Si vous continuez à naviguer sur ce site, vous acceptez l’utilisation de cookies. SlideShare utilise les cookies pour améliorer les fonctionnalités et les performances, et également pour vous montrer des publicités pertinentes. 3 Ostwald ripening is described by the Kelvin equation (also called the Ostwald–Freundlich equation):So, to summarize, considering both the van’t Hoff and Kelvin equations, it can be gathered that a major obstacle to maintaining usefulness of suspensions is the reinforcement, or amplification, of the strength of interparticulate cohesion, especially at distances in the range of closer PE minima (i.e., intermolecular interactions).
Consultez nos Personnalisez le nom d’un clipboard pour mettre de côté vos diapositives. This is not always true, but is the most common scenario. With regard to drug delivery systems, this means particles located at the furthest energy minimum are more easily redispersed than are particles at the closer minimum where they are bound more tightly together.As previously mentioned, when particles separate from their dispersion medium, sedimentation of the particles normally occurs. The two potential courses of action include: 1) attempting to avoid suspensoid interactions or 2) trying to manage the interactions. Interfacial tension (The dilemma for dealing with suspensions then can become the ‘redispersability’ of the sedimented particles. This outcome can be avoided if particles are induced to approach each other no closer than the distance represented by the outer energy minimum.As the particle size is reduced (such as is accomplished through trituration), the free energy increases. Intentionally causing flocculation of a suspension is one method by which resuspendability can be ensured.The outer PE minimum (approximately 1000–2000 Å apart) is where successful flocculation holds loosely aggregated particles and the inner PE minimum is where coagulation is likely to occur. SlideShare utilise les cookies pour améliorer les fonctionnalités et les performances, et également pour vous montrer des publicités pertinentes. The goal is to force irregular packing of the particles when they settle, with large interparticulate distances, allowing weak attractive interactions among the particles. When they settle they do not compact well. Variations of either extreme are also commonly employed.Creation of a flocculated system is the approach to precluding or delaying interactions among the components of a suspension and can involve use of a structured vehicles to slow sedimentation rate (velocity).
If settling is slow, measurement and use of the drug delivery system is easier than if particles sediment quickly.Sedimentation rate of suspension dispersed phases roughly follows Stokes’ law:Stokes’ law operates under the assumption that the particles are small, perfect spheres that create no turbulence and have no collisions (ideal conditions). First, two terms must be defined. Ultimately, the goal of either path is to keep the suspension delivery system usable. Once settled on the bottom of a container, particles threaten to crystallize, creating a dense cake or aggregate (the ‘compact’ settling) that can be extremely difficult to redisperse. Aucun clipboard public n’a été trouvé avec cette diapositive Typically, suspensions are coarse dispersions consisting of solid particles (100–50000 nm in diameter) in liquid dispersion media.To briefly review, when two dispersed particles approach each other, because of inequity between attractive and repulsive forces over distance, there are two net PE ‘wells,’ or minima, where particles have PE optima (the most energetically stable distances from neighboring particles). Deflocculation, then, is the antithesis: the intentional creation of a coagulated system. Some of the choices described above pertain to early stages in the sedimentation process and involve manipulation of sedimentation velocity (Two important components regarding suspension caking include temperature fluctuations and crystal growth via Ostwald ripening.Ostwald ripening is a process by which particles that do arise, such as those from temperature fluctuations, tend to become larger and tend to deposit on progressively larger particles at the expense of smaller particles. A suspension may be for internal, external or parenteral use.
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