PHYSICO-CHEMICAL STUDIES ON THE BEHAVIOUR OF CHROMIUM, NICKEL, COBALT & COPPER SOAPS IN NON AQUEOUS SOLUTIONS

Abstract

Soap solutions,In contrast to other colloids,are characterised by the unique behaviour of existing in almost a perfect state of thermodynamical stability and In possess ing physical properties,although within a limited concentra tion range,siirllar to those exhibited by the solutions of strong electrolytes. These colloids have been termed as colloidal electrolytes and are recognised as association colloids(l) by virtue of the clustering of the insoluble or hydrophobic part of the soap molecules, existence of aggregated Ions formed in this manner,impart surface active properties to soap solutions,thereby mating them useful as detergents,emul3ifires,solubilising agents.and as the main constituents of high temperature greases. Fundamental studies on soap solution mainly report the results on Ionic micelles and their structure. A number of brilliant colloid chemist like Fc Sain(2), LottermoserO),Hartley(4 ),i» right (3), Raits on (6) etc.,have mid* useful contribution in t*-is direction. The pioneering work of He Bain,however,deserves special mention who with the aid of physical methods,especially osmotic pressure and conductivity measurerents(7),gave proof of the existence of micelles in solutions and introduced the tarm critical jrlcella concentration. *lth >ugh his investigation on the nature of micelles met with severe criticism at the hands of Hartley and others(6-11),little doubt is left about m 2 - the ingenuity of Pc Baln*s experimental techniques and his brilliant approach in straightening the various complexities associated with the behaviour of soaps in solutions. y Anumber of physical methods are used in determin ing the c.m.c. of soap solutions. a few of them,viz., based on measurements of conductivity(12-16),freezing point (17-19), osmotic prassure(20),vapour pressure(21-22), turbidity(23),partial molal volume(29-3l),refractivity (32),transport number (33) and surface tension(34-36) have found extensive applications while others requiring knowledge of solubility (24-28),vlscosity(37-4l), lipole moment(43-44),spectrophotometry(42) and fluorlmetry need extensive investigations. Hartiey(45) and others(46) referred t> changes in the flouresence of sore dye stuffs at the c.m.c. in the presence of surface active agents for these measurements. Har*ins(47) «Colthoff and Jtricks (48) used this property and determined the critical concentration of soma surface active agents. Recently tfallk and Co-workers(19) have employed the spectrophoto metry method for the determination of the c.m.c. of ionic and non-ionic soaps. Other mathods,used in recent years,are those based on the measurement of electrophor>? tic mobility,used by Taraamushi and 3hiara(50),for the determination of the c.m.c. of long chain amine hydro chlorides,ultrasonic veloclty(5l) and the meth >d of - 3 - » tracer technique (52). Indirect evidence for tha existence of micelles is available from the study of tha phenomenon of solubilization (53). Physico-chemical matbois like spectrophotometry(54), X-ray diffraction(55),turbidometry(55),surface tension(57) etc.have been used to stuly it. Different theories(58-60) have bean proposed from time to time to explain tha mechanism of solubilization. Apart from the above aspect* there are quite a few others worth considering. The problem concerning the structure of micelles remains unresolved to this day. Pe Bain had conceived the existence of different kinds,sizes,shapes and composition of micelles and had postulated the existence of at least two;the so ea1J ed"nearly neutral" or "slightly ionl3ed lamellar micella" to explain the fall in conductance above critical concentration$and the spherical ioric mica1 las consisting of a number of ions of like sign. Hartley,on tha other hand,basing his arguments on the general applicability of Dsbye-Huckel theory had considered tha existence of only one type of micelle,representing a sphere of fitty : iquid, close packed, paraffin chains with their polar heads outwards and few gegenions in tha surrounding ionic atmosphere