Biomedical subjects

Denis Bartolo

Publications and source records attributed to Denis Bartolo.

5 recordsLinked to original sources

PubMed2006

Singular jets and bubbles in drop impact.

We show that when water droplets gently impact on a hydrophobic surface, the droplet shoots out a violent jet, the velocity of which can be up to 40 times the drop impact speed. As a function of the impact velocity, two different hydrodynamic singularities are found that correspond to the collapse of the air cavity formed by the deformation of the drop at impact. It is the collapse that subsequently leads to the jet formation. We show that the divergence of the jet velocity can be understood using simple scaling arguments. In addition, we find that very large air bubbles can remain trapped in the drops. The surprising occurrence of the bubbles for low-speed impact is connected with the nature of the singularities, and can have important consequences for drop deposition, e.g., in ink-jet printing.

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PubMed2004

Effects of intermediate bound states in dynamic force spectroscopy.

We revisit some aspects of the interpretation of dynamic force spectroscopy experiments. The standard theory predicts that the typical unbinding force f* is linearly proportional to the logarithm of the loading rate r when a single energy barrier controls the unbinding process. For a more complex situation of N barriers, it predicts at most N linear segments for the f* vs. log(r) curve, each segment characterizing a different barrier. Here we extend this existing picture using a refined approximation, provide a more general analytical formula, and show that in principle up to N(N + 1) / 2 segments can show up experimentally. As a consequence, the determination of the positions and even the number of the energy barriers from the experimental data can be ambiguous. A further possible consequence of a multiple-barrier landscape is a bimodal or multimodal distribution of the unbinding force at certain loading rates, a feature recently observed experimentally.

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PubMed2003

Effective interactions between inclusions in complex fluids driven out of equilibrium.

The concept of fluctuation-induced effective interactions is extended to systems driven out of equilibrium. We compute the forces experienced by macroscopic objects immersed in a soft material driven by external shaking sources. We show that, in contrast with equilibrium Casimir forces induced by thermal fluctuations, their sign, range, and amplitude depend on specifics of the shaking and can thus be tuned. We also comment on the dispersion of these shaking-induced forces, and discuss their potential application to phase ordering in soft materials.

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PubMed2002

Fluctuations of fluctuation-induced casimir-like forces.

The force experienced by objects embedded in a correlated medium undergoing thermal fluctuations-the so-called fluctuation-induced force-is actually itself a fluctuating quantity. Using a scalar field model, we compute the corresponding probability distribution and show that it is a Gaussian centered on the well-known Casimir force, with a nonuniversal standard deviation that can be typically as large as the mean force itself. The relevance of these results to the experimental measurement of fluctuation-induced forces in soft condensed matter is discussed, as well as the influence of the finite temporal resolution of the measuring apparatus.

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PubMed2002

Dynamic response of adhesion complexes: beyond the single-path picture.

We analyze the response of molecular adhesion complexes to increasing pulling forces (dynamic force spectroscopy) when dissociation can occur along either one of two alternative trajectories in the underlying multidimensional energy landscape. A great diversity of behaviors (e.g., nonmonotonicity) is found for the unbinding force and time as a function of the rate at which the pulling force is increased. In particular we identify a class of "harpoon" stickers that bind easily but resist strong pulling efficiently. Using existing data, we also demonstrate the consequent difficulty of unambiguously determining the features of the energy landscape from such single-molecule pulling experiments.

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