Heat Inverted Hydration Repulsion

Hydration repulsion is a common physical effect that repels two wet surfaces that get too close together. A bit like the normal contact force it only exists as an opposition to things like Van De Waals forces which would act to pull the two materials together and expel all the water from between them. It is strongly linked to the surface tension and adherence factor of the liquid as this is the main source of hydration repulsion. Almost all biological systems and macrochemicals have  some form of intermolecular forces acting over a fluid plane, at which point hydration repulsion will come in as a universal affect to oppose this.

These forces also act between colloidal (granular) materials that are hydrated as well. As you would expect the binding of these gritty substances begins to break down at high temperatures and general structural collapse is common. But it has recently been shown that dextran, a long polysacharide (many sugar molecules turned into a polymer), that as temperature increases the structure becomes more secure. Even more interesting is that this stability was only found in dextran as part of a solution of calcium chloride. When it was instead dissolved in magnesium chloride the structure broke down as expected with a temperature raise. This is very puzzling as magnesium and calcium are in the same group in the periodic table and so should have very similar properties in their molecules.


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