The Flory-Huggins (FH) theory for polymer solutions, and steric stabilization of colloids is well documented in the literature. There is also many experimental results, showing that even small molecules, as oleic or stearic acid, fatty amines, can stabilize colloidal dispersions, in non-aqueous media, by adsorption. But, the concept of 'chi' FH or solvency parameter, can be used in case of such small molecules? The 'chi' parameter can be > 1, if calculated with Hansen solubility parameters? FH theory "for the entropy of mixing of polymer and solvent corresponds to volume fraction statistics." Small molecules, like dispersions of solids in dodecane, stabilized with small amounts of short chain, like oleic acid, would be also volume fraction, or mole fraction statistics (Bragg-Williams)? See e.g. page 34 Napper book: "Polymeric Stabilization of Colloidal Dispersions"
You might want to read some of the papers by Cary Chiou: For example Environ. Sci. Technol., 17:227-231, 1983, where he uses FH theory for dissolution of small molecules in soil organic carbon. I recently was faced with a related problem where volume fraction was undefined, so I reverted to the theoretically unacceptable unit of "mass fraction" - for C60 - and got the paper accepted. See: Environ. Sci. Technol., 43:7370-7375, 2009. You may also enjoy reading: Environ. Sci. Technol., 42:845-851, 2008. I mention this paper because for solutions containing what you may consider all small molecules, Wohl's equation specifically overcomes the issue of difference in molecular size by involving interaction parameters that account for molecular size (as opposed to Margules equations, which are based purely on mole fractions. In American lingo, "punt, when you need to punt".
Dear Professor Jafvert, many thanks for your help! Your comments, and paper recommendations helped me a lot. I will follow your American lingo: "punt, when you need to punt". ;~) Kind regards, Antonio
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