Two likely causes of Type C Damping in highly entangled polymers are interfacial slip and shear banding. To isolate these mechanisms, we use confocal microscopy and particle image velocimetry to visualize flow in a planar-Couette shear. Polybutadiene (Mw=200K, 1.1 M) solutions with different entanglement densities (8≤Z≤56) are sheared in narrow gaps ∼35μm. Not only does the velocity at the boundaries violate the no-slip condition, but the velocity profiles are linear. This is inconsistent with shear banding. The measured shear rates and stresses are used to characterize interfacial slip.

Determining the depth dependence of the shear properties of articular cartilage is essential for understanding the structure-function relation in this tissue. Here, we measured spatial variations in the shear modulus G of bovine articular cartilage using a novel technique that combines shear testing, confocal imaging and force measurement.

At high area fractions, monolayers of colloidal dimer particles form a degenerate crystal (DC) structure in which the particle lobes occupy triangular lattice sites while the particles are oriented randomly along any of the three lattice directions. We report that dislocation glide in DCs is blocked by certain particle orientations. The mean number of lattice constants between such obstacles is Z̄exp=4.6±0.2 in experimentally observed DC grains and Z̄sim=6.18±0.01 in simulated monocrystalline DCs.

Hard peanut-shaped colloids were synthesized and organized into a degenerate crystal (DC), a phase previously observed only in simulations. In this structure, particle lobes tile a triangular lattice while their orientations uniformly populate the three underlying crystalline directions. © The Royal Society of Chemistry 2008.

The formation of dislocations is central to our understanding of yield, work hardening, fracture, and fatigue1 of crystalline materials. While dislocations have been studied extensively in conventional materials, recent results have shown that colloidal crystals offer a potential model system for visualizing their structure and dynamics directly in real space 2. Although thermal fluctuations are thought to play a critical role in the nucleation of these defects, it is difficult to observe them directly.

We present experimental results on the snap-off dynamics of a drop with viscosity λη dripping through a fluid of viscosity η. This paper focuses on the Stokes regime where both the inner and outer fluid viscous stresses are balanced by the pressure gradients arising from the interfacial curvature. We track the time dependence of the drop profiles near snap-off and find that successive profiles can be rescaled onto a single curve. We explore the dependence of this scaling on the nozzle diameter, surface tension, density mismatch, and viscosity ratio λ.