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).