Development of Dielectric Barrier Discharge Apparatus for Continuous Treatment of Polymer Tubes and Plasma-Induced Surface Wettability Effects
Creators: name: Myers, Andrew P
Publisher: name: Purdue University Graduate School
Year: 2023
Subjects: Aerospace engineering not elsewhere classified

description: In the time after their conception, Dielectric Barrier Discharge (DBD) systems have become highly utilized in the field of plasma research, with applications ranging from medicine to water treatments to airfoil design. One of the more recent applications for DBD systems has been the plasma treatment of polymers, overcoming the deficits of previously used chemical treatment systems such as environmental hazards, high cost, and other complexities. A novel development occurring within the past three years was the use of a DBD system to treat the inner surface of small-diameter polymer tubing to improve the wettability and adhesion characteristics as compared to untreated polymer tubing. This work is interested in improving that DBD system. This thesis focuses on the development and implementation of two additional systems for an atmospheric pressure DBD system that treats the inner surface of narrow-diameter polymer tubes. The first, a pulsed-DC HV generator, will improve the plasma treatment. The fast rise times of the applied voltage prevent any stochastic behavior in plasma ignition and reignition, the resulting homogeneity of the plasma means that the plasma conditions of the treatment are more easily reproduced, and the increase in plasma intensity allows for quicker treatment of the tubing, the feed rates can reach the level of industrial production without lessening the effects induced by the treatment. The second, a Capstan-driven spooling system, will also improve the industrial capabilities of the DBD system. The higher feed rates that the spooling system reaches provide a means to rapidly produce treated tubing at a continuous rate, and the user-friendly interface means that system operation increases to a broader range of potential personnel. Investigation of the effect that tube feed rate (plasma exposure time) has on surface wettability was performed for the feed rates of the spooling systems. Feed rates of 2.5, 10, 50, 200, and 800 mm/min were performed on tubing samples for a 100% Helium plasma at a power level of 5 mW and a 98%He-2%O2 plasma at a power level of 20 mW. The temporal evolution of wettability was determined by taking the water contact angle (θ) of the treated tubing surface 0, 1, 2, 4, 16, 24, and 120 hours after plasma treatment. The resulting water contact angles initially fluctuate but eventually decay to reach a steady-state hydrophilicity that remains up to five days. The steady-state contact angles ranged from 42.3o &lt; θss &lt; 70.2o for a Helium plasma and 39.9o &lt; θss &lt; 62.7o for a Helium-Oxygen plasma. Investigation of the plasma power achieved with a pulsed-DC HV generator was also performed. The pulsed DC-driven plasma, which has a characteristic rise time of ~300 ns, ignites at Vbd = 4.5 kV. This breakdown voltage is 1.3 times higher than the minimum for the system, Vbd,min = 3.45 kV, so the resulting overvoltage of the pulsed-DC generator is approximately 1.3 times the minimum breakdown voltage. The electrical power deposited to the discharge for the pulsed-DC driven discharge (133.2 mW) is 6 times the power of the previous AC-driven discharge (21.4 mW). Resulting surface wettability was also calculated for the two generators. The stronger plasma treatment of the pulsed-DC HV generator resulted in a steady-state contact angle 11.4o more hydrophilic than the AC HV generator (θss = 44.6o for pulsed-DC-driven discharge compared to θss = 56o for AC-driven discharge).