Sufficient Physical Stability

For the very first clinical studies it is often possible to find a polymorph with sufficient physical stability to permit completion of Phase I trials. The most stable polymorph usually exhibits the highest density, the lowest solubility (and often the lowest bioavailability). Very detailed evaluations of polymorphism and the inter-relationships between the different polymorphs and pseudopolymorphs usually need to be delayed until the candidate salt has been chosen and larger quantities of drug from several batches are available. These studies are often started around the initiation of Phase 11 clinical trials. 

For high-performance HEMFC applications, HEMs and HEIs are required to have high hydroxide conductivity, excellent chemical stability, sufficient physical stability, controlled solubility, and other important properties. 

Equation (8.29) provides no guarantee of stability. It is a necessary condition for stability that is imposed by the discretization scheme. Practical experience indicates that it is usually a sufficient condition as well, but exceptions exist when reaction rates (or heat-generation rates) become very high, as in regions near thermal runaway. There is a second, physical stability criterion that prevents excessively large changes in concentration or temperature. For example. An, the calculated change in the concentration of a component that is consumed by the reaction, must be smaller than a itself Thus, there are two stability conditions imposed on Az numerical stability and physical stability. Violations of either stability criterion are usually easy to detect. The calculation blows up. Example 8.8 shows what happens when the numerical stability limit is violated. 

These results strongly indicate that DSSCs show sufficient physical and chemical stability during extended periods of illumination. Nevertheless, stability tests at high temperatures and high humidity must be carried out for outdoor applications. 

To further study the physical stability of these long-lived microbubbles, Johnson and Cooke also applied small negative and positive changes in pressure to the contents of the observation cell. When sufficient negative pressure was applied, the microbubbles expanded. These authors observed that expansion proceeded... 

Under moderate operating conditions, chemically efficient commercial stabilizers having molecular weights in the range 350 to 500 daltons ensure sufficient service stability of polymere. Physical factors mentioned in the Sect. 1.3.1 limit the efficiency in aggressive conditions, however. The seriom problem of the physical loss of stabilizers can be solved by a chemical modification of the structure of physically non-persistent stabilizers. This involves the application of salts or metallic complexes of statalizers or an inc -ease of the molecular weight of stabilizers. 

Sedimentation ratio is often used to assess suspension stability. Byron reported the sedimentation ratios for a 1% sodium fluoresein suspension formulation with different amounts of surfactant (sorbitan trioleate) after standing for 20 days at room temperature. The suspension formulation with the lowest sedimentation ratio had thebest-flocculated system. However, all formulations were easily redispersible one complete revolution of the container was sufficient to produce a homogeneous dispersion. There was no clear difference in the times taken to reach apparent sedimentation equilibrium. Physical stability of the formulation was determined according to ... 

Emulsions have been widely used as vehicles for oral, topical, and parenteral delivery of medications. Although the product attributes of an emulsion dosage form are dependent on the route of administration, a common concern is the physical stability of the system, in particular the coalescence of its dispersed phase and the consequent alteration in its particle-size distribution and phase separation. The stabilization mechanism(s) for an emulsion is mainly dependent on the chemical composition of the surfactant used. Electrostatic stabilization as described by DLVO theory plays an important role in emulsions (0/W) containing ionic surfactants. For 0/W emulsions with low electrolyte content in the aqueous phase, a zeta potential of 30 mV is found to be sufficient to establish an energy maximum (energy barrier) to ensure emulsion stability. For emulsions containing... 

These are suspensions with a size range of 20 to 200 nm. Like suspensions, they are kinetically stable but, due to the small size of the particles, they have much longer physical stability (i) an absence of sedimentation, as the Brownian motion is sufficient to prevent separation by gravity and (ii) an absence of flocculation, as the repulsive forces (electrostatic and/or steric) are much larger than the weak van der Waals attraction. 

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