Hydrophobic silanization

Oxane bonds, M—O—Si, are hydroly2ed during prolonged exposure to water but reform when dried. Adhesion in composites is maintained by controlling conditions favorable for equiUbrium oxane formation, ie, maximum initial oxane bonding, minimum penetration of water to the interface, and optimum morphology for retention of silanols at the interface. The inclusion of a hydrophobic silane, such as phenyltrimethoxysilane [2996-92-17, with the organofunctional silane increases thermal stabiUty of the silane and make the bond more water resistant (42). 

Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino functional silanes, such as epoxies and urethane silanes, are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines that could not react are hydrophilic and, therefore, responsible for the poor water resistance of bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [42]. 

Fig. 2.3.11 Left the ingress of a hydrophobic silane coating into building sandstone. Right subsequent water ingress and pumping through a treated surface.

Keywords Adhesion silane composites hydrophobic silane crosslinked silane ionomer bonding. 

Blends of 10% aminosilane F and 90% hydrophobic silanes, i.e. vinylsilane A, chloropropylsilane B, methylsilane G, and phenylsilane I, gave superior adhesion of three types of polyurethane (RIM, thermoplastic, and one-component rigid) to glass compared with aminosilane F alone. Table 3 shows that the blend with phenylsilane I gave the best adhesion overall to all three polyurethanes after 5 h in boiling water. This improved performance is attributed to the enhanced hydrophobicity of the interphase region which is conferred by the replacement of most of the hydrophilic aminosilane with hydrophobic silane. 

Bonding of urethanes to glass with a hydrophobic silane primer (peel strength, N/cm)... 

I I natural binder matrix. j hydrophobic silane layer... 

Attachment of Lipophilic Biomolecules to Hydrophobic Silane-Treated Surfaces... 

Fig. 7. Procedure for immobilizing lipid-linked biomolecules to glass slides treated with hydrophobic silane.

Figure 11.4 Structure of a hydrophobic silane coupling agent.

A number of reports have described theoretical calculations for superhydrophobic surfaces. Marmur [10] and Quere and co-workers [11,12] show the theoretical background for surface roughness. There are also many reports regarding creation of superhydrophobic surfaces using hthography [13], fractal structure of wax [14], chemical vapor deposition (CVD) of poly(tetrafluoroethylene) (PITH) [15] carbon nanotubes and web-like structures [16-18] and by coating hydrophobic silanes onto aluminum acetylacetonate [19] and so on. These micro-structured surfaces show a decrease in apparent surface free energies. 

A. Buguin conducted the first quantitative study of the dewetting of water on highly hydrophobic silanized glass. ° With the help of a very simple optical setup, he was able to follow the time evolution of the profile of a water film. He identified several distinct regimes, which we proceed to describe in the next section. 

Work at the Mobil Corporation showed that mesoporous silica could be formed by hydrolysis of tetraethoxysilane entrained in a highly concentrated water/silane/surfactant system. In this regime, the three-component mixture forms ordered structures with a range of symmetries. In one hexagonal phase, rods of water are surrounded by surfactant and embedded in a hydrophobic silane matrix. Hydrolysis of the silane under suitable conditions, followed by drying and sintering, results in a porous silica with aligned pores of a few nanometers diameter. 

Adhesion can also be improved by using blends of silanes. A hydrophobic silane in combination with a hydrophiUc silane will often improve bonding and improve retention of wet strength compared to use of... 

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