Carboxymethyl chitosan has sensitive two-way CO2-responsive hydrophilic/hydrophobic feature

Carboxymethyl chitosans (CMC) with various degrees of carboxymethyl substitution were prepared and investigated on their changes in water solubility in response to bubbling of CO2 or N2 as a function of the relative concentrations of COOH and NH2 side groups. When having similar concentrations of COOH and NH2, the produced CMC was water soluble at pH 10 and consecutively experienced peculiar dissolution-to-precipitation-to-dissolution during bubbling of CO2, and experienced reverse dissolution-to-precipitation-to-dissolution process during subsequently bubbling of N2. With the concentration of COOH much higher than that of NH2, the water soluble CMC at pH 10 exhibited no phase changes in response to bubbling of CO2 and N2. This newly developed CMC solution system with novel CO2 responsive amphiphilic feature has a potential use as a CO2 switchable surfactant to control interface of mixtures of hydrophilic and hydrophobic species in emulsification/demulsification applications.