Abstract:Colloidal particles adsorbed at fluid-fluid interfaces interact via mechanisms that can be specific to the presence of interfaces, for instance, lateral capillary interactions induced by nonspherical particles. Capillary interactions are highly relevant for self-assembly and the formation of surface microstructures, however, these are very challenging to model due to the multibody nature of capillary interactions. This work pursues a direct comparison between our computational modelling approach and experiment… Show more
“…Hence, the clustering of CS-165 is a result of the capillary interactions appearing for anisotropic particles. The main difference between the simulation of Luo et al 40 and the experiment in this study is that the clusters in simulations were not compressed with external barriers within one direction and, as a result, no prominent orientation of these clusters was observed.…”
Section: Analysis Of the Experimentally Obtained Monolayercontrasting
confidence: 60%
“…In addition, the phase behavior of anisotropic particles is influenced by their aspect ratio, size, wetting angle and contact line. [38][39][40] For example, the shape of the compression isotherms differentiates when ellipsoids with different aspect ratios are compared. 38 Similar to the spherical case an even more complex behavior for compression isotherms can be envisioned when a microgel shell is added to an anisotropic core.…”
Anisotropic, submicrometer sized particles are versatile systems providing interesting features in creating ordering in 2-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report a rich 2D phase behavior and show how softness affects the ordering of anisotropic particles at fluid oil-water interfaces. Three different core-shell systems were synthesized such that they have the same elliptical hematitesilica core but differ with respect to thickness and stiffness of the soft microgel shell.Compression isotherms, the shape of individual core-shell microgel as well as their 2D order at a decane-water interface are investigated by means of the Langmuir-Blodgett technique combined with ex-situ Atomic Force Microscopy (AFM) imaging, as well as by Disspiative Particle Dynamics (DPD) simulations. We show how softness, size and anisotropy of the microgel shell affect the side-to-side-vs. tip-to-tip ordering of
“…Hence, the clustering of CS-165 is a result of the capillary interactions appearing for anisotropic particles. The main difference between the simulation of Luo et al 40 and the experiment in this study is that the clusters in simulations were not compressed with external barriers within one direction and, as a result, no prominent orientation of these clusters was observed.…”
Section: Analysis Of the Experimentally Obtained Monolayercontrasting
confidence: 60%
“…In addition, the phase behavior of anisotropic particles is influenced by their aspect ratio, size, wetting angle and contact line. [38][39][40] For example, the shape of the compression isotherms differentiates when ellipsoids with different aspect ratios are compared. 38 Similar to the spherical case an even more complex behavior for compression isotherms can be envisioned when a microgel shell is added to an anisotropic core.…”
Anisotropic, submicrometer sized particles are versatile systems providing interesting features in creating ordering in 2-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report a rich 2D phase behavior and show how softness affects the ordering of anisotropic particles at fluid oil-water interfaces. Three different core-shell systems were synthesized such that they have the same elliptical hematitesilica core but differ with respect to thickness and stiffness of the soft microgel shell.Compression isotherms, the shape of individual core-shell microgel as well as their 2D order at a decane-water interface are investigated by means of the Langmuir-Blodgett technique combined with ex-situ Atomic Force Microscopy (AFM) imaging, as well as by Disspiative Particle Dynamics (DPD) simulations. We show how softness, size and anisotropy of the microgel shell affect the side-to-side-vs. tip-to-tip ordering of
“…Similar simulations for large numbers of native globular protein molecules are not yet available because of computational limitations 32 . Recent simulations on interfaces stabilized by ellipsoidal colloidal particles, interacting through capillary interactions 33 , do however show similar types of heterogeneous structures, varying from randomly aggregated clusters at low surface coverage, to strand-like structures at high surface coverage.Figure 4Structures formed by block copolymers at the liquid-vapor interface: ( a ) linear strands (effective dimension d e =1), ( b ) in-plane clusters (1≤ d e ≤2), ( c ) 3d clusters (2≤ d e ≤3), and ( d ) 3d films ( d e =3). The top row shows the side view and the bottom row shows the top view of the interfacial film.…”
Complex interfaces stabilized by proteins, polymers or nanoparticles, have a much richer dynamics than those stabilized by simple surfactants. By subjecting fluid-fluid interfaces to step extension-compression deformations, we show that in general these complex interfaces have dynamic heterogeneity in their relaxation response that is well described by a Kohlrausch-Williams-Watts function, with stretch exponent β between 0.4–0.6 for extension, and 0.6–1.0 for compression. The difference in β between expansion and compression points to an asymmetry in the dynamics. Using atomic force microscopy and simulations we prove that the dynamic heterogeneity is intimately related to interfacial structural heterogeneity and show that the dominant mode for stretched exponential relaxation is momentum transfer between bulk and interface, a mechanism which has so far largely been ignored in experimental surface rheology. We describe how its rate constant can be determined using molecular dynamics simulations. These interfaces clearly behave like disordered viscoelastic solids and need to be described substantially different from the 2d homogeneous viscoelastic fluids typically formed by simple surfactants.
“…In case of nanopore-confined colloids, these deviations are especially significant when the size of the suspended particles or macromolecules is comparable to the size of the hosting nanopore. Experimental [1][2][3][4][5] , theoretical [6][7][8][9][10][11] and simulation [12][13][14][15][16][17][18][19][20][21] studies on confined colloidal suspensions have shown the existence of a rich realm of nanostructures that are not observed in the bulk. Additionally, depending on the adhesive interactions established between the fluid and the pore walls and their relevance with respect to the cohesive interactions between fluid particles, several new phenomena, such as wetting, capillary condensation and evaporation, layering, anchoring, are detected [22][23][24][25][26][27] .…”
Understanding how colloidal suspensions behave in confined environments has a striking relevance in practical applications. Despite the fact that the behaviour of colloids in the bulk is key to identify the main elements affecting their equilibrium and dynamics, it is only by studying their response under confinement that one can ponder the use of colloids in formulation technology. In particular, confining fluids of anisotropic particles in nanopores provides the opportunity to control their phase behaviour and stabilise a spectrum of morphologies that cannot form in the bulk. By properly selecting pore geometry, particle architecture and system packing, it is possible to tune thermodynamic, structural and dynamical properties for ad hoc applications. In the present contribution, we report Grand Canonical and Dynamic Monte Carlo simulations of suspensions of colloidal cubes and cuboids constrained into cylindrical nanopores of different size. We first study their phase behaviour, calculate the chemical potential vs density equation of state and characterise the effect of the pore walls on particle anchoring and layering. In particular, at large enough concentrations, we observe the formation of concentric nematic-like coronas of oblate or prolate particles surrounding an isotropic core, whose features resemble those typically detected in the bulk. We then analyse the main characteristics of their dynamics and discover that these are dramatically determined by the ability of particles to diffuse in the longitudinal and radial direction of the nanopore.
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