Equilibrium orientations of non-spherical and chemically anisotropic particles at liquid–liquid interfaces and the effect on emulsion stability

Ballard, Nicholas; Bon, Stefan Antonius Franciscus

doi:10.1016/j.jcis.2015.02.069

Cited by 45 publications

(30 citation statements)

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“…In this approximation, which is geometrically far from trivial for nonspherical particles, the (free) energy of the particle configuration follows from the particle surface areas below and above the interface plane and from the intersection area of the particle with the interface plane. Numerical techniques employed for these calculations are, e.g., the triangular tessellation technique (TTT) [35][36][37][38][39], and a hit and miss Monte Carlo method [40,41]. However, in this Letter, we will show that neglecting the capillarity can lead to significant overestimates of the energy, and even to erroneous equilibrium configurations of the particle.…”

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confidence: 88%

Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions

2016

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Particles adsorbed at a fluid-fluid interface induce capillary deformations that determine their orientations and generate mutual capillary interactions which drive them to assemble into 2D ordered structures. We numerically calculate, by energy minimization, the capillary deformations induced by adsorbed cubes for various Young's contact angles. First, we show that capillarity is crucial not only for quantitative, but also for qualitative predictions of equilibrium configurations of a single cube. For a Young's contact angle close to 90°, we show that a single-adsorbed cube generates a hexapolar interface deformation with three rises and three depressions. Thanks to the threefold symmetry of this hexapole, strongly directional capillary interactions drive the cubes to self-assemble into hexagonal or graphenelike honeycomb lattices. By a simple free-energy model, we predict a density-temperature phase diagram in which both the honeycomb and hexagonal lattice phases are present as stable states. DOI: 10.1103/PhysRevLett.116.258001 Over a century ago, it had already been observed that submm sized particles strongly adsorb at fluid-fluid interfaces [1,2]. Indeed, a fluid-fluid interface of area A and surface tension γ has a free energy cost γA, and particles can reduce A by adsorbing at the interface. The bonding potential is usually strong enough to allow stable monolayers of particles. Since a pioneering study by Pieranski [3], a lot of interest has been devoted to these quasi-2D systems, which have many applications, e.g., emulsions [4][5][6][7][8][9], coatings [10,11], optics [12], and new material development [13]. Because of the contact angle constraint imposed by Young's Law, an adsorbed particle in general induces deformations in the shape of the fluid-fluid interface. These so-called capillary deformations are responsible for capillary interactions between the adsorbed particles [14,15], which regulate the particle self-assembly at the interface [16][17][18]. These interactions can be tuned by varying, e.g., the particle shape and chemistry [10,[19][20][21], or the curvature of the fluidfluid interface [22][23][24]. Very recent experiments [25][26][27] have shown that adsorbed nanocubes with truncated corners can assemble into graphenelike honeycomb and hexagonal lattices. The origin of these structures is unknown, although ligand adsorption and van der Waals forces between specific facets of the truncated cubes have been suggested [25]. In this Letter, however, we show that generic cubes with homogeneous surface properties generate hexapolar capillary deformations which are largely responsible for the observed structures. Cubes of other materials or dimensions could, therefore, form similar structures.A primary step for understanding adsorbedparticle systems is the study of an isolated particle at a macroscopically flat fluid-fluid interface. Important issues are the equilibrium configuration of the particle at the interface [28][29][30][31] and the adsorption energy [32-34] which depend on the particl...

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confidence: 88%

Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions

2016

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“…Works that focused on the mechanism of stabilizing Pickering emulsions by non-spherical solid particles have been published, which demonstrated that this stabilizing effect not only relates to steric effect that has been discussed for spherical particles, but also may results from capillary forces on the oil–water interface (Bresme and Oettel, 2007; Madivala et al, 2009). Besides, a computational method was also created to analyze the interfacial activity of non-spherical particles, which at the same time demonstrated that the hydrophilic balance commonly used to estimate the effect of surfactants might have less effect in solid particle-stabilizing colloidal systems (Ballard and Bon, 2015). …”

Section: Morphologymentioning

confidence: 99%

An Overview of Pickering Emulsions: Solid-Particle Materials, Classification, Morphology, and Applications

et al. 2017

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Pickering emulsion, a kind of emulsion stabilized only by solid particles locating at oil–water interface, has been discovered a century ago, while being extensively studied in recent decades. Substituting solid particles for traditional surfactants, Pickering emulsions are more stable against coalescence and can obtain many useful properties. Besides, they are more biocompatible when solid particles employed are relatively safe in vivo. Pickering emulsions can be applied in a wide range of fields, such as biomedicine, food, fine chemical synthesis, cosmetics, and so on, by properly tuning types and properties of solid emulsifiers. In this article, we give an overview of Pickering emulsions, focusing on some kinds of solid particles commonly serving as emulsifiers, three main types of products from Pickering emulsions, morphology of solid particles and as-prepared materials, as well as applications in different fields.

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“…For example, numerical methods applying this approximation are used in Refs. [26,[110][111][112][113][114][115][116]. However, neglecting capillary deformations can lead to…”

Section: Appendix B: Nc Interface-adsorption Energy Calculationsmentioning

confidence: 99%

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Soligno

Vanmaekelbergh

2019

Phys. Rev. X

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Using a coarse-grained molecular dynamics model, we simulate the self-assembly of PbSe nanocrystals (NCs) adsorbed at a flat fluid-fluid interface. The model includes all key forces involved: NC-NC shortrange facet-specific attractive and repulsive interactions, entropic effects, and forces due to the NC adsorption at fluid-fluid interfaces. Realistic values are used for the input parameters regulating the various forces. The interface-adsorption parameters are estimated using a recently introduced sharpinterface numerical method which includes capillary deformation effects. We find that the final structure in which the NCs self-assemble is drastically affected by the input values of the parameters of our coarsegrained model. In particular, by slightly tuning just a few parameters of the model, we can induce NC selfassembly into either silicene-honeycomb superstructures, where all NCs have a f111g facet parallel to the fluid-fluid interface plane, or square superstructures, where all NCs have a f100g facet parallel to the interface plane. Both of these nanostructures have been observed experimentally. However, it is still not clear their formation mechanism, and, in particular, which are the factors directing the NC self-assembly into one or another structure. In this work, we identify and quantify such factors, showing illustrative assembled-phase diagrams obtained from our simulations. In addition, with our model, we can study the self-assembly dynamics, simulating how the NCs' structures evolve from few-NCs aggregates to gradually larger domains. For example, we observe linear chains, where all NCs have a f110g facet parallel to the interface plane as typical precursors of the square superstructure, and zigzag aggregates, where all NCs have a f111g facet parallel to the interface plane as typical precursors of the silicene-honeycomb superstructure. Both of these aggregates have also been observed experimentally. Finally, we show indications that our method can be applied to study defects of the obtained superstructures.

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Equilibrium orientations of non-spherical and chemically anisotropic particles at liquid–liquid interfaces and the effect on emulsion stability

Cited by 45 publications

References 50 publications

Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions

Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions

An Overview of Pickering Emulsions: Solid-Particle Materials, Classification, Morphology, and Applications

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

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