Aliphatic acid esters of (2-hydroxypropyl) cellulose—Effect of side chain length on properties of cholesteric liquid crystals

A series of aliphatic acid esters of (2-hydroxypropyl) cellulose (C_nPC) were synthesized via the esterification of aliphatic acid chloride and (2-hydroxypropyl) cellulose (HPC). The liquid crystalline (LC) phases and transitions were investigated using differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized light microscope (PLM) techniques. This series of C_nPC polymers exhibited characteristic features of cholesteric LC phases between their glass transition and isotropization temperatures. The cholesteric LC characteristics were studied utilizing an ultraviolet/visible/near infrared spectrometer in a reflection mode. It was confirmed that, with an increase in the number of methylene units in the side chains of this series of C_nPC polymers, there was an increase, on the scale of nanometers, in the layer spacing values for the cholesteric LC phases measured by WAXD. This periodic layer spacing represents the thickness of the neighboring twisted layers in a helical structure. Based on a unique significant red shift of the maximum reflection peak for the LC phases in this series of C_nPCs, it is evident that the pitch distance in the helical structure also increases with an increase in the length of methylene units in the side chains.