Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R9: Bubbles VI: Nanobubbles and Acoustics |
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Chair: Jiansheng Feng, Massachusetts Institute of Technology Room: 333 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R9.00001: Generation and acoustic characterization of monodisperse lipid-coated microbubbles Miguel A. Parrales, Juan M. Fernandez, Miguel Perez-Saborid The acoustic attenuation spectrum for different lipid-coated microbubble suspensions was measured in order to characterize the linear acoustic behavior of ultrasound contrast agents. For that purpose, microbubbles were generated with a very narrow size distribution by using microfluidics techniques operated at two different regimes: flow-focusing and co-flow. We show that monodisperse agents optimize the acoustic echo response by narrowing the attenuation spectrum, which presents a maximum peak for a frequency value corresponding to that of the single bubble resonance. In consequence, the low polydispersity index of our samples increases the accuracy in the estimation of the lipid shell viscoelastic properties. As it has been reported, the non-linear behavior of the coating makes the viscoelastic parameters to change with the equilibrium bubble radius. Our experimental procedure permits the acoustic measurements to be acquired for virtually single-sized suspensions of bubbles, thus reducing the uncertainty in the estimation when using samples with a broad size distribution. The results show the great advantage of dealing with monodisperse populations rather than polydisperse for the acoustic characterization of ultrasound contrast agents. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R9.00002: Theory and simulation of linear wave propagation in bubbly liquids accounting for direct bubble-bubble interactions Daniel Fuster, Hugo Marcus, Jean-Marc Conoir, Tim Colonius, Francois Coulouvrat The effect of direct bubble-bubble interactions in the response of bubble clusters remains relatively unexplored. In this work we extend the classical linear theory of wave propagation in bubbly liquids [1] to account for the effect of bubble-bubble interactions on the attenuation and the phase speed of acoustic waves. The results are tested against new simulation results obtained by applying the model presented by Fuster \& Colonius [2], which is able to capture the effect of direct bubble-bubble interactions. The results are also compared against data previously reported in the literature.\\[4pt] [1] Linear pressure waves in bubbly liquids: Comparison between theory and experiments. K.W. Commander and A. Prosperetti. J. Ac. Soc. Am. 85. 732-746. 1989.\\[0pt] [2] Modeling bubble clusters in compressible liquids. D. Fuster and T. Colonius. J. Fluid Mech. 688. 352-389. 2011. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R9.00003: Realtime Visualization of Surface Nanobubbles Formation Manish Arora, Chon U. Chan, Claus-Dieter Ohl Nanobubbles nucleate and reach a stable state on the solid-liquid interface after ethanol-water exchange. Understanding the thermodynamic stability beyond their formation requires observation of their dynamical response. Total internal reflection microscopy [1] allows resolving the dynamics of nanobubbles, i.e. their formation, shrinkage, and coalescence. While the lateral resolution is limited by diffraction, their tens of nanometer height profile can be nicely resolved. Here we report on nanobubble dynamics induced by the exchange process in a microfluidic channel on a glass surface.. The water-ethanol mixing results in non-monotonic changes in the refractive index of the medium which can be inferred from TIRF images. Formation of attached nanobubbles at 50 frames per second is observed during the transition from water-to-ethanol as well as ethanol-to-water. Bubbles dissolve within a second in ethanol but persist in water. Though new nanobubbles keep appearing over several seconds, no further change in their size is observed. However, we find occasionally spontaneous merging of neighbouring nanobubbles which we relate to the liquid flow. \\[4pt] [1] Chan and Ohl, Phys. Rev Lett. 109, 174501 (2012) [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R9.00004: On the Surface Tension of Nanobubbles Haim Bau, Joseph Grogan, Michael Norton, Frances Ross Using our custom-made liquid cell, the nanoaquarium [1], we imaged with a transmission electron microscope the formation, growth, and detachment of single nanobubbles, nucleating in a supersaturated aqueous solution [2]. The supersaturation results from electron-induced radiolysis of water. The bubbles are first observed when their radii are about 20nm and detach when their radii are about 200nm. Based on our experimental data, we determined the bubbles' growth rates as functions of time, and found the growth rates to be highly reproducible and nearly independent of time (and bubbles' radii). Comparison of the theoretical predictions for bubble growth rate with our experimental observations suggests that the surface tension of the bubble-liquid interface must depend on the bubble's radius. \\[4pt] [1] Grogan J., and Bau, H., H., 2010, IEEE/ASME Journal of Microelectromechanical Systems 19 (4) 885-894.\\[0pt] [2] http://arxiv.org/abs/1210.3380 [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R9.00005: Observations of Nanobubble Dynamics with Transmission Electron Microscopy Meera Kanakamma Mohan, Manish Arora, Utkur Mirsaidov, Claus-Dieter Ohl Recent developments in transmission electron microscopy (TEM) allow the imaging of liquids with high spatial resolution. Here we report on novel studies of water trapped between two monolayers of graphene sheets. The geometry prevents evaporation of the liquid into the low pressure environment of the TEM while providing excellent electron-optical properties for investigations. The graphene sheets are supported by a conventional TEM grid. We report on the nucleation of bubbles, the coalescence between neighbouring bubbles, rupture of thin liquid filaments, and their slow shrinkage. At a dose rate of 100-155~e$^{-}${\AA}$^{-2}$s$^{-1}$ these events are observed conveniently at video frame rate. The correlation with the local electron beam dose rate suggests that the radiolysis induced by the electron beam is the main driving force for most events. In general, we observed bubbles with lateral sizes between 20nm and 100nm and estimated heights between 6nm and 30nm. Likely, the bubbles connect both graphene sheets. In the absence of the electron beam the nanobubbles do not dissolve completely but surprisingly remain stable for even up to one hour. This resembles the stability of surface attached nanobubbles. [Preview Abstract] |
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