Organic water repellency

Soap is one example of a broader class of materials known as surface-active agents, or surfactants (qv). Surfactant molecules contain both a hydrophilic or water-liking portion and a separate hydrophobic or water-repelling portion. The hydrophilic portion of a soap molecule is the carboxylate head group and the hydrophobic portion is the aUphatic chain. This class of materials is simultaneously soluble in both aqueous and organic phases or preferential aggregate at air—water interfaces. It is this special chemical stmcture that leads to the abiUty of surfactants to clean dirt and oil from surfaces and produce lather. 

Admixtures are sometimes used to reduce permeabiUty of concrete (80—82). These iaclude pore-filling materials such as chalk. Fuller s earth, or talc water repellents such as mineral oil, asphalt, or wax emulsions organic polymers (acryflc latexes, epoxies) and salts of fatty acids, especially stearates. 

High phenyl content resins are compatible with organic resins of the P-F, U-F, M-F, epoxy-ester and oil-modified alkyd types but are not compatible with non-modified alkyds. Silicone resins are highly water repellent. 

Water repellant To impart water-resistant properties, particularly in greases Aliphatic amines, hydroxy fatty acids and some organic silicone polymers... 

Bisdom EBA, Dekker LW, Schoute JFT. Water repellency of sieve fractions from sandy soils with organic material and soil structure. Geoderma 1993 56 105-118. 

This work describes the application to soil of compounds of a previous study (11) which dealt primarily with organic synthesis and physical properties of reaction products of pure fatty acids with BETA. In this study derivatives were prepared from various industrial fatty materials. In addition, water infiltration studies on sand, sandy soil, and clay soils were carried out on the previously prepared and new compounds. Finally, an investigation was initiated to determine the biological effects of one water-repelling chemical, the partially hydrogenated tallow-fatty acid-DETA reaction product, on seed germination and plant growth. 

A different approach to blanketing anodic areas involves dissolving organic anions with appropriate hydrophobic (i.e., water-repellent) substituents. The anionic heads of the molecules specifically seek out a positively charged anodic spot, and the hydrophobic tails serve to isolate it from the aqueous solution and so block the ionic part of the corrosion circuit or, at least, modify the electrical double layer (Fig. 16.13). Sodium benzoate and especially sodium cinnamate are particularly effective in this regard. 

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. 

These aqueous emulsions can also be used to size paper for improving its water repellency and antiadhesion properties (529). An increased level of organic titanate can be used to ensure the rapid curing (<5 s) for fast-paced paper or fiber curing operations (519). 

The bulk constituent of cells is water (H20). The cell membrane or plasma membrane (PM) that encloses the living cell is basically composed of a phospholipid bilayer, a 0.01 micrometre ( xm) (10 nm) thick bimolecular layer of hydrophobic (or water repelling) fatty molecules. In eukaryotes (organisms having a nucleus) there is a phospholipid bilayer PM enclosing the cell. Similar membranes bound specialized intracellular organelles, namely the endoplasmic reticulum (ER), ER-associated Golgi vesicles, lysosomes, vacuoles, peroxisomes, nucleus and mitochondria (and, additionally, the chloroplasts in plant cells). 

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