Real-Space Structure of Colloidal Hard-Sphere Glasses

Abstract

The real-space structure of hard-sphere glasses quenched from colloidal liquids in thermodynamic equilibrium has been determined. Particle coordinates were obtained by combining the optical sectioning capability of confocal fluorescence microscopy with the structure of specially prepared fluorescent silica colloids. Both the average structure and the local structure of glasses, with volume fractions ranging from 0.60 to 0.64, were in good agreement with glasses and random close packings generated by computer simulations. No evidence of a divergent correlation length was found. The method used to obtain the three-dimensional particle coordinates is directly applicable to other colloidal structures, such as crystals, gels, and flocs. dius of 200 nm, a total radius of 525 nm, and a polydispersity in size of 1.8%. The synthesis and characterization of these hybrid organic-inorganic spheres are described in (1 7). The hard-sphere potential was created by dispersing the particles in dimethvlformamide (in which the refractive index ~ -was almost matched) to decrease the van der Waals forces and bv addine 0.1 M LiCl w to decrease the double layer to a very small value relative to the radius. As measured bv confocal microscopy, the average distance of closest approach of the particles was 1052 nm in a dried glass and 1082 nm in the glass with solvent; the difference is probably attributable to a solvation laver that Drotects the particles from aggregation. The crystallization and melting volume fractions calDespite recent progress, neither the glass computer simulations can become imporculated from this interaction distance of transition nor the structure of glasses is fully tant, especially if the goal is to find a diverclosest approach were 0.50 and 0.55

Preparation of Monodisperse, Fluorescent PMMA–Latex Colloids by Dispersion Polymerization

“…However, as soon as these particles are closer together, on average, than the wavelength of visible light, particle positions cannot be resolved in three dimensions. This will only be possible by using particles with a fluorescent core and a nonfluorescent shell (6,7).…”

“…Recently a number of real-space studies of colloidal systems using confocal scanning laser microscopy (CSLM) have been published (see, e.g., (6)(7)(8)). Compared to conventional optical (video) microscopy, the advantage of CSLM is that out-of-focus blur is essentially absent from confocal images, mainly due to a pinhole in front of the detector.…”

Bridging length scales in colloidal liquids and interfaces from near-critical divergence to single particles

“…We carried out standard Monte Carlo simulations at constant particle number, volume and temperature for an LJ system (u LJ ) = 4w((σ/r) 12 − (σ/r) 6 )), where the interaction was truncated at 2.5σ and shifted such that u LJ (2.5σ) = 0. We used 4,000 particles, equilibrated with up to 2 × 10 8 steps.…”

“…We used two colloid-polymer mixtures. The small colloids (radius a = 230 nm) allowed us to approach criticality to ε ∼ 10 −3 , whereas the larger colloids (a = 650 nm) permitted full 3D resolution of the colloid coordinates 12 , see the Methods section. Confocal micrographs of the small-particle system are shown in Fig.…”

Dynamical Heterogeneity and Jamming in Glass-Forming Liquids

“…We refer to a system as dynamically heterogeneous if it is possible to select a dynamically distinguishable subset of particles by experiment or computer simulation [20]. Simulations [21,22,23,24,25,26,27] and experiments [28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43] have demonstrated the cooperative and spatially heterogeneous nature of the liquid dynamics (for reviews of the experimental evidence for spatially heterogeneous dynamics, see, e. g., Refs. [44,45,46]).…”