Cholesteric liquid crystalline polymer networks as optical sensors

In the past decade, chiral nematic liquid crystals (LCs) have emerged as an attractive material for the development of stimuli-responsive systems (White et al. 2010; Ge and Yin 2011; Fenzl et al. 2014; Mulder et al. 2014; Stumpel et al. 2014). Due to the periodic alteration of their refractive indices, they act as one-dimensional photonic structures and reect circularly polarized light of same handedness. The reection of light is governed by Bragg’s law: λ θb = nP cos where λb is the wavelength of Bragg reection, n is the average refractive index, and P is the length of the helical pitch. The pitch of a chiral nematic is dened as the length traversed by the molecular director nˆ on 360° rotation (Figure 4.1a). It is inversely proportional to the concentration [C] as well as the helical twisting power β