Effect of Dysprosium-Doped Nanoparticles on Structural, Thermal, and Optical Properties of Liquid Crystalline p-(n-Heptyloxy) Benzoic Acid

Abstract

This study probes into the structural, thermal, and optical transformations induced in liquid crystalline p-(n-heptyloxy) benzoic acid (7-OBA) by dispersion of dysprosium-doped lithium zinc phosphate nanoparticles [Li₄Zn(PO₄)₂:Dy³⁺] (DLZP-NPs) via the thermal combustion method. X-ray diffraction confirmed the successful incorporation of DLZP-NPs, maintaining the inherent liquid crystalline structure of 7-OBA. Detailed morphological studies using scanning electron microscopy revealed a uniform dispersion of nanoparticles, while energy-dispersive X-ray spectroscopy verified the consistent presence of Dy³⁺ ions throughout the matrix. Fourier-transform infrared spectroscopy identified functional groups within the nanocomposites, with distinct shifts in the stretching regions of C=O, C=C, and C–H bonds, indicative of molecular interactions between the 7-OBA matrix and the nanoparticles. These shifts suggest a reorganization of the molecular environment, facilitated by the synergistic effects of DLZP-NPs. Thermal and phase transition behaviors of the nanocomposites were examined using differential scanning calorimetry and polarized optical microscopy, which highlighted subtle yet significant alterations in phase transition temperatures and liquid crystalline textures. Optical absorption studies revealed a reduction in the energy bandgap of 7-OBA from 3.97 to 3.64 eV with increasing nanoparticle concentrations, emphasizing the potential for bandgap tuning. Spectroscopic ellipsometry further demonstrated a decrease in optical permittivity with increased nanoparticle dispersion, reflecting modifications in electronic polarizability.