title: Sol/gel transition of chitosan solutions.
abstract: This work studies the occurrence of sol/gel transition and the gel rheology for chitosan solution under various conditions. Experiments were conducted in an oscillatory shear apparatus with small amplitude, using a Rheometrics SR-5 rheometer, with Couette and parallel plate geometries. The experimental results demonstrate that the sol/gel transition concentration and the elastic modulus (G') for CS gel decrease as the pH value and the molecular weight (Mw) increase. However, the sol/gel transition concentration and G' became independent of Mw when Mw exceeded a threshold. The higher ionization constant, Kp, is responsible for the higher sol/gel transition concentration in a formic acid solution than in an acetic acid solution with equivalent molar concentration. The elastic modulus G' of a CS gel increases with temperature, which relationship differs from that for many polysaccharides, and can be understood through classical rubber elastic theory. Finally, a gel whose concentration was barely above the sol/gel point exhibited aging, and its G' and G" declined rather than increase with time, accompanied by a reversal from the sol/gel state back to the sol state. This is an uncommon aging behavior for a polysaccharide and a detailed explanation is provided.
authors.affiliation: Institute of Organic and Polymeric Materials, National Taipei University of Technology, No. 1, Sec. 3, Chung-Hsiao E. Road, Taipei, Taiwan, ROC.
authors.forename: S P
authors.initials: SP
authors.lastname: Rwei
authors.forename: T Y
authors.initials: TY
authors.lastname: Chen
authors.forename: Y Y
authors.initials: YY
authors.lastname: Cheng
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000464:Alginates / Q000737:chemistry; D048271:Chitosan / Q000737:chemistry*; D005561:Formates / Q000737:chemistry; D005782:Gels; D007700:Kinetics; D008956:Models, Chemical; D008970:Molecular Weight; D009991:Oscillometry; D004364:Pharmaceutical Preparations; D044367:Phase Transition; D011092:Polyethylene Glycols; D011108:Polymers; D011134:Polysaccharides / Q000737:chemistry; D012212:Rheology; D012685:Sepharose / Q000737:chemistry; D012996:Solutions; D013696:Temperature; D013997:Time Factors; D014783:Viscosity
chemical_list: D000464:Alginates; D005561:Formates; D005782:Gels; D004364:Pharmaceutical Preparations; D011108:Polymers; D011134:Polysaccharides; D012996:Solutions; C030544:formic acid; D011092:Polyethylene Glycols; D012685:Sepharose; D048271:Chitosan; D019342:Acetic Acid