Bubble Assembly Research Articles

A Double Bubble Assembly as a New Phase of a Ternary Inhibitory System

A ternary inhibitory system is a three component system characterized by two properties: growth and inhibition. A deviation from homogeneity has a strong positive feedback on its further increase. In the meantime a longer ranging confinement mechanism prevents unlimited spreading. Together they lead to a locally self-enhancing and self-organizing process. The model considered here is a planar nonlocal geometric problem derived from the triblock copolymer theory. An assembly of perturbed double bubbles is mathematically constructed as a stable stationary point of the free energy functional. Triple junction, a phenomenon in which the three components meet at a single point, is a key issue addressed in the construction. Coarsening, an undesirable scenario of excessive growth, is prevented by a lower bound on the long range interaction term in the free energy. The proof involves several ideas: perturbation of double bubbles in a restricted class; use of internal variables to remove nonlinear constraints, local minimization in a restricted class formulated as a nonlinear problem on a Hilbert space; and reduction to finite dimensional minimization. This existence theorem predicts a new morphological phase of a double bubble assembly.

Soluble Polymer-Based, Blown Bubble Assembly of Single- and Double-Layer Nanowires with Shape Control

We present here an efficient blown bubble method for large-scale assembly of semiconducting nanowires, with simultaneous control on the material shape. As-synthesized Te nanowires in powder form are dispersed in a polymethylmethacrylate (PMMA) solution, assembled in a large size bubble blown from the solution, and then transferred (repeatedly) to arbitrary substrates. By this way, we have obtained single-layer (aligned) and double-layer (crossed) Te nanowires as well as buckled Te nanosprings which are converted from initially straight nanowires in situ during bubble blowing. The PMMA bubble film can be removed by direct dissolution in acetone to expose nanostructures with clean surface while maintaining original configuration. After matrix removal, these clean nanowire and nanospring arrays can be fabricated into functional nanoelectronic devices such as photodetectors and gas sensors with high performance.

Methods for studying biofilm formation: flow cells and confocal laser scanning microscopy.

In this chapter methods for growing and analyzing biofilms under hydrodynamic conditions in flow cells are described. Use of flow cells allows for direct microscopic investigation of biofilm formation. The flow in these chambers is essentially laminar, which means that the biofilms can be grown under highly controlled conditions, and that perturbations such as addition of antibiotics or change of the growth medium can be done efficiently at a defined time point. The protocol includes construction of the flow cell and the bubble trap, assembly and sterilization of the flow cell system, inoculation of the flow cells, running of the system, confocal laser scanning microscopy and image analysis, and disassembly and cleaning of the system.

Study of the properties of bubbly flows in Boger-type fluids

Experiments were conducted to study the properties of bubbly flows in elastic fluids with nearly constant viscosity (Boger-type fluids). The effect of gas volume fraction was investigated by injecting bubbles with a narrow size distribution in a vertical column filled with the test fluid. It was found that the dispersion of bubble changes dramatically depending on the bubble size: if the diameter of the bubbles is small, large vertical clusters are formed; on the other hand, the bubble assembly rises in a dispersed manner if the bubble size is increased. To understand the condition for which agglomeration occurs two additional experiments were conducted: the interaction of two side-by-side bubble chains was analyzed; and, the unsteady behavior of the first normal stress difference was studied in a rheometric flow. These analysis suggest that there is a process of accumulation of elastic stress. When the accumulated elastic stress surpasses the viscous repulsive stress, aggregation can occur. Interestingly, the critical diameter at which the bubble dispersion was observed to occur is close to that for which the velocity of an isolated bubble becomes discontinuous: the so-called bubble velocity discontinuity. This suggests that both phenomena share the same fundamental nature. We attributed the change of behavior to the modification of the gas–liquid interface.

Growing and Analyzing Biofilms in Flow Chambers

This unit describes the setup of flow chamber systems for the study of microbial biofilms, and methods for the analysis of structural biofilm formation. Use of flow chambers allows direct microscopic investigation of biofilm formation. The biofilms in flow chambers develop under hydrodynamic conditions, and the environment can be carefully controlled and easily changed. The protocols in this unit include construction of the flow chamber and the bubble trap, assembly and sterilization of the flow chamber system, inoculation of the flow chambers, running of the system, image capture and analysis, and disassembly and cleaning of the system. In addition, embedding and fluorescent in situ hybridization of flow chamber-grown biofilms are addressed.

Permeability of a bubble assembly: From the very dry to the wet limit

Bubble assemblies offer the remarkable property of adjusting their packing fraction over three orders of magnitude, thus providing an interesting system for the study of liquid flows through granular matter. Although significant work has been done in several fields of research, e.g., foams, porous media, and suspensions, a complete set of data over such a wide range of porosity ε is still lacking. In this paper, we measure the permeability of a bubbly system in the range 0.1<ε<0.8 and we connect these new data with a recently published set obtained for foams corresponding to ε<0.2 [E. Lorenceau et al., Eur. Phys. J. E 28, 293 (2009)]. Moreover, measurements performed with two different surfactants, the so-called “mobile” and “nonmobile” interfaces, allow us to determine the influence of the bubbles’ surface mobility, which is proved to be a significant parameter up to ε≈0.6, thus well above the bubbles packing fraction. Above ε≈0.6, surface elasticity is fully mobilized over the bubbles’ surface and the behavior of rigid spheres is observed for both solutions. We show that all the permeability values obtained for the bubble assembly with “nonmobile” interfaces are properly described with the Carman–Kozeny model.

Membrane elasticity molds aggregates of simple cells

At first glance, quite a few tissues in simple animals or in the early development look similar to an assembly of soap bubbles. The undeniable appeal of this correspondence, the seemingly elementary surface-tension Hamiltonian, and the prospect of a mechanical model of biological structures have fueled research in the field for over a century. However, the correspondence is far from perfect and the Hamiltonian of soap-froth-like systems hard to solve. Yet the prospects of a physical interpretation of the form of some cell aggregates are good.

Low frequency sound scattering from spherical assemblages of bubbles using effective medium theory

The determination of the acoustic field scattered by an underwater assembly of gas bubbles or similar resonant monopole scatterers is of considerable theoretical and practical interest. This problem is addressed from a theoretical point of view within the framework of the effective medium theory for the case of spherically shaped assemblages. Although being valid more generally, the effective medium theory is an ideal instrument to study multiple scattering effects such as low frequency collective resonances, acoustically coupled breathing modes of the entire assembly. Explicit expressions for the scattering amplitude and cross sections are derived, as well as closed form expressions for the resonance frequency and spectral shape of the fundamental collective mode utilizing analytical S-matrix methods. This approach allows, in principle, a simultaneous inversion for the assembly radius and void fraction directly from the scattering cross sections. To demonstrate the validity of the approach, the theory is applied to the example of idealized, spherically shaped schools of swim bladder bearing fish. The analytic results of the theory are compared to numerical first-principle benchmark computations and excellent agreement is found, even for densely packed schools and frequencies across the bladder resonance.

Water electrolysis under microgravity: Part II. Description of gas bubble evolution phenomena

Water electrolysis is carried out in both alkaline (25 and 2 wt.% KOH) and acidic (0.1N H 2SO 4) solutions for 8 s under a microgravity (μ-G) environment realized in a drop shaft. The effects of gravitational strength on gas bubble evolution behavior are analyzed in consideration of various factors (bubble movement, bubble assembly and single bubble). Under a μ-G environment, a collection of fine gas bubbles forms a froth layer in alkaline solutions, whereas bubbles frequently coalesce in acidic solution. Moreover, H 2 gas bubbles in alkaline jump from a cathode surface and O 2 bubbles often coalesce on an anode. In acidic solution both H 2 and O 2 bubbles frequently coalesce on electrode surfaces. Such gas bubble movements are reflected in the coalescence number and bubble residence time. A single bubble is characterized by the bubble size and the dynamic contact angle between a gas bubble and a Pt electrode, however, these factors are not essentially influenced by the gravitational strength.

Growing and Analyzing Biofilms in Flow Cells

The setup of flow cell systems for the study of microbial biofilms and methods for the analysis of structural biofilm development are described in this unit. Use of flow cells allows direct microscopic investigation of biofilm development. The biofilms in flow cells develop under hydrodynamic conditions, and the environment can be carefully controlled and easily changed. The protocols in this unit include construction of the flow cell and the bubble trap, assembly and sterilization of the flow cell system, inoculation of the flow cells, running of the system, image capture and analysis, and disassembly and cleaning of the system. In addition, embedding and fluorescent in situ hybridization of flow cell-grown biofilms are addressed.

The bubble cloud as an N-degree of freedom harmonic oscillator

The dynamics of a two-dimensional N-bubble static cloud is investigated and shown to be well described by an N-degree of freedom harmonic oscillator model, at least at low enough frequencies. Eigenmodes and eigenfrequencies are calculated and compared with experimental results obtained with an assembly of bubbles caught up under a net in a water tank. Accordance is found to be excellent in the frequency range of validity of the model, the limits of which are discussed. An interpretation of the low-frequency branch of Foldy's dispersion relation in bubbly liquids is suggested in terms of "bubble waves" in a quasi-incompressible medium.

Formation of conducting clusters of polyaniline films detected by light scattering

Abstract As a polyaniline film was irradiated by a laser with 668 nm in acidic solution, the light was dispersed by Rayleigh scattering when a negative potential was applied to the film. From the angular dependence of the scattering light intensity which was detected with a photo-diode on an x – y stage, clusters 4 to 5 μm in average diameter were detected. The size was estimated by applying the theory of interference of the light scattering at large particles. A pattern like an assembly of bubbles was found through an optical microscope only at negative potentials. It was also found when the chemically reduced film was exposed to air. When 1-methyl-2-pyrrolidone, a solvent of polyaniline, was mixed with water as a solvent in the electrochemical scattering experiment, the intensity decreased with an increase in the molar ratio of 1-methyl-2-pyrrolidone, being more than the loss of the film by dissolution. The size of the clusters increased linearly with the logarithm of the electrochemical reduction time. This is the slow relaxation or the memory effect of conducting polymers. The cluster was thought to be an aggregation of the conducting species.

Direct numerical simulation of the acoustic behavior of bubble clouds

The description of a bubble assembly, or cloud, by means of an ‘‘effective medium’’ approximation has found widespread application in the underwater acoustics community. In this approach the bubbly liquid is regarded as a continuum endowed with properties different from those of the pure liquid. In this study the effective medium results are compared with those of a direct numerical simulation in which the effects of the mutual interaction of the bubbles are simulated. A spherical assembly of bubbles immersed in an incompressible liquid is studied. The potential problem is solved numerically with a singularity expansion method including both volume pulsations and translational oscillations of the bubbles. Numerical results for both single realizations and ensemble averages are presented and discussed. [Work supported by the Office of Naval Research.]

Coherent and incoherent scattering by oceanic bubbles

A substantial amount of research on acoustic scattering by underwater bubbles is based on the theory of incoherent scattering. More recent work, devoted to much denser bubble assemblies, has instead used effective-media formulations that presuppose coherent effects. Here the mutual relationship between the two approaches is elucidated. It is shown that, underlying the incoherent results, is a WKB approximate solution of the effective equations. As an application, the scattering by tenuous subsurface bubble layers and acoustical bubble counting techniques are examined. Significant differences with previous results are found.

Kelvin's conjecture on minimal froths and the counter-example of Weaire and Phelan

Abstract Weaire and Phelan's recent discovery of a clathrate structure (that of β-tungsten) as an ordered minimal froth (space-filling assembly of polyhedral bubbles) with less surface per unit volume than Kelvin's b.c.c. arrangement of truncated octahedra suggests searching among other known tetrahedrally close-packed crystalline phases for a structure with even less surface per unit volume. Two possible candidates are proposed, the α-phase (β-uranium) and the T-phase of Bergman, Waugh and Pauling (1957, Acta crystallogr, 10, 254). A general expression for the energy of tetrahedrally close-packed structures with equal bubble volume is given.

On the form and formation of rubber particles in impact polystyrene and their relationship to natural and synthetic materials

Correlations are drawn between the morphological features of high-impact polystyrene (HIPS), bubble assemblies, adipose tissue, pith and foams. It is concluded that their morphological forms are the same and that similar interfacial tensile forces are responsible for the HIPS morphology as for the others. The synthesis of HIPS, from a solution of rubber in styrene, is discussed in terms of a phase diagram and it is concluded that the mechanism is consistent with the generation of that characteristic morphology throughout the sample in the absence of stirring and in resticted volume elements in the presence of stirring during polymerization of the styrene. An example is quoted of the generation of the same morphology in a blend prepared by mixing immiscible solutions of a homopolymer and a copolymer.

Calculation of aerosol collection in fluidized filter beds

AbstractA method is proposed for calculating aerosol collection in fluidized filter beds. The method employs the bubble assembly model of fluidization and considers the bed to be a series of compartments, each of which comprises two or three phases. Aerosol collection is assumed to occur in these phases in accordance with existing theories of particle deposition. The validity of the method is tested against available experimental data.