105 research outputs found
Stability of bicontinuous cubic phases in ternary amphiphilic systems with spontaneous curvature
We study the phase behavior of ternary amphiphilic systems in the framework
of a curvature model with non-vanishing spontaneous curvature. The amphiphilic
monolayers can arrange in different ways to form micellar, hexagonal, lamellar
and various bicontinuous cubic phases. For the latter case we consider both
single structures (one monolayer) and double structures (two monolayers). Their
interfaces are modeled by the triply periodic surfaces of constant mean
curvature of the families G, D, P, C(P), I-WP and F-RD. The stability of the
different bicontinuous cubic phases can be explained by the way in which their
universal geometrical properties conspire with the concentration constraints.
For vanishing saddle-splay modulus , almost every phase considered
has some region of stability in the Gibbs triangle. Although bicontinuous cubic
phases are suppressed by sufficiently negative values of the saddle-splay
modulus , we find that they can exist for considerably lower
values than obtained previously. The most stable bicontinuous cubic phases with
decreasing are the single and double gyroid structures since
they combine favorable topological properties with extreme volume fractions.Comment: Revtex, 23 pages with 10 Postscript files included, to appear in J.
Chem. Phys. 112 (6) (February 2000
Numerical observation of non-axisymmetric vesicles in fluid membranes
By means of Surface Evolver (Exp. Math,1,141 1992), a software package of
brute-force energy minimization over a triangulated surface developed by the
geometry center of University of Minnesota, we have numerically searched the
non-axisymmetric shapes under the Helfrich spontaneous curvature (SC) energy
model. We show for the first time there are abundant mechanically stable
non-axisymmetric vesicles in SC model, including regular ones with intrinsic
geometric symmetry and complex irregular ones. We report in this paper several
interesting shapes including a corniculate shape with six corns, a
quadri-concave shape, a shape resembling sickle cells, and a shape resembling
acanthocytes. As far as we know, these shapes have not been theoretically
obtained by any curvature model before. In addition, the role of the
spontaneous curvature in the formation of irregular crenated vesicles has been
studied. The results shows a positive spontaneous curvature may be a necessary
condition to keep an irregular crenated shape being mechanically stable.Comment: RevTex, 14 pages. A hard copy of 8 figures is available on reques
Numerical simulations of complex fluid-fluid interface dynamics
Interfaces between two fluids are ubiquitous and of special importance for
industrial applications, e.g., stabilisation of emulsions. The dynamics of
fluid-fluid interfaces is difficult to study because these interfaces are
usually deformable and their shapes are not known a priori. Since experiments
do not provide access to all observables of interest, computer simulations pose
attractive alternatives to gain insight into the physics of interfaces. In the
present article, we restrict ourselves to systems with dimensions comparable to
the lateral interface extensions. We provide a critical discussion of three
numerical schemes coupled to the lattice Boltzmann method as a solver for the
hydrodynamics of the problem: (a) the immersed boundary method for the
simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for
multi-component fluids in combination with (b) an additional
advection-diffusion component for surfactant modelling and (c) a molecular
dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.Comment: 24 pages, 12 figure
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