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

Cidade, M. T.; Pereira, Gonçalo; Bubnov, Alexej; Hamplová, Věra; Casquilho, J. P.

doi:10.1080/02678292.2011.628702

Cited by 12 publications

(5 citation statements)

References 29 publications

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“…The most important parameters that affect the apparent viscosity of ER fluids are the electric field and the flow field. Figure 2 demonstrates a competition between these fields in which a variation of the angle formed between the LC director and the flow direction (θ) is observed [19]. When the applied electric field is strong enough, the molecules will orient along the electric field direction (θ is approximately 90°), thus increasing the viscosity.…”

Section: Electrorheologymentioning

confidence: 99%

“…The effect of an electric field on the viscosity has been studied for different LCs such as N-(4-methoxybenzyldiene)-4 butyaniline (MBBA) [21] and 4-(4′-bis-2-hydroxymethyl) propyloxyhexyloxybiphenyl-4-hexyloxybenzoate (HBP 6/6) [19]. MBBA has shown a decrease in the viscosity under the application of an external electric field due to its negative dielectric anisotropy.…”

Section: Electrorheologymentioning

confidence: 99%

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Electrorheological characterization of dispersions in silicone oil of encapsulated liquid crystal 4-n-penthyl-4′-cyanobiphenyl in polyvinyl alcohol and in silica

Brehm¹,

Pereira²,

Leal³

et al. 2015

Phys. Scr.

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The electrorheological (ER) effect is known as the change in the apparent viscosity upon the application of an external electric field perpendicular to the flow direction. In this work we present the electrorheological behaviour of suspensions in silicone oil of two different dispersed phases: foams of liquid crystal 4-n-penthyl-4′-cyanobiphenyl (5CB) encapsulated in polyvinyl alcohol (PVA) and nano/microspheres of 5CB encapsulated in silica. We will present the viscosity curves under the application of an electric field ranging between 0 and 3 kV mm−1. The ER effect was observed for the suspensions of 5CB/PVA but not in the case of 5CB/silica. For the case of the suspensions of 5CB/PVA, the effect of the viscosity of the continuum phase and the concentration of the dispersed phase was analysed, showing that the enhancement of the viscosity of the suspension increases with the concentration, as expected, however the continuum phase viscosity has no significant effect, at least in the investigated viscosity range.

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Section: Electrorheologymentioning

confidence: 99%

Section: Electrorheologymentioning

confidence: 99%

Electrorheological characterization of dispersions in silicone oil of encapsulated liquid crystal 4-n-penthyl-4′-cyanobiphenyl in polyvinyl alcohol and in silica

Brehm¹,

Pereira²,

Leal³

et al. 2015

Phys. Scr.

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show abstract

“…In this respect, nematic phases have a lower viscosity than the isotropic ones of the same molecules. However, smectic phases have a significantly higher viscosity than isotropic liquids as well as other LC types in comparable conditions [14,[23][24][25][26]. Moreover, the viscosity of mesophases as anisotropic substances is not the same in different directions: along and perpendicular to molecular axes (in nematics) or layers (in smectics).…”

Section: Introductionmentioning

confidence: 99%

Alkylbenzoic and Alkyloxybenzoic Acid Blending for Expanding the Liquid Crystalline State and Improving Its Rheology

Yadykova,

Konstantinov,

Vlasova

et al. 2023

IJMS

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Thermotropic mesogens typically exist as liquid crystals (LCs) in a narrow region of high temperatures, making lowering their melting point with the temperature expansion of the mesophase state an urgent task. Para-substituted benzoic acids can form LCs through noncovalent dimerization into homodimers via hydrogen bonds, whose strength and, consequently, the temperature region of the mesophase state can be potentially altered by creating asymmetric heterodimers from different acids. This work investigates equimolar blends of p-n-alkylbenzoic (kBA, where k is the number of carbon atoms in the alkyl radical) and p-n-alkyloxybenzoic (kOBA) acids by calorimetry and viscometry to establish their phase transitions and regions of mesophase existence. Non-symmetric dimerization of acids leads to the extension of the nematic state region towards low temperatures and the appearance of new monotropic and enantiotropic phase transitions in several cases. Moreover, the crystal–nematic and nematic–isotropic phase changes have a two-step character for some acid blends, suggesting the formation of symmetric and asymmetric associates from heterodimers. The mixing of 6BA and 8OBA most strongly extends the region of the nematic state towards low temperatures (from 95–114 °C and 108–147 °C for initial homodimers, respectively, to 57–133 °C for the resulting heterodimer), whereas the combination of 4OBA and 5OBA gives the most extended high-temperature nematic phase (up to 156 °C) and that of 6BA and 9OBA (or 12OBA) provides the existence of a smectic phase at the lowest temperatures (down to 51 °C).

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“…Utilisation of the various types of polymeric backbones (polyacrylate [ 16 ], polymethacrylate [ 4 , 21 , 22 , 24 ], polysiloxane [ 23 , 25 , 26 , 27 , 28 ], polyurethane [ 29 ], etc.) for the design of LC macromolecular materials requires a specific molecular structure of the reactive terminal groups (acrylate [ 16 , 30 , 31 , 32 , 33 ], methacrylate [ 4 , 21 , 22 , 32 ], vinyl [ 12 , 23 , 27 , 34 ], thiols [ 35 , 36 , 37 ], etc.) of the respective monomeric LC materials used as functional reactive mesogens.…”

Section: Introductionmentioning

confidence: 99%

Design and Self-Assembling Behaviour of Calamitic Reactive Mesogens with Lateral Methyl and Methoxy Substituents and Vinyl Terminal Group

Bubnov

Cigl

Penkov³

et al. 2021

Polymers

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Smart self-organising systems attract considerable attention in the scientific community. In order to control and stabilise the liquid crystalline behaviour, and hence the self-organisation, the polymerisation process can be effectively used. Mesogenic units incorporated into the backbones as functional side chains of weakly cross-linked macromolecules can become orientationally ordered. Several new calamitic reactive mesogens possessing the vinyl terminal group with varying flexible chain lengths and with/without lateral substitution by the methyl (methoxy) groups have been designed and studied. Depending on the molecular structure, namely, the type and position of the lateral substituents, the resulting materials form the nematic, the orthogonal SmA and the tilted SmC phases in a reasonably broad temperature range, and the structure of the mesophases was confirmed by X-ray diffraction experiments. The main objective of this work is to contribute to better understanding of the molecular structure–mesomorphic property relationship for new functional reactive mesogens, aiming at further design of smart self-assembling macromolecular materials for novel sensor systems.

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

Cited by 12 publications

References 29 publications

Electrorheological characterization of dispersions in silicone oil of encapsulated liquid crystal 4-n-penthyl-4′-cyanobiphenyl in polyvinyl alcohol and in silica

Electrorheological characterization of dispersions in silicone oil of encapsulated liquid crystal 4-n-penthyl-4′-cyanobiphenyl in polyvinyl alcohol and in silica

Alkylbenzoic and Alkyloxybenzoic Acid Blending for Expanding the Liquid Crystalline State and Improving Its Rheology

Design and Self-Assembling Behaviour of Calamitic Reactive Mesogens with Lateral Methyl and Methoxy Substituents and Vinyl Terminal Group

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