STUDIES ON THE SOLUBILITY AND MICELLAR BEHAVIOUR OF SURFACTANTS AND HEAVY METAL SOAPS

Abstract

The name 'surface active agents' or simply surfactants has been given to those substances which even in small Quantity alter the conditions orevalling at the interfaces. The effect is invariably a lowering rather than an increase of the surface eneny. The best known and often quoted surfactant is soap which Is an alkali metal salt of higher fatty acids. In industry the term 'syndet' is widely used which Is a contraction of the term 'synthetic detergent'. 'Surfactant' a shorter term for surface active agent, reoresents an organic molecule or an unformulated comoound having surface active properties while 'syndet' reoresents orlmarlly a detergent formulation. Within the oast two decade?, however, the newer synthetic surfactants, with their obvious advantage over ordinary soaps with regard to their stability towards hard or acidic water, have received an increaslnqly wider recognition. The first synthetic Product, 'Turkey red oil' was oreoared by the action of sulphuric acid on castor oil and was oredomlnantly a mixture of sulphuric acid esters. Many other products were made in this way from a variety of natural fats. The development of synthetic surfactants reached its most active phase in the period between the two World Wars. The tendency of surfactants to be adsorbed at the interfaces or surfaces is most fre^ently due to a orooerty, termed 'amphipethy' by G.S.Hartley. %ohio*thy means the occurence In a single molecule or Ion, with a suitable degree of separation, of one or more groups which have affi nity (sympathy) for the ohase in which the molecule or Ion Is dissolved, together with one or more grouos wh<ch are antipathic to the medium (i.e., which tend to be expelled by it). It Is convenient, from analooy in colloid chemistry to refer to these types of groups as 'lyophllic' and 'lyophobic', respectively end hence these compounds are also known as 'colloidal electrolyte'. WcBaln called all of them by the name of 'soap'. Classification of Surface Active Agent si Surface active agents may be classified under two general heads: (1) water soluble and (11) wateT insoluble surf act ant a. Water soluble surfactants: Most of the Interest in surface chemistry has been centered about the behaviour of surfactants In anueous solution although examples of the water Insoluble type sur factants involving the use of organic solvents to bring them Into solution are by no means scarce. The water soluble surfactants can be further divided und*r two heads, the Ionic and the non-Ionic surfactants. The Ionic surfactants may be further sub-dlvlded under following heads: (a) Anionic surfactants: The anionic surfactants live an anion contain ing the elongated hydrophobic portion of the surfactant mole cule on dissociation in water. This class of surfactants "2 Includes soaps, Twltchell's reagents(alkyl aryl sulphonateO, alkyl sulphates, alkane sulphonlc acids etc. (b) Catlonlc surfactants: The catlonlc surfactants on Ionization give a cation containing the elongated hydrophobic oortlon of the surfactant molecule. The class consists ef ouarternary ammo nium compounds, salts of long chain orlmary, secondary and tertiary amines, alkyl pyrldlnlum halldes. (c) Amphoteric surfactants* Amphoteric or ampholytic surfactants Ionize In solution resulting In the long chain carrying positive or negative charge depending upon the oH of the solution. The most important among them are N-alkyl taurines, dimethyl dodecyl amine oxide, lmldazolln derivative etc. Besides there are surfactants which fall under oolymerlc phosphates, silicates and fluorocarbons. Non-ionic surfactants: Non-Ionic surfactants do not ionize In aoueous solution. They contain non-ionlzable hydrophlllc grouos, usually containing a number of oxygen or nitrogen atoms In non-lonlzlng configuration. This class of surfactants mainly Includes surfactants derived from ethylene oxide. These sur factants have the general formula R UCH2CH2°'mH^ n wh#rt m and n are each unity or ireater, and R 1? an organic residue which usually, but not always, contains a hydrophobic irouo such as a long paraffin chain, an aromatic residue or an alkyl aromatic group. V. There are several advantages of this class of surfactants. These surfactants ire chemically Inert and stable towards »H chanqe and therefore, are particularly well suited for preparing mixtures of formulations for soeciflc purposes. The most Important advantage Is that the solublllzlng effect Is Independent of Ionization and the properties of the surfactants can be modified by simply changing the length of polyethylene oxide chain.