Air-filled Bubbles Research Articles

Microbubble-Assisted Cleaning-in-Place Process for Ultrafiltration System and Its Environmental Performance

Membrane filtration is a key technology in dairy processing for the separation of dairy liquids to clarify, concentrate, and fractionate a variety of dairy products. Ultrafiltration (UF) is widely applied for whey separation, protein concentration and standardization, and lactose-free milk production, though its performance can be hindered by membrane fouling. As an automated cleaning process commonly used in the food and beverage industries, cleaning in place (CIP) uses large amounts of water, chemicals, and energy, resulting in significant environmental impacts. This study introduced micron-scale air-filled bubbles (microbubbles; MBs) with mean diameters smaller than 5 μm into cleaning liquids to clean a pilot-scale UF system. During the UF of model milk for concentration, cake formation was identified as the dominant membrane fouling mechanism. The MB-assisted CIP process was conducted at two bubble number densities (2021 and 10,569 bubbles per mL of cleaning liquid) and two flow rates (130 and 190 L/min). For all the cleaning conditions tested, MB addition largely increased the membrane flux recovery by 31-72%; however, the effects of bubble density and flow rate were insignificant. Alkaline wash was found to be the main step in removing proteinaceous foulant from the UF membrane, though MBs did not show a significant effect on the removal due to the operational uncertainty of the pilot-scale system. The environmental benefits of MB incorporation were quantified by a comparative life cycle assessment and the results indicated that MB-assisted CIP had up to 37% lower environmental impact than control CIP. This is the first study incorporating MBs into a full CIP cycle at the pilot scale and proving their effectiveness in enhancing membrane cleaning. This novel CIP process can help reduce water and energy use in dairy processing and improve the environmental sustainability of the dairy industry.

Measuring biofoam anisotropy using optical coherence tomography

Optical coherence tomography enables quick scans of translucent objects in a simple environment. Here, we apply this technique to wood-based biofoam. We measure the geometrical properties of the foam, such as bubble eccentricity and density fluctuations, in addition to characterising the possible orientation of fibres. We find that the wood-based foams are extremely suitable for optical coherence tomography due to their translucent nature and large changes of optical density between air-filled bubbles and solid films. Measurement of bubble eccentricity revealed a reasonably high aspect ratio of 1:2, enabling the orientation of long cellulose fibres if added to the mixture. The results demonstrate an effective method to characterise foamlike metamaterials. Furthermore, focusing on eccentricity enables the adjustment of the foam’s manufacturing method and, in turn, helps to produce anisotropic structures.Graphical abstract

A facile approach to achieve subambient radiative cooling through aluminum foils and polyethylene bubble wrap

Subambient radiative cooling is an emerging passive cooling strategy that simultaneously reflects the incident solar irradiance to depress the heat gain and radiates heat from objects to enhance the heat loss without any electricity consumption from compressor-based air-conditioning. Although numerous efforts have been dedicated to developing materials, such as complicated photonic crystals and metamaterials or expensive polymer composites with both high solar reflectance and infrared emittance, the gap still exists between efficient radiative cooling performance and an affordable radiative cooling device. Here, a facile, low-cost, and home-built approach to achieve efficient subambient radiative cooling, which employs commercially available materials of the polyethylene (PE) bubble wrap and aluminum foils, is reported for scalable industrial and domestic applications. The aluminum foils are infrared-reflective and sunlight-opaque, acting as a solar shield and infrared waveguide, which can both block the solar irradiation and guide infrared thermal radiation to the cold outer space. PE thin film is infrared-transparent with a high mid-infrared transmittance that allows mid-infrared thermal radiation to pass through. It is thermally insulating with a low thermal conductivity of 0.038 W/m ⋅ K after being fabricated into air-filled bubbles to minimize parasitic non-radiative heat transfer. An average subambient temperature reduction of 4.0°C has been achieved during the noontime in summer. These commercially available materials make this design a practical technique for people to realize an affordable and comfortable interior environment during the summer in a cost-effective manner without any professional constructions. The nature of low-cost, home-built, and easily integrated into buildings renders it attractive for everyone, especially for those in developing regions.

NUMERICAL INVESTIGATION OF MICROSTRUCTURE EFFECT ON ACOUSTIC PROPERTIES OF UNDERWATER ANECHOIC COATINGS

This paper presents a simulation-based model for predicting the acoustic properties of underwater anechoic structures with its main layer made of viscoelastic sound absorbing materials including air-filled cavities. Some preliminary numerical results are first compared with the published analytical and experimental data to validate the proposed modeling. Then, a developed design of anechoic using two arrays of air-filled bubbles is considered. It is observed from the investigation results that the new coating shows an interesting sound absorbing performance (i.e., absorbing > 80% incident energy in a large frequency range 25 MHz) compared with the original one having a single air cavity array. The developed structure allows broadening and tailoring their acoustic performance (peak frequency and averaging level) by tuning some microstructural parameters of the air-filled cavity (shape and size) and its distribution (location and fraction).

Air-Filled Bubbles Stabilized by Gold Nanoparticle/Photodynamic Dye Hybrid Structures for Theranostics.

Microbubbles have already reached clinical practice as ultrasound contrast agents for angiography. However, modification of the bubbles’ shell is needed to produce probes for ultrasound and multimodal (fluorescence/photoacoustic) imaging methods in combination with theranostics (diagnostics and therapeutics). In the present work, hybrid structures based on microbubbles with an air core and a shell composed of bovine serum albumin, albumin-coated gold nanoparticles, and clinically available photodynamic dyes (zinc phthalocyanine, indocyanine green) were shown to achieve multimodal imaging for potential applications in photodynamic therapy. Microbubbles with an average size of 1.5 ± 0.3 μm and concentration up to 1.2 × 109 microbubbles/mL were obtained and characterized. The introduction of the dye into the system reduced the solution’s surface tension, leading to an increase in the concentration and stability of bubbles. The combination of gold nanoparticles and photodynamic dyes’ influence on the fluorescent signal and probes’ stability is described. The potential use of the obtained probes in biomedical applications was evaluated using fluorescence tomography, raster-scanning optoacoustic microscopy and ultrasound response measurements using a medical ultrasound device at the frequency of 33 MHz. The results demonstrate the impact of microbubbles’ stabilization using gold nanoparticle/photodynamic dye hybrid structures to achieve probe applications in theranostics.

Optoacoustic/Fluorescent/Acoustic Imaging Probe Based on Air-Filled Bubbles Functionalized with Gold Nanorods and Fluorescein Isothiocyanate.

Liquid/surfactant/gas interfaces are promising objects for nanoengineered multimodal contrasts, which can be used for biomedical imaging in preclinical and clinical applications. Microbubbles with the gaseous core and shell made of lipids/proteins have already acted as ultrasound (US) contrast agents for angiography. In the present work, microbubbles with a shell composed of Span 60 and Tween 80 surfactants functionalized with fluorescein isothiocyanate and gold nanorods to achieve a multimodal combination of US, fluorescence, and optoacoustic imaging are described. Optimal conditions for microbubble generation by studying the surface tension of the initial solutions and analyzing the size, stability, and charge of the resulting bubbles were found. By controlling and modifying bubbles’ surface properties, an increase in stability and storage time can be achieved. The functionalization of bubbles with gold nanoparticles and a dye by using an optimally selected sonication protocol was performed. The biomedical application’s potential in imaging modalities of functionalized microbubbles using a medical US device with a frequency of 50 MHz, fluorescence tomography, and raster-scanning optoacoustic mesoscopy measurements was evaluated. The obtained results are important for optimum stabilization and functionalization of gas/liquid interfaces and the following applications in the multimodal biomedical imaging.

Sistem Pakar dengan Metode Certainty Factor dalam Analisis Penyakit Herpes Zoster pada Manusia

Herpes zoster atau cacar api adalah suatu infeksi yang disebabkan oleh virus varicella zoster. Penyakit Herpes Zoster disebut juga cacar api karena akan muncul lepuhan pada kulit berupa garis atau area kecil disalah satu sisi wajah atau tubuh dan rasanya cukup panas seperti terbakar. Biasanya penderita mengalami keluhan berupa bercak kemerahan dan muncul gelembung-gelembung berisi air. Merancang sistem pakar agar dapat membantu user dalam mengenali gejala awal penyakit Herpes Zoster, serta mengetahui jenis penyakit Herpes Zoster yang mana dideritanya melalui hasil konsultasi secara langsung lewat sistem. Data yang digunakan dalam penelitian ini diperoleh dari hasil wawancara secara langsung dengan pakar yaitu dr.Qaira Anum Sp.KK dirumah sakit RSI. Ibnu Sina Padang selaku dokter spesalis penyakit kulit dan kelamin. Data yang diperoleh berupa data jenis penyakit Herpes Zoster, gejala dari masing-masing jenis penyakit Herpes Zoster, bobot dari masing-masing gejala yang ada, dan solusi atau pencegahan dari masing-masing jenis penyakit Herpes Zoster. Serta dalam penelitian ini dibantu dengan menggunakan metode Certainty Factor agar dapat mempermudah dalam proses penentuan jenis penyakit Herpes Zoster apa yang diderita oleh user yang melakukan konsultasi melalui sistem berdasarkan dari gejala yang dirasakan oleh masing-masing user. Hasil dari pengujian terhadap metode ini adalah terdapat 100% dari 10 data pengujian. Berdasarkan akurasi dari hasil identifikasi terhadap sistem ini, maka penelitian ini sangat tepat dalam tingkat mengidentifikasi tingkat akurasi penyakit Herpes Zoster pada manusia. Sistem pakar pengujian telah dapat mengidentifikasi penyakit Herpes Zoster secara spesifik. Melalui metode Certainty Factor ini, tingkat akurasi yang di dapat cukup akurat dan dapat membantu dokter hewan dalam meningkatkan akurasi untuk mengidentifikasi penyakit Herpes Zoster pada manusia.

Characterization of Submicron Bubbles Formed by the Hydrophobin Cerato-ulmin.

Cerato-ulmin is a fungal hydrophobin protein with a high surface activity due to its amphipathic nature. When aqueous dispersions are gently agitated by hand, cerato-ulmin (CU) assembles into cylindrical bubbles visible in an optical microscope. After approximately 1 h the larger micron-sized bubbles rise out of the solution, leaving only submicron particulates, which persist indefinitely. Dynamic light scattering experiments show that these persistent particles shrink when positive air pressure is applied to the suspension and expand when vacuum is applied. Small-angle X-ray scattering at ambient pressure suggests an extended core-shell structure, consistent with small air-filled bubbles stabilized by a protein film. A comparison between the SAXS of the persistent submicron bubbles and AFM of the buoyant larger bubbles found immediately after agitation show that both have similar film thickness of 13-15 nm or five protein molecules. The extended shapes confirm the solid-like properties of these CU membranes, even in submicron particulate structures, consistent with microtensiometry results on interfacial CU membranes.

Measurements of resonance frequencies and damping of large encapsulated bubbles in a closed, water-filled tank

The ultimate goal of this work is to accurately predict the resonance frequencies of large (on the order of 10 cm radius) tethered encapsulated bubbles used in an underwater noise abatement system, and also to investigate ways to enhance the system’s efficacy over the use of air-filled bubbles alone. Toward that end, a closed water-filled tank was developed for the purpose of measuring the resonance frequency and damping of single large tethered encapsulated bubbles. The tank was designed to be operated in the long wavelength limit for frequencies below the lowest tank resonance, which was chosen to be 500 Hz, using the method described be Leighton, et al. [J. Acoust. Soc. Am. 112, 1366--1376 (2002)]. Individual bubble resonance frequencies and Q-factors were measured for encapsulated bubbles of various sizes. The effects of the encapsulating material and wall thickness were investigated, along with the effects of alternative fill gases and internal heat transfer materials. Experimental results are compared with an existing predictive model [J. Acoust. Soc. Am. 97, 1510--1521 (1995)] of bubble resonance and damping. [Work supported by Shell Global Solutions.]

Nonlinear property of slightly compressible media permeated with air-filled bubbles

Based on the nonlinear oscillation of an air-filled bubble in weakly compressible media at prestressed state, the effective medium method is used to study the nonlinear property of the slightly compressible media permeated with air bubbles. It is this nonlinear oscillation of air bubbles that results in the nonlinear property of the porous media. Numerical results have confirmed that the nonlinearity of the porous media is usually high, though the optimal porosity is very small. Moreover, the nonlinear property is greatly affected by the prestressed state, porosity, and shear modulus of the matrix media.

Effective medium method of slightly compressible elastic media permeated with air-filled bubbles

An effective medium method is developed for the slightly compressible elastic media permeated with air-filled bubbles, according to the nonlinear oscillation of the bubble, which happens when compressional wave travels through the porous media. The effective Lame coefficients of the porous medium and the nonlinear elastic wave equation are deduced, based on the fact that the micro-unit of the effective medium should have the same stress and strain as the micro-unit of the porous media. The linearized properties obtained by this method are in good agreement with the results of Gaunaurd’s classic theory [Gaunaurd G.C. and Uberall H., J. Acoust. Soc. Am., 1978, 63: 1699–1711]. Furthermore, the nonlinear coefficient, which is an important property of the porous media, can also be acquired by this method.

Influence of the surrounding pressure on acoustic properties of slightly compressible porous media permeated with air-filled bubbles

The effective wave velocity, attenuation, and nonlinear properties of slightly compressible porous media permeated with air-filled bubbles are studied numerically by employing the nonlinear Hooke’s law for different surrounding pressures. Numerical simulations show that the acoustic properties of porous media are greatly affected by the surrounding pressure if the shear modulus of the elastic medium is very small due to the fact that the acoustic wave propagation in porous media are strongly influenced by the nonlinear oscillation of bubbles; moreover, the oscillation of a bubble depends on the equilibrium bubble radius, which is affected by the surrounding pressures.

Nanobubble Formation at the Solid-Liquid Interface Studied by Atomic Force Microscopy

AbstractThe formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase. While nanobubbles do not form on flat hydrophilic (silicon oxide wafer) surfaces immersed in water, they appear spontaneously at the interface of water against smooth, hydrophobic (silanized wafer) surfaces. From the experimental observations we draw the conclusion that the features observed in the AFM images are deformable, air-filled bubbles. In addition to the hydrophobicity of the solid surface, differences in solubility of air between two miscible fluids can also lead to formation of nanobubbles. We observe that nanobubbles appear at the interface of water against hydrophilic silicon oxide surfaces after in-situ mixing of ethanol and water in the fluid-cell.The shapes of the nanobubbles are well approximated by spherical caps, with width much larger than the height of the caps. We quantify the morphological distribution of nanobubbles by evaluating several important bubble parameters including surface coverage and radii of curvature. In conjunction, with an analytical model available in the literature, we use this information to estimate that the present nanobubble morphology may give rise to slip lengths ∼1–2 µm in pressure driven flows for water flowing over the hydrophobic surface. The consistency of the calculated slip length with the experimental values reported in the literature, suggests that the apparent fluid slip observed experimentally at hydrophobic surfaces may arise from the presence of nanobubbles.

Proteinaceous bubble and nanoparticle flows in microchannels

Proteinaceous bubbles of 185 nm average diameter were synthesized by a sonochemical treatment of bovine serum albumin (BSA) in an aqueous solution and the nanoparticles (TiO2) solution was made by ultrasonic irradiation. To study the macroscopic flow behavior associated with the changes in the state of the microparticles, a flow test of these solutions in microchannels was done. Also, the size distributions of the proteinaceous bubbles in solution before and after the flow test were measured by a light scattering method. Test results show that the air-filled proteinaceous bubbles in solution adjust their size to reduce the shear stress encountered in the flow through the microchannel. On the other hand, the mass flow rate of the solution with nanoparticle suspensions becomes smaller than that of deionized water in a microchannel of dimension 100×100 μm2.

Phase transition and acoustic localization in arrays of air bubbles in water

Wave localization is a ubiquitous phenomenon. It refers to situations that transmitted waves in scattering media are trapped in space and remain confined in the vicinity of the initial site until dissipated. Here, we report a phase transition from acoustically extended to localized states in arrays of identical air-filled bubbles in water. It is shown that the acoustic localization in such media is coincident with the complete band gap of a corresponding lattice arrangement of the air bubbles. When the localization or the band gap occurs, a collective behavior of the bubbles appears, a unique feature differentiating the localization effect from the residual absorption effect.

Phase order and energy localization in acoustic propagation in random bubbly liquids

Propagation of acoustic waves in liquid media containing many air-filled bubbles is studied using a self-consistent approach. It is shown that under proper conditions, multiple scattering leads to a peculiar phase transition in acoustic propagation. When the phase transition occurs, not only the acoustic waves are confined in the neighborhood of the transmitting source, but a previously unsuspected collective behavior of the air bubbles appears, responsible for effective cancellation of the propagating wave. A novel phase diagram method is used to depict the phase transition.

Effect of filling gases on the backscatter from contrast microbubbles: theory and in vivo measurements

Two surfactant-based contrast agents, ST44 and ST68, were produced according to US Patent # 5,352,436 and filled with either air, C 4F 10 (perfluorobutane) or SF 6 (sulfur hexaflouride). Ten rabbits received IV injections of each agent/gas combination with 5 repetitions of each dose (range: 0.005–0.13 mL/kg). A custom-made 10-MHz cuff transducer was placed around the surgically exposed distal aorta and audio Doppler signals were acquired in vivo. Quantitative in vivo dose responses were calculated off-line using spectral power analysis and compared to a theoretical model of microbubble dissolution and enhancement. For qualitative comparisons, 10 rabbits were imaged pre- and postcontrast administration (dose: 0.1 mL/kg) in gray-scale and colour. All agent/gas combinations produced marked Doppler enhancement with air bubbles enhancing least of all ( p < 0.0001) and ST68-SF 6 best of all (maximum: 27.6 ± 2.04 dB; p < 0.012). There were no significant differences between other agent/gas combinations (0.30 < p < 0.70). Theoretical enhancement was within 1 order of magnitude of the experimental observations ( i.e., deviations of up to 10 dB). The duration of contrast enhancement was 1–2 min for air-filled bubbles, 3–5 min for SF 6-filled bubbles and more than 7 min for C 4F 10-filled bubbles. In conclusion, ST68-SF 6 microbubbles produced most in vivo enhancement of the agent/gas combinations studied. Theory matched the measurements within an order of magnitude.

A Numerical Algorithm of the Multiple Scattering from an Ensemble of Arbitrary Scatterers

Sound scattering by a finite number of arbitrary scatterers has remained a complicatedproblems. For this reason, only limited numerical results have been documented in the liter-ature. The main difficulty perhaps has been associated with the lack of efficient numericalalgorithmsandthelimitedcomputingcapability.Amongmanyusefulformalismssuggestedfor describing sound scattering by a finite group of arbitrary scatterers, three approachesappear to be particularly useful, that is, the self-consistent approach [1, 2], theT-matrixmethod [3, 4], and the method of moments [5].The recent expanding capability of digital computers has in principle made it possibleto compute the more complicated problem of multiple scattering from a finite numberof scatterers. Following the self-consistent scheme in Foldy [1], the multiple scatteringprocesses can be represented by a set of coupled linear equations. The solution to theseequations can be obtained by a matrix inversion. Such a procedure has been used previouslyto investigate multiple scattering by isotropic scatterers, especially the acoustic localizationin bubbly liquids in which air-filled bubbles are isotropic scatterers [6]. The purpose ofthis paper is to generalize the numerical matrix method in Ye and Alvarez [6] to morecomplicated cases involving many anisotropic scatterers. It will be clear from the derivationthat the present approach can be used for scattering from many scatterers with arbitraryconfigurations for a wide range of situations.

Localization transition in acoustic propagation in bubbly liquids

In the past, it was suggested that localization can be achieved for acoustic wave propagation in liquids with even a very small concentration of air-filled bubbles. In this paper we present an ab initio numerical investigation of acoustic localization in bubbly liquids. The results show that the localization of acoustic waves is reached when the bubble volume fraction is greater than a threshold value about 10 −5. This is in good agreement with the previous prediction [Sornette, Souillard, Europhys. Lett. 7 (1988) 169].

Acoustic Localization in Bubbly Liquid Media

Acoustic wave propagation in liquid media containing many air-filled bubbles is ab initio considered. A self-consistent method is used to derive a set of coupled equations describing rigorously the multiple scattering of waves in such media. The wave transmission and backscattering are then solved exactly. The numerical results indicate localization of acoustic waves in a range of frequency.