Dispersions shear-sensitive systems

Shear-Sensitive Systems. In addition to hydrodynamic effects and simple viscous behavior, the act of pigmentation creates a certain amount of complex behavior (13). If the particles are fine. Brownian movement (14-17) and rotational diffusion (14. 18. 19) are among the phenomena that cause dispersed systems to display complex rheology. The role of van der Waals forces in inducing flocculation (20) and the countervailing role of two electroviscous effects (17. 21. 22) in imparting stability, particularly in aqueous systems, have been noted. Steric repulsions appear to be the responsible factor in nonaqueous systems (23. 24). The adsorbed layer can be quite large (25-28). as detected by diffusion and density measurements of filled systems or by viscometry and normal stress differences (29). 

Evaluation of Mechanical Properties Viscosity of Shear-Sensitive Materials Dispersed Systems Polymer Solutions Viscoelasticity... 

Multiple emulsions are complex systems wherein droplets of (he dispersed phase contain additional but smaller droplets, identical to or different from the continuous phase. Even so there are many interesting fields of potential research and applications, such as vaccine formulations, enzyme immobilization, and drug overdose treatment (122). Ttie disadvantages of current multiple emulsions are obvious. Internal droplet growth and release as well as degradation to heterogeneous O/W or W/O formulations results in shear sensitivity and bad long-term multiplicities. Besides, those systems are problematic to produce al industrial scale. 

The ever-increasing raw material choice available to the adhesive formulator is demonstrated with particular reference to Hercules resin dispersions for the modification of acrylic latex polymer systems used in pressure sensitive adhesive formulations. The requirements of a tackil g resin are examined and the advantages afforded by such products from Hercules as Tacolyn 1070, Tacolyn 3179 and Res A-2603 are discussed, in terms of their ability to offer balances of peel, tack and shear and consistently high levels of stability, it is claimed. 5 refs. 

Static Melt Intercalation This method involves the mechanical mixing of a polymer with an appropriately modified filler and subsequent annealing above the softening temperature of the polymer. This approach provides the best route to test with sensitivity the thermodynamic arguments detailed above and to yield well-defined systems for fundamental studies. However, due to the quiescent processing conditions (absence of external shear), which eliminate any mechanical contribution for the dispersion of fillers, and to the very slow interca-lation-exfohation kinetics," " such methods are typically very slow, thus having very limited applicabihty in industry. 

The main factors which affect the viscosity of emulsions are listed in Table 8.6. The properties of the disperse phase, the continuous phase and the emulsifying agent or agents all influence the emulsion viscosity. Each factor does not act independently and the interpretation of emulsion viscosity data is complicated by this fact and the fact that particles can deform under shear depending on the nature of the interfacial film. As we have also discussed, emulsions are complex systems, often highly structured, and at phase boundaries or on the point of inversion are very sensitive to small perturbations in the system. We will deal here first with mobile emulsions and then consider briefly the semi-solid state. 

The rheology of HA-Na is extremely sensitive to protein contamination [39, 40]. Comparable results are obtained using protein free samples obtained from bacterial sources. Some of these studies were conducted in saline aqueous medium to reproduce physiological conditions in which dilute and semidilute HA-Na dispersions exhibit Newtonian behavior in a wide shear rate range. Equihbrium and release properties of aqueous systems PE-dmg dispersions can be reasonably... 

Uses Gum providing suspension of solids slurries and rheological control for aq. systems for industrial use in systems requiring dispersibility antitackifier improving cohesive str. and shear resist, at high temps, for pressure-sensitive adhesives emulsifier... 

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