Dynamic viscosity

Definition

Dynamic viscosity is a measure of a fluid's resistance to flow when an external force is applied, quantifying how 'thick' or 'sticky' a fluid is. This property is crucial in understanding the flow behavior of colloidal dispersions, as it influences how these mixtures behave under shear stress and affects their stability, processing, and application in various industries.

5 Must Know Facts For Your Next Test

1. Dynamic viscosity is typically measured in units of pascal-seconds (Pa·s) or poise (P), where 1 P = 0.1 Pa·s.
2. In colloidal dispersions, higher dynamic viscosity can lead to increased stability by preventing sedimentation and phase separation.
3. Temperature has a significant impact on dynamic viscosity; as temperature increases, dynamic viscosity usually decreases for most fluids.
4. Dynamic viscosity can be affected by the concentration of particles in a colloidal dispersion; higher concentrations often lead to increased viscosity.
5. In applications like food processing or pharmaceuticals, understanding the dynamic viscosity helps in optimizing formulations for better texture and stability.

Review Questions

• How does dynamic viscosity influence the stability of colloidal dispersions?
  • Dynamic viscosity plays a critical role in the stability of colloidal dispersions by affecting how particles interact with each other. A higher dynamic viscosity can help prevent particles from settling out of suspension, as the increased resistance to flow means that any movement is restricted. This resistance helps maintain homogeneity in the mixture, which is essential for many applications where uniformity is crucial.
• What are the differences between Newtonian and non-Newtonian fluids in terms of dynamic viscosity?
  • Newtonian fluids have a constant dynamic viscosity regardless of the shear rate applied; their flow behavior is predictable and linear. In contrast, non-Newtonian fluids exhibit variable dynamic viscosity depending on the shear rate. This variability can manifest as shear-thinning (decreasing viscosity with increased shear) or shear-thickening (increasing viscosity with increased shear), making non-Newtonian fluids more complex to analyze in colloidal systems.
• Evaluate how temperature changes can affect the dynamic viscosity of colloidal dispersions and its implications for industrial applications.
  • Temperature changes can significantly influence the dynamic viscosity of colloidal dispersions. Typically, increasing temperature lowers the dynamic viscosity, allowing for easier flow and processing. In industrial applications, this relationship means that manufacturers must carefully control temperature during mixing and handling to ensure optimal consistency and stability of their products. A decrease in viscosity at higher temperatures can enhance processing efficiency but may also require adjustments to maintain desired product characteristics as it cools.

Related terms

shear stress:

The force per unit area exerted parallel to the surface of a material, which plays a significant role in the flow behavior of fluids.

non-Newtonian fluids: Fluids that do not have a constant viscosity and whose flow behavior changes under different shear rates, often seen in colloidal dispersions.

yield stress:

The minimum stress required to initiate flow in a material, important for understanding how colloidal systems behave under applied forces.