disgregation

from The Century Dictionary.

• noun Separation; specifically, in chem., the separation of the molecules within a substance, which is brought, about by heat or other chemical agents: as, the disgregation of a body is greater in the gaseous than in the liquid state.
• noun In thermodynamics, the transformation-value of configuration of a body or system. The disgregation added to the transformation-value of the heat contained in a system equals the entropy of the system.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physiol.) The process of separation, or the condition of being separate, as of the molecules of a body.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics separation, especially of molecules