OBSERVATION OF MICELLE FORMATION AND MICELLAR STRUCTURAL TRANSITION FROM SPHERE TO ROD BY MICROCALORIMETRY

Enthalpies of mixing for three binary systems, sodium dodecyl sulfate (SDS)-water, hexadecyl trimethylammonium bromide (CTAB)-water, and i-C 8H17C6H4O(C2H4O)(9.5)H (Triton X100)-water, have been measured at 302. 65 K by a LKB2107-121 flow microcalorimeter equipped with a compositio n scanning setup, With the constructed setup we have made the step by step titration continuous by simply keeping the volumetric flow rate r atio (U-1/U) of the solution with constant concentration C-1 to the so lution with varying concentration C-i at about one tenth, From the rec orded curves, the critical micelle concentration and heat of micelle f ormation of surfactant have been derived, The micellar structural tran sition from sphere to rod for an aqueous solution containing SDS and 0 .6 M NaCl at 298.75 and 302.65 K can be observed directly, and the ent halpy changes of micellar transition can also be calculated. (C) 1996 Academic Press, Inc.