Why addition of detergent into water decreases its surface tension?
It is because detergents contain compounds called surfactants. These surfactants are amphiphilic, so they have one end that is hydrophobic and one end that is hydrophilic. It is this combination that allows for the surfactant to reduce surface tension and act as a wetting agent, because it basically binds to the surface and keeps the water from beading up. Imagine a waxed car. You put water on it and the water beads up. Now imagine a car that has never been waxed. You put water on it and it just flows everywhere. That is the same concept on a larger scale….without the detergent containing the surfactant, on a microscopic level that water is beading up like the waxed car….whereas when you add the surfactant and the hydrophobic and hydrophilic ends go to work, it allows for that water to spread out (on a microscopic level) like the un-waxed car.
