Self-assembled membranes of amphiphilic diblock copolymers enable compariso
ns of cohesiveness with lipid membranes over the range of hydrophobic thick
nesses d = 3-15 nm. At zero mechanical tension the breakdown potential V-c
for polymersomes with d = 15 mn is 9 V, compared to 1 V for liposomes with
d = 3 mn. Nonetheless, electromechanical stresses at breakdown universally
exhibit a V-c(2) dependence, and membrane capacitance shows the expected st
rong d dependence, conforming to simple thermodynamic models. The viscous n
ature of the diblock membranes is apparent in the protracted postporation d
ynamics.