Silicon plasma-polymerized

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

It is also important to recognize that HFE plasma is a good etching agent for silicon, and the substrate (plasma polymerized TMS) contains silicon. Consequently, the deposition of HFE plasma polymers on the surface might partially etch the loose... 

Figure 29.1 A simplified schematic view of a plasma polymerization coating applied on a phase-separated silicone-hydrogel polymer.

SAIE by low-pressure plasma polymerization of TMS was extended to pure iron [8]. Polished pure iron samples (3x3 cm) were plasma pretreated before deposition of TMS plasma polymer. Two to six samples of pure iron were placed on a CRS plate (15 X 10 cm) maintaining the electrical contact so that each pure iron sample acts as the cathode of DC discharge. A few small pieces of silicon water were also placed on the CRS plate to maintain the electrical contact and were used for the estimation of the thickness of TMS plasma polymer by ellipsometry. 

VOCs can also be removed by applying vacuum and using composite membranes as, for example, in the VaporSep process commercialized by the MTR, where a porous support is used for a silicone membrane coating in a spiral wound configuration. Hydrophobic polypropylene hollow fibers with an ultrathin and highly VQC-permeable plasma-polymerized nonporous silicone skin on the outer surface can be also effective [31-33]. 

NH, NH-, -CN), silicon and olefinic double bonds are more polymerizable while those containing oxygen (e.g. -C=0,-0-,-0H), chlorine, aliphatic hydrocarbon and cyclic hydrocarbons tend to decompose. Brown (13) reported in his studies of a series of vinyl halides that the dihaloethylenes polymerize more rapidly than the corresponding monohalides and that chlorides and bromides polymerize more rapidly than the fluorides. Kobayashi, et. al. (IJ) found that the additons of certain halo-genated compounds to hydrocarbon monomer streams often dramatically increases the polymerization rate. Thus, these halogenated compounds may be considered to act as gas phase catalysts for the plasma polymerization of hydrocarbons. 

Stancell et. al. ( 0) reported the possible use of ultrathin films deposited onto relatively permeable substrates as permselective membranes. Ultrathin and highly crosslinked coatings effectively distinguish between molecules of different sizes and increase the permselectivity of the substrate film. Chang et. al. ( ) demonstrated that the permeability coefficient of silicone rubber to oxygen decreased noticeably after depositing a plasma-polymerized ethylene film on the surface. Colter, et. al. (92.93) found similar effects of plasma polymerized films as diffusion barriers in controlled-released drug delivery systems. 

Hexamethylcyclotrisilazane and hexamethylcyclotrisiloxane were purified by rectification in vacuum following which their purity was tested by gas chromatography. Plasma polymerizations were carried out in an electrode system described previously ( ). Thin film were deposited in a 20 kHz glow discharge on the surface of stainless steel electrodes or on gold or silicon electrodes in the case of thin layers intended for further studies of electrical properties. All polymerizations were carried out at constant discharge parameters current density j = 1 mA/cm2, discharge duration t = 30 sec, monomer vapour pressure p = 0.3 Torr. 

Our earlier structural studies (15) have shown that in the case of plasma-polymerized HMCTSN and HMCTSO other crosslinking reactions may take place. Ultraviolet radiation emitted by the plasma may cause a hemolytic cleavage of Si-C and C-H bonds in SiCH groups, fo-lowed by crosslinking in the polymer via formation of methylene and ethylene linkages between silicon atoms. 

In the HBMs described above, enhanced stability derives from multivalent inter-molecular interactions among linear lipo-polymers in the outer monolayer, relative to the fewer number of interactions expected per monomer in an unpolymerized HBM. An alternative strategy is to link covalently the lipid tail(s) to the inner monolayer, as described by Krishna et al. [60], They used a four-step approach to create poly(acrylatePC) coatings on silicone catheters (Fig. 3) (1) plasma polymerization of allyl alcohol on the catheter surface (2) reaction with acryloyl chloride (3) vesicle fusion of monoacryloyl-terminated lipids on the acryloyl functionalized... 

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