Chain length mismatch and packing effects on the thermotropic phase behavior of salt-free catanionic surfactants

• Type: Article in International Scientific Journal
• Date: 2013

Authors

Marta R A Matos (Author) FCUP; Bruno F B Silva (Author) Other; Eduardo F Marques (Author) FCUP

Journal

Title: Journal of Colloid and Interface Science

Vol. 405

Pages: 134-144

ISSN: 0021-9797

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 16 Citations

Scopus - 17 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Associated Projects

115212_2009 - Uma nova abordagem à veiculação de fármacos: lipossomas cataniónicos e nanotubos baseados em derivados de aminoácidos

Other information

Authenticus ID: P-006-7YH

DOI: 10.1016/j.jcis.2013.05.029

Abstract (EN): Thermotropic liquid crystal formation by salt-free catanionic surfactants (alkyltrimethylammonium alkylsulfonates, herein designated as TA(m)So(n)) has been investigated as a function of chain length mismatch (asymmetry). Previous studies on these compounds have revealed an unusual and rich asymmetry-dependent lyotropic phase behavior. Herein, phase transition temperatures and transition enthalpies/entropies were determined by differential scanning calorimetry, while mesophases were assigned by polarized light microscopy. Three series of compounds were investigated, namely: the TA(16)So(n) series, where n = 6-10; the TA(m)So(8) series, where m = 12-16; and a constant m + n series, TA(m)So(n) where m + n = 22. Typically, several solid phases and two smectic mesophases are found prior to isotropization to the liquid phase. As asymmetry decreases, two somewhat counterintuitive tendencies emerge: a general decrease in enthalpy/entropy for solid-solid and solid-first mesophase transitions, and an increase in solid-first mesophase transition temperatures. Yet, solid phases are seen to be more stable for the most asymmetric compounds, while the second mesophase is more stable for the least asymmetric ones, in what appears to be a more complex behavior than expected. The results are globally interpreted in terms of subtle differences in chain interdigitation and packing, and odd-even chain effects.

Language: English

Type (Professor's evaluation): Scientific