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All twist and no bend makes raft edges splay: Spontaneous curvature of domain edges in colloidal membranes

  • Miller, Joia M
  • Hall, Doug
  • Robaszewski, Joanna
  • Sharma, Prerna
  • Hagan, Michael F
  • Grason, Gregory M
  • Dogic, Zvonimir
Publication Date
Jul 31, 2020
eScholarship - University of California
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Using theory and experiments, we study the interface between two immiscible domains in a colloidal membrane composed of rigid rods of different lengths. Geometric considerations of rigid rod packing imply that a domain of sufficiently short rods in a background membrane of long rods is more susceptible to twist than the inverse structure, a long-rod domain in a short-rod membrane. The midplane tilt at the interdomain edge forces splay, which, in turn, manifests as spontaneous edge curvature with energetics controlled by the length asymmetry of constituent rods. A thermodynamic model of such tilt-curvature coupling at interdomain edges explains a number of experimental observations, including annularly shaped long-rod domains, and a nonmonotonic dependence of edge twist on domain radius. Our work shows how coupling between orientational and compositional degrees of freedom in two-dimensional fluids gives rise to complex shapes of fluid domains, analogous to shape transitions in 3D fluid vesicles.

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