Studies of amphiphilic systems with and without additives

Abstract

Amphiphilic compounds bear an ionic (cationic, anionic or zwitterionic) or nonionic polar head group and a nonpolar hydrophobic portion. The polar portion exhibits a strong affinity for polar solvents, particularly water, and it is often called hydrophilic part or hydrophile while nonpolar is called hydrophobe or lipophile. They play an essential role in the existence of life and are widely used in the industry, medicine, pharmacology, etc [1, 2]. On dissolving in water they lower the surface tension and can form many types of aggregates (micelles) in which solvated hydrophilic groups are located at the surface of aggregate. Micelle is a Latin term means small bit and was coined by J. W. McBain [3] in 1920 to describe colloidal sized particles of detergents and soaps, and the phenomenon of self-association of amphiphilic monomers into the micelle was called micellization. The driving force behind micellization is the hydrophobic effect which was proposed by G. S. Hartley in 1936 [4]. In most practical applications, mixtures of surfactants, rather than individual surfactants, are used or purposely mixed to improve the properties of the final product [5]. Mixing of two or more surfactants in an aqueous solution leads to the formation of mixed micelles. The cmc of the mixed micelles fall within the highest and lowest individual cmc values of components. In some cases, two surfactants interact in such a fashion that the cmc of the mixture is always intermediate in value between those of two pure components. In other cases, they interact in such a way that the cmc of the mixture at some ratio of the two surfactants is less than either of the cmc. When this situation arises, the system is said to exhibit synergism, the condition in which the properties of the mixture are better than those attainable with the individual components by themselves.