Influence of dilution by polydimethylsiloxane on electrorheological effect of side-chain liquid crystalline polysiloxane

Abstract

A liquid crystalline polysiloxane (LCP), having an ether bond in the spacer between its siloxane main chain and its mesogenic-group side chains, exhibited a very small electrorheological (ER) effect or increase in shear stress upon application of an electric field, but mixtures of the LCP and polydimethylsiloxane (PDMS) exhibited a sharply increasing ER effect with increasing PDMS content throughout the tested range of up to 0.5 of PDMS weight fraction. When phenyl-substituted PDMS (Ph-PDMS) at a weight fraction of 0.3 was used instead of PDMS, however, the ER effect decreased with increasing phenyl content and became nearly undetectable with Ph-PDMS having a phenyl content (ratio of substituted phenyl groups to initial methyl groups) of approximately 15%. DSC analyses showed that the ER effect of the LCP/ PDMS mixtures occurred undiminished throughout a temperature range in which LCP itself is an isotropic liquid in the absence of an applied electric field and suggested that the LC structure of the LCP was maintained even when it was diluted with PDMS in weight fractions of 0.5 or higher, but disrupted when diluted by a 0.3 weight fraction of Ph-PDMS having a 15% phenyl content. Optical microscopic observation of the mixtures of the LCP with a 0.3 weight fraction of PDMS or Ph-PDMS (15% phenyl content) showed that both consisted of uniformly dispersed micron-sized droplets which became elongated in the direction of the applied electric field when it was applied alone but became smaller when both the electric field and shear were applied. These results suggest that the phase separation between the LCP and the dilution oil, as well as the existence and orientation of LC domains, is essential for the generation of a large ER effect.

Three-dimensional observation of an immiscible polymer blend subjected to a step electric field under shear flow

“…One was a liquid-crystalline polymer (LCP) (Fig. 1) [10]. The other was a polyisobutylene (PIB), which was a mixture of two PIB's with different molecular weights of 1350 and 500.…”

“…In fact, for two fluids with mismatched electric properties, such as permittivity and conductivity, under the application of an electric field, remarkable changes have been reported [9][10][11][12][13]. The morphological change is accompanied by a viscosity change.…”

Electrorheological Properties of Liquid Crystalline Gold Nanoparticles in a Nematic Solvent

“…To date, there have been many experimental and theoretical studies of both their fundamental and their practical applications [1][2][3][4][5][6][7][8][9][10] since the first investigation of the phenomenon by Winslow [11]. ER fluids are mainly divided into two types on the basis of the component of the fluids and the mechanism of the effect.…”

Layer Formation and Annihilation in an Immiscible Polymer Blend in Electric and Shear Flow Fields

“…Some studies have fully explained the ER mechanism. [2][3][4][5][6][7] In immiscible polymer blend ER fluids, it is considered that the viscosity change may be brought about by the morphological change. These blends are composed of a liquid crystalline polymer (LCP) and dimethylsiloxane (DMS); where the LCP is greater than the DMS in viscosity, permittivity, and conductivity.…”

“…[2][3][4]7,9) In the absence of an electric field, the apparent viscosity is low because the droplets can flow easily with sliding over each other in the matrix of DMS with low viscosity. When subjected to an electric field, the droplets of LCP with high viscosity become elongated along the field due to the electrostriction exerted on the interface between the LCP and DMS, and join to form bridges between the electrodes, resulting in an increase of apparent viscosity.…”