RESUMEN
The short-time diffusivity of dicolloid particles as a function of particle volume fraction Ï from 0.01 ≤ Ï ≤ 0.6 is measured using diffusing wave spectroscopy. The diffusivities of symmetric and asymmetric dicolloids are compared with similarly sized spheres. The short-time diffusivity is independent of salt concentration and decreases with increasing volume fraction for both spheres and asymmetric dicolloids. Symmetric dicolloids have a higher diffusivity than spheres at similar volume fractions. This difference is accounted for by rescaling the dicolloid volume fraction based on the ratio of the random close-packing volume fractions of spheres and dicolloids. Finally, a useful method is provided for calculating the diffusivity of symmetric dicolloid particles of arbitrary aspect ratio based on the calculated hydrodynamic resistance of Zabarankin [Proc. R. Soc. A 463, 2329 (2007)].
Asunto(s)
Coloides/química , Difusión , Simulación por Computador , Luz , Microscopía Electrónica de Rastreo , Modelos Químicos , Tamaño de la Partícula , Cloruro de Potasio/química , Dispersión de Radiación , Análisis Espectral , Tiempo , Agua/químicaRESUMEN
The assembly of ordered dicolloid monolayers is directed by an electric field. The dicolloid particles are polystyrene latex with a maximum equatorial diameter 3.45 µm and length 4.63 µm. The monolayer structure is characterized using small-angle light scattering and bright-field microscopy. With increasing field strength from 26.7 to 200 V(RMS)/cm, a transition from a disordered monolayer, to first orientationally ordered, and then translationally ordered two-dimensional (2D) arrays occurs. A c2mm plane group symmetry dominates the ordered structure but is present alongside structures with p2 symmetry, leading to a spread in the angular distribution of the light scattering peaks. The order-disorder transition dependence on field strength and frequency is similar to that observed for colloidal spheres; at higher frequencies, stronger fields are required to assemble particles. Optimal ordered structures reflect a balance between inducing sufficiently strong interparticle interactions while limiting the rate of formation to ensure the growth of large crystalline domains.