Periodic Formation/Breakdown of Lamellar Aggregates with Anionic Cyanobiphenyl Surfactants

Masanobu Sagisaka*, Yayoi Fujita, Yusuke Nakanishi, Hisayuki Takahashi, Narumi Tsuyoshi, Craig James, Atsushi Yoshizawa, Azmi Mohamed, Frédéric Guittard, Julian Eastoe

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

This study reports unusual behavior of aqueous-phase lamellar aggregates with a new class of hybrid surfactant, CB-B2ES, having mesogenic units {6-[4-(4-cyanophenyl)phenyloxy]hexyl} and temperature-sensitive oxyethylated (butoxyethoxyethyl) tails. These tails are poorly miscible and likely to microsegregate if the surfactant molecules assemble. Lamellar aggregates appear at CB-B2ES concentrations higher than 5 wt % and were found to undergo repeat formation/breakdown periodically at 30 °C, with an average domain lifetime of ∼10 s. To investigate effects of the temperature-sensitive oxyethylene units on the hydrophilic/lipophilic balance (HLB) of the CB-B2ES bilayers, a fluorescence probe 1-pyrene-carboxaldehide was solubilized in the mixtures to sense the micro-environmental polarities. Fluorimetric measurements suggested that the polarity of CB-B2ES bilayers is very similar to that of the non-ethoxylated CB-B2ES analogue at high temperatures (≥65 °C). However, for CB-B2ES, polarity increased with a decreasing temperature, in contrast with the small decrease in polarity observed for analogous non-ethoxylated bilayers. This is consistent with increased hydration of the oxyethylene units in CB-B2ES bilayers at low temperatures. The periodic formation/breakdown and cooling-induced hydrophilicity of the CB-B2ES lamellar aggregates did not appear in the non-hybrid and/or non-ethoxylated surfactant systems. Therefore, the combination of two unsymmetrical tails, one containing oxyethylene units and the other containing cyanobiphenyl terminal tips, must play an important role promoting this unusual behavior.

Original languageEnglish
Pages (from-to)13040-13047
Number of pages8
JournalLangmuir
Volume31
Issue number47
DOIs
Publication statusPublished - 5 Nov 2015

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