Gelation thermoreversible

If these particles are suspended in a solvent that is marginal for the grafted chains, then at high temperature, above the theta point for the chains in the solvent (see Section 2.3.1.2), the chains repel each other, and the particles remain dispersed. If, however, the temperature 

T is reduced below the theta temperature 6, attractive particle-particle interactions occur, eventually producing flocculation at low enough T. Thus, in such a dispersion, the strength of the particle-particle interactions can be controlled by adjusting the temperature, and a dispersion that has been flocculated at a low temperature can be redispersed merely by increasing T.  

One system with these desirable features is a suspension of small a 50 nm) silica particles onto which octadecyl chains have been densely grafted (Stober et al. 1968 van Helden et al. 1981 Woutersen and de Kruif 1991). The octadecyl chains have a theta point near room temperature in various solvents, including benzene, dodecane, and hexadecane. 

The properties of the above system at modest particle concentrations are relatively simple to model, because the grafted octadecyl layer is thin compared to the particle radius and because the particle-particle interactions are weak enough that the properties of the dispersion are not sensitive to the detailed shape of the particle-particle interaction potential. These considerations have motivated the use of a simple square-well potential as a model of the particle-particle interactions (Woutersen and de Kruif 1991) (see Fig. 7-3). This potential consists of an infinite repulsion at particle-particle contact (where D — 0), bounded by an attractive well of width A and depth e. There are no interactions at particle-particle gaps greater than A. Near the theta point, the well depth s depends on temperature as follows (Hory and Krigbaum 1950)  

The strength of the particle-particle interactions produced by this potential depend on both the depth e and width A of the potential. However, for narrow wells, A /a 1, the particle-particle interactions are controlled only by the combination parameter (Baxter 1968) 

---

Guenet JM (1992) Thermoreversible gelation of polymers and biopolymers. Academic, London... 

J. M. Guenet, Thermoreversible Gelation of Polymers and Biopolymers. Academic Press, 1992. 

Eliot, C., Dickinson, E. (2003). Thermoreversible gelation of caseinate stabilized emulsions at around body temperature. International Dairy Journal, 13, 679- 684. 

Supporting material for clinical analysis, cell immobilization Cell encapsulation and immobilization, immobilization of enzymes, controlled release, injectable microcapsules Microencapsulation, thermoreversible gelation Lubrication applications... 

Richtering W, Fuchs T, Burchard W (1998) Dynamics during thermoreversible gelation of the polysaccharide schizophyllan. Ber Bunsenges Phys Chem 102 1660-1664 Rosiak JM (1998) Gel/sol analysis of irradiated polymers. Radial Phys Chem 51 13-17 Riihe J et al (2004) Polyelectrolyte bmshes. Adv Polym Sci 165 79-150... 

Shlrasakl Y, Tanaka J, Makazu H, Tashlro K, Shoji S, Tsukita S, Funatsu T (2006) On-chip cell sorting system using laser-induced heating of a thermoreversible gelation polymer to control flow. Anal Chem 78(3) 695-701... 

Lee DS, Shim MS, Kim SW, Lee H, Park I, Chang T. Novel thermoreversible gelation of biodegradable PLGA-block-PEO-block-PLGA triblock copolymers in aqueous solution. Macro-mol Rapid Commun 2001 22 587-592. 

Jeong B, Bae YH, Kim SW. Thermoreversible gelation of PEG-PLGA-PEG triblock copolymer aqueous solutions. Macromolecules 1999 32 7064-7069. 

Mangione, M.R., Giacomazza, D., Bulone, D., Martorana, V, San Biagio, P.L., 2003. Thermoreversible gelation of k-carrageenan Relation between conformational transition and aggregation. Biophys. Chem. 104, 95-105. 

Guenet, J.P. Thermoreversible Gelation cf Polymers and Biopolymers Acad. Press Ltd. London. 1992. 

Schmidtke S, Russo P, Nakamatsu J, Buyuktanir E, Turfan B, Temyanko E, Negulescu I (2000) Thermoreversible gelation of isotropic and liquid crystalline solutions of a sticky rodlike polymer. Macromolecules 33 4427 1432... 

Tipton DL, Russo PS (1996) Thermoreversible gelation of a rodUke polymer. Macromolecules 29 7402-7411... 

Lin, H. H. Cheng, Y. L. (2001) In-situ thermoreversible gelation of block and star copolymers of poly(ethylene glycol) and poly(N-isopropylaciylamide) of varying architectures. Macromolecules, 34, 3710-3715. 

Choi, S.W. et al, 1999. Thermoreversible gelation of poly(ethylene oxide) biodegradable polyester block copolymers. II. Journal of Polymer Science Part A Polymer Chemistry, 37, 2207-2218. 

Zhou, J., G. Wang, et al. (2008). Viscoelastic behavior and in vivo release study of microgel dispersions with inverse thermoreversible gelation. Biomacromolecules 9(1) 142-148. 

Rubinstein M, Semenov AN (1998) Thermoreversible gelation in solutions of associating polymers. 2. Linear dynamics. Macromolecules 31(4) 1386-1397... 

Lee C-U, Lu L, Chen J et al (2013) Crystallization-driven thermoreversible gelation of coil-crystalline cyclic and linear diblock copolypeptoids. ACS Macro Lett 2 436-440... 

Arvidson SA, Lott JR, McAllister JW, Zhang J, Bates FS, Lodge TP, Sammler RL, Li Y, Brackhagen M (2013) Interplay of phase separation and thermoreversible gelation in aqueous methylcellulose solutions. Macromolecules 46 300-309... 

---