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RHEOLOGY-3

RHEOLOGY-3 PART-3

PHARMAROCKS
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RHEOLOGY-3

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  1. RHEOLOGY • INSTRUMENTATION • Ostwald Viscometer • Falling Sphere Viscometer • Cup and Bob Viscometer • Cone and Plate Viscometer • Brookfield Viscometer PART-3

  2. RHEOLOGY Rheology is the science which deals with flow of liquid and deformation of solid.

  3. RHEOLOGY Rheology is a Greek word Rheo Means “Flow” & Logia, “study of” THUS RHEOLOGY MEANS STUDY OF FLOW Rheology is the science/physics that concerns with the flow of liquids and the deformation of solids.

  4. Instrumentation Viscometer

  5. INSTRUMENTATION “One point" instruments Provide a single point on the rheogram. Extrapolation of a line through this point to the origin will result in the complete rheogram. Used for Newtonian fluids. Since the rate of shear is directly proportional to the shearing stress.

  6. Ostwald Viscometer

  7. Ostwald Viscometer Ostwald viscometer is used to determine the viscosity of a Newtonian liquid. Both dynamic and kinematic viscosities can be obtained. When a liquid flows by gravity, the time required for the liquid to pass between two marks (A and B shown in Figure) through a vertical capillary tube is determined.

  8. VISCOSITY OSWALD VISCOMETER

  9. Falling Sphere Viscometer

  10. Falling Sphere Viscometer

  11. Falling Sphere Viscometer The sample & ball are placed in the inner glass tube & allowed to reach temperature equilibrium with the water in the surrounding constant temperature jacket.

  12. Falling Sphere Viscometer The tube & jacket are then inverted, which effectively places the ball at the top of the inner glass tube. The time for the ball to fall between two marks is accurately measured & repeated several times.

  13. “Multi-point" instruments “Multi-point" instruments Used with Non-Newtonian systems. The instrumentation used must be able to operate at a variety of rates of shear. Cup and Bob , Cone and Plate viscometers may be used with both types of flow system.

  14. Cup and Bob Viscometer

  15. Cup and Bob Viscometer

  16. Cup and Bob Viscometer This is a multipoint viscometer and belongs to the category of rotational viscometers. The sample is placed in the cup and the bob is placed in the cup up-to an appropriate height. The sample is accommodated between the gap of cup and bob. Cup or bob is made to rotate and the torque (shearing stress) from the viscous drag is measured by a spring or sensor in the drive of the bob.

  17. Cone and Plate Viscometer

  18. Cone and Plate Viscometer

  19. Cone and Plate Viscometer The sample is placed at the center of the plate which is then raised into position under the cone. The cone is driven by a variable speed motor & the sample is sheared in the narrow gap between the stationary plate and the rotating cone.

  20. Cone and Plate Viscometer The rate of shear in rev./min. is increased & decreased by a selector dial & the torque (shearing stress) produced on the cone is read on the indicator scale.

  21. Brook field Viscometer

  22. Brook field Viscometer Brookfield Viscometer measures this friction, and therefore functions as a tool of rheology. The purpose of this chapter is to acquaint you with the different types of flow behavior and use of the Brookfield Viscometer as a rheological instrument to enable you to conduct a detailed analysis of virtually any fluid.

  23. Brook field Viscometer Determine viscosity by measuring the resistance on a shaft rotating in the fluid. They are designed to make a direct measurement of the absolute Viscosity. The theory of operation of a rotational viscometer is based on the Couette flow model for fully developed, steady and laminar flow between two surfaces, one of which is moving Pointer displacement is directly proportional to fluid viscosity.

  24. Brook field Viscometer

  25. Visco elasticity Visco elasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied.

  26. Visco elasticity With cone-plate geometry the sample appears to ‘roll up’ and at high shear rates and is ejected from the gap. With concentric cylinder geometry the sample will climb up the spindle of the rotating inner cylinder (Weissenberg effect).

  27. Pharmaceutical Applications The viscosity of creams and lotions may affect the rate of absorption of the products by the skin. A greater release of active ingredients is generally possible from the softer, less viscous bases. The viscosity of semi-solid products may affect absorption of these topical products due to the effect of viscosity on the rate of diffusion of the active ingredients.

  28. Pharmaceutical Applications The rate of absorption of an ordinary suspension differs from thixotropic suspension. Thixotropy is useful in the formulation of the all pharmaceutical suspensions and emulsions. They must be poured easily from containers (low viscosity)

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