*7.5.2 Polymer scaffolding morphology*

the same side of sample cell, transmission grating will be formed, with grating planes perpendicular to the sample cell surface as shown in **Figure 47(a)**. If the writing beams are incident from both sides of the samples, reflection grating will be formed, with grating planes parallel to the sample cell surface as shown in

*Types of HPDLC grating: (a) transmission grating and (b) reflection grating.*

The grating period depends on the writing wavelength and intersection beam

Here, *Λ* is the grating period, *λ* is the writing wavelength and *n* is the average refractive index of the material mixture. A grating with varied period can be obtained by inserting a refractive cylindrical lens in conventional double interference optical path. It varies the angle of incidence of one of the two interference laser

<sup>2</sup>*<sup>n</sup>* sin ð Þ *<sup>θ</sup>i=*<sup>2</sup> (30)

*<sup>n</sup>Λ*<sup>2</sup> (31)

*<sup>Λ</sup>* <sup>¼</sup> *<sup>λ</sup>*

This parameter depends on the grating period and thickness of grating:

*<sup>Q</sup>* <sup>¼</sup> <sup>2</sup>*<sup>π</sup> <sup>λ</sup><sup>d</sup>*

Here, λ is the wavelength of incident light, and *d* is the thickness of the grating. If the value of Q < 1, then it is a Raman-Nath-type grating. It is thin grating and

If the value of Q > 1, then it is Bragg-type grating. It is thick or volume grating, and only zero order or first order of diffraction can be found. Since the optical losses

are low in Bragg-type-grating, it is preferred for practical applications.

**Figure 47(b)**.

**Figure 47.**

angle:

beams [167].

**64**

*7.4.2 Cook-Klein parameter*

multiple diffraction orders can be found.

**7.4 HPDLC grating parameters**

*Liquid Crystals and Display Technology*

*7.4.1 Grating period/grating pitch*

In transmission gratings prepared from acrylate-based material systems under slow curing process, polymer scaffolding morphology can be obtained (**Figure 49**). Here instead of small LC droplets, large LC domains or LC layer is obtained. If the curing process is relatively slow as compared to that in "LC droplet-like morphology", transverse polymer filaments are obtained in polymer-rich region, in between

**Figure 48.** *LC droplet-like morphology: (a) schematic and (b) SEM image of HPDLC film [164, 168].*

**Figure 49.** *Polymer scaffolding morphology: (a) schematic and (b) SEM image of HPDLC film [164, 169].*

When the monomer concentration is higher than the LC concentration, HPDLC films get formed. HPDLC films are known to be a promising technology because they can be used in 3D display, fiber optics, data storage, zoom lenses, image

*An Overview of Polymer-Dispersed Liquid Crystal Composite Films and Their Applications*

It can be concluded that the LC's inherent optical and dielectric anisotropy can

This chapter encompasses a wide range of LC-related subject matter. It begins

The detailed study of each of the above composite films is about the following:

2.Morphological analysis, which portrays their size, shape, configuration and

3.Electro-optic study: It comprises definition and formulation of various electrooptic parameters, such as transmittance difference, contrast ratio, hysteresis,

4.Dielectric study: Calculation of relaxation frequency, distribution parameter and breakdown strength using Debye and Cole-Cole plots is incorporated in

Precisely, this chapter gives a deep and comprehensive knowledge about LC and

1.Fabrication technique using the most suited phase separation process.

threshold and saturation voltages and response time, with examples.

with the basics of LC materials, such as definition, history, types, phases and properties of LCs. Information about properties of LC materials offer deep insight in choosing LC material for particular application and also benefit in innovating new applications. Initially applications of LC materials are limited to display world only; now it is finding scope in a non-display world too. A brief outline about applications of LC devices has been followed by an extensive study of polymer-LC composites. The three types of composite films reported in this chapter are as

capture systems, beam vibration sensor, etc. [172].

*DOI: http://dx.doi.org/10.5772/intechopen.91889*

**9. Summary**

follows:

this study.

**67**

some of their applications.

be effectively used in a display as well as non-display devices.

1.Low monomer concentration composite: PSLC film

2.Moderate monomer concentration composite: PDLC film

3.High monomer concentration composite: HPDLC film

defects in LC droplet/domain structure.

**Figure 50.** *Sliced polymer morphology: (a) schematic and (b) SEM image of HPDLC film [164, 170].*

two LC domains/layers, as shown in SEM image (**Figure 49(b)**). As LC droplets are absent, scattering losses are low [164, 169].
