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The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in an aqueous solution and to be excluded by water. [ 1 ] [ 2 ] The word hydrophobic literally means "water-fearing", and it describes the segregation of water and nonpolar substances, which maximizes the entropy of water and minimizes the area of contact ...
Water on hydrophobic surfaces will exhibit a high contact angle. Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds. [2]
The hydrophobic effect represents the tendency of water to exclude non-polar molecules. The effect originates from the disruption of highly dynamic hydrogen bonds between molecules of liquid water. Polar chemical groups, such as OH group in methanol do not cause the hydrophobic effect.
Reactions within the fuel cell produce waste gas CO 2 which can be vented out through these hydrophobic membranes. [62] The membrane consists of many microcavities which allow the gas to escape, while its hydrophobicity characteristic prevents the liquid fuel from leaking through.
Cloth, treated to be hydrophobic, shows a high contact angle. The theoretical description of contact angle arises from the consideration of a thermodynamic equilibrium between the three phases: the liquid phase (L), the solid phase (S), and the gas or vapor phase (G) (which could be a mixture of ambient atmosphere and an equilibrium concentration of the liquid vapor).
Also known are protocols for cycloadditions such as Diels-Alder reactions, 1,3-dipolar cycloadditions of azomethine ylides and azide–alkyne cycloaddition reactions. [25] One example is a DA reaction assisted by chromium hexacarbonyl and high pressure. [26] The I D /I G ratio for reaction with Danishefsky's diene is 2.6.
Such materials are produced by reaction of silica gel with trimethoxyoctadecylsilane]]. The individual links involve silanol groups displacing the methoxy groups, forming an Si-O-Si bonds. This reaction changes the hydrophilic silanol groups into hydrophobic coatings.
Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism.