Nematic lyotropic liquid crystalline ordering in rhizome powder of Curcuma species and water mixtures: rheological properties and antioxidant applications

Abstract

This study focuses on developing a self-assembled lyotropic phase in four Curcuma species viz. Curcuma amada (CA), Curcuma caesia (CC), Curcuma Longa (CL), and Curcuma Zedoaria (CZ) using their rhizome powder in an aqueous environment. Polarizing optical microscopy (POM) depicts the maltese cross textures with twisted thread and fractional topological charge of +1/2, which confirms the formation of nematic phases in CA, CC, CL, and CZ/water mixtures along with orientation order parameters 0.34, 0.44, 0.54, and 0.46, respectively. X-ray diffraction (XRD) analysis shows a broad diffraction peak at 2θ ≅ 20°, which further validates the nematic ordering in these mixtures. Fourier transform infrared (FTIR) spectroscopy analysis confirms the inter- and intramolecular hydrogen bonding among keto/enol forms of curcumin and starch molecules with water. Rheological studies demonstrate the shear-thinning behaviour with negative values of power-law exponent n, and strong elastic properties of nematic phases in all the cases. The viscosity of these species varies according to their molecular alignment. Specifically, CL exhibited the highest molecular alignment and viscosity. Nematic lyotropic mixtures are further explored for antioxidant potential through DPPH and phosphomolybdenum assays. The lowest IC₅₀ (25.3 and 26.6, respectively) values for CL-based nematic lyotropic phases are noted for both assays, predicting their best antioxidant potential. The biodegradable and non-toxic nature of Curcuma-based nematic lyotropic liquid crystals (LLCs) offers their potential for advanced material formulations, therapeutic delivery systems, cosmetic applications, and anti-aging formulations, aligning with global trends toward sustainable and green product development.