The term surfactant is short for surface acting agent. Surfactants are amphillic compounds, meaning they contain two or more groups that in pure form are insoluble in each other. These groups include oil, water, silicone and fluoro compounds. The structure has a hydrophobic tail and a hydrophilic head. Surfactants lower surface tension and provide wetting, emulsification, foam and detergency. Conventional surfactants have one head and one tail. An example of a conventional surfactant is sodium lauryl sulfate.
Gemini surfactants, sometimes called dimeric surfactants, have two hydrophilic head groups and two hydrophobic groups in the molecules, in contrast to conventional surfactants that generally have a single hydrophilic head group and a single hydrophobic group in the molecule. Gemini surfactants can be ten to a thousand times more surface active than conventional surfactants with similar but single hydrophilic and hydrophobic groups in the molecules.1
Gemini surfactants are considerably more surface-active than conventional surfactants.2 Gemini surfactants have remarkably low CMC values compared to the corresponding conventional surfactants of equivalent chain length. The bi-layer structure of the Gemini surfactant sodium dicocamide PEG-15 sulfate makes it compatible with skin ceramides and provides skin barrier properties.3 Gemini surfactants are even reported in the patent literature to reduce skin irritation.4
Gemini surfactants have good commercial utilization potential. Therefore, their preparation should be cost-effective. As lower amounts of gemini surfactants are needed for a particular performance, cost-effectiveness may not stand in the way. Costly gemini surfactants may, however, be used as additives to the conventional surfactants to enhance the surface-active properties. Colgate Palmolive, Dow Chemicals, Hampshire Chemical Corp., Reckitt and Colman, Rhone-Poulenc Surfactants and Specialities, Texaco Inc. and Witco Corp. have contributed a lot to the synthesis and characterization of useful Gemini surfactants.5
2. FM Menger and CA Littau, J Am Chem Soc 113 1451–1452 (1991)
3. Woodruff, John Personal Care Feature: Bathroom Products, SPC 2 (2005)
4. US Pat 5,900,379 to Tracy et al (May 1999)
5. SK Hait and SP Moulik, Current Science, 82(9) (May 10, 2002)