Melting of Colloidal Crystals

Abstract

8903wileyonlinelibrary.com ClassificationCrystal melting can be categorized into two types: homogeneous melting in which the melting is equally likely to occur anywhere in the crystal, and heterogeneous melting in which the melting is more likely to occur at the surfaces and defects than the defectfree regions. Heterogeneous melting can be divided into surface melting from a free surface (i.e., the solid-vapor interface), interfacial melting from the interface of two materials (e.g., a crystal and its substrate), grain-boundary melting and melting at weaker defects such as dislocations and vacancies. Homogeneous melting exists in defect-free crystals whose surface melting is suppressed. This type of melting is of theoretical importance but is difficult to achieve experimentally because most crystals melt from surfaces and are not defect-free, which leads to heterogeneous melting. However, homogeneous melting can be conveniently studied by simulation using defect-free crystals under periodic boundary conditions.In heterogeneous melting, particles at the surfaces or defects usually have a higher free energy than those in a perfect crystal. If the free energy is high enough, melting can take place even before the melting point is reached, which is known as premelting. If none of the surfaces and defects has a high enough free energy, then the crystal can be superheated to form a metastable crystal above the bulk melting point. The bulk melting point is the point at which the solid and liquid phases share the same chemical potential, and surfaces are negligible at the thermodynamic limit, i.e., the crystals are infinitely large. For 3D crystals, the likelihood of inducing melting in decreasing order is roughly as follows: 0D corners and 1D edges (intersection of three or two free surfaces) > 1D surface grain boundaries (intersection of a free surface and a bulk grain boundary) > free surfaces > bulk triple junctions > high-angle grain boundaries > the interface between two solids (e.g., on a flat substrate) > lowangle grain boundaries > dislocations > partial dislocations > vacancies > interstitials. [4] Melting starts from the strongest defects and spreads rapidly into the crystal, and thus usually preempts the melting from other weaker defects. Note that this order may not always hold. For example, the energy of free surfaces and grain boundaries varies with their orientations and the interfacial energy at the substrate depends on the affinity between the two solids. Consequently, most free surfaces, some grain boundaries and some solid interfaces will premelt below the bulk melting point T m , while other solid interfaces and grain boundaries and a few free surfaces will only induce melting above T m , i.e., they can be superheated.Crystal melting is affected by many factors such as defects, surfaces, dimensionality, lattice structure, and particle interaction, and thus exhibits rich phenomenology. It is usually a first-order phase transition which currently lacks a fundamental theory. Despite numerous studies ove...

Grain-Boundary Roughening in Colloidal Crystals

“…The top and bottom walls help us to form ribbonlike grain boundaries with uniform shape in the z direction, but the fluctuations in the xy plane are much weaker in a 20-layer crystal than in a monolayer crystal. This can be understood from a simple lattice-spring model [50]: A 2D square lattice has half of its springs connected in series and half connected in parallel; a two-layer square lattice has 2=5 of its springs in series and 3=5 in parallel; and a 3D cubic lattice has 1=3 of its springs in series and 2=3 in parallel. A higher fraction of springs in series corresponds to a softer structure.…”

Ptychographic X‐Ray Imaging of Colloidal Crystals

“…Colloidal crystals are being actively employed as an important model system to study melting, freezing, and solid‐solid phase transitions as a function of osmotic pressure and anisotropy of interparticle interaction due to particle shape, patchiness, or dipolar interactions . The flexibility of colloidal crystals and their response to external stimuli along with their unique optical properties such as the strongly pronounced structural color and photonic band gap makes them attractive for many applications .…”

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dipolar interactions. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The flexibility of colloidal crystals and their response to external stimuli [16][17][18] along with their unique optical properties such as the strongly pronounced structural color and photonic band gap makes them attractive for many applications. [19][20][21][22][23][24][25] Moreover, defects, which determine the mechanical properties of many engineering materials such as metals, [26] can be studied with "atomic" resolution using colloidal crystals.

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“…The broadening of the Bragg peaks may be attributed to coherent illumination of the sample as well as to defect structure of the colloidal crystal (see, for example, ref. [50]).Small 2018,14, 1702575…”

Computational Study on Homogeneous Melting of Benzene Phase I

“…In an earlier study, the limit of superheating was predicted using two different parameters based on vibrational instability and elastic shear instability, the Lindemann [1] and Born criteria [2], respectively. Even though experimental observation of the initial stage of homogeneous melting remains challenging because of the random creation of a liquid nucleus and its subsequent fast growth [5][6][7][8][9][10][11][12][13], recent developments in computer simulation have enabled us to closely examine its microscopic details [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Using molecular-dynamics (MD) simulations for a Lennard-Jones fluid, a study by Jin et al observed that homogeneous melting is initiated by clusters of vibrationally destabilised particles by satisfying the Lindemann and Born criteria [16,28].…”