Determine Physical Stability

Molecular mobility in amorphous materials is related to the macromolecular properties like viscosity it is generally quantified in terms of mean relaxation time and it determines physical stability and reactivity. The relaxation time is defined as the time necessary for a molecule or chain segment to diffuse across the distance of one molecule or chain segment. The relaxation time varies with temperature and the typical relaxation times at Tg are estimated to be 100-200 s (Ediger et al. 1996). Molecular relaxation times can be characterized by the change of several bulk properties like enthalpy or volume or spectroscopic properties. The extent of relaxation is described empirically by the Kohlrausch-Williams-Watts equation (Hodge 1994) ... 

We will first illustrate how chemical variables affect surface charge and surface potential. Then we will discuss more quantitatively a physical stability model which depends on the surface potential (which, in turn, has been determined by chemical factors). 

Crystallization of milk fat largely determines the physical stability of the fat globule and the consistency of high-fat dairy products, but crystal behavior is also complicated by the wide range of different triglycerides. 

The physical properties of silica are determined by its specific surface area, pore volume, average pore diameter, porosity, and the particle diameter and shape [8]. The latter two are responsible for the efficiency, the physical stability and the pressure drop of the packed columns and do not contribute to retention and selectivity. 

Probably the only general statement which can be made about the experimental studies on zeolites is that the majority of published data is inapplicable directly to natural minerals. This is due either to the excessively high temperatures under which the experiments are performed, outside of the physical limits of zeolite stability, or to short time spans of observation which do not allow the silicates to come to equilibrium with the fluids of the experiments. Those studies designed to determine zeolite stability indicate that the most silica-poor alkali zeolite, analcite, is not stable above 180°C. More silica-rich species will be found below this temperature. However, the reasons for the crystallization of one or another of the silica-rich alkali zeolites are not yet elucidated. 

In general terms these problems are not unlike those encountered in the manufacture of other colloidal products such as paints, face creams, and printing inks and toners, for example. The difference, of course, is that the inks and toners are hardly appetizing and one seldom cares about how they taste (Of course, physical stability alone does not determine the taste or the worthiness of a food product. Chemical reactions play a role in taste and in determining the structure, and other considerations such as nutritional value and esthetic appeal may also apply.)... 

The physical stability, on applying heat at 45 °C, was mainly determined on creams. 

Aso Y, Yoshioka S, Otsuka T, Kojima S. The physical stability of amorphous nifedipine determined by isothermal microcalorimetry. Chem Pharm Bull 1995 43(2) 300-303. 

The need for high chemical and physical stability in the substances that will hold nuclear waste ions in an immobilized state has stimulated extensive materials research. In support of the candidacy of the cation-linked tetrahedral compounds having the monazite, scheelite or zircon crystal structure, studies have sought to determine the extent to which various elements occurring in the waste can occupy stable substitutional positions on the host lattice sites.(l)... 

Other methods of determining foam stability include monitoring physical properties related to the foam. For example, several researchers discuss the use of NMR spectroscopic or MRI imaging monitoring of foam stability [109,124]. 

Proteins from extremophilic organisms, particularly thermophiles, have been the subject of intensive research in recent years. This work has been the subject of numerous reviews (Jaenicke and Bohm, 1998 Russel and Taylor, 1995 Vogt and Argos, 1997 Gerday et al., 1997 Somero, 1995), and we will make no attempt at an in-depth summary. We will confine ourselves to briefly stating the major trends identified thus far. Explaining these trends becomes complicated because the many weak interactions that determine enzyme stability and activity have complex temperature dependencies (see Section II). And evolution injects considerable confusion beyond the laws of physical chemistry. 

Simple determination of physical stability, i.e., are there particles in solution, is the solution the correct color/turbidity Is the container closure system seemingly intact ... 

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