Using the Quartz Crystal Microbalance to Monitor the Curing of Drying Oils.

Drying oils such as linseed oil form a polymer network through a complex free-radical polymerization process. We have studied polymerization in this challenging class of polymers using a quartz crystal microbalance (QCM). The QCM is able to measure the evolution of polymer mass and mechanical properties as the oil transitions from a liquid-like to a solid-like state.

Digital Microfluidics─How Magnetically Driven Orientation of Pillars Influences Droplet Positioning.

Interfaces between a water droplet and a network of pillars produce eventually superhydrophobic, self-cleaning properties. Considering the surface fraction of the surface in interaction with water, it is possible to tune precisely the contact angle hysteresis (CAH) to low values, which is at the origin of the poor adhesion of water droplets, inducing their high mobility on such a surface. However, if one wants to move and position a droplet, the lower the CAH, the less precise will be the positioning on the surface.

Interaction between Compliant Surfaces: How Soft Surfaces Can Reduce Friction.

We describe how a long-range repulsive interaction can surreptitiously modify the effective geometry of approaching compliant surfaces, with significant consequences on friction. We investigated the behavior under shear and compression of mica surfaces coated with poly(-isopropylacrylamide) pNIPAM-based cationic microgels. We show that local surface deformations as small as a few nanometers must be considered to understand the response of such surfaces under compression and shear, in particular when the range of action of normal and friction forces are significantly different, as is often the case for macromolecular lubrication.

New Platform for Gravitational Microfluidic Using Ferrofluids.

Among the large variety of microfluidic platforms, surface devices are a world apart. Electrowetting systems are used to control the displacement of droplets among predetermined pathways. More confidential, superhydrophobic surfaces are more and more described as new elements to guide spherical droplet reactors.

Large strain viscoelastic dissipation during interfacial rupture in laminated glass.

In the dynamic rupture of laminated glass, it is essential to maximize energy dissipation. To investigate the mechanisms of energy dissipation, we have experimentally studied the delamination and stretching of a polymeric viscoelastic interlayer sandwiched between glass plates. We find that there is a velocity and temperature domain in which delamination fronts propagate in a steady state manner.

Wetting against the nap - how asperity inclination determines unidirectional spreading.

We have carried out wetting experiments on textured surfaces with high aspect ratio asperities in the Wenzel state. When inclination is imparted to the asperities, we observe a strictly unidirectional spreading opposite to the direction in which the asperities point. The advancing contact angle decreases markedly as inclination increases.

Evolution of bone biomechanical properties at the micrometer scale around titanium implant as a function of healing time.

The characterization of the biomechanical properties of newly formed bone tissue around implants is important to understand the osseointegration process. The objective of this study is to investigate the evolution of elastic properties of newly formed bone tissue as a function of healing time. To do so, nanoindentation and micro-Brillouin scattering techniques are coupled following a multimodality approach using histological analysis.

Finite size effects on textured surfaces: recovering contact angles from vagarious drop edges.

A clue to understand wetting hysteresis on superhydrophobic surfaces is the relation between receding contact angle and surface textures. When the surface textures are large, there is a significant distribution of local contact angles around the drop. As seen from the cross section, the apparent contact angle oscillates as the triple line recedes.

Contact interaction of double-chained surfactant layers on silica: bilayer rupture and capillary bridge formation.

The contact between two layers of double-chained C18 surfactants adsorbed on silica has been investigated. Using a custom-made surface forces apparatus with high stiffness, we have studied the process of (1) compression and collapse of the layers and (2) surface separation after layer collapse. A continuum mechanics model accounts for the compression and collapse of the surfactant layers.

Role of kinks in the dynamics of contact lines receding on superhydrophobic surfaces.

We have investigated the depinning of the contact line on superhydrophobic surfaces with anisotropic periodic textures. By direct observation of the contact line conformation, we show that the mobility is mediated by kink defects. Full 3D simulations of the shape of the liquid surface near the solid confirm that kinks account for the measured wetting properties.

How does adhesion induce the formation of telephone cord buckles?

Compressively stressed thin films with low adhesion frequently buckle and delaminate simultaneously into telephone cords. Although these buckles have been studied for decades, no complete understanding of their propagation has so far been presented. In this study, we have coupled a nonlinear plate deformation with a cohesive zone model to simulate the kinematics of a propagating telephone cord buckle in very close agreement with experimental observations.

Nanoindentation measurements of biomechanical properties in mature and newly formed bone tissue surrounding an implant.

The characterization of the biomechanical properties of newly formed bone tissue around implants is important to understand the osseointegration process. The objective of this study is to investigate the evolution of the hardness and indentation modulus of newly formed bone tissue as a function of healing time. To do so, a nanoindentation device is employed following a multimodality approach using histological analysis.

Mode III cleavage of a coin-shaped titanium implant in bone: effect of friction and crack propagation.

Endosseous cementless implants are widely used in orthopaedic, maxillofacial and oral surgery. However, failures are still observed and remain difficult to anticipate as remodelling phenomena at the bone-implant interface are poorly understood. The assessment of the biomechanical strength of the bone-implant interface may improve the understanding of the osseointegration process.

All-silica nanofluidic devices for DNA-analysis fabricated by imprint of sol-gel silica with silicon stamp.

We present a simple and cheap method for fabrication of silica nanofluidic devices for single-molecule studies. By imprinting sol-gel materials with a multi-level stamp comprising micro- and nanofeatures, channels of different depth are produced in a single process step. Calcination of the imprinted hybrid sol-gel material produces purely inorganic silica, which has very low autofluorescence and can be fusion bonded to a glass lid.

Adsorption and onset of lubrication by a double-chained cationic surfactant on silica surfaces.

In the context of glass fiber manufacture, the onset of lubrication by a C(18) double-chained cationic surfactant has been investigated at high normal contact pressures. Comparison with adsorption kinetics demonstrates that lubrication is not directly connected to the surfactant surface excess but originates from the transition to a defect-free bilayer that generates limited dissipation. The impact of ionic strength and shear rate has also been studied.

How do silanes affect the lubricating properties of cationic double chain surfactant on silica surfaces?

The effect of an aminosilane on the lubricant properties of a C(18) double-chained cationic surfactant has been investigated in the context of glass fiber forming process. The surfactant adsorption was studied on silica by Fourier transform infrared (FT-IR) spectroscopy in the attenuated total reflexion (ATR) mode as a function of the aminosilane concentration in an organic water based formulation (sizing) used to coat the glass fibers during the process. A reciprocating ball-on-plate tribometer was used to compare friction properties of silica in contact with the aminosilane-surfactant mixture and in presence of each component of the sizing.

An approximate model for the adhesive contact of rough viscoelastic surfaces.

Surface roughness is known to easily suppress the adhesion of elastic surfaces. Here, a simple model for the contact of viscoelastic rough surfaces with significant levels of adhesion is presented. This approach is derived from our previous model (Barthel, E.