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Nanostructures of Aggregates and Gels Formed by Fully Atomistic Molecular Dynamics Simulations
Published in Junko Habasaki, Molecular Dynamics of Nanostructures and Nanoionics, 2020
In 1984, Mishima and coworkers [30] reported the formation of high-density amorphous ice (HDA) under the pressure at 77 K. This ice was different from the low-density amorphous ice (LDA), which was obtained by the rapid cooling of water or by the deposition of the vapor. The change between LDA and HDA seems to be the first-order transition with the changes of ~20% in volume. The existence of different kinds of amorphous ice is called “polyamorphism.”
Production of stable amorphous form by means of spray drying
Published in Particulate Science and Technology, 2019
Igor Nežić, Aleksandra Sander, Ernest Meštrović, Dražen Čavužić
FTIR spectra of representative samples obtained by spray drying at different inlet temperatures and flowrates of nitrogen, as well as at different two-fluid atomizer diameter and solution flowrates were normalized to investigate any difference between them and are shown in Figure 9. Comparing the FTIR spectra, slight differences can be observed. By increasing the temperature of drying, intensity of the stretching band is decreasing and intensity ratio of peaks in the range of 3500–3100 cm−1, corresponding to OH stretching from liquid water, amine NH2 stretching, and amide N–H stretching are slightly changing as well. This difference is observed in FTIR spectra of samples obtained by spray drying with different atomizer diameter as well. With faster solvent evaporation at higher temperatures and by drying smaller droplets (higher evaporation surface), lack of interactions observed in FTIR spectra indicate alteration in molecular structure of amorphous material. Changing the feed solution and N2 flowrate, no significant differences are observed. Spectral differences are hard to find and difficult to quantitatively describe. Special statistical processing based on factor analysis is required to adequately interpret such variations (Brus et al. 2011). Comparing the XRD patterns, no significant differences can be observed. Slight differences can be seen from 5 to 18°, 2θ indicating possible formation of partially ordered domain or different amorphous forms. In addition to that, existence of two crystallization peaks on DSC curves of all obtained samples, except the one obtained at the most efficient process conditions, may be explained with formation of slightly different amorphous powder that on heating first transforms to some metastable crystalline structure and finally to the most stable one. The ability of API to exist in different amorphous structures (polyamorphism) needs to be further investigated since the differences in the actual local structure in an amorphous substance can influence its physicochemical properties (Policianova et al. 2014).