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27 Cards in this Set
- Front
- Back
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What substances tend to follow a Non-Newtonian rate of flow?
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Colloidal solutions
Emulsions Liquid Suspensions Ointments They fail to follow Newton's equation of flow. |
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What are the 3 types of Non-Newtonian materials?
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Plastic, Pseudoplastic and Dilatant.
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Substances that exhibit plastic flow are called this.
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Bingham bodies
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When does plastic flow begin?
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When the shearing stress exceeds the yield value. The materials are elastic below the yield value.
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What is an example of a pseudoplastic substance?
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A gel
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What is another name for pseudoplastic systems?
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Shear thinning systems
They don't show a yield value like the plastic substances. They show a decrease in viscosity to a lesser extent when shear rate is increased. |
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What is the relationship between Shear rate and viscosity in a Dilatant system?
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Viscosity increases as shear rate increases.
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What is the relationship between Shearing stress and Rate of Shear in a Dilatant system?
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Rate of shear increases with Shearing stress, but fades off.
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What is another name for Dilatant systems?
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Shear-thickening systems
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What is unique about a thixotropic gel?
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It can transform between a gel and solution. The gel is a matrix of gel polymers and adds viscosity.
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What is the advantage of such a system clinically?
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1) Body heat can melt the gel to a solution in the body
2) It improves stability in the gel form. There is less random movement of molecules. |
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What is the Stokes equation?
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Defines the rate or velocity of settling
dx/dt = d^2(P1-Pe)g/18n |
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What is dx/dt?
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rate of settling
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What is d?
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diameter of particles
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What is p1? pe?
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Density of the particle
Density of the medium |
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What is g? n?
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Gravitational constant
viscosity of the medium |
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What 3 factors can enhance the physical stability of a suspension?
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Diameter of particles
Density of medium Viscosity of medium |
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What happens to rate of settling with an increase in particle size?
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It increases
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What happens to rate of settling with increased medium density?
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It decreases
Medium density is the most influential factor |
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What are the 4 assumptions of the sedimentation rate law?
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The settling is unhindered
The suspended particles should be spherical in shape The suspended particles should be truly dispersed and not flocculated The suspended particles should settle in a laminar flow and not under turbulence |
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Behavior and Natural Tendency questions
Do suspended particles have a large or small surface area? |
Large surface area and hence large surface free energy.
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Because of this large surface free energy, the system is thermodynamically unstable. What is its tendency as a result of this?
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To reduce surface free energy to achieve stability.
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What is the equation for Surface free energy?
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Interfacial tension x change in surface area
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Suspended particles can have entrapped air or be hydrophobic. They need to be wetted. What are the two agents that can accomplish this?
How do they work? |
Glycerin - Occupies interparticulate pores and is subsequently displaced by water in the suspension.
Glycerin has viscosity enhancing, solubilizing, preservative and sweetening effects. Surfactants - They dissolve in dispersion medium and lower interfacial tension. |
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What is controlled flocculation? Why is it
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flocculation = aggregation of particles
Reduced particle size = high surface energy |
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This reduced particle size created by a mortar and pestle causes high surface energy. What can be done to increase flocculation?
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Transient bridging - flocculating
The particles will settle relatively quickly and re-disperse much better. |
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What are the three categories of agents?
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Electrolytes - They alter the electrical charge barrier between particles and also can create an inter-particulate bridge.
More effective = Surfactants and Polymers bc they don't create charge on surface but have length and size that forms a physical bridge between particles. Also decrease interfacial tension. Thickening agents |
