Grainsize Effects on Lateral Islands in Hard Sphere Crystals (ENHANCEMENT)

Due to the in-plane stacking disorder, random hexagonally closed packed hard sphere crystals consist of lateral islands with different lateral positions A, B, and C, and as a consequence, different stacking. We investigate the extent of lateral stacking disorder as a function of grain size, and as a function of the fraction of FCC-stacked particles α by laser scanning confocal microscopy and Monte Carlo simulations. We compare the simulations and microscopy data to relate stacking islands (2D domains with identical stacking type and direction) to lateral islands. Small crystals mainly contain single hexagonal planes, whereas larger crystals consist of a much larger number of lateral islands. Furthermore, the typical stacking island size is related to the FCC fraction. At high α, more FCC islands nucleate, and these are more likely to combine into larger islands than the HCP islands

Grainsize Effects on Lateral Islands in Hard Sphere Crystals (AGGREGATION CH 4)

Due to the in-plane stacking disorder, random hexagonally closed packed hard sphere crystals consist of lateral islands with different lateral positions A, B, and C, and as a consequence, different stacking. We investigate the extent of lateral stacking disorder as a function of grain size, and as a function of the fraction of FCC-stacked particles α by laser scanning confocal microscopy and Monte Carlo simulations. We compare the simulations and microscopy data to relate stacking islands (2D domains with identical stacking type and direction) to lateral islands. Small crystals mainly contain single hexagonal planes, whereas larger crystals consist of a much larger number of lateral islands. Furthermore, the typical stacking island size is related to the FCC fraction. At high α, more FCC islands nucleate, and these are more likely to combine into larger islands than the HCP islands

Grain Boundary Pinning in Doped Hard-Sphere Crystals (AGGREGATION CH 6)

We report on how grain boundaries are pinned in between large spherical impurities in hard sphere colloidal crystals, studied by confocal microscopy. We introduce a frustration length ξ, connected to the extent to which the orientational order of a crystal is reduced in the vicinity of impurities. Initially, ξ increases with the impurity size ratio due to fluid particles near the impurity, but it reduces again later when particles form layers on the impurity surface. If two impurities are separated by a distance smaller than their combined frustration lengths, straight, strongly pinned grain boundaries directly form in between the impurities. At larger separations the grain boundaries can still form in between the impurities due to the enhanced stability of the fluid phase in between the impurities during crystallization, but the pinning is much weaker. Our results indicate that in between impurities, strongly pinned grain boundaries form in a well defined region in the parameter space of impurity volume fractions and impurity-to-particle size ratio

In-plane Stacking Disorder in Hard-Sphere Crystals (ENHANCEMENT)

In-plane stacking disorder is not only characterised by the discontinuous transitions through line-defects presented in the previous chapter, but also by continuous transitions through lattice deformations. We introduce an interplanar bond order criterion to distinguish AB and AC type transitions between two consecutive hexagonal layers. Many of these are found to be Shockley partial screw dislocations, with a characteristic deformation that is spread across two consecutive layers. How the deformation is spread between the layers varies from case to case, which decreases positional order even more strongly than the continuous transitions presented in the previous chapter. These deformations can be traced until far away from the dislocation, both in layers above and below. The relative deformation between two consecutive hexagonal layers does have a well defined width. The deformed layers act as templates for the consecutive layers, which are deformed as well. The transitions between lateral position therefore take place even far away from the dislocation core, but the transition between AB and AC stacking does not. The full island boundary usually consists of a complex combination of both discontinuous and continuous transitions. Furthermore, we show that the regions, in which the stacking changes, contain a much higher concentration of vacancies. These vacancies cause tiny lattice deformations themselves due to the osmotic pressure imbalance caused by the missing particle, pointing towards a mechanism for the stabilisation of lattice deformations through vacancies

The transport of a wettable sphere through a fluid-fluid interface : high Bond numbers (ENHANCEMENT)

In the previous chapter, we studied the transport of wettable spheres through the interface of a demixed colloid-polymer mixture at low Reynolds and Bond numbers by confocal microscopy. Here we consider the high Bond number - low Reynolds number scenario. The sphere approaches the interface from the polymer-rich phase and is eventually transported to the colloid-rich phase. In the high Bond number limit, wetting forces do not play a large role in the transport, even though the spheres are wettable by the colloid-rich phase. Depending on the Bond number, we find two scenarios. At moderately high Bond numbers, the sphere leaves a V-shaped interface behind, which recovers due to interfacial flow. At higher Bond numbers, the so-called tailing regime is observed. In this regime, the spheres leave long columns of gas behind, which break up through a Rayleigh-Plateau instability. Furthermore we find that the theoretical expression for the approach of a sphere toward an undeformable free interface holds surprisingly well for strongly deforming interfaces

Grainsize Effects on Lateral Islands in Hard Sphere Crystals (THESIS VERSION)

Due to the in-plane stacking disorder, random hexagonally closed packed hard sphere crystals consist of lateral islands with different lateral positions A, B, and C, and as a consequence, different stacking. We investigate the extent of lateral stacking disorder as a function of grain size, and as a function of the fraction of FCC-stacked particles α by laser scanning confocal microscopy and Monte Carlo simulations. We compare the simulations and microscopy data to relate stacking islands (2D domains with identical stacking type and direction) to lateral islands. Small crystals mainly contain single hexagonal planes, whereas larger crystals consist of a much larger number of lateral islands. Furthermore, the typical stacking island size is related to the FCC fraction. At high α, more FCC islands nucleate, and these are more likely to combine into larger islands than the HCP islands

Grain Boundary Pinning in Doped Hard-Sphere Crystals (ENHANCEMENT)

We report on how grain boundaries are pinned in between large spherical impurities in hard sphere colloidal crystals, studied by confocal microscopy. We introduce a frustration length ξ, connected to the extent to which the orientational order of a crystal is reduced in the vicinity of impurities. Initially, ξ increases with the impurity size ratio due to fluid particles near the impurity, but it reduces again later when particles form layers on the impurity surface. If two impurities are separated by a distance smaller than their combined frustration lengths, straight, strongly pinned grain boundaries directly form in between the impurities. At larger separations the grain boundaries can still form in between the impurities due to the enhanced stability of the fluid phase in between the impurities during crystallization, but the pinning is much weaker. Our results indicate that in between impurities, strongly pinned grain boundaries form in a well defined region in the parameter space of impurity volume fractions and impurity-to-particle size ratio

Statistics of a colloidal fluid-fluid interface (THESIS VERSION)

We report on measurements made by laser scanning confocal microscopy on the statistics of the interface of phase separated colloid-polymer systems. Due to the Brownian character of the process, the statistics vary with the chosen measurement interval Δt. We focus in particular on the residence times of capillary waves above a given height h and on the waiting times in between such fluctuations. The discrete scanning times are a practical cutoff and we are able to measure the waiting time as a function of this cutoff. The measurement interval dependence of the observed waiting and residence times turns out to be solely determined by the time dependent height-height correlation function g(t). The accompanying distributions of time intervals are predictable in terms of g(t) as well. We find excellent agreement between the theory presented here and the experiments

Hard Sphere Crystallization near Large Spherical Impurities (AGGREGATION CH 5)

Impurities affect the nucleation, growth and structure of crystals. We report the effect of large spherical poly-methyl-methacrylate impurities on the crystal nucleation and growth of monodisperse, hard poly-methyl-methacrylate colloids in a density and optically matching apolar solvent mixture. Crystallization, initiated either at the sample wall or at the impurity surface, was studied by imaging sequences of two-dimensional xy-slices in the plane of the impurity’s centre with a laser scanning confocal microscope. Sufficiently large impurities can induce crystal nucleation. During crystal growth, impurities function as large immovable objects that eventually slow down growth. The resulting structure of the obtained crystals is characterized by relatively small grains. n