Molecular Dynamics and Physical Stability of Pharmaceutical Co-amorphous Systems: Correlation Between Structural Relaxation Times Measured by Kohlrausch-Williams-Watts With the Width of the Glass Transition Temperature (ΔTg) and the Onset of Crystallization

Calorimetric Investigation of the Relaxation Phenomena in Amorphous Lyophilized Solids

“…The relaxation processes themselves are classified into different modi concerning their behavior in a broadband relaxation spectroscopy measurement. They are sorted into α -, β -, and γ -relaxations [ 22 , 46 , 49 ], with α -relaxations being the slowest relaxations (time scale from seconds to months), followed by β -relaxations (time scales of milli- to picoseconds) and γ -relaxations (beyond β -relaxations in the time scale of picoseconds) [ 22 , 43 , 46 , 50 ]. Apart from a limited number of exceptions, calorimetric methods capture only α -relaxations [ 51 , 52 ].…”

“…Thus, this review focuses on the properties of α -relaxations and refers to other excellent publications for more information on other types of relaxation modi [ 46 , 50 , 53 ]. For the investigation of further relaxation modi, other methods are appropriate, such as inelastic neutron scattering ( -relaxations), ss-NMR ( -relaxations), and dielectric spectroscopy ( - and -relaxations) [ 22 , 46 ].…”

“…Summarized, it states that the matrix becomes more and more rigid during its formation in such a manner that any movement of molecules and functional groups is finally impossible. In this context, movement is seen as an essential factor for reaction processes that are impeded in this way [ 22 , 23 ]. This theory is the major basis of the topics discussed in this review and thus is further explained in the Theoretical Background section.…”

“…Several methods were used and developed in the last few decades to investigate matrix relaxations. These include, inter alia, measurements of viscosity [ 16 , 32 ], solid state nuclear magnetic resonance spectroscopy (ss-NMR) [ 22 , 33 ], dielectric spectroscopy [ 16 , 22 , 34 ], terahertz spectroscopy [ 22 , 35 ], thermally stimulated depolarization current [ 36 , 37 ], electron spin resonance spectroscopy [ 38 ], incoherent neutron scattering [ 39 , 40 ] and, last but not least, calorimetric methods [ 17 , 22 , 41 , 42 ]. With the exception of the latter, all these methods require very well-trained scientific operators and a great deal of experience to obtain and evaluate the relaxation data.…”

Physical Ageing of Amorphous Indapamide Characterised by Differential Scanning Calorimetry

“…It should be noted that the relaxation time value for any given ageing condition can vary depending on the sample preparation. Chieng et al [ 72 ] reported that the relaxation times for the samples prepared by freeze-drying have significantly shorter relaxation times than samples prepared by quenching from the melt.…”