The Cahn-Hilliard system has been used to describe a wide number of phase separation processes, from co-polymer systems to lipid membranes. In this work the convergence properties of a closest-point based scheme is investigated. In place of solving the original fourth-order system directly, two coupled second-order systems are solved. The system is solved using an approximate Schur-decomposition as a preconditioner. The results indicate that with a sufficiently high-order time discretization the method only depends on the underlying spatial resolution.

In many interfacial flow systems, variations of surface properties lead to novel and interesting behaviors. In this work a three-dimensional model of flow dynamics for multicomponent vesicles is presented. The surface composition is modeled using a two-phase surface Cahn-Hilliard system, while the interface is captured using a level set jet scheme. The interface is coupled to the surrounding fluid via a variation of energy approach. Sample energies considered include the total bending, variable surface tension energy, and phase segregation energy. The fully coupled system for surface inhomogeneities, and thus varying interface material properties is presented, as are the associated numerical methods. Numerical convergence and sample results demonstrate the validity of the model.

In this work, the nonlinear hydrodynamics of a three-dimensional multicomponent vesicle in shear flow are explored. Using a volume- and area-conserving projection method coupled to a gradient-augmented level set and surface phase field method, the dynamics are systematically studied as a function of the membrane bending rigidity difference between the components, the speed of diffusion compared to the underlying shear flow, and the strength of the phase domain energy compared to the bending energy. Using a pre-segregated vesicle, three dynamics are observed: stationary phase, phase-treading, and a new dynamic called vertical banding. These regimes are very sensitive to the strength of the domain line energy, as the vertical banding regime is not observed when the line energy is larger than the bending energy. The findings demonstrate that a complete understanding of multicomponent vesicle dynamics requires that the full three-dimensional system be modeled, and show the complexity obtained when considering heterogeneous material properties.