By Max Planck Institute of Colloids and Interfaces
Hydroxypropyl cellulose (HPC) is another cellulose derivative that exhibits vibrant colours in its liquid crystalline phase and responds to external stimuli. As with the CNCs, the bright colours exhibited by HPCs are due to structural colouration. When mixed with water in the right proportions, the polymer chains self-assemble into a twisted stack that selectively reflects light within a narrow range of wavelengths matching the periodic dimensions of the structure. This property makes it an easily fabricated, processable coloured material, with colour tuning achievable simply by altering the water content. Additionally, HPC is responsive to changes in pressure and temperature. HPC offers the benefits of being biocompatible and edible, making it a common thickening agent in pharmaceuticals and food products (for example, it serves as a thickener in sauces and dips, as well as a stabiliser in whipped cream). In our lab, we have explored how helicoidal structures in hydroxypropyl cellulose respond to vertical compression. Using a roll-to-roll machine, we developed a large-scale pressure sensor that visually maps pressure in a way that is intuitive and easy to interpret.
