F. Diotallevi

INO - Istituto Nazionale di Ottica, Florens, Tuscany, Italy

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Publications (12)28.13 Total impact

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    ABSTRACT: We study the impact of wall corrugations in microchannels on the process of capillary filling by means of three broadly used methods: computational fluid dynamics (CFD), lattice Boltzmann equations (LBE), and molecular dynamics (MD). The numerical results of these approaches are compared and tested against the Concus-Finn (CF) criterion, which predicts pinning of the contact line at rectangular ridges perpendicular to flow for contact angles of theta > 45 degrees . Whereas for theta = 30, 40 (no flow), and 60 degrees (flow) all methods are found to produce data consistent with the CF criterion, at theta = 50 degrees the numerical experiments provide different results. Whereas the pinning of the liquid front is observed both in the LB and CFD simulations, MD simulations show that molecular fluctuations allow front propagation even above the critical value predicted by the deterministic CF criterion, thereby introducing a sensitivity to the obstacle height.
    Langmuir 10/2009; 25(21):12653-60. DOI:10.1021/la901993r · 4.38 Impact Factor
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    ABSTRACT: The authors investigate the formation of liquid layers at corners of lithographically made microchannels during capillary filling. The microflow and shape of the liquid-air interface is studied through an optically transparent microfluidic device. The experimental findings at early stages of layer formation are supported by three-dimensional lattice Boltzmann simulations, allowing to predict the shape and dynamics of the corner films and highlighting their dependence on the fluid contact angle.
    Applied Physics Letters 04/2009; 94(17):171901-171901-3. DOI:10.1063/1.3123804 · 3.52 Impact Factor
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    ABSTRACT: Numerical simulations of two-dimensional capillary filling using the pseudo-potential lattice Boltzmann model for multiphase fluids are presented. It is shown that whenever the density of the light-phase exceeds about ten percent of the dense phase, the front motion proceeds through a combined effect of capillary advection and condensation.
    The European Physical Journal Special Topics 04/2009; 171(1):237-243. DOI:10.1140/epjst/e2009-01034-6 · 1.76 Impact Factor
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    S. Chibbaro, L. Biferale, F. Diotallevi, S. Succi
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    ABSTRACT: We present a systematic study of capillary filling for a binary fluid by using mesoscopic a lattice Boltzmann model describing a diffusive interface moving at a given contact angle with respect to the walls. We compare the numerical results at changing the ratio the typical size of the capillary, H, and the wettability of walls. Numerical results yield quantitative agreement with the theoretical Washburn law, provided that the channel height is sufficiently larger than the interface width and variations of the dynamic contact angle with the capillary number are taken into account.
    The European Physical Journal Special Topics 04/2009; 171(1):223-228. DOI:10.1140/epjst/e2009-01032-8 · 1.76 Impact Factor
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    Fabiana Diotallevi, Andrea Puglisi, Antonio Lamura, Sauro Succi
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    ABSTRACT: The motion of an air-fluid interface through an irregularly coated capillary is studied by analyzing the Lucas-Washburn equation with inertia, viscosity and a random capillary force. Below a critical velocity, the front enters a strongly intermittent dynamic regime, as recently observed in experiments. Analytical estimates for the average asymptotic front trajectory and pinning length distribution are obtained, and a numerical procedure for predicting quantities of experimental interest is also illustrated.
    Journal of Statistical Mechanics Theory and Experiment 02/2009; 2(02). DOI:10.1088/1742-5468/2009/02/L02001 · 2.06 Impact Factor
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    ABSTRACT: We report on simulations of capillary filling of high-wetting fluids in nano-channels with and without obstacles. We use atomistic (molecular dynamics) and hydrokinetic (lattice-Boltzmann) approaches which point out clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. The dynamics of the precursor films is found to obey a square-root law as the main capillary front, z^2(t) ~ t, although with a larger prefactor, which we find to take the same value for the different geometries (2D-3D) under inspection. The two methods show a quantitative agreement which indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level. This can be considered as a validation of the Lattice-Boltzmann (LB) method and opens the possibility of using hydrokinetic methods to explore space-time scales and complex geometries of direct experimental relevance. Then, LB approach is used to study the fluid behaviour in a nano-channel when the precursor film encounters a square obstacle. A complete parametric analysis is performed which suggests that thin-film precursors may have an important influence on the efficiency of nanochannel-coating strategies. Comment: 16 pages, 8 figures; To be published on JSTAT: Journal of statistical mechanics: Theory and experiments
    Journal of Statistical Mechanics Theory and Experiment 01/2009; 2009(06). DOI:10.1088/1742-5468/2009/06/P06007 · 2.06 Impact Factor
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    ABSTRACT: The dynamics of capillary filling in the presence of chemically coated heterogeneous boundaries is investigated both theoretically and numerically. In particular, by mapping the equations of front motion onto the dynamics of a dissipative driven oscillator, an analytical criterion for front pinning is derived under the condition of diluteness of the coating spots. The criterion is tested against two-dimensional lattice Boltzmann simulations and found to provide satisfactory agreement as long as the width of the front interface remains much thinner than the typical heterogeneity scale of the chemical coating.
    Physical Review E 10/2008; 78(3 Pt 2):036305. DOI:10.1103/PhysRevE.78.036305 · 2.33 Impact Factor
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    ABSTRACT: We present hydrokinetic Lattice Boltzmann and Molecular Dynamics simulations of capillary filling of high-wetting fluids in nano-channels, which provide clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. The dynamics of the precursor films is found to obey the Lucas-Washburn law as the main capillary front, z2(t) proportional to t, although with a larger prefactor, which we find to take the same value for both geometries under inspection. Both hydrokinetic and Molecular Dynamics approaches indicate a precursor film thickness of the order of one tenth of the capillary diameter. The quantitative agreement between the hydrokinetic and atomistic methods indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level, thereby opening the possibility of using hydrokinetic methods to space-time scales and complex geometries of direct experimental relevance. Comment: 11 pages, 6 figures. submitted to PRL
    EPL (Europhysics Letters) 06/2008; 84(4). DOI:10.1209/0295-5075/84/44003 · 2.27 Impact Factor
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    S. Chibbaro, L. Biferale, F. Diotallevi, S. Succi
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    ABSTRACT: We present a systematic study of capillary filling for a binary fluid by using mesoscopic a lattice Boltzmann model describing a diffusive interface moving at a given contact angle with respect to the walls. We compare the numerical results at changing the ratio the typical size of the capillary, H, and the wettability of walls. Numerical results yield quantitative agreement with the Washburn law in all cases, provided the channel lenght is sufficiently larger then the interface width. We also show that in the initial stage of the filling process, transient behaviour induced by inertial effects are under control in our lattice Boltzmann equation and in good agreement with the phenomenology of capillary filling. Finally, at variance with multiphase LB simulations, velocity and pressure profiles evolve under the sole effect of capillary drive all along the channel.
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    ABSTRACT: We present a systematic study of capillary filling for multi-phase flows by using mesoscopic lattice Boltzmann models describing a diffusive interface moving at a given contact angle with respect to the walls. We compare the numerical results at changing the density ratio between liquid and gas phases and the ratio between the typical size of the capillary and the interface width. It is shown that numerical results yield quantitative agreement with the Washburn law when both ratios are large, i.e. as the hydrodynamic limit of a infinitely thin interface is approached. We also show that in the initial stage of the filling process, transient behaviour induced by inertial effects and ``vena contracta'' mechanisms, may induce significant departure from the Washburn law. Both effects are under control in our lattice Boltzmann equation and in good agreement with the phenomenology of capillary filling.
    The European Physical Journal Special Topics 08/2007; DOI:10.1140/epjst/e2009-00889-7 · 1.76 Impact Factor
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    ABSTRACT: A simple model of inelastic hard rods subject to a one-dimensional array of identical wells is introduced. The energy loss due to inelastic collisions is balanced by the work supplied by an external stochastic heat bath. We explore the effect of the spatial nonuniformity on the steady states of the system. The spatial variations of the density, granular temperature, and pressure induced by the gradient of the external potential are investigated and compared with the analogous variations in an elastic system. Finally, we study the clustering process by considering the relaxation of the system starting from a uniform homogeneous state.
    The Journal of Chemical Physics 10/2004; 121(11):5125-32. DOI:10.1063/1.1782812 · 3.12 Impact Factor
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    ABSTRACT: We study the properties of a one-dimensional (1D) granular gas consisting of N hard rods on a line of length L (with periodic boundary conditions). The particles collide inelastically and are fluidized by a heat bath at temperature Tb and viscosity gamma. The analysis is supported by molecular dynamics simulations. The average properties of the system are first discussed, focusing on the relations between granular temperature Tg=mv2, kinetic pressure, and density rho=N/L. Thereafter, we consider the fluctuations around the average behavior obtaining a slightly non-Gaussian behavior of the velocity distributions and a spatially correlated velocity field; the density field displays clustering: this is reflected in the structure factor which has a peak in the k approximately 0 region suggesting an analogy between inelastic hard core interactions and an effective attractive potential. Finally, we study the transport properties, showing the typical subdiffusive behavior of 1D stochastically driven systems, i.e., </x(t)-x(0)/2> approximately Dt(1/2), where D for the inelastic fluid is larger than the elastic case. This is directly related to the peak of the structure factor at small wave vectors.
    The Journal of Chemical Physics 02/2004; 120(1):35-42. DOI:10.1063/1.1630957 · 3.12 Impact Factor