A method of decreasing a water contact angle and/or increasing a surface energy of a liquid is disclosed herein, the method comprising exposing the liquid to a plasma treatment. Further disclosed is a plasma-treated liquid exhibiting a decreased water contact angle and/or increased surface energy, compared to the water contact angle and/or surface energy, respectively, of a non-treated corresponding liquid. Methods for combining a first liquid and a second liquid, or for enhancing an adhesion between a liquid and a surface of another substance, the methods comprising exposing a liquid to plasma treatment, are further disclose herein, as well as a method of predicting an apparent contact angle of a liquid droplet on a surface of a substance.

Disclosed is a control circuit of an atmospheric plasma generating device, comprising: a power supply suppling power to the control circuit, a switching element, a first set of resistors, a second set of resistors, a set of Zener diodes, a set of transistors electrically coupled to the switching element, the set of Zener diodes, the first set of resistors and the second set of resistors. The control circuit further includes a capacitor, an inductor, and a set of diodes electrically coupled to the first set of resistors or the second set of resistors.

A system for plasma ignition and maintenance of an atmospheric pressure plasma. The system has a variable frequency alternating current (AC) power source, a transformer, a cable connected to a secondary winding of the transformer, a programmed microprocessor for control of power to the atmospheric pressure plasma. The microprocessor is configured to a) at pre-ignition, power the AC power source at an operational frequency f.sub.op higher than the resonant frequency f.sub.r, b) decrease the operational frequency f.sub.op of the AC power source until there is plasma ignition, and c) after the plasma ignition, further decrease the operational frequency f.sub.op of the AC power source to a frequency lower than the resonant frequency f.sub.r.

A system for determining an operational state of an atmospheric pressure plasma. The system has a transformer for coupling power into the atmospheric pressure plasma, a current sampling circuit configured to sample at least one current pulse flowing through a primary winding of the transformer, and a programmed microprocessor configured to determine, from a waveform of the current pulse, the operational state of the atmospheric pressure plasma. The operational state is one of: a no plasma state, a plasma origination state indicative of an ignited arc expanding into a plasma by gas flow thereinto, and a plasma maintenance state indicative of the plasma being expanded.

A method includes plasma treating one or more surfaces of a metal matrix composite substrate. The metal matrix composite substrate includes a metal matrix and composite fibers. After said plasma treating, the method also includes applying a sol-gel layer on the one or more surfaces of the metal matrix composite substrate.