Surfactants in Textile Processing

Study Notes

Surfactant is a shortened form of "surface active agent", which possesses surface activity due to its chemical structure.
A surfactant molecule has two ends with diametrically opposed polarities: a non-polar (lyophilic) end and a strongly polar (lyophobic) end that is hydrophilic.
The duality of polarity causes the molecule to align itself with respect to the polar nature of the surfaces it contacts.

Surfactants contain two structural elements:
- A hydrophilic part (polar) that interacts with water molecules, which can bear a positive or negative charge, or contain multiple polar groups.
- A hydrophobic part (non-polar) that exhibits low polarity and does not interact with water molecules, represented by long chain hydrocarbons, perfluoroalkyl groups, and alkylaromates.

By Use:
- Wetting Agents: reduce surface tension, enabling liquids to spread on non-polar solid surfaces, and are used to wet out repellent fabrics.
- Detergents: reduce water's surface tension, adsorb onto soil surfaces, and keep soil suspended to prevent redeposition.
- Emulsifying Agents: convert water-insoluble oils into stable, aqueous suspensions, and add a charge-charge repulsion field to keep droplets separated.
- Dispersing Agents: disperse solid particulate matter, similar to emulsifying agents, but with a lyophilic part that adsorbs onto the particle's surface.

Anionic surfactants: develop a negative charge on the water solubilizing end, and comprise almost 70% of commercial surfactants, with a negatively charged group in their active molecule part.
Cationic surfactants: develop a positive charge on the water solubilizing end, with a positively charged group in their active molecule part.