Solid-state properties crystal morphology

The solid-state properties like crystallinity, polymorphism (crystal structure), shape (morphology), and particle size of drugs are important in the stability, dissolution, and processibility of drugs. Some commonly used methods in solid-state studies include microscopy, hot stage microscopy with polarized light, x-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared FTIR/Raman, and solid-state NMR. 

Since in most applications conjugated materials are used in the solid form, an important advantage of oligomers is therefore that the solid state properties can be investigated in crystals or in vapor-deposited (thin) films. However, in the solid state morphological and supramolecular effects may play an important role and lead to different properties than those found in solution. 

The complexity and small size of the ionic phase and crystallinity in ionomers continue to interest the research community. Many studies have been conducted employing various analytical techniques, such as SAXS [2-5], NMR [6], EXAFS [7-11], AFM [12], STEM [13-15], DSC [16], and rheology [17-18], to explore the ionic structures and crystallinity of ionomers. Morris and Chen [19] proposed a refined morphological model (Figure 1) to include the fine secondary crystals in the morphology and suggested the significant role of the secondary crystals to the network structure, and thus the solid state properties. 

Most drug and inactive excipients used in tablet formulation are in the solid state as amorphous powder or crystals of various morphological structures. There may be substantial differences in particle size, surface area, crystal morphology, wetting, and flowability as well as many physical properties of drug, excipients, and their blends [16]. Table 12 describes common micromeritic topics important to pharmaceutical preformulation. 

The solid state displacement reaction method and wet chemical precipitation method were employed for synthesizing the ceria powders, and thus the ceria properties showed different features in several experiments. Figure 15.10 shows the morphology of the ceria particles observed with high-resolution scanning electron microscopy (SEM S900, Hitachi, Japan) and transmission electron microscopy (TEM JEM-2010, JEOL, Japan). In the figure, the ceria particles have a polyhedral shape. Both of the powders have nearly the same size. The primary particle size is approximately 40 mn. However, the difference in crystal shape of the ceria particles was found on TEM analysis. 

The main difference between the solid-state reaction synthesis route and hydro(sol-vo)thermal synthesis route lies in reactivity , which is reflected in reaction mechanisms. Reactions in solid-state synthesis depend on the diffusion of the reactants at the interface, whereas individual reactant molecules existing in the liquid phase can react with each other in hydro(solvo)thermal synthesis. Variation in the reaction mechanism leads to the formation of different structures from the same or similar starting materials. In addition, even the same material that can be obtained by both preparation routes can have totally different morphology and properties due to different formation mechanisms. For instance, perfect single crystals can usually be formed from liquid-phase synthesis, while being very difficult to obtain in solid-state synthesis. 

Solid-state extrusion has also yielded some of the highest properties for uniaxially oriented morphologies. Tensile moduli (210 GPa) nearing the theoretical value of a polyethylene single crystal have been attained.f ... 

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