  This work presents a self-contained continuum formulation for coupled
chemical, mechanical and thermal contact interactions. The formulation is very
general and hence admits arbitrary geometry, deformation and material behavior.
All model equations are derived rigorously from the balance laws of mass,
momentum, energy and entropy in the framework of irreversible thermodynamics,
thus exposing all the coupling present in the field equations and constitutive
relations. In the process, the conjugated kinematic and kinetic variables for
mechanical, thermal and chemical contact are identified, and the analogies
between mechanical, thermal and chemical contact are highlighted. Particular
focus is placed on the thermodynamics of chemical bonding distinguishing
between exothermic and endothermic contact reactions. Distinction is also made
between long-range, non-touching surface interactions and short-range, touching
contact. For all constitutive relations examples are proposed and discussed
comprehensively with particular focus on their coupling. Finally, three
analytical test cases are presented that illustrate the thermo-chemo-mechanical
contact coupling and are useful for verifying computational models. While the
main novelty is the extension of existing contact formulations to chemical
contact, the presented formulation also sheds new light on thermo-mechanical
contact, since it is consistently derived from basic principles using only few
assumptions.
