The rotational dynamics of anisotropic particles advected in a turbulent fluid flow are important in many industrial and natural setting. Particle rotations are controlled by small scale properties of turbulence that are nearly universal, and so provide a rich system where experiments can be directly compared with theory and simulations. Here we report the first three-dimensional experimental measurements of the orientation dynamics of rod-like particles as they are advected in a turbulent fluid flow. We also present numerical simulations that show good agreement with the experiments and allow extension to a wide range of particle shapes. Anisotropic tracer particles preferentially sample the flow since their orientations become correlated with the velocity gradient tensor. The rotation rate is heavily influenced by this preferential alignment, and the alignment depends strongly on particle shape

Composite colloidal gels are formed by the pH-induced electrostatic assembly of silica and gelatin nanoparticles. These injectable and moldable colloidal gels are able to withstand substantial compressive and tensile loads, and exhibit a remarkable self-healing efficiency. This study provides new, critical insight into the structural and mechanical properties of composite colloidal gels and opens up new avenues for practical application of colloidal gels.

The relationship between the microstructure of a porous medium and the observed flow distribution is still a puzzle. We resolve it with an analytical model, where the local correlations between adjacent pores, which determine the distribution of flows propagated from one pore downstream, predict the flow distribution. Numerical simulations of a two-dimensional porous medium verify the model and clearly show the transition of flow distributions from δ-function-like via Gaussians to exponential with increasing disorder. Comparison to experimental data further verifies our numerical approach.

We derive a scaling relationship for the mean square rotation rate of rods with lengths in the inertial range in turbulence: ∝ l(-4/3). We present experimental measurements of the rotational statistics of neutrally buoyant rods with lengths 2.8

We study the dynamics of rod shaped particles in two-dimensional electromagnetically driven fluid flows. Two separate types of flows that exhibit chaotic mixing are compared: one with time-periodic flow and the other with constant forcing but nonperiodic flow. Video particle tracking is used to make accurate simultaneous measurements of the motion and orientation of rods along with the carrier fluid velocity field. These measurements allow a detailed comparison of the motion and orientation of rods with properties of the carrier flow. Measured rod rotation rates are in agreement with predictions for ellipsoidal particles based on the measured velocity gradients at the center of the rods. There is little dependence on length for the rods we studied ͑up to 53% of the length scale of the forcing͒. Rods are found to align weakly with the extensional direction of the strain-rate tensor. However, the alignment is much stronger with the direction of Lagrangian stretching defined by the eigenvectors of the Cauchy-Green deformation tensor. A simple model of the stretching process predicts the degree of alignment of rods with the stretching direction.