Interaction between lipid bilayers

Nearby lipid bilayers experience attractive van der Waals forces, screened electrostatic repulsion, and fluctuation-induced steric repulsion.

The Hamaker constant sets the strength of pairwise-summed van der Waals attraction between macroscopic bodies across a medium.

The Debye–Hückel screening length is the distance over which mobile ions suppress an electrostatic potential in the linearized electrolyte theory.

Helfrich repulsion is the entropic interaction produced when neighboring membranes suppress each other's thermal undulations. Its free energy per area scales as $(k_{B}T{)}^2/(k_c{d}^2)$.

A membrane unbinding transition sends the equilibrium layer spacing to infinity. In a dilute lamellar stack, competition between a quadratic virial attraction and cubic Helfrich repulsion gives a continuous transition with spacing exponent one.