Water-Triggered Chemical Transformation of Perovskite Nanocrystals.

Recently emerged lead-halide perovskite nanocrystals (PNCs) are promising optoelectronic material due to their easy solution processability, wide range of color tunability, as well as very high photoluminescence quantum yield. Despite their significant success in lab-scale optoelectronic applications, the long-term stability becomes the main issue, hindering them towards commercialization. The highly ionic nature of such lead-halide structure makes them extremely unstable in water and air. But a very few groups have taken the advantage of such nature of the crystal structure for water-triggered chemical transformation towards shape, composition, and morphology controlled stable and bright PNCs, which are otherwise difficult to obtain by typical direct approach. Furthermore, using polymer as an encapsulating layer for the PNCs, water-soluble stable PNCs have been prepared. In this review, the recent progress on the water-hexane interface chemistry towards chemical transformation to produce several PNCs is described. Such method not only ensure to yield several shape-controlled perovskites nanocrystals, but also formation of perovskites in aqueous phase that show promising application towards bio-imaging.

Evidence of Size Stratification in Colloidal Glass Microgranules Realized by Rapid Evaporative Assembly.

Evaporation is a ubiquitous phenomenon. Rapid evaporation of the continuous phase from micrometric colloidal droplets can be used to realize nanostructured microgranules, constituting the assembled nanoparticles. One of the important aspects of such nonequilibrium assembly is the nature of the packing of nanoparticles in the microgranules. The present work demonstrates the evidence of size stratification of the nanoparticles in such far-from-equilibrium configurations. Small-angle X-ray scattering, in combination with particle packing simulation, reveals the "large on top"-type stratification in such assembled microgranules, where the larger particles get concentrated at the outer shell of the granules while the smaller particles reside in the core region. It also reveals the presence of local clusters in such a rapid evaporative assembly in aerosolized colloidal droplets.

Amphiphilic interaction-mediated ordering of nanoparticles in Pickering emulsion droplets.

For various industrial processes, the stabilization of an oil phase is crucial and demands a proper balance of complex interactions in an emulsion system. In Pickering emulsions, this is achieved by introducing nanoparticles, which become organized at the oil-water interface. The influence of interparticle interactions towards the formation of a stable emulsion and the ordering of the stabilizing nanoparticles is intriguing and needs attention. In this work, the role of amphiphilic interactions between hydrophilic silica nanoparticles and the Pluronic F127 tri-block co-polymer towards the spontaneous formation of a fairly stable Pickering emulsion has been studied using small-angle X-ray scattering. Unlike the usual random arrangements of the nanoparticles in a conventional Pickering emulsion, we observed highly organized silica nanoparticles at the oil-water interface. The established standard raspberry structural model of the Pickering emulsion fails to explain such strong ordering as observed in the present case. A plausible formation mechanism of the present Pickering emulsion with a high on-surface silica correlation is elucidated on the basis of the combined interactions of the block co-polymer and silica particles. A computer model is developed to elucidate the effects of size and distribution of the surface-decorating nanoparticles and their positional correlation.

Pattern of an Evaporated Colloidal Droplet on a Porous Membrane Dictated by Competitive Processes of Flow and Absorption.

Understanding the deposition pattern formed by an evaporated colloidal drop is of fundamental and technological interest. Such an evaporative process is important in various applications starting from inkjet printing to disease diagnosis. In this work, it is shown that the deposit pattern on a porous membrane can be tuned by varying the colloidal viscosity and membrane pore size. We have used small-angle X-ray scattering (SAXS) in scanning mode for profiling of deposit morphology and also for estimation of the interparticle correlation. It is demonstrated that low viscosity and small pore size favor a centrally dipped pattern owing to the coffee ring effect, which can be modified to a contrasting centrally peaked pattern by increasing the viscosity and pore size. To comprehend the experimental observations, a computer model has been developed using a continuity equation that well corroborates the experimental observations on the final deposited pattern and also provides the time evolution of the pattern. The work provides a way to tune the pattern of colloidal stain on a porous substrate by controlling flow and absorption.

Jamming of Nano-Ellipsoids in a Microsphere: A Quantitative Analysis of Packing Fraction by Small-Angle Scattering.

The packing of particles is ubiquitous, and it is of fundamental importance, particularly in materials science in the nanometric length scale. It becomes more intriguing when constituent particles deviate from spherical symmetry owing to the inherent complexity in quantifying their positional and rotational correlation. For quantitative estimation of packing fraction, it requires a thorough analysis of the positional correlation of jammed particles. This article adopts a novel approach for determination of the packing fraction of strongly correlated nano-ellipsoids in a microsphere using small-angle scattering. The method has been elucidated through a quantitative analysis of structural correlation of nano-hematite ellipsoids in 3D micrometric granules, which are realized using rapid evaporative assembly. Owing to the deviation from spherical symmetry, the conventional analysis of scattering data fails to interpret the actual packing fraction of the anisotropic particles. The structural correlation gets smeared out because of orientation distribution among the packed anisotropic particles, which leads to an anomaly in the estimation of packing fraction using the conventional analysis approach. It is illustrated that consideration of an interparticle distance distribution function of the correlated nano-ellipsoids becomes indispensable in determining their packing fraction.

Hollow TiO2/SiO2 composite microspheres through reactive assembly across immiscible liquid interfaces.

Titania (TiO2) based photocatalysts have shown tremendous potential in tackling important issues related to energy, the environment, and water purification. The tunable morphologies of the TiO2 based multicomponent composites are promising for the improvement of photocatalytic characteristics for practical applications. In this work, we report a one-step facile approach to achieve hollow silica/titania microspheres through the process of reactive assembly at the immiscible interface of micrometer-sized droplets. Scanning electron microscopy and small-angle neutron scattering revealed the hierarchal structure of the microspheres. Elemental mapping of the composite microspheres provided direct evidence of the incorporation of silica nanoparticles into the microspheres. The diffusion of reactant molecules and hydrolysis/condensation reactions across the phase boundary of the interface of two immiscible liquids controls the morphology of the microspheres and the size of TiO2 nanoparticles. The silica/titania composite microspheres show excellent thermal stability against the anatase to rutile phase transition caused by inhibition of the growth of TiO2 nanoparticles due to proximity of the silica nanoparticles. The photoelectrochemical measurements show that TiO2-SiO2 microspheres exhibit superior photocatalytic characteristics compared to the TiO2 microspheres. The kinetics of dye degradation for TiO2-SiO2 microspheres is found to be significantly faster compared to TiO2 microspheres which confirms the superior photocatalytic properties of the composite microspheres.

Origin of the Hierarchical Structure of Dendritic Fibrous Nanosilica: A Small-Angle X-ray Scattering Perspective.

The discovery of dendritic fibrous nanosilica (DFNS) has attracted great attention to the field of catalysis, CO2 capture, drug delivery due to its distinct morphology, and pore size distribution. Despite extensive research, the understanding of the DFNS formation process and its internal structure remains incomplete as microscopy and gas sorption techniques were not able to provide necessary in-depth structural information due to their inherent limitations. In the current work, we present a structural model of DFNS derived using small-angle X-ray scattering (SAXS) supported by 129Xe nuclear magnetic resonance (NMR), which provided intricate details of DFNS and its internal structure. Mechanistic understanding of the DFNS formation and growth process was achieved by performing time-resolved SAXS measurements during the synthesis of DFNS, which unveils the evolution of two levels of a bicontinuous microemulsion structure responsible for intricate DFNS morphology. The validity and the accuracy of the SAXS method and the model were successfully established through a direct correlation among the functionality of the DFNS scattering profile and its pore size distribution, as well as results obtained from the 129Xe NMR studies. It has been established that the DFNS structure originates from direct modulation of the bicontinuous structure controlled by a surfactant, a co-surfactant, and the silicate species formed during hydrolysis and the condensation reaction of the silica precursor.

Polymer-mediated interaction between nanoparticles during hydration and dehydration: a small-angle X-ray scattering study.

Polymer-mediated interactions such as DNA-protein binding, protein aggregation, and filler reinforcement in polymers play crucial roles in many important biological and industrial processes. In this work, we report a detailed investigation of interactions between nanoparticles in the presence of high volume fractions of an adsorbing polymer. Small-angle X-ray scattering (SAXS) revealed the existence of a stable gel-like structure in the polymer-nanoparticle dispersion, whereby anchored polymer molecules on nanoparticles acted as bridging centres, while basic interactions between nanoparticles remained repulsive. Time-resolved SAXS measurements showed that the local volume fraction of nanoparticles increased during the drying of the dispersion owing to the shrinkage of the gel-like structure. Further, nanoparticle clusters in the dehydrated composite films showed percolated networks of nanoparticles, except for 5% loading that showed a phase-separated morphology as the volume fraction of nanoparticles remained lower than the percolation threshold. A significant restructuring of nanoparticle clusters occurred upon the hydration of nanocomposite films caused by the expansion of polymer networks induced by hydration forces. Temporal evolution of the volume fraction of nanoparticles during dehydration unveiled three distinct stages similar to the logistic growth function and this was attributed to the evaporation of free, intermediate, and bound water in the different stages. A plausible mechanism was elucidated based on the spring action analogy between anchored polymer chains and nanoparticles during hydration and dehydration processes.

Dynamic modulation of inter-particle correlation during colloidal assembly in a confined medium: revealed by real time SAXS.

Using real time small-angle X-ray scattering, we ellucidate a hitherto unobserved non-monotonic evolution of inter-particle correlation while colloidal particles assemble across pore boundary in a confined medium under influence of solvent evaporation. Time variation of local volume fraction of the particles passes through distinct modulation prior to reaching equilibrium. It has been demonstrated that the amplitude of oscillation depends strongly on size of the assembling particles. We comprehend such non-linear temporal evolution of particle correlation through density functional theory and molecular dynamics simulation.

Unraveling the Formation Mechanism of Dendritic Fibrous Nanosilica.

We studied the formation mechanism of dendritic fibrous nanosilica (DFNS) that involves several intriguing dynamical steps. Through electron microscopy and real-time small-angle X-ray scattering studies, it has been demonstrated that the structural evolution of bicontinuous microemulsion droplets (BMDs) and their subsequent coalescence, yielding nanoreactor template, is responsible for to the formation of complex DFNS morphology. The role of cosurfactant has been found to be quite crucial, which allowed the understanding of this intricate mechanism involving the complex interplay of self-assembly, dynamics of BMDs formation, and coalescence. The role of BMDs in formation of DFNS has not been reported so far and the present work allows a deeper molecular-level understanding of DFNS formation.

Introducing Alkyl Selenocyanates as Bifunctional Reagents in Photoredox Catalysis: Divergent Access to Ambident Isomers of -SeCN.

Owing to their diverse biological activities and versatility as synthetic precursors, organoselonocyanes categorize themselves as vital compounds. However, a limited reagent pool restricts their utility. In the present work, alkyl selenocyanates are hereby established as new bifunctional reagents for the simultaneous transfer of an alkyl group in addition to -SeCN. These reagents, when merged with photocatalysis, provide a key to accessing organoselenocyanates from feedstock olefins in an efficient and atom-economic fashion. A route to the analogous isoselenocyanate isomers facilitated by Lewis acid catalysis is also reported, presenting a divergent strategy for accessing both ambident isomers of -SeCN in an efficient manner.

Sulfotransferase-mediated phase II drug metabolism prediction of substrates and sites using accessibility and reactivity-based algorithms.

Sulphotransferases (SULTs) are a major phase II metabolic enzyme class contributing ~20 % to the Phase II metabolism of FDA-approved drugs. Ignoring the potential for SULT-mediated metabolism leaves a strong potential for drug-drug interactions, often causing late-stage drug discovery failures or black-boxed warnings on FDA labels. The existing models use only accessibility descriptors and machine learning (ML) methods for class and site of sulfonation (SOS) predictions for SULT. In this study, a variety of accessibility, reactivity, and hybrid models and algorithms have been developed to make accurate substrate and SOS predictions. Unlike the literature models, reactivity parameters for the aliphatic or aromatic hydroxyl groups (R/Ar-O-H), the Bond Dissociation Energy (BDE) gave accurate models with a True Positive Rate (TPR)=0.84 for SOS predictions. We offer mechanistic insights to explain these novel findings that are not recognized in the literature. The accessibility parameters like the ratio of Chemgauss4 Score (CGS) and Molecular Weight (MW) CGS/MW and distance from cofactor (Dis) were essential for class predictions and showed TPR=0.72. Substrates consistently had lower BDE, Dis, and CGS/MW than non-substrates. Hybrid models also performed acceptablely for SOS predictions. Using the best models, Algorithms gave an acceptable performance in class prediction: TPR=0.62, False Positive Rate (FPR)=0.24, Balanced accuracy (BA)=0.69, and SOS prediction: TPR=0.98, FPR=0.60, and BA=0.69. A rule-based method was added to improve the predictive performance, which improved the algorithm TPR, FPR, and BA. Validation using an external dataset of drug-like compounds gave class prediction: TPR=0.67, FPR=0.00, and SOS prediction: TPR=0.80 and FPR=0.44 for the best Algorithm. Comparisons with standard ML models also show that our algorithm shows higher predictive performance for classification on external datasets. Overall, these models and algorithms (SOS predictor) give accurate substrate class and site (SOS) predictions for SULT-mediated Phase II metabolism and will be valuable to the drug discovery community in academia and industry. The SOS predictor is freely available for academic/non-profit research via the GitHub link.

Giant Exciton Stokes Shift in Interfacially Prepared Cs(Mn/Pb)Cl3 Alloy Nanoplatelets.

Controlling the reabsorption of light by an emitting material is one of the keys to improving the performance of light-emitting devices. We prepare a set of size-dependent Cs(Mn/Pb)Cl3 alloy nanoplatelets (NPls) with substantial enhancement in the exciton Stokes shift, reducing the light-reabsorption significantly. We perform interfacial Mn-alloying using a shuttling ligand that transports MnCl2 from aqueous to nonaqueous phase and delivers it to NPls. While the exciton Stokes shift in 2-5 monolayer (ML) CsPbBr3 NPls rises from 20 to 108 meV, the exciton Stokes shift increases drastically up to 600 meV in 2 ML Cs(Mn/Pb)Cl3 NPls and further reduces upon increasing the thickness. Moreover, the exciton PL peak in the Mn-alloy NPls remains unperturbed by the quantum-confinement effect. A model based on the interplay between Mn2+/Mn3+ during the charge transfer process is proposed, accounting for such a large exciton Stokes shift. Finally, we utilize the large exciton Stokes-shifted alloy NPls for successful demonstration of white-light generation.

Performance of small- and wide-angle x-ray scattering beamline at Indus-2 synchrotron.

A Small- and Wide-Angle X-ray Scattering (SWAXS) beamline (BL-18) is installed and commissioned at a 1.5 T bending magnet port (5°) of Indus-2 synchrotron at RRCAT, Indore, India. The ∼40-m-long beamline has tunable x-ray energy in the range of 5-20 keV by using a double crystal monochromator. A 1.5-m-long toroidal mirror is used to focus the x-ray beam at the detector position. The beamline is equipped with a 6-m-long movable detector stage to access different wave-vector transfer ranges. At present, an online image plate area detector and a linear position-sensitive gas detector are installed for Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) measurements, respectively. The beamline is operational in simultaneous SAXS/WAXS mode to probe the mesoscopic as well as molecular level structure over a wide range of wave-vector transfer. The specification of the beamline and its performance are reported here. A few recent experimental results, as obtained from BL-18, are also described in brief.

Probing Microscale Structuring-Induced Phase Separation with Fluorescence Recovery Diffusion Dynamics in Poly(ethylene glycol) Solutions.

Apart from biocompatibility, poly(ethylene glycol) (PEG)-based biomedical constructs require mechanical tunability and optimization of microscale transport for regulation of the release kinetics of biomolecules. This study illustrates the role of inhomogeneities due to aggregates and structuring in the PEG matrix in the microscale diffusion of a fluorescent probe. Comparative analysis of fluorescence recovery after photobleaching (FRAP) profiles with the help of diffusion half-time is used to assess the diffusion coefficient (D). The observations support a nontrivial dependence of diffusion dynamics on polymer concentration (volume fraction, φ) and that of fillers carboxymethyl cellulose (CMC) and nanoclay bentonite (B). D values follow the Rouse scaling D ∼ φ-0.54 in PEG solutions. The diffusion time of the fluorescent probe in the PEG+bentonite matrix reveals the onset of depletion interaction-induced phase separation with an increase in bentonite concentration in the PEG matrix beyond 0.1 wt %. Beyond this concentration, structure factors obtained from prebleach FRAP images show a rapid increase at low Q. The two-phase system (PEG-rich and bentonite-rich) was characterized by the hierarchical structural topology of bentonite aggregates, and aggregate sizes were obtained at different length scales with phase contrast imaging, small-angle neutron scattering, and small-angle X-ray scattering. The microscale transport detection presented captures sensitively the commencement of phase separation in the PEG + bentonite matrix, as opposed to the PEG or PEG + CMC matrix, which are observed to be one-phase systems. This method of diffusion half-time and prebleach image analysis can be used for the fast, high-throughput experimental investigation of microscale mechanical response and its correlation with structuring in the polymer matrix.

Real-time monitoring the color changes of large yellow croaker (Larimichthys crocea) fillets based on hyperspectral imaging empowered with artificial intelligence.

Vis-NIR hyperspectral imaging (HSI) system combined with artificial neural networks was investigated for the first time to monitor color changes of large yellow croaker (Larimichthys crocea) fillets during low-temperature storage. Feed-forward neural networks (FNN) empowered with the leaky rectified linear unit (Leaky-Relu) have been developed as a non-linear quantitative analysis model. It presented accurate predictive power for color changes based on optimal spectra (with R2P of 0.908, 0.915, and 0.977; and RMSEP of 1.062, 3.315, and 0.082 for L*, a*, and b*, respectively). In final, the simplified FNN-Leaky-Relu model (S-FNN-L) was utilized to visualize the distribution maps of color parameters in the fillets. The results demonstrated the feasibility of HSI could replace the traditional colorimeter to determine the spatial distribution in the color measurement of fish fillets with a rapid and non-invasive technique.

Artificial Intelligence Empowered Multispectral Vision Based System for Non-Contact Monitoring of Large Yellow Croaker (Larimichthys crocea) Fillets.

A non-contact method was proposed to monitor the freshness (based on TVB-N and TBA values) of large yellow croaker fillets (Larimichthys crocea) by using a visible and near-infrared hyperspectral imaging system (400-1000 nm). In this work, the quantitative calibration models were built by using feed-forward neural networks (FNN) and partial least squares regression (PLSR). In addition, it was established that using a regression coefficient on the data can be further compressed by selecting optimal wavelengths (35 for TVB-N and 18 for TBA). The results validated that FNN has higher prediction accuracies than PLSR for both cases using full and selected reflectance spectra. Moreover, our FNN based model has showcased excellent performance even with selected reflectance spectra with rp = 0.978, R2p = 0.981, and RMSEP = 2.292 for TVB-N, and rp = 0.957, R2p = 0.916, and RMSEP = 0.341 for TBA, respectively. This optimal FNN model was then utilized for pixel-wise visualization maps of TVB-N and TBA contents in fillets.

Spray drying of colloidal dispersions containing ellipsoids.

HYPOTHESIS: Spray drying is a facile technique to transform colloidal dispersion into micro-granules of controlled size, shape, and morphology. There is significant interest to understand the structural integrity, different morphology of the granules obtained post spray drying which find potential application in many technological fields. The shape of the constituent particles in the colloidal dispersion that is spray dried is expected to influence the micro-structural features of the micro-granules. EXPERIMENTS: We investigate the formation of micro-granules consisting of nano-ellipsoids through controlled spray drying. The morphological features and the packing of ellipsoids in the granules are quantitatively analyzed by using small angle neutron scattering, small angle X-ray scattering and high-resolution field emission scanning electron microscopy. The time evolution of the micro-structure and the structural integrity of the granules are investigated by re-dispersing the powder granules in water. FINDINGS: The morphology of the granules are found to be strongly correlated with the aspect ratio of the ellipsoid. While the drying of droplets containing lower aspect ratio ellipsoids give rise to mostly spherical granules, in stark contrast, for higher aspect ratio ellipsoids, micro-granules of different morphologies are formed including doughnut shaped granules. A plausible mechanism explaining such an aspect ratio dependent shape transformation is proposed.

E. coli imprinted nano-structured silica micro-granules by spray drying: optimization of calcination temperature.

We have synthesized nano-structured silica-Escherichia coli composite micro-granules by spray drying of mixed suspension of silica and E. coli through evaporation-induced assembly. Synthesized micro-granules were subjected to calcination in order to form shape-matched macro-pores by removing the bacterial cells. The optimization of calcination temperature is crucial because calcination process leads to two contrasting effects, namely, (i) removal of E. coli from the granules and (ii) alteration of mesoscopic structure in the silica network. We have used small-angle neutron scattering and thermo-gravimetric analysis to determine the optimum temperature for calcination of these granules. It was found that calcination in the temperature range of 200°C to 400°C removes the cells without significant alteration of the nano-structured silica network. However, beyond 500°C, calcination results significant coalescence between the silica particles. Calcination at 600°C eventually collapses the meso-pore network of silica interstices.