Hydrophobic film

Clearly, it is important that there be a large contact angle at the solid particle-solution-air interface. Some minerals, such as graphite and sulfur, are naturally hydrophobic, but even with these it has been advantageous to add materials to the system that will adsorb to give a hydrophobic film on the solid surface. (Effects can be complicated—sulfur notability oscillates with the number of preadsoibed monolayers of hydrocarbons such as n-heptane [76].) The use of surface modifiers or collectors is, of course, essential in the case of naturally hydrophilic minerals such as silica. 

The flotation of sphalerite, the sulfidic mineral source of zinc, is next considered as an example to illustrate the role of activators. This mineral is not satisfactorily floated solely by the addition of the xanthate collector. This is due to the fact that the collector products formed, such as zinc xanthate, are soluble in water, and so do not furnish a hydrophobic film around the mineral particles. It is necessary to add copper sulfate which acts as an... 

We have found that hydrophilic oiganic polymers treated with TiCLi have much higher etching selectivities than organosilicon polymers in an O2 plasma. This paper examines some of the parameters that influence the reaction of TiCLi with a variety of polymers. We find that TiCLi, readily functionalizes hydrophilic as well as moderately hydrophobic polymers, but fails to functionalize very hydrophobic films. Rutherford backscattering analysis reveals that TiCl4 is hydrolyzed at hydrophilic polymer surfaces that have sorbed water. Lack of surface water on hydrophobic polymers explains the absence of a TiC>2 layer on these polymer surfaces. 

TiCU readily functionalizes hydrophilic polymers such as poly(vinyl alcohol), m-ciesol novolac and methacrylic acid copolymers as well as moderately hydrophobic polymers such as poly(methyl methacrylate), poly(vinyl acetate), poly(benzyl methacrylate) and fully acetylated m-cresol novolac. HCI4 did not react with poly(styrene) to form etch resistant films indicating that very hydrophobic films follow a different reaction pathway. RBS analysis revealed that Ti is present only on the surface of hydrophilic and moderately hydrophobic polymer films, whereas it was found diffused through the entire thickness of the poly(styrene) films. The reaction pathways of hydrophilic and hydrophobic polymers with HCI4 are different because TiCl is hydrolysed by the surface water at the hydrophilic polymer surfaces to form an etch resistant T1O2 layer. Lack of such surface water in hydrophobic polymers explains the absence of a surface TiC>2 layer and the poor etching selectivities. 

The porous hydrophobic film of previous electrode designs has now been substituted with a new layer based on a mixture of particles of hydrophobic carbon and PTFE binder. This mixture is very similar in composition to the catalytic layer. This particular modification provides several advantages ... 

A pulsed system, called Time-Clock System, has been developed. It comprises a solid dosage form coated with a hydrophobie surfactant layer to which a water-soluble polymer is attached to improve adhesion to the core [66]. The thickness of the outer layer determines the time required to disperse in an aqueous environment. Following the dispersion of the outer layer, the eore becomes available for dispersion. An advantage is that eommon pharmaceutical excipients can be used to manufacture this system. Studies performed on human volunteers showed that the lag time was not affeeted by gastrie residence time. Furthermore, the dispersion of the hydrophobic film was not influenced by the presence of intestinal digestive enzymes or by the mechanieal aetion of the stomach. 

The traditional view of moisturizers is that they increase the moisture content of the skin by forming an occlusive, hydrophobic film on the surface of the SC, thereby trapping moisture in the underlying tissue. However, restoration of barrier function after disruption can be accelerated by the application of lipids, like free fatty acids, cholesterol, and nonphysiological lipids like the complex hydrocarbon mixture petrolatum.4 Barrier repair can be measured within an hour after barrier disruption and leads to normalization of barrier function within hours to days, depending on the initial insult. 

The homogeneity and uniformity of the hydrophobic film formed on the surface of the fibres has been supported by an electron microscope study of the replicas of the surface of the waterproofed cotton fibres. The same result has been given by the study of the film on polyester fibres. Cellulose fibre, treated with waterproofing GKZh-94 catalysed with AHM-9 dissolved in a copper ammonia solution leaves a film which repeats the form of the fibre. 

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. 

In the water desorption test the VTES films on flamed silica proved to be more resistant to change than the VTES films on air-dried silica. This difference is illustrated by the data in Figure 7. On air-dried surfaces after one hour adsorption time the VTES produced a film that initially had a low water contact angle and was not significantly altered in the desorption experiment. By allowing 20 hours contact with the solution a more hydrophobic film was obtained but it was quickly desorbed to a condition equivalent to that for only an hour adsorption time. On flamed silica, in contrast, the film adsorbed after 20 hours adsorption time showed only a slight tendency to lose its hydrophobic character. 

The case for increased organization in hydrophobic films caused by nonhydrogen-bonding solvents is not as well documented. It is difficult for us to see how benzene can increase the shear modulus of paraffin wax or how tetrahydrofuran can do the same for poly (vinyl chloride). It is possible that we are dealing with a van der Waals bonding in swollen polymers in these cases but much more evidence would be needed before a definite theory can be advanced. 

By applying a highly hydrophobic film to the surface, snow was reported to be less likely to adhere to the surface due to the large amount of air between the surface and snow. A satellite antenna covered with a highly hydrophobic film, reduced the disruption of communication by the adherence of snow to the antenna [78,82], Besides, these results portended well for techniques to apply highly hydrophobic film coatings to traffic lights, billboards, and roofs in areas with heavy snowfall. 

It was reported that the friction resistance between the highly hydrophobic surface and water was reduced to 20-45%, by supplying a small amount of air to the highly hydrophobic surface, as a film of air flow formed along the surface in water [83,84], This report suggests that the highly hydrophobic films are effective for use on the hulls of ships and for tubes or pipes. 

In addition one sees that the oxidation potential for water Is Increased to about 2.0 volts. Thus this hydrophobic film has excluded water from the electrode Interface to such an extent that one must apply 1.3 volts more In order to oxidize the water. This hydrophobic behavior Is similar to the behavior expected In micelle systems. 

Martin-Polo, M., Mauguin, C., and Voilley, A. (1992). Hydrophobic films and their efficiency against moisture transfer. 1. Influence of the film preparation technique. J. Agricult. Food Chem. 40,401-412. 

At an air interface, water arranges itself like a hydrophobic film (I) ... 

Not unexpectedly, marine crankcase oils are sometimes contaminated with water, which is normally removed by the lubricating oil centrifuge. To assist further in protecting against rusting, inhibitors such as alkyl sulphonates, phosphonates, amines and alkyl succinic acids/esters can be added. They work by forming a hydrophobic film on the metal surface but must be selected with due regard to the other additives present. 

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