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RHEOLOGY-2

RHEOLOGY PHARMACY

PHARMAROCKS
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RHEOLOGY-2

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  1. RHEOLOGY • NEWTON’S LAW • FLOW OF LIQUIDS • NEWTONIAN SYSTEM • NON NEWTONIAN SYSTEM • PLASTIC FLOW • PSEUDO PLASTIC FLOW • DILATANTS FLOW

  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. NEWTON’S LAW According to NEWTONS LAW higher the viscosity of a liquid, the greater is the force per unit area (shearing stress F) required to produce a certain rate of shear (G) Rate of shear α shearing stress F α G F= ηG η= viscosity

  5. Rate of shear The shear rate is defined as the gradient in velocity, that is, the difference in velocity between the two surfaces containing the fluid, divided by the distance between them.

  6. NEWTON’S LAW Shear stress (F) is defined as force per unit area. F= f/A unit dyne/cm2or Newton/m2 Higher viscosity of liquid , greater shear stress (F) required to produce a certain G rate of shear (dv/dt) F ∞ dv/dt F= η dv/dt F= η G

  7. NEWTONIAN SYSTEM Sir Isaac Newton was first to study the flow properties of liquids in quantitative terms. E.g. Simple organic liquids, true solutions, water, dilute suspension and emulsions. “Liquids that follow the Newton’s law of low are known as Newtonian System” Sir Isaac Newton

  8. FLOW OF LIQUIDS Two types of flow 1. Newtonian Flow 2. Non Newtonian Flow Plastic Flow Pseudo plastic Flow Dilatants flow

  9. NEWTONIAN FLOW A Newtonian fluid is a fluid whose stress versus rate of shear curve is linear and passes through the origin. The constant of proportionality is known as the viscosity. F= ηG where η= viscosity Water, chloroform, Castor oil, ethyl Alcohol etc are Newtonian fluid

  10. NON NEWTONIAN SYSTEM

  11. NON NEWTONIAN SYSTEM

  12. NON NEWTONIAN SYSTEM Non - Newtonian bodies are those substances, which fail to follow Newton's law i.e. liquid & solid, heterogeneous dispersions such as colloidal solutions, emulsions, liquid suspensions and ointments. They are classified into 3 types of flow: Plastic flow. Pseudoplastic flow. Dilatant flow

  13. NON NEWTONIAN SYSTEM A non newtonian flow is defined as one for which the relation between F and G is not linear. In other words when the shear rate (G) is varied, the shear stress (F) is not varied in the same proportion. The viscosity of such a system thus varies as the shearing stress varies.

  14. NON NEWTONIAN SYSTEM A non newtonian flow is defined as one for which the relation between F and G is not linear. In other words when the shear rate (G) is varied, the shear stress (F) is not varied in the same proportion. The viscosity of such a system thus varies as the shearing stress varies.

  15. PLASTIC FLOW In which curve does not pass through the origin Zero, the substance behaves initially Elastic body and it fails to flow when less amount of stress is applied. Also called Bingham bodies.

  16. PLASTIC FLOW The plastic flow curve does not pass through the origin & it intersects the shearing stress axis (or will if the straight part of the curve is extrapolated to the axis) at a particular point referred to as yield value. (f)

  17. PLASTIC FLOW The equation describing plastic flow is, U = F – f / G Where, f = Yield value F = Shearing stress G = Rate of shear

  18. PLASTIC FLOW As increase the stress, leads to non-linear increase in shear rate but after that curve is linear. The linear portion extrapolated intersects the x axis at the point called as yield value So, plastic flow shows Newtonian flow above the yield value. Bingham bodies does not flow until the shearing stress is corresponding to yield Value exceeded.

  19. PLASTIC FLOW The reciprocal of mobility is Plastic viscosity ZnO in mineral oil, certain pastes , paints & ointments Plastic flow explained by flocculated particles in concentrated suspensions, ointments, pastes and gels.

  20. PSEUDO PLASTIC FLOW In which curve is passing from origin Zero shear stress No yield value is Obtained As shear stress increases, shear rate increases but not linear.

  21. PSEUDO PLASTIC FLOW The curve for a pseudoplastic material begins at the origin (or at least approaches it at low rates of shear). The curved rheogram for pseudoplastic materials is due to shearing action on the long chain molecules of materials such as linear polymers.

  22. PSEUDO PLASTIC FLOW Shear thinning systems. make or become less dense or viscous Decrease in viscosity as the shear rate increases. Flow curve passes through the origin. Gives responses on low shear rates. Resulting Thixotropy

  23. PSEUDO PLASTIC FLOW Many Pharmaceutical products liquid dispersion of natural & synthetic gums shows pseudo plastic flow 1. Tragacanth in water 2. Sod. Alginate in water 3. Methyl cellulose in water 4. Sodium CMC in water

  24. PSEUDO PLASTIC FLOW With increase in the shearing stress the disarranged molecules orient themselves in the direction of flow, thus reducing friction and allows a greater rate of shear at each shearing stress. Some of the solvent associated will be released resulting in decreased viscosity. This type of flow behavior is also called as shear thinning system.

  25. PSEUDO PLASTIC FLOW Pseudo plastic flow can be explained by Long chain molecules of polymer.

  26. PSEUDO PLASTIC FLOW The exponential equation shows this flow FN= η G N = no. of given exponent η = Viscosity coefficient In case of pseudo plastic flow, N > 1. i.e. More N >1, the greater pseudo plastic flow of material. If N = 1, the flow is Newtonian.

  27. DILATANT FLOW Certain suspensions with a high percentage of dispersed solids exhibit an in resistance to flow with increasing rates of shear. Such systems actually increase in volume when sheared & are called dilatant.

  28. DILATANT FLOW Dilatant materials "shear thickening systems. " When the stress is removed, a dilatant system returns to its original state of fluidity. Deflocculated suspension containing 50% solid content

  29. DILATANT FLOW A dilatant (also termed shear thickening) material is one in which viscosity increases with the rate of shear strain. Such a shear thickening fluid, also known by the initialism STF, is an example of a Non-Newtonian fluid

  30. DILATANT FLOW In which, particles are closely packed with less voids spaces, also amount of vehicle is sufficient to fill the void volume. This leads particles to move relative to one another at low rate of shear.

  31. DILATANT FLOW So therefore, dilatant suspension can be poured from bottle because in these condition it is fluid. When stress is increased, the particles shows the open packing and bulk of system (void volume is increase) is increased. But the amount of vehicle is insufficient to fill this void space.

  32. DILATANT FLOW Thus particles are not wetted or lubricated and develop resistance to flow Resulting increase in viscosity Finally system show the paste like consistency. Because of this type of behavior, the dilatant suspension can be process by high speed mixers, blenders or mills.

  33. PSEUDO PLASTIC FLOW The exponential equation shows this flow FN= η G N = no. of given exponent η = Viscosity coefficient In case of Dilatant flow, N < 1. In which N < 1, and decrease as the dilatancy increase If N = 1, the flow is Newtonian.

  34. THIXOTROPY The property of becoming less viscous when subjected to an applied stress, shown for example by some gels which become temporarily fluid when shaken or stirred Thixotropy is a rheological property whereby the viscosity of a liquid decreases when it is agitated Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity

  35. Thixotropy in Formulation In suspension, particles will not settle down in the container (gel form), will become fluid (sol) on shaking for a dose to dispense. At rest, it will retain its consistency to maintain the particles suspended. This is also applied to emulsions, lotions and creams. Parenteral suspensions used for intramuscular depot therapy, e.g. procaine penicilline G 40- 70% w/v in water

  36. THIXOTROPY “Change by touch” Thixotropy is defined as an isothermal & comparatively slow recovery process on standing of a material of a consistency lost through shearing. This is applied for plastic & pseudoplastic system This is also called as gel to sol to gel transformation.

  37. ANTITHIXOTROPY This is also called as negative thixotropy, this represents an increase in consistency on the down curve. The down curve shifts to the right of the up curve. This is also called as sol to gel to sol transformation

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