Physical Pharmaceutics Rheology

Which of the following is true about Newtonian fluids?

• Their viscosity is constant regardless of the applied shear rate.
  

• Their viscosity changes with temperature but is unaffected by shear rate.

• Their viscosity decreases with increasing shear rate.

• Their viscosity increases with increasing shear rate.

What is the general effect of increasing temperature on the viscosity of a liquid?

• Viscosity increases

• Viscosity remains constant

• Viscosity fluctuates

• Viscosity decreases

For a typical liquid, which of the following is true regarding its viscosity as temperature increases?

• The decrease in viscosity with increasing temperature follows an exponential relationship.

• The decrease in viscosity with increasing temperature is linear.

• Viscosity increases with temperature due to increased molecular interactions.

• The viscosity of the liquid becomes independent of temperature after a certain threshold.

In a non-Newtonian fluid, the relationship between shear stress and shear rate is nonlinear. What phenomenon is often observed in fluids exhibiting shear-thinning behavior?

• Viscosity increases as shear rate increases.

• Viscosity remains constant regardless of shear rate.

• Viscosity decreases as shear rate increases.

• Viscosity first decreases, then increases as shear rate increases.

Which of the following best describes the behavior of dilatant fluids when subjected to increasing shear rate?

• Their viscosity decreases significantly with increasing shear rate.

• Their viscosity increases significantly with increasing shear rate.

• They exhibit a yield stress and do not flow below a certain stress.

• They exhibit a constant viscosity over a wide range of shear rates.

The Bingham plastic model is used to describe:

• Fluids that exhibit a yield stress and flow only after this stress is surpassed.

• Fluids whose viscosity is independent of the shear rate.

• Fluids whose viscosity decreases with increasing shear rate.

• Fluids with constant density regardless of temperature or pressure.

In a thixotropic material, which of the following occurs when shear stress is applied over time?

• The viscosity of the material increases gradually.

• The material gradually thickens and becomes more resistant to flow.

• The viscosity of the material decreases, but it recovers once shear stress is removed.

• The material flows as if it were a Newtonian fluid.

why is thixotropy a desirable property in certain pharmaceutical or cosmetic formulations?

• It improves the mechanical properties of the product during packaging.

• It increases the shelf life of the product by preventing phase separation.

• It ensures the product remains stable at both high and low temperatures.

• It allows the product to flow freely under low shear conditions and remain stable under high shear.

In the context of viscosity measurement, what is the primary limitation of the capillary viscometer method?

• It is only suitable for highly viscous liquids.

• It requires a high shear rate to achieve accurate results.

• It is difficult to perform at high temperatures.

• It assumes that the fluid is incompressible and that the flow is laminar.

In a falling sphere viscometer, which factor most directly affects the time it takes for a sphere to fall through a fluid?

• The radius of the sphere.

• The density of the fluid.

• The temperature of the fluid.

• All of the above.