Polar molecule hydrophilic group effect

To understand the role of surfactants in different systems, it is important to know what basic effects are exhibited by the surfactants. For this, let us again take the simple case of water surface in equilibrium with air the liquid phase (polar water) is in equilibrium with the gas phase (nonpolar air) in the presence of a surfactant. The surfactant molecule has a head (polar or hydrophilic group) attached to a tail (nonpolar or hydrophobic group) the tail would not like water, whereas the head wonld not like air, and vice versa. As a result, the surfactant molecules would neither go into the bulk of water nor into the bulk of air in fact they would remain at the interface negotiating with both phases (Fignre 17.12). For staying at the interface, the surfactant molecules reorient themselves in such a way that the head part bends toward the water, whereas the tail part extends toward the air. This way, surfactant molecules form a bridge between the water-air interface, and this results in a decrease in surface tension. 

Hydrophobic and hydrophilic are categories of hydration effects in aqueous liquids. Classical ions such as Na+ or polar molecules such as urea [(NH2)2 CO] are simply recognized hydrophihc solutes. In contrast, the interactions of hydrophobic solutes or groups with water molecules do not display classic electrostatic... 

Silanes exhibit hydrophilic and hydrophobic properties. The molecule has both a non-polar and a polar component. The non-polar organic alkyl group is the vehicle for the water-repellent action. The effectiveness, durability and stability of the waterproofing agent depends on the size and nature of this group (Huls, 1991). 

A hydrophilic molecule or a hydrophilic group of a molecule is generally polar and capable of H-bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents. It has a strong affinity with water tending to dissolve in, mix with, or be wetted by water. When two solute molecules repel each other in water it is called hydrophilic interaction. However there is no phenomenon known as the hydrophilic effect. 

To what extent the non-polar lipoid components of long-chain hydrocarbon molecules screen the effect of the polar hydrophile, and outwardly attain the ascendancy through their own f rce effects, cannot be stated with certainty. It is, however, very probable that the COOH group is responsible, in the sense discussed above, for the presence of double molecules of benzoic acid in benzene whereas, for an association effect in water, it is rather a case of interaction of benzene nuclei, because in aqueous solution the COOH groups must certainly be extensively hydrated. 

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