Interfacing of Surface Functionalized Carbon Quantum Dots with Antiferroelectric Liquid Crystalline Molecules to Enhance Electro-Optical Characteristics

We have studied the effects of carbon quantum dots (CQDs) in a wide temperature range room-temperature antiferroelectric liquid crystal mixture. Multiple techniques, including Raman, UV-vis Fourier transform infrared spectroscopies, and high-resolution transmission electron microscopy (HRTEM), are used to characterize the synthesized CQDs. The HRTEM image indicates the quasi-spherical shape of CQDs of particle size 1.0-5.5 nm. Textural and switching characteristics of mixture W-287 and its nanocomposites (with CQDs) are investigated in the wide temperature range of the antiferroelectric chiral smectic C (SmC*_a) phase and the narrow range of the ferroelectric chiral smectic C (SmC*) phase. Observed textures and other switching characteristics were used to identify the appearance of different mesophases. Compared to the pure W-287 AFLC mixture, a drastic increase in spontaneous polarization (329 to 706 nC/cm²), a substantial decrease of switching time (3 ms to 20 μs), rotational viscosity (49 to 7 mPa s), and anchoring energy coefficients for the composite systems were found for the SmC*_a phase in the present investigation. The observed changes are due to the enhanced dipolar ordering as a consequence of the sp³/sp² hybridization of CQDs, which forms an intense coupling in the liquid crystal matrix. This study signifies that the dispersed CQDs have effectively settled in the matrix of the present AFLC mixture without interfering with the hosts’ molecular ordering. These findings are useful for the potential applicability of composite systems for optical devices with a microsecond response.