Brownian dynamics and dynamic Monte Carlo simulations of isotropic and liquid crystal phases of anisotropic colloidal particles: A comparative study

We investigate the phase behaviour and self-assembly of convex spherical caps using Monte Carlo simulations. This model is used to represent the main features observed in experimental colloidal particles with mushroom-cap shape [Riley et al., Langmuir, 2010, 26, 1648. The geometry of this non-centrosymmetric convex model is fully characterized by the aspect ratio χ * defined as the spherical cap height to diameter ratio. We use NPT Monte Carlo simulations combined with free energy calculations to determine the most stable crystal structures and the phase behaviour of convex spherical caps with different aspect ratios. We find a variety of crystal structures at each aspect ratio, including plastic and dimer-based crystals; small differences in chemical potential between the structures with similar morphology suggest that convex spherical caps have the tendency to form polycrystalline phases rather than crystallising into a single uniform structure. With the exception of plastic crystals observed at large aspect ratios (χ * > 0.75), crystallisation kinetics seem to be too slow, hindering the spontaneous formation of ordered structures. As an alternative, we also present a study of directing the self-assembly of convex spherical caps via sedimentation onto solid substrates. This study contributes to show how small changes to particle shape can significantly alter the self-assembly of crystal structures, and how a simple gravity field and a template can substantially enhance the process.

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“…These are calculated using NV T -MC simulations with fixed values for the maximum particle displacement and rotation 78 .…”

Section: Bulk Simulationsmentioning

confidence: 99%

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

McBride

Avendaño

2017

Soft Matter

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“…The system consists of N = 100 particles confined to a two dimensional channel of radius R p in the y-direction and length L along the x-axis, where periodic boundaries are also employed. Particles are moved using the standard Metropolis MC scheme [59] as a simple approximation to Brownian motion [60]. A MC trial move involves the random selection of a particle, followed by the random selection of a trial step in both the x and y-directions up to a maximum step size of |∆x| = |∆y| = 0.05.…”

Section: B Hopping Time Calculationsmentioning

confidence: 99%

Diffusion in quasi-one-dimensional channels: A small system n, p, T, transition state theory for hopping times

Ahmadi

Bowles

2017

The Journal of Chemical Physics

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Particles confined to a single file, in a narrow quasi-one dimensional channel, exhibit a dynamic crossover from single file diffusion to Fickian diffusion as the channel radius increases and the particles can begin to pass each other. The long time diffusion coefficient for a system in the crossover regime can be described in terms of a hopping time, which measures the time it takes for a particle to escape the cage formed by its neighbours. In this paper, we develop a transition state theory approach to the calculation of the hopping time, using the small system isobaric-isothermal ensemble to rigorously account for the volume fluctuations associated with the size of the cage. We also describe a Monte Carlo simulation scheme that can be used to calculate the free energy barrier for particle hopping. The theory and simulation method correctly predict the hopping times for a two dimensional confined ideal gas system and a system of confined hard discs over a range of channel radii, but the method breaks down for wide channels in the hard discs case, underestimating the height of the hopping barrier due to the neglect of interactions between the small system and its surroundings.

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“…For such small steps, the "dynamics" of the system is similar to Brownian dynamics and produces the same behaviour on long time-scales. [23][24][25] The system consisted of N = 10 386 prolate hard ellipsoids with an aspect ratio of a/b = 1.25, where a is the length of the axis of symmetry and b is the length of any axis in the perpendicular plane. To simplify notation, we introduce the dimensionless pressure P * = P 8ab 2 k B T (where k B is Boltzmann's constant).…”

Section: Simulation Technique and Data Analysismentioning

confidence: 99%

Crystallization in glassy suspensions of hard ellipsoids

Dorosz

Schilling

2013

The Journal of Chemical Physics

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We have carried out computer simulations of overcompressed suspensions of hard monodisperse ellipsoids and observed their crystallization dynamics. The system was compressed very rapidly in order to reach the regime of slow, glass-like dynamics. We find that, although particle dynamics become sub-diffusive and the intermediate scattering function clearly develops a shoulder, crystallization proceeds via the usual scenario: nucleation and growth for small supersaturations, spinodal decomposition for large supersaturations. In particular, we compared the mobility of the particles in the regions where crystallization set in with the mobility in the rest of the system. We did not find any signature in the dynamics of the melt that pointed towards the imminent crystallization events.

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Brownian dynamics and dynamic Monte Carlo simulations of isotropic and liquid crystal phases of anisotropic colloidal particles: A comparative study

Cited by 77 publications

References 32 publications

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

Diffusion in quasi-one-dimensional channels: A small system n, p, T, transition state theory for hopping times

Crystallization in glassy suspensions of hard ellipsoids

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