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The generation of liquid jets and drops using tightly focused femtosecond laser pulses near a liquid-air interface is a convenient contactless solution for printing functional materials as well as bio-materials. Jets and drops emerge following the nucleation of a cavitation bubble in the liquid bulk by a laser-induced plasma. During the initial expansion of the bubble, a thin and fast jet is produced at the liquid surface. Moments later a second thick and slow jet emanates from the surface when the bubble has nearly deflated. Despite potential applications, little is known about the mechanism behind this complex phenomenology. Here, experiments and simulations are used to investigate this two-jet process. Counter-intuitively, the second jet is not the result of bubble expansion, as with the first jet, but originates from the secondary flows induced by the bubble dynamics. Our study links the second jet properties to the control parameters of the problem and establishes a phase diagram for its emergence. [ABSTRACT FROM AUTHOR]

By examining the rupture of fluid necks during droplet formation of surfactant-laden liquids, we observe deviations from expected behaviour for the pinch-off of such necks. We suggest that these deviations are due to the presence of a dynamic (time-varying) interfacial tension at the minimum neck location and extract this quantity from our measurements on a variety of systems. The presence of such dynamic interfacial tension effects should change the rupture process drastically. However, our measurements show that a simple ansatz, which incorporates the temporal change of the interfacial tension, allows us to understand the dynamics of thinning. This shows that this dynamics is largely independent of the exact details of what happens far from the breakup location, pointing to the local nature of the thinning dynamics. [ABSTRACT FROM PUBLISHER]

We study flows and interface deformations produced by the scattering of a laser beam propagating through non-absorbing turbid fluids. Light scattering produces a force density resulting from the transfer of linear momentum from the laser to the scatterers. The flow induced in the direction of the beam propagation, called ‘optical streaming’, is also able to deform the interface separating the two liquid phases and to produce wide humps. The viscous flow taking place in these two liquid layers is solved analytically, in one of the two liquid layers with a stream function formulation, as well as numerically in both fluids using a boundary integral element method. Quantitative comparisons are shown between the numerical and analytical flow patterns. Moreover, we present predictive simulations regarding the effects of the geometry, of the scattering strength and of the viscosities, on both the flow pattern and the deformation of the interface. Finally, theoretical arguments are put forth to explain the robustness of the emergence of secondary flows in a two-layer fluid system. [ABSTRACT FROM AUTHOR]

We present an analytical model of the time-dependent, small-amplitude deformation of a free liquid surface caused by a spatially localized, axisymmetric, pulsed or continuous, acoustic or electromagnetic radiation pressure exerted on the surface. By exactly solving the unsteady Stokes equation, we predict the surface dynamics in all dynamic regimes, namely inertial, intermediate and strongly damped regimes. We demonstrate the validity of this model in all dynamic regimes by comparing its prediction to experiments consisting of optically measuring the time-dependent curvature of the tip of a hump created at a liquid surface by the radiation pressure of an acoustic pulse. Finally, we present a numerical scheme simulating the behaviour of a fluid–fluid interface subjected to a time-dependent radiation pressure and show its accuracy by comparing the numerical predictions with the analytical model in the intermediate and strongly damped regimes. [ABSTRACT FROM PUBLISHER]

We report on the direct experimental observation of laser-induced flows in isotropic liquids that scatter light. We use a droplet microemulsion in the two-phase regime, which behaves like a binary mixture. Close to its critical consolute line, the microemulsion undergoes large refractive index fluctuations that scatter light. The radiation pressure of a laser beam is focused onto the soft interface between the two phases of the microemulsion and induces a cylindrical liquid jet that continuously emits droplets. We demonstrate that this dripping phenomenon takes place as a consequence of a steady flow induced by the transfer of linear momentum from the optical field to the liquid due to light scattering. We first show that the cylindrical jet guides light as a step-index liquid optical fiber whose core diameter is self-adapted to the light itself. Then, by modelling the light-induced flow as a low-Reynolds-number, parallel flow, we predict the dependence of the dripping flow rate on the thermophysical properties of the microemulsion and the laser beam power. Satisfying agreement is found between the model and experiments. [ABSTRACT FROM AUTHOR]

Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state. [ABSTRACT FROM AUTHOR]

Rayleigh-Plateau instability is known to impose a stability limit for the length of a liquid bridge in weightless conditions. This fundamental limit may be exceeded by using a light field to form and stabilize dielectric fluid bridges (A. Casner, J.P. Delville, Europhys. Lett. 65, 337 (2004)). Using both new experimental data as well as a new theoretical approach, we show that both the size and the stability of such light-sustained dielectric bridge can be qualitatively explained. We present a ray optics model that encompasses the competition between surface tension effects and optical radiation pressure arising from total internal reflection inside the bridge. A critical power below which a liquid bridge can no longer be sustained by light is predicted and confirmed experimentally. The observed power dependence of the bridge diameter also agrees with the proposed stabilization mechanism. [ABSTRACT FROM AUTHOR]

Bernard Soulier Syndrome (BSS) is a rare inherited bleeding disorder caused by a defect in the glycoprotein (GP)Ib/IX/V complex. A patient with a bleeding problem was diagnosed as having BSS based on the prolonged bleeding time, the absence of ristocetin induced platelet aggregations, thrombocytopenia and the presence of giant platelets. Analysis of the platelets of the propositus, a 39-year-old Belgian female, by flow cytometry revealed a decreased expression of the GPIb/IX polypeptides. Western blotting confirmed these results and showed moreover that there was a decreased disulfide bridge formation between GPIbα and GPIbβ. After sequence analysis of the GPIbα, GPIbβ and GPIX genes, only a mutation in the GPIX gene at position 1826 (A→G) was identified, changing Asn45→Ser. Restriction analysis with Fnu4H1 demonstrated that the patient was homozygous for this mutation. As this Asn45→Ser mutation in the GPIX gene was already found in four unrelated families, i.e. in a British, Austrian, Swedish and Finnish one, the occurrence of this mutation in a Belgian patient supports the hypothesis of Koskela et al. (1999) that the Asn45Ser mutation in GPIX appears to be an ancient mutation shared by northern and central European populations. Our present observation of a decreased disulfide bridge formation between GPIbα and GPIbβ shows that GPIX is not only needed for the correct assembly of the complex but might also be needed for the disulfide bridge formation between GPIbα and GPIbβ. [ABSTRACT FROM AUTHOR]

A particular case of marginal zone B-cell lymphoma (MZBCL) presenting with leukemic lymphocytes is reported. In the present observation, the leukemic cells not only displayed a remarkable morphological fluctuation but also had an unusual phenotype, changing with time. These phenotypic features, which have been functionaly investigated by in vitro assays, might simply reflect an activation state depending on the microenvironment. Because of its disconcerting similarities with hairy cell leukemia (HCL) and splenic lymphoma with villous lymphocytes (SLVL), this case relaunches the debate about whether close relationships might exist between the splenic marginal zone, SLVL and HCL. [ABSTRACT FROM AUTHOR]