Evaporation Rate and Its Dependencies

Evaporation Rate and Its Dependencies

Theory

Evaporation rate is defined as the amount of material evaporated per unit time from a surface. It is an important parameter in processes like thin film deposition.

Factors Affecting Evaporation Rate

1. Equilibrium Vapor Pressure

Equilibrium vapor pressure is the pressure exerted by vapor when it is in equilibrium with its solid or liquid phase.

Higher vapor pressure → Higher evaporation rate
Lower vapor pressure → Slower evaporation

2. Molecular Weight

Molecular weight determines how easily particles escape from the surface.

Lower molecular weight → Faster evaporation
Higher molecular weight → Slower evaporation

3. Temperature Dependency

Temperature strongly affects evaporation rate. As temperature increases, vapor pressure increases rapidly, leading to higher evaporation.

Higher temperature → Exponential increase in evaporation rate

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Mathematical Expression

Rate ∝ P / √(M · T)

P → Vapor pressure
M → Molecular weight
T → Absolute temperature

Summary

• High vapor pressure increases evaporation
• Low molecular weight increases evaporation
• Temperature has the strongest effect