Water Release Kinetics of Hygroscopic Acrylamide Enbibed in CaCl2 by Thermogravimetric and Differential Scanning Calorimetry Methods

Abstract

Hygroscopic thermo-responsive materials, such as poly(acrylamide) gel (PAAG), are appropriate candidates for building atmospheric water generators (AWGs) to address freshwater stresses for innovative industrial endeavors. The PAAG has been synthesized by radical polymerization of acrylamide and N,N'-methylenebisacrylamide in the presence of carbon nanotubes. The dry gel was embedded with calcium chloride to produce a deliquescent acrylamide hydrogel (DHG) capable of capturing environment vapor by 20% of its mass per day. Its highest water release rate was at temperatures close to 45 °C, the temperatures that can be achieved through the photothermal effect of sunlight. The Ea of DHG to release water has been found to be about 46 kJmole-1, which is close to the vaporization energy of water. The highest water release rate was closed to 45 °C, at the heating rate of 0.50 Kmin-1, and moved to a higher temperature as the heating rate increased due to the thermal lag effects. The DSC thermogram showed a transition centered around 50 °C, which coincides with TGA’s maximum water release rate. This indicates that the release of water by DHG was due to its phase transition from hydrophilic to hydrophobic, a phenomenon that also has been confirmed by other researchers.