Form Of Microdroplets Research Articles

Multi-Bioinspired Fog Harvesting Structure with Asymmetric Surface for Hydrogen Revolution.

The urgent need for sustainable energy storage drives the fast development of diverse hydrogen production based on clean water resources. Herein, a unique type of multi-bioinspired functional device (MFD) is reported with asymmetric wettability that combines the curvature gradient of cactus spines, the wetting gradient of lotus, and the slippery surface of Nepenthes alata for efficient fog harvesting. The precisely printed MFDs with microscale features, spanning dimensions, and a thin wall are endowed with asymmetric wettability to enable the Janus effects on their surfaces. Fog condenses on the superhydrophobic surface of the MFDs in the form of microdroplets and unidirectionally penetrates its interior due to the Janus effects, and drops onto the designated area with a better fog harvesting rate of 10.64gcm-2 h-1. Most significantly, the collected clean water can be used for hydrogen production with excellent stability and durability. The findings demonstrate that safe, large-scale, high-performance water splitting and gas separation and collection with fog collection based on MFDs are possible.

Novel atomization-assisted phosgenation for TDI synthesis from TDA: A theoretical study on single droplet reactivity

TDI is a highly versatile chemical product with a significant market demand. The state-of-the-art production method is gas phase phosgenation, but it has drawbacks of high energy consumption and unwanted side reactions at high temperatures. In this study, we propose a novel atomization-assisted phosgenation method for TDI synthesis from toluene diamine (TDA) that addresses these limitations. The proposed method involves atomizing TDA in a reactor and introducing in the form of micro-droplets, which reduces the energy consumption required for TDA vaporization and superheating. Through a comprehensive theoretical investigation of droplet reactivity and a comparative analysis of reaction conditions, we have demonstrated that the method proposed in this study has the potential to achieve higher product yield and a reduced probability of side reactions, thus highlighting its superiority over conventional methods. This study demonstrates the feasibility and superiority of the atomization-assisted phosgenation method and its potential application in industrial TDI production.

Preparation and Orthogonal Analysis for Dual-Responsive Electrochromic Polymer Dispersed Liquid Crystal Devices.

In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.

Confined Silver Nanoparticles in Ionic Liquid Films.

This work reports the formation of silver nanoparticles (AgNPs) by sputter deposition in thin films of three different ionic liquids (ILs) with the same anion (bis(trifluoromethylsulfonyl)imide) and cation (imidazolium), but with different alkyl chain lengths and symmetries in the cationic moiety ([C4C1im][NTf2], [C2C2im][NTf2], and [C5C5im][NTf2]). Ionic liquid (IL) films in the form of microdroplets with different thicknesses (200 to 800 monolayers) were obtained through vacuum thermal evaporation onto glass substrates coated with indium tin oxide (ITO). The sputtering process of the Ag onto the ILs when conducted simultaneously with argon plasma promoted the coalescence of the ILs' droplets and the formation, incorporation, and stabilization of the metallic nanoparticles in the coalesced IL films. The formation/stabilization of the AgNPs in the IL films was confirmed using high-resolution scanning electron microscopy (SEM) and UV-Vis spectroscopy. It was found that the IL films with larger thicknesses (600 and 800 monolayers) were better media for the formation of AgNPs. Among the ILs used, [C5C5im][NTf2] was found to be particularly promising for the stabilization of AgNPs. The use of larger IL droplets as capture media was found to promote a better stabilization of the AgNPs, thereby reducing their tendency to aggregate.

Spreading of water microdroplets simulating human sweating in polyester yarns and fabrics

Thermo-physiological comfort of human body is highly influenced by the moisture transmission behaviour of the fabric. For active sportswear, intimate apparels and inner layer of extreme cold weather clothing, moisture transport is very crucial. The liquid moisture transport of fabrics is analysed using standardised test methods like vertical wicking, absorbency test and moisture management through moisture management tester. These test methods use large reservoir of liquid in contrast to human sweating behaviour. The human skin generates sweats in the form of microdroplets through sweating glands. Hence, the standard test procedures employed to assess the fabric’s liquid moisture transport fail to capture preciously the sweat transport from human skin to the fabrics. Hence, in this work, the spreading behaviour of water microdroplets simulating human sweat through yarns which are the building block of fabrics and knitted fabrics that are widely used as sportswear or inner layer of extreme cold weather clothing are investigated. The purpose of this study is to understand how the microfluid move along the capillary channels in yarns (in the forms of network of yarns crossing over each other and fabric) by keeping yarn count and twist same for all yarns. A single micro drop representing accumulated sweat droplets and multiple drops showing continuous sweating through sweat glands were allowed to wick through the yarns made up of coarser and finer fibres to understand the role of fibre diameter on wicking kinetics. Results from the conventional wicking test were compared with microfluidic wicking. It is found that the initial wicking speed in coarser-fibres yarn is faster in comparison to finer-fibres yarn, but the final wicking height is longer in finer fibre yarn. Overall liquid spreading length found to be similar for both the yarns. Yarn to yarn liquid transfer at crossover junctions is faster with finer-fibre yarn compared to coarser-fibre yarn. Same trends are found in fabrics constructed with these yarns. The effect of yarn tortuosity on liquid spreading behaviour has also been studied. As the yarn path becomes torturous (straight yarn to fabric form) wicking length also decreases.

Single Step Metal Nanoparticle Fabrication Using Atmospheric Pressure Plasma Jets

The interaction of atmospheric pressure plasma discharges with liquid or vapour phases is a hot-topic in plasma science and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attracts more attention because of its simplicity and cost effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction reaction of metal salts which leads to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasmas, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and could be achieved by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in vapour phase or from aerosols and in solutions of the precursors. The interface between plasmas and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have employed an atmospheric pressure plasma jet setup operating with a mixture of He and Ar gases to produce gold nanocrystals onto a silicon wafer substrate. In this study, it reveals an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using atmospheric pressure plasma jet working with a high voltage source. A solution of the precursor in water acts as the feed solution for the process which is introduced to plasma in the form of microdroplets and metal nanoparticles were formed inside the plasma from the vapours containing the precursor molecules. Since the plasma-liquid/vapour chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were collected on to a Si wafer substrate downstream of the plasma jet and characterized via scanning electron microscopy, Raman spectroscopy, transition electron microscopy etc. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger microdroplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies on the silicon wafer substrate. These results would lead to the development of low cost and mobile, user-friendly atmospheric pressure plasma devices for the synthesis of nanoparticles without any toxic chemicals for the reduction of metal salt.The challenge in this process is in creating a vapour-plasma interface directly. This problem has been solved by incorporating a vaporizer directly to plasma. The vaporizer would introduce a new phase which would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface an inert gas has been introduced to the vaporizer as a carrier. At the interface, high energy electrons are introduced to the vapors containing the precursor metal ions and these wet electrons play the key role as initiators for the reduction process inside the plasma. Nanoparticles are formed inside the plasma by simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the qualitative analysis carried our during the process implies the formation of short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the residence time of the particles inside the plasma and the population density of the metal ions. Whereas the purity in turn the reduction rate of metal ions are dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.Concisely, atmospheric pressure plasma jets are outstanding choice for the synthesis of gold nanoparticles from chloroauric acid without any external reducing agents. The synthesized gold nanoparticles are promising for different applications because of its geometry and shape. Because of its polygonal geometries the particles are plasmonic active surfaces, the functional for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapour interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed.

Single Step Synthesis and Deposition of Gold Nanoparticles Using Atmospheric Pressure Plasma Jet

The interaction of atmospheric pressure plasma discharges with liquid or vapor phase is a hot topic in plasma nanoscience and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attract wide attention because of its simplicity and cost-effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction of metal salts, leading to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasma, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors, as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in the vapor phase or from aerosols and in solutions of the precursors. The interface between plasma and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have demonstrated an atmospheric pressure plasma jet (APPJ) setup operating with a mixture of He and Ar gases to deposit gold nanocrystals on a silicon substrate. In this study, we revealed an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using an APPJ working with a high voltage source and He gas. Chloroauric acid in water is used as the precursor for the process which is introduced to plasma in the form of micro droplets produced by the insertion of Ar gas to the precursor solution. The metal nanoparticles are formed inside the plasma by the plasma-assisted reduction of precursor molecules. Since the plasma-liquid/vapor chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were deposited on a Si wafer substrate downstream of the plasma jet, and characterized via scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger micro droplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies of gold nanocrystals on the silicon. These results would lead to the development of low cost and mobile, eco-friendly atmospheric pressure plasma devices to synthesis the nanoparticles without any hazardous chemical reducing agents.To create a plasma-vapor interaction, a vaporizer has been employed and the new interaction phase would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface Ar gas has been used to as a carrier. At the interface, high energy electrons play the key role as initiators for the reduction of metal ions inside the plasma. Nanoparticles were formed by a simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the optical emission spectra taken during the process implies the formation OH radicals which may form short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the plasma parameters by controlling the population density of the metal ions. Whereas the purity, in turn, the reduction rate of metal ions, is dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.The application of gold nanoparticles are promising for different applications depends on its geometry and shape. Therefore, the synthesized gold nanoparticles in this work with polygonal geometries can be potential candidates for plasmonic active surfaces for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapor interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed, which will open a new era of plasma-surface interaction.

Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Antimicrobial Susceptibility Testing.

The advent of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) in clinical microbiology has dramatically improved the accuracy and speed of diagnostics. However, this progress has mainly been limited to the identification of microorganisms, whereas the practical improvement of antimicrobial susceptibility testing (AST) still lags behind. MALDI-TOF MS-based approaches include the detection of selected resistance mechanisms and the universal phenotypic AST. This minireview focuses on the discussion of those MALDI-TOF MS methods that allow universal growth-based phenotypic AST. The method of minimal profile change concentrations (MPCC) is based on detecting proteome modification in the presence of an antimicrobial. Using stable-isotope labeling, characteristic mass shifts in the presence of an antimicrobial indicate the incorporation of the isotopic labels, and thus the viability and resistance of the microorganism. For MALDI Biotyper antibiotic susceptibility test rapid assay (MBT-ASTRA), microorganisms are incubated with or without an antimicrobial, followed by cell lysis, protein extraction, and transfer of the cell lysate onto a MALDI target plate. Using the internal standard, peak intensities are correlated to the amount of microbial proteins, and the relative microbial growth is calculated. Most recent development in the field is the direct-on-target microdroplet growth assay (DOT-MGA). Here, incubation of microorganisms with antimicrobials takes place directly on spots of a MALDI target in the form of microdroplets. After incubation, nutrient medium is removed by dabbing with absorptive material. Resistant microorganisms grow despite the presence of antimicrobial, and their amplified biomass is detected by MALDI-TOF MS. Finally, an outlook is provided for further assay improvements.

Optical trapping of organic solvents in the form of microdroplets in water

In this work, we demonstrate the optical trapping of 1,2-dichlorobenzene, chloroform and toluene microdroplets in water. The trapping was done by using near infrared laser with wavelength 915 nm. Power spectrum for the microdroplets at 6.3 MW/cm2 laser power were analysed to obtain the corner frequency. It was found that 1,2-dichlorobenzene had the highest corner frequency at 6.3 MW/cm2 among the three organic solvents. The difference in corner frequency of the organic solvents microdroplets could be associated with their indices of refraction.

Comparison of Laser Sintering of Silver Nanoparticles in Form of Microdroplets of Nanoink and Dry Nanoparticles Obtained in a Gas Discharge

This article presents a comparison of laser sintering of deposited nanoparticles obtained by two methods of aerosol jet printing. The first printing method was based on the use of silver nanoparticles in the form of microdroplets contained in nanoink. In the second method, dry nanoparticles were obtained as a result of gas-discharge synthesis without the use of solvents. The nanoparticles in both experiments were deposited on a glass substrate in the form of a line with a width of about 50 ± 5 μm and a height of about 1.0 ± 0.2 μm. Then, the obtained lines were sintered using laser radiation with a wavelength of 1064 nm. As a result of experiments on the deposition and sintering, it was found that the electrical resistivity of the lines of sintered nanoparticles in the form of nanoink and dry nanoparticles obtained in a gas discharge was 8.1 and 4.9 μΩ·cm, respectively. Thus, it has been demonstrated that laser sintering of nanoparticles obtained in a gas discharge makes it possible to achieve a lower specific resistance of lines than the method of aerosol printing using nanoink. In addition, the electrical resistivity of the lines of sintered nanoparticles obtained in a gas discharge is 3 times greater than the electrical resistivity of bulk silver, which is a sufficient result for the creation of conductive elements of printed electronics.

THERMAL BEHAVIOR OF PYROLYSIS OIL - DIESEL OIL EMULSION IN EVAPORATING MICRONIC DROPLETS

ABSTRACT Transformations inside emulsion droplets of 82 µm have been studied by using laser diagnostics. Arrays of calibrated droplets of emulsion 70/30 w/w diesel oil/pyrolysis oil were injected in pre-heated air flow inside a tubular reactor. Four thermal regimes have been studied: room temperature, 150°C, 250°C, and 350°C. For comparison, droplets of the diesel oil used to form the emulsion were studied in the same experimental conditions. The investigation has been performed by applying the Generalized Scattering Imaging laser technique that allows the simultaneous determination of size and optical properties of droplets. This optical diagnostic technique permitted to infer the chemical-physical changes inside the emulsion droplet by measuring the imaginary part of their refractive index. At 150°C and 250°C, the emulsion droplets suffered progressive depletion of the diesel oil phase. The pyrolysis oil, dispersed in the diesel oil matrix in the form of microdroplets 2 µm sized, underwent partial evaporation, liquid phase pyrolysis, and polymerization. At 350°C almost all the diesel oil had evaporated and the pyrolysis oil microdroplets dispersed in the emulsion droplet had merged to form a single droplet. These residual droplets showed a very narrow size distribution and an absorption coefficient greater than that of the original PO in agreement with the assessment that they represent the combined outcome of evaporation, liquid phase pyrolysis and polymerization of the pyrolysis oil. Samples of residual droplets were captured at the exit of the reactor and analyzed by means of optical microscopy. The microscope analysis was consistent with the laser diagnostics results.

Synthesis of ZnS nanoparticles of required size by precipitation in aerosol microdroplets

ABSTRACTZinc sulphide (ZnS) nanoparticles were prepared by an aerosol method from zinc acetate and sodium sulphide (Na2S) aqueous solutions. Aqueous solution of zinc acetate was dispersed into the form of microdroplets, which were introduced by airflow to vigorously stirred aqueous solution of Na2S, which was in excess. Microdroplets served as microreactors, so the reaction took place only in limited volume. Particle size distribution was studied by transmission electron microscopy and by dynamic light scattering measurements. In this work, the equation that allows us to predict the final size distribution of ZnS nanoparticles using exact concentration of zinc acetate was derived and ZnS nanoparticles with predicted mean particle diameter around 50 and 70 nm were successfully synthetised.

Influence of the Fluid on the Parameters and Limits of Bubble Detonation

The compression and inflammation of reactive gas bubbles in bubble detonation waves have been studied, and the considerable influence of the fluid (liquid or vapor) on the detonation parameters has been found. It has been shown numerically that the final values of the pressure and temperature significantly decrease if the temperature dependence of the adiabatic index is taken into account at the compression stage. The parameters of reactive gas combustion products in the bubble have been calculated in terms of an equilibrium model, and the influence of the fluid that remains in the bubble in the form of microdroplets and vapor on these parameters has been investigated.

Online multi-channel microfluidic chip-mass spectrometry and its application for quantifying noncovalent protein-protein interactions.

To establish an automatic and online microfluidic chip-mass spectrometry (chip-MS) system, a device was designed and fabricated for microsampling by a hybrid capillary. The movement of the capillary was programmed by a computer to aspirate samples from different microfluidic channels in the form of microdroplets (typically tens of nanoliters in volume), which were separated by air plugs. The droplets were then directly analyzed by MS via paper spray ionization without any pretreatment. The feasibility and performance were demonstrated by a concentration gradient experiment. Furthermore, after eliminating the effect of nonuniform response factors by an internal standard method, determination of the association constant within a noncovalent protein-protein complex was successfully accomplished with the MS-based titration indicating the versatility and the potential of this novel platform for widespread applications.

Growth behaviours of pentacene films confined in engineered shapes of ionic-liquid in vacuum

Ionic liquid (IL) films not only in the form of micro-droplets, but also of a homogeneously thick submicron-layer were deposited under vacuum on indium tin oxide (ITO) substrates by chemically modifying their wettability to the substrate. When pentacene was deposited on these IL-coated ITO substrates, pentacene crystals were grown via the IL. Depending on the shape and size of the IL films: a small-droplet (ϕ: 5 μm), a large-droplet (ϕ: 20 μm) and a homogeneously thick layer (about 0.1 μm in thickness), there were found significant differences in the growth behaviour of pentacene and the resultant adhesion ability of these pentacene films to the substrate, the mechanism of which is discussed with the aid of in situ observation of the crystal growth process in the IL in view of the wettability of the IL, the nucleation and the subsequent growth of the pentacene crystals.

Post-discharge treatment of air effluents polluted by butyl-mercaptan: the role of nitrate radical

Dry air polluted by butyl-mercaptan was treated in a dielectric barrier discharge reactor at atmospheric pressure using air as plasmagene gas in discharge and post-discharge modes. The energy density was varied between 200 and 1300 J l−1. To assess the treatment efficiency, the concentrations of butyl-mercaptan, total volatile organic compounds (VOCs) and SO2 were determined in the exhaust gas. Whatever the energy density was, the treatment efficiency was better in the post-discharge mode. Butyl-mercaptan could be completely eliminated from 400 J l−1 and SO2 selectivity was always low, below 10%. Measurements of CO, CO2 and total VOCs indicated that 50–70% of the reaction products were condensed on the reactor wall in the form of micro-droplets, depending on the energy density. FTIR and XPS techniques were used to characterize the reaction products which were soluble in water. These analyses indicated that the reaction products contained oxygen, nitrogen and sulfur in an oxidized form. A reaction mechanism involving hydrogen abstraction from the –SH bond by the nitrate radical was proposed, pointing out the important role of nitrate radicals NO3 in the reactivity of air flowing post-discharge.

Post-discharge treatment of air effluents polluted by butyl-mercaptan: role of nitrate radical

Dry air polluted by butyl-mercaptan was treated in a Dielectric Barrier Discharge (DBD) reactor at atmospheric pressure using air as plasmagene gas in discharge and post-discharge modes. The energy density was varied between 200 to 1300 J/L. To assess the treatment efficiency, the concentrations of buty-mercaptan, total Volatile Organic Compounds (VOCs) and SO2 were determined in the exhaust gas. Whatever the energy density was, the treatment efficiency was better in post-discharge mode. The butyl-mercaptan could be completely eliminated from 400 J/L and SO2 selectivity was always low, below 10%. Measurements of CO, CO2 and total VOCs indicated that 50 to 70% of the reaction products were condensed on the reactor wall in the form of micro-droplets, depending on the energy density. FTIR and XPS techniques were used to characterize the reaction products which were soluble in water. These analyses indicated that the reaction products contain oxygen, nitrogen and sulphur in an oxidized form. A reaction mechanism involving hydrogen abstraction from the -SH bond by the nitrate radical was proposed, pointing out the important role of nitrate radicals NO3 in the reactivity of air flowing post-discharge.

N,N-Butyl-decamethylferrocenyl-amine reactivity at liquid | liquid interfaces: electrochemically driven anion transfer vs. pH driven proton transfer

We have developed a permethylated ferrocene redox system with a butylamine substituent for application in liquid | liquid ion sensors. The steric hindrance associated with the methyl groups results in an electrochemical system where the ferricenium derivative is chemically inert and the redox system remains chemically reversible, even for applications in aqueous or biphasic media. N,N-Butyl-decamethylferrocenyl-amine is soluble in hydrophobic organic solvents, such as 4-(3-phenylpropyl)pyridine (PPP) and N-octyl-pyrrolidone (NOP), and is employed here under “microphase” conditions, deposited in the form of microdroplets onto an electrode and immersed in aqueous buffer solutions. It is shown that under these conditions, electron transfer and proton transfer are only weakly coupled, and that anion transfer dominates the microphase redox process over the entire pH range. The corresponding biphasic Pourbaix diagram is discussed.

Native β-Lactoglobulin Self-Assembles into a Hexagonal Columnar Phase on a Solid Surface

Using electron scanning microscopy, we have studied the protein deposit left on silicon and mica substrates by dried droplets of aqueous solutions of bovine beta-lactoglobulin at low concentration and pH = 2-7. We have observed different self-assembled structures: homogeneous layers, hexagonal platelets and flower-shaped patterns laying flat on the surface, and rods formed by columns. Homogeneous layers covered the largest area of the droplet deposit. The other structures were found in small isolated regions, where the protein solution dried in the form of microdroplets. The presence of hexagonal platelets, flower-shaped patterns and columnar rods shows that beta-lactoglobulin self-assembles at the surface in a hexagonal columnar phase, which has never been observed in solution. A comparison with proteins showing similar aggregates suggests that beta-lactoglobulin structures grow from hexagonal germs composed of discotic nanometric building blocks, possibly possessing an octameric structure. We propose that discotic building blocks of beta-lactoglobulin may be produced by the anisotropic interaction with the solid surface.

Encapsulation of Pediococcus acidilactici cells in corn and olive oil microcapsules emulsified by peptides and stabilized with xanthan in oil-in-water emulsions: Studies on cell viability under gastro-intestinal simulating conditions

Three different encapsulation systems were developed in the form of oil-in-water acidic emulsions (pH 3.0) with the oil phase in the form of microdroplets in which Pediococcus acidilactici cells were enclosed. The first emulsion contained corn oil microdroplets (mean diameter 1.5 μm) emulsified with peptides and stabilized with SDS. The other two, were food grade systems with microdroplets of corn or olive oil (m.d. 2.1 and 2.2 μm, respectively) emulsified with peptides and stabilized with xanthan. In all systems, meat peptone, a rich source of peptides and amino acids, was provided in aqueous solution in which the cultures were suspended. Peptone derived peptides acted as emulsifiers and at the same time as nutrient substrates and osmoprotectants for cells. Emulsions were stored for 30 days at 4 °C. During this period, samples were examined for physical stability and viability of the encapsulated and freely suspended microorganisms present in the emulsions. Examinations were made through phase contrast microscopy and subsequent image capture and analysis with an automatic image analysis system. Viable and non-viable cells were discriminated on the basis of color differences produced through staining with trypan blue. The method permitted extraction of a large amount of information and produced large amounts of data through automated measurements on images. Emulsion characteristics and cell viabilities were also examined under conditions simulating the gastro-intestinal environment. Encapsulation proved to be critical since, following successive treatments of samples with simulated gastric juice (pH 2.0) and intestinal juice (pH 7.4), it ensured viability rates of encapsulated cells as high as 85% and delivered as much as 92% of the initially encapsulated cells to the target point. The formulated emulsion systems may have a large number of applications in the food sector provided further studies on engineering properties and improvements of stability over a wide pH range are carried out.