Critical Role of the Spacer Length of Gemini Surfactants on the Formation of Ionic Liquid Crystals and Thermotropic Behavior

• Type: Article in International Scientific Journal
• Date: 2017

Authors

Fernandes, RMF (Author) Other; Wang, YJ (Author) Other; Tavares, PB (Author) Other; Nunes, SCC (Author) Other; Pais, AACC (Author) Other; Eduardo F Marques (Author) FCUP

Journal

Title: Journal of Physical Chemistry B

Vol. 121

ISSN: 1520-6106

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 16 Citations

Scopus - 17 Citations

Other information

Authenticus ID: P-00N-700

DOI: 10.1021/acs.jpcb.7b08618

Abstract (EN): Numerous reports have shown that the self assembling properties of 12-s-12 bis(quaternary ammonium) gemini surfactants in aqueous solution are significantly influenced by s, the number of methylene groups in the covalent spacer. However, the role played by s on the phase behavior of the single compounds has not been investigated in a similarly systematic way. Here, we report on the thermotropic phase behavior of the anhydrous compounds with s = 2-6, 8, 10, and 12, resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM), and Xray diffraction (XRD). All of the compounds show a stepwise melting behavior, decomposing at 200 degrees C. As the spacer length increases, nonmonotonic trends are observed for the thermodynamic parameters of the thermotropic phase transitions, mesophase formation, and solid-state door spacings. In particular, the number and type of mesophases (ordered smectic phases and/or fluid smectic liquid crystals) depend critically on s. Further, upon heating molecules with s < 8 decompose before the liquid phase, while those with long spacers, s = 8-12, reach the isotropization (clearing) temperature, hence forming both ionic liquid crystals and ionic liquid phases. We demonstrate that the melting behavior and type of ionic mesophases formed by gemini molecules can be usefully manipulated by a simple structural parameter like the length of the covalent linker.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 10