Carboxymethyl chitosan has sensitive two-way CO-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 CO or N as a function of the relative concentrations of COOH and NH side groups. When having similar concentrations of COOH and NH, the produced CMC was water soluble at pH 10 and consecutively experienced peculiar dissolution-to-precipitation-to-dissolution during bubbling of CO, and experienced reverse dissolution-to-precipitation-to-dissolution process during subsequently bubbling of N. With the concentration of COOH much higher than that of NH, the water soluble CMC at pH 10 exhibited no phase changes in response to bubbling of CO and N. This newly developed CMC solution system with novel CO responsive amphiphilic feature has a potential use as a CO switchable surfactant to control interface of mixtures of hydrophilic and hydrophobic species in emulsification/demulsification applications.