Colloidal Stability and Mesoglobules

When polymer solutions encounter situations for which the thermodynamic quality of the solvent becomes poor, individual chains undergo a coil-to-globule collapse, the globules associate immediately, and macroscopic phase separation seems unavoidable. However, it has been reported that a number of polymers in water or in organic solvents form equilibrium globules, i.e. single-chain globules that remain in solution without immediate association and precipitation. 

For example, in the case of PS and applying the Smoluchowski equation [333], it is possible to estimate the precipitation time, fpr, of globules of radius R and translation diffusion coefficient D in solutions of polymer concentration Cp (the number of chains per unit volume) [334]. Assuming a standard diffusion-limited aggregation process, two globules merge every time they collide in the course of Brownian motion. Thus, one can write Eq. 2 ipr m (2) 

Factors affecting the size of the mesoglobules include polymer concentration, i.e. the size increases with solution concentration and, more importantly, heating rate (Fig. 34). Thus, a fast increase in temperature (nonequilibrium heating) leads to mesoglobules of smaller size than those formed upon slow heating through the sample LCST [ 141 -145,147]. The chemical composition of 

The stability of the dispersions upon dilution at 50 °C and zero value of the osmotic second virial coefficient suggests that the surface of the particles at temperatures above the LCST may possess some hydrophilic character the macromolecules self-organise and build up particles with hydrated po- 

What could be the reason for this remarkable slowing down of aggregate association Why are mesoglobules not as sticky as anticipated, given the thermodynamically poor conditions to which they are subjected  

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