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We report on a fluorescent-droplet-based acid-sensing scheme that allows limits of detection below 100 pM for weak acids. The concept is based on a strong partitioning of acid from an aqueous phase into octanol droplets. Using salicylic acid as a demonstration, we show that at a high concentration, the acid partitions into the organic phase by a factor of 260, which is approximately consistent with literature values. However, at lower concentrations, we obtain a partition coefficient as high as 10

This investigation is aimed at determining the conditions for the oxidation/stabilization of asphaltene fibers through extensive physicochemical characterization and evaluation of mechanical properties of the resulting carbon fibers. Melt spinning was used to fabricate green fibers using asphaltenes, from both straight solvent-de-asphalting (SDA) processing and subsequent thermal treatment. Thermal pretreatment of SDA asphaltenes was found to yield much improved carbon fiber properties. An oxidation treatment of HT300-derived (thermal pretreatment at 300 °C) carbon fibers provided the best mechanical properties with an average tensile strength of ∼1130 MPa and an average Young’s modulus of 71 GPa. Thermal treatment of SDA asphaltenes led to much lower sulfur content in both oxidized and carbonized fibers when oxidation was performed at ∼300 °C. BET, XPS, and XRD analyses showed that carbon fibers fabricated from treated asphaltenes with improved mechanical properties had a lower surface area, lower pore volume, higher amount of stable functional groups than SDA asphaltene-derived carbon fibers.

In the present work, we investigate the dynamic phenomena induced by solvent evaporation from ternary solutions confined in a Hele-Shaw cell. The model solutions consist of ethanol, water, and oil, and with the decrease in ethanol concentration by selective evaporation, they may undergo microdroplet formation via the ouzo effect or macroscopic liquid-liquid phase separation. We varied the initial concentration of the three components of the solutions. For all ternary solutions, evaporation of the good solvent ethanol from the gas-liquid interface, aligned with one side of the cell, leads to a Marangoni instability at the early stage of the evaporation process. The presence of the Marangoni instability is in agreement with our recent predictions based on linear stability analysis of binary systems. However, the location and onset of subsequent microdroplet formation and phase separation are the result of the interplay between the Marangoni instability and the initial composition of the ternary mixtures. We classified the ternary solutions into different groups according to the initial concentration of oil. For each group, based on the ternary diagram of the mixture, we offer a rationale for the way phase separation takes place and discuss how the instability influences droplet nucleation. Our work helps us to understand under what conditions and where droplet nucleation can take place when advection is present during phase separation inside a microfluidic device.

Compartmentalizing reagents within small droplets is promising for highly efficient conversion and simplified procedures in many biphasic chemical reactions. In this work, surface nanodroplets (i.e., less than 100 nm in their maximal height) were employed to quantitatively understand the size effect on the chemical reaction rate of droplets. In our systems, a surface-active reactant in pure or binary nanodroplets reacted with the reactant in the bulk flow. Meanwhile, the product was removed from the droplet surface. The shrinkage rate of the nanodroplets was characterized by analyzing the lateral size as a function of time, where the droplet size was solely determined by the chemical reaction rate under a given flow condition for the transport of the reactant and the product. We found that the overall kinetics increases rapidly with the decrease in droplet’s lateral radius R, as dR/dt ∼ R–2. The faster increase in the concentration of the product in smaller droplets contributes to accelerating reaction kinetics. The enhancement of reaction rates from small droplet sizes was further confirmed when a nonreactive compound was present inside the droplets without reducing the concentrations of the reactant and the product on the droplet surface. The results of our study improve the understanding of chemical kinetics with droplets. Our findings highlight the effectiveness of small droplets for the design and control of enhanced chemical reactions in a broad range of applications.

Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined space via propelling microdroplets. These microdroplets can form spontaneously from localized liquid-liquid phase separation as a ternary mixture is diluted by a diffusing poor solvent. High speed images reveal how the microdroplets grow, break up and propel rapidly along the solid surface, with a maximal velocity up to ∼160 μm s-1, in response to a sharp concentration gradient resulting from phase separation. The microdroplet propulsion induces a replenishing flow between the walls of the confined space towards the location of phase separation, which in turn drives the mixture out of equilibrium and leads to a repeating cascade of events. Our findings on the complex and rich phenomena of propelling droplets suggest an effective approach to enhanced flow motion of multicomponent liquid mixtures within confined spaces for time effective separation and smart transport processes. This journal is

In this work, we investigate the crystallization of droplets formed on micropatterned surfaces. By solvent exchange in a microchamber, a ternary solution consisting of a model compound β-alanine, water, and isopropanol was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on surfaces with chemical micropatterns could be simply mediated by the flow conditions of solvent exchange. More uniform crystals formed on hydrophilic microdomains compared to hydrophobic microdomains or homogeneous surfaces. Varying flow rates or channel heights led to the formation of thin films with microholes, connected networks of crystals, or small diamond-shaped crystals. Physical microstructures (represented by microlenses) on the surface allowed the easy detachment of crystals from the surface. Beyond oiling-out crystallization, we demonstrated that the crystal formation of another solute dissolved in the droplets could be triggered by solvent exchange. The length of crystal fibers after the solvent-exchange process was shorter at a faster flow rate. This study may provide further understanding to effectively obtain the crystallization of surface droplets through the solvent-exchange approach.

Supraparticles are large clusters of much smaller colloidal particles. Controlling the shape and anisotropy of supraparticles can enhance their functionality, enabling applications in fields such as optics, magnetics, and medicine. The evaporation of self-lubricating colloidal ouzo droplets is an easy and efficient strategy to create supraparticles, overcoming the problem of the “coffee-stain effect” during drop evaporation. Yet, the parameters that control the shape of the supraparticles formed in such evaporating droplets are not fully understood. Here, we show that the size of the colloidal particles determines the shape of the supraparticle. We compared the shape of the supraparticles made of seven different sizes of spherical silica particles, namely from 20 to 1000 nm, and of the mixtures of small and large colloidal particles at different mixing ratios. Specifically, our in situ measurements revealed that the supraparticle formation proceeds via the formation of a flexible shell of colloidal particles at the rapidly moving interfaces of the evaporating droplet. The time tc0 when the shell ceases to shrink and loses its flexibility is closely related to the size of particles. A lower tc0, as observed for smaller colloidal particles, leads to a flat pancake-like supraparticle, in contrast to a more curved American football-like supraparticle from larger colloidal particles. Furthermore, using a mixture of large and small colloidal particles, we obtained supraparticles that display a spatial variation in particle distribution, with small colloids forming the outer surface of the supraparticle. Our findings provide a guideline for controlling the supraparticle shape and the spatial distribution of the colloidal particles in supraparticles by simply self-lubricating ternary drops filled with colloidal particles.

Cleaner analytic technique for quantifying compounds in dense suspension is needed for wastewater and environment analysis, chemical or bio-conversion process monitoring, biomedical diagnostics, food quality control among others. In this work, we introduce a green, fast, one-step method called nanoextraction for extraction and detection of target analytes from sub-milliliter dense suspensions using surface nanodroplets without toxic solvents and pre-removal of the solid contents. With nanoextraction, we achieve a limit of detection (LOD) of 10^(-9) M for a fluorescent model analyte obtained from a particle suspension sample. The LOD lower than that in water without particles 10^(-8) M, potentially due to the interaction of particles and the analyte. The high particle concentration in the suspension sample thus does not reduce the extraction efficiency, although the extraction process was slowed down up to 5 min. As proof of principle, we demonstrate the nanoextraction for quantification of model compounds in wastewater slurry containing 30 wt% sands and oily components (i.e. heavy oils). The nanoextraction and detection technology developed in this work may be used as fast analytic technologies for complex slurry samples in environment industrial waste, or in biomedical diagnostics., This is an unedited, original author's version of the manuscript

A combinative approach for chemical analysis makes it possible to distinguish a mixture of a large number of compounds from other mixtures in a single step. This work demonstrates a combinative analysis approach using surface nanodroplets for integrating nanoextraction and colorimetric reactions for the identification of multicomponent mixtures. The model analytes are acidic compounds dissolved in an oil that are extracted into aqueous droplets on a solid substrate. The proton from acid dissociation reacts with the halochromic chemical compounds inside the droplets, leading to the color change of the droplets. The rate of the colorimetric reaction exhibits certain specificity for the acid type, distinguishing acid mixtures with the same pH value. The underlying principle is that the acid transport rate is associated with the partition coefficient and the dissociation constant of the acid, as well as to the concentration in the oil. As a demonstration, we showed that droplet-based combinative analysis can be applied for anti-counterfeiting of various alcoholic spirits by comparing the decoloration time of organic acid mixtures in the spirits. The readout can be done by a common hand-hold mobile phone.

Droplets abound in nature and technology. In general, they are multicomponent, and, when out of equilibrium, have gradients in concentration, implying flow and mass transport. Moreover, phase transitions can occur, in the form of evaporation, solidification, dissolution or nucleation of a new phase. The droplets and their surrounding liquid can be binary, ternary or contain even more components, with several in different phases. Since the early 2000s, rapid advances in experimental and numerical fluid dynamical techniques have enabled major progress in our understanding of the physicochemical hydrodynamics of such droplets, further narrowing the gap from fluid dynamics to chemical engineering and colloid and interfacial science, arriving at a quantitative understanding of multicomponent and multiphase droplet systems far from equilibrium, and aiming towards a one-to-one comparison between experiments and theory or numerics. This Perspective discusses examples of the physicochemical hydrodynamics of droplet systems far from equilibrium and the relevance of such systems for applications. Droplets in general are multicomponent and experience gradients in concentration, often leading to transport phenomena and phase transitions. This Perspective discusses recent progress on the physicochemical hydrodynamics of such droplet systems and their relevance for many important applications.

This study systematically investigated the phytotoxicity of chicken manure co-composted with tobacco powder and mushroom substrate on seed germination during active phase of composting. All compost products met the sanitation requirements specified in the Chinese national standard; however, only the mushroom substrate compost satisfied the maturity standard. From day 28, the composting entered the end of active phase and the concentrations of K+, Zn2+, Na+, Cu2+ and Fe3+ decreased gradually. Redundancy analysis indicated that the germination index, catalase and peroxidase activities was positively correlated with K+, Zn2+, Na+, Cu2+, Fe3+ and NO3--N, and negatively correlated with NH4+-N, Mg2+ and Ca2+, among which the most significant ions were Fe3+, Mg2+ and Zn2+ for all treatments. The malondialdehyde concentration of germinated seeds had adverse correlation with the above ions parameters.

The compartmentalization of chemical reactions within droplets has advantages in low costs, reduced consumption of reagents, and increased throughput. Reactions in small droplets have also been shown to greatly accelerate the rate of many chemical reactions. The accelerated growth rate of nanobubbles from nanodroplet reactions is demonstrated in this work. The gaseous products from the reaction at the nanodroplet surface promoted nucleation of hydrogen nanobubbles within multiple organic liquid nanodroplets. The nanobubbles were confined within the droplets and selectively grew and collapsed at the droplet perimeter, as visualized by microscopy with high spatial and temporal resolutions. The growth rate of the bubbles was significantly accelerated within small droplets and scaled inversely with droplet radius. The acceleration was attributed to confinement from the droplet volume and effect from the surface area on the interfacial chemical reaction for gas production. The results of this study provide further understanding for applications in droplet enhanced production of nanobubbles and the on-demand liberation of hydrogen.

To understand the unexpected and puzzling long-term stability of nanoscale gas bubbles, it is crucial to probe their nature and intrinsic properties. We report herein synchrotron-based scanning transmission X-ray microscopy (STXM) evidence of highly condensed oxygen gas molecules trapped as surface nanobubbles. Remarkably, the analysis of absorption spectra of a single nanobubble revealed that the oxygen density inside was 1-2 orders of magnitude higher than that in atmospheric pressure, and these bubbles were found in a highly saturated liquid environment with the estimated oxygen concentration to be hundreds of times higher than the known oxygen solubility in equilibrium. Molecular dynamics simulations were performed to investigate the stability of surface nanobubbles on a heterogeneous substrate in gas-oversaturated water. These results indicated that gas molecules within confinement such as the nanobubbles could maintain a dense state instead of the ideal gas state, as long as their surrounding liquid is supersaturated. Our findings should help explain the surprisingly long lifetime of the nanobubbles and shed light on nanoscale gas aggregation behaviors.

We present a curious effect observed during the dissolution process of water-immersed long-chain alcohol drops with an entrapped air bubble. These droplets dissolve while entrapping an air bubble pinned at the substrate. We qualitatively describe and explain four different phases that are found during the dissolution of this kind of system. The dissolution rate in the four phases differ dramatically. When the drop-water interface and the air bubble contact each other, rapid cyclic changes of the morphology are found: The breakage of the thin alcohol layer in between the bubble and the water leads to the formation of a three phase contact line. If the surface tension of the water-air interface supersedes those of the alcohol-water and alcohol-air interfaces, alcohol from the droplet is pulled upwards, leading to a closure of the air-water interface and the formation of a new thin alcohol film, which then dissolves again, leading to a repetition of the series of events. We call this sequence of events Marangoni puffing. This only happen for alcohols of appropriate surface tension. The Marangoni puffing is an intermediate state. In the final dissolution phases the Marangoni forces dramatically accelerate the dissolution rate, which then becomes one order of magnitude faster than the purely buoyancy-convective driven dissolution. Our results have bearing on various dissolution processes in multicomponent droplet systems.

The electrocatalytic CO2 reduction to yield C2 products is of particular interest in solar-to-fuel conversion schemes. The nanocrystalline oxide derived copper (ODCu) electrodes are specifically attractive due to their high faradaic efficiency towards C2 hydrocarbons like ethylene, ethane, acetate and ethanol. However, the mechanistic understanding of this special selectivity is still an impediment. In this work, ODCu is obtained from Cu2O nanowires and employed for electrocatalytic CO2 reduction, during which ethylene is found to be the major product with a faradaic efficiency of 65% at -0.8 V (vs. RHE). By in situ photoresponse measurement, combined with the ex situ structure and composition analysis, Cu2O is demonstrated to be persistent on the surface of ODCu throughout the CO2 reduction reaction (CO2RR) even at high applied bias (-1.0 V vs. RHE), while Cu2O is not present on the bulk Cu foil. Density functional theory calculations are employed to further investigate the correlation between the surface Cu2O on ODCu and its C2 selectivity performance, which is attributed to the orbital interactions between the persistent oxide and CO2 reduction intermediates. It should be noted that uncovering the active sites is the initial step to understand the surface reaction chemistry in CO2RR; here, we propose that the presence of Cu2O is the key for C2 selectivity during CO2RR in the ODCu system, which may facilitate the development of highly efficient catalysts.

Plasmonic nanobubbles are bubbles that are formed from local heat generated by noble metal nanoparticles under illumination of light at resonance. Understanding the formation and behavior of plasmo...

Photoelectrochemical reduction of CO2 is an efficient way to overcome the limited supply of fossil fuels and mitigate the greenhouse effect, as well as produce carbonaceous fuels from the sunlight. CuBi2O4 is a p-type semiconductor with conduction band potential negative enough for CO2 reduction. Nanoporous CuBi2O4 photocathodes are prepared by electrodeposition with subsequent annealing and are comprised of well-crystallized nanoparticles, which exhibit good visible-light response. The film thickness can be adjusted readily by changing the deposition time. The charge behavior in the CuBi2O4 photocathodes and its relationship with the film thickness are thoroughly investigated by using photocurrent and intensity modulated photocurrent spectroscopy. It is found that CuBi2O4-4 min possesses the optimized charge generation and transfer performance, and shows the highest activity with CO as the only product of photoelectrochemical reduction of CO2 under 0 V vs Ag/AgCl. The results indicate that CuBi2O4 can be a promising photocathode for CO2 photoelectrochemical reduction under low bias.

Poly(9-vinylcarbazole) (PVK) was introduced to modify the interface of perovskite/PCBM. The modified PVK material can induce the formation of the quasi-continuous sheet-shaped perovskite film at the surface of 3D perovskite layer, which may reduce the exposed grain boundaries. Besides, the PVK modified perovskite layer can reduce carrier recombination and accumulation at the interface of perovskite/PCBM and improve the crystallinity of perovskite layer and the interface contact properties. The PVK modification can greatly improve the PCEs and thermal and moisture stability and suppress the J-V hysteresis of perovskite solar cells (PSCs). PSCs with PVK modification achieved champion PCE of 19.03% (average PCE of 18.40%), maintained 80% of the original PCE value aging for 50 days under ambient conduction without encapsulation. Furthermore, PSCs with PVK modification can maintain 87% of the origin PCEs aging for 3 h under 85 °C thermal stress, which are greatly higher than that (26%) of PSCs without PVK modification.

The oil-water partition coefficient of organic compounds is an essential parameter for the determination of their behaviors in environments, food, drug delivery, and biomedical systems, just to name a few. In this work, we establish a highly efficient approach to quantify the partition/distribution coefficient using surface femtoliter droplets. In our approach, droplets of 1-octanol were produced on the surface of a solid substrate in contact with the flow of an aqueous solution of the analyte. The analyte was rapidly enriched in the droplets from the flow and reached the partition equilibrium in a few seconds. The entire procedure was automated by continuous solvent exchange, and the analyte partition in the droplets was quantified from the in situ UV-vis spectrum collected by a microspectrophotometer. Our approach was validated for several substances with the octanol-water partition/distribution coefficient ranging from -1.5 to 4, where our results were in good agreement with the values reported in the literature. This method took ∼3 min to detect one analyte with the volume of the organic solvent at ∼50 μL. Thus, our surface droplet platform can greatly minimize the consumption of both solvent and analytes and can shorten the time for the determination of the partition of new compounds, which overcomes the drawbacks of the traditional shake-flask method and presents excellent reproducibility, high accuracy, cost-effectiveness, and labor-saving operation. The highly efficient micro/nanoextraction, partition, and real-time detection enabled by the surface droplets has the potential for many other high-throughput applications.

HYPOTHESIS: Microscopic droplets integrating multiple functionalities are essential in the microcompartmentalized related reaction and applications. Solvent exchange is a simple approach for producing femtoliter surface droplets by the transit oversaturation created at the mixing front of a solution by a poor solvent. But it remains challenging to control the compositions in nanodroplets. Our hypothesis is the new liquid component can be added to the pre-formed surface droplets at certain ratios controlled by solvent exchange. EXPERIMENTS: In this work we investigate the growth of the droplets during addition of a new component by solvent exchange. Two-component droplets were formed on a microdomain patterned substrate as highly ordered arrays. The physical and chemical parameters that control droplet composition and a possible application of the binary droplet arrays were presented in this work. FINDINGS: The added amount of the second component in the binary droplet can be quantitatively controlled by the solution and flow conditions. The theoretical prediction of the component ratio based on the droplet diffusive growth dynamics mode shows a good agreement with the experimental results. The results show that the solvent exchange on the surface with pre-formed droplets provides a highly efficient method to tune the droplet compositions to desired ratio. The unique feature of this approach enables a gradient structure of droplet composition over the surface, demonstrated by an application of different microlens performance on a surface.

The rapid assessment of earthquake-stricken regions immediately after a seismic event is crucial for earthquake relief operations. Since unmanned aerial vehicles (UAVs) can quickly reach the affected areas and obtain images, they are widely used in the post-earthquake rapid assessment. However, sensor noise and other unavoidable errors can affect the quality of images acquired by sensors attached to the UAVs, which can, in turn, reduce the quality of the assessment. We defined a new problem in the application of multiple UAVs in the rapid assessment of earthquake-stricken regions. The rapid-assessment task-assignment problem (RATAP) was used to construct the assignment plan for multiple UAVs in a rapid-assessment task while considering the weights of potential targets, the endurance of the UAVs, and the sensor errors. The RATAP was formulated as a variant of the team orienteering problem (TOP) called the revisit-allowed TOP with reward probability (RTOP-RP). We then developed an efficient hybrid particle swarm optimization with simulated annealing (HPSO-SA) algorithm, which produced a high-quality solution for the RATAP, and confirmed the effectiveness and rapidity of our algorithm through numerical experiments. Finally, we conducted a case study based on real-world data from the 2008 Wenchuan earthquake in China to demonstrate our approach.

Fabrication of hybrid system coupling inorganic semiconductor photosensitizer with molecular catalyst provides a promising approach to achieve highly efficient CO2 reduction into solar fuels, as the semiconductor nanomaterials can meet the prerequisites of visible-light photoresponse and high charge-separation efficiency for achieving high photocatalytic efficiency. In this work, CdS/Bi2S3 heterostructures have been prepared via an ion-exchange reaction and employed as the photosensitizer to couple with tetra(4-carboxyphenyl)porphyrin iron(III) chloride (FeTCPP) molecular catalyst for photoreduction of CO2 into CO and H2 under visible-light irradiation. The sulfur vacancy in CdS surface can be reduced by the formation of CdS/Bi2S3 heterostructure. The content of Bi2S3 can be modulated via tailoring the ion-exchange reaction time. The resulting effect on the performace of CO2 photoreduction has been investigated in detail. Benefiting from the enhanced separation and utilization of charge carriers, CdS/Bi2S3-0.5 h/FeTCPP hybrid catalyst exhibits 8.2 times CO yield (1.93 mmol/g/h) and 1.7 times H2 yield (6.08 mmol/g/h) of CdS/FeTCPP hybrid catalyst. More important, the results of energy level alignment, electron spin resonance and photocatalysis indicate that electron-transfer direction can be changed once the CdS/Bi2S3 heterostructure is coupled with FeTCPP. In the CdS/Bi2S3 heterostructure, electrons transfer mainly from the conduction band of CdS to Bi2S3, while it is mainly from the conduction band of CdS to FeTCPP in the CdS/Bi2S3/FeTCPP hybrid.

Solvent exchange is a flow process to induce a transient oversaturation for forming nanobubbles or nanodroplets on solid surfaces by displacing the solution of gases or droplet liquids with a controlled flow of a poor solvent. In this work, we experimentally and numerically investigate the effect of the flow rate and other control parameters on the formation of microbubbles on hydrophobic cavity arrays during the solvent exchange process. We find that the growth rate, location, and number density of microbubbles are closely related to flow rate, solvent concentration, cavity distance, and spatial arrangement. Higher growth rates and number densities of the bubbles were obtained for faster solvent exchange flow rates. The competition of neighbouring growing bubbles for dissolved gas is greatly alleviated when the inter-cavity distance is increased from 13 μ m to 40 μ m. The effects of the flow rate and the cavity spacing on the bubble growth are in agreement with the observations from our three-dimensional numerical simulations. The findings reported in this work provide important insight into the formation of multiple interacting surface microbubbles under various flow conditions. The understanding may be extended to a smaller scale for the growth of surface nanobubbles during solvent exchange, which is much harder to visualize in experiments.

We investigated the dynamics of a liquid column consisting of ouzo emulsion under the impact generated when the liquid container lands on a hard ground. At a cavitation number of 0.36, where cavitation is expected to occur, our high-speed videography captured the traveling jet and cavitation bubbles while the oil microdroplets in ouzo after different runs of impact were visualized by an optical microscope. Importantly, the impact on an ouzo column can eject a focused jet of the emulsion and deposit a small volume of emulsion on a solid substrate. As revealed by our still photography, the deposited emulsion formed an oil-lubricated drop immediately. Our findings have implications for jetting applications such as inkjet printing of emulsions or fast deposition of self-lubricating drops for assembling supraparticles. We also discuss the jet formation mechanism in terms of the existence of oil microdroplets.

Technological progress is the engine for a country’s long-term stable economic growth. Since China has put forward the development requirements of finding a new driving force for economic growth, optimizing industrial structure and improving the quality of economic development, technological progress has become the key object of economic research. Based on the spatial autoregression model, this paper constructs a spatial weight matrix from three perspectives: geographical distance, economic distance, and comprehensive economic geographical distance, and took 13 cities in Beijing-Tianjin-Hebei region as the research objects to analyze the impact of technological progress on the upgrading of regional industrial structure and the spatial effect from 2010 to 2017. The results show that there is an inverted “U” relationship between the technological progress and the upgrading of industrial structure in the Beijing-Tianjin-Hebei region. The empirical results indicate that technological progress can significantly promote the upgrading of industrial structure in the region, but has no significant impact on the upgrading of industrial structure in the surrounding areas.

The removal of microbubbles from substrates is crucial for the efficiency of many catalytic and electrochemical gas evolution reactions in liquids. The current work investigates the coalescence and detachment of bubbles generated from catalytic decomposition of hydrogen peroxide. Self-propelled detachment, induced by the coalescence of two bubbles, is observed at sizes much smaller than those determined by buoyancy. Upon coalescence, the released surface energy is partly dissipated by the bubble oscillations, working against viscous drag. The remaining energy is converted to the kinetic energy of the out-of-plane jumping motion of the merged bubble. The critical ratio of the parent bubble sizes for the jumping to occur is theoretically derived from an energy balance argument and found to be in agreement with the experimental results. The present results provide both physical insight for the bubble interactions and practical strategies for applications in chemical engineering and renewable energy technologies like electrolysis.

Biphasic chemical reactions compartmentalized in small droplets offer advantages, such as streamlined procedures for chemical analysis, enhanced chemical reaction efficiency and high specificity of conversion. In this work, we experimentally and theoretically investigate the rate for biphasic chemical reactions between acidic nanodroplets on a substrate surface and basic reactants in a surrounding bulk flow. The reaction rate is measured by droplet shrinkage as the product is removed from the droplets by the flow. In our experiments, we determine the dependence of the reaction rate on the flow rate and the solution concentration. The theoretical analysis predicts that the life time $\tau$ of the droplets scales with Peclet number $Pe$ and the reactant concentration in the bulk flow $c_{re,bulk}$ as $\tau\propto Pe^{-3/2}c_{re,bulk}^{-1}$, in good agreement with our experimental results. Furthermore, we found that the product from the reaction on an upstream surface can postpone the droplet reaction on a downstream surface, possibly due to the adsorption of interface-active products on the droplets in the downstream. The time of the delay decreases with increasing $Pe$ of the flow and also with increasing reactant concentration in the flow, following the scaling same as that of the reaction rate with these two parameters. Our findings provide insight for the ultimate aim to enhance droplet reactions under flow conditions.

Background The fungal pathogen Leptosphaeria maculans (Lm). causes blackleg disease on canola/rapeseed in many parts of the world. It is important to use resistant cultivars to manage the disease and minimize yield losses. In this study, twenty-two Lm isolates were used to identify resistance genes in a collection of 243 canola/rapeseed (Brassica napus L.) accessions from Canada and China. These Lm isolates carry different compliments of avirulence genes, and the investigation was based on a genome-wide association study (GWAS) and genotype-by-sequencing (GBS). Results Using the CROP-SNP pipeline, a total of 81,471 variants, including 78,632 SNPs and 2839 InDels, were identified. The GWAS was performed using TASSEL 5.0 with GLM + Q model. Thirty-two and 13 SNPs were identified from the Canadian and Chinese accessions, respectively, tightly associated with blackleg resistance with P values − 4. These SNP loci were distributed on chromosomes A03, A05, A08, A09, C01, C04, C05, and C07, with the majority of them on A08 followed by A09 and A03. The significant SNPs identified on A08 were all located in a 2010-kb region and associated with resistance to 12 of the 22 Lm isolates. Furthermore, 25 resistance gene analogues (RGAs) were identified in these regions, including two nucleotide binding site (NBS) domain proteins, fourteen RLKs, three RLPs and six TM-CCs. These RGAs can be the potential candidate genes for blackleg resistance. Conclusion This study provides insights into potentially new genomic regions for discovery of additional blackleg resistance genes. The identified regions associated with blackleg resistance in the germplasm collection may also contribute directly to the development of canola varieties with novel resistance genes against blackleg of canola.

Enhancement of the detection signal of fluorescence microscopy in highly diluted solutions is of great importance in chemical analysis, sensing, and bioassay applications. Surface nanodroplets with atto- to femto-liter volumes are promising tools for sensitive online detection by integrating their extremely efficient nano-extraction and optical advantages. In this paper, the development of novel basic units of nanodroplets-in-a-microdroplet by simple solvent exchange is reported. The encapsulated nanodroplets are applied for ultrasensitive and online detection in fluorescence imaging. The biphasic nature of the droplet composite enables simultaneous extraction and enrichment of both hydrophobic and hydrophilic compounds. Furthermore, the desirable lensing effect of the curved surface of the nanodroplets enhances the collection of light emitted from the fluorophore extracted in the droplets by ≈60-fold, allowing sensitive and quantitative analysis of the fluorophore using fluorescence microscopy. The results highlight the potential of encapsulated nanodroplets as a simple and innovative method of signal enhancement in chemical analysis. By integrating selective concentration, extraction, and sensitive detection, the encapsulated nanodroplets reported here may have broad applications in many chemical and biological matrices.

Solvent exchange is a simple method to produce surface nanodroplets on a substrate for a wide range of applications by displacing a solution of good solvent, poor solvent and oil (Solution A) by a poor solvent (Solution B). In this work, we show that the growth and coalescence of nanodroplets on a homogeneous surface is mediated by the viscosity of the solvent. We show that at high flow rates of viscous Solution B, the final droplet volume deviates from the scaling law that correlates final droplet volume to the flow rate of non-viscous Solution B, reported in previous work. We attribute this deviation to a two-regime growth in viscous Solution B, where transition from an initial, fast regime to a final slow regime influenced by the flow rate. Moreover, viscous solution B hinders the coalescence of growing droplets, leading to a distinct bimodal distribution of droplet size with stable nanodroplets, in contrast to a continuous size distribution of droplets in non-viscous case. We demonstrate that the group of small droplets produced in high viscosity environment may be applied for enhanced fluorescence detection with higher sensitivity and shorter response time. The finding of this work can potentially be applied for mediating the size distribution of surface nanodroplets on homogeneous surface without templates., This is an unedited author's version of the submitted work that has been peer-reviewed and accepted in the Journal of Physical Chemistry C

Moving contact lines of more than two phases dictate a large number of interfacial phenomena. Despite their significance in fundamental and applied processes, the contact lines at a junction of four-phases (two immiscible liquids, a solid and gas) have been addressed only in a few investigations. Here, we report an intriguing phenomenon that follows after the four phases oil, water, solid and gas make contact through the coalescence of two different three-phase contact lines. We combine experimental studies and theoretical analyses to reveal and rationalize the dynamics exhibited upon the coalescence between the contact line of a micron-sized oil droplet and the receding contact line of a millimeter-sized water drop that covers the oil droplet on the substrate. We find that after the coalescence a four-phase contact line is formed for a brief period. However this quadruple contact line is not stable, leading to a 'droplet splitting' effect and eventually expulsion of the oil droplet from the water drop. We then show that the interfacial tension between the different phases and the viscosity of the oil droplet dictate the splitting dynamics. More viscous oils display higher resistance to the extreme deformations of the droplet induced by the instability of the quadruple contact line and no droplet expulsion is observed in such cases.

The evaporation of droplets occurs in a large variety of natural and technological processes such as medical diagnostics, agriculture, food industry, printing, and catalytic reactions. We study the different droplet morphologies adopted by an evaporating droplet on a surface with an elliptical patch with a different contact angle. We perform experiments to observe these morphologies and use numerical calculations to predict the effects of the patched surfaces. We observe that tuning the geometry of the patches offers control over the shape of the droplet. In the experiments, the drops of various volumes are placed on elliptical chemical patches of different aspect ratios and imaged in 3D using laser scanning confocal microscopy, extracting the droplet’s shape. In the corresponding numerical simulations, we minimize the interfacial free energy of the droplet, by employing Surface Evolver. The numerical results are in good qualitative agreement with our experimental data and can be used for the design of micropatterned structures, potentially suggesting or excluding certain morphologies for particular applications. However, the experimental results show the effects of pinning and contact angle hysteresis, which are obviously absent in the numerical energy minimization. The work culminates with a morphology diagram in the aspect ratio vs relative volume parameter space, comparing the predictions with the measurements.

The understanding of the shrinkage dynamics of plasmonic bubbles formed around metallic nanoparticles immersed in liquid and irradiated by a resonant light source is crucial for the usage of these bubbles in numerous applications. In this paper we experimentally show and theoretically explain that a plasmonic bubble during its shrinkage undergoes two different phases: first, a rapid partial bubble shrinkage governed by vapor condensation and, second, a slow diffusion-controlled bubble dissolution. The history of the bubble formation plays an important role in the shrinkage dynamics during the first phase, as it determines the gas-vapor ratio in the bubble composition. Higher laser powers lead to more vaporous bubbles, while longer pulses and higher dissolved air concentrations lead to more gaseous bubbles. The dynamics of the second phase barely depends on the history of bubble formation, i.e. laser power and pulse duration, but strongly on the dissolved air concentration, which defines the concentration gradient at the bubble interface. Finally, for the bubble dissolution in the second phase, with decreasing dissolved air concentration, we observe a gradual transition from a $R(t) \propto (t_0 - t) ^{1/3}$ scaling law to a $R(t) \propto (t_0 - t) ^{1/2}$ scaling law, where $t_0$ is the lifetime of the bubble and theoretically explain this transition.

A laser-dressed V-type atom trapped in a two-mode optical cavity is investigated, which induces a SWAP gate on the two modes of the cavity. Two laser fields are imposed to interact with the atom dispersively, which leads to an effective interaction between two atomic excited states. The state of the atom prepared initially in the ground state keeps invariant, but the photon exchange between the two cavity modes occurs. Compared with the schemes (Lin et al. in Phys Rev A 77:064301, 2008 and Yan et al. in Quantum Inf Process 17:71, 2018) that use $$\nabla $$-type atoms, the present scheme is more practical, because usually the $$\nabla $$-type atom may be hardly obtained due to the dipole transition selection rule. In addition, the robustness of the SWAP gate against the pulse control error is strengthened by using time-dependent shaped pulses. The effect of the atomic spontaneous radiation and the photon loss is discussed by means of the numerical simulations.

In this paper we study the formation of microbubbles upon the irradiation of an array of plasmonic Au nanoparticles with a laser in n-alkanes ($C_{n}H_{2n+2}$, with n = 5-10). Two different phases in the evolution of the bubbles can be distinguished. In the first phase, which occurs after a delay time {\tau}d of about 100 {\mu}s, an explosive microbubble, reaching a diameter in the range from 10 {\mu}m to 100 {\mu}m, is formed. The exact size of this explosive microbubble barely depends on the carbon chain length of the alkane, but only on the laser power $P_l$. With increasing laser power, the delay time prior to bubble nucleation as well as the size of the microbubble both decrease. In the second phase, which sets in right after the collapse of the explosive microbubble, a new bubble forms and starts growing due to the vaporization of the surrounding liquid, which is highly gas rich. The final bubble size in this second phase strongly depends on the alkane chain length, namely it increases with decreasing number of carbon atoms. Our results have important implications for using plasmonic heating to control chemical reactions in organic solvents.

The hybrid coupling between inorganic semiconductor and molecular catalyst can provide a promising approach for the construction of highly efficient and selective photocatalytic CO2 reduction systems. This hybrid system can take full advantage of the strong light harvesting capability of semiconductor and high selectivity of molecular catalyst. The interaction linker bridging the semiconductor and molecular catalyst plays an important role in supplying efficient electron transfer channels. In this study, both CdS with and without ethylenediamine functionalization (i.e., CdS-EF and CdS) have been successfully synthesized and further respectively coupled with tetra(4-carboxyphenyl)porphyrin iron(III) chloride (FeTCPP) for CO2 photoreduction. It is found that CdS-EF exhibits inferior photocatalytic activity to CdS, while CdS-EF/FeTCPP hybrid photocatalyst shows much higher activity than CdS/FeTCPP. This is because hydrogen bonding exists between the amino groups in CdS-EF and carboxyl groups in FeTCPP, which can act as electron transfer channels from CdS to FeTCPP in the obtained hybrid system.

Nickel oxide (NiOx) hole transport layer (HTL)-based planar perovskite solar cells (PSCs) have attracted much attention due to high power conversion efficiency (PCE) and simple processing. In this work, smooth and compact Sr-doped NiOx films with different Sr doping concentration were successfully prepared through a simple low temperature sol-gel method. The 1 at.% Sr-doped NiOx HTL-based PSCs exhibited the best performance with PCE of 20.07%, which is greatly higher than PCE of reference NiOx based PSCs (15.73%). Furthermore, the unencapsulated PSCs based on Sr:NiOx HTL still retains over 60% of the original PCE value aging for 100 days under ambient air, showing better stability. The superior performance of Sr-doped NiOx based PSCs is attributed to better electrical conductivity, crystallinity of perovskite film and energy level matching with perovskite layer, which can greatly improve hole transport and extraction abilities and reduce carrier recombination, resulting in high PCE and better stability.

Microscopic lenses are paramount in solar energy harvesting, optical devices, and imaging technologies. This work reports an extraordinary focusing effect exhibited by a surface nanolens (i.e., with at least one dimension of subwavelength) that is situated in an evanescent field from the total internal reflection (TIR) of light illuminated to the supporting substrate above the critical angle. Our measurements show that the position, shape, and size of the surface area with enhanced light intensity are determined by the geometry of the nanolens and the incident angle, in good agreement with simulation results. This strong focusing effect of the surface nanolens is shown to significantly promote the plasmonic effect of deposited gold nanoparticles on the lens surface inlight conversion and to vaporize surrounding water to microbubbles by using low laser power. This work further demonstrates that the light redistribution by the surface nanolens in TIR enables a range of novel applications in selectively local visualization of specimens in fluorescence imaging, optical trapping of colloids from an external flow, and selective materials deposition from photoreactions., Small scale lenses demonstrated a remarkable focusing effect when illuminated near the critical angle. This attribute yielded an enhanced plasmonic bubble formation, fluorescence signal, and local photoreaction.

The crystallization of oil droplets is critical in the processing and storage of lipid-based food and pharmaceutical products. Arrays of femtoliter droplets on a surface offer a unique opportunity to study surfactant-free colloidlike systems. In this work, the crystal growth process in these confined droplets was followed by cooling a model lipid (trimyristin) from a liquid state utilizing synchrotron small-angle X-ray scattering (SAXS). The measurements by SAXS demonstrated a reduced crystallization rate and a greater degree of supercooling required to trigger lipid crystallization in droplets compared to those of bulk lipids. These results suggest that surface droplets crystallize in a stochastic manner. Interestingly, the crystallization rate is slower for larger femtoliter droplets, which may be explained by the onset of crystallization from the three-phase contact line. The larger surface nanodroplets exhibit a smaller ratio of droplet volume to the length of three-phase contact line and hence a slower crystallization rate.

We experimentally demonstrate a convenient approach to fabricate large area photorefractive photonic microstructures by a spliced lens device. Large area two-dimensional photonic microstructures are optically induced inside an iron-doped lithium niobate crystal. The experimental setups of our method are relatively compact and stable without complex alignment devices. It can be operated in almost any optical laboratories. We analyze the induced triangular lattice microstructures by plane wave guiding, far-field diffraction pattern imaging and Brillouin-zone spectroscopy. By designing the spliced lens appropriately, the method can be easily extended to fabricate other complex large area photonic microstructures, such as quasicrystal microstructures. Induced photonic microstructures can be fixed or erased and re-recorded in the photorefractive crystal.

Deformation and crack initiation of industrial Ti-6Al-4V titanium alloy sheet were investigated using in-situ scanning electron microscopy (SEM) at room temperature. The results showed that slip band originated from α/α and α/β interfaces when the tension reaches the yield stage, and the slip mode develops from single slip to multi slip and finally the cross-slip occurs. Microcracks initiate primarily at the phase boundary or along the slip band within α phase, cracks are mainly connected along the 45° line. The fracture surface is full of dimples. Intergranular cracking is the main fracture mechanism.

Multicomponent surface droplets that consist of more than one compound are of great interest for fundamental studies of microwetting, evaporation, and dissolution behaviors, as well as for practical applications in high-throughput screening, microcompartmentalized chemical reactions, and microanalytics. In this work, we study the formation of multicomponent surface nanodroplets from heterogeneous nucleation and growth induced by the process of solvent exchange. In our experiments, as a solution of two oils in their good solvent was displaced by a poor solvent of the oils in the standard solvent exchange, binary droplets of oils were produced on an immersed substrate. The concentration of one oil was constant in the initial solution, whereas the other oil was increased gradually. We characterized the ratio of the two oils inside individual binary droplets by an infrared microspectrometer. Our results show that the ratio of two oils within binary nanodroplets could be varied from 0 to 100% by tuning the com...

Surface nanobubbles are nanoscopic spherical-cap shaped gaseous domains on immersed substrates which are stable, even for days. After the stability of a {\it single} surface nanobubble has been theoretically explained, i.e. contact line pinning and gas oversaturation are required to stabilize them against diffusive dissolution [Lohse and Zhang, Phys.\ Rev.\ E 91, 031003 (R) (2015)], here we focus on the {\it collective} diffusive interaction of {\it multiple} nanobubbles. For that purpose we develop a finite difference scheme for the diffusion equation with the appropriate boundary conditions and with the immersed boundary method used to represent the growing or shrinking bubbles. After validation of the scheme against the exact results of Epstein and Plesset for a bulk bubble [J. Chem. Phys. 18, 1505 (1950)] and of Lohse and Zhang for a surface bubble, the framework of these simulations is used to describe the coarsening process of competitively growing nanobubbles. The coarsening process for such diffusively interacting nanobubbles slows down with advancing time and thus increasing bubble distance. The present results for surface nanobubbles are also applicable for immersed surface nanodroplets, for which better controlled experimental results of the coarsening process exist.

Modification of a wide-bandgap semiconductor with noble metals that can exhibit surface plasmon effect is an effective approach to make it responsive to the visible light. In this work, a series of cubic and all-edge-truncated SrTiO3 with and without thermal pretreatment in air are modified by Ag nanoparticles via photodeposition method. The crystal structure, morphology, loading amount of Ag nanoparticles, and optical properties of the obtained Ag-SrTiO3 nanomaterials are well characterized by powder X-ray diffraction, scanning microscope, transmission electron microscope, energy disperse X-ray spectroscopy, ICP-MS and UV–vis diffuse-reflection spectroscopy. The loading amount and size of the Ag nanoparticles can be controlled to some extent by tuning the photodeposition time via growth-dissolution mechanism. The Ag nanoparticles are inclined to deposit on different locations on the surface of cubic and truncated SrTiO3 with and without thermal pretreatment. The resultant SrTiO3 modified by Ag nanoparticles exhibits visible light activity for photocatalytic reduction of CO2, which is closely related to the oxygen vacancy induced by thermal pretreatment, size and amount of Ag nanoparticles. Accordingly, there is an optimized photodeposition time for the synthesis of the photocatalyst that exhibits the highest photocatalytic activity.

Camellia oleifera is one of the four woody oil plants in the world, which is widely cultivated in South China. To examine the genetic diversity of C. oleifera in China, the diversity and genetic relationships among and within major populations of 109 varieties of C. oleifera were analyzed using ISSR markers. Twenty-three ISSR primers out of 49 primers yielded approximately 487 legible bands. A total of 335 of these bands were polymorphic markers, and the ratio of polymorphism was 68.86%. From the results, Zhejiang province showed the highest populations genetic diversity (H value 0.18), while Guangxi population showed the lowest genetic diversity (H 0.0851). Base on the bands, the genetic similarity coefficient ranged from 0.61 to 0.93 using NTSYS2.10e software. When coefficient was 0.75, 109 cultivars were divided into 11 categories and categories I contain 79 varieties by UPGMA cluster analysis. The test varieties divided into 7 sub-groups when categories were 0.75, which show a close genetic relationship. Results advised that Hunan is the main producing area of C. oleifera, with enriched C. oleifera variety and complex topography, and therefore has a high genetic diversity. Meanwhile, the main varieties of C. oleifera in Hubei are imported from Hunan, which results in fewer varieties and reduces the genetic diversity of C. oleifera. The ISSR profiles can improve C. oleifera germplasm management and provide potential determine correlations between different varieties and its distribution in different province.

Photocatalytic reduction of CO 2 into value-added chemicals is particularly attractive as it could produce renewable energy and capture greenhouse gas. Photoreduction of CO 2 can be realized over molecular and inorganic catalysts. The former usually exhibit high activity, but low stability and often inactive under visible-light irradiation; the latter has low activity, but good stability. Here we use g-C 3 N 4 nanosheets as the photosensitizer to integrate with Fe tetra(4-carboxylphenyl)porphyrin chloride (FeTCPP) molecular catalyst. Besides π-π stacking between tri- s -triazine unit and porphyrin, the carboxyl group modified Fe porphyrin is used for the first time in CO 2 photoreduction so as to form hydrogen bonding with the rich amino groups in g-C 3 N 4 nanosheets. g-C 3 N 4 /FeTCPP heterogeneous catalysts are prepared via a facile self-assembly approach, in which light harvest is separated from catalysis spatially and temporally. The obtained g-C 3 N 4 /FeTCPP heterogeneous catalysts exhibit high activity for CO 2 reduction under visible-light irradiation, with CO yield of 6.52 mmol g −1 in 6 h and selectivity up to 98%. Fluorescence data indicate that the electrons can efficiently transfer from the g-C 3 N 4 nanosheets to FeTCPP. The mechanism for CO 2 reduction over the g-C 3 N 4 /FeTCPP heterogeneous catalysts is proposed based on the results of quasi in-situ ESR and UV–vis measurements. This work may pave a facile approach for fabricating the high-efficient photocatalysts for CO 2 reduction, as well as better understanding the related mechanism.

Mesoporous solids have been widely used in various biomedical areas such as drug delivery and tumor therapy. Although deformability has been recognized as a prime important characteristic influencing cellular uptake, the synthesis of deformable mesoporous solids is still a great challenge. Herein, deformable thioether-, benzene-, and ethane-bridged hollow periodic mesoporous organosilica (HPMO) nanocapsules have successfully been synthesized for the first time by a preferential etching approach. The prepared HPMO nanocapsules possess uniform diameters (240–310 nm), high surface areas (up to 878 m2·g–1), well-defined mesopores (2.6–3.2 nm), and large pore volumes (0.33–0.75 m3·g–1). Most importantly, the HPMO nanocapsules simultaneously have large hollow cavities (164–270 nm), thin shell thicknesses (20–38 nm), and abundant organic moiety in the shells, which endow a lower Young’s modulus (EY) of 3.95 MPa than that of solid PMO nanoparticles (251 MPa). The HPMOs with low EY are intrinsically flexible and d...

Construction of solid solution semiconductors has attracted much attention in photocatalysis by virtue of their tunable elemental composition and band structure. The integration of semiconductor sensitizers with molecular catalysts provides a promising way to fabricate highly efficient, selective and stable systems for CO2 photoreduction. Here ZnxCd1-xS (ZCS) solid solutions with a well-defined floccule-like morphology composed of nanoribbons are synthesized and used as the photosensitizer to couple with tetra(4-carboxyphenyl)porphyrin iron(iii) chloride (FeTCPP) for CO2 reduction. The effects of changes in surface atoms of the ZCS solid solution on the performance of CO2 photoreduction are investigated. Regardless of the presence of FeTCPP, our results show that the introduction of Zn into CdS can affect the activity and selectivity of CO2 photoreduction, as well as the stability of the obtained photocatalysts. More importantly, the presence of Zn can build efficient electron transfer channels from ZCS to FeTCPP and, thus, greatly facilitate the interfacial charge transfer. Benefitting from the efficient charge separation and electron transfer, ZCS-1/FeTCPP (Zn0.14Cd0.84S/FeTCPP) exhibits the highest activity for CO2 reduction under visible-light irradiation, with a CO yield of 1.28 μmol and a selectivity up to 93% after 4 h.