Influence of Tetramethyldisiloxane‐Oxygen Mixtures on the Physical Properties of Microwave PECVD Coatings and Subsequent Post‐Plasma Reactions

Abstract

Coatings deposited by microwave plasma enhanced CVD have potential for applications as protective coatings against mechanical and environmental damage. The properties of plasma polymer coatings can, however, vary markedly with deposition conditions, and we report here that this is also the case for coatings deposited from mixtures of tetramethyldisiloxane (TMDSO) and oxygen. Hardness, modulus, stress, mass, and surface chemical compositions all varied considerably with the TMDSO/O 2 ratio. Post-plasma reactions led to changes in the physical properties of coatings, which were found to be dependent on the oxygen concentration at the time of deposition. Coatings deposited at low oxygen concentration lost mass, became more rigid, became less tensile in stress, and underwent a large increase in hardness and modulus. These coatings were found to craze over periods of up to six months. Coatings deposited at high oxygen concentrations were observed to gain mass, became less rigid, and showed reduced compressive stress. They were more stable but their mechanical mismatch with polymer substrates affects their performance as protective coatings.

Chemical seeding via propanol plasma pretreatment for improving adhesion and properties of PECVD siloxane coatings on polymers

“…This suggests that the pretreatment results in a harder and stiffer coating and potentially that the adhesion is related to these two properties as well. It was shown by Hall et al that an increase in oxygen ratio in the coating resulted in an increase in their hardness and moduli values as they become more inorganic (more siliceous) in nature.…”

“…Coating thickness was also measured with a Bruker Dektak stylus profilometer. Adhesion was monitored to investigate variations with time and changes due to post‐plasma reactions . Initial adhesion characterisation ASTM D3359‐02 was followed, the grade was determined by assessing the amount of coating removed from the cross‐hatch area with adhesive tape, and 3M #600 (pull‐off force on metal 44N/100 mm width) .…”

“…These protective coatings can be deposited in number of different ways including: chemical vapour deposition (CVD), plasma‐enhanced chemical vapour deposition (PECVD) and sputtering . The chemical and physical properties of the coatings can be easily altered by varying the deposition conditions which can include type of precursor, type of process gases, flow rate, temperature, pressure, deposition time, etc . Of particular interest in this study is the deposition via PECVD of amorphous SiO x C y H z (a:SiO x C y H z ) coatings which can also be referred to as siloxane coatings.…”

“…In this study microwave PECVD was used with tetramethyldisiloxane (TMDSO) and oxygen, mixed as process vapours to deposit a siloxane coating onto a plastic substrate . The concentration of the oxygen was increased from low to a higher concentration, this resulted in a ‘graded coating’ . A propanol plasma pretreatment (pretreatment) was employed to alter the properties of the graded coating.…”

Characterising a Custom-Built Radio Frequency PECVD Reactor to Vary the Mechanical Properties of TMDSO Films

“…Protective coatings have been created using organosilane coatings, predominately for polymer substrates. Siloxane precursors, such as hexamethyldisiloxane (HMDSO) [ 1 , 2 , 3 ] and tetramethyldisiloxane (TMDSO) [ 4 , 5 , 6 ], have been used to safely deposit these organosiloxane coatings via plasma-enhanced chemical vapour deposition (PECVD) for many years. TMDSO films can be deposited with controllable mechanical properties by increasing the O 2 concentrations in the monomer feed, which results in harder films and higher Young’s moduli because of the increase of Si-O-Si bonds within the film [ 4 , 5 , 7 ].…”