Contact Angle Decay Model to Study Plasma Afterglow Activation of Polymers

Treatment time-dependent contact angles of polyethylene samples activated in the afterglow of a dielectric barrier discharge are investigated. A semi-empirical model is proposed describing the contact angle behavior by two simultaneously occurring exponential decay processes. Fitted parameters are used to examine the influence of barrier thickness, gas flow rate and electrode length on the contact angle decay. Results reveal a faster contact angle decrease with reduced barrier thickness and higher gas flow rate. The influence of each activation process varies when the gas flow rate and the electrode length are changed. The different speed and behavior of contact angle decay are explained by altered active species densities and a changing extent of UV radiation.