Radial droplet

Note 2 The radial droplet texture shows four dark brushes located in the regions where the director is in the polarization plane of either the polarizer or the analyser. 

The radial configuration occurs when the liquid crystal molecules are anchored with their long axes perpendicular to the droplet wall (Figure 3B). The radial droplet is not birefringent. Application of an external field switches the radial droplet to an axial configuration. As with the bipolar case the films switch from scattering to transparent upon application of an electric field if np=n0. 

Figure 11.15 Liquid crystal director configurations confined in droplets in PDLCs (a) bipolar droplet, (b) toriodal droplet, (c) radial droplet, and (d) axial droplet.

Figure 11.16 Microphotographs of PDLCs (a) bipolar droplets, (h) radial droplets.

Besides the four droplet configurations discussed above, other droplet configurations could exist under appropriate conditions. For example, there is a twisted bipolar droplet where the splay and bend elastic energy is reduced by introducing twist deformation. The point defect in the radial droplet could escape away from the center in an effort to reduce the total free energy. 

Figure 5. NMR spectra of the radial left) and bipolar droplet right) for different values of the diffusion parameter A A = 0 corresponds to the no-diffusion limit, while A = 32 corresponds to the fest diffusion limit. Radial droplet The Pake-type powder spectrum obtained for A = 0 collapses into a single line centered at zero quadrupolar splitting for A = 32. Bipolar droplet The mckgnetic field is aligned along the bipolar symmetry ajds, which results in a spectrum consisting of two lines both in absence of diffusion and in the fest diffusion limit.

We now turn to radial droplets for which, in absence of external fields (with 1) = 0) and for T = 0.8 the hedgehog -like structure is stable. As discussed above, the spectrum of the radial droplet for 7/ = 0 is the Pake-type powder pattern consisting of two asymmetric peaks at S(jJqS [25],... 

Figure 6. NMR spectra of the radial droplet in the nematic phase at T = 0.8...

Figure 1. Order parameters calculated for the radial droplet at T = 0.8 (nematic phase). Local nematic (5, le/t) and external field right) order parameter...

The perpendicular arrangement of the long axes of the 5CB molecules on the droplet walls resulted in a homeotropic alignment, which was visualized under POM as radial droplets. In addition, when the PDLC samples were heated to the upper isotropization temperature of the liquid crystal, the isotropic droplets remained surrounded by a birefringent shadow—the signature of a polymer matrix ordering... 

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