Effect of Thermal Undulations on the Bending Elasticity and Spontaneous Curvature of Fluid Membranes

Using numerical simulations, we characterized the behavior of an elastic membrane immersed in an active fluid. Our findings reveal a nontrivial folding and re-expansion of the membrane that is controlled by the interplay of its resistance to bending and the self-propulsion strength of the active components in solution. We show how flexible membranes tend to collapse into multi-folded states, whereas stiff membranes oscillates between an extended configuration and a singly fol...

We present a theory that combines the framework of irreversible thermodynamics with modified integral theorems to model arbitrarily curved and deforming membranes immersed in bulk fluid solutions. We study the coupling between the mechanics and permeability of a viscous and elastically-bendable membrane, and a multi-component bulk fluid solution. An equation for the internal entropy production for irreversibilities at the membrane is derived, determining the generalized therm...

We explore thermal fluctuations of thin planar membranes with a frozen spatially-varying background metric and a shear modulus. We focus on a special class of $D$-dimensional ``warped membranes'' embedded in a $d-$dimensional space with $d\ge D+1$ and a preferred height profile characterized by quenched random Gaussian variables $\{h_\alpha({\bf q})\}$, $\alpha=D+1,\ldots, d$, in Fourier space with zero mean and a power law variance $\overline{ h_\alpha({\bf q}_1) h_\beta({\b...

We set up the statistical mechanics for a nearly flat, thermally equilibrated fluid membrane, attached to an elastic network through one of its sides. We predict that the resulting structural (inversion) asymmetry of the membrane, notably due to the elastic network attached to one of its sides, can generate a local spontaneous curvature $C_0$, that may in turn destabilize the otherwise flat membrane. As $C_0$ rises above a threshold at a fixed temperature, a flat tethered mem...

We consider the thermal undulation, or shape fluctuation, of an almost planar fluid membrane surrounded by the same near-critical binary fluid mixtures on both sides. A weak preferential attraction is assumed between the membrane and one component of the mixture. We use the Gaussian free-energy functional to study the equilibrium average of the undulation amplitude within the linear approximation with respect to the amplitude. According to our result given by a simple analyti...

We study a Gaussian model of the membrane of red blood cells: a "phantom" triangular network of springs attached at its vertices to a fluid bilayer with curvature elasticity and tension. We calculate its fluctuation spectrum and we discuss the different regimes and non-monotonic features, including the precise crossover at the mesh size between the already known limits with two different tensions and the renormalisation of the bending rigidity at low wavevectors. We also show...

We study the dynamics of elastic interfaces-membranes-immersed in thermally excited fluids. The work contains three components: the development of a numerical method, a purely theoretical approach, and numerical simulation. In developing a numerical method, we first discuss the dynamical coupling between the interface and the surrounding fluids. An argument is then presented that generalizes the single-relaxation time lattice-Boltzmann method for the simulation of hydrodynami...

In recent years it has been argued that the tension parameter driving the fluctuations of fluid membranes, differs from the imposed lateral stress, the 'frame tension'. In particular, stress-free membranes were predicted to have a residual fluctuation tension. In the present paper, this argument is reconsidered and shown to be inherently inconsistent -- in the sense that a linearized theory, the Monge model, is used to predict a nonlinear effect. Furthermore, numerical simula...

Using analytical calculations and computer simulations we consider both the lateral diffusion of a membrane protein and the fluctuation spectrum of the membrane in which the protein is embedded. The membrane protein interacts with the membrane shape through its spontaneous curvature and bending rigidity. The lateral motion of the protein may be viewed as diffusion in an effective potential, hence, the effective mobility is always reduced compared to the case of free diffusion...

Induced by proteins within the cell membrane or by differential growth, heating, or swelling, spontaneous curvatures can drastically affect the morphology of thin bodies and induce mechanical instabilities. Yet, the interaction of spontaneous curvature and geometric frustration in curved shells remains still poorly understood. Via a combination of precision experiments on elastomeric spherical bilayer shells, simulations, and theory, we show a spontaneous curvature-induced ro...