Effect of sodium chloride and water-soluble polymers on thermochromic properties of hydroxypropyl cellulose solution

Abstract

Hydroxypropyl cellulose (HPC) and its rather low lower-critical-solution-temperature (LCST) were the main research targets in many recent publications. In this study, a simple and affordable approach to measure LCST using a Brookfield viscometer was presented. The setup using a popular hot plate and a silicone oil bath could well detect the HPC solution’s LCST values. The result was in good agreement with the particle size change obtained using the dynamic light scattering technique. The effect of polyacrylic acid (PAA) and other cellulose derivatives including hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (HEC), or sodium carboxymethyl cellulose (CMC) on HPC’s LCST was investigated. The mixture of HPC with PAA, HPMC, and CMC showed the lowest LCST. However, the effect of NaCl seemed to be stronger when the LCST value of only 28.5 °C was obtained with 1 wt% of HPC and 5 wt% of NaCl. Fourier-transformed infrared spectroscopy results also showed a stronger interaction of HPC/NaCl compared to the mixture with PAA of HPMC. The differential scanning calorimetry only detected the signal change correlated with LCST in the cooling cycle. The glass window fabricated with the current thermochromic solution was able to block and transmit visible light well at low and elevated temperatures, respectively.