LCVD coating

A nanofilm of plasma polymer (up to about 100 nm) has sufficient electrical conductance as evidenced by the fact that an LCVD-coated metal plate can be coated by the electrolytic deposition of paint (E coating), i.e., plasma polymer-coated metals can be used as the cathode of the electrolytic deposition of paint (see Chapter 31). Thus, the plasma polymer layer remains in the same electrical potential of the cathode (within a limited thickness) and the work function for the secondary electron emission does not increase significantly. When the thickness of plasma polymer deposition increases beyond a certain value, the coated metal becomes eventually insulated, and DC discharge cannot be sustained. DC cathodic polymerization is primarily aimed to lay down a nanofilm (10-100 nm) on the metal surface that is used as the cathode (see Chapter 13). 

In microwave plasma, electrons adhere to the wall because the microwave energy propagates on surface. In this case, the inner surface of the vacuum chamber becomes the core of the luminous gas phase for LCVD. If the inner surface of a vacuum chamber is the main substrate surface on which LCVD coating is aimed, such as the case of the coating the irmer surface of a plastic bottle, the microwave discharge is the most efficient LCVD. 

Figure 6.1 ESR signal of dangling bond of LCVD coating of trimethylsilane (TMS).

ESR signals [7] observed with LCVD-coated glass rods are shown in Figures 6.5, and 6.6. By removing plasma polymer coating from the surface of a glass rod, it is possible to quantitatively examine both the free spins in the plasma... 

When a polymer substrate is employed the situation becomes much more complex because the formation of free radicals in the polymer matrix by photon irradiation depends on the chemical structure of the polymer and the energy level of irradiation. The adhesion of LCVD coating is generally stronger to a polymer... 

This film system was seen to outperform others not incorporating the adhesion-promoting HFE film when a primer is applied to the LCVD coated alloy surface. The alloy panels were always treated with O2 plasma to remove any organic contaminants from the alloy surface prior to film deposition. The entire steps involved in the plasma coating process are ... 

Carbon fibers treated with HMDSO/O2 plasma showed the highest DPPH consumption per unit surface (2 x 10 mol/cm ) among plasma treatments employed, and also showed a significant reduction of the time needed to reach the maximal temperature (1070 s compared to 1170 s for untreated fibers). These are the similar trends found with plasma-treated X-ray-opaque powders. All of these trends strongly indicate that the plasma-treated fillers acting as the additional initiator of MMA polymerization, i.e., PMMA polymers are covalently bonded to the LCVD-coated fillers. 

Figure 32.22 shows the comparison of average corrosion widths from both (a) SO2 salt spray-tested and (b) Prohesion salt spray-tested IVD panels. Both SO2 and Prohesion test results show that chromate-free LCVD coating systems provided excellent corrosion protection on IVD Al-coated A1 alloys, having comparable or... 

In comparison TMS LCVD coatings in flow system (Tfs), LCVD coating in closed system TMS (Tcs) provided equally good corrosion protection of IVD... 

The three unique and important features of type A LCVD nanofilm—imperturbable surface (Chapter 29), nanoscale molecular sieve (Chapter 34), and new surface state of material (Chapter 24) make LCVD coating an ideal tool in preparation of biomaterials. It should be reiterated that these three features of LCVD films are limited to type A plasma polymers described in Chapter 8, and type B plasma polymers should be excluded in LCVD coatings for biomaterials based on the concept of imperturbable surface. The particularly important aspect is that the LCVD nanofilm becomes the new surface state of the substrate material, i.e., it is not just a coating placed on the surface. The first and second features describe the nature of the new surface state. 

LCVD coating for biomaterials is the neutral approach illustrated by the athrombogenic surface. The advantage of the neutral approach in biomaterials is not well recognized, simply because finding such a surface in the domains beyond the imperturbable surfaces of type A plasma polymers is extremely difficult. 

APPLICATIONS OF LCVD COATING ON SILICONE CONTACT LENS... 

The three key features of LCVD coating ideally suited for biomaterial surface, and the important balance between the bulk properties and the surface properties, could be best illustrated by examples of nanofilms of methane plasma polymer on a contact lens made of polydimethylsiloxane elastomer. Hence, some details of processing factors and their influence on the overall properties of the product are described in the following sections. 

LCVD coating of the inner surface of a small-diameter tube, e.g., 3 mm ID and 10 cm long, requires a special equipment that creates a luminous gas phase in the inside volume of the tube. If such a tube is placed in a reactor used for the coating of... 

Figure 35.14 Effect of LCVD coating on proteins deposition on contact lens surface.

Figure 35.14 depicts the effect of LCVD coating on the deposition of proteins on the contact lens surface in comparison with a commercially available reference lens [6]. The protein adsorptions were measured after continuous wearing, i.e., 1 week for the control and 1 month for LCVD-coated lens shown at left. The deposition on... 

The protein adsorption becomes much more complicated when multicomponent systems are involved. One surface modification to reduce adsorption of one protein could lead to increased adsorption of other proteins, and it is generally very diiScult to reduce the protein adsorption from living biological (multicomponent) system by surface modification. In this context, the remarkable reduction in protein adsorption from a live biological system shown in the figure is an outstanding performance, which is a testimony to the biocompatibility by virtue of an imperturbable surface of LCVD coating. 

When a similar plasma polymerization coating was applied on the surface of a memory-expandable stainless steel stent, whose bare surface has notoriously poor blood compatibility, and implanted in a pig without using any drug to suppress blood coagulation, all five coated samples stayed patent, whereas uncoated stents with drug showed partial to total closure [7]. Such a clear-cut result, i.e., 5 out of 5 patency, has been scarcely seen in any animal experiments, which again seems to indicate the superior biocompatibility of imperturbable surfaces created with LCVD coatings. 

Table 36.1 Cost Estimate of Materials and Equipment for LBL and LCVD Coatings...

Factor Rear-end approach (LBL coating) Front-end approach (LCVD coating) ... 

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