Biomedical subjects

Jean-Pierre Delville

Publications and source records attributed to Jean-Pierre Delville.

7 recordsLinked to original sources

PubMed2006

Bistability of a compliant cavity induced by acoustic radiation pressure.

We report on the first observation of multiple-order bistability due to acoustic radiation pressure in a compliant acoustic cavity formed between a spherical ultrasonic transducer immersed in water and the free liquid surface located at its focus. The hysteretic behavior of the cavity length, observed both with amplitude ramps and frequency sweeps, is accurately described using a one-dimensional model of a compliant Fabry-Pérot resonator assuming the acoustic radiation pressure to be the only coupling between the cavity and the acoustic field.

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PubMed2006

Light-induced deformation and instability of a liquid interface. I. Statics.

We study in detail the deformations of a liquid-liquid interface induced by the electromagnetic radiation pressure of a focused cw laser beam. Using a simple linear model of static equilibrium of the interface under the effect of radiation pressure, buoyancy, and Laplace pressure, we explain the observed hump height variations for any value of the optical Bond number Bo=(omega0/lc)2 (lc is the capillary length and omega0 is the waist of the beam) in the regime of weak deformations and show that the deformations are independent of the direction of propagation of the laser. By increasing the beam power, we observe an instability of the interface leading to the formation of a long jet when the laser propagates from the more refringent phase to the less refringent one. We propose that the total internal reflection of the incident light on the highly deformed interface could be at the origin of this instability. Using a nonlinear model of static equilibrium of the interface taking account of the angular dependance of radiation pressure, we explain the measured beam power threshold of the instability P, as well as the shape of the interface deformations observed at large waists just below the instability onset. According to this model, the instability should occur when the interface slope reaches the angle of total reflection, theta(TR). We find experimentally that, just below the instability threshold, the maximum incidence angle along the interface, theta(imax), is significantly smaller than theta(TR) and that our nonlinear model does not present any instability up to theta(imax)=theta(TR). Thus, although the proposed instability model correctly predicts the instability threshold P, it fails to describe the actual instability mechanism. We finally discuss possible additional effects that could explain the instability.

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PubMed2006

Light-induced deformation and instability of a liquid interface. II. Dynamics.

We study the dynamics of the deformation of a soft liquid-liquid interface by the optical radiation pressure of a focused cw Gaussian laser beam. We measured the temporal evolution of both the hump height and the hump curvature by direct observation and by detecting the focusing effect of the hump acting as a lens. Extending the results of Yoshitake [J. Appl. Phys. 97, 024901 (2005)] to the case of liquid-liquid interfaces and to the Bo approximately =1 regime [Bo=(omega0/lc)2, , where omega0 is the beam waist and lc the capillary length], we show that, in the Bo<<1 and Bo approximately =1 ranges, the small-amplitude deformations are correctly described by a linear hydrodynamic theory predicting an overdamped dynamics. We also study the dynamics of the large-amplitude interface deformations at the onset of optohydrodynamic instability [Phys. Rev. Lett. 90, 144503 (2003)]. Using a simple, phenomenological model for the nonlinear evolution of the hump height, we interpret the observed interface dynamics at the instability onset as the signature of an imperfect subcritical instability.

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PubMed2005

Growth of monodisperse mesoscopic metal-oxide colloids under constant monomer supply.

In closed systems, control over the size of monodisperse metal-oxide colloids is generally limited to submicrometric dimensions. To overcome this difficulty, we explore the formation and growth of silica particles under constant monomer supply. The monomer source is externally driven by the progressive addition into the system of one of the precursors. Monodisperse spherical particles are produced up to a mesoscopic size. We analyze their growth versus the monomer addition rate at different temperatures. Our results show that in the presence of a continuous monomer addition, growth is limited by diffusion over the investigated temporal window. Using the temperature variation of the growth rate, we prove that rescaling leads to a data reduction onto a single master curve. Contrary to the growth process, the final particle's size reached after the end of the reagent supply strongly depends on the addition rate. The variation of the final particle size versus addition rate can be deduced from an analogy with crystal formation in jet precipitation. Within this framework, and using the temperature dependences of both the particle growth law and the final size, we determine the value of the molecular heat of dissolution associated to the silica solubility. These observations support the fact that classical theories of phase-ordering dynamics can be extended to the synthesis of inorganic particles. The emergence of a master behavior in the presence of continuous monomer addition also suggests the extension of these theories to open systems.

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PubMed2004

Kinetic control of surface patterning by laser-induced photochemical deposition in liquid solutions. I. Theoretical developments.

We theoretically analyze the real-time formation of holographic grating driven by laser-photochemical deposition in liquid solutions. Considering the one-photon excitation of a two-level system, we present a reaction/diffusion description of the species produced photochemically by the excitation of a continuous laser wave. By assuming that a deposit is heterogeneously nucleated on the substrate when concentration of the reaction product reaches solubility, we develop a thermodynamic analysis of its late-stage growth under laser irradiation. A rate equation is proposed and used to describe the kinetics of three different types of patterning: dot array, periodic line writing, and holographic grating formed by two interfering beams. In each case, the predicted deposit growth laws show the emergence of scaling regimes that give rise to a universal picture of the processes involved, whatever the initial photosensitive medium is. Due to the crucial role played by patterned coatings in numerous practical applications (lithography or holography, for instance), this control in situ of the kinetics offers the opportunity to totally monitor the desired patterning. It also suggests the way to develop a unified description for holographic grating formation driven by photochemical deposition.

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PubMed2004

Kinetic control of surface patterning by laser-induced photochemical deposition in liquid solutions. II. Experimental investigations.

We experimentally analyze the real-time formation of periodic surface patterning resulting from laser-driven photochemical deposition in liquid solutions. Using photochemical deposition of chromium hydroxide layers driven by a continuous Ar+ laser wave in a potassium chromate solution, we analyze the kinetic formation of three different types of patterning: dot array, periodic line writing, and holographic grating formed by interfering beams. Results are also presented for both flat and curved substrates. In each case, the deposit growth laws are measured and they show the emergence of scaling regimes that are predicted by our model [Phys. Rev. E 69, 051605 (2004)]]. Data taken from literature are also confronted to the model. The observed agreement suggests that a unified picture of the processes involved for photodeposition driven by a one-photon absorption can be devised, whatever the initial photosensitive medium is. This kinetic control of photodeposition, associated to the versatility in monitoring the geometry of laser/medium interaction and the flexibility in deposited materials by various photochemical reactions, offers a valuable level of development in substrate patterning for lithographic or holographic applications.

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PubMed2003

Laser-induced hydrodynamic instability of fluid interfaces.

We report on a new class of electromagnetically driven fluid interface instability. Using the optical radiation pressure of a cw laser to bend a very soft near-critical liquid-liquid interface, we show that it becomes unstable for sufficiently large beam power P, leading to the formation of a stationary beam-centered liquid microjet. We explore the behavior of the instability onset by tuning the interface softness with temperature and varying the size of the exciting beam. The instability mechanism is experimentally demonstrated. It simply relies on total reflection of light at the deformed interface whose condition provides the universal scaling relation for the onset P(S) of the instability.

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