title: Phase diagram studies in two-surfactant ternary systems employing positron annihilation spectroscopy.
abstract: Positron annihilation lifetime parameters in condensed media are sensitive to structural and conformational changes. This property has been exploited to study the phase diagrams of two ternary cationic surfactant systems. Positron lifetime measurements were performed in cetyltrimethylammonium bromide (CTAB)/water/hexanol and tetradecyltrimethylammonium bromide (TTAB)/water/pentanol systems having varying concentrations of hexanol and pentanol respectively. For both the systems, changes were observed in the positron lifetime parameters whenever a phase transformation occurred. The various phase boundaries demarcated by this technique agrees well with those obtained by other conventional techniques. Besides this, the present work suggests the existence of two kinds of lamellar structures referred to as DI and DII phases in both the systems, which were otherwise considered to be a single D phase by other conventional techniques. The existence of such lamellar structures has been demonstrated by a change in the trend of o-Ps lifetime when the system passes from one type of lamellar structure to the other type. The results of these investigations are presented.
authors.affiliation: Department of Physics, Sri Venkateswara College (University of Delhi), Dhaula Kuan, New Delhi 110021, India. kongbam_c@hotmail.com
authors.forename: K Chandramani
authors.initials: KC
authors.lastname: Singh
authors.forename: P H
authors.initials: PH
authors.lastname: Khani
authors.forename: R
authors.initials: R
authors.lastname: Yadav
authors.forename: P C
authors.initials: PC
authors.lastname: Jain