Polymer Dispersed Cholesteric Liquid Crystal Mixtures for Optical Time–Temperature Integrators

Abstract

Low molecular weight cholesteric liquid crystals (CLCs) can be trapped as droplets or particles inside a polymer binder, forming polymer dispersed cholesteric liquid crystal (PDCLC) systems, which are typically used for smart windows, displays, and optical sensors. While dispersing a single CLC mixture via emulsification, rendering reflective PDCLC films upon drying with a stable optical response, is well studied, the incorporation of distinct microdroplets inside a PDCLC coating is barely explored. Here, structural colored PDCLC coatings are prepared by mixing distinctive thermosensitive photonic microdroplets, featuring an optical time–temperature response that is visualized as a reflective color loss or shift dependent on the composition of the CLC mixtures. The presented optical time–temperature response is induced by diffusion of CLCs between adjacent liquid crystal domains via interconnecting passageways, causing an irreversible optical response until homogeneous mixing is attained. Hence, blending distinct CLC microdroplets in a polymer matrix provides a facile and scalable method for fabricating optical time–temperature integrators; moreover, alternative optical time–temperature responses can be realized when adjusting the composition of the photonic mixtures, demonstrating the potential of this method to acquire novel photonic applications based on low molecular weight CLCs.

A multifunctional structural coloured electronic skin monitoring body motion and temperature

“…Please do not adjust margins Please do not adjust margins induce CLC droplet formation. [21][22][23] Whereas PVA is frequently utilized for biomedical purposes due to its beneficial biocompatibility, 24,25 glycerol acts as a plasticizer in the final free-standing PDCLC film, improving the e-skin's stretchability.…”

“…When the body temperature decreases again, the reflective colour reappears as the thermochromic response of the emulsified PDCLC systems is reversible (Video S1, ESI). 21 Polarized optical microscopy (POM) revealed randomly dispersed CLC microdroplets (average droplet diameter = 16 µm) trapped throughout the polymer matrix (Fig. 2c).…”

“…When the body temperature decreases again, the reflective colour reappears as the thermochromic response of the emulsified PDCLC systems is reversible (Video S1, ESI†). 21…”

“…After adding the CLC mixture to an aqueous polyvinyl alcohol (PVA)/glycerol solution in a 20/80 ratio (step 1), emulsification was conducted via shear mixing (step 2) to induce CLC droplet formation. [21][22][23] Whereas PVA is frequently utilized for biomedical purposes due to its beneficial biocompatibility, 24,25 glycerol acts as a plasticizer in the final free-standing PDCLC film, improving the e-skin's stretchability.…”

“…2a and b). 21,29,30 Easily distinguishable colours were observed for temperature changes per 1 1C, hence these photonic wearables are suitable for the detection of subtle body temperature variations via optical feedback.…”