H. Casimir proved in 1948 that two metallic parallel plates attract each other due to the quantum fluctuations induced by the electric field of the vacuum between the plates [1]. The dependence of this force with the temperature was calculated by Lifschitz [2].
Granular matter, because of lack of energy conservation, are systems out of equilibirum. Then usual approaches based on Thermodynamics of Statistical mechanics are not applicable a priori. Phenomenology in these systems is very rich.