Surface modification silanization

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Chemical surface modifications The first surface modification for the purpose of eliminating EOF and protein adsorption was recommended by Hjerten.28 The attachment of vinyl silanes allowed the polymerization of a variety of molecules to the surface. Most of the chemical modifications used for preparing capillaries for electrophoresis originated from the experience acquired over the years preparing GC and LC stationary phases. Chemical modification should conform to certain requirements, including the prevention of adsorption, the provision of stable and constant EOF over a wide pH range, chemical stability, ease of preparation, and reproduciblity of preparation. The effects of silanization of the inner surface of capillaries on electrophoretic separations have been extensively studied.26-29... 

The first report on living carbocationic surface-initiated polymerization (LCSIP) using a defined surface modification is by Vidal and Kennedy [268-270]. They prepared poly(isobutene) (PIB) brushes from silica surfaces using a silane functionalized benzylchloride activated by a Lewis acid. 

Rochow, E.G. (1951). An Introduction to the Chemistry of Silane. 2nd, ed.. Chapman Hall. London. Rostami, H., Iskandarni, B. and Kamel, I. (1992). Surface modification of Spectra 900 polyethylene fibers using RE-plasma, Polym. Composites 13, 207-212. 

Avseenko et al. (2001) immobilized antigens onto aluminum-coated Mylar films by electrospray (ES) deposition. Various surface modifications of the metallized films were studied to determine their abilities to enhance sensitivity. The plastic surfaces were firsf cleaned by plasma discharge treatment, followed by coating with proteins (BSA and casein) or polymers such as poly (methyl methacrylate) or oxidized dextran, or they were exposed to dichlorodimethyl silane to create hydrophobic surfaces. Protein antigen was prepared in 10-fold excess sucrose and sprayed onto the surfaces to form arrays with spot diameters between 7 and 15 pm containing 1 to 4 pg protein. 

Scheme 12.1.1 Surface modification with silane coupling agent.

The production of mica for polymer applications has been reviewed by Hawley [89]. The aim of the processing is to purify the deposit and to produce particles of relatively small diameter with an aspect ratio of 50-200. The natural minerals are generally of much larger size than required and so the milling has both to delaminate and fracture the particles. The milling is the key process and a variety of methods, both wet and dry, are used, accompanied by various classification methods. Surface modification is important in many mica applications and a variety of treatments are used, especially organo-silanes. The methods of treatment are generally not disclosed. 

Many surface modifications are used with aluminium hydroxide, which responds to both silane and fatty acid treatments. Special proprietary silane coatings seem to be preferred for polypropylene applications [99]. Despite the production being water based, the preference seems to be for dry coating procedures. 

I was fortunate as an industrial scientist for Plaskon and Dow Corning to be allowed to concentrate for over 40 years on organofunctional silanes and their applications in surface modification of minerals. I chose a scientific ladder rather than an administrative ladder, so I could stay in the laboratory with one or two assistants and develop a practical feel for polymer composites. Understanding of interfacial phenomena was helped immensely by academic workers such as Professors Koenig and Ishida at Case Western Reserve University and Professor Boerio at the University of Cincinnati. They and their students conducted extensive analytical studies of the interface to demonstrate the reality of some of the concepts I had proposed from indirect evidence of performance tests. 

Keywords Silanes fluoroalkyl-functional groups surface modification surface tension adhesion control lubrication silylating agents release agents. 

A recent study by DePalma and Tillman [ 10] also demonstrates the potential of surface modification by self-assembled monolayers of low surface energy fiuoroalkyl-containing silanes. Fatty acids, amines and alcohols have long been known to adsorb as monomolecular films on metals. Silane coupling agents have featured strongly in new studies to develop more robust films, covalently bound together and to the metal substrate. 

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