Authors:F. Mallet, S. Petit, S. Lafont, P. Billot, D. Lemarchand, and G. Coquerel
Solid-solid transformations between solvates of pharmaceutical compounds are investigated under various conditions. In the
case of Roxithromycin, it is shown that starting from single crystals of the acetonitrile solvate, a transformation towards
the monohydrate occurs according to a cooperative mechanism. This smooth exchange of solvent probably involves a transport
of matter within channels, and the comparison of crystal structures is consistent with the persistence of the main features
of the 3D lattice. By contrast, starting from the DMSO solvate of Dexamethasone acetate, the transformation towards the sesquihydrated
form, induced by the immersion of the DMSO solvate in water, is fully destructive and reconstructive. This occurs far-from-equilibrium
and is therefore controlled by kinetic factors. The existence of an intermediate liquid phase within the particle is postulated
to account for the appearance of whisker-like crystals growing first on high-energy sites of the former particle. An extended
analysis of these transformations between solvates shows that they could be classified according to rules previously proposed
in the case of desolvation mechanisms.
Authors:V. Balek, V. Zeleňák, T. Mitsuhashi, S. Bakardjieva, J. Šubrt, and H. Haneda
Results of emanation thermal analysis (ETA) characterizing microstructure changes of SiC based materials during heat treatment in argon are demonstrated. This method made it possible to reveal fine changes of the texture of SiC nano-sized powders, SiC micro-sized powders and SiC whiskers under in situconditions of the heating. ETA curves can serve as fingerprints of the respective samples.
Solid dispersions of the antidiabetic drug glibenclamide and polyethylene glycol 4000 (macrogol 4000) were prepared by the
melting method in order to increase the solubility of this poorly water-soluble compound. The temperature/composition phase
diagram of the components was analyzed by hot-stage microscopy and differential scanning calorimetry, showing a monotectic.
Polarized light hot stage microscopy and X-ray-powder diffraction confirmed, that glibenclamide is mainly present in a non-crystalline
state after melting and solidifying of a 10% (w/w) mixture, which results in an enhanced solubility compared to physical mixtures. The solubility and dissolution rate of the
drug increases clearly with decreasing drug/polymer ratio. Moreover, it was observed for the first time that a drug could
crystallize as whiskers at the surface of aged solid dispersion particles. Besides relaxation phenomena, this crystallization
mechanism may be responsible for a deterioration of liberation properties and bioavailability of solid dispersion based drug
products with increasing storage time.
Authors:Alper Kiziltas, Douglas J. Gardner, Yousoo Han, and Han-Seung Yang
with unique properties compared to inorganic materials. The main advantages of cellulose is its renewable nature, high-specific strength and modulus (the elastic modulus for cellulose whiskers is about 145 GPa, while that of glass fibers averages about
Authors:Zhiyong Wei, Wanxi Zhang, Guangyi Chen, Jicai Liang, Ying Chang, Lian Liu, Pei Wang, and Juncai Sun
As one-dimensional functional materials, whiskers have attracted great attention because they exhibit unique structure and various excellent physical, chemical, and mechanical properties, which are distinctive from those of
Authors:Lingli Peng, Xiangyu Xu, Zhi Lv, Jiaqing Song, Mingyuan He, Qian Wang, Lijun Yan, Yang Li, and Zhaofei Li
], nanosheets [ 16 ], nanobelts [ 15 ], nanofibers [ 17 , 18 ], and whiskers [ 19 ] had been obtained by a variety of methods in the past a few years. The concept of surfactant templating has been introduced into the synthesis of most nanostructured Al 2 O 3
-nucleating agent which could effectively induce the formation of β-modification [ 25 ]. Using this β-NA, we have successfully prepared PP/whisker/β-NA composites with β-form as main modification [ 26 ]. Moreover, when the whiskers were replaced by Kevlar fibers