Optical signal and optical axes in uniaxial and biaxial nematic phases

ABSTRACT

In this work we will study the behavior of the optical signal and optical axes along the continuous transition of a lyotropic system from a nematic discotic ($N_D$) phase to a nematic calamitic ($N_C$) phase; we will study in detail the case in which there is a biaxial nematic ($N_B$) phase at the interstice between these two uniaxial phases. It will be shown that the optical signal and optical axes change simultaneously in order to agree with the optical signals of the uniaxial phases at their borders: the optical signal is positive at the frontiers with the $N_D$ phase and it turns to be negative at the frontiers with the $N_C$ phase. Concomitantly, the optical axes rotates from the ${\overrightarrow{e}}_z$ direction to the ${\overrightarrow{e}}_x$ direction. We will illustrate these findings with experimental data that confirm our results.

KEYWORDS:

• Optical signal
• optical axes
• biaxial nematic phase
• refractive indices

PACS:

• 61.30.-v
• 42.65.Jx

Acknowledgments

Many thanks to T.A. Pedreira (Brazil) for the careful proofreading of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

T. Davincy http://orcid.org/0000-0002-6484-3512

O.R. Santos http://orcid.org/0000-0002-0987-1465

N.M. Kimura http://orcid.org/0000-0002-9369-4966

A.J. Palangana http://orcid.org/0000-0002-1291-7903

Additional information

Funding

From Brazil, the National Council for Scientific and Technological Development (CNPq – 465259/2014-6), the Coordination for the Improvement of Higher Education Personnel (CAPES), the National Institute of Science and Technology Complex Fluids (INCT-FCx), and Fundação Araucária (PR).