title: Calorimetric and Light Scattering Investigations of the Transition from Spherical to Wormlike Micelles of C₁₄TAB Triggered by Salicylate.
abstract: Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil.
authors.forename: Thiago Heiji
authors.initials: TH
authors.lastname: Ito
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil.
authors.forename: Roberta Kamei
authors.initials: RK
authors.lastname: Rodrigues
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil.
authors.forename: Watson
authors.initials: W
authors.lastname: Loh
authors.affiliation: Department of Physical Chemistry, Institute of Chemistry, University of Campinas, P.O. Box 6154, 13084-862 Campinas, SP Brazil.
authors.forename: Edvaldo
authors.initials: E
authors.lastname: Sabadini