| Shrnutí: | <p>The structural and dynamic behaviour of two-dimensional binary colloidal polycrystals and fluids are studied through optical microscopy and optical tweezing. Firstly, grain size evolution in an impurity doped polycrystalline monolayer is studied. A model is developed, combining crystallisation and curvature driven grain growth, which works well in describing grain size evolution at different impurity concentrations. The amount of dopant is found to affect the frustration of crystallisation and pinning of grain boundaries. Next studied is grain rotation in polycrystals. The rate of rotation for a single grain is well described by a model combining grain size and the grain boundary misorientation. The rate of rotation induced grain coalescence is placed in the context of grain size evolution and the trajectories of particles and dislocations are studied. To study the pinning forces of impurities in grain boundaries, active microrheology with optical tweezing is utilised. A model accounting for grain boundary deformation, contact angles between the impurity and grain boundary, and elastic response from the crystal is used to measure the pinning force on the impurity. An anomalously high depinning force is found, corresponding
to the creation of a entity analogous to a dislocation. Next, the thermal fluctuations of a grain boundary between two pinned impurities are studied for different impurity spacings. The form of the fluctuations is dominated by the mode with a wavelength twice the impurity spacing. This spacing is also found to impact the mobility of the grain boundary and the mean-squared displacement. Finally, a binary system is placed on an angle to set up sedimentation-diffusion equilibrium. The particle sizes and materials are chosen to prevent fractionation. The structure of the system is found to be amorphous for all area fractions. The entire system for different tilt angles is found to be diffusive, with dynamics slowing down with a steeper tilt angle. The cause of the diffusive dynamics at all area fractions is found to be due to dynamic heterogeneities, which propagate from low to high densities, with higher tilt angles having a greater activation energy for this mechanism.</p>
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