PowerPoint Presentation: AMIST UNIVERSITY MALAYSIA
PowerPoint Presentation: RHEOLOGY The term rheology is derived from the Greek words Rheo, ”to flow, "and logos,' science” Rheology-study of the deformation and flow properties of matter. Rheology can be applied to solid, liquid and gaseous Solid-completely resistance Gaseous-non resistance Liquid- less resistance Focuses primarily on liquid and semisolid Emulsion,paste,cream,lotion tablet coating soln,suspention EX. pouring from a bottle Extrusion from tube Passage through a syringe needle
PowerPoint Presentation: pouring from a bottle Extrusion from tube Passage through a syringe needle
PowerPoint Presentation: Viscosity-resistance to flow of fluid – Units (poise, centi poise, milli poise) Rheology means simply –to study the flow properties of fluids flow viscosity viscosity flow
PowerPoint Presentation: Similar to deck of cards Bottom consider as fixed and top plan layer of liquid moved at a greater Velocity. Then each lower layer will move with a velocity. flow of liquid Top layer velocity Second layer velocity Third layer velocity bottom layer velocity constant
PowerPoint Presentation: A dv dr dv-velocity dr-distance traveled A-area
PowerPoint Presentation: Mathematical equation-viscosity Shear stress = F’/A force per unit area applied to bring liq. flow Flow force Rate of shear Shearing stress Shear stress F (force ) = F’/A G-FLOW F-FORCE Rate of shear G (flow) = dv/ dr , change in velocity with distance Liquid viscosity Shear stress F (force ) to bring rate of shear (flow) apply
PowerPoint Presentation: Relationship between shear stress (force ) and rate of shear (flow) Shearing stress α Rate of shear Force α Flow F’/A α dv/ dr (or) F’/A dv/ dr η (or) G-FLOW F-FORCE F = η G η - coefficient of viscosity
PowerPoint Presentation: viscosity is calculated by η = F/G Coefficient viscosity is defined as the F/G required to maintain Unit difference in velocity between two parallel layers in the liquid. Units (poise, centi poise, milli poise) Kinematic viscosity defined as viscosity divided by density of the liquid. Units (stokes and centi stokes) Fluidity θ = reciprocal of viscosity θ = 1/ η
PowerPoint Presentation: According to flow Newtonian system - liquid that obey newton’s law of flow Non Newtonian systems - liquid that doesn't obey newton’s law of flow
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) G-FLOW F-FORCE Shearing stress α Rate of shear Newtonian flow Force α Flow liquid that obey newton’s law of flow eqn is F= η G shear stress-shear rate relationship is normally represented in the form of a cure namely rheogram Ex.water,glycerin,chloroform,Dil.colloidal soln
PowerPoint Presentation: G-FLOW F-FORCE Yield value Force Liquid fails to flow ( non linear) Force Liquid start to flow (linear) Linear portion extrapolated to x axis at a point Called yield value Plastic flow Particle-bonded Friction force-high Yield value Particle-individual Friction force-nil Futher stress flow Ex.susp,butter,ointment,paste and gel Bingham bodies
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) Pseudoplastic flow Ex. Tragacanth in water Sod. Alginate in water MC in water SCMC in water Curve is not linear Shear thinning system
PowerPoint Presentation: Pseudoplastic flow rheogram - F Ν = η ’G where N is a exponent and η viscosity Pseudoplastic flow
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) Dilatant flow Shear thickening system Ex. Susp.more than 50% deflo-susp Susp . of starch in water Kaolin 12% in water Zinc oxide 30% in water
PowerPoint Presentation: Conti… At rest close packed mini Void volume sufficient vehicle Relatively low consistency Open packed high void volume Insufficient vehicle relatively High consistency Increasing rate of shear
PowerPoint Presentation: THIXOTROPY Thixotropy is defined as an isothermal and comparatively slow recovery, on standing Material, of a consistency lost through shearing POSITIVE THIXOTROPY NEGATIVE THIXOTROPY
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) POSITIVE THIXOTROPY Plastic system Up curve ab Down curve bc (left) a b c Plastic system Pseudoplastic system Pseudoplastic system Up and down curve superimposed
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) Material showing a bulge in the hysteresis Loop(swelling) Ex.aqueous bentonite magma(10-15% by wt) At rest: crystalline plate Are irregularly arranged On shear: crystalline plate Are arranged to form house Of cards
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) The spure value represents a sharp point of Structural break down at a low shear rate in the up-curve Ex.procaine penicillin gel in IM inj
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) NEGATIVE THIXOTROPY Ex.Magnesia Megma Rheopexy is a phenomenon in which a soln transforms to a gel state more readily rather than keeping a soln at rest (gentle shaking)
PowerPoint Presentation: Rate of shear Shearing stress (F) (G) Measurement of thixotropy a b c d t 2 t 1 1/U 1 1/U 2 e
PowerPoint Presentation: Rate of shear Shearing stress (F) (G)
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