Layering transitions in confined colloidal crystals: The hcp-like phase

Ramiro‐Manzano, Fernando; Bonet, E.; Rodríguez, Isabelle; Meseguer, F.

doi:10.1103/physreve.76.050401

Cited by 24 publications

(42 citation statements)

References 15 publications

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“…Full details of the crystal structures are provided in the Supplemental material [26]. We did not observe a buckling phase, nor the prismatic, hcp-like, hcp(100), and hcp⊥ phases observed for hard spheres [3,[5][6][7]17]. Their absence is most likely due to the increased softness of the interaction, which causes a weaker confinement and a different role of packing entropy in the phase behavior, which is also apparent from the bulk bcc phase being different from close packed structures observed for bulk hard spheres.…”

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confidence: 79%

“…More detailed investigations since then disclosed that many intermediate phases exist, such as a buckling phase in between 1△ → 2□, a rhombic phase in between n□ → n△, and prismatic, hexagonal close packing (hcp)-like, hcp(100), hcp⊥, and pre-square phases in between n△ → ðn þ 1Þ□ [3,[5][6][7]. All these structures have been verified by computer simulations [8][9][10][11][12][13], and the consistency between experiments and simulations gives us confidence in our understanding of the nature of the transitions for hard spheres.…”

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confidence: 99%

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Confinement Induced Plastic Crystal-to-Crystal Transitions in Rodlike Particles with Long-Ranged Repulsion

et al. 2015

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Colloidal particles in geometrical confinement display a complex variety of packing structures different from their three-dimensional (3D) bulk counterpart. Here, we confined charged rodlike colloids with longranged repulsions to a thin wedge-shaped cell and show, by quantitative 3D confocal microscopy, that not only their positional but also their orientational order depends sensitively upon the slit width. Synchronized with transitions in lattice symmetry and number of layers confinement induces plastic crystal-to-crystal transitions. A model analysis suggests that this complex sequence of more or less rotationally ordered states originates from the subtle competition between the electrostatic repulsion of a rod with the wall and with its neighbors. DOI: 10.1103/PhysRevLett.115.078301 PACS numbers: 82.70.Dd, 64.75.Yz When a colloidal suspension is confined to a quasi-twodimensional geometry, many fascinating crystal structures appear due to the partial restriction of translational degrees of freedom in the third dimension [1][2][3]. In the case of particles interacting with a hard potential the structure greatly depends on their packing efficiency in the confined geometry. One of the first studies in this limit was performed by Pieranski et al., who used nearly hard spherical colloids confined in a wedge-shaped cell. At increasing slit width they found a sequence of transitions that can be represented as:where n denotes the number of crystal layers and △ and □ denote layers with hexagonal and square symmetry, respectively [4]. More detailed investigations since then disclosed that many intermediate phases exist, such as a buckling phase in between 1△ → 2□, a rhombic phase in between n□ → n△, and prismatic, hexagonal close packing (hcp)-like, hcp(100), hcp⊥, and pre-square phases in between n△ → ðn þ 1Þ□ [3,[5][6][7]. All these structures have been verified by computer simulations [8][9][10][11][12][13], and the consistency between experiments and simulations gives us confidence in our understanding of the nature of the transitions for hard spheres.Fewer intermediate phases are found for charged spheres, which interact via long-ranged electrostatic interactions, both with each other and with the walls [14][15][16][17]. Using colloids with κa ¼ 0.79 and 0.37 (where κ is the inverse Debye screening length characterizing the range of the repulsive interactions, and a is the particle radius) we found a phase sequence very similar to Ref. [16]: 1△ → 2□ → 2R → 2△ → 3□ → 3R → 3△ → 4□ → 4R → 4△ (R denotes a rhombic phase) [17]. These observations imply that long-ranged electrostatic interactions play an important additional role in the packing of charged particles.The packing behavior of shape anisotropic particles has also begun to be explored. For nearly hard dimer-shaped particles so-called "side" and "out-of-plane" structures were reported [18,19]. This leads to questions about the effect of confinement on particle orientational order in a system where this effect can be separated from packingdominated changes ...

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Confinement Induced Plastic Crystal-to-Crystal Transitions in Rodlike Particles with Long-Ranged Repulsion

et al. 2015

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“…Colloids are useful thermodynamic model systems for melting studies in films; the trajectories of all particles in the field of view are measurable by video microscopy with single-particle resolution, and the interparticle interactions are simple and well understood. Thus far, phase diagrams for hard spheres between two walls in the relatively thin-film limit (<6 layers) have been determined by simulation [8,9], and experiments have identified predicted static crystalline structures [10][11][12]. Their melting transitions, however, have not been measured because it is difficult to drive the melting transition in situ using conventional colloids.…”

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Melting of Colloidal Crystal Films

et al. 2010

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“…Other techniques used to probe the structure of micron-sized colloids in thin geometries include electron microscopy 17,18 , x-ray microscopy 19 , and laser-diffraction microscopy 20 . The combination of confocal microscopy and image analysis algorithms offers two key advantages for studies of confined colloidal suspensions.…”

Section: Discussionmentioning

confidence: 99%

“…A common feature of these applications is that the particles must be flowed through fine geometries, such as nozzles, print heads, microchannels, or porous media, and/or be shaped into thin films or rods. Techniques used to probe the structure of micron-sized colloids in confined geometries, including electron microscopy 17,18 , x-ray microscopy 19 , and laser-diffraction microscopy 20 , can be used to measure the structure and dynamics of particles on the microscale. These techniques, however, do not allow access to the trajectories of individual particles, from which structural and dynamic metrics can be computed for direct comparison to numerical simulations 21,22 .…”

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Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

Pandey

Spannuth

Conrad

2014

JoVE

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The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly [1][2][3] , drug delivery 4 , improved hydrocarbon recovery [5][6][7] , and flowable electrodes for energy storage 8 . Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained 9 . Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems 10 . Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions [11][12][13][14][15][16]37 . In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density-and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow. Video LinkThe video component of this article can be found at

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Layering transitions in confined colloidal crystals: The hcp-like phase

Cited by 24 publications

References 15 publications

Confinement Induced Plastic Crystal-to-Crystal Transitions in Rodlike Particles with Long-Ranged Repulsion

Confinement Induced Plastic Crystal-to-Crystal Transitions in Rodlike Particles with Long-Ranged Repulsion

Melting of Colloidal Crystal Films

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

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