The effect of shear flow on the Helfrich interaction in lyotropic lamellar systems

Abstract

We study the effect of shear flow on the entropic Helfrich interaction in lyotropic surfactant smectic fluids. Arguing that flow induces an effective anisotropic surface tension in bilayers due to a combination of intermonolayer friction, bilayer collisions and convection, we calculate the reduction in fluctuations and hence the renormalised change in effective compression modulus and steady-state layer spacing. We demonstrate that non-permeable or slowly permeating membranes can be susceptible to an undulatory instability of the Helfrich-Hurault type, and speculate that such an instability could be one source of a transition to multilamellar vesicles.

Orientation transition of defective lyotropic triblock copolymer lamellar phase

“…The mechanism of the layer orientation transition in the lyotropic lamellar phase was theoretically argued by some researchers [13][14][15]. Ramaswamy argued that the suppression of undulations triggers the transition [13].…”

“…Instability of the lamellar phase is explained by the Helfrich-Hurault mechanism [13][14][15][16][17]. The HelfrichHurault effect is undulation instability of the smectic phase subjected to the external electric or magnetic field [17].…”

“…Thus reduced repulsive force generates effective dilation along the layer normal of the membrane in order to retain the equilibrium layer spacing. It has been anticipated that, as the dilation becomes larger than the critical value, coherent buckling of the lamellar membranes appears and either the onion phase formation or the layer orientation is eventually triggered [13][14][15][16]. However, experimental observations present that the onion phase formation and the layer orientation transition occur in different shear rate range [1,4,5].…”

Kinetics of the orientation transition in the lyotropic lamellar phase

“…One is a thermodynamically stable multilamellar vesicle (mLV) phase formation under shear flow [1][2][3][4][5]. And another one is an orientation transition of the lamellae from parallel to perpendicular orientation [5][6][7][12][13][14][15][16][17]. Since there are many reports on the orientation transition for many systems such as thermotropic smectic phase, amphiphilic lamellar phase, and block copolymer melt [18][19][20][21], the orientation transition is likely to be an universal structural transition in the layered system.…”

“…theoretical studies expect that the lamellar will lose its stability as the shear rate gradually increases because of suppression of the undulation fluctuation [12][13][14][15][16]. therefore the reduced repulsive force generates effective dilation along the layer normal of the lamellae in order to retain the equilibrium layer spacing.…”