Dilatant fluids, or shear thickening fluids, exhibit increased viscosity with applied shear stress, behaving more like solids under pressure due to particle interactions in heterogeneous systems. This phenomenon is observed in colloidal suspensions, influenced by the ratio of interparticle forces, leading to hydroclustering and order-disorder transitions in particle arrangements. Examples include mixtures like cornstarch and water, as well as non-food substances such as wet sand and slime.

1. Dilatant fluids are basically shear
thickening fluids and vice versa…
Presented by-
Vedant sawant
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2. • DILATANCY-
a phenomenon caused by the nature of
the stacking or fitting together of particles
or granules in a heterogeneous system, such as the
solidification of certain sols under pressure.
• Dilatant fluids
 a non-Newtonian fluid
 shear viscosity increases with applied shear stress.
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3. • Dilatant fluids(contd)
• This behaviour usually occur
in suspensions.
• as the shear rate is increased,
viscosity of the system also
increases.
• This behavior observed
because the system crystallizes
under stress and behaves more
like a solid than a solution.
• presence of suspended
particles affects the viscosity
of a solution. 3

4. •Non newtonian behaviour- deviation from newton’s law
of viscosity.
•Newton’s law of viscosity-ratio of shear stress to shear
rate is a constant.
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5. Shear thickening behavior of dilatant fluids
• Dilatancy in a colloid , dependent on the ratio of
interparticle forces.
• As long as interparticle forces like Van der Waals
forces dominate, the suspended particles
remain in ordered layers.
• Once shear forces dominate, particles enter a
state of flocculation ; they begin to behave like a
solid.
• When shear forces are removed, the particles
spread apart and once again.
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6. • Shear thickening behavior occurs when
colloidal suspension transitions from a
stable state to a state of flocculation.
• highly dependent on the volume fraction
of solid particulate suspended in the
liquid.
• higher the volume fraction, less shear
required to initiate the shear thickening
behavior.
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7. Theories behind shear thickening
behavior of dilatant fluids
1. Hydroclustering
• particles of a stabilized suspension
transition from an immobile state to
mobile state
• small groupings of particles form
hydroclusters
• increases the viscosity.
• composed of particles momentarily
compressed together, forming an
irregular, rod-like chain of particles .
• The particles have extremely small
interparticle gaps.
• additional hydroclusters will form through
aggregation. 7

8. 2. Order to disorder transition
• At relatively low shear rate, the repulsive particle-
particle interactions keep the particles in an
ordered, equilibrium structure.
• At shear rates above the critical shear rate, the
shear forces pushing the particles together.
• overcome the repulsive particle-particle
interactions.
• This forces the particles to come out of their
equilibrium positions.
• This leads to a disordered structure, causing an
increase in viscosity. 8

9. Dilatant fluid examples
1. Cornstarch and water(oobleck)
• 1:1.25 mixture of water and cornstarch
• It is a liquid, but when stirred it becomes thicker and
more difficult to stir.
• If hit with a hammer, it will shatter like a brittle
solid; but if left it will return to a liquid.
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10. 2 Chilled caramel topping
• The sudden application of force—by stabbing the
surface with a finger, or rapidly inverting the
container holding it—causes the fluid to behave like
a solid rather than a liquid.
• More gentle treatment, such as slowly inserting a
spoon, will leave it in its liquid state.
• Trying to jerk the spoon back out again, will trigger
the return of the temporary solid state.
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11. Non -food examples of dilatant fluids
1. Wet sand
2 Slime
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