Equilibrium fluid-crystal interfacial free energy of bcc-crystallizing aqueous suspensions of polydisperse charged spheres

Palberg, Thomas; Wette, Patrick; Herlach, D.M.

doi:10.1103/physreve.93.022601

Cited by 8 publications

(8 citation statements)

References 171 publications

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“…The typical time and length scales of colloidal systems allow for time-resolved observations of solidification with easily manageable experimental techniques, even real space imaging of nucleation events with 'atomic' resolution [41, 42, [43]. More recently, it was demonstrated from scattering experiments that also the thermodynamics of crystallization can be accessed in a quantitative manner and the Turnbull coefficients of bcc forming metals and colloids are very similar [44]. That stresses the applicability of colloidal suspensions as model systems for nucleation studies, which are not directly applicab systems.…”

Section: Ducting Materials If the Eriences A Timementioning

confidence: 99%

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Overview: Experimental studies of crystal nucleation: Metals and colloids

Herlach

Palberg

Klassen

et al. 2016

The Journal of Chemical Physics

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Crystallization is one of the most important phase transformations of first order. In the case of metals and alloys, the liquid phase is the parent phase of materials production. The conditions of the crystallization process control the as-solidified material in its chemical and physical properties. Nucleation initiates the crystallization of a liquid. It selects the crystallographic phase, stable or meta-stable. Its detailed knowledge is therefore mandatory for the design of materials. We present techniques of containerless processing for nucleation studies of metals and alloys. Experimental results demonstrate the power of these methods not only for crystal nucleation of stable solids but in particular also for investigations of crystal nucleation of metastable solids at extreme undercooling. This concerns the physical nature of heterogeneous versus homogeneous nucleation and nucleation of phases nucleated under non-equilibrium conditions. The results are analyzed within classical nucleation theory that defines the activation energy of homogeneous nucleation in terms of the interfacial energy and the difference of Gibbs free energies of solid and liquid. The interfacial energy acts as barrier for the nucleation process. Its experimental determination is difficult in the case of metals. In the second part of this work we therefore explore the potential of colloidal suspensions as model systems for the crystallization process. The nucleation process of colloids is observed in situ by optical observation and ultra-small angle X-ray diffraction using high intensity synchrotron radiation. It allows an unambiguous discrimination of homogeneous and heterogeneous nucleation as well as the determination of the interfacial free energy of the solid-liquid interface. Our results are used to construct Turnbull plots of colloids, which are discussed in relation to Turnbull plots of metals and support the hypothesis that colloids are useful model systems to investigate crystal nucleation.

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Section: Ducting Materials If the Eriences A Timementioning

confidence: 99%

“…The scheme according to Figure 27 is further used to estimate the molar entropy of fusion [44]. It is assumed that ∆S f does not change with increasing metastability, i.e., with increasing particle number density.…”

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Overview: Experimental studies of crystal nucleation: Metals and colloids

Herlach

Palberg

Klassen

et al. 2016

The Journal of Chemical Physics

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“…In principle, polydispersity could make this difference. In a recent study we observed a clear anti-correlation between size-polydispersity and the interfacial free energy involved in homogeneous nucleation 89 . Therefore, we carefully checked the low nominal polydispersity index of the present system of PI = 0.011 with several additional measurements to find a corrected value of PI ≈ 0.05 (Fig.…”

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confidence: 81%

Formation of a transient amorphous solid in low density aqueous charged sphere suspensions

Niu

Heidt

Sreij

et al. 2017

Sci Rep

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Colloidal glasses formed from hard spheres, nearly hard spheres, ellipsoids and platelets or their attractive variants, have been studied in great detail. Complementing and constraining theoretical approaches and simulations, the many different types of model systems have significantly advanced our understanding of the glass transition in general. Despite their early prediction, however, no experimental charged sphere glasses have been found at low density, where the competing process of crystallization prevails. We here report the formation of a transient amorphous solid formed from charged polymer spheres suspended in thoroughly deionized water at volume fractions of 0.0002–0.01. From optical experiments, we observe the presence of short-range order and an enhanced shear rigidity as compared to the stable polycrystalline solid of body centred cubic structure. On a density dependent time scale of hours to days, the amorphous solid transforms into this stable structure. We further present preliminary dynamic light scattering data showing the evolution of a second slow relaxation process possibly pointing to a dynamic heterogeneity known from other colloidal glasses and gels. We compare our findings to the predicted phase behaviour of charged sphere suspensions and discuss possible mechanisms for the formation of this peculiar type of colloidal glass.

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“…where the subscripts fcc, bcc and fcc-bcc refer to the fcc-fluid, bcc-fluid and fcc-bcc interfaces with γ bcc ≈ 0.12 k B T a 2 and γ fcc ≈ 0.40 k B T a 2 [46] with an extended comparison of experimental and theoretical values provided by [45]. The angles refer to the directions of the interfaces close to the triple junction.…”

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“…In these systems, a face-centered cubic (fcc) crystal, a bodycentered cubic (bcc) crystal and a fluid can coexist. Colloids have long been used as model systems to explore such situations, including nucleation [26][27][28][29], crystallization [30][31][32][33][34], melting [16,35,36], defects [37], glass transition [38][39][40][41], solid-liquid interfaces [42][43][44][45][46], solid-solid phase transformations [47][48][49][50] as well as the microscopic response to external forces [51][52][53][54].…”

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Triple Junction at the Triple Point Resolved on the Individual Particle Level

et al. 2017

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At the triple point of a repulsive screened Coulomb system, a face-centered-cubic (fcc) crystal, a bodycentered-cubic (bcc) crystal and a fluid phase coexist. At their intersection, these three phases form a liquid groove, the triple junction. Using confocal microscopy, we resolve the triple junction on a single particle level in a model system of charged PMMA colloids in a nonpolar solvent. The groove is found to be extremely deep and the incommensurate solid-solid interface to be very broad. Thermal fluctuations hence appear to dominate the solid-solid interface. This indicates a very low interfacial energy. The fcc-bcc interfacial energy is quantitatively determined based on Young's equation and, indeed, it is only about 1.3 times higher than the fcc-fluid interfacial energy close to the triple point. PACS numbers:According to the traditional Gibbs phase rule of thermodynamics [1], in a one-component system up to three phases can coexist. Their coexistence is represented by a triple point in the temperature-pressure phase diagram and a triple line in the temperature-density phase diagram. At triple conditions, the three phases are in mutual mechanical, thermal and chemical equilibrium. The three possible interfaces only occur at the same time if the interfacial energies are similar; if an interfacial energy is larger than the sum of the other two, this interface is unstable and the third phase intervenes. When the three interfaces intersect, they form an interfacial line, the triple junction line (which is a point in the slice shown in Fig. 1). Triple junctions have been studied on the macroscopic level, for example in metals where liquid lenses form on top of a crystallite surrounded by coexisting vapor [2,3]. Another classical example is the triple point of water where vapor, liquid water and ice coexist. Such a gas-liquid-solid triple point involves two disordered and one ordered phase and can exist in systems governed by sufficiently long-ranged attractive interparticle interactions [4][5][6]. In contrast, the coexistence of a fluid and two different solids involves two ordered structures and hence an interface between two crystallites that are not commensurate. The corresponding phase behavior has been studied in suspensions of charged colloids [7][8][9][10][11][12][13][14][15][16] Using charged colloids [24,25], we investigate the triple junction at the triple point on an individual-particle level, i.e. including the smallest relevant length scale. At the triple point, we find a deep and tight fluid groove between the two solid phases and a very broad solid-solid interface. This indicates a small solid-solid interfacial energy and hence a considerable effect of thermal fluctuations. Indeed, a quantitative determination of the interfacial energy using Young's equation confirms this suggestion. The interactions of highly charged colloids in the presence of small ions can be described by a purely repulsive screened Coulomb (or Yukawa) effective pair interaction U(r) = (Q 2 4π 0 r) exp(−r λ) with the partic...

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Equilibrium fluid-crystal interfacial free energy of bcc-crystallizing aqueous suspensions of polydisperse charged spheres

Cited by 8 publications

References 171 publications

Overview: Experimental studies of crystal nucleation: Metals and colloids

Overview: Experimental studies of crystal nucleation: Metals and colloids

Formation of a transient amorphous solid in low density aqueous charged sphere suspensions

Triple Junction at the Triple Point Resolved on the Individual Particle Level

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