An experimental and theoretical study of the inward particle drift in contact line deposits.

The coffee ring effect, which refers to the formation of a ring-like deposit along the periphery of a dried particle laden sessile drop, is a commonly observed phenomenon. The migration of particles from the interior to the edge of a drying drop as a result of evaporation driven flow directed outwards, is well studied. In this article, we document the inward drift of a coffee stain, which is governed by the descent of the water-air interface of the drying drop due to solvent evaporation. A combination of experimental study and model predictions is undertaken to elucidate the effect of the diameter of particles in the drying drop, the wettability of the substrate on which the drop resides, and the concentration of particles on the inward drift of the coffee stain. This work also suggests a novel method to estimate the coefficient of friction between the particles and the substrate.

Mechanical response of polyacrylamide breast tissue phantoms: Formulation, characterization and modeling.

In the context of breast cancer detection, mechanical imaging is an emerging technique for screening breast cancer. In view of its promise, it deserves a detailed investigation. Development of material that can emulate tissue behavior is essential for research. This work is concerned with the fabrication of polymeric specimens to capture the mechanical behavior of human breast tissues. Three types of tissue phantoms are fabricated: fat, glandular and ductal carcinoma tissues. The fabricated phantoms are compared to available human breast tissue data obtained through compression tests and stress relaxation tests. Further, the fabricated tissue phantoms are subjected to stress relaxation tests to characterize their viscoelastic response. A finite strain viscoelastic constitute model is proposed to describe the mechanical response of the breast tissue phantoms. The model is calibrated using experimental data for phantom tissue specimens. Both phantom tissue specimens and model predictions show reasonable trends. The phantom tissues and model may be of utility in developing mechanical imaging setups.

Further Insights into Patterns from Drying Particle Laden Sessile Drops.

The evaporation of colloidal dispersions is an elegant and straightforward route to controlled self-assembly of particles on a solid surface. In particular, the evaporation of particle laden drops placed on solid substrates has received considerable attention for more than two decades. Such particle filled drops upon complete evaporation of the solvent leave behind a residue, commonly called particulate deposit pattern. In these patterns, typically, more particles accumulate at the edge compared to the interior, a feature observed when coffee drops evaporate. Consequently, such evaporative patterns are called coffee stains. In this article, the focus is on the evaporation of highly dilute suspension drops containing particles of larger diameters ranging from 3 to 10 µm drying on solid substrates. This helps us to investigate the combined role of gravity-driven settling of particles and capillary flow-driven particle transport on pattern formation in drying drops. In the highly dilute concentration limit, the evaporative patterns are found to show a transition, from a monolayer deposit that consists of a single layer of particles, to a multilayer deposit as a function of particle diameter and initial concentration of particles in the drying drop. Moreover, the spatial distribution of particles as well as the ordering of particles in the deposit patterns are found to be particle size dependent. It is also seen that the order-disorder transition, a feature associated with the organization of particles at the edge of the deposit, observed typically at moderate particle concentrations, disappears at the highly dilute concentrations considered here. The evaporation of drops containing particles of 10 µm diameter, where the effect of gravity on the particle becomes significant, leads to uniform deposition of particles, i.e, suppression of the coffee-stain effect and to the formation of two-dimensional percolating networks.

The Effect of Oxidation on the Mechanical Response of Isolated Elastin and Aorta.

Oxidation of aorta by hydroxyl radicals produces structural changes in arterial proteins like elastin and collagen. This in turn results in change in the mechanical response of aorta. In this paper, a thermodynamically consistent constitutive model is developed within the framework of mixture theory, to describe the changes in aorta and isolated elastin with oxidation. The model is then studied under uniaxial extension using experimental data from literature.