Structure and dynamics of biphasic colloidal mixtures

We investigate the structure and dynamics of biphasic colloidal mixtures composed of coexisting attractive and repulsive microspheres by confocal microscopy. Attractive gels formed in the presence of repulsive microspheres are more spatially homogeneous and, on average, are both more locally tenuous and have fewer large voids than their unary counterparts. The repulsive microspheres within these mixtures display heterogeneous dynamics, with some species exhibiting freely diffusive Brownian motion while others are trapped within the gel network during aggregation.

Figure 1

(Color) (a) Confocal two-dimensional (2D) image of the biphasic colloidal mixture containing attractive and repulsive particles $({\varphi }_{att}={\varphi }_{rep}=0.05)$. (b) MSD of the respective populations.

Figure 2

Probability distribution of Voronoi polyhedra volumes of the gel phase, assembled from attractive particles within biphasic $({\varphi }_{total}=0.47)$ and unary $({\varphi }_{rep}=0)$ systems.

Figure 3

(Color) Local number density fluctuations. The open squares correspond to a unary sample composed of purely attractive particles. The solid symbols represent the number density fluctuations of the gel phase assembled from biphasic mixtures; the solid triangles correspond to a fixed ${\varphi }_{total}=0.47$ where the horizontal axis represents ${\varphi }_{att}$, and the solid circles correspond to a fixed ${\varphi }_{att}=0.14$ where the horizontal axis represents ${\varphi }_{rep}$. Number density fluctuations of unary repulsive suspensions at the corresponding $\varphi$ are also plotted for comparison (open triangles). Each point reports the average of three independent experiments, with standard deviations shown as error bars. The inset shows 3D reconstructions of the gel structures.

Figure 4

Probability distribution of the number of interparticle bonds per particle, for gels assembled from biphasic $({\varphi }_{total}=0.47)$ and unary $({\varphi }_{rep}=0)$ systems.

Figure 5

(Color) (a) Probability distribution of repulsive particle displacements in a biphasic mixture at ${\varphi }_{att}=0.14$, ${\varphi }_{rep}=0.33$. (b) Repulsive particle trajectories over $125\mathrm{s}$.