Electro-rheology study of a series of liquid crystal cyanobiphenyls: experimental and theoretical treatment

Patrício, Pedro; Leal, Catarina Marques Mendes Almeida da Rosa; Pinto, L. F. V.; Boto, A.; Cidade, M. T.

doi:10.1080/02678292.2011.610471

Cited by 33 publications

(12 citation statements)

References 27 publications

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“…Such fluids whose viscosity can be controlled by electric fields are referred to as electrorheological (ER) fluids [20]. Although typical ER fluids consist of suspensions of dielectric particles in an electrically insulating oil, some studies have also investigated the ER properties of NLCs [21][22][23]. In NLCs, the electrorheological effect is dependent on the dielectric anisotropy, as was clearly demonstrated by Nagaya et al in experiments using a series of mixtures of two NLCs with positive and negative dielectric anisotropies [16].…”

Section: Introductionmentioning

confidence: 99%

Negative viscosity of a liquid crystal in the presence of turbulence

et al. 2019

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We report on the discovery of enormous negative viscosity in a nematic liquid crystal in the presence of turbulence induced by electric fields. As the negative viscosity in this system is so large, we are able to observe several phenomena originating from it. For example, we observe a spontaneous shear flow that rotates the upper disk of a rheometer, as well as the reversal of the rotational direction upon applying an external torque in the opposite direction. Hysteresis loops are also observed in the shear-stress-shear-rate curves, which is reminiscent of those seen for ferromagnetic and ferroelectric materials. The similarities between the phenomena observed for our system and ferroic materials are comprehensively demonstrated, although the two systems are fundamentally different in that the former is out of equilibrium. We elucidate the origin of the negative viscosity and propose a simple model that reproduces the phenomena observed in this active fluid.

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Section: Introductionmentioning

confidence: 99%

Negative viscosity of a liquid crystal in the presence of turbulence

et al. 2019

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“…We finally discuss difference of our method with existing methodology in connection with the electrorheology of disclinations. Within Leslie-Ericksen (LE) theory in one dimension using free energy minimization technique, both the effect of rheology 64 and nonuniform electric field 40 has been exercised. Traditionally, LE theory is suitable in deep within the nematic phase where it is assumed that { S , B 2 , l } are constant in the orientation tensor and elastic distortion is concealed in n only.…”

Section: Methodsmentioning

confidence: 99%

Controlling motile disclinations in a thick nematogenic material with an electric field

Bhattacharjee

2018

Sci Rep

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Manipulating topological disclination networks that arise in a symmetry-breaking phase transformation in widely varied systems including anisotropic materials can potentially lead to the design of novel materials like conductive microwires, self-assembled resonators, and active anisotropic matter. However, progress in this direction is hindered by a lack of control of the kinetics and microstructure due to inherent complexity arising from competing energy and topology. We have studied thermal and electrokinetic effects on disclinations in a three-dimensional nonabsorbing nematic material with a positive and negative sign of the dielectric anisotropy. The electric flux lines are highly nonuniform in uniaxial media after an electric field below the Fréedericksz threshold is switched on, and the kinetics of the disclination lines is slowed down. In biaxial media, depending on the sign of the dielectric anisotropy, apart from the slowing down of the disclination kinetics, a nonuniform electric field filters out disclinations of different topology by inducing a kinetic asymmetry. These results enhance the current understanding of forced disclination networks and establish the presented method, which we call fluctuating electronematics, as a potentially useful tool for designing materials with novel properties in silico.

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“…Rotational viscosity of the liquid crystals were determined at room temperature by means of dynamic light scattering (DLS) measurements (frequency-doubled diodepumped ND:YAG laser (532 nm, 80 mW), an ALV APD based "pseudo" cross correlation detector, ALV-6010/160 correlator and single mode optical fiber with a GRIN lens was used to collect the scattered light within one coherence area). By choosing the appropriate geometry, pure modes can be measured with relaxation rates // is affected by the backflow, which is in the case of cyanobiphenyls and E7 in general small 27,29,36,37 and so .…”

Section: Determination Of Basic Materials Parametersmentioning

confidence: 99%

Director reorientation dynamics of ferromagnetic nematic liquid crystals

et al. 2018

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Successful realization of ferromagnetic nematic liquid crystals has opened up the possibility to experimentally study a completely new set of fundamental physical phenomena. In this contribution we present a detailed investigation of some aspects of the static response and the complex dynamics of ferromagnetic liquid crystals under the application of an external magnetic field. Experimental results are then compared with a macroscopic model. Dynamics of the director were measured by optical methods and analyzed in terms of a theoretical macroscopic model. A dissipative cross-coupling coefficient describing the dynamic coupling between the two system order parameters, the magnetization and the nematic director, is needed to explain the results. In this contribution we examine the dependency of this coefficient on material parameters and the saturation magnetization and the liquid crystal host. Despite the complexity of the system, the theoretical description allows for a proper interpretation of the results and is connected to several microscopic aspects of the colloidal suspension.

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Electro-rheology study of a series of liquid crystal cyanobiphenyls: experimental and theoretical treatment

Cited by 33 publications

References 27 publications

Negative viscosity of a liquid crystal in the presence of turbulence

Negative viscosity of a liquid crystal in the presence of turbulence

Controlling motile disclinations in a thick nematogenic material with an electric field

Director reorientation dynamics of ferromagnetic nematic liquid crystals

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