Quasi-variational principle for interface kinematics

A quasi-variational principle has been formulated for the interface motion during phase transition. We use two types of interface description: a parametric definition as a function of the arc length and the time and a new definition of the complete interface evolution through a field of the unit tangent vector of the interface. In the second case the proposed quasi-variational principle can be interpreted as the Prigogine principle of the minimum entropy production. The steady rotation of the spiral interface has been considered as an example of application of the direct variational principle.