Real-space analysis of grain boundary fluctuations in two dimensional colloidal crystals

The characteristics of grain boundary motion and evolution are of fundamental importance in material science. Optical microscopy is used to analyse grain boundary fluctuations in two-dimensional colloidal crystals. Colloidal systems are particles (colloids) on the order of 1µm dispersed in a solvent where they display rich phase behaviour of colloidal 'crystal', liquid' and 'gas' phases. They are widely used as a model system to study many fundamental issues in condensed matter physics and statistical mechanics. The intrinsic slowness and increased length scales of colloidal systems make them an excellent model system to study grain boundaries as an analogy to atomic systems. Static and dynamic correlation functions are compared with capillary wave theory to calculate the grain boundary mobility and stiffness. These fundamental properties of grain boundaries determine the kinetics of curvature-driven grain growth.</jats:p

Frustrated crystallisation and melting in two-dimensional pentagonal confinement

The crystallisation and melting behaviour of superparamagnetic colloidal particles confined within a two-dimensional pentagonal environment is studied by systematically varying either the external magnetic field or the number of particles. A system containing 16 confined particles melts monotonically from a commensurate crystalline configuration to a confined liquid-like state as the magnetic field is reduced. When the magnetic field is kept constant and the number of confined particles is increased from 11 to 21, highly non-monotonic behaviour is observed involving re-entrant structural ordering and dynamically frustrated states

Dynamic heterogeneities and non-Gaussian behavior in two-dimensional randomly confined colloidal fluids

A binary mixture of super-paramagnetic colloidal particles is confined between glass plates such that the large particles become fixed and provide a two-dimensional disordered matrix for the still mobile small particles, which form a fluid. By varying fluid and matrix area fractions and tuning the interactions between the super-paramagnetic particles via an external magnetic field, different regions of the state diagram are explored. The mobile particles exhibit delocalized dynamics at small matrix area fractions and localised motion at high matrix area fractions, and the localization transition is rounded by the soft interactions [T. O. E. Skinner et al, Phys. Rev. Lett. {\bf 111}, 128301 (2013)]. Expanding on previous work, we find the dynamics of the tracers to be strongly heterogeneous and show that molecular dynamics simulations of an ideal gas confined in a fixed matrix exhibit similar behavior. The simulations show how these soft interactions make the dynamics more heterogenous compared to the disordered Lorentz gas and lead to strong non-Gaussian fluctuations

Dynamic heterogeneities and non-Gaussian behavior in two-dimensional randomly confined colloidal fluids

A binary mixture of super-paramagnetic colloidal particles is confined between glass plates such that the large particles become fixed and provide a two-dimensional disordered matrix for the still mobile small particles, which form a fluid. By varying fluid and matrix area fractions and tuning the interactions between the super-paramagnetic particles via an external magnetic field, different regions of the state diagram are explored. The mobile particles exhibit delocalized dynamics at small matrix area fractions and localised motion at high matrix area fractions, and the localization transition is rounded by the soft interactions [T. O. E. Skinner et al, Phys. Rev. Lett. {\bf 111}, 128301 (2013)]. Expanding on previous work, we find the dynamics of the tracers to be strongly heterogeneous and show that molecular dynamics simulations of an ideal gas confined in a fixed matrix exhibit similar behavior. The simulations show how these soft interactions make the dynamics more heterogenous compared to the disordered Lorentz gas and lead to strong non-Gaussian fluctuations