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ABSTRACT
Dilute solution properties of chitosan in propionic acid aqueous solutions with various pH values were studied using intrinsic viscosity, static light scattering (SLS), and dynamic light scattering (DLS). We demonstrated that the particle sizes (intrinsic viscosity [η], average hydrodynamic radius ⟨R h⟩, and average radius of gyration ⟨R G⟩) of chitosan molecules in dilute propionic acid/water solutions increased with decreasing pH value. SLS data also demonstrated that second virial coefficient (A 2) increased with decreasing pH value suggesting that solubility of chitosan in water increased with increasing propionic acid concentration. Differential refractive index increment (dn/dC), depolarization ratio (ρ v ), and ratio of ⟨R G ⟩/⟨ R h ⟩ increased with decreasing pH value indicating the increment of chitosan molecular chain anisotropy with increasing propionic acid concentration. Increasing propionic acid concentration in chitosan aqueous solution caused an increase of −NH3 + group on chitosan molecules leading to an increase in intra-molecular electrostatic charge repulsion and chain expansion of chitosan molecules. Thus, the molecular size, A 2, ρ ν , dn/dC, and ⟨R G ⟩/⟨R h ⟩ of chitosan increased with increasing propionic acid concentration.
ACKNOWLEDGMENT
The authors would like to thank the National Science Council of the Republic of China for research support through grant NSC-89-2216-E155-006.