Membranes are an important subject of study in physical chemistry and biology.
They can be considered as material surfaces with a surface energy depending on the
curvature tensor. Usually, mathematical models developed in the literature consider
the dependence of surface energy only on mean curvature with an added linear
term for Gauss curvature. Therefore, for closed surfaces the Gauss curvature
term can be eliminated because of the Gauss–Bonnet theorem. Rosso and
Virga (Proc. Roy. Soc. Lond. A 455:1992 (1999), 4145–4168) considered the
dependence on the mean and Gaussian curvatures in statics and under a
restrictive assumption of the membrane inextensibility. The authors derived the
shape equation as well as two scalar boundary conditions on the contact
line.
In this paper — thanks to the principle of virtual working — the equations of
motion and boundary conditions governing the fluid membranes subject to general
dynamical bending are derived without the membrane inextensibility assumption. We
obtain the dynamic “shape equation” (equation for the membrane surface) and the
dynamic conditions on the contact line generalizing the classical Young–Dupré
condition.