The influences of vapor environment and temperature on the contact angle-drop size relationship

Abstract

Advancing contact angles have been measured for the systems water-PTFE, water-copper, water-stainless steel, n-decane-PTFE, n-undecane-PTFE, and cyclohexane-PTFE using drop sizes varying in base diameter from 1–15 mm. For the water-PTFE/copper/stainless steel systems, a decrease in contact angle with decreasing drop size is observed in saturated argon or nitrogen at 25°C. An increase in contact angle, however, occurs with decreasing drop size at the boiling point for water drops residing on Teflon PTFE and copper in its vapor. For n-decane and n-undecane drops on a Teflon PTFE surface in argon saturated with their respective vapors at 25°C no change of contact angle with drop size is observed. However, for cyclohexane there is a change which is attributed to surface absorption. In further experiments where the water drops residing on a PTFE surface were surrounded by n-decane, n-undecane, or cyclohexane saturated argon vapors at 25°C no change of contact angle with different environments is detected, demonstrating that the equilibrium film pressure is negligible.