Stefan adhesion

Stefan adhesion is the normal stress (force per unit area) acting between two discs when their separation is attempted. Stefan's law governs the flow of a viscous fluid between the solid parallel plates and thus the forces acting when the plates are approximated or separated. The force $$F$$ resulting at distance $$h$$ between two parallel circular disks of radius $$R$$, immersed in a Newtonian fluid with viscosity $$\eta$$, at time $$t$$, depends on the rate of change of separation $$ \frac{d h}{d t}  $$ :
 * $$F=\frac{3\pi \eta\ R^4}{2h^3} \frac{d h}{d t}  $$

Stefan adhesion is mentioned in conjunction with bioadhesion by mucus-secreting animals. Nevertheless, most such systems violate the assumptions of the equation. In addition, these systems are much more complex when the fluid is non-Newtonian or inertial effects are relevant (high flow rate).