![]() The famous formula, used for 40+ years is: The smaller Ra, the more likely they are to be compatible. The HSP Distance between two molecules, conventionally called Ra, is the measure of how alike they are. Older references use (cal/cc) ½ which are a factor of 2.0455 smaller. The units of solubility parameters are MPa ½. This gives us the classic formula for Hansen Solubility Parameters where the total parameter, δ, is broken into δD, δP and δH for Dispersion, Polar and Hydrogen-bonding: The cohesive energy density is more conveniently handled in terms of the To scale them so that molecules in a series are more comparable we need theĬohesive energy density which is obtained by dividing by molar volume V: Bigger molecules in a molecular series, not surprisingly, have bigger cohesive energies. The relationship between them is:Ĭohesive energy is not so useful on its own. Instead we know the latent heat of vaporization H v, R the universal gas constant, and T the absolute temperature. We are generally not familiar with cohesive energy. If E is broken into 3 components of Dispersion, Polar and Hydrogen-bonding then we get: how much energy is required to break it apart into gas molecules. If they are very different then energy in and out don't balance and the miscibility is low.Ĭohesive energy, E, of a solvent, i.e. If you evaporate a portion of a solvent and then condense in an equal volume of a different solvent, if the two solvents are alike then the energy cost of doing this is minimal and the solvents are miscible. You get all that energy back when you condense it. It takes energy (enthalpy of vapourisation) to evaporate a solvent. So if we have a formula for "like" we can judge the solubility of a polymer in a solvent or the compatibility of a polymer and plasticiser or the stability of a nanoparticle in a solvent dispersion by how alike they are. Here we show where they come from, why they work and give you the HSP values of ~1000 chemicals.Īnother simple way to look at the basics is via the Lattice Theory app. HSP are three numbers that provide a lot of practical formulation power. ![]()
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