Preferential Root Tropisms in 2D Wet Granular Media with Structural Inhomogeneities.

We investigate certain aspects of the physical mechanisms of root growth in a granular medium and how these roots adapt to changes in water distribution induced by the presence of structural inhomogeneities in the form of solid intrusions. Physical intrusions such as a square rod added into the 2D granular medium maintain robust capillary action, pumping water from the more saturated areas at the bottom of the cell towards the less saturated areas near the top of the cell while the rest of the medium is slowly devoid of water via evaporation. The intrusion induces "preferential tropism" of roots by first generating a humidity gradient that attracts the root to grow towards it.

Effect of geometry on the dewetting of granular chains by evaporation.

Understanding evaporation or drying in granular media still remains complex despite recent advancements. Evaporation depends on liquid transport across a connected film network from the bulk to the surface. In this study, we investigate the stability of film networks as a function of the geometry of granular chains of spherical grains.

Quantifying "Softness" of Organic Coatings on Gold Nanoparticles Using Correlated Small-Angle X-ray and Neutron Scattering.

Small-angle X-ray and neutron scattering provide powerful tools to selectively characterize the inorganic and organic components of hybrid nanomaterials. Using hydrophobic gold nanoparticles coated with several commercial and dendritic thiols, the size of the organic layer on the gold particles is shown to increase from 1.2 to 4.

Dendron-Mediated Engineering of Interparticle Separation and Self-Assembly in Dendronized Gold Nanoparticles Superlattices.

Self-assembly of nanoparticles into designed structures with controlled interparticle separations is of crucial importance for the engineering of new materials with tunable functions and for the subsequent bottom-up fabrication of functional devices. In this study, a series of lipophilic, highly flexible, disulfide dendritic wedges (generations 0-4), based on 2,2-bis(hydroxymethyl)propionic acid, was designed to bind Au nanoparticles with a thiolate bond. By controlling the solvent evaporation rate, the corresponding dendron-capped Au hybrids were found to self-organize into hexagonal close-packed (hcp) superlattices.

Structural and micromechanical characterization of type I collagen gels.

In this paper we report a study where we use a novel optical tweezers technique to measure the local viscoelastic properties of type I collagen solutions spanning the sol-to-gel transition. We use phase contrast optical microscopy to reveal dense and sparse regions of the rigid fibril networks, and find that the spatial variations in the mechanical properties of the collagen gels closely follow the structural properties. Within the dense phase of the connected network in the gel samples, there are regions that exhibit drastically different viscoelastic properties.