Chemical modification techniques

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. 

Sample surfaces are atomically smooth surfaces of cleaved mica sheets for SFA, and various colloidal spheres and plates for a colloidal probe AFM. These surfaces can be modified using various chemical modification techniques, such as Langmuir-Blodged (LB) deposition [12,19] and silanization reactions [20,21]. For more detailed information, see the original papers and references texts. 

Other examples include the generation (via photohthography and surface chemical modification techniques) of substrates bearing alkyl or perfluori-nated hydrophobic backgroimds and carboxyhc-terminated areas to which ONDs can be immobihzed (Fig. 23) [46,87,88]. 

However, extreme caution43 is necessary when applying chemical modification techniques. In general, 3 requirements have to be fulfilled ... 

Surface thermoplasticization of solid wood or particles is one of the more useful chemical modification techniques because most of the inherent properties of wood are retained. External plasticizers can only be applied to wood... 

The maximal fluorescence, Fmax, reflects the binding strength of substrates and the area under the curve. A, reflects the catalytic rate (56, 57). Direct examination of the enzyme-substrate complex therefore allows determination of individual rate and equilibrium constants for a given substrate (57), direct deduction of modes of inhibition (56,57), and the mechanistic consequences of inactivation of the enzyme by chemical modification techniques (48,57). 

The motive behind supramolecular carbene chemistry is to modify the inter- and intramolecular reactions of entrapped carbenes in order to manipulate product formation. Such would be achieved through physical modification as opposed to the more conventional chemical modification techniques, e.g., appending bulky substituents, which would necessarily alter the reactant s potential energy surface (PES). Selectively directing carbene reactions wherein more than one product may be formed would, therefore, confound conventional predictions. 

The other approach is to modify the cellulose chemically. Rowell et al. (1994) discussed the application of both thermal and chemical modification techniques to modify fibre used to manufacture low density fibreboards. The acetylation technique appears to offer significant improvement in the stability of panels, but the technique has not achieved significant commercial success largely because of the cost of the chemicals required. 

Structural composites can range widely in performance from high-performance materials used in the aerospace industry down to wood-based composites, which have lower performance requirements. Within the wood-based composites, performance varies from multilayered plywood and laminated lumber to low-cost particleboard. Structural wood-based composites intended for indoor use are usually made with a low-cost adhesive, which is not stable to moisture, while exterior-grade composites use a thermosetting resin that is higher in cost but stable to moisture. Performance can be improved in wood-based as well as jute and kenaf composites by using chemical modification techniques, fire retardant, and decay control chemicals, etc. 

Two important chemical modification techniques for PE arc chlorination and sulphochlorination [6,7,8]. Chlorinated-PE is used for a variety of different applications depending on the level of chlorine incorporation [6]. Chlorinated-PEs with mass fractions of (10 to 40) % chlorine are used as synthetic rubbers. Those with mass fractions of (25 to 50) % chlorine arc used as a high molecular weight plasticizer, and those with mass fractions of (40 to 75) % chlorine are used as a binder for paints. Chlorinated-PE is also used as an impact modifier for poly(vinyl chloride). 

Improving the hemocompatibility of medically used materials via chemical modification techniques means altering the surface of the bulk material by, for example, polymerization, ligand binding, or coating. This is aimed at the development of either a bioinert or a bioactive material [6,8,10,11]. 

C) is 4 X 10" . In the USA, this type of ware is termed Chemical Porcelain . Chemical Surface Coating (CSC). This low-temperature chemical modification technique has three stages activation of the substrate formation of the new ceramic precursor by chemical action heat treatment to convert the new precursor into a new ceramic coating. 

Along with physical modification, chitosan is most commonly modified by a number of chemical techniques including traditional chemical modification techniques such as photochemical, enzymatic, radiation, and plasma-induced graft copolymerization. Figure 1.6 summarizes some of the commercially used modification techniques for surface modification of chitosans. 

A summary of the different chemical modification techniques used to alter the surface characteristics of nanocellulose can be found in reference [47]. 

Chemical modification techniques of polymers primarily aim at altering the surface and bulk properties of the final product in order to enhance its performance in the biological environment. Currently applied polymers, e.g. for dialysis membranes, have reached a satisfactory level. They offer a high degree of both, performance adaptability and blood compatibility after an appropriate chemical modification. As an example, the sieving coefficient curve of dialysis membranes can be shifted towards larger molecular weights and thus be adapted to medical needs (Fig. 13.11). 

Surface modification techniques used to charge the substrates on which the nanolayers are to be deposited can be categorized as physical or chemical. Chemical modification techniques include surface patterning, photobleaching or plasma treatment. Methods of physical modification primarily... 

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