Water Repellency of Materials

In many cases, such as with umbrellas and raincoats, the material used must be nonwetting in water. As mentioned earlier, if the contact angle is 

Larger than 90°, a nonwetting solid surface is present. 

Inorganic salts (polyphosphate, silicates) Optical brighteners 

In Young s equation, the quantity (ys - ySL) can be made negative. This is achieved by coating the solid material with some suitable material (such as Teflon). That means yc should be reduced to less than 30 mN/m. 

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Processing of textile materials by silicones also imparts antimicrobial properties to these clothes. Some authors state that textile material sizing by water repellents imparts them sufficient antimicrobial activity. Water repellency of materials may reduce the adverse impact of microoiganisms, because the quantity of adsorbed moisture is reduced. However, Hydrophobic finishing itself may not fully ehminate the adverse effect of microorganisms. Therefore, antimicrobial properties imparted to some textile materials during silicone finishing may be related to application of metal salts as catalysts, such as copper, chromium and aluminum. 

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