Rheological characterization of pH‐responsive carboxymethyl starch/β‐cyclodextrin microgels

Abstract

Carboxymethyl starch (CMS)/b-cyclodextrin (b-CD) microgels with pH and ionic strength sensitivities have been synthesized by chemical crosslinking. The characterization of microgels was investigated by thermogravimetric analysis, zeta potential measurements, swelling, and rheological analyses. Thermogravimetric analysis data showed that the initial degradation temperature of microgels was higher than that of CMS, but lower than that of b-CD. The zeta potentials of microgels decreased with increasing weight ratio R b-CD/CMS and ionic strength, but increased with increasing pH. The swelling degree of microgels showed an abrupt increase in the pH range 3-6 due to the ionization of carboxylic groups, and then remained almost constant. However, it decreased with increasing ionic strength. Viscosity results revealed that all samples exhibited non-Newtonian shear-thinning behavior. All microgels exhibited dominant elastic behavior over the entire frequency range with polymer concentrations of 7%. These results suggested that the properties of microgels could be controlled by pH and ionic strength.