Thermally reversible gelation

The property of thermal, reversible gelation is obtained by the addition of water-soluble proteins and protein degradation products to an aqueous solution of poly (vinyl alcohol) 2). Protein products such as albumin, gelatin, glue, a-amino acids, and their condensation products—diketopiperazines—may be used. A typical formulation for the preparation of a thermally reversible gel is ... 

Han CK, Bae YH. Inverse thermally reversible gelation of aqueous N-isopropylacrylamide copolymer solution. Polymer 1998 39 2809-2814. 

Douglas, J. F. Theoretical issues relating to thermally reversible gelation by super-molecular fiber formation. Langmuir, 2009, 25(15), 8386-8391. 

Yamaguchi, R., Hirano, S., Arai, Y. and Ito, T. (1978) Chitosan salt gels thermally reversible gelation of chitosan. Agricultural and Biological Chemistry, 42,1981-1982. 

Attwood, D., Tait, C.J. and Collett,J.H. (1987) Thermally reversible gelation characteristics, poly(oxyethy-lene)-poly(oxypropylene) block copolymer in aqueou.s solution after exposure to high-energy irradiation (Chapter 10), in Controlled-Release Technology Pharmaceutical Applications, Lee P.I., and Good, W. (eds), American Chemical Society, Washington D.C. 

Han, C. K., Bae, Y. H. (1998). Inverse thermally-reversible gelation of aqueous A-isopropy-lacrylamide copolymer solutions. Polymer, 39, 2809-2814. 

Order in solutions of atactic polymers such as indicated by thermally reversible gelation,33-36 to be discussed in Section IV ... 

The thermally-reversible gel returns to the solution because the droving forces are noncovalent bonds such as hydrogen bonding, hydrophobic interaction, n-n interaction and electrostatic interaction. These noncovalent bonds are broken down by heating, so the gel reverts to the sol. Since the thermally-irreversible gel forms a network structure by firm chemical covalent bonds, the gel formed never changes to the sol. This is why the thermally-irreversible gel is called physical gel and the thermally-irreversible gel is referred to as chemical gel. Moreover, the gelation ability is found in not only biopolymers but also low molecular weight compounds. 

In chemical gels the network connection (crosslink) is usually a covalent bond, which leads to a thermally irreversible gel. When the crosslinking is purely physical in nature, a physical gel is formed which is thermally reversible. There have been at least two excellent works published in the last few years. Reversible Polymeric Gels and Related Systems by Russo [2] and Thermoreversible Gelation of Polymers and... 

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