Gelation liquid/polymer gels

One type of gel which has been extensively investigated in relation to pharmaceutical applications is that formed by certain PEO-PPO-PEO block copolymers (153). These systems are particularly interesting since even a concentrated polymer solution is quite low-viscous in nature at low temperature, whereas a very abrupt gelation (liquid crystal formation (25, 187, 188)) occurs on increasing the temperature. The precise value of the transition temperature depends on the polymer molecular weight, composition and concentration, the concentration and nature of the drug, etc., but by... 

Gelation of liquid electrolytes to obtain a gel that effectively penetrates into the pores of the 2 can be obtained by addition of appropriate additives such as small molecules,49 polymers, inorganic nanoparticles,49 50 and carbon nanotubes.51... 

Figure 3.13 shows the variation of the gel conversion of the limiting reactant as a function of the stoichiometric ratio. For r > 3, no gel is formed and the polymer remains in the liquid state after complete reaction of epoxy groups. If the amount of epoxy monomer necessary to obtain a stoichiometric system is added in a second step, polymerization restarts, leading to gelation and the formation of a network. The two-step polymerization is the basis of several commercial thermosetting polymers. 

Despite their solid appearance, within the gel the liquid component is mobile and is only held by capillary forces. The solid network can be either a covalent polymer or a supramolecular assembly of small molecules. The latter class of compound, termed low molecular weight gelators (LMWG) of which 14.11 14.15 are examples, is perhaps of most interest to supramolecular chemists. Perhaps the most well known gels are metal oxide based polymeric materials produced by the sol-gel process. The sol-gel process involves the hydrolysis and polycondensation of monomeric metal salts such as early transition... 

---