Tensides

Tensides are common textile chemicals.
Tensides are the active component of detergents, emulsifying agents, dispersing agents and wetting agents.
Tensides are surface active molecules, they enrich at interfaces (i.e. the boundary between two different phases for example water and oil).
When enriched at the interface the tensides decrease the surface tension.

Molecules in the bulk of the liquid are attracted to its neighbours equally in all directions. At the interface molecules are not surrounded by neighbours in all directions. This results in an attractive force directed downwards (into the bulk).

Or expressed in another way: it is more energetically favourable for molecules to be in the bulk than at the surface.

Moving molecules from bulk to interface (i.e. creating new surface area) cost energy. As little surface area as possible is energetically favourable and this is why water droplets are spherical (smallest possible surface area).

Organic chemistry

Tensides