Rheology
-term used to describe the flow of liquids and deformation of solids.
viscosity, elasticity
Rheology has 2 principle components; what are they?
viscosity
-shearing force required to produce a velocity of 1 cm/sec between two parallel planes of a liquid separated by 1 cm and each having an area of 1cm2.
high
A suspension exhibiting low viscosity should exhibit what kind of shear?
low
A suspension exhibiting high shear should exhibit what kind of viscosity?
Rate of shear
-the difference in velocity between two planes of a liquid separated by an extremely small distance.
G
Symbol for rate of shear?
Shear stress
-the force per unit area required to bring about flow.
viscosity (n) * rate of shear
Formula for shearing stress?
newtonian
Which Rheological system has a shearing stress directly proportional to the rate of shear?
newtonian systems
In _________, viscosity does not change with shear stress.
viscosity; fluidity
In Newtonian systems, the ______ decreases and the _________ as the temperature increases.
colloidal dispersions, emulsions, suspensions, ointments
What are some examples of Non-Newtonian systems?
non-newtonian systems
Which Rheological system exhibits a nonlinear plot of Rate of shear (F) vs. Shear stress (G)?
Newtonian
What type of flow does this graph represent?
Simple Plastic flow
What type of flow does this graph represent?
Simple pseudoplastic flow
What type of flow does this graph represent?
Dilatant flow
What type of flow does this graph represent?
dilatant
These systems increase in volume or dilate when sheared.
Dilatant
Pseudo plastic
Simple plastic
Newtonian
no yield value; viscosity decreasing with increased stress (shear thinning)
What are special characteristics of Pseudoplastic Flow?
Pseudoplastic flow
When stress is applied, long polymers align themselves in the direction of flow, facilitating motion. This applies to what kind of flow?
-Dilatant
-Pseudo plastic
-Simple Plastic
-Newtonian
Dilatant
Which type of flow is observed in highly concentrated suspensions?
-Dilatant
-Pseudo plastic
-Simple Plastic
-Newtonian
Pseudoplastic
Which type of Flow is found in polymers that are in solutions?
-Dilatant
-Pseudo plastic
-Simple Plastic
-Newtonian
non-newtonian shear thinning systems
Thixotropy is only applicable to _________
dilatant
Which newtonian system is a "shear thickening system"?
Dilatant
-increased resistance to flow with increased rates of shear
Dilatant materials
_______ can be poured at low stress.
Dilatant flow
increase in stress= bulk of system expands and particles take on an open form of packing
particles are no longer wetting
Why are dilatant materials resistant to flow?
dilatant flow
Which suspension can become a paste when stress is increased enough?
high-speed mixing, blending, milling
What appropriate precautions are needed when processing dilatant materials?
thixotropy
-comparatively slow recovery of the material structure that lost through shearing.
shearing
-the change of shape, without change of volume, of a layer of the substance, produced by a pair of equal forces acting in opposite directions along the two faces of the layer.