Shear-induced flow and dynamics of the nematic phase of Sunset Yellow lyotropic chromonic liquid crystal

ABSTRACT

Fundamental understanding of rheological properties of lyotropic chromonic liquid crystals is inadequate compared to their thermotropic counterparts in spite of the growing interest in these materials. Here, we investigate the rheological properties of a lyotropic chromonic nematic liquid crystal (LCLC), prepared by dissolving 32 wt% of Sunset Yellow (SSY) in water. The flow curves (stress-strain rate, $\mathit{\sigma }-\dot{\gamma }$) at different temperatures exhibit three flow regimes R1, R2 and R3, respectively. At room temperature, in R1 ($\dot{\gamma }<{\dot{\gamma }}_{\mathit{cl}}$) and R3 ($\dot{\gamma }>{\dot{\gamma }}_{\mathit{cu}}$) the sample exhibits Newtonian flow behaviour ($\mathit{\sigma }\propto \dot{\gamma }$), whereas, in R2 (${\dot{\gamma }}_{\mathit{cl}}<\dot{\gamma }<{\dot{\gamma }}_{\mathit{cu}}$), it shows a power-law dependence ($\mathit{\sigma }\sim {\dot{\gamma }}^{\mathit{\beta }}$). With increasing shear rate the change of stress from R1 to R2 is continuous, whereas the change is discontinuous from R2 to R3. We observe stress fluctuations under steady shear in regime R2 similar to those reported in worm-like micellar systems and in thermotropic twist-bend nematic liquid crystals. The non-monotonic flow behaviour and the stress dynamics are corroborated using in situ rheo-microscopy.

Graphical abstract

KEYWORDS:

• Chromonic liquid crystal
• Rheology
• Sunset Yellow
• Rheo-microscopy

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Surajit Dhara (Conceptualisation, Data Analysis and Writing), M. V. Saisavadas (Experiments, Data Analysis and Writing), M. Praveen Kumar (Experiments) and B. V. R. Tata (Discussions). We thank Dr. G. Ravikumar for useful suggestions.

Data availability statement

The data that support the findings of this study are available within the article.

Additional information

Funding

This work is supported by the Science and Engineering Research Board (SERB), Core Grant Project (CRG) of the Department of Science and Technology (DST), India (Project number: DST-SERB/CRG/2019/003714). BVR acknowledges DAE-RRF fellowship. SD acknowledges support from IoE (UoH/IoE/RC1-20-010).