Eur. Phys. J. E (2015) 38: 4
https://doi.org/10.1140/epje/i2015-15004-9

Regular Article

pH-switchable structural evolution in aqueous surfactant-aromatic dibasic acid system

¹ Department of Chemistry, NIT Calicut, 673601, Kerala, India
² Condensed Matter Physics Division, IGCAR, Kalpakkam, Tamilnadu
³ Solid State Physics Division, BARC, 40008, Mumbi, India
⁴ Chemistry Division, BARC, 40008, Mumbi, India
⁵ Department of Chemical Engineering, Technion-Israel Institute of Technology, 3200003, Haifa, Israel

^* e-mail: lisa@nitc.ac.in

Received: 11 July 2014
Revised: 31 December 2014
Accepted: 5 January 2015
Published online: 29 January 2015

Abstract

Structural transitions triggered by p H in an aqueous micellar system comprising of a cationic surfactant (cetylpyridinium chloride) and an aromatic dibasic acid (phthalic acid) was investigated. Reversible switching between liquid-like and gel-like states was exhibited by the system on adjusting the solution p H. Self-assembled structures, responsible for the changes in flow properties were identified using rheology, light scattering techniques and cryogenic Transmission Electron Microscopy (cryo-TEM). High-viscosity, shear-thinning behavior and Maxwell-type dynamic rheology shown by the system at certain p H values suggested the growth of spheroidal/short cylindrical micelles into long and entangled structures. Light scattering profiles also supported the notion of p H-induced microstructural transitions in the solution. Cryo-TEM images confirmed the presence of spheroidal/short cylindrical micelles in the low-viscosity sample whereas very long and entangled thread-like micelles in the peak viscosity sample. p H-dependent changes in the micellar binding ability of phthalic acid is proposed as the key factor regulating the morphological transformations and related flow properties of the system.