Plasma Polymerization:Theory and Practice
Plasma polymerization is gaining importance for last several years as a tool to modify material surfaces. Organic vapors can be polymerized at low temperatures using plasma enhancement. Plasma polymerization can also be used to produce polymer films of organic compounds that do not polymerize under normal chemical polymerization conditions because such processes involve electron impact dissociation and ionization for chemical reactions.
Organosilicone films prepared by plasma polymerization provide good optical and mechanical properties. Most used monomers in this family of compounds include tetramethylsilane, vinyltrimethylsilane, HMDSO and hexamethyldisilazane containing Si, H, C, O or N atoms. HMDSO is a choice of industries because it is a non-toxic material and no harmful materials are produced during processing.It can be used in production environment without any special safety considerations. Basic research studies on plasma polymerized organosilicones are reviewed by various authors. The films were found to be amorphous and pinhole free.
Various applications of plasma polymer films include anticorrosive surfaces, humidity sensors, electrical resistors, scratch resistance coatings, optical filters, protective coatings, chemical barrier coatings, etc. Metallized surfaces of synthetic materials can be protected against corrosion with a thin polymer layer deposited by plasma polymerization. The processes can be customized to produce hydrophobic or hydrophilic (antifogging effect) coatings.
Scratch resistant coatings have been successfully applied on optical lenses but three-dimensional objects, such as reflectors for the motor car and lighting industries are complicated by the fact that power input may not be uniform over the entire substrate surface during the polymerization process.A magnetron based plasma polymerization process is described here with HMDSO as the active ingredient. Deposition rate, power input, system pressure and chemical analysis results are discussed.
Magnetron Plasma Polymerization results were presented in this paper with respect to flow rate of monomer, power input, XPS analysis of the film etc. It seems that the film had Si, O, C as main elements but target sputtering was present which added Fe, Cr, Ni and color to the film. Corrosion protection of the film was also not to the desired level. Another process is since developed in our labs which provides a better quality film. In any event, plasma polymerization can be used to synthesize materials with custom surface chemistries.