On the coexistence of uniaxial nematic phases in the lyotropic mixture sodium dodecyl sulphate/1-decanol/D₂O

GRAPHICAL ABSTRACT

ABSTRACT

Previously examined lyotropic mixtures sodium dodecyl sulphate (SDS) - 1-decanol (DeOH) - D₂O were prepared in four different molar ratios, M = [D₂O]/[SDS], where M = 30, 31, 32 and 33, to study the coexistence of uniaxial discotic (N_D) and calamitic (N_C) nematic phases as was claimed in recent articles. Those mixtures were investigated in a specific temperature range by laser conoscopy, polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) to construct partial phase diagram. By combining the results obtained from all these techniques, we could not observe the N_D − N_C phase coexistence in the phase diagram of SDS/DeOH/D₂O after the detailed investigation, as it was formerly reported. The results obtained in this study are in a good agreement with symmetry arguments and theoretical predictions but not with literature claims. The present results are also consistent with experimental investigations of other lyotropic mixtures whose phase diagrams were previously identified.

KEYWORDS:

• Coexistence
• lyotropic
• nematic
• phase
• phase diagram

Additional information

Funding

This work was financially supported by the Scientific and Technological Research Council of Turkey (TÜBITAK, grant number: 113Z469), and the Abant Izzet Baysal University Directorate of Research Projects Commission (BAP, grant number: 2017.03.03.1154), the National Council for Scientific and Technological Development, Brazil (CNPq, grant number: 465259/2014-6), the Coordination for the Improvement of Higher Education Personnel (CAPES), the National Institute of Science and Technology of Complex Fluids (INCT-FCx), the Research Support Center for Complex Fluids (NAP-FCx), and the São Paulo Research Foundation (FAPESP, grant numbers: 2014/50983-3, 2011/13616-4).