Shear-Induced Collapse in a Lyotropic Lamellar Phase

An entropically stabilized cetylpyridinium chloride, hexanol, and heavy brine lyotropic lamellar phase subjected to shear flow has been observed here by small angle neutron scattering to undergo collapse of smectic order above a threshold shear rate. The results are compared with theories predicting that such a lamellar phase sheared above a critical rate should lose its stability by a loss of resistance to compression due to the suppression of membrane fluctuations.

Figure 1

Small angle neutron scattering patterns in radial and tangential geometries for a $\varphi =0.05$ lamellar phase as a function of steady shear rate.

Figure 2

Excess scattering from the $\varphi =0.05$ lamellar phase in the $\nabla V$ direction, $I_{\nabla V}-I_Z$, at various shear rates.

Figure 3

Tangential geometry scattering anisotropy of the lamellar phase $A_{\mathrm{TAN}}=(I_{\nabla V}-I_Z)/(I_{\nabla V}+I_Z)$ as a function of shear rate, $\dot{\gamma }$, for membrane volume fractions $\varphi =0.03–0.07$.

Figure 4

Variation of the critical shear rate for collapse, ${\dot{\gamma }}_c$, with interlamellar spacing, $d$, with predictions of the model of Bruinsma and Rabin [27], showing the $d^{-3}$ dependence. Error bars show shear rates determined for $A_{\mathrm{TAN}}=0.4$ and 0.6.