  The bending rigidity $k_c$ of bilayer vesicles self-assembled from
amphiphilic diblock copolymers has been measured using single and
dual-micropipet techniques. These copolymers are nearly a factor of 5 greater
in hydrophobic membrane thickness $d$ than their lipid counterparts, and an
order of magnitude larger in molecular weight $\bar{M}_n$. The macromolecular
structure of these amphiphiles lends insight into and extends relationships for
traditional surfactant behavior. We find the scaling of $k_c$ with thickness to
be nearly quadratic, in agreement with existing theories for bilayer membranes.
The results here are key to understanding and designing soft interfaces such as
biomembrane mimetics.
