ABSTRACT
Switchable liquid crystal (LC) composites are a unique and attractive class of functional materials due to their extensive use in various applications including smart and privacy windows. Demand for developing smart windows with good switchable performance has steadily increasing in the past decades due to their importance in energy saving. Herein, we present the use of novel and highly active switchable LC composite material-octadecanol-doped LC-prepared via a facile, low-cost, and scalable process, for thermally or electrically controlled transparency windows. A systematic study of the switchable behavior reveals the formation of a reversible molecular arrangement between the LC and the octadecanol, which allows control of the transparency through scattering modulation of the device by voltage or temperature. The devices fabricated by sandwiching the LC composite material between two ITO-covered glass slides present switchable performance with high potential for cost-effective utilization in various applications, such as light shutters, smart or privacy windows.
ABSTRACT
We report the design, synthesis, detailed characterization, and analysis of a new multifunctional π-conjugated bola-amphiphilic chromophore: oligo-(p-phenyleneethynylene)dicarboxylic acid with dialkoxyoctadecyl side chains (OPE-C18-1). OPE-C18-1 shows two polymorphs at 123 K (OPE-C18-1') and 373 K (OPE-C18-1â³), whose crystal structures were characterized via single crystal X-ray diffraction. OPE-C18-1 also exhibits thermotropic liquid crystalline property revealing a columnar phase. The inherent π-conjugation of OPE-C18-1 imparts luminescence to the system. Photoluminescence measurements on the mesophase also reveal similar luminescence as in the crystalline state. Additionally, OPE-C18-1 shows mechano-hypsochromic luminescence behavior. Density functional theory (DFT)-based calculations unravel the origins behind the simultaneous existence of all these properties. Nanoindentation experiments on the single crystal reveal its mechanical strength and accurately correlate the molecular arrangement with the liquid crystalline and mechanochromic luminescence behavior.
ABSTRACT
Effect of a polymer network on the threshold voltage of the Fréedericksz transition, Frank elastic constants, switching speed, and the rotational viscosity are investigated in a polymer-stabilized bent-core nematic liquid crystal with different polymer concentrations. These polymer networks form virtual surfaces with a finite anchoring energy. The studies bring out several differences in comparison to similar studies with a calamitic liquid crystal as the nematic host. For example, on varying the polymer content the threshold voltage decreases initially, but exhibits a drastic increase above a critical concentration. A similar feature-reaching a minimum before rising-is seen for the bend elastic constant, which gets enhanced by an order of magnitude for a polymer content of 2.5 wt %. In contrast, the splay elastic constant has a monotonic variation although the overall enhancement is comparable to that of the bend elastic constant. The behavior changing at a critical concentration is also seen for the switching time and the associated rotational viscosity. The presence of the polymer also induces a shape change in the thermal dependence of the bend elastic constant. We explain the features observed here on the basis of images obtained from the optical and atomic force microscopy.
