Eur. Phys. J. E (2016) 39: 107
https://doi.org/10.1140/epje/i2016-16107-5

Regular Article

Role of kosmotrope-chaotrope interactions at micelle surfaces on the stabilization of lyotropic nematic phases

¹ Arts and Sciences Faculty, Department of Chemistry, Abant Izzet Baysal University, Golkoy, 14030, Bolu, Turkey
² Instituto de Física, Universidade de São Paulo, Rua do Matão, 1371, SP, 05508-090, São Paulo, Brazil

^* e-mail: akpinar_e@ibu.edu.tr

Received: 31 July 2016
Accepted: 26 October 2016
Published online: 16 November 2016

Abstract

Three lyotropic quaternary systems of ionic surfactants were prepared to investigate the role of kosmotrope-chaotrope interactions at the micelle surfaces on stabilizing the different nematic phases. The ionic surfactants were potassium laurate (KL), sodium dodecylsulfate (SDS) and tetradecyltrimethylammonium bromide (TDTMABr), where KL is a kosmotrope surfactant, and others are chaotrope. The first system consisted of KL/decanol (DeOH)/water/alkali sulfate and the second of SDS/DeOH/water/alkali sulfate. The third system was prepared by adding sodium salts of chaotropic or kosmotropic anions to the primary mixture of TDTMABr/DeOH/water, separately. The characteristic textures of discotic nematic (N _D), biaxial nematic (N _B) and calamitic nematic (N _C) phases were identified under polarizing light microscope. Laser conoscopy was employed to determine the uniaxial-to-biaxial phase transitions. The kosmotrope-kosmotrope or chaotrope-chaotrope interactions between the head groups of the surfactants and the ions of the electrolytes led to the stabilization of the N _D phase. On the other hand, kosmotrope-chaotrope interactions stabilize the N _B and/or N _C phases.