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 $\frac{dh}{dt}$ :

$F=\frac{3\pi \eta R^4}{2h^3}\frac{dh}{dt}$

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).