An emulsifier has an amphi-
philic molecular structure;
the structure consists of hydro-
philic group at one end, head, and lipophilic (hydrophobic) group of hydrocarbon chain at the other end, tail. By definition, the hydrophilic group has a strong affinity for water and the lipophilic group for oil.

When incorporated into a mixture of two immiscible substances such as water and oil, the emulsifier resides at the interface in such a way that it aligns its hydrophilic part into water and its lipophilic part into oil.

The hydrophilic and lipophilic properties of emulsifiers are identified by the Hydrophilic/Lipophilic Balance (HLB) value. HLB value describes the relative composition of a hydrophilic group and a lipophilic group within an emulsifier. Ranging from 1 to 20, this scale indicates the attraction either to oil or to water. High HLB values are assigned to more hydrophilic (more water-soluble) emulsifiers suitable for oil-in-water emulsions, and low HLB values to more lipophilic (more oil-soluble) ones suitable for water-in-oil emulsions.
Different applications require different HLB values.
For instance, canned coffee,
which is more hydrophilic,
requires emulsifiers with high
HLB values, and margarine,
which is more lipophilic,
requires emulsifiers with low HLB values.