Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

Abstract

We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of sheartreatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.

Transition due to base roughness in a dense granular flow down an inclined plane

“…When a shear is imposed, this tends to break the layers and create defects. This defectcreation mechanism has been known for some time now in the field of lamellar liquid crystals, 46 and it has also been observed in experiments 47 and more recently simulations of lamellar mesophases, 48 provided the system size is sufficiently large compared to the layer spacing. An important distinction between a liquid crystal and the present system is that a liquid crystal has no surface tension, but only a bending energy penalty which provides a term in the force density proportional to the fourth derivative of the displacement field with respect to x.…”

Rheological behavior of surfactant-based precursors of silica mesoporous materials

“…The rheology of polymer-like micelles networks can be altered by addition of cosurfactants, electrolytes, organic salts with strongly hydrophobic counter-ions and submicron-sized colloidal particles, because they modify the inter-micellar interactions and the micellar packing and in some cases, it may even result in phase transitions and the formation of novel complexes [12][13][14][15][16][17][18].…”

Universal properties of lamellar systems under weak shear

“…Experiments on the rheological bulk properties of lamellar systems [1] have shown beyond evidence the important role played by the texture (defects, instabilities) in the rheological response of these materials, whether this texture is made, e.g., of multilamellar vesicles (MLV, also called onions) in swollen surfactants [2] and in a block copolymer system [3], of oily streaks [4] or, in less recent works, of classical focal conic domains (FCD) in the sense of G. Friedel [5]. To each type of those textures corresponds a different type of steady-state rheological responsė γ = A(T, ...)σ m (or, equivalently, η = σ γ = B(T )γ −α , where η is the viscosity and α = 1 − m −1 ) [6], each of them characterized by a different type of exponent m. In principle the Newtonian case (m = 1, η = const) is not typical of a defect-driven steady state, since one expects that it is exhibited by perfect samples (not so easy to prepare), when the layers are strictly parallel to the shear velocity.…”