Elastic Cellulose Derivatives for Novel Mechanical Stress Sensing

Abstract

This review article highlights an overview of cellulose derivatives for novel mechanical stress sensing. Natural polymers such as cellulose are known to form cholesteric liquid crystal (CLC) phase typically over 100 °C after chemical modification of their side chains. Bragg reflection is one of the most unique and important optical properties of the CLC helical structures. When hydroxypropyl cellulose (HPC) was esterified with both propionyl and another groups, we serendipitously found the continuous changes of Bragg reflection peak throughout the full visible-wavelength range between 400 nm and 800 nm at relatively low CLC mesophase temperatures below 100 °C. Furthermore, full-color imaging could be realized by crosslinkable HPC derivatives tethering acryloyl side chains. More interestingly, we succeeded in the demonstration of novel mechanical stress sensing by the elastic CLC films of crosslinked HPC derivatives, leading to the visualization of external mechanical stress as the changes in Bragg reflection color. In this way, the elastic cellulose CLC films are available as the social infrastructure sensors for deterioration or damage of concretes, wearable sensors for human medical care, and so forth.