Micelles, vesicles and microemulsions

Mitchell, D. J.; Ninham, Barry W.

doi:10.1039/f29817700601

Cited by 828 publications

(499 citation statements)

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“…Taken over to light and neutron scattering experiments the preconception embodied in such cartoons is fraught and limiting. Some of the defects of the theory discussed above were removed in a later paper [11,12].…”

Section: First Ideasmentioning

confidence: 99%

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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: First Ideasmentioning

confidence: 99%

“…(However, even a proper description of micellisation of non ionic micelles is extremely complicated [11,12]. )…”

Section: First Ideasmentioning

confidence: 99%

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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“…5 Because of its two branched hydrocarbon chains (see Figure 1), this molecule possesses a high ratio of hydrophobic tail volume to headgroup surface area, which is predicted by basic thermodynamic models to be a key factor in reverse micelle formation. 40 AOT is attractive as a model surfactant because it does not require cosurfactants to form reverse micelles. Aqueous AOT reverse micelles can be characterized over a wide range of water and surfactant concentrations by a single parameter, which is proportional to the micellar radius.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles

2000

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Aqueous reverse micelles, which are surfactant aggregates in nonpolar solvents that enclose packets of aqueous solution, have been widely studied experimentally and theoretically, but much remains unknown about the properties of water in the interior. The few previous molecular dynamics simulations of reverse micelles have not examined how the micelle size affects these properties. We have modeled the interior of an aqueous reverse micelle as a rigid spherical cavity, treating only the surfactant headgroups and water at a molecular level. Interactions between the interior molecules and the cavity are represented by a simple continuum potential. The basic parameters of the modelsmicelle size, surface ion density, and water contentsare based on experimental measurements of Aerosol OT reverse micelles but could be chosen to match other surfactant systems as well. The surfactant head is modeled as a pair of atomic ions: a large headgroup ion fixed at the cavity surface and a mobile counterion. The SPC/E model is used for water. The simulations indicate that water near the cavity interface is immobilized by the high ion concentration. Three structural regions of water can be identified: water trapped in the ionic layer, water bound to the ionic layer, and water in the bulklike core. The basic properties of bulk water reemerge within a few molecular layers. Both the structure and dynamics of water near the interface vary with micelle size because of the changing surface ion density. The mobility of water in the interfacial layers is greatly restricted for both translational and rotational motions, in agreement with a wide range of experiments.

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“…In a nutshell, one reduces the self-assembly process to a geometric packing problem of identical particles. The particle shape is largely quantified by the surfactant packing parameter, s 0 ¼ v m / (a m l m ), where a m is the effective head-group area, v m is the volume and l m is the length of the (fluctuating) lipid tail, [51][52][53][54][55] with an implicit assumption that particles are monodisperse in volume (or size). The actual chemical parameters, such as salt concentration, temperature, etc.…”

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confidence: 99%

Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains

et al. 2013

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Inverse bicontinuous cubic phases with two aqueous network domains separated by a smooth bilayer are firmly established as equilibrium phases in lipid/water systems. The purpose of this article is to highlight the generalisations of these bicontinuous geometries to polycontinuous geometries, which could be realised as lipid mesophases with three or more network-like aqueous domains separated by a branched bilayer. An analysis of structural homogeneity in terms of bilayer width variations reveals that ordered polycontinuous geometries are likely candidates for lipid mesophase structures, with similar chain packing characteristics to the inverse micellar phases (that once were believed not to exist due to high packing frustration). The average molecular shape required by global geometry to form these multi-network phases is quantified by the surfactant shape parameter, v/(al); we find that it adopts values close to those of the known lipid phases. We specifically analyse the 3etc(187 193) structure of hexagonal symmetry P6 3 /mcm with three aqueous domains, the 3dia(24 220) structure of cubic symmetry I 43d composed of three distorted diamond networks, the cubic chiral 4srs(24 208) with cubic symmetry P4 2 32 and the achiral 4srs(5 133) structure of symmetry P4 2 /nbc, each consisting of four intergrown undistorted copies of the srs net (the same net as in the Q G II gyroid phase). Structural homogeneity is analysed by a medial surface approach assuming that the headgroup interfaces are constant mean curvature surfaces. To facilitate future experimental identification, we provide simulated SAXS scattering patterns that, for the 4srs(24 208) and 3dia(24 220) structures, bear remarkable similarity to those of bicontinuous Q G II -gyroid and Q D II -diamond phases, with comparable lattice parameters and only a single peak that cannot be indexed to the wellestablished structures. While polycontinuous lipid phases have, to date, not been reported, the likelihood of their formation is further indicated by the reported observation of a solid tricontinuous mesoporous silicate structure, termed IBN-9, which formed in the presence of surfactants [Han et al

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Micelles, vesicles and microemulsions

Cited by 828 publications

References 1 publication

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

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles

Polycontinuous geometries for inverse lipid phases with more than two aqueous network domains

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