Reversible Gel Formation

Control of the aggregation state in an organogel offers other attractive means for modulation of materials properties and nondestructive read-out. A photoactive gela-tor (40) was obtained by Shinkai et al.[80] by connecting 4-methoxyazobenzene through an ester linkage to cholesterol. The trans-isomer 40 formed a stable gel with 

Irradiation at X 460 nm gave a fast cis-trans isomerization, with a concomitant increase in Tg. The sol-gel phase transition could be controlled in this way by light, while read-out of the states could be performed by measuring the modulation of the transmission or CD. For instance, the traras-azobenzene gelators displayed a CD effect, presumably due to the formation of helical aggregates, whereas the cis-isomers did not. 

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Pezron E, Leibler L, Ricard A, Audebert R. 1988. Reversible gel formation induced by ion complexation. 2. Phase diagrams. Macromolecules 21(4) 1126 1131. 

Heat reversible gel formation Agar Microbiological solid medio Synthetic meot gels... 

Meet reversible gel formation in the presence of potassium ions Carrageenan Synthetic meat gels Instant desserts... 

Water-soluble proteins as natural biopolymers are irreplaceable components in various technologies used in the development of new functional products in food, cosmetic, pharmaceutical medical application and so on. Gelatin occupies an important place in this case due to its unique capability to thermal reversible gel formation in the bulk as well as at liquid interfaces [1-3]. 

The main mechanisms of membrane fouling are adsorption of feed components, clogging of pores, chemical interaction between solutes and membrane material, gel formation and bacterial growth. Fet us first consider bacterial growth on membranes. Microbiological fouling of reverse osmosis membranes is one of the main factors in flux decline and loss of salt rejection [25-29] (Table 11.1). 

The formation of a photo-reversible gel is explained as foUows. The azobenzene groups in the surface region of the polymer coil help the coil overlap. When they change to a more polar cis form, the interactions are strengthened. The change in the interpolymer interactions is responsible for the change in the gel melting temperature. 

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