Microbial Bio-Based Amphiphiles (biosurfactants): General Aspects on Critical Micelle Concentration, Surface Tension, and Phase Behavior

Biosurfactants of microbial origin are compounds obtained from the microbial fermentation of glucose and vegetable oils. Developed for their surface active properties combined to a high biodegradability and low toxicity, these molecules have a complex behavior in water and addressing them as bio-based amphiphiles, or bioamphiphiles, is more appropriate. This chapter illustrates the most important properties in solutions of microbial bioamphiphiles, from hydrophilic-lipophilic balance, hydrophilic-lipophilic difference, critical micelle concentration, and surface tension, typically illustrating their surfactant character, to more complex self-assembly properties, including phase behavior, rather illustrating their amphiphilic character. These data are critically discussed in the perspective of classical head-tail but also bolaform amphiphiles.