Physics: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 [math]\displaystyle{ F }[/math] resulting at distance [math]\displaystyle{ h }[/math] between two parallel circular disks of radius [math]\displaystyle{ R }[/math], immersed in a Newtonian fluid with viscosity [math]\displaystyle{ \eta }[/math], at time [math]\displaystyle{ t }[/math], depends on the rate of change of separation [math]\displaystyle{ \frac{d h}{d t} }[/math] :

[math]\displaystyle{ F=\frac{3\pi \eta\ R^4}{2h^3} \frac{d h}{d t} }[/math]

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).