Ternary microemulsions as model disordered media

Knackstedt, Mark; Ninham, Barry W.

doi:10.1002/aic.690410524

Cited by 7 publications

(5 citation statements)

References 39 publications

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“…[85]. The important observation is knowing that head group area is fixed then the entire microstructure can be predicted by simple global packing constraints, in agreement with NMR, conductivity and neutron scattering [86][87][88][89][90].…”

Section: Phase Diagrams In Ternary Microemulsionsmentioning

confidence: 83%

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited

Ninham

Larsson

Nostro

2017

Colloids and Surfaces B: Biointerfaces

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a b s t r a c tHofmeister, specific ion effects, hydration and van der Waals forces at and between interfaces are factors that determine curvature and microstructure in self assembled aggregates of surfactants and lipids; and in microemulsions. Lipid and surfactant head group interactions and between aggregates vary enormously and are highly specific. They act on the hydrophilic side of a bilayer, micelle or other self assembled aggregate. It is only over the last three decades that the origin of Hofmeister effects has become generally understood. Knowledge of their systematics now provides much flexibility in designing nanostructured fluids.The other side of the coin involves equally specific forces. These (opposing) forces work on the hydrophobic side of amphiphilic interfaces. They are due to the interaction of hydrocarbons and other "oils" with hydrophobic tails of surfactants and lipids. The specificity of oleophilic solutes in microemulsions and lipid membranes provides a counterpoint to Hofmeister effects and hydration. Together with global packing constraints these effects determine microstructure.Another factor that has hardly been recognised is the role of dissolved gas. This introduces further, qualitative changes in forces that prescribe microstructure.The systematics of these effects and their interplay are elucidated. Awareness of these competing factors facilitates formulation of self assembled nanostructured fluids. New and predictable geometries that emerge naturally provide insights into a variety of biological phenomena like anaesthetic and pheromone action and transmission of the nervous impulse (see Part 2).

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Section: Phase Diagrams In Ternary Microemulsionsmentioning

confidence: 83%

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited

Ninham

Larsson

Nostro

2017

Colloids and Surfaces B: Biointerfaces

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“…Recently we showed that a class of ternary microemulsions provides such a system [13,14]. By tuning experimental variables one can realize a disordered "porous" medium with specific prescribed microstructures.…”

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confidence: 99%

Diffusion in Model Disordered Media

1995

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We perform water self-diffusion measurements in ternary DDAB microemulsions near the structural transition point. This allows experimental investigation of the predicted anomalous diffusion behavior exhibited near a static percolation transition.Near the transition point time-dependent behavior is observed. The scaling behavior is consistent with theory for a static percolative medium. This is the first time anomalous diffusion has been experimentally measured in a well-characterized porous media.PACS numbers: 66.10.Cb, 05.70.Jk, 47.55.Mh, 64.60.Ak The prediction of effective transport properties of heterogeneous systems such as porous media is of considerable interest. In many cases, classical theories of transport, valid for homogeneous systems, do not apply if the heterogeneities are strong and broad enough. For example, transport and, in particular, diffusion in heterogeneous materials can be anomalous in the sense that classical laws of transport, such as Fick's law of diffusion with a constant diffusivity, are not valid, and instead one has a time-dependent transport coefficient. Much of our understanding of heterogeneous porous media and transport therein has been obtained by using percolation theory [1 -4]. Of particular interest is the behavior of transport properties near a percolation threshold p, . As p, is approached the correlation length s "diverges. The length scale s~m easures the macroscopic homogeneity of the system. For any length scale L ) se~the system is macroscopically homogeneous, and the classical equations of transport with constant transport coefficients are applicable. For length scales L~$~the system is heterogeneous, and the classical equations fail. For the classical Fick law of diffusion the mean square displacement of particles x2(t) is related to the effective (constant) diffusivity D, and time t as x (t) = D, t, where D, is a constant. For a heterogeneous system near its percolation threshold the diffusion law becomes anomalous [5 -7] and theory suggestsx'(t) = t', where 6 ( 1. Thus the diffusivity D, = x (t)/t is time dependent and vanishes as t~~. Two examples are a porous catalyst particle near its deactivation point (the point at which macroscopic diffusion in the pore space of the catalyst is no longer possible due to the plugging of the pores) and a porous medium that contains two immiscible phases, where one of the phases is disconnected. The slowing down of transport is associated with particles diffusing within dangling ends of percolation clusters.While a large body of theoretical work and simulations have predicted anomalous diffusion in percolative media [5,8 -12], no experimental system with a wellcharacterized microstructure has been available to test the prediction. Recently we showed that a class of ternary microemulsions provides such a system [13,14]. By tuning experimental variables one can realize a disordered "porous" medium with specific prescribed microstructures. This allows independent measurements of mechanical and transport properties.As volume fra...

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“…Cubic phases of zero average curvature can pack at surfactant parameters around and above 0.8, and cylinders with junctions probably correspond to the onset of connected random disordered phases. These are ubiquitous in cationic microemulsions where curvature is a delicate balance of oil penetration into surfactant tails. ,, …”

Section: Resultsmentioning

confidence: 99%

“…These are ubiquitous in cationic microemulsions where curvature is a delicate balance of oil penetration into surfactant tails. 29,49,50 Finally, there are two further mechanisms that promote the formation of branchpoints: (i) this process requires a partial dehydration of the polar headgroups and some hydrating water molecules are pushed back into the bulk aqueous phase (with an increment in entropy), and (ii) when the concentration of branches increases, the semispherical endcaps can fuse together to form a continuous cylindrical bridge that connects different rods. In the present system, the formation of connections is strongly suggested by the following experimental observations:…”

Section: Resultsmentioning

confidence: 99%

Interconnected Networks: Structural and Dynamic Characterization of Aqueous Dispersions of Dioctanoylphosphatidylcholine

et al. 2008

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Aqueous dispersions of the phospholipid dioctanoylphosphatidylcholine (diC 8PC) phase-separate below a cloud-point temperature, depending on lipid concentration. The lower phase is viscous and rich in lipid. The structure and dynamics of this system were explored via cryo-transmission electron microscopy (cryo-TEM), small-angle X-ray scattering (SAXS), and NMR. The lower phase comprises a highly interconnected tridimensional network of wormlike micelles. A molecular mechanism for the phase separation is suggested.

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Ternary microemulsions as model disordered media

Cited by 7 publications

References 39 publications

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited

Diffusion in Model Disordered Media

Interconnected Networks: Structural and Dynamic Characterization of Aqueous Dispersions of Dioctanoylphosphatidylcholine

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