Mechanisms behind the Faceting of Catanionic Vesicles by Polycations:  Chain Crystallization and Segregation

Antunes, Filipe E.; Brito, Rodrigo O.; Marques, Eduardo F.; Lindman, Björn; Miguel, Maria

doi:10.1021/jp063994+

Cited by 36 publications

(48 citation statements)

References 42 publications

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“…The balance is described by the dimensionless Föppl-von Kármán number Γ vK = YR 2 0 =κ (where Y and κ are the 2D Young's modulus and the bending rigidity, respectively). For buckling (13 (12,16,17); similar effects may (18,19) also play a dominant role in forming icosahedral mixed-amphiphiles vesicles (18,(20)(21)(22)(23). However, our emulsions fundamentally differ from those systems by the interfacial alkanes' ability to freely exchange with bulk alkanes, as in a grand-canonical ensemble.…”

Section: Faceting Dictated By Topologymentioning

confidence: 77%

“…Whereas buoyancy-squashing (SI Appendix) is negligible for vesicles (18,20) and virus capsids (13), it sets a low limit on γ for the largest emulsion droplets, precluding conversion into an icosahedron. Importantly, most previous studies of self-assembled icosahedra (13,14,16,19,21,22) addressed submicrometer objects, which cannot be visualized by conventional optical microscopy. Our droplets preserve the icosahedral symmetry for much larger R 0 , thanks to the large lateral size of their interfacially frozen monocrystals, mediating the interdefect repulsion.…”

Section: Faceting Dictated By Topologymentioning

confidence: 99%

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How faceted liquid droplets grow tails

Guttman

Sapir

Schultz

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

224

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Liquid droplets, widely encountered in everyday life, have no flat facets. Here we show that water-dispersed oil droplets can be reversibly temperature-tuned to icosahedral and other faceted shapes, hitherto unreported for liquid droplets. These shape changes are shown to originate in the interplay between interfacial tension and the elasticity of the droplet's 2-nm-thick interfacial monolayer, which crystallizes at some T = T s above the oil's melting point, with the droplet's bulk remaining liquid. Strikingly, at still-lower temperatures, this interfacial freezing (IF) effect also causes droplets to deform, split, and grow tails. Our findings provide deep insights into molecular-scale elasticity and allow formation of emulsions of tunable stability for directed self-assembly of complex-shaped particles and other future technologies.emulsions | membranes' buckling | topological defects | two-dimensional crystals | spontaneous emulsification O f all same-volume shapes, a sphere has the smallest surface area A. Microscopic liquid droplets are, therefore, spherical, because this shape minimizes their interfacial energy γA for a surface tension γ > 0. Spontaneous transitions to a flat-faceted shape, which increases the surface area, have never been reported for droplets of simple liquids. Here we demonstrate that surfactantstabilized droplets of oil in water, of sizes ranging from 1 to 100 μm, known as "emulsions" or "macroemulsions" (1), can be tuned to sharp-edged, faceted, polyhedral shapes, dictated by the molecular-level topology of the closed surface. Furthermore, the physical mechanism which drives the faceting transition allows the sign of γ to be switched in a controllable manner, leading to a spontaneous increase in surface area of the droplets, akin to the spontaneous emulsification (SE) (1, 2), yet driven by a completely different, and reversible, process.At room temperature, the spherical shape of our emulsions' surfactant-stabilized oil droplets indicates shape domination by γ > 0 (oil: 16-carbon alkane, C 16 ; surfactant: trimethyloctadecylammonium bromide, C 18 TAB, see SI Appendix, Fig. S1). However, the observed shape change to an icosahedron at some T = T d , below the interfacial freezing temperature T s (Fig. 1A), demonstrates that γ has become anomalously low and no longer dominates the shape. This γ-decrease upon cooling starkly contrasts with the behavior of most other liquids, where γ increases upon cooling (1). Direct in situ γ-measurements in our emulsions (SI Appendix), as well as pendant drop tensiometry of millimetersized droplets, confirm the positive dγðTÞ=dT here (Fig. 2). Wilhelmy plate method γðTÞ measurements (3, 4) on planar interfaces between bulk alkanes and aqueous C 18 TAB solutions (blue circles in Fig. 2A) also demonstrate the same dγðTÞ=dT > 0 at T < T s . Thus, the anomalous positive dγ=dT below T s is confirmed for the C 16 /C 18 TAB system by three independent methodologies.To elucidate the implications of the positive dγ=dT, we note that thermodynamics equates an inte...

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Section: Faceting Dictated By Topologymentioning

confidence: 77%

Section: Faceting Dictated By Topologymentioning

confidence: 99%

How faceted liquid droplets grow tails

Guttman

Sapir

Schultz

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

224

View full text Add to dashboard Cite

show abstract

“…These parameters have a direct connection with the previous discussion [33]. While the physical meaning of G is related to the density of the active links in the system, the relaxation time indicates the required time for the solid-liquid transition, which is related to the strength of the active links [34].…”

Section: Assessment Of Active Linksmentioning

confidence: 94%

Aggregation and gelation in hydroxypropylmethyl cellulose aqueous solutions

Silva

Pinto

Antunes

et al. 2008

Journal of Colloid and Interface Science

Self Cite

116

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In this work we present an analysis of the thermal behavior of hydroxypropylmethyl cellulose aqueous solutions, from room temperature to higher temperatures, above gelation. We focus on significant aspects, essentially overlooked in previous work, such as the correlation between polymer hydrophobicity and rheological behavior, and the shear effect on thermal gelation. Micropolarity and aggregation of the polymer chains were monitored by both UV/vis and fluorescence spectroscopic techniques, along with polarized light microscopy. Gel formation upon heating was investigated using rheological experiments, with both large strain (rotational) tests at different shear rates and small strain (oscillatory) tests. The present observations allow us to compose a picture of the evolution of the system upon heating: firstly, polymer reptation increases due to thermal motion, which leads to a weaker network. Secondly, above 55 • C, the polymer chains become more hydrophobic and polymer clusters start to form. Finally, the number of physical crosslinks between polymer clusters and the respective lifetimes increase and a three-dimensional network is formed. This network is drastically affected if higher shear rates, at nonNewtonian regimes, are applied to the system.

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“…The experiments were performed far from the melting transition of the surfactants alkyl chains to prevent the network properties to be influenced by the different states [32].…”

Section: Methodsmentioning

confidence: 99%

Gelation of charged bio-nanocompartments induced by associative and non-associative polysaccharides

Antunes

Coppola

Rossi

et al. 2008

Colloids and Surfaces B: Biointerfaces

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a b s t r a c tVesicles composed of sodium oleate (NaO) and monoolein (MO) are adequate candidates for drug nanoencapsulation and controlled release due to their stability and perceived biocompatibility. The object of the present study is to design hydrogels based on those anionic vesicles and polymers of both non-associative and associative type. The selected macromolecules were k-carrageenan (KC), carboxymethyl cellulose (CMC) and hydrophobically modified carboxymethyl cellulose (HMCMC). While the polymer-vesicle association was probed by rheology, the influence of the polymer on the vesicle stability was monitored by cryo-TEM and calorimetric measurements.The effects of the polymer on the rheological properties of surfactant aggregate solutions clearly depend on the polymer type: the storage moduli of the polymer-vesicle mixtures, compared to the vesicles alone, increases around 2 orders of magnitude if the polymer is non-associative and 4 orders of magnitude if the macromolecule is of associative type.As the vesicles are added, the non-associative polymer networks tend to be disrupted, while the networks formed by associative polymer get more robust. These observations can be explained by fundamental changes in electrostatic/hydrophobic interactions: vesicles entrapped in KC networks convert the polysaccharide in a highly charged entity and favor high electrostatic repulsions between the chains; this encourages network collapse. The opposite picture is experienced in HMCMC systems, i.e., such network is stabilized by the presence of vesicles. This is ascribed to the enhanced hydrophobic association, compensating the electrostatic repulsions between vesicles and polymer chains.

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Mechanisms behind the Faceting of Catanionic Vesicles by Polycations: Chain Crystallization and Segregation

Cited by 36 publications

References 42 publications

How faceted liquid droplets grow tails

How faceted liquid droplets grow tails

Aggregation and gelation in hydroxypropylmethyl cellulose aqueous solutions

Gelation of charged bio-nanocompartments induced by associative and non-associative polysaccharides

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