Grain refinement and partitioning of impurities in the grain boundaries of a colloidal polycrystal

Ghofraniha, Neda; Tamborini, Elisa; Oberdisse, Julian; Cipelletti, Luca; Ramos, Laurence

doi:10.1039/c2sm25488c

Cited by 31 publications

(59 citation statements)

References 48 publications

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“…Previous investigation has focused on the effect of impurities that are either much larger [14,15,23] or much smaller [24] than their host colloids on crystallisation in three dimensions. These studies demonstrate that the texture of a colloidal polycrystal can be controlled through suitable choice of impurity size and concentration.…”

Section: Introductionmentioning

confidence: 99%

Structural characterisation of polycrystalline colloidal monolayers in the presence of aspherical impurities

Gray

Mould

Royall

et al. 2015

J. Phys.: Condens. Matter

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Abstract.Impurities in crystalline materials introduce disorder into an otherwise ordered structure due to the formation of lattice defects and grain boundaries. The properties of the resulting polycrystal can differ remarkably from those of the ideal single crystal.Here we investigate a quasi-two-dimensional system of colloidal spheres containing a small fraction of aspherical impurities and characterise the resulting polycrystalline monolayer. We find that, in the vicinity of an impurity, the underlying hexagonal lattice is deformed due to a preference for 5-fold co-ordinated particles adjacent to impurities. This results in a reduction in local hexagonal ordering around an impurity. Increasing the concentration of impurities leads to an increase in the number of these defects and consequently a reduction in system-wide hexagonal ordering and a corresponding increase in entropy as measured from the distribution of Voronoi cell areas.Furthermore, through both considering orientational correlations and directly identifying crystalline domains we observe a decrease in the average polycrystalline grain size on increasing the concentration of impurities.Our data show that, for the concentrations considered, local structural modifications due to the presence of impurities are independent of their concentration, while structure on longer lengthscales (i.e the size of polycrystalline grains) is determined by the impurity concentration.arXiv:1407.8490v2 [cond-mat.soft]

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Section: Introductionmentioning

confidence: 99%

Structural characterisation of polycrystalline colloidal monolayers in the presence of aspherical impurities

Gray

Mould

Royall

et al. 2015

J. Phys.: Condens. Matter

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“…A steady state is eventually reached at all probed length scales, preceded by an aging regime whose duration is unexpectedly length-scale dependent. and the rateṪ at which the temperature is increased to induce crystallization [29]. Here, we fixṪ = 0.02…”

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confidence: 99%

“…The sample microstructure can be tuned by varying the NP concentration and the rateṪ at which the temperature is increased to induce crystallization [29]. Here, we fixṪ = 0.02…”

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confidence: 99%

Plasticity of a Colloidal Polycrystal under Cyclic Shear

2014

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We use confocal microscopy and time-resolved light scattering to investigate plasticity in a colloidal polycrystal, following the evolution of the network of grain boundaries as the sample is submitted to thousands of shear deformation cycles. The grain boundary motion is found to be ballistic, with a velocity distribution function exhibiting non-trivial power law tails. The shearinduced dynamics initially slow down, similarly to the aging of the spontaneous dynamics in glassy materials, but eventually reach a steady state. Surprisingly, the cross-over time between the initial aging regime and the steady state decreases with increasing probed length scale, hinting at a hierarchical organization of the grain boundary dynamics. The mechanical properties of amorphous solids are a topic of intense research. Recent works focus on the irreversible (or plastic) rearrangements at the microscopic level [1][2][3][4][5][6][7], resulting from an applied deformation or stress, which are ultimately responsible for the macroscopic mechanical behavior. Research on amorphous solids is also relevant to crystalline materials [8]. On the one hand, simulations and experiments have revealed that particles in the grain boundaries (GBs) separating crystalline grains exhibit glassy dynamics [9,10]. On the other hand, polycrystals may be regarded as an amorphous assembly of crystalline grains separated by GBs. In fact, driven polycrystals display mechanical features similar to those of amorphous solids [11] and GB process has been shown to be at the origin of the plasticity of polycrystals in the limit of small grain sizes [11][12][13][14][15].A large number of numerical works have explored the microscopic dynamics induced in amorphous systems by a continuous shear, finding quite generally diffusive dynamics at the particle level [1][2][3], once the affine component of the displacement is removed, as also confirmed by experiments on sheared colloidal glasses [2,7,16]. By contrast, the effect of a cyclic shear has been less investigated, in spite of its relevance to the fatigue tests commonly adopted in material science. Furthermore, cyclic deformation tests allow one to unambiguously identify irreversible rearrangements (as opposed to the non-affine displacement measured in continuous shear, which may be reversible) and to follow the evolution, or aging, of the dynamics as the sample is kept under an oscillatory deformation.Similarly to the case of continuous shear, the microscopic dynamics in cyclically deformed amorphous solids have been found to be diffusive (or even subdiffusive), in simulations [18,19] as well as in experiments on colloids [2,20] or granular matter [21,22]. Aging effects have been reported for macroscopic quantities, e.g. pressure or compacity [23,24], or for the microscopic dynamics. In the latter case, however, aging has been probed over a few tens of cycles at most [22,25].In this Letter, we report on experiments probing the irreversible rearrangements induced in a colloidal polycrystal by thousands of sh...

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“…We now provide a model to account for the presence of a small amount of NPs of diameter σ P that are added to the copolymer suspension, at a volume fraction φ P . We have previously observed that upon solidification the NPs concentrate in the grain-boundaries and influence the microstructure of the polycrystals [33]. In the following, we neglect the effect of the diffusion of NPs on crystal growth, which could occur because of NPs partitioning, and thus assume that v G remains unchanged (Eq.…”

Section: B Nucleation Rate Growth Rate and The Effect Of Nanopartimentioning

confidence: 99%

“…We have shown using confocal microscopy [33] that the average grain size of Pluronics polycrystals can be tuned by changing the heating rate, a property well established for molecular and atomic systems, but hardly investigated in colloidal materials. In this paper, we deepen the experimental study of the role of the heating rate on Pluronics concentrated samples [34].…”

Section: Pacs Numbersmentioning

confidence: 99%

Nucleation and growth of micellar polycrystals under time-dependent volume fraction conditions

et al. 2013

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We study the freezing kinetics of colloidal polycrystals made of micelles of Pluronic F108, a thermosensitive copolymer, to which a small amount of silica nanoparticles of size comparable to that of the micelles are added. We use rheology and calorimetry to measure T c , the crystallization temperature, and find that T c increases with the heating rateṪ used to crystallize the sample. To rationalize our results, we first use viscosity measurements to establish a linear mapping between temperature T and the effective volume fraction, ϕ, of the micelles, treated as hard spheres. Next, we reproduce the experimentalṪ dependence of the crystallization temperature with numerical calculations based on standard models for the nucleation and growth of hard spheres crystals, classical nucleation theory and the Johnson-Mehl-Avrami-Kolmogorov theory. The models have been adapted to account for the peculiarities of our experiments: the presence of nanoparticles that are expelled in the grain boundaries, and the steady increase of T and hence ϕ during the experiment. We moreover show that the polycrystal grain size obtained from the calculations is in good agreement with light microscopy data. Finally, we find that the ϕ dependence of the nucleation rate for the micellar polycrystal is in remarkable quantitative agreement with that found in previous experiments on colloidal hard spheres. These results suggests that deep analogies exist between hard-sphere colloidal crystals and Pluronics micellar crystals, in spite of the difference in particle softness. More generally, our results demonstrate that crystallization processes can be quantitatively probed using standard rheometry.

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Grain refinement and partitioning of impurities in the grain boundaries of a colloidal polycrystal

Cited by 31 publications

References 48 publications

Structural characterisation of polycrystalline colloidal monolayers in the presence of aspherical impurities

Structural characterisation of polycrystalline colloidal monolayers in the presence of aspherical impurities

Plasticity of a Colloidal Polycrystal under Cyclic Shear

Nucleation and growth of micellar polycrystals under time-dependent volume fraction conditions

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