Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

ABSTRACT

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.

Graphical Abstract

KEYWORDS:

• Lyotropic nematic phases
• surfactant alkyl chain length
• phase transition
• IBM model of nematic phases
• laser conoscopy
• small-angle X-ray scattering

Acknowledgements

The authors thank the following funding agencies, commissions and projects for supporting this work. From Turkey: the Scientific and Technological Research Council of Turkey (TÜBİTAK) [grant number 113Z469]; Abant Izzet Baysal University Directorate of Research Projects Commission (BAP) [grant number 2014.03.03.766]. From Brazil: Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPQ); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Instituto Nacional de Ciência e Tecnologia de Fluidos Complexos (INCT-FCx); Núcleo de Apoio à Pesquisa de Fluidos Complexos (NAP-Fcx); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors thank the following funding agencies, commissions and projects for supporting this work. From Turkey: the Scientific and Technological Research Council of Turkey (TÜBİTAK) [grant number 113Z469] and Abant Izzet Baysal University Directorate of Research Projects Commission (BAP) [grant number 2014.03.03.766]. From Brazil: Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPQ); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Instituto Nacional de Ciência e Tecnologia de Fluidos Complexos (INCT-FCx); Núcleo de Apoio à Pesquisa de Fluidos Complexos (NAP-Fcx) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).