Deposition of functional coatings from acrylic acid and octamethylcyclotetrasiloxane onto steel using an atmospheric pressure dielectric barrier discharge

A parallel plate dielectric barrier glow discharge operating at around atmospheric pressure was used to deposit functional coatings onto thin (< 3 mm) sheets of steel. An organic precursor was introduced with helium into a mixing chamber connected to the plasma region. X-ray photoelectron spectroscopy showed that at high precursor flow rate and low power, the monomer was only slightly fragmented during the plasma process. Coatings containing a range of concentrations (12.6 to 29.7%) of carboxylate were prepared from acrylic acid. The surfaces with higher concentrations of carboxylates had low (< 20°) contact angles with water. Coatings with a range of concentrations of carbon, silicon and oxygen were prepared from octamethylcyclotetrasiloxane. Extremely hydrophobic coatings (contact angles > 130°) were produced using lower power and higher flow rate of octamethylcyclotetrasiloxane whereas relatively more hydrophilic coatings (contact angles 50 to 100°) resulted when a lower flow rate of octamethylcyclotetrasiloxane was used.