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.