Entropic stabilization

Two mechanisms of steric stabilization can be distinguished entropic stabilization and osmotic repulsion. Entropic stabilization arises when two opposing adsorbed polymer layers of adjacent particles overlap, resulting in compression and interpenetration of their... 

Another way to interpret the above observations would be in terms of the general principle that effective steric stabilization of polymer-coated droplets requires that the continuous phase be a good quality solvent for the polymeric stabilizer. Under poor quality solvent conditions (asi-casein at high ionic strength), the required entropic stabilizing repulsion of the adsorbed protein layer is converted into a destabilizing polymer-mediated attraction (Dickinson and Stainsby, 1982 Dickinson, 2006). 

Suppose AHr and ASR are both negative. In this case ASR opposes aggregation while AHr favors it. Since the resistance to aggregation decreases with decreasing temperature, aggregation is expected as T is lowered. Poly(12-hydroxystearic acid) adsorbed from n-heptane and polyoxyethylene adsorbed from methanol are examples of systems that display a CFT with decreasing temperature. Since ASR is the source of the stabilization in these cases, this mechanism is called entropic stabilization. 

Discuss polymer-colloid interactions and steric stability from a thermodynamic perspective. What is enthalpic stabilization What is entropic stabilization What is the critical flocculation temperature (CFT) ... 

The net result is the same two different states with nearly identical geometry and, presumably, nearly identical energy. This is favorable for entropical reasons and we expect considerable entropic stabilization of the disordered flip-flop hydrogen bonds. 

Berezovsky IN, Chen WW, Choi PJ, Shakhnovich EL Entropic stabilization of proteins and its proteomic consequences. PLoS. Comput. Biol. 2005 l e47. 

Evans R, Davison JB, Napper DH. The preparation of aqueous entropically stabilized latices. J Polym Sci Polym Letters 1972 10 449-453. 

The third mechanism of imparting steric stabilization differs from the preceding two in that the enthalpy and entropy contributions to the free energy of flocculation act in concert instead of in opposition. Both now contribute to stability since AHp is positive and dSp is negative. The magnitudes of their respective contributions to AGp are no longer important This is termed combined enthalpic-entropic stabilization. 

Note that certain limiting cases implicit in Table 7.1 can stifl result in a positive free energy of flocculation. IThiese are ASp=Q for enthalpic stabilization and AHp=0 for entropic stabilization. Note, too, that if AHp=ti, the system is said to be athermal. 

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