Abstract
This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films. The effective permittivity of the composite was simulated at sufficiently high frequency, where the permittivity is constant, obtaining results on its dependency on the constituents’ permittivity and concentrations. The two models are compared and discussed. The method used for simulating the doped PDLC retains its general character and can be applied for other similar multiphase composites. The methods can be used to calculate the effective permittivity of a LC composite, or, in the case of a composite in which one of the phases has an unknown permittivity, to extract it from the measured composite permittivity. The obtained data are necessary in the design of the electrical circuits.
Highlights
Composite electro-optic materials, such as polymer/liquid crystal (LC) blends cover a large area of two phase mixtures as, for example: polymer-Ddspersed liquid crystal (PDLC) films [1], liquid crystal dispersed in an electrospun cellulose acetate network [2,3], cellulose film/LC composite [4], polymer balls/nematic LC films [5].Polymer-dispersed liquid crystal (PDLC) films consist of micrometer or sub-micrometersized nematic droplets dispersed in a polymer matrix [6]
The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films
ΕLC−ε ply εLC+2ε ply ε ply εLC−ε ply εLC+2ε ply where εe f f,Maxwell Garnett (MG) is the effective dielectric constant of the composite PDLC film, ε ply is the dielectric constant of the polymeric matrix, εLC is the dielectric constant of the dispersed liquid crystal, and fLC is the volume fraction of the LC
Summary
Composite electro-optic materials, such as polymer/liquid crystal (LC) blends cover a large area of two phase mixtures as, for example: polymer-Ddspersed liquid crystal (PDLC) films [1], liquid crystal dispersed in an electrospun cellulose acetate network [2,3], cellulose film/LC composite [4], polymer balls/nematic LC films [5]. Polymer-dispersed liquid crystal (PDLC) films consist of micrometer or sub-micrometersized nematic droplets dispersed in a polymer matrix [6]. Their optical transmission response is based on the electrically controlled light scattering properties of the droplets. The LC droplets inside the polymer matrix form a bi-phase system, and to study the dielectric permittivity, the Maxwell Garnet [8] and the Bruggeman [9,10] effective medium models are considered in this paper. The contribution of the third phase formed by the dispersed NPs both in the LC droplets and in the polymer matrix is taken into account at the calculation of the effective dielectric permittivity of NPs-doped PDLC films. Because LC doping with small fractions of NP is a very delicate process that might lead to tricky experimental results, it is important to use models to gain information about the effective dielectric constant of NPs containing multiphase systems
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