Effect of co-amphiphiles on the stiffness of lipid lamellae

We use coarse-grained molecular dynamics simulations to study the mechanics of lamellae and vesicles formed by the self-assembly of dodecyldimethylammoniumbromide lipids in water. We observe various ordered morphologies such as micelles, uni- and multi-lamellar vesicles as well as bilayers and lamellae with increasing lipid concentration. By fitting the vesicle-water interface in terms of spherical harmonics, we track the reduced volume and correlate it with the resulting dynamics of the vesicle in shear flow. Further, we calculate the Poisson's ratio of the lamellar structures under uniaxial extension. We discover that Poisson ratio of the lamella decreases with increasing concentration of co-amphiphilic molecules stacked parallel to the lipids. Remarkably, this is similar to salt-induced stiffening observed in micellar assemblies (Dhakal and Sureshkumar, ACS Macro Lett. 2016, 5 (1), pp 108). Finally, a shear-induced structure transition from lamellae to multi-lamellar vesicles will be discussed.