Wet Chemical Surface Modification

with a self-cleaning Ti02 layer, exhibited better hardness and scratch resistance as well as good photocatalytic and mechanical properties. 

On the other hand, treatment of these surfaces first with ethyl chloroformate followed by pentadecylfluorooctylamine produced a hydrophobic fluorinated surface. Modifying a pristine polyolefin surface allows for further processing of the polymer, an increase in the appHcation range, and impact of the material in the market. 

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The possibility of a selective interaction between proteins and the outermost surface of polyelectrolyte multilayers [108] may become of outstanding importance in the development of engineering protein resistant surfaces for various biomedical applications by wet chemical surface modification. 

In wet chemical surface modification, a material is treated with liquid reagents to generate reactive functional groups on the surface. 

The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

In order to metallize a polymer surface, electroless plating can be applied. This process typically consists of a pretreatment process in order to improve the adhesion. In the second step a surface seeding of the electroless catalyst is done. Wet chemical methods of pretreatment are using strong acids such as chromic acid, sulfuric acid and acidified potassium permanganate in order to achieve a surface modification of the polymers (96). 

Biomaterials are non-viable materials used in medical devices, which are biocompatible with minimal non-specific protein adsorption. This paper describes some functionalization techniques of surfaces against non-specific protein adsorption, such as (1) photo-immobilization, (2) y-activation or a rf plasma modification and (3) a wet-chemical treatment. The modification changes the chemical surface composition within the first 10 nm. 

Surface modification prior to metallization is another important area of research. For example, presputtering can be an important treatment for adhesion enhancement (21,22) but contamination effects due to redeposition effects are common. Wet chemical treatments and dry (gas phase) etchings are other areas of oretreatments under active current investigation (44,45). 

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

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. 

The hydrophobicity of the surface prevents the wetting by tear and tends to expose dry surface of a contact lens. Therefore, rapid dehydration of the corneal tissues could occur, which could cause the damage of corneal epithelium. However, this explanation seems to be oversimplified in light of the adsorption of protein, which makes a hydrophobic surface wettable by tear fluid, as described in Chapter 26. Moreover, the highly hydrophobic surface characteristic of silicone rubber tends to encourage the deposition of protein and mucus of the tear on the surface of the lens. Lipids and lipid-soluble materials follow the same track and eventually penetrate into the bulk phase of the contact lens. Because of these undesirable factors, the use of silicone contact lenses of various chemical compositions and with surface treatments has not been successful but rather disastrous because of the interfacial characteristics of silicone contact lens on the cornea, which cannot be oflfset by these efforts. It indicates that more profound surface modification to cope with the problems rather than mere surface treatment is needed in capitalizing on the advantageous bulk properties of silicone polymers. 

Polymer surface modifications are omnipresent in applications where the surface properties of materials with favorable bulk properties are insufficient. By altering the surface characteristics using physical or chemical modification the desired surface properties may be achieved. Such treatments are required e.g. to enhance printability of films, the adhesion of paints, metal or other coatings, biocompatibility, protein resistances/reduced biofouling, etc. The diverse approaches met in practice include, among others, wet chemical and gas phase chemistry, plasma or corona, UV/ozone and flame treatments. In most cases surface chemical modification reactions take place that alter the surface energy in a desired way. For example,... 

Lohbach, C., U. Bakowsky, C. Kneuer, D. Jahn, T. Graeter, H.-J. Schafers, C.-M. Lehr, Wet chemical modification of PTFE implant surfaces with a specific cell adhesion molecule. Chem. Commun., 2002,... 

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