‘‘Layering’’ effect in a sheared lyotropic lamellar phase

Swelling kinetics of a compressed lamellar phase

“…The systematic study as a function of the shear rate leads to Figure 1(b) where we see that d decreases continuously withγ above the jump-of-size transition. Meanwhile, the numerous Bragg spots of the small-angle light scattering patterns [13] not only show that the onions still exist but also that they are extremely well ordered under shear. The combination of these results (light+neutron scattering) suggests that the onions have expelled some of the inner water and subsequently this state will be referred to as compressed onions.…”

“…At high temperature (26 < T < 31 • C), the sequence is analogous, apart from the high shear rate regime. Instead of oriented membranes, a new transition takes place (the jump-of-size transition) whose main features are the following: 1) at the transition the size of the onions increases discontinuously from 1 to 10 µm typically and then does not depend any more on the shear rate [14]; 2) the transition is accompanied with a decrease of the smectic period of the lamellar phase [13].…”

“…The combination of these results (light+neutron scattering) suggests that the onions have expelled some of the inner water and subsequently this state will be referred to as compressed onions. While not proven, it was argued in reference [13] that the shear rate-usually fixing the size of the vesicles (through a mechanism where the viscous stress is balanced against the energetical cost of making a vesicle [1])-now acts as a compression force. This could be the reason why the size of the vesicles does not depend anymore on the shear rate and, instead, the shear rate controls the compression.…”

“…Recently, the opportunity to control additionally the spatial organisation of the onions was demonstrated [13][14][15]. Indeed, for one particular L α phase a series of dynamic transitions leads to a population of shear-ordered onions, in a close analogy with the shear ordering of concentrated colloidal suspensions [16].…”

Reversible size of shear-induced multi-lamellar vesicles

“…In fact, many different shear effects have been reported: transformation from lamellar phases to Multi-lamellar vesicles, MLVs (or ''onions''), in different amphiphilic systems and followed by different techniques [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]; formation of MLVs in presence of submicron-size particles (''stuffed onions'') [21]; changes in lamellar orientation [17,22,23]; formation of intermediates with cylindrical structure between a lamellar and MLV phases [24][25][26]; reduction in lamellar spacing [27]; transitions from MLVs to unilamellar vesicles [28] and ''layering'' effects on onions [8,29]. As a practical application, these MLVs can be used, for instance, to encapsulate chemicals leading to a new kind of controlled micro-reactor [30] or as carriers for oligonucleotide delivery [31].…”