Water-repellent films

Cyclopentasiloxane is a volatile silicone used to make the film water-repellent, and to eliminate tackiness. It is a thickener it acts as a lubricant and gives the resulting coating a silkier feel. 

Flotation. The slurry of ground ore leaving the grinding circuit may be separated from part of the water in thickeners or may go directly to the flotation cells. The latter are rectangular tanks into which air is injected or drawn via impellers. Flotation is based on producing a water-repellent chemical film on the exposed sulfide minerals in the ground ore. The sulfide minerals collect on the surface of the air bubbles and rise to the top of the flotation cell, where they can be removed from the froth. The froth overflows the cells in collector troughs called launders. 

In principle, emulsified sunscreen products are similar to emollient skin-care products in which some of the emollient Hpids are replaced by uv absorbers. The formulation of an effective sunscreen product generally requites combination of a uvB and a uvA absorber if an SPF above about 12 is desired. Two or more of the sunscreens Hsted in Table 13 normally constitute about one-half of the nonvolatiles found in sunscreen lotions. The other half consists of an em ollient (solvent) and emulsifying and bodying agents. If water-resistant quaUties are desired, polymeric film formers, for example, acrylates—octylacrylamide copolymers [9002-93-1] or water-repellent Hpids, for example, dimetbicone [9006-65-9] are included. 

A/-substituted, long-chain alkyl monomethylol cycHc ureas have also been used to waterproof cotton through etherification. Other water repellent finishes for cotton are produced by cross-linked siHcone films (56). In addition to the polymeri2ation of the phosphoms-containing polymers on cotton to impart flame retardancy and of siHcone to impart water repeUency, polyduorinated polymers have been successfuUy appHed to cotton to impart oil repeUency. Chemical attachment to the cotton is not necessary for durabUity oU repeUency occurs because of the low surface energy of the duorinated surface (57). 

Figure 12.30 Potential uses of polyphosphazenes (a) A thin film of a poly(aminophosphazene) sueh materials are of interest for biomedical applications, (b) Fibres of poly[bis(trifluoroethoxy)phosphazene] these fibres are water-repellant, resistant to hydrolysis or strong sunlight, and do not burn, (c) Cotton cloth treated with a poly(fluoroalkoxyphosphazene) showing the water repellaney eonferred by the phosphazene. (d) Polyphosphazene elastomers are now being manufaetured for use in fuel lines, gaskets, O-rings, shock absorbers, and carburettor eomponents they are impervious to oils and fuels, do not bum, and remain flexible at very low temperatures. Photographs by eourtesy of H. R. Allcock (Pennsylvania State University) and the Firestone Tire and Rubber Company.

PDMS macromonomer was used as a component of block segment to obtain a graft block copolymer with PMMA (Scheme 1) [51-53]. This graft block copolymer is characteristic of surface water repellence, easy peeling, and weatherability superior to simple graft copolymers of the same members. PDMS-b-PVC film also shows long life surface water repellency with weatherability and very low coefficiency of abrasion [18,54]. 

Cook, M. A. and Nixon, J. C., 1950. Theory of water-repellent films on solids formed by adsorption fi-om aqueous solutions of heteropolar compounds. J. Phys. Colloid Chem., 54 445 - 459... 

Employ environmentally compatible aqueous based compositions as a means of affording substantially non-discoloring water-repellent films to masonry surfaces. 

Flake aluminum pigments with varying platelet thicknesses and shapes are used for corrosion protection [5.175]. For standard specifications, see Table 1 ( Aluminum pastes and pigments ). They are coated with a water-repellent, fatty film and are therefore particularly suitable for conventional solventbome coating systems. They have outstandingly good weather resistance [5.175]—[5.177]. 

By varying the nature of the side chain, R, various elastomers, plastics, films, and fibers have been obtained. These materials tend to be flexible at low temperatures, and water and fire resistant. Some fluoroalkoxy-substituted polymers (R = CHXFJ are so water repellent that they do not interact with living tissues and promise to be useful in fabrication of artificial blood vessels and prosthetic devices. 

Chemical modification of the wax can improve smear resistance (5). Silicones, which do not harm furniture finishes (6), are incorporated as film-forming ingredients in furniture polishes. The lubricant properties of silicones improve ease of application of the polish and removal of insoluble soil particles. In addition, silicones make dry films easier to buff and more water-repellent, and provide depth of gloss, ie, ability to reflect a coherent image as a result of a high refractive index (7). Wax-free polishes, which have silicones as the only film former, can be formulated to deliver smear resistance (8). Another type of film former commonly used in oil-base furniture polishes is a mineral or vegetable oil, eg, linseed oil. 

The wax vapor tends to condense on all surfaces because of its marginal volatility and it is concluded that cell wall surfaces within the board also condense wax. Heat treating in the press or oven serves to redistribute the wax into a monomolecular film on all fiber surfaces with a coincident increase in water repellency. Both springback decreases and repellency increases are attributable to the desorption of materials by the board conversion operations conducted at high temperatures. 

The rest of the chapter has been devoted to special topics and in materials science there are many possibilities. Those selected include the mechanism of the flotation of minerals in which the addition of a certain organic to the solution causes a specific mineral to become hydrophobic so that it is exposed to air bubbles, the bubbles stick to it and buoy the mineral up to the surface, leaving unwanted minerals on the bottom of the tank. It turns out that the mechanism of this phenomenon involves a mixed-potential concept in which the anodic oxidation of the organic collector, often a xanthate, allows it to form a hydrophobic film upon a semiconducting sulfide or oxide, but only if there is a partner reaction of oxygen reduction. This continues until there is almost full coverage with the dixanthate, and the surface is thereby made water-repelling. 

Waxes and greases are employed as temporary protectives. Steel sheets, bars, tubes, etc. are transported with a water-repellent film of oil or grease. A secondary method of protecting car bodies, especially door and sill voids, is to spray wax through the small access ports and form an even layer which protects the metal from water, salt, and road dirt. 

WATER-REPELLENT FILMS FROM ORGANOSILICON MATERIALS... 

The same reaction is found to occur with cotton cloth and with wood, and in a less pronounced way with wool, silk, leather, and many other materials. Glass and other ceramic surfaces also react readily with the methylchlorosilane vapor to give very effective water-repellent films,2 but only if the surface had upon it an adsorbed film of water. Completely dry glass, baked out under vacuum, does not become distinctly water-repellent upon treatment. Glass which has stood at ordinary room conditions usually has on its surface a film of... 

Measurements which have been made on the water-repellent films... 

This and other organosilicon preparations for making surfaces water-repellent are produced and marketed by the General Electric Company under the registered trade-mark of Dri-Film. 

Besides such electrical applications as water-repellent surface films, there are many applications where water repellency is an end in itself. Treated glass windowpanes or windshields are not wet by muddy water, and so they stay clean longer and are easier to clean whenever washing is required. Rain docs not flood the surface of a treated windshield but stands in small droplets when the car is in motion the air stream blows the droplets off, leaving the glass clear. Treated tumblers are easier to wash and dry treated chemical glassware holds water with a flat meniscus treated vitreous enamel does not stain easily and has improved luster. Cloth and paper may be made water-repellent for protection against rain, and it is possible that all clothes could be so treated. 

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