Amorphous Blue Phase Liquid Crystal Gelation Modulated by Functionalized CdSe/ZnS Quantum Dots: Implications for Oil Recovery

Abstract

Physical gelation of liquid crystals (LCs), brought about by noncovalent interactions, is known to play a significant role in enhancing the mechanical as well as electro-optical properties of the LC phases. The present study investigates the effect of surface-functionalized quantum dots (QDs) on the mechanical properties of the amorphous blue phase (BPIII) liquid crystal physical gel. The BPIII, which occurs in highly chiral LCs, is known to exhibit electric-field-driven switching between dark and bright states with submillisecond response time. The gelation of BPIII is achieved by the addition of a low molecular weight organogelator to a blue phase liquid crystal (BPLC). The Pristine-BPIII-gel, without QDs, exhibits continuous and dense fibers visible even with an optical microscope, indicating the formation of a strong gel. The QD-doped BPLC, on the other hand, shows no semblance of gelation in BPIII. The electro-optical measurements show a residual birefringence effect in the field-off state in both samples. Further investigations using Cryo-scanning electron microscopy (Cryo-SEM) show the presence of fragmented gel fibers in the case of QD-doped BPLC. High-resolution SEM studies reveal that each fiber consists of a bundle of fibrils, with the diameter of a fibril being ∼25 nm, indicating the formation of a “nanogel.” Quantitative rheological measurements show a significant reduction (a factor of 30) in storage modulus and an increased linear viscoelastic regime, characteristics of a weak yet robust gel in the case of QD-doped-BPIII-gel, compared to that of Pristine-BPIII-gel. The Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) data indicate hindered hydrogen bonding and dimerization, the mechanisms responsible for gelation. The data also reveal a possible ligand exchange between the surface functional group and organogelator responsible for gelation modulation, with possible applications in drug delivery systems and oil recovery agents.