Rheological Theory and Simulation of Surfactant Nematic Liquid Crystals

Rey, Alejandro D.; Herrera‐Valencia, E. E.

doi:10.1002/9781118336632.ch2

Cited by 9 publications

(10 citation statements)

References 158 publications

(249 reference statements)

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“…Both the direct and converse membrane flexoelectric effects are sensor-actuator properties when membrane curvature and polarization are coupled as in nematic LCs. Membrane flexoelectricity due to its inherent sensoractuator capabilities is an area of current interest in soft matter materials [1,7,8,[14][15][16][17][18][19][20][21][22][23][24]. Over the years, much literature has dealt with the problem of measuring flexoelectric coefficients in various LCs [11,13].…”

Section: (B) Materialsmentioning

confidence: 99%

“…where H is the average curvature and K the Gaussian curvature, which follows from the nematic Frank elastic energy [11][12][13][14][15]: 8) where K 1 is the splay and K 24 is the saddle-splay constant; the geometrical quantities and definitions used in this paper are reported elsewhere [11,[17][18][19]. Nemato-membranology is applied by identifying the director n with the outer unit normal n = k in equation (1.8), and considering surface gradient ∇ s , we obtain…”

Section: (B) Materialsmentioning

confidence: 99%

“…Nematic liquid crystals are multifunctional self-organizing viscoelastic anisotropic materials whose orientational order responds to external flow, electromagnetic, chemical, optical and surface fields [11,[17][18][19]; the orientational order is defined by the director n and the elastic distortions by director gradients ∇n [11,[17][18][19]. A distinguishing and novel property of nematics is flexoelectricity [1][2][3][4]11], which describes the coupling between orientational gradients and electric polarization, such that an applied electric field creates orientational distortions and distortions create macroscopic polarization [1][2][3][4]11,[17][18][19].…”

Section: (B) Materialsmentioning

confidence: 99%

“…which coincides with E H , and gives 4k c = (K 1 + 8K 24 ),k c = −2K 24 ; the surface gradient is given by the tangential projection of the total gradient: ∇ s (·) ≡ I s · ∇(·), I s = I − kk, since thin layers and membranes behave like LCs, membranes should also exhibit flexoelectricity or couplings between polarization and bending [1][2][3][4]7,11,[17][18][19]. Figure 2 shows a schematic of flexoelectric polarization in rod-like and banana-like molecules and the corresponding membrane flexoelectric polarization; as noted above the physics and modelling are affected by identifying the director field n with the membrane normal k. Using the same approach as above, equation (1.4) gives the membrane polarization P due to membrane bending (∇ s · k): 10) where c f is the membrane flexoelectric coefficient, as indeed found experimentally [4].…”

Section: (B) Materialsmentioning

confidence: 99%

“…A distinguishing and novel property of nematics is flexoelectricity [1][2][3][4]11], which describes the coupling between orientational gradients and electric polarization, such that an applied electric field creates orientational distortions and distortions create macroscopic polarization [1][2][3][4]11,[17][18][19]. The polar nature of splay S = n∇ · n and bend B = −n × ∇ × n orientational deformations can polarize the nematic LC medium [11][12][13] (b) Flexoelectricity in biological membranes due to bending curvature described by surface gradients of the unit normal k. The correspondence between nematic flexoelectricity and membrane flexoelectricity is obtained when the director n is identified with the membrane unit normal k (adapted from [11]).…”

Section: (B) Materialsmentioning

confidence: 99%

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Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells

Herrera‐Valencia

Rey

2014

Phil. Trans. R. Soc. A.

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Liquid crystal flexoelectric actuation uses an imposed electric field to create membrane bending, and it is used by the outer hair cells (OHCs) located in the inner ear, whose role is to amplify sound through generation of mechanical power. Oscillations in the OHC membranes create periodic viscoelastic flows in the contacting fluid media. A key objective of this work on flexoelectric actuation relevant to OHCs is to find the relations and impact of the electromechanical properties of the membrane, the rheological properties of the viscoelastic media, and the frequency response of the generated mechanical power output. The model developed and used in this work is based on the integration of: (i) the flexoelectric membrane shape equation applied to a circular membrane attached to the inner surface of a circular capillary and (ii) the coupled capillary flow of contacting viscoelastic phases, such that the membrane flexoelectric oscillations drive periodic viscoelastic capillary flows, as in OHCs. By applying the Fourier transform formalism to the governing equation, analytical expressions for the transfer function associated with the curvature and electrical field and for the power dissipation of elastic storage energy were found.

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Section: (B) Materialsmentioning

confidence: 99%

Section: (B) Materialsmentioning

confidence: 99%

Section: (B) Materialsmentioning

confidence: 99%

Section: (B) Materialsmentioning

confidence: 99%

Section: (B) Materialsmentioning

confidence: 99%

See 3 more Smart Citations

Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells

Herrera‐Valencia

Rey

2014

Phil. Trans. R. Soc. A.

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Thermal fluctuation spectrum of flexoelectric viscoelastic semiflexible filaments and polymers: A line liquid crystal model

et al. 2022

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In this paper, we generalize the internal viscosity model developed by Professor Williams to semiflexible polymers, biofilaments, and worm‐like micelles, where molecular dissipation is generated by bending. Current models for viscoelasticity with internal viscosity in semiflexible polymers and filaments are based on generalizations of the worm‐like model, but they neglect potential electromechanical couplings such as flexoelectricity. In this paper, inspired by the early work of Professor Williams, we develop a model for worm‐like viscoelastic flexoelectric filaments based on the “line liquid crystal model”. The electroelastic free energy and entropy production are formulated and used to derive the shape equation for these filaments undergoing thermal fluctuations. The resulting time relaxation spectrum is a useful tool to characterize experimentally viscoelastic material parameters. We show that flexoelectricity or polarization‐induced bending softens the filaments. The predicted time relaxation spectrum shows that at longer wavelength modes, the filament behaves like a rigid rod in a viscous solvent, but at shorter wavelengths, it reaches a plateau defined by the bending time scale. The key effect of flexoelectricity is to shift the entire spectrum to higher values, slowing down the response. The model itself is validated using the worm‐like chain and the viscoelasticity of liquid crystals, and the predictions are shown to be in qualitative consistency with the data. Since filament flexoelectricity is associated with 1D sensor‐actuator functionalities, the presented model has many potential novel applications in reduced geometries.

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Stress‐Sensor Device Based on Flexoelectric Liquid Crystalline Membranes

2013

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Membrane flexoelectricity is an electromechanical coupling process that describes membrane bending and membrane electrical polarization caused by bending under electric fields. In this paper we propose, formulate, and characterize a stress-sensor device for mechanically loaded solids, consisting of a soft flexoelectric thin membrane attached to the loaded deformed solid. Because the curvature of the deformed solid is transferred to the attached flexoelectric membrane, the electromechanical transduction of the latter produces a charge that is proportional to the stress of the solid. The model of the stress-sensor device is based on the integration of the thermodynamics of polarizable membranes with isotropic solid elasticity, leading to a transfer function that identifies the elastic, electromechanical, and geometrical parameters involved in electrical-signal generation. The model is applied to representative normal bending and then to more complex off-axis bending of elastic bars. In all cases, a common transfer function shows the generic material and its geometric contributions. The sensor sensitivity increases linearly with flexoelectricity and the membrane-solid interface, and the sensitivity decreases with increasing membrane thickness and Young's modulus of the solid. The theoretical results contribute to ongoing experimental efforts towards the development of anisotropic soft-matter-based stress-sensor devices through solid-membrane interactions and electromechanical transduction.

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Rheological Theory and Simulation of Surfactant Nematic Liquid Crystals

Cited by 9 publications

References 158 publications

Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells

Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells

Thermal fluctuation spectrum of flexoelectric viscoelastic semiflexible filaments and polymers: A line liquid crystal model

Stress‐Sensor Device Based on Flexoelectric Liquid Crystalline Membranes

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