The entropic role in exfoliation

The entropic part of the Gibb s free energy in forming intercalates and exfoliates is of critical importance. In the classical treatment of entropy, the entropy of mixing should be positive and contribute to the spontaneous formation of intercalates and exfoliated systems. Countering this increase in entropy is the decrease in entropy experienced by the polymer chain, as it must uncoil in order first, to intercalate and, second, to exfoliate the nanoparticle, yielding the maximum interfacial interaction between the polymer and clay nanoparticles. 

One exception to this general picture is where the polymer intercalates onto the clay surface and displaces a large number of small molecules. This is exactly what happens in the case of intercalating sodium mont-morillonite with PEO or PVP. In these examples, each mole of polymer displaces hundreds of moles of water molecules. The entropy decrease experienced by the polymer in uncoiling is offset strongly by the increase in entropy of the many moles of water displaced from the hydration sphere of the sodium cation on the clay surface. 

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