Droplet Technique Research Articles

The effect of organic acids and salinity on the interfacial tension of n-decane/ water systems

We have investigated how a homologous series of straight-chain carboxylic acids with a cyclohexyl substituent in the opposite end of the functional groups impacts the interfacial tension (IFT) between decane (oil) and water. The employed method was the pendant droplet technique. We do not observe any striking effect of expanding the chain length: all acids reduced the IFT compared to water by approximately 20 mN/m. Additionally, the effect of changing the chemical character and the concentration of the cation in a series of brines where studied too, and again we do not observe a significant IFT impact. The only modification that significantly reduces the IFT is the modification of the anion from chloride to carbonate, a change that results in an increased pH and thus a transformation of the constituent acids from their neutral to their anionic form. This is expected to result in a reduced IFT because of the polar end of the surfactant is even more polar which alleviates the stress on the surface.

Investigation of evaporation and auto-ignition of isolated lubricating oil droplets in natural gas engine in-cylinder conditions

The auto-ignition of isolated lubricating oil droplets in cylinder conditions is one of main causes of abnormal combustion of natural gas engines. The evaporation behavior of less volatile lubricating oil droplets is the key parameter controlling the auto-ignition event. The suspended droplet technique was used and a fully transient multi-component model was developed to study the evaporation and auto-ignition behaviors of oil droplets. The transient model is closed against mass, species, and energy conservation, and the global one-step chemistry is used to estimate the chemical reaction source term. The boundary conditions at the gas-liquid interface are based on mass, species, and energy flux continuity, as well as the fugacity equilibrium. The model predictions were validated against experimental results, including the evaporation rate of binary-component droplets (n-heptane/n-decane), as well as the overall ignition delay of single-component (n-dodecane) and base oil droplets. The results show that the overall ignition delay of based oil droplets is very sensitive to the initial size and ambient temperature. The ignitable diameter limit is decreased with an increase in ambient pressure and temperature, and the ignitable temperature limit decreases as the ambient pressure increases. The dependence of ignition delay on pressure is determined by the ambient temperature. The ignition radius is reduced as the ambient temperature, pressure, and the initial droplet size increase. The involved methane concentration in natural gas engine in-cylinder conditions shows moderate effects on the ignition delay time of oil droplets depending on the initial size.

Contactless Fluid Manipulation in Air: Droplet Coalescence and Active Mixing by Acoustic Levitation

Acoustic manipulation by an ultrasonic phased array provides an entirely new approach to processes such as coalescence, mixing, separation, and evaporation occurring in the generation of new materials, physical property measurement, the biomedical industry, etc. However, to date, ultrasonic phased arrays have not been fully investigated for applications in fluid manipulation. This paper provides contactless coalescence and mixing techniques for droplets in air by controlling the acoustic potential by using an ultrasonic phased array. We focused on mode oscillation to propose an efficient mixing technique for liquid without contact. A comparison of mixing performance between cases with mode oscillation and without mode oscillation showed that the flow induced by mode oscillation promotes droplet mixing. Our paper demonstrates the feasibility of contactless coalescence and mixing as a first step in fluid manipulation with a phased array.

Inventions and Innovations in Preclinical Platforms for Cancer Research

Three-dimensional (3D) cell culture systems can be regarded as suitable platforms to bridge the huge gap between animal studies and two-dimensional (2D) monolayer cell culture to study chronic diseases such as cancer. In particular, the preclinical platforms for multicellular spheroid formation and culture can be regarded as ideal in vitro tumour models. The complex tumour microenvironment such as hypoxic region and necrotic core can be recapitulated in 3D spheroid configuration. Cells aggregated in spheroid structures can better illustrate the performance of anti-cancer drugs as well. Various methods have been proposed so far to create such 3D spheroid aggregations. Both conventional techniques and microfluidic methods can be used for generation of multicellular spheroids. In this review paper, we first discuss various spheroid formation phases. Then, the conventional spheroid formation techniques such as bioreactor flasks, liquid overlay and hanging droplet technique are explained. Next, a particular topic of the hydrogel in spheroid formation and culture is explored. This topic has received less attention in the literature. Hydrogels entail some advantages to the spheroid formation and culture such as size uniformity, the formation of porous spheroids or hetero-spheroids as well as chemosensitivity and invasion assays and protecting from shear stress. Finally, microfluidic methods for spheroid formation and culture are briefly reviewed.

The Experimental Investigation of Wetting Property for Liquid Lead Bismuth Alloy With ADS Materials

The accelerator-driven subcritical system (ADS) has potential economy and safety and relatively mature technology base, which has been chosen as a priority development advanced nuclear system. Liquid lead bismuth eutectic (LBE) is selected as the spallation target material and core coolant. The reduced activation ferritic/martensitic (RAFM) steel and the silicon carbide composite (SiC ${_{f}}$ ) are selected as its structural material and functional material, respectively. In the present experimental investigation, the special vacuum experimental device has been built, and the “dispensed droplet” modification of the classic sessile droplet technique has been used to investigate the wetting property and interfacial interactions for LBE/RAFM steel, LBE/316L, LBE/SiC, and LBE/SiC f couples. The contact angles were measured between the liquid LBE and the various candidate materials under working temperature from 300 °C to 480 °C. The results could provide meaningful compatibility database of liquid LBE and valuable engineering design reference of candidate structural materials and functional material for future ADS.

Particle Measurement Techniques in Fluid Process Engineering

AbstractDroplets, bubbles, or solid particle concentrations and their particle size distributions markedly influence the process conditions. In this article, an overview with respect to popular invasive and non‐invasive local measurement techniques for bubbles and droplets will be given. It starts with capillary suction probes, laser Doppler anemometry and finally covers actual developments in tomography and optical endoscopic measurement techniques. Furthermore, the possibilities and limitations of analyzing particle size distributions with these different methods in various application fields will be discussed.

Surface tension driven aggregation of organic nanowires via lab in a droplet.

Directing the architecture of complex organic nanostructures is desirable and still remains a challenge in areas of materials science due to their structure-dependent collective optoelectronic properties. Herein, we demonstrate a simple and versatile solution strategy that allows surface tension to drive low-dimensional nanostructures to aggregate into complex structures via a lab in a droplet technique. By selecting a suitable combination of a solvent and an anti-solvent with controllable surface tension difference, the droplets can be automatically cracked into micro-droplets, which provides an aggregation force directed toward the centre of the droplet to drive the low-dimensional building blocks to form the special aggregations during the self-assembly process. This synthetic strategy has been shown to be universal for organic materials, which is beneficial for further optimizing the optoelectronic properties. These results contribute to gaining an insightful understanding on the detailed growth mechanism of complex organic nanostructures and greatly promoting the development of organic nanophotonics.

The Effect of Atmospheric Oxygen on the Puffing and Bursting Phenomena during Vegetable Oils Droplets Vaporization Process for Their Use as Biofuel in Diesel Engine

The past literature on the use of vegetable oils as fuel in diesel engine revealed that utilizing vegetable oil fuels in diesel engines may require property changes in the oil or perhaps, some minor engine modifications or operating changes. This study was conducted to search for the effect of atmospheric oxygen on the puffing and bursting phenomena that occur during vegetable oils droplet vaporization process in their use as fuel in diesel engine. The fiber-suspended droplet technique was used, and the normalized square droplet diameter as well as the temperature evolution vicinity the droplet was analyzed. The results show that puffing and bursting phenomena highly depend on oxygen. In presence of atmospheric oxygen, there is an increase of the puffing and bursting intensity and therefore the evaporation rate of the vegetable oil droplets, but in an inert environment or when the environment is oxygen-depleted puffing and bursting phenomena disappearing and make place of a series of explosions with lower magnitude. The lack of oxygen reduces the thermal degradation, polymerization and oxidation reactions and consequently the vaporization rate of vegetable oils droplets; and could therefore lead to the formation of deposits in the form of polymers. This is unsuitable for their use as a fuel in diesel engines. It can also be concluded that atmospheric oxygen has some positive effects on engine performance and emissions when operating with vegetable oil. These results help to address the challenge for the use of alternative fuels such as non-edible vegetable oils.

Investigation of wetting property between liquid lead lithium alloy and several structural materials for Chinese DEMO reactor

The dual-cooled lead lithium (PbLi) blanket is considered as one of the main options for the Chinese demonstration reactor (DEMO). Liquid PbLi alloy is used as the breeder material and coolant. Reduced activation ferritic/martensitic (RAFM) steel, stainless steel and the silicon carbide ceramic matrix composite (SiCf) are selected as the substrate materials for different use. To investigate the wetting property and inter-facial interactions of PbLi/RAFM steel, PbLi/SS316L, PbLi/SiC and PbLi/SiCf couples, in this paper, the special vacuum experimental device is built, and the ‘dispensed droplet’ modification for the classic sessile droplet technique is made. Contact angles are measured between the liquid PbLi and the various candidate materials at blanket working temperature from 260 to 480 °C. X-ray photoelectron spectroscopy (XPS) is used to characterize the surface components of PbLi droplets and substrate materials, in order to study the element trans-port and corrosion mechanism. Results show that SiC composite (SiCf) and SiC ceramic show poor wetting properties with the liquid PbLi alloy. Surface roughness and testing temperature only provide tiny improvements on the wetting property below 480 °C. RAFM steel performs better wetting properties and corrosion residence when contacted with molten PbLi, while SS316L shows low corrosion residence above 420 °C for the decomposition of protective surface film mainly consisted of chromic sesquioxide. The results could provide meaningful compatibility database of liquid PbLi alloy and valuable reference in engineering design of candidate structural and functional materials for future fusion blanket.

Oscillating Ferrofluid Droplet Microrheology of Liquid-Immersed Sessile Droplets.

The damped oscillations of liquid-immersed ferrofluid sessile droplets were studied with high-speed imaging experiments and analytical modeling to develop a novel microrheology technique. Droplet oscillations were induced with an external magnetic field, thereby avoiding transients in the resulting vibrational response of the droplet. By following the droplet relaxation with a high-speed camera, the frequency and relaxation time of the damped harmonic oscillations were measured. We extend upon existing analytical theories to describe our liquid-immersed sessile droplet system, and directly quantify the droplet relaxation with the viscosity of the internal and external fluid as well as the interfacial tension between these. The easily controllable magnetic droplets make our oscillating ferrofluid droplet technique a potential candidate for high-throughput microrheology and tensiometry in the future.

Transformation dynamics of Ni clusters into NiO rings under electron beam irradiation

We report the transformation of nickel clusters into NiO rings by an electron beam induced nanoscale Kirkendall effect. High-purity nickel clusters consisting of a few thousand atoms have been used as precursors and were synthesized with the superfluid helium droplet technique. Aberration-corrected, analytical scanning transmission electron microscopy was applied to oxidise and simultaneously analyse the nanostructures. The transient dynamics of the oxidation could be documented by time lapse series using high-angle annular dark-field imaging and electron energy-loss spectroscopy. A two-step Cabrera-Mott oxidation mechanism was identified. It was found that water adsorbed adjacent to the clusters acts as oxygen source for the electron beam induced oxidation. The size-dependent oxidation rate was estimated by quantitative EELS measurements combined with molecular dynamics simulations. Our findings could serve to better control sample changes during examination in an electron microscope, and might provide a methodology to generate other metal oxide nanostructures.

Biocompatibility and Effectiveness Evaluation of a New Hemostatic Embolization Agent: Thrombin Loaded Alginate Calcium Microsphere.

Background. Until now, there has been no ideal embolization agent for hemorrhage in interventional treatment. In this study, the thrombin was encapsulated in alginate calcium microsphere using electrostatic droplet technique to produce new embolization agent: thrombin loaded alginate calcium microspheres (TACMs). Objectives. The present work was to evaluate the biocompatibility and hemostatic efficiency of TACMs. Methods. Cell cytotoxicity, hemolysis, and superselective embolization of dog liver arteries were performed to investigate the biocompatibility of TACMs. To clarify the embolic effect of TACMs mixed thrombus in vivo, hepatic artery injury animal model of 6 beagles was established and transcatheter artery embolization for bleeding was performed. Results. Coculture with VECs revealed the noncytotoxicity of TACMs, and the hemolysis experiment was negligible. Moreover, the histological study of TACMs in liver blood vessel showed signs of a slight inflammatory reaction. The results of transcatheter application of TACMs mixed thrombus for bleeding showed that the blood flow was shut down completely after the TACMs mixed thrombus was delivered and the postprocedural survival rate of animal models at 12 weeks was 100%. Conclusions. With their good biocompatibility and superior hemostatic efficiency, TACMs might be a promising new hemostatic agent with a wide range of potential applications.

Publisher's Note

We report the transformation of nickel clusters into NiO rings by an electron beam induced nanoscale Kirkendall effect. High-purity nickel clusters consisting of a few thousand atoms have been used as precursors and were synthesized with the superfluid helium droplet technique. Aberration-corrected, analytical scanning transmission electron microscopy was applied to oxidise and simultaneously analyse the nanostructures. The transient dynamics of the oxidation could be documented by time lapse series using high-angle annular dark-field imaging and electron energy-loss spectroscopy. A two-step Cabrera-Mott oxidation mechanism was identified. It was found that water adsorbed adjacent to the clusters acts as oxygen source for the electron beam induced oxidation. The size-dependent oxidation rate was estimated by quantitative EELS measurements combined with molecular dynamics simulations. Our findings could serve to better control sample changes during examination in an electron microscope, and might provide a methodology to generate other metal oxide nanostructures.

Advances of Microfluidic Technologies Applied in Bio-analytical Chemistry

Abstract Compared with conventional analysis system, microfluidics-based analysis system has many advantages, such as low consumption of sample and reagent, high efficiency in mass and heat transfer, good biocompatibility, high-throughput parallel analysis, as well as its integration, miniaturization and automation. It has been widely applied in the analytical chemistry, especially in the field of bio-analytical chemistry. In this review, we mainly focused on the progress of microfluidic technologies for cellular application during the past five years, such as the chip material and fabrication, surface modification and droplet techniques. Then we briefly summarized the applications of microfluidic techniques in drug screening and cellular analysis.

Experimental techniques for thermal product determination of coaxial surface junction thermocouples during short duration transient measurements

The measurement of transient surface heat flux is a crucial parameter for short duration aerodynamic experiments. They are generally obtained from temperature histories by mounting calorimetric gauges (such as thin film sensors and coaxial surface junction thermocouples) on the aerodynamic surfaces. While recovering the surface heat fluxes from transient temperatures, the appropriate form of one-dimensional heat conduction modeling is employed. However, such predictions of surface heat fluxes mainly depend on the correctness of thermal properties commonly known as, “thermal product (TP)” of the sensing surface and the accuracy in surface temperature history. Many a times, the TP values do change due to the nature/type of materials and during the fabrication of the gauge. In the present study, it is intended to evaluate the thermal product values of the in-house fabricated coaxial surface junction thermocouples (CSJT: E and J-types) for short duration experiments. These CSJTs are in-situ designed, fabricated and calibrated in the laboratory. For estimating thermal product in millisecond time scales, two laboratory experiments are designed viz., “water droplet technique and water plunging technique” by which impulse heat loads are applied for 8ms and the transient temperature responses are acquired from CSJTs. The experimental evaluations of TP values are compared with the corresponding theoretical estimates for both types of CSJTs. Subsequently, the effects of TP values on surface heat fluxes are analyzed by comparing them with peak and average heat loads. It is observed that surface temperature histories and average heat flux for all the experiments are in very good agreement. The experimental determination of TP values for E-type CSJTs are in close resemblance (within ±3% accuracy) while a significant under-prediction of about 29% is noticed for experimentally determined TP values with respect to its theoretical estimates for J-type CSJT during “water-plunging” experiments. In turn, it affects the peak heat flux predictions from surface temperature histories. Based on the results of experiments, the E-type CSJTs are found to be better in comparison to J-type CSJTs in terms of its sensitivity and consistency in predicting surface heat flux accurately.

Spontaneous wettability patterning via creasing instability

Surfaces with patterned wettability contrast are important in industrial applications such as heat transfer, water collection, and particle separation. Traditional methods of fabricating such surfaces rely on microfabrication technologies, which are only applicable to certain substrates and are difficult to scale up and implement on curved surfaces. By taking advantage of a mechanical instability on a polyurethane elastomer film, we show that wettability patterns on both flat and curved surfaces can be generated spontaneously via a simple dip coating process. Variations in dipping time, sample prestress, and chemical treatment enable independent control of domain size (from about 100 to 500 μm), morphology, and wettability contrast, respectively. We characterize the wettability contrast using local surface energy measurements via the sessile droplet technique and tensiometry.

Heterogeneous nucleation of entrained eutectic Si in high purity melt spun Al-Si alloys investigated by entrained droplet technique and DSC

Entrained droplet technique and DSC analyses were employed to investigate the influence of trace elements of Sr, Eu and P on the heterogeneous nucleation of entrained eutectic Si in high purity melt spun Al-5wt.% Si alloys. Sr and Eu addition was found to exert negative effects on the nucleation process, while an increased undercooling was observed. This can be attributed to the formation of phosphide compounds having a lower free energy and hence may preferentially form compared to AlP. Only a trace P addition was found to have a profound effect on the nucleation process. The nucleation kinetics is discussed on the basis of the classical nucleation theory and the free growth model, respectively. The estimated AlP patch size was found to be sufficient for the free growth of Si to occur within the droplets, which strongly indicates that the nucleation of Si on an AlP patch or AlP particle is a limiting step for free growth. The maximum nucleation site density within one droplet is directly related to the size distribution of AlP particles or AlP patches for Si nucleation, but is independent of the cooling rates. Although the nucleation conditions were optimized in entrained droplet experiments, the observed mechanisms are also valid at moderate cooling conditions, such as in shape casting.

Internal fluid motion and particle transport in externally heated sessile droplets

Experiments and numerical simulations were carried out for an evaporating sessile droplet. The droplet was confined in the narrow gap between two glass plates, making it a “Hele‐Shaw” droplet and particle image velocimetry technique was used. In case of the evaporating droplet with pinned contact line and exposed to ambient condition, two symmetric but counterrotating convection cells were observed. After complete evaporation, the particles deposited on the substrate near the contact line. The direction of the flow was reversed for a droplet placed on uniformly heated substrate, and the final deposition pattern was a large spot at the center with a thin line at the periphery. For asymmetrically heated substrate a single convection cell appeared, and the final deposition was also asymmetric. When the liquid was subjected to localized heating, the contact line no longer remains pinned and a relatively uniform deposition was obtained after complete drying. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1308–1321, 2016

Modified QuEChERS in combination with dispersive liquid-liquid microextraction based on solidification of the floating organic droplet method for the determination of organophosphorus pesticides in milk samples.

In this work, a rapid, environment friendly and sensitive method was established for the extraction and analysis of five organophosphorus pesticides (OPPs) (chlorpyrifos, chlorpyrifos-methyl, isocarbophos, malathion and phorate) in milk samples by means of gas chromatography-flame photometric detection. The pesticides were first extracted with acetonitrile from milk samples by using the modified "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method. No other clean-up was required after extraction. Then the above-mentioned acetonitrile extract was concentrated by using the dispersive liquid-liquid microextraction combined with solidification of floating organic droplets technique. Several factors that could influence the extraction efficiency, such as type of extraction solvent, disperser solvent, volume of extraction and disperser solvent, salt effect, sample pH, and extraction time, were investigated and optimized. As a result, 15 µL of 1-dodecanol were used as the extractant because of its lower toxicity, 300 µL methanol was chosen as dispersant and the extraction time was set to 1 min. Under the optimized conditions, good linearity was exhibited from 0.01 to 1.0 mg/L with the correlation coefficients higher than 0.9968. The limits of detection of the five OPPs were ranged in 0.1-0.3 μg/L, and the limits of quantification were at the range of 0.3-1.0 μg/L. Moreover, the recoveries of the target analytes from milk samples at spiking levels of 0.01, 0.05 and 0.1 mg/L were between 80.5 and 106.5% with the relative standard deviations varied from 3.6 to 6.3%. This method has been successfully applied to detect OPPs in real milk samples.

Vaporization characteristics of suspended droplets of biodiesel fuels of Indian origin and their diesel blends – An experimental study

For a liquid fuel, its vaporization characteristics are important. The determination of vaporization rates for alternative fuels such as biodiesel and its diesel blends is reported in this work. For this purpose, suspended droplet technique in conjunction with optical measurement of the droplet diameter is used. The physical processes occurring during the vaporization are studied at temperatures lower than the boiling point of the respective fuels to ascertain all the regimes of vaporization. Further, the vaporization characteristics are related to the composition of the fuel, which governs its thermal and physical properties. This study becomes important due to absence of such a comprehensive data in literature, and attempts to create a useful data-base for vaporization rates and related features of biodiesel fuels produced from sources such as jatropha, karanja, palm and coconut, and their diesel blends. The overall evaporation rates of neat and fuel blends are reported systematically. For neat fuels, the vaporization rates are seen to correlate directly with two parameters namely, heat transport and mass transport parameters, constituted using the gas-phase thermal and physical properties, as well as the liquid-phase density. Also, the vaporization rate is seen to inversely vary with a parameter called long chain saturation factor. All these parameters depend on the composition of the fuel.