Surface Tension

Definition

Surface tension is the property of a liquid that causes its surface to behave like a stretched elastic membrane, due to cohesive forces between liquid molecules. This phenomenon is crucial in understanding fluid behavior at interfaces, influencing how liquids interact with solids and gases. Surface tension plays a vital role in various applications, especially in microfluidics and nanofluidics, where controlling fluid behavior at small scales is essential.

5 Must Know Facts For Your Next Test

1. Surface tension is typically measured in units of force per unit length, such as Newtons per meter (N/m).
2. The value of surface tension varies with temperature; generally, it decreases as the temperature increases.
3. Surface tension enables small insects, like water striders, to walk on water without sinking.
4. In microfluidics, surface tension affects droplet formation and movement within channels, influencing device performance.
5. Additives like surfactants can significantly reduce surface tension, altering how fluids behave at interfaces.

Review Questions

• How does surface tension affect the behavior of liquids in microfluidic devices?
  • Surface tension plays a critical role in microfluidic devices by influencing how liquids interact with channel surfaces and with each other. It determines the shape and stability of droplets within channels, impacting flow rates and mixing. Understanding these effects allows engineers to design more effective microfluidic systems for applications like drug delivery and biochemical analysis.
• Discuss the relationship between cohesion and surface tension in liquids.
  • Cohesion refers to the attractive forces between molecules of the same substance, which are responsible for surface tension. In a liquid, molecules at the surface experience an imbalance of forces because they are pulled inward by neighboring molecules more than they are pulled outward. This creates a net effect that forms a 'skin' on the liquid's surface, demonstrating how strong cohesive forces contribute to higher surface tension.
• Evaluate how temperature variations impact surface tension and the implications for fluid dynamics in both macro and micro scales.
  • Temperature variations directly influence surface tension; as temperature increases, surface tension usually decreases due to increased molecular motion disrupting cohesive forces. This shift can significantly affect fluid dynamics on both macro and micro scales. In larger systems, reduced surface tension can enhance mixing and flow rates. Conversely, in microfluidics, lower surface tension may alter droplet formation and stability, thereby affecting device efficacy in applications like diagnostics and chemical synthesis.

Related terms

Cohesion: The attractive force between molecules of the same substance, which contributes to surface tension in liquids.

Capillarity:

The ability of a liquid to flow in narrow spaces without the assistance of external forces, often influenced by surface tension.

Meniscus: The curved surface of a liquid in a container, which is shaped by the balance of cohesive and adhesive forces, related to surface tension.