Ablation and Polymerization

These two early findings lead to the concept of competitive ablation and polymerization (CAP) which emphasizes the importance of a balance between polymer formation and ablation [3]. The first finding demonstrated the control of ablation due to extremely reactive fluorine-related species (atomic fluorine, F , etc.) by chemical reactions, and the second demonstrated the role of discharge conditions that control the production of highly ablative species. 

What happens in a low-pressure plasma process cannot be determined in an a priori manner based only on the nature of the plasma gas or on the objective of the process. The plasma sensitivity series of elements involved, in both the luminous gas phase and the solids, that make contact with the luminous gas phase seems to determine the balance between ablation and polymerization by influencing the fragmentation pattern of molecules in the luminous gas environment. 

Figure 10.1 Schematic diagram of the Competitive Ablation and Polymerization (CAP) principle (1) dissociation (ablation) of monomer to form reactive species, (2) deposition of plasma polymer and ablation of solid including plasma polymer deposition, (3) deposition to and ablation from nonsubstrate surfaces, and (4) removal of stable molecules from the system.

Competitive Ablation and Polymerization (CAP) Mechanisms of Glow Discharge Polymerization... 

CAP (COMPETITIVE ABLATION AND POLYMERIZATION) SCHEME OF GLOW DISCHARGE POLYMERIZATION... 

Fig. 8. CAP (Competitive Ablation and Polymerization) (Scheme of glow dndiarge polymerization by H. Yasuda)...

Figure 5. Competitive ablation and polymerization (CAP) and plasma induced polymerization (PIP) mechanisms.

Hiroshi Fukumura received his M.Sc and Ph.D. degrees from Tohoku University, Japan. He studied biocompatibility of polymers in the Government Industrial Research Institute of Osaka from 1983 to 1988. He became an assistant professor at Kyoto Institute of Technology in 1988, and then moved to the Department of Applied Physics, Osaka University in 1991, where he worked on the mechanism of laser ablation and laser molecular implantation. Since 1998, he is a professor in the Department of Chemistry at Tohoku University. He received the Award of the Japanese Photochemistry Association in 2000, and the Award for Creative Work from The Chemical Society Japan in 2005. His main research interest is the physical chemistry of organic molecules including polymeric materials studied with various kinds of time-resolved techniques and scanning probe microscopes. 

Laser ablation of many metallic compounds will produce not only the bare metal ion M+ but also ions such as [MX]+, where X = O, S, Cl. The early bare transition metals ions react vigorously with background water in the mass spectrometers and the [MO]+ ion is always present when metals such as Ti are ablated. The [MX]+ ions can undergo several types of reaction and three types will be considered here substitution, addition, and polymerization reactions. Table II gives examples of the reactions of [MX]+ and [ML]+ ions. 

Unexpected elements in a plasma polymer often are due to the redeposition of ablated materials. The presence of nitrogen found in a plasma polymer of a monomer that does not contain nitrogen can be traced to contamination of the reactor, which has been used for plasma polymerization of nitrogen-containing monomers [1]. The ablation of electrode material has been utilized to create a graded metal-polymer and polymer-metal interfaces to obtain an excellent adhesion [2,3]. Ablation, therefore, could be utilized in a beneficial way in the engineering of interfaces if we know the nature of ablation and how to control it. 

M. F. Jensen, J. E. McCormack, and B. Helbo, Rapid prototyping of polymer microsystems viaexcimer laser ablation of polymeric mould. Lab on a Chip, 4(4), 391-395, 2004. 

Jensen, M.F., McCormack, J.E., Helbo, B Christensen, L.H., Christensen, T.R., and Geschke, O. (2004) Rapid prototyping of polymer microsystems via excimer laser ablation of polymeric moulds. Lab-on-Chip, 4, 391-395. 

For more profound textile surface modifications, gases such as tetrafluoromethane (CF4) are useful. Specifically, tetrafluoromethane will form a thin hydrophobic layer over textile fibers after use within a plasma discharge. There are a number of studies which indicate that ablation accompanies the deposition of these thin films on fiber surfaces. In reference [30], Yip et al. suggested that shorter CF4 plasma exposure time will lead to more efficient polymerization effects, whereby longer CF4 plasma exposures lead to better surface ablation and lowered surface tension. 

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