonstrated. For the example of acetyl salicylic acid, it is shown how dielectric spectra can be used to evenpredict rheological ones. The limits of the central parameter governing these mutual transformations, the electroviscoelastic materialconstant, and indications for its correlation with the dielectric relaxation strength are discussed. For pharmaceuticals characterized bya strong dynamical decoupling of the electrical from the mechanical degrees of freedom, the modified GDB model is not expected to be applicable

Automated summary

Acetaminophen, nicotine, and lidocaine hydro-chloride were studied in their deeply supercooled liquid states using oscillatory shear rheology. A modified version of the GDB model successfully predicted the dielectric spectra for all liquids except lidocaine hydrochloride. The reverse transformation, calculating rheological spectra based on dielectrics, was also demonstrated.