*An Overview of Polymer-Dispersed Liquid Crystal Composite Films and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.91889*

structure is a splay deformation with a point defect (*s* = 1) in the volume centre known as hedgehog [19, 130]. This is shown in **Figure 33**. The defects (also known as disclinations) arise when the elastic energy density of a nematic grows sufficiently large, and the orientation of the nematic director becomes indistinct [131]. Radial structure is generally found by dispersing LC in low-surface energy fluids like polysiloxane or in glycerine containing a small amount of lecithin.


**Figure 33.**

*A schematic illustration of splay and bend elastic deformations dictating the nematic ordering in radial and bipolar LC droplets.*

material, alignment properties of the LC at the polymer surface, elastic constants of the bulk nematic, temperature and the presence of external fields. Out of these factors, preferred alignment of the nematic at the surface of the polymer-LC interface determines the droplet configuration. If the anchoring energy is stronger than the elastic forces inside LC droplets, then the nematic director adopts a uniform tilt angle either (0° or 90°) at all points on the droplet surface, and the final configuration of nematic director within LC droplet is to minimize the total free energy. However, if the anchoring energy is weaker than the elastic forces inside LC droplets, then the tilt angle of the nematic varies spatially within the droplet to minimize curvature in the bulk of the droplet. Strong or weak anchoring conditions depend on the chemical nature of the polymer interface up to a certain degree. However, typically anchoring energy is more influential. Anchoring effects are magnified in small droplets, because of their shorter length scale and increased surface-to-volume ratio. Along with anchoring energy, balance of elastic constants is an imperative factor in determining the director configuration. Contribution of elastic constants to the system's free energy determines whether director configuration inside the droplet is simple or complex. The shape and size of cavity affects droplet structure. In submicron-sized droplets, the close proximity of surfaces and defects can distort the nematic structure throughout the droplet, whereas in large-sized droplets, it is easy to form multiple defect structures. The director configuration is isomorphic in a symmetric cavity and unpredictable in irregular-shaped cavity. The presence of external fields may influence the alignment direction of a nematic without altering the director configuration. Four commonly found director config-

a. Radial configuration (**Figure 32(a)**): In this configuration, director field is anchored perpendicular (homeotropic) to the droplet wall. A radial droplet possesses spherical symmetry, and the only elastic deformation present in this

*Director configurations in a droplet of PDLC (a) radial, (b) axial, (c) bipolar, (d) toroidal and (e) three-*

urations in PDLCs [127–129] are illustrated in **Figure 32**.

*Liquid Crystals and Display Technology*

**Figure 32.**

**46**

*dimensional view of the toroidal configuration.*
