Organic surfaces, hydrophobic, wettable

The addition of water to immiscible nonpolar liquids increases the sedimentation volume of the solid of the.particles containing polar spots,.because the water helps form bridges. On the other hand, if partly hydrophobic particles are dispersed in water, the sedimentation volume is high because of association between the hydro-phobic spots on particles. This is reduced when a polar solvent such as dioxane is added, which renders all of the surface water-wettable by adsorption of the polar organic material at the hydrophobic areas. These factors are important to consider when silica is used as a thickening agent. 

Adsorbed films of ethykriethoxysilane and vinyltriethoxy-silane were formed on silica and alumina by retraction from hydrocarbon solution and their wettabilities and water-stabilities determined. The vinyltriethoxysilane films were generally more oleophobic, more hydrophobic and more resistant to contact with water than the films formed by the ethyl analog. Neither adsorbate formed stable films on a-alumina. The addition of low molecular weight organic acids or bases to the adsorbate solution resulted in both the ethyl and vinyl compound forming hydrophobic and water-stable films on silica and ot-alumina. Films of p-chloro-phenyl-ft-ethyltrichloro, -trimethoxy, and -triethoxysilane were also studied and found to be water-stable and to have wettabilities characteristic of a surface comprised of closely-spaced p-chlorophenyl groups. 

Natural, unmodified montmorillonite-Na (MMT-Na) has cation exchange capacity, typically 80-90 mequiv/100 g. Although some polymers, such as polyethylene oxide or polyvinylpyrrolidone, are of sufficient polarity to be able to directly exfoliate unmodified MMT-Na, organic modification of the layered clay is usually required to render the hydrophilic surface of the clay more hydrophobic and thus more compatible with most polymers, thereby improving the wettability and dispersibility of the clay in the polymer matrix. 

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