Plasma polymerization electrical discharge process

Photopolymerization and Plasma Polymerization. The use of ultraviolet light alone (14) as well as the use of electrically excited plasmas or glow discharges to generate monomers capable of undergoing VDP have been explored. The products of these two processes, called plasma polymers, continue to receive considerable scientific attention. Interest in these approaches is enhanced by the fact that the feedstock material from which the monomer capable of VDP is generated is often inexpensive and readily available. In spite of these widespread scientific efforts, however, commercial use of the technologies is quite limited. 

Figure 8.8 The system pressure dependence of deposition rate of TMS on Si wafer with electrical contact to the powered electrode in DC (cathode), 40-kHz, and 13.56-MHz plasma polymerization processes discharge conditions are 1 seem TMS, 5-W power input.

A general introduction to the field of plasma polymerization is given in Ref. [31]. The plasma used in polymerization processes is the low-temperature plasma or low-pressure plasma, which is usually created by an electric glow discharge caused by, for example. 

Flame, hot air, electrical discharge, and plasma treatments physically and chemically change the nature of polymeric surfaces. The plasma treating process has been found to be very successful on most hard-to-bond plastic surfaces. Table 7.10 shows that plasma treatment results in improved plastic joint strength with common epoxy adhesives. Plasma treatment requires high vacuum and special processing equipment. 

PECVD causes the reactive gases to decompose and enhance chemical reaction rates of the precursors via the electrical discharge rather than via thermal heating. This allows films to deposit at lower temperatures than CVD. The lower temperatures also allow for the deposition of organic coatings, such as, plasma polymers. Usually, the operational pressures in these systems are 0.1-10 Torr, the plasma density in PECVD discharges is 10 -10" cm and the ionization degrees are 10 -10 [6]. The process is also often referred to as plasma polymerization. PECVD/plasma-polymerization processes are performed both at low and atmospheric pressure, as described later. 

The plasma process can be divided into plasma polymerization and plasma treatment (. In the former, organic vapors (monomers) arc subjected to electric discharge, and their polymers are formed, b the latter process, gases that are introduced into the glow discharge are nonpolymerizable in nature (5). The APG plasma process can be applied to both polymerization and surface treatment. Previously, surface fluorination of PET fihns, carbon thin film deposition, and polymerization of ethylene by APG plasma were examined (2,5, 6). However, the preparation of separation membranes by APG plasma treatment has not been reported. 

The most important way of plasma generation, as a medium to conduct the polymerization, is the electric glow discharge. For that a direct (DC) or alternate (AC) current with frequencies ranging from 50 Hz to 5 GHz can be used. A t3q)ical plasma polymerization is conducted at low gas pressure of the order of 10 -10 Pa. The course of process in plasma may vary depending on the method of conducting the reaction. For this reason a distinction between the following is made. 

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