Surface Modification by Chemical Reaction

The membrane surface can also be modified by chemical reaction. It is reported that direct fluorination can be effectively used to enhance commercial properties of polymer articles, such as barrier properties of polymer vessels, bottles, and packaging films and envelopes gas-separation properties of polymer membranes adhesion and printability properties of polymer articles and mechanical properties of polymer-based composites [68]. 

Dai et al. [69] modified the surface of microporous polypropylene (PP) membranes with phospholipid polymer using a new economic and convenient method. The process included the photo-irradiated graft polymerization of N-N-dimethylaminoethyl methacrylate (DMAEMA) and the ring-opening reaction of the grafted polyDMAEMA with 2-alkyloxy-2-oxide-l,3,2-dioxophospholanes (AOP). The FTIR spectra confirmed the chemical changes of the membrane surface and supported that PP membrane with excellent blood compatible surface could be fabricated by their novel method. 

As already explained in Section 3.15, this is a process of polymerization in which two reactive monomers, each dissolved in different solvents that are mutually immiscible, react at the interface between the two solutions. This process provides a method for depositing a thin layer upon a porous support. In this case, a polymerization reaction occurs between two very reactive monomers (or one prepolymer) at the interface of two 

Liu and Kim [71] modified the PES membrane surfaces using grafting and IP via UV/ozone pretreatment to graft PVA, PEG and chitosan on three samples of PES, and coating PVA, PEG and chitosan layers through interfacial polymerization. The description of the modification experimental design is shown in Table 2.1. 

Plasma polymerization process is a technique that allows us to obtain highly crosslinked polymers from nonfunctional monomers that are not utilized in conventional polymer synthesis. Plasma surface modification can improve biocompatibility and biofunctionality. 

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Table 23 Surface implications in polyphosphazenes surface modification by chemical reactions...

In order to construct functional microspheres by modification of the surface with adsorbed proteins, e.g., enzymes and antibodies, the conformation and orientation of adsorbed proteins must be controlled to keep them as active as free proteins. If hydrophilic particles are used as a carrier, they hardly suffer nonspecific adsorption, but even antibody cannot be adsorbed. In this case, antibody is immobilized on the particles by chemical reactions such as those mentioned in the previous section (9). 

The second topic of this chapter is the role of coordination compounds in advancing electrochemical objectives, particularly in the sphere of chemically modified electrodes. This involves the modification of the surface of a metallic or semiconductor electrode, sometimes by chemical reaction with surface groups and sometimes by adsorption. The attached substrate may be able to ligate, or it may be able to accept by exchange some electroactive species. Possibly some poetic licence will be allowed in defining such species since many interesting data have been obtained with ferrocene derivatives thus these organometallic compounds will be considered coordination compounds for the purpose of this chapter. 

Chemical modification (<chemical bonding). An electroactive species is immobilized on the electrode surface by chemical reaction. Normally the fact that the electrode is covered by hydroxyl groups owing to the oxygen in the atmosphere is used. For example, the silanization process is... 

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. 

Surface modification of fluoropolymers either by ionizing radiation (gamma radiation or electron beam radiation) [20,21] or by chemical reactions [22], introduces reactive sites for additional chemical reactions or improves wear [20]. 

Most applications of liquid column chromatography are now made on silica which has been chemically modified (bonded phase chromatography). The modification is made by chemical reaction between the silanol groups and a chlorosilane compound. The carbon radicals of the chlorosilane compound determines the nature of the final column material. Using silanes containing alkyl carbon chains with 8-22 carbon atoms gives the particles hydrophobic surfaces, but more polar surfaces may be obtained by incorporation of alcohol, amino, cyano or other groups in the alkyl chain. 

Chemical modification The surface of a membrane can be modified by chemical reactions. For example, when the surface of a polyamide composite membrane is brought into contact with a strong hydrofluoric acid solution, the top polyamide layer becomes sHghtly thinner by a chemical reaction with hydrofluoric acid. As a result, the flux increases considerably while the rejection of sodium chloride is unchanged or slightly increased [8]. 

The interface is a region at least several molecular layers thick with properties intermediate between those of the fiber and matrix phases and arises due to the peculiar restrictions on molecular motions in this zone. Matrix molecules may be anchored to the fiber surface by chemical reaction or adsorption and determine the extent of interfacial adhesion. Fiber modification reduces hydrophilicity of the fiber and improves the physical/chemical interactions between the fiber and matrix. Treatment makes the surface of the fiber very rough and provides better mechanical interlocking with the polymer matrix. 

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