Cholesteryl ester liquid crystals exhibit thermochromic properties related to the existence of a twisted nematic phase. When used in applications such as thermal mapping, a color change is often monitored by video cameras. Thus, quantitative methods to evaluate thermochromic behavior (e.g., blue-start, red-start, red-end, color play and bandwidth) from video analysis are desirable. However, obtaining quantitative color measurements from digital images remains a significant technical challenge, especially for highly reflective samples such as liquid crystals (for which ultraviolet−visible (UV−vis) reflectance spectroscopy is typically used). We developed a method to determine thermochromic properties from videos of liquid crystal cooling under polarized light microscopy. We relate observed color transitions to quantifiable changes in the cumulative color difference in the International Commission on Illumination (CIE) L*a*b* color space and validate this method with UV−vis reflectance spectroscopy. The measured thermochromic behavior and associated measurement uncertainties (coefficient of variations) were comparable to UV−vis reflectance measurements.

Cholesteryl ester liquid crystals exhibit thermochromic properties related to the existence of a twisted nematic phase. We formulate ternary mixtures of cholesteryl benzoate (CB), cholesteryl pelargonate (CP), and cholesteryl oleyl carbonate (COC) to achieve thermochromic behavior. We aim to achieve thermochromic fibers by incorporating the liquid crystal formulations into electrospun fibers. Two methods of incorporating the liquid crystal (LC) are compared: (1) blend electrospinning and (2) coaxial electrospinning using the same solvent system for the liquid crystal. For blend electrospinning, intermolecular interactions seem to be important in facilitating fiber formation since addition of LC can suppress bead formation. Coaxial electrospinning produces fibers with higher nominal fiber production rates (g/hr) and with higher nominal LC content in the fiber (wt. LC/wt. polymer assuming all of the solvent evaporates) but larger fiber size distributions as quantified by the coefficient of variation in fiber diameter than blend electrospinning with a single nozzle. Importantly, our proof-of-concept experiments demonstrate that coaxially electrospinning with LC and solvent in the core preserves the thermochromic properties of the LC so that thermochromic fibers are achieved.

Performing reactions in the presence of self-assembled hierarchical structures of amphiphilic macromolecules can accelerate reactions while using water as the bulk solvent due to the hydrophobic effect. We leveraged non-covalent interactions to self-assemble filled-polymer micelle nanoreactors (NR) incorporating gold nanoparticle catalysts into various amphiphilic polymer nanostructures with comparable hydrodynamic nanoreactor size and gold concentration in the nanoreactor dispersion. We systematically studied the effect of the hydrophobic co-precipitant on self-assembly and catalytic performance. We observed that co-precipitants that interact with gold are beneficial for improving incorporation efficiency of the gold nanoparticles into the nanocomposite nanoreactor during self-assembly but decrease catalytic performance. Hierarchical assemblies with co-precipitants that leverage noncovalent interactions could enhance catalytic performance. For the co-precipitants that do not interact strongly with gold, the catalytic performance was strongly affected by the hydrophobic microenvironment of the co-precipitant. Specifically, the apparent reaction rate per surface area using castor oil (CO) was over 8-fold greater than polystyrene (750 g/mol, PS 750); the turnover frequency was higher than previously reported self-assembled polymer systems. The increase in apparent catalytic performance could be attributed to differences in reactant solubility rather than differences in mass transfer or intrinsic kinetics; higher reactant solubility enhances apparent reaction rates. Full conversion of 4-nitrophenol was achieved within three minutes for at least 10 sequential reactions demonstrating that the nanoreactors could be used for multiple reactions.