Tunable colloids: control of colloidal phase transitions with tunable interactions

Yethiraj, Anand

doi:10.1039/b704251p

Cited by 203 publications

(185 citation statements)

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“…Because the phase behaviour of colloidal monolayers on surfaces is similar to that of atomic systems 27 , we expect that structures comparable to those in Fig. 3 deposited on the 5-fold surface of icosahedral AlPdMn quasicrystals reveal that above a few monolayers the copper atoms are arranged in rows spaced in a Fibonacci sequence 10,28 .…”

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“…Particles at distance r interact through a repulsive screened electrostatic-pair potential u(r)! 1 r exp ({kr) whose range depends on the Debye screening length k 21 given by the ion concentration of the suspension 23 . Particle positions are observed in real space with digital video microscopy, which allows us to determine their positions relative to the substrate potential with a precision of about 50 nm (Fig.…”

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Archimedean-like tiling on decagonal quasicrystalline surfaces

Mikhael

Roth

Helden

et al. 2008

Nature

205

195

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Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases 1 . Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional 2 , catalytical 3 or optical properties 4,5 . Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals 6,7 . Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling 8,9 consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al 70 Pd 21 Mn 9 surfaces 10 . In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.Quasicrystals are unusual materials: they are aperiodic but retain true long-range order 11 . Although quasicrystalline structures have been theoretically also predicted in systems with a single type of particle 12,13 , experimentally their spontaneous formation has been observed only in binary, ternary or even more complex alloys 14 . Accordingly, their surfaces exhibit a high degree of structural and chemical complexity and show unexpected mechanical, electrical and optical properties 15 . To understand the origin of those characteristics it is useful to disentangle structural and chemical aspects; this can be achieved by growing single-element monolayers to quasicrystalline surfaces 16,17 . Apart from adding to our understanding of how quasicrystalline properties can be transferred to such monolayers 18 , this approach might permit the fabrication of materials with previously unobserved properties. Heteroepictatic growth experiments on decagonal and icosahedral surfaces did indeed show the formation of Bi and Sb monolayers with a high degree of quasicrystalline order as determined by low-energy electron diffraction and elastic heliumatom scattering experiments 6,18 . In comparison with reciprocal space studies, it was only recently that scanning tunnelling microscopy permitted an atomic resolution of the adsorbate morphology 7 . Even then, however, it was difficult to relate the structure of the adsorbate to that of the underlying substrate.Here we report an experi...

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confidence: 99%

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confidence: 99%

Archimedean-like tiling on decagonal quasicrystalline surfaces

Mikhael

Roth

Helden

et al. 2008

Nature

205

195

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“…Due to their size, colloidal particles are observable directly in real space. Moreover, interactions are widely tunable, ranging from hard spheres to long-range repulsive, short-range attractive, and dipolar [3,4]. Consequently, colloidal particles can be assembled into a multitude of different structures: from clusters [5][6][7] and stable molecules [8,9] composed of a few particles to extended bulk structures like ionic binary crystals [10].…”

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Self-Assembly of Colloidal Molecules due to Self-Generated Flow

2017

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The emergence of structure through aggregation is a fascinating topic and of both fundamental and practical interest. Here we demonstrate that self-generated solvent flow can be used to generate longrange attractions on the colloidal scale, with sub-pico Newton forces extending into the millimeterrange. We observe a rich dynamic behavior with the formation and fusion of small clusters resembling molecules, the dynamics of which is governed by an effective conservative energy that decays as 1/r. Breaking the flow symmetry, these clusters can be made active.Colloidal particles acting as "big" artificial atoms have been instrumental in studying microscopic processes in condensed matter, from the kinetics of crystallization [1] to the vapor-liquid interface [2]. Due to their size, colloidal particles are observable directly in real space. Moreover, interactions are widely tunable, ranging from hard spheres to long-range repulsive, short-range attractive, and dipolar [3,4]. Consequently, colloidal particles can be assembled into a multitude of different structures: from clusters [5][6][7] and stable molecules [8,9] composed of a few particles to extended bulk structures like ionic binary crystals [10]. In addition, self-assembly into useful superstructures can be controlled by factors such as confinement [11] and particle shape [12], which make colloids a versatile and fascinating form of matter [13].What is still missing are truly long-range attractions of like-charged (or uncharged) identical colloidal particles. There is much interest in the basic statistical physics of systems with such interactions, which play a role in gravitational collapse, two-dimensional elasticity, chemotactic collapse, quantum fluids, and atomic clusters [14]. One proposed realization are colloidal particles trapped at an interface [15] that experience screened, long-range attractions due to capillary fluctuations of the interface [16]. The attractive interactions then correspond to Newtonian gravity in two dimensions. Complex patterns are also known to arise for bacteria due to longrange chemotactic interactions [17]. Critical long-range Casimir forces have been reported for colloidal particles in a binary solvent [18], which are tunable by temperature and surface chemistry. Finally, a recent theoretical proposal are catalytically active colloidal particles that interact through producing or consuming chemicals [19,20]. For simple diffusion the concentration profile of a chemical decays as inverse distance, implying long-range interactions that can be tuned through activity (how chemicals are produced or consumed) and mobility (how particles react to gradients).Here, we implement long-range attractions through hydrodynamic flows coupling suspended particles [21,22]. We report on experiments using spherical ion exchange resin particles sedimented to the negatively charged substrate. The particles have diameters of 15 µm, for which Brownian diffusion is practically negligible on the experimental time scale. They interact due to self-genera...

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“…Brownian colloidal suspensions with tunable interactions are important model systems for understanding phase transitions in atomic systems [1][2][3][4]. Real-space microscopy and light scattering experiments have been carried out on crystal nucleation dynamics [5,6] as well as structure and dynamics at the colloidal glass transition [7][8][9].…”

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Low-Density Ordered Phase in Brownian Dipolar Colloidal Suspensions

Agarwal

Yethiraj

2009

Phys. Rev. Lett.

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We study the low volume fraction and electric field phase behavior of a Brownian colloidal suspension. On the application of a uniform ac field, we find a novel phase where chains of particles aggregate to form a well defined cellular network, consisting of particle-free ''voids'' surrounded by a percolating network of particle-rich walls. This cellular structure is stable to very long times, indicative of an equilibrium thermodynamic phase. The cell-cell spacing is not sensitive to the concentration of the sample but scales with sample thickness. Any self-consistent mechanism for the existence of this void phase must consist of long-ranged repulsions and shorter-ranged attractions. DOI: 10.1103/PhysRevLett.102.198301 PACS numbers: 47.57.JÀ, 64.70.pv Brownian colloidal suspensions with tunable interactions are important model systems for understanding phase transitions in atomic systems [1][2][3][4]. Real-space microscopy and light scattering experiments have been carried out on crystal nucleation dynamics [5,6] as well as structure and dynamics at the colloidal glass transition [7][8][9]. In the presence of an external electric field, Brownian colloidal spheres experience an anisotropic dipolar interaction and form chains (the ''string fluid'') and multichain aggregates [10,11], as well as body centered tetragonal (BCT) crystals [12][13][14]. Multiple competing interactions lead to richer phase behavior. In colloid-polymer mixtures both network-forming gel phases and glassy behavior can be observed by control of competing attractive and repulsive interactions [15,16]. Anisotropic interactions between colloids [17] in a liquid crystal medium also lead to a network of particle aggregates [18]. In dipolar colloids with added electrostatic repulsions, numerous crystalline phases are observed [19,20]. The dipolar interaction is of great interest because it consists of both competing on-axis (along the electric field) attractions and in-plane repulsions, and because it is an important driving force for nanoparticle selforganization [21].Simulations of spheres with both dipolar and van der Waals interactions have shown many variants (linear aggregates, droplets, columns) of phase separation into regions of higher and lower densities [22,23]. However, structure formation in the low-density regime of Brownian colloidal suspensions in an electric field has not attracted much experimental attention. Recently, interesting field induced cellular structures were reported in a granular medium [24], but the mechanism (and whether they represented equilibrium structures) was not clear.In this Letter, we report real-space confocal microscopy studies of the effect of an ac external electric field on the low-density structure of Brownian colloidal suspensions. We report the existence of a novel ''gel-like'' phase at low volume fractions ( < 4:0%) where chains of particles aggregate in time to form a cellular structure composed of ''voids''-particle-free domains enclosed completely by particle-rich walls. We propose that the co...

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Tunable colloids: control of colloidal phase transitions with tunable interactions

Cited by 203 publications

References 204 publications

Archimedean-like tiling on decagonal quasicrystalline surfaces

Archimedean-like tiling on decagonal quasicrystalline surfaces

Self-Assembly of Colloidal Molecules due to Self-Generated Flow

Low-Density Ordered Phase in Brownian Dipolar Colloidal Suspensions

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