Polymeric surfaces chemical vapor deposition

More recently, an approach for low permeability materials is to deposit parylene-C into the poly-(dimethylsiloxane). The base matrix is coated with parylene-C by chemical vapor deposition polymerization in the usual way [78]. Then the parylene-C on the surface is removed by oxygen plasma etching and only what is in the pores of the matrix remains there. 

Nowadays research efforts are mainly directed to the synthesis of microporous and dense inorganic membranes. The multilayer casting method based on sol-gel technology is not the sole approach for the preparation of these membranes. CVD and hydrothermal synthesis are currently used as well as the sol-gel process. CVI (chemical vapor infiltration) for support infiltrated membranes, PE-CVD (plasma enhanced chemical vapor deposition) for surface modification of existing membranes, growing of zeolite membrane layers, pyrolysis of polymeric preciusors have been described as alternative preparation methods... 

Figure 10.6 Si solid-state CP-MAS NMR spectra for imprinted materials prepared by the chemical vapor deposition (CVD) and subsequent hydrolysis-polymerization of SifOCHs). (a)-(d) solid lines represent the imprinted materials on Rh monomer/Si02, and dotted lines correspond to the Si02 support (al)-(dl) difference spectra, which correspond to be surface Si02-matrix overlayers.

Alternatively PAA can be obtained without solvent by vapor deposition polymerization as described first by Salem et al. [2], In this technique the dianhydride py-romellitic and the dianhydride diamine (4,4 -oxidianiline) are codeposited onto a substrate, where they react to form PAA. Again the transformation to Polyimide is obtained by subsequent heating to temperatures up to 350°C. By comparison to spun dn films, initial interaction of the polymer with the substrate occurs in the uncomplexed PAA state. The chemical interaction between PAA and the metal establishes the adhesion of the final polyimide film. This is discussed in this communication for evaporated gold cluster and bulk silver surfaces. 

Other approaches to reducing the membrane pore size are being investigated. Many of them are based on the sol-gel process or chemical vapor deposition as discussed in Chapter 3. An example is the preparation of small-pore silica membranes. Amorphous silica membranes have been prepared from solutions of silicate-based polymers. More specifically, some strategies are employed aggregation of fractal polymeric clusters, variation of sol composition, the use of organic molecular templates and modification of pore surface chemistry [Wallace and Brinker, 1993]. 

Fig. 22.6 solid-state MAS NMR spectra of imprinted materials prepared by the chemical vapor deposition of Si(OCHj) and the subsequent hydrolysis-polymerization. (A-D) The solid lines represent the imprinted materials on SiO, and dotted lines correspond to the SiO support, (a-d) These are difference spectra corresponding to the surface SiO -matrix overlayers [57]... 

Alumina nanoporous templates have also been used in gas-phase growth of CPNTs. It has been reported that isolated nanotubes consisting of poly(p-phenylenevinylene) (PPV) and carbonized-PPV bilayers can be synthesized in an alumina template by chemical-vapor deposition (CVD) polymerization. In a smdy done by Kim and colleagues, CVD polymerization of PPV was carried out by passing monomer vapor through a pyrolysis zone at 625 °C to form precursor polymer nanotubes on the inner surface of the alumina nanochannels. The nanotubes were further thermally treated in vacuum at 270 °C for an extended time (14 h) to be converted into PPV nanotubes. In order to create PPV/ carbonized PPV bilayer nanotubes, the PPV nanotubes were then carbonized at 850 °C... 

A doped Si substrate with as-grown multiwalled (MW) CNTs synthesized through a thermal chemical vapor deposition (CVD) method was attached to a stainless steel working electrode, as shown in Fig. 27a [141]. A P3HT layer with a thickness of 20 nm was directly deposited on the surface of the MWCNTs using an electrochemical polymerization method. The electrolyte for the electrochemical polymerization consisted of 3-HT monomers, BMIMPFs as the ionic liquid, and anhydrous acetonitrile as the solvent. 

The methods of the preparation of parylene nanofibers by oblique angle vapor deposition polymerization have been detailed [114]. Monomer vapors produced by the pyrolysis of chemically functionalized / -xylylene precursors are directed in an oblique angle toward a surface to initiate a structured polymer growth. 

The second way to enhance the usability of ICPs is to apply coatings thereof on textile materials. A very thin layer of conductive polymers can be applied on the surface of textile substrates by solution casting, inkjet printing, in situ polymerization, vapor phase polymerization, and chemical vapor deposition techniques [26—29]. The nano-microscale conductive coatings not only provide high level of conductivity but also preserve the flexibility and elasticity of substrate fibers. However, due to the health-related issues of some carbon-based materials one has to be observant about what is possible and what is not in apparel applications. 

Plasma treatment is a method of modifying the chemistry and often the topography of a surface. It uses a highly ionized, activated gas to react with the molecules of a surface. The plasma gas can vary from an inert gas, such as argon or helium, which would be expected to cause the species at the surface to react with one another, or a polymeric monomer, which could polymerize on the surface and create a thin plasma-treated layer. Plasmas can also be employed to clean surfeces before modification. Chemical vapor deposition is a technique in which the sample is exposed to a vapor that reacts with the surface to modify it. 

Poly(p-phenylenevinylene) (PPV) could be obtained in the form of nanotubes, nanorods and nanofilms by the chemical vapor deposition (CVD) polymerization of a,a -dichloro-/7-xylene followed by thermal dehydrochlorination. The polymerizations were conducted on the inner surface of or inside the nanopores of alumina or polycarbonate membrane filters or on the surface of silicon wafers. The PPVs thus obtained could be thermally converted to the corresponding carbonized tubes, rods, and films. We also could obtain nanopatterns and nanowells of PPV and carbon on silicon wafers by utilizing nanolithographed poly(methyl methacrylate) patterns. The PPV films obtained on the silicon wafers are semicrystalline and produce highly conducting (a 0.7 x 10 Scm ) graphitic films even when treated only at 850 C. Field-emission properties of some of the graphitic nanotubes are also described in this report. 

Vapor deposition is a highly desirable method for modifying surfaces with fluo-ropolymers and has been extensively reviewed [1-6], In chemical vapor deposition (CVD), one or more reactants are metered into a vacuum chamber. Inside the CVD reactor, monomer vapors undergo polymerization and thin film formation in a single step. In the case of vinyl polymerization, monomer vapors are inttoduced directly into the CVD chambers as reactants. Alternatively, less stable monomers, such as difluorocarbene (CFj ), can be generated via in situ reaction (Table 7.1). 

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