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.