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Ceutics II Test 1
Part 1(Rheology)
| Question | Answer |
|---|---|
| Which of the following have flow properties:solid,liquid,or gas? | All of them |
| What represents the internal friction of a system and is the resistance to flow? | viscosity |
| What determines the system viscosity? | The strength that a layer exerts on adjacent layers. |
| Which type of fluids have a linear relationship between rate of shear and shearing stress? | Newtonian Fluids |
| What is the Newtonian law of flow? | The higher the viscosity, the greater the shearing stress required to produce a certain rate of shear. |
| How do you calculate rate of shear? | G=dv/dr G-rate of shear dv-thickness of layers dr-difference of velocity |
| How do you calculate shearing stress given the force? | F=force/A F-shearing stress A-area |
| Calculate shearing stress or rate of shear given the other. | F=nG F-Shearing stress n-coefficient of viscosity(poise) G-Rate of shear |
| The greater the force the ______ the rate of shear. | greater |
| What are the three non-Newtonian flows? | Plastic flow pseudo-plastic flow dilatant flow |
| What is the relationship between viscosity and fluidity? | Fluidity is the reciprocal of viscosity 1/n |
| How do you calculate kinematic viscosity? | viscosity(n)/density(p) units are stokes or centistokes depending on poise or cp |
| What is poise? | The force required to move adjacent layers 1cm apart at 1cm/s velocity. |
| Differentiate plasic and elastic. | plastic=flexible elastic=rigid |
| What does a Newtonian rheogram look like? | a linear line going through the origin |
| What does a Platsic flow rheogram look like? | curved at the bottom but linear going up. -intersects x-axis at yield value(f) |
| What does a pseudoplastic flow rheogram look like? | curve increasing in slope . . .. ... |
| What does a Dilatant flow rheogram look like? | curve decreasing in slop ... .. . . |
| What do plastic flow compounds act as if: 1)F<f 2)F>f F=shearing stress f=yield value | 1)elastic(solid) 2)Newtonian |
| What kind of flow are characterized by bingham bodies? | plastic flow |
| How do you calculate plastic viscosity? | plastic viscosity(U)=(F-f)/G units are still poise |
| What are flocculated suspensions an example of? | a plastic material |
| The more flocculated the suspension, the _______ the yield value is. | larger |
| What contributes to yield value? | van der waals forces inter-particle friction |
| What flow is in between Newtonian and plastic? | pseudo-plastic flow |
| What flow represents shear thinning systems? | pseudo-plastic flow |
| What is apparent viscosity? | viscosity at a given F that is determined by the slope of the tangent. |
| Natural and synthetic gums are an example of which material? ex-tragacanth, methylcellulose, Na-CMC, Na-alginate | pseudo-plastic material |
| With increasing force in pseudo-plastic materials, uncoiling cause the viscosity to _______. | decrease **greater flow |
| Which flow is opposite to pseudo-plastic and viscosity increases with force? | Dilatant flow |
| What is the flow, looking at F^N=nG 1)F=1 2)F>1 3)F<1 | 1)newtonian 2)pseudoplastic 3)dilatant |
| Which system is shear thickening? | dilatant flow |
| Which system is characteristic of suspensions(>50% solids) with small deflocculated particles ? | Dilatant |
| Are dilatants closed packing or open dilated with increasing rates of shear? | open dilated |
| What are the two one point viscometers and which type of fluid can they measure? | - Capillary and Falling Shpere - Newtonian fluids only |
| What are the two multipoint viscometers and which fluids do they measure? | -Cub&Bob and Cone&Plate -Newtonian and Nonnewtonian |
| Differentiate one point and multipoint viscometers. | -One-point systems operate at only at a single shearing stress(F) and give only one force of shear(G) -Multi-point work at multiple shearing stresses (F) and provide complete rheograms |
| Give the relating names to each 1)Capillary Viscometer 2)Falling ball viscometer 3)Cup&Bob viscometer 4)Cone&plate viscometer | 1)Ostwald 2)Hoeppler 3)Rotovisco 4)Brookfield |
| Describe the Capillary Viscometer | Measures the time for a liquid to pass between two marks as it goes down a capillary tube. Then its compared to water to obtain relative viscosity. use n1/p1t1=n2/p2t2 |
| Describe the Falling ball viscometer | the rate the ball falls is an inverse function of the viscosity. n=t(Sb-Sf)B B=factor provided by manufacturer |
| Describe the Cup&Bob viscometer | sample is sheared between cup and bob. rotation causes torque which is proportional to the viscosity of the sample |
| What is the disadvantage of a cup&bob viscometer called "plug flow"? | shearing stress decreases with the distance away from bob so use as big of a bob as possible |
| Differentiate Couette type and Searle type rotations. | Couette type is cup rotation Searle type is bob rotation. |
| Describe cone and plate viscometer. | the sample is sheared at the gap between cone and plate. n=CT/V C-instrumental constant T-shearing stress(read off scale) V-rate of shear |
| What happens when shearing stress is removed from Newtonian system? | rate of shear decreases exactly as it increases. linearly |
| What happens when shearing stress is removed from plastic systems? | rate of shear decreases (in a linear fashion) slower than it increases. (shifts left) |
| What happens when shearing stress is removed from pseudo-plastic systems? | rate of shear decreases (in a curved fashion) slower than it increases. slow recovery |
| What is thixotropy? | an isothermal and comparatively slow recovery of consistency lost through shearing |
| What are rheograms of thixotropic systems dependent on? | rate at which stress is applied and released and the length of time of the stress |
| What kind of system and flow is thixotropy applicable to? | pseudoplastic flow shear-thinning systems only |
| What are thixotropic systems like at rest? | a loose 3D network resembling a gel |
| What are thixotropic systems like under shear flow? | loose network breaks resulting in shear thinning and gel to solution transformation |
| Once stress is removed, do thixotropic systems recover instantaneously? | no asymetric particles have to overcome brownian motion. |
| What is negative thixotropy? | upon stress, viscosity increases rather than decrease |
| What kind of flow is associated with negative thixotropy? | pseudo-plastic flow |
| When a negative thixotropic material is left sitting is the material sol-like or gel-like? | sol-like |
| What is rheopexy? | a material that increases viscosity at a much faster rate when under shear than when allowed to rest. |
| What does rheopexy apply to? | Dilatant flow and shear thickening systems |
| How do you measure thixotropy? | by building a hysteresis loop |
| What expresses thixotropy? | thixotropic coefficient |
| How are hysteresis loops used to measure thixoptropy? | 1)determining structural breakdown with time at a constant rate of shear OR 2)determining structural breakdown due to increasing rate of shear |
| Why is thixotropy desirable? | it keeps a high container consistency for suspensions(etc) and yet pour and spread easily when needed. -also good for I.M slow release yet easy to inject |
| What are poloxamers? | aka Pluronics (clear/nontoxic/waterbase gels) --sol at low temp/conc(newtonian) --non-newtonian at high temp/conc Ex-aloevera gel, plural??? |
| What kind of system do you want in opthalmic solutions? | shear thinning so that when you blink it keeps at high shear rate |
| Does viscosity increase or decrease with increasing temperature? | decrease (melting) |
| What is the equation used to solve for activation energy? | ln(n)=ln(A)+(Ev/R)*(1/T) n=viscosity A=constant depending on MW Ev=Activation energy T=kelvin R=8.314 J/mol*k |
| How do you find activation energy given the temperatures and viscosity? | 1)convert temp to kelvin and take inverse 2)plot ln(n) vs 1/T 3)Find equation of line ln(n)=###### + ####x 4) the ##### in front of x= Ev/R 5)divide number by R *units in example were cal/mol |
| Liquid property is to viscosity as solid property is to what? | elasticity |
| Liquid property is to Newton as solid property is to who? | Hooke |
| What is Hooke's law? | E=F/y elasticity=stress/strain |
| What is viscoelasticity? | the possession of both viscous properties of liquids and elastic properties of solids |
| What do viscoelasticity measurements test? | rheologic ground state |
| Match quantifiable properties with these psychorheologic properties. 1)body 2)slip 3)spreadability 4)feel 5)sensory satisfaction | 1)viscosity 2)yield value 3)thixotropy 4)kinematic viscosity 5)viscoelasticity |
Created by:
JCummins
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