Log-rolling micelles in sheared amphiphilic thin films

Using molecular dynamics simulations, we show that sheared solutions of cylindrical micelle-forming amphiphiles behave very differently under extreme confinement as compared to the bulk. When confined to ultrathin films, the self-assembled cylindrical micelles roll along the shearing direction and align parallel to each other with their axes along the vorticity direction, as opposed to aligning parallel to the shearing direction in the bulk. It is shown that this new "log-rolling" phase arises due to a strong coupling between the rotational degree of freedom of the micelles and the steady sliding motion of the confining surfaces. We examine the microscopic mechanism of the log-rolling phenomenon and also discuss its dependence on the segregation strength and length of the amphiphile, the shear rate, and the film thickness.