Surface modification process using plasma

Fig. 8.8 Surface modification processes using the plasma dischaige [53]...

PDMS in its native form does not possess reactive groups that can be used for the covalent attachment of NAs [51]. However, the PDMS surface can be plasma induced oxidized and then fimctionaUzed with organosilanes carrying the desired head group. For example, a PDMS surface has been modified with 3-mercaptotrimethoxysilane to yield a thiol-terminated surface, to which a 5 -acrylamide modified DNA has been covalently attached [52]. See Fig. 13 for a representation of the PDMS surface-modification process. 

As effective as these surface modification processes might be, they present limitations in terms of the extent to which the surfaces of polymers can be modified. Plasma-induced grafting offers another method by which chemical functional groups can be incorporated. In this process, free radicals are generated on the surface of a polymer through the use of an inert gas plasma. Because of the nonreactive nature of the inert gas plasma, surface chemical modification of the polymer does not occur. If the polymer surface that has been... 

Polyolefins, such as PE and PP, are commonly used in many applications in the biomedical sector. PE and PP can achieve biocompatible and antimicrobial properties using the suitable surface treatment [131, 132]. Many modification methods of the polymer surfaces have been employed, for example, techniques based on the plasma treatment [133]. A deposition of chitosan on the plasma-pretreated PP surface provides antifungal and antibacterial properties because chitosan exhibits an efficient antimicrobial activity [134]. If PE films were modified by a multistep process using plasma discharge, carboxylic groups and antibacterial agent can be developed over the surface. Immersion of these films into the solution of chitosan leads most likely to the adherence of a chitosan monolayer on the treated film. Small concentration of chitosan was enough for the induction of antimicrobial properties to the modified material [135]. 

Plasma treatment refers to the surface modification processes of materials using nonequUibrium gas plasmas. Nonequilibrium plasmas with a low degree of ionization, so-called cold plasmas or low-temperature plasmas, are mainly composed of electrons, ions, free radicals, and electronically excited atomic and molecular species. These highly reactive plasma species interact nonthermally with material surfaces and can react with and bond to various substrate surfaces or combine together to form an ultrathin layer of plasma coating and consequently alter the surface chemistry and surface properties. The plasma-treated nanoparticles and/or nanotubes with desired surface functionalities can strongly interact with liquid molecules and thus better disperse into the base fluid to form stable suspension. 

In spite of these disadvantages, plasma treatment of polymers is an attractive process to produce the required surface modification. By using different types of gas, various chemical functionalities can be introduced on the surface. In general, more uniform surfaces are produced by plasmas than by flame and corona treatments. The modification is typically confined to the surface without changing the bulk physical and chemical properties of the pol)uner. 

The fundamental surface-modification methods applied to solid fillers in polymer biocomposites, such as those previously outlined, are based on techniques and surface chemistries that have been utilized for several decades. More recently, new methods have been applied to the surface modification of solid fillers intended for use in polymeric biocomposites for orthopedic applications. Plasma polymerization forms polymeric materials, such as nanoscale-thick polymer coatings, via partially ionized gas (plasma) (Larranaga et al., 2013 Nichols et al., 2007). This rapid and solvent-free alternative approach to the conventional wet-surface modification processes previously described has several advantages that may be particularly appealing for the... 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

In the following section, a new technique of surface modification of fillers and curing agents will be discussed plasma polymerization. This technique allows for surface coating of powders, whereby the chemical structure of the coating is determined by the monomer used for the process. The morphology of the substrate is preserved, which is an important precondition for filler treatment. The polarity of the functional groups can be chosen to fit the matrix of the polymer wherein it will be applied. 

The surface chemical structure of several thin polyimide films formed by curing of polyamic acid resins was studied using X-ray photoelectron spectroscopy (ESCA or XPS). The surface modifications of one of the polymer systems after exposure to KOH, after exposure to temperature and humidity, after exposure to boiling water, and after exposure to O2 and 02/CF plasmas were also evaluated. The results showed imide bond formation for all cured polyimide systems. It was found that (a) K on the surface of the polyamic acid alters the "normal" imidization process, (b) cured polyimide surfaces are not invarient after T H and boiling water exposures, and (c) extensive modifications of cured polyimide surfaces occur after exposures to plasma environments. Very complex surfaces for these polymer films were illustrated by the C Is, 0 Is, N Is and F Is line characteristics. 

This fibre and fabric modification is based on photophysical and photochemical processes induced by exposure to plasma gases. Reactive gases are used to create chemical fibre surface modifications such as repellency of water, oil and soil and higher fibre resistance against aggressive chemicals. These modifications are mainly restricted to the fibre surface to avoid damaging the fibre bulk, for example... 

Above all of these requirements, SAIE must produce products that are superior to the conventional products. In other words, low-pressure plasma SAIE is not an alternative process it should be a new approach to create superior composite materials that could not be obtained by other means, which is of utmost importance with respect to the use of LCVD. It is often mentioned that plasma polymerization was successfully used in the surface modification but that a conventional, more economical, wet chemical process later replaced it. Such an attempt to use LCVD process based only on the laboratory curiosity is an absolutely wrong approach. This aspect is explored in Chapter 12. 

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