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

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

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).

References

1. Smith AM (2002). "The Structure and Function of Adhesive Gels from Invertebrates". Integr. Comp. Biol. 42 (6): 1164–1171. doi:10.1093/icb/42.6.1164. PMID 21680401.

• Intermolecular forces