scholarly journals Molecular-Theory of High Frequency Dielectric Susceptibility of Nematic Nanocomposites

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 970
Author(s):  
Mikhail A. Osipov ◽  
Alexey S. Merekalov ◽  
Alexander A. Ezhov
Keyword(s):  
Plasmon Resonance ◽  
High Frequency ◽  
Volume Fraction ◽  
Simple Expression ◽  
Dielectric Anisotropy ◽  
Dielectric Susceptibility ◽  
Nanoparticle Volume Fraction ◽  
Effective Polarizability ◽  
Dielectric And Optical Properties ◽  
Analytical Expressions

A molecular-statistical theory of the high frequency dielectric susceptibility of the nematic nanocomposites has been developed and approximate analytical expressions for the susceptibility have been obtained in terms of the effective polarizability of a nanoparticle in the nematic host, volume fraction of the nanoparticles and the susceptibility of the pure nematic phase. A simple expression for the split of the plasmon resonance of the nanoparticles in the nematic host has been obtained and it has been shown that in the resonance frequency range the high frequency dielectric anisotropy of the nanocomposite may be significantly larger than that of the pure nematic host. As a result, all dielectric and optical properties of the nanocomposite related to the anisotropy are significantly enhanced which may be important for emerging applications. The components of the dielectric susceptibility have been calculated numerically for particular nematic nanocomposites with gold and silver nanoparicles as functions of the nanoparticle volume fraction and frequency. The splitting of the plasmon resonance has been observed together with the significant dependence on the nanoparticle volume fraction and the parameters of the nematic host phase.

scholarly journals Statistical Theory of Helical Twisting in Nematic Liquid Crystals Doped with Chiral Nanoparticles

Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1432
Author(s):  
Mikhail A. Osipov ◽  
Alexey S. Merekalov ◽  
Alexander A. Ezhov
Keyword(s):  
Field Theory ◽  
Statistical Theory ◽  
Liquid Crystals ◽  
Optical Activity ◽  
High Frequency ◽  
Low Frequency ◽  
Helical Structure ◽  
Dielectric Susceptibility ◽  
Effective Polarizability ◽  
Nematic Solvent

A molecular field theory of the cholesteric ordering in nematic nanocomposites doped with chiral nanoparticles was developed taking into consideration chiral dispersion interaction between rod-like nanoparticles. It was shown that the inverse pitch of the cholesteric helical structure is proportional to the anisotropy of the effective polarizability and the anisotropy of the effective gyration tensor of a nanoparticle in the nematic host. The theory enables one to predict the helical sense inversion induced by a change of the low-frequency dielectric susceptibility of the nematic host phase. The components of the high-frequency effective polarizability and the effective optical activity of a gold rod-like nanoparticle in a particular nematic solvent were calculated numerically.

scholarly journals Active, Reactive, and Apparent Power in Dielectrophoresis: Force Corrections from the Capacitive Charging Work on Suspensions Described by Maxwell-Wagner’s Mixing Equation

Micromachines ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 738
Author(s):  
Jan Gimsa
Keyword(s):  
Volume Fraction ◽  
Inhomogeneous Field ◽  
Effective Polarizability ◽  
Polarization Mechanism ◽  
Free Transition ◽  
Lossy Media ◽  
New Perspective ◽  
A Chain ◽  
A Charge ◽  
Induced Changes

A new expression for the dielectrophoresis (DEP) force is derived from the electrical work in a charge-cycle model that allows the field-free transition of a single object between the centers of two adjacent cubic volumes in an inhomogeneous field. The charging work for the capacities of the volumes is calculated in the absence and in the presence of the object using the external permittivity and Maxwell-Wagner’s mixing equation, respectively. The model provides additional terms for the Clausius-Mossotti factor, which vanish for the mathematical boundary transition toward zero volume fraction, but which can be interesting for narrow microfluidic systems. The comparison with the classical solution provides a new perspective on the notorious problem of electrostatic modeling of AC electrokinetic effects in lossy media and gives insight into the relationships between active, reactive, and apparent power in DEP force generation. DEP moves more highly polarizable media to locations with a higher field, making a DEP-related increase in the overall polarizability of suspensions intuitive. Calculations of the passage of single objects through a chain of cubic volumes show increased overall effective polarizability in the system for both positive and negative DEP. Therefore, it is proposed that DEP be considered a conditioned polarization mechanism, even if it is slow with respect to the field oscillation. The DEP-induced changes in permittivity and conductivity describe the increase in the overall energy dissipation in the DEP systems consistent with the law of maximum entropy production. Thermodynamics can help explain DEP accumulation of small objects below the limits of Brownian motion.

Linear bounded potential model for semiconductor band bending

2022 ◽  
Author(s):  
Facundo Villavicencio ◽  
Jorge Mario Ferreyra ◽  
German Bridoux ◽  
Manuel Villafuerte
Keyword(s):  
Potential Model ◽  
Simple Expression ◽  
Linear Potential ◽  
Charge Balance ◽  
Band Bending ◽  
Mass Approximation ◽  
Hole Confinement ◽  
Dimensional Electron Gas ◽  
Analytical Expressions ◽  
Franz Keldysh Effect

Abstract We propose a simple but unexplored model for the semiconductor band bending with the aim to obtain a relatively simple expression to calculate the energy spectrum for the confined levels and the analytical expressions for wave-functions. This model consists of a linear potential but it is bounded or trimmed in energy unlike the well known wedge potential model. We present exact solutions for this potential in the frame of the effective mass approximation and they are valid for electron or hole confinement potential. This model provides a more adequate physical scenario than the wedge potential since it takes into account the charge balance involved in the band bending potential. These results allow to treat confined potential problems as in the case of a two-dimensional electron gas (2DEG) in a simplified way. We discuss the application of this approximation to the recombination time of electrons an holes and for the Franz-Keldysh effect.

scholarly journals Marangoni convection in layers of water-based nanofluids under the effect of rotation

2021 ◽  
Vol 19 (1) ◽  
pp. 1029-1046
Author(s):  
Abeer H. Bakhsh ◽  
Abdullah A. Abdullah
Keyword(s):  
Marangoni Convection ◽  
Volume Fraction ◽  
Steady State Solution ◽  
Horizontal Layer ◽  
Brownian Diffusion ◽  
Nanoparticle Volume Fraction ◽  
Rigid Surface ◽  
Fixed Temperature ◽  
Modified Model ◽  
Conservation Condition

Abstract A linear stability analysis is performed for the onset of Marangoni convection in a horizontal layer of a nanofluid heated from below and affected by rotation. The top boundary of the layer is assumed to be impenetrable to nanoparticles with their distribution being determined from a conservation condition while the bottom boundary is assumed to be a rigid surface with fixed temperature. The motion of the nanoparticles is characterized by the effects of thermophoresis and Brownian diffusion. A modification model is used in which the effects of Brownian diffusion and thermophoresis are taken into consideration by new expressions in the nanoparticle mass flux. Also, material properties of the nanofluid are modelled by non-constant constitutive expressions depending on nanoparticle volume fraction. The steady-state solution is shown to be well approximated by an exponential distribution of the nanoparticle volume fraction. The Chebyshev-Tau method is used to obtain the critical thermal and nanoparticle Marangoni numbers. Different stability boundaries are obtained using the modified model and the rotation.

Mesomorphic, dielectric, and optical properties of fluorosubstituted biphenyls, terphenyls, and quaterphenyls

2008 ◽  
Vol 16 (4) ◽  
Author(s):  
P. Kula ◽  
A. Spadło ◽  
J. Dziaduszek ◽  
M. Filipowicz ◽  
R. Dąbrowski ◽  
...  
Keyword(s):  
Optical Properties ◽  
Liquid Crystal ◽  
Dielectric Anisotropy ◽  
Polar Group ◽  
The Novel ◽  
Vertical Alignment ◽  
Rigid Core ◽  
High Birefringence ◽  
Low Viscosity ◽  
Dielectric And Optical Properties

AbstractCompounds with moderate and large negative dielectric anisotropy (Δɛ) are very attractive liquid crystal (LC) for vertical alignment mode (VA). Materials with such properties can be achieved by lateral substitution of a polar group into a mesogenic molecule. We synthesized some new LC materials with a negative value of Δɛ, a moderately high birefringence (Δn), and a low viscosity. The mesomorphic and physical behaviour of the novel biphenyls, terphenyls and quaterphenyls fluorosubstituted in the rigid core and also with fluorinated alkyl and alkoxy chains are investigated. The prepared series of four LC compounds are promising for new LC mixtures for various applications. Examples of nematic mixtures with Δɛ∼−3.25 will be presented.

Blade coating analysis of viscous nanofluid having Cu–water nanoparticles using flexible blade coater

2020 ◽  
Vol 36 (4) ◽  
pp. 348-367 ◽  
Author(s):  
Marya Kanwal ◽  
Xinhua Wang ◽  
Hasan Shahzad ◽  
Yingchun Chen ◽  
Hui Chai
Keyword(s):  
Pressure Gradient ◽  
Shooting Method ◽  
Volume Fraction ◽  
Volumetric Flow Rate ◽  
Lubrication Approximation ◽  
Nanoparticle Volume Fraction ◽  
Porous Substrate ◽  
Flow Equations ◽  
The Impact ◽  
Blade Coating

This article presents the blade coating analysis of viscous nanofluid passing over a porous substrate using a flexible blade coater. Water-based copper nanoparticles are considered to discuss the blade coating process. The lubrication approximation theory is applied to develop the flow equations. The analytical solution is obtained for velocity, volumetric flow rate, and pressure gradient, while shooting method is applied to obtain the pressure, thickness, and load. Different models for dynamic viscosity have been applied to observe the impact of related parameters on pressure, pressure gradient, and velocity. These results are presented graphically. Interesting engineering quantities such as load, deflection, and thickness are computed numerically and are shown in the tabulated form. It is found that nanoparticle volume fraction increases the pressure gradient, pressure and has minor effects on velocity. For model 1, an increase in the volume fraction reduces the coating thickness, load, and deflection, while model 2 has opposite effects on the mentioned quantities. Also, model 2 has a greater impact on pressure and pressure gradient when compared to model 1.

scholarly journals Fluid Flow and Entropy Generation Analysis of Al2O3–Water Nanofluid in Microchannel Plate Fin Heat Sinks

Entropy ◽  
2019 ◽  
Vol 21 (8) ◽  
pp. 739 ◽  
Author(s):  
Hao Ma ◽  
Zhipeng Duan ◽  
Liangbin Su ◽  
Xiaoru Ning ◽  
Jiao Bai ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Microchannel Plate ◽  
Heat Sinks ◽  
Entropy Generation Rate ◽  
Nanoparticle Volume Fraction ◽  
Channel Aspect Ratio

The flow in channels of microdevices is usually in the developing regime. Three-dimensional laminar flow characteristics of a nanofluid in microchannel plate fin heat sinks are investigated numerically in this paper. Deionized water and Al2O3–water nanofluid are employed as the cooling fluid in our work. The effects of the Reynolds number (100 < Re < 1000), channel aspect ratio (0 < ε < 1), and nanoparticle volume fraction (0.5% < Φ < 5%) on pressure drop and entropy generation in microchannel plate fin heat sinks are examined in detail. Herein, the general expression of the entropy generation rate considering entrance effects is developed. The results revealed that the frictional entropy generation and pressure drop increase as nanoparticle volume fraction and Reynolds number increase, while decrease as the channel aspect ratio increases. When the nanoparticle volume fraction increases from 0 to 3% at Re = 500, the pressure drop of microchannel plate fin heat sinks with ε = 0.5 increases by 9%. It is demonstrated that the effect of the entrance region is crucial for evaluating the performance of microchannel plate fin heat sinks. The study may shed some light on the design and optimization of microchannel heat sinks.

Influence of chemically radiative nanoparticles on flow of Maxwell electrically conducting fluid over a convectively heated exponential stretching sheet

2019 ◽  
Vol 16 (6) ◽  
pp. 791-805
Author(s):  
Atul Kumar Ray ◽  
Vasu B.
Keyword(s):  
Stretching Sheet ◽  
Volume Fraction ◽  
Maxwell Fluid ◽  
Nanoparticle Volume Fraction ◽  
Analysis Method ◽  
Content Type ◽  
Electrically Conducting ◽  
Exponential Stretching ◽  
Homotopy Analysis ◽  
Exponential Stretching Sheet

Purpose This paper aims to examine the influence of radiative nanoparticles on incompressible electrically conducting upper convected Maxwell fluid (rate type fluid) flow over a convectively heated exponential stretching sheet with suction/injection in the presence of heat source taking chemical reaction into account. Also, a comparison of the flow behavior of Newtonian and Maxwell fluid containing nanoparticles under the effect of different thermophysical parameters is elaborated. Velocity, temperature and nanoparticle volume fractions are assumed to have exponential distribution at boundary. Buongiorno model is considered for nanofluid transport. Design/methodology/approach The equations, which govern the flow, are reduced to ordinary differential equations using suitable transformation. The transformed equations are solved using a robust homotopy analysis method. The convergence of the homotopy series solution is explicitly discussed. The present results are compared with the results reported in the literature and are found to be in good agreement. Findings It is observed from the present study that larger relaxation time leads to slower recovery, which results in a decrease in velocity, whereas temperature and nanoparticle volume fraction is increased. Maxwell nanofluid has lower velocity with higher temperature and nanoparticle volume fraction when compared with Newtonian counterpart. Also, the presence of magnetic field leads to decrease the velocity of the nanofluid and enhances the skin coefficient friction. The existence of thermal radiation and heat source enhance the temperature. Further, the presence of chemical reaction leads to decrease in nanoparticle volume fraction. Higher value of Deborah number results in lower the rate of heat and mass transfer. Originality/value The novelty of present work lies in understanding the impact of fluid elasticity and radiative nanoparticles on the flow over convectively heated exponentially boundary surface in the presence of a magnetic field using homotopy analysis method. The current results may help in designing electronic and industrial applicants. The present outputs have not been considered elsewhere.

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