Probing the boundaries of miscibility in model carbohydrates consisting of chemically derivatized dextrans using DSC and FTIR spectroscopy

Miscibility of carbohydrate polymers consisting of mixtures of chemically derivatized dextrans with charged side chains were studied as model systems. The effect of total polymer concentration and added NaCl on miscibility was investigated using DSC and FTIR Spectroscopy. DSC results showed a single Tg for samples prepared at low, medium and high polymer concentrations in the absence of NaCl; and at high concentrations in the presence of NaCl, indicating miscible systems. Two separate Tgs were obtained for samples prepared at low and medium polymer concentrations in the presence of NaCl, indicating immiscible systems. FTIR spectroscopy showed significantly different behavior for 1 Tg and 2 Tgs systems. The systematic changes in the FTIR spectra of miscible blends were assigned to the change in hydrogen bond distribution of the pure components in the mixture resulting from inter-molecular interactions. No such significant systematic change was observed in the FTIR spectra of immiscible systems.