Optimal concentrations in nectar feeding

in Proceedings of the National Academy of Sciences of the United States of America (2011), 108(40), 16618

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra ... [more ▼]

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest ener- getic rewards, the sharp increase of viscosity with sugar concentra- tion makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We iden- tify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we deduce the dependence of the volume intake rate on the nectar viscosity and thus infer an optimal sugar concentration consistent with laboratory mea- surements. Our results provide the first rationale for why suction feeders typically pollinate flowers with lower sugar concentration nectar than their counterparts that use viscous dipping. [less ▲]

From a bouncing compound drop to a double emulsion

in Langmuir (2010), 26(14), 11680

We show that a double emulsion (oil in water in oil) can be created starting from a compound droplet (surfactant solution in oil). The compound drop bounces on a vertically vibrated liquid surface. When ... [more ▼]

We show that a double emulsion (oil in water in oil) can be created starting from a compound droplet (surfactant solution in oil). The compound drop bounces on a vertically vibrated liquid surface. When the amplitude of the vibration exceeds a threshold value, the oil layer penetrates the water content and leaves a tiny oil droplet within. As this phenomenon occurs at each vigorous impact, the compound drop progressively transforms into a double emulsion. The emulsification threshold, which is observed to depend on the forcing frequency but not on the drop size, is rationalized by investigating the impact of compound drops onto a static liquid surface. The droplet creation occurs when the kinetic energy released at impact is larger than the energy required to deform the compound drop, namely when the Weber number is higher than a given threshold value. [less ▲]

The mayonnaise droplet

Conference (2009, November 23)

A compound drop is made of a millimetric water drop encapsulated by an oil shell. They are obtained by merging one drop of each component (water and oil). Afterwards, they are laid on a high viscosity oil ... [more ▼]

A compound drop is made of a millimetric water drop encapsulated by an oil shell. They are obtained by merging one drop of each component (water and oil). Afterwards, they are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a given threshold, compound drops can bounce on the surface. We show that above a second threshold some oil contained in the shell enters in the inner water droplet. In a second experiment, we drop the compound droplet on the oil bath at rest. We can determine the range of impact speed in which capillary waves developed on the surface are able to generate an oil drop (coming from the shell) in the water drop. When the bouncing trajectories of the droplets are analyzed a correlation between the emulsion threshold and the static analysis can be made. [less ▲]

The mayonnaise droplet

Poster (2009, September)

Compound drops are made of a millimetric water drop encapsulated by an oil shell. They are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a ... [more ▼]

Compound drops are made of a millimetric water drop encapsulated by an oil shell. They are laid on a high viscosity oil bath which is vertically vibrated. When the forcing acceleration is higher than a given threshold, compound drops can bounce on the surface. We show that above an another threshold a double emulsion occurs in the drop. We measured this emulsion threshold for various size and water/oil volume ratio of the compound drop. [less ▲]

Antibubbles, liquid onions and mayonnaise droplets

Poster (2009, May)

The mayonnaise droplet

Poster (2009, March)

The fluid trampoline: droplets bouncing on a soap film

in Journal of Fluid Mechanics (2009), 625

We present the results of a combined experimental and theoretical investigation of droplets falling onto a horizontal soap film. Both static and vertically vibrated soap films are considered. In the ... [more ▼]

We present the results of a combined experimental and theoretical investigation of droplets falling onto a horizontal soap film. Both static and vertically vibrated soap films are considered. In the static case, a variety of behaviours were observed, including bouncing, crossing and partial coalescence. A quasi-static description of the soap film shape yields a force–displacement relation that provides excellent agreement with experiment, and allows us to model the film as a nonlinear spring. This approach yields an accurate criterion for the transition between droplet bouncing and crossing. Moreover, it allows us to rationalize the observed constancy of the contact time and scaling for the coefficient of restitution in the bouncing states. On the vibrating film, a variety of bouncing behaviours were observed, including simple and complex periodic states, multi-periodicity and chaos. A simple theoretical model is developed that captures the essential physics of the bouncing process, reproducing all observed bouncing states. The model enables us to rationalize the observed coexistence of multiple periodic bouncing states by considering the dependence of the energy transferred to the droplet on the phase of impact. Quantitative agreement between model and experiment is deduced for simple periodic modes, and qualitative agreement for more complex periodic and chaotic bouncing states. Analytical solutions are deduced in the limit of weak forcing and dissipation, yielding insight into the contact time and periodicity of the bouncing states. [less ▲]

Antibubbles, liquid onions and bouncing droplets

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2009), 344

Metastable bouncing droplets

in Physics of Fluids (2009), 21

From bouncing to boxing

in Chaos (2008), 18(4),