Concentrated stable systems, rheology

The above rheological parameters can be used to assessment and predict the long-term physical stability of suspension concentrates. They offer valuable tools to the formulation chemist for the development of stable systems. In addition, one can design a simple rheological technique for evaluation of the suspension concentrate during manufacture (quality assurance test). 

P.Y.175 does not bloom. It may safely be overcoated up to 140°C. At higher temperatures, bleeding is observed to a small extent in various systems. The pigment is heat stable up to 180°C. The commercially available type exhibits good rheological properties in paints and may therefore be used at higher concentrations. 

The results of this study have been published [37]. Evaluation samples of several candidate energetic hydrocarbon fuel systems have been sent to Prof. Segal for his combustion studies (see Scheme 14). More recently. Prof. Segal and his co-workers have studied rheological properties and burning rates of a mixture of isomeric methylated PCU alkene dimers (2b). A stable 18% w/w solution of 2b in JP-10 was achieved. More concentrated solutions (up to 25% w/w) were unstable and produced sediments after standing for ca. 2 weeks under ambient conditions. An 18% w/w solution of 2b in JP-10 increased the kinematic viscosity of JP-10 by 1.3 centistokes at 30 °C and by 0.65 centistokes at 70 °C, thereby effectively matching the viscosity of RJ-4. 

The crosslink density ultimately defines the rheological and mechanical properties of the polymer. Polymers that have a high crosslink density are thermosets and are infusible, insoluble, and dimensionally stable under load. These properties make epoxy resin systems useful as structural adhesives as well as important materials in other applications. Polymers that have a low crosslink density are more flexible and show greater resistance to stress concentration, impact, and cold. 

This section on concentrated suspensions discusses the rheological behavior of sj tems which are colloidally stable and colloidally unstable suspensions. For stable sj tems, the rheology of sterically stabilized and electrostatically stabilized systems wiU be considered. For sterically stabilized suspensions, a hard sphere (or hard particle) model has been successfid. Concentrated suspensions in some cases behave rheologically like concentrated polymer solutions. For this reason, a discussion of the viscosity of concentrated polymer solutions is discussed next before a discussion of concentrated ceramic suspensions. 

The turbidity methods are unsatisfactory for lar particles and/or high particle number concentrations when multiple scattering effects intrude. As shown by Hunter et al. (1975), rheological measurements can then be used to detect flcK ulation. Stable dispersions exhibit an Ostwald-type flow curve whereas flocculated systems behave in a pseudoplastic fashion. Bocculation is thus accompanied by a large increase in the Bingham yield value, t, of the dispersion (see Fig. 5.4). 

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