Electrorheological Effect of “Side‐on” Liquid Crystalline Polysiloxane

Abstract

Liquid crystals have attracted great attention in the field of engineering. Their application to the development of screens and displays is a representative example of their unique properties, because it demonstrates their excellent molecular-orientation ability. To develop further uses of liquid crystals, we have investigated the electrorheological (ER) effect, in which viscosity is controlled by the strength of an applied electric field.Since the discovery of the ER effect by Winslow in 1949, [1] several ER fluids have been widely studied as smart materials for industrial uses. After extensive research on ER fluids, it has been found that side-chain liquid crystalline polymers (LCPs) show a relatively large change in shear stress upon applying an electric field, because the thermal motion of terminal mesogenic groups is independent from that of the polymer backbone. [2][3][4][5][6][7][8] In addition, ER effects of the side-chain LCPs have been commonly observed at temperatures above the clearing point. This observation can be attributed to the enhanced order, which results from the formation of the liquid crystalline phase. From a practical viewpoint, side-chain LCPs exhibiting a smectic phase have a high viscosity in the phase, which causes a poor response to the application of an electric field. This limits the temperature range at which ER effects can be measured when LCPs showing a smectic phase are used as the ER fluids. It is widely known that the viscosity in the smectic phase is usually higher than that of the nematic phase, in accordance with the different order parameters of the various liquid crystalline phases. The generated shear stress is defined as the difference between the shear stress in the presence and that in the absence of an applied electric field. Therefore, a lower shear stress in the absence of an electric field is expected to enhance the ER effect.

Electric‐Field‐Induced Viscosity Change of a Nematic Liquid Crystal with Gold Nanoparticles

“…For the further development of the utility of LCs, we have investigated the electro-rheological (ER) effect in which viscosity is controlled by the strength of an applied electrical field. [1][2][3][4] ER fluids have been widely studied as smart materials for industrial utilities [5][6][7][8][9][10] since the ER effect was first discovered by Winslow in 1949. [11] ER fluids are divided into two types on the basis of the component of the fluids and the mechanism of the effect.…”

Tuning Quantum‐Dot Organization in Liquid Crystals for Robust Photonic Applications

“…The characterization data matched that of a previous report. [33] Synthesis of Methyl 2-Hydroxy-4-(Octyloxy)benzoate (3) Methyl 2,4-dihydroxybenzoate 2 (7.8 g, 46.4 mmol) was dissolved in butanone (155 mL) and treated with 10 g of molecular sieves (4A) and potassium carbonate (32.1 g, 232 mmol). The whole reaction was heated to reflux.…”

Rheological characterisation of a liquid-crystalline diol and its dependence with an applied electric field

“…This phenomenon was found in particular for the polysiloxanes-based LC polymers [12][13][14], where a significant increase of the viscosity, of about one order of magnitude, was observed and explained in terms of the orientation effect of side-chain mesogenic groups attached to the polymeric backbone. A similar increase was also found for miscible blends of liquid-crystalline polymers [15].…”