Equilibrium onions?

Ramos, Laurence; Roux, D.; Olmsted, Peter D.; Cates, M. E.

doi:10.1209/epl/i2003-10260-6

Cited by 26 publications

(30 citation statements)

References 35 publications

(58 reference statements)

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“…1. From polarizing microscopy we know that in the lamellar phase our samples consist of closely packed onion vesicles [25]. Using cryo-TEM, we observe that upon transformation into the Q D II cubic phase, the rounded multilamellar vesicles are transformed into cubosomes [26] of approximately the same dimensions as the onion vesicles.…”

Section: IImentioning

confidence: 88%

Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

et al. 2006

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The liquid crystalline lamellar (L ) to double-diamond inverse bicontinuous cubic (Q D II ) phase transition for the amphiphile monoelaidin in excess water exhibits a remarkable sequence of structural transformations for pressure or temperature jumps. Our data imply that the transition dynamics depends on a coupling between changes in molecular shape and the geometrical and topological constraints of domain size. We propose a qualitative model for this coupling based on theories of membrane fusion via stalks and existing knowledge of the structure and energetics of bicontinuous cubic phases. DOI: 10.1103/PhysRevLett.96.108102 PACS numbers: 87.16.Dg, 61.10.Eq, 87.17.Ee, 64.70.Md Lyotropic liquid crystalline phases form when amphiphilic molecules are mixed with a polar solvent [1,2]. The many structures they can adopt, their complex phase behavior and their energetics have received a great deal of attention over the past half century. Much is now understood about their equilibrium behavior and this has informed the development of surfactant technologies and our understanding of how amphiphiles in biological membranes can control biochemical activity [3,4]. By comparison the study of the nonequilibrium structure and dynamics of lyotropic liquid crystalline systems is in its infancy and little is understood about the mechanisms by which one phase transforms into another [5,6]. Understanding the dynamics of lyotropic phase transformations is of practical interest for applications where amphiphilic materials are processed and of relevance in biological systems where membrane fusion or division occurs.The present work focuses on a phase transition where membrane fusion occurs: the fluid lamellar to inverse bicontinuous cubic phase transition, Fig. 1. Models for the process of membrane fusion between apposed lipid bilayers have been proposed by a number of groups [7][8][9]. All rely on the formation of transient lipid contacts known as stalks, which subsequently break through to form the beginnings of the tubular connections that are the fundamental connecting element in the inverse bicontinuous cubic phases. Recent theoretical models of the structure and energy of the stalk have incorporated both elastic energy, accounting for the splay, saddle splay, and tilt deformations of the membrane, as well as hydration repulsion acting between the apposing membranes [10 -12]. The models have been used to estimate the energy of stalk formation and mesoscopic models have been used to simulate the entire fusion process [13]. However, very few measurements have been made to test these models. To date the most convincing evidence has been structural evidence that is consistent with the existence of fusion stalks [14]. As for the structural dynamics, a limited amount of experimental work has been carried out on the lamellar to inverse bicontinuous cubic phase transition [15][16][17][18][19]. The major problem to date with these dynamical studies is the lack of reproducibility in results [20,21]. FIG. 1 (color online). In these im...

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Section: IImentioning

confidence: 88%

Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

et al. 2006

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“…Dense arrangements of MLVs [17,18] provide ideal samples to test in great details the notion of internal stress as a driving force for the slow dynamics. As mentioned above, the fluid-to-solid transition of this material can be driven by a temperature jump.…”

Section: Internal Stress Relaxationmentioning

confidence: 99%

“…For the MLVs, the physical origin of the internal stress is the elastic energy stored in the deformation of the vesicles, which are expected to depart from a spherical, elastically relaxed shape, due to their rapid and disordered growth at the fluid-to-solid transition. On the other hand, the linear elastic modulus G 0 is equal to the density of elastic energy stored by the material when it is deformed in the linear regime [18]. Therefore, both the internal stress and G 0 share the same microscopic origin, i.e.…”

Section: Internal Stress Relaxationmentioning

confidence: 99%

Slow dynamics in glassy soft matter

Cipelletti¹,

Ramos

2005

J. Phys.: Condens. Matter

364

410

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Abstract.Measuring, characterizing and modelling the slow dynamics of glassy soft matter is a great challenge, with an impact that ranges from industrial applications to fundamental issues in modern statistical physics, such as the glass transition and the description of out-of-equilibrium systems. Although our understanding of these phenomena is still far from complete, recent simulations and novel theoretical approaches and experimental methods have shed new light on the dynamics of soft glassy materials. In this paper, we review the work of the last few years, with an emphasis on experiments in four distinct and yet related areas: the existence of two different glass states (attractive and repulsive), the dynamics of systems very far from equilibrium, the effect of an external perturbation on glassy materials, and dynamical heterogeneity.

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“…Such reconstruction arises under shear, sometimes to an extreme degree, for instance in the shearinduced transition from an ordered lamellar stack to an onion phase in lyotropic smectics [4][5][6][7] . (The onion phase comprises a space-filling packing of multilayer vesicles; under some conditions similar defect textures can arise without shear [8][9][10][11] . )…”

Section: Introductionmentioning

confidence: 99%

Rheology of lamellar liquid crystals in two and three dimensions: a simulation study

et al. 2012

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We present large scale computer simulations of the nonlinear bulk rheology of lamellar phases (smectic liquid crystals) at moderate to large values of the shear rate (Peclet numbers 10 − 100), in both two and three dimensions. In two dimensions we find that modest shear rates align the system and stabilise an almost regular lamellar phase, but high shear rates induce the nucleation and proliferation of defects, which in steady state is balanced by the annihilation of defects of opposite sign. The shear rateγ c at onset of this second regime is controlled by thermodynamic and kinetic parameters; we offer a scaling analysis that relatesγ c to a critical "capillary number" involving those variables. Within the defect proliferation regime, the defects may be partially annealed by slowly decreasing the applied shear rate; this causes marked memory effects, and history-dependent rheology. Simulations in three dimensions show instead shear-induced ordering even at the highest shear rates studied here. This suggests thatγ c shifts markedly upward on increasing dimensionality. This may in part reflect the reduced constraints on defect motion, allowing them to find and annihilate each other more easily. Residual edge defects in the 3D aligned state mostly point along the flow velocity, an orientation impossible in two dimensions.

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Equilibrium onions?

Cited by 26 publications

References 35 publications

Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

Dynamics of Structural Transformations between Lamellar and Inverse Bicontinuous Cubic Lyotropic Phases

Slow dynamics in glassy soft matter

Rheology of lamellar liquid crystals in two and three dimensions: a simulation study

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