Self-assembly of azobenzene bilayer membranes in binary ionic liquid-water nanostructured media

Tejwant Singh Kang, Keita Ishiba, Masa-Aki Morikawa, Nobuo Kimizuka

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Anionic azobenzene-containing amphiphile 1 (sodium 4-[4-(N-methyl-N- dodecylamino)phenylazo]benzenesulfonate) forms ordered bilayer membranes in binary ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C 2mim][C2OSO3])-water mixtures. The binary [C2mim][C2OSO3]-water mixture is macroscopically homogeneous at any mixing ratio; however, it possesses fluctuating nanodomains of [C2mim][C2OSO3] molecules as observed by dynamic light scattering (DLS). These nanodomains show reversible heat-induced mixing behavior with water. Although the amphiphile 1 is substantially insoluble in pure water, it is dispersible in the [C 2mim][C2OSO3]-water mixtures. The concentration of [C2mim][C2OSO3] and temperature exert significant influences on the self-assembling characteristics of 1 in the binary media, as shown by DLS, transmission electron microscopy (TEM), UV-vis spectroscopy, and zeta-potential measurements. Bilayer membranes with rod- or dotlike nanostructures were formed at a lower content of [C2mim] [C2OSO3] (2-30 v/v %), in which azobenzene chromophores adopt parallel molecular orientation regardless of temperature. In contrast, when the content of [C2mim][C2OSO3] is increased above 60 v/v %, azobenzene bilayers showed thermally reversible gel-to-liquid crystalline phase transition. The self-assembly of azobenzene amphiphiles is tunable depending on the volume fraction of [C 2mim][C2OSO3] and temperature, which are associated with the solvation by nanoclusters in the binary [C 2mim][C2OSO3]-water media. These observations clearly indicate that mixtures of water-soluble ionic liquids and water provide unique and valiant environments for ordered molecular self-assembly.

Original languageEnglish
Pages (from-to)2376-2384
Number of pages9
JournalLangmuir
Volume30
Issue number9
DOIs
Publication statusPublished - Mar 11 2014

Fingerprint

Ionic Liquids
Azobenzene
Ionic liquids
Self assembly
self assembly
membranes
Membranes
Water
liquids
Amphiphiles
water
Dynamic light scattering
light scattering
azobenzene
Molecular orientation
Nanoclusters
Solvation
Zeta potential
Chromophores
mixing ratios

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

Cite this

Self-assembly of azobenzene bilayer membranes in binary ionic liquid-water nanostructured media. / Kang, Tejwant Singh; Ishiba, Keita; Morikawa, Masa-Aki; Kimizuka, Nobuo.

In: Langmuir, Vol. 30, No. 9, 11.03.2014, p. 2376-2384.

Research output: Contribution to journalArticle

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abstract = "Anionic azobenzene-containing amphiphile 1 (sodium 4-[4-(N-methyl-N- dodecylamino)phenylazo]benzenesulfonate) forms ordered bilayer membranes in binary ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, [C 2mim][C2OSO3])-water mixtures. The binary [C2mim][C2OSO3]-water mixture is macroscopically homogeneous at any mixing ratio; however, it possesses fluctuating nanodomains of [C2mim][C2OSO3] molecules as observed by dynamic light scattering (DLS). These nanodomains show reversible heat-induced mixing behavior with water. Although the amphiphile 1 is substantially insoluble in pure water, it is dispersible in the [C 2mim][C2OSO3]-water mixtures. The concentration of [C2mim][C2OSO3] and temperature exert significant influences on the self-assembling characteristics of 1 in the binary media, as shown by DLS, transmission electron microscopy (TEM), UV-vis spectroscopy, and zeta-potential measurements. Bilayer membranes with rod- or dotlike nanostructures were formed at a lower content of [C2mim] [C2OSO3] (2-30 v/v {\%}), in which azobenzene chromophores adopt parallel molecular orientation regardless of temperature. In contrast, when the content of [C2mim][C2OSO3] is increased above 60 v/v {\%}, azobenzene bilayers showed thermally reversible gel-to-liquid crystalline phase transition. The self-assembly of azobenzene amphiphiles is tunable depending on the volume fraction of [C 2mim][C2OSO3] and temperature, which are associated with the solvation by nanoclusters in the binary [C 2mim][C2OSO3]-water media. These observations clearly indicate that mixtures of water-soluble ionic liquids and water provide unique and valiant environments for ordered molecular self-assembly.",
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