Incipient Flocculation and the Thermodynamics of Sterically Stabilized Nonaqueous Dispersions
The results of recent measurements of the incipient flocculation behaviour of some sterically stabilized nonaqueous dispersions are rationalized using concepts of recent polymer solution theories. Utilizing a macroscopic temperature dependent expression for (1/2 -χ) in the expression for the free energy of interpenetration (ΔG I M ) of sterically stabilized particles it is predicted that, in principle, all such dispersions should show both a lower and an upper critical flocculation temperature. A microscopic expression for(1/2 - χ) shows that there are three contributions to ΔG I M ; (1) a combinatorial contribution, (ii) a contact energy dissimilarity term and (iii) a free volume dissimilarity contribution. The combinatorial entropy contribution to is the cause of stability of such particles, while the contributions from (ii) and (iii) always act to flocculate the latices. In principle the contact energy dissimilarity contribution causes the particles to flocculate at the LCFT while the free volume dissimilarity contribution is the cause of flocculation at the UCFT.
KeywordsFree Volume Dispersion Polymerization Exclude Volume Effect Contact Energy Butyl Chloride
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