New insights into hydroxypropyl cellulose (HPC) mesophases-functionalisation and colour-responsive materials

Hydroxypropyl cellulose (HPC) is a derivative of the most abundant biopolymer, cellulose. HPC is known to organize itself to lyotropic cholesteric phases in aqueous solutions [1]. This liquid crystalline phase reflects light in the visible wavelength range depending on the HPC concentration and furthermore, the reflection is selective towards right-handed circular polarized light due to the twisted stacking of the cholesteric layers [2]. In this talk, we will share our new insights on the formation of these mesophases and restructure the HPC phase diagram as a function of further functionalisation of HPC polymers with dicarboxylic acids with different chain lengths to modulate the colour response. By introducing water-based esterification chemistry, it is possible to alter the reflection wavelength of the HPC mesophases in liquid as well as the solid state, also the scattering distribution and the polarization response can be modulated. Furthermore, through 3 d printing of these mesophases, we are able to create two-degree hierarchical order in the cholesteric arrangement of the HPC as a function of the shear pressure applied through the printing system [3], Figure 1. Through the rheological properties, it is possible to predetermine the colour response and we will demonstrate how these new insights can help us to design materials with distinct colour responses to their environment.

Figure 1. a) Illustration of the 3d printing of the functionalized HPC mesophases with b) uniform structurally coloured filaments and c) the second-degree microstructural hierarchy induced by the shear forces through the 3d processing