Formation Of Nanodroplets Research Articles

Dissolution, phase behavior and mass transport of amorphous solid dispersions in aspirated human intestinal fluids

Amorphous solid dispersions (ASDs) typically show improved dissolution and generate supersaturated solutions, enhancing the oral bioavailability of poorly soluble drugs. To gain insights into intraluminal ASD behavior, we utilized two poorly soluble drugs with different crystallization tendencies, atazanavir and posaconazole, prepared as ASDs at a 10% drug loading with hydroxypropyl methylcellulose acetyl succinate (HPMCAS). We evaluated their release in aspirated fasted-state human intestinal fluid (FaHIF), and multi-component fasted-state simulated intestinal fluid (composite-FaSSIF), characterizing the supersaturation profiles and drug-rich nanodroplets that formed. Complete release was observed for atazanavir ASDs over a 90 min period. Flux for dissolved atazanavir ASDs remained high over the experimental time period of 3 h. In contrast, posaconazole solution concentrations were initially high and then decreased. Likewise, flux was initially high and then decreased where these changes are attributed to crystallization of the drug. Generation of spherical nano-sized amorphous droplets of ∼100-150 nm was found to occur in ex vivo FaHIF media for both ASDs, maximizing the diffusive flux during the supersaturation window. Moreover, buffer capacity differences were postulated to influence release rates of ASDs in simulated vs aspirated fluids. Importantly, the solution phase phenomena observed during ASD release in simulated fluids, namely amorphous nanodroplet formation and drug crystallization, were also found to occur in aspirated luminal fluids.

Optimal conditions for nano-emulsified vegetable oil synthesis for the biostimulation of 1,1,2-trichloroethane and vinyl chloride contaminated groundwater in bioreactors

Contamination of groundwater with chlorinated aliphatic hydrocarbons (CAHs) has become increasingly widespread. Enhanced reductive dechlorination (ERD) by emulsified vegetable oil (EVO) is an environmentally friendly, low-carbon and sustainable technology that effectively eliminates the threat from CAHs. To improve the permeability and bioavailability of EVO in the low-permeability substratum, nano-emulsified vegetable oil (nanoEVO) can be synthesized using a modified phase inversion composition method (MPIC) by increasing the emulsification temperature that reduces the shear force required for the formation of nanodroplets and the interfacial tension between the mixed phase and water. The emulsification temperature of 60 °C, the water content of 40–70%, the droplet diameter (DD) of nanoEVO prepared by MPIC is ∼200 nm, and had good monodispersion (≤0.2). The high molecular weight and low solubility of vegetable oil, and similar size of droplet make nanoEVO remains homogeneous after storage for > one year. NanoEVO can effectively biostimulate indigenous bacteria in CAHs-contaminated groundwater to dechlorinate 1,1,2-trichloroethane (1,1,2-TCA) to ethene via vinyl chloride (VC). The maximum dihaloelimination rate of 1,1,2-TCA was ∼66.06 μM·Cl−·day−1 and the maximum hydrogenolysis rate of VC was ∼35.67 μM·Cl−·day−1. NanoEVO effectively increased the relative abundance of Dehalococcoides from <0.10 to 9.61%. The abundances of Dhc 16S rRNA gene and dehalogenase gene vcrA increased by 102 and 103, respectively. Biostimulation shaped the structure of microbial communities and promoted hydrolytic acidification and anaerobic fermentation. Moreover, the syntrophic VFA-oxidizing bacteria participated in secondary fermentation and were closely correlated with H2 consumption metabolism. By providing carbon sources and maintaining an anaerobic environment with stable pH and ORP, nanoEVO biostimulated the hydrolytic acidification led by fermentative bacteria, secondary fermentation with syntrophic VFA-oxidizing bacteria and reductive dechlorination carried out by dechlorinator, thus greatly increasing the CAH-dechlorinating ability of indigenous microbial communities.

Modes of Nanodroplet Formation and Growth on an Ultrathin Water Film.

Using nanobubbles as geometrical confinements, we create a thin water film (∼10 nm) in a graphene liquid cell and investigate the evolution of its instability at the nanoscale under transmission electron microscopy. The breakdown of the water films, resulting in the subsequent formation and growth of nanodroplets, is visualized and generalized into different modes. We identified distinct droplet formation and growth modes by analyzing the dynamic processes involving 61 droplets and 110 liquid bridges within 31 Graphene Liquid Cells (GLCs). Droplet formation is influenced by their positions in GLCs, taking on a semicircular shape at the edge and a circular shape in the middle. Growth modes include liquid mass transfer driven by Plateau-Rayleigh instability and merging processes in and out-of-plane of the graphene interface. Droplet growth can lead to the formation of liquid bridges for which we obtain multiview projections. Data analysis reveals the general dynamics of liquid bridges, including drawing liquids from neighboring residual water films, merging with surrounding droplets, and merging with other liquid bridges. Our experimental observations provide insights into fluid transport at the nanoscale.

Drug-Polymer Nanodroplet Formation and Morphology Drive Solubility Enhancement of GDC-0810.

Nanodroplet formation is important to achieve supersaturation of active pharmaceutical ingredients (APIs) in an amorphous solid dispersion. The aim of the current study was to explore how polymer composition, architecture, molar mass, and surfactant concentration affect polymer-drug nanodroplet morphology with the breast cancer API, GDC-0810. The impact of nanodroplet size and morphology on dissolution efficacy and drug loading capacity was explored using polarized light microscopy, dynamic light scattering, and cryogenic transmission electron microscopy. Poly(N-isopropylacrylamide-stat-N,N-dimethylacrylamide) (PND) was synthesized as two linear derivatives and two bottlebrush derivatives with carboxylated or PEGylated end-groups. Hydroxypropyl methylcellulose acetate succinate grade MF (HPMCAS-MF) and poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) were included as commercial polymer controls. We report the first copolymerization synthesis of a PVPVA bottlebrush copolymer, which was the highest performing excipient in this study, maintaining 688 μg/mL GDC-0810 concentration at 60 wt % drug loading. This is likely due to strong polymer-drug noncovalent interactions and the compaction of GDC-0810 along the PVPVA bottlebrush backbone. Overall, it was observed that the most effective formulations had a hydrodynamic radius less than 25 nm with tightly compacted nanodroplet morphologies.

Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy.

Transparent conductive oxides such as indium tin oxide (ITO) are standards for thin film electrodes, providing a synergy of high optical transparency and electrical conductivity. In an electrolytic environment, the determination of an inert electrochemical potential window is crucial to maintain a stable material performance during device operation. We introduce operando ellipsometry, combining cyclic voltammetry (CV) with spectroscopic ellipsometry, as a versatile tool to monitor the evolution of both complete optical (i.e., complex refractive index) and electrical properties under wet electrochemical operational conditions. In particular, we trace the degradation of ITO electrodes caused by electrochemical reduction in a pH-neutral, water-based electrolyte environment during electrochemical cycling. With the onset of hydrogen evolution at negative bias voltages, indium and tin are irreversibly reduced to the metallic state, causing an advancing darkening, i.e., a gradual loss of transparency, with every CV cycle, while the conductivity is mostly conserved over multiple CV cycles. Post-operando analysis reveals the reductive (loss of oxygen) formation of metallic nanodroplets on the surface. The reductive disruption of the ITO electrode happens at the solid-liquid interface and proceeds gradually from the surface to the bottom of the layer, which is evidenced by cross-sectional transmission electron microscopy imaging and complemented by energy-dispersive X-ray spectroscopy mapping. As long as a continuous part of the ITO layer remains at the bottom, the conductivity is largely retained, allowing repeated CV cycling. We consider operando ellipsometry a sensitive and nondestructive tool to monitor early stage material and property changes, either by tracing failure points, controlling intentional processes, or for sensing purposes, making it suitable for various research fields involving solid-liquid interfaces and electrochemical activity.

Rational Design and Development of a Soluble Mesoporous Carrier for the Solidification of a Preconcentrated Self-Nanoemulsion Formulation.

The solidification of self-preconcentrated nanoemulsion without changes in nanodroplet formation gains particular consideration due to the interaction between solidified carriers. This work aimed to develop mannitol mesoporous as a soluble carrier for supersaturated self-nanoemulsion (SSNE) using a design of experiment (DoE) approach. The mesoporous carrier was prepared by a spray-drying technique. The type of templating agent (TA) used to form a porous system, the amount of TA, and solid loading in the spray-drying process were studied. Several characterizations were performed for mannitol mesoporous formation, namely, powder X-ray diffraction, thermal analysis, scanning electron microscopy, and surface area analyzer. Solidification of SSNE incorporated into the mesoporous mannitol was carried out, followed by compaction behavior, flowability, and nanodroplet formation. The results revealed several process parameters for preparing the mesoporous mannitol, notably TA, which gained more significant consideration. Solid loading in the mesoporous preparation system reduced the surface area and pore size and did not affect solid SSNE flowability. The amount of TA increased the pore size and volume dramatically as well as the compactibility and flowability. Ammonium carbonate was the preferable TA for preparing the mesoporous carrier, particularly for the nanodroplet formulation process. In addition, synergistic and antagonistic interactions between factors were also observed. The optimized mesoporous carrier was applied for solidification, and there was no difference between SSNE and solid SSNE in the performance of nanodroplet formation.

Ultrafast and Large-Scale Fabrication of PEDOT:PSS Nanofilms Using Electrical-Field-Assisted Direct Ink Deposition.

The importance of conductive polymers has significantly increased over the decade due to their various applications, such as in electronic devices, sensors, and photovoltaics. Poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most successfully and widely used polymers in practical applications. Spin coating is extensively used to fabricate these conductive films; however, it has disadvantages. It is inherently a batch process with relatively low output and high solution wastage. To address these issues, we developed a novel printing process called electrical-field-assisted direct ink deposition (EF-DID), which yields a continuous, homogenous film with high electrical conductivity. In this process, we studied the formation of nanodroplets under an electrical field and their effects on film characteristics. Furthermore, dimethyl sulfoxide (DMSO) was considered as an additive solvent to increase the conductivity and wettability of the films. We then compared EF-DID-printed PEDOT:PSS films with spin-coated films to better understand the film properties. Finally, inverted perovskite solar cell devices were fabricated and compared, where the PEDOT:PSS layers were prepared by EF-DID printing and spin coating. Based on the experimental results, a solution of 20% PEDOT:PSS in DMSO (vol/vol) printed by EF-DID for 15 s provided optimal morphology.

What Controls the Hole Formation of Nanodroplets: Hydrodynamic or Thermodynamic Instability?

Using molecular dynamics simulations, we investigate the air hole formation of water nanodroplets impacting hydrophilic to hydrophobic surfaces in the range of static contact angles from 30° to 140° with different initial surface temperatures ranging from 300 to 1000 K. We show that the hole dynamics of nanodroplets are different from those observed in millimeter-sized droplets. The hole formation can be observed on smooth surfaces for nanodroplets; however, it only occurs on nonsmooth surfaces for millimeter-sized droplets. We clarify that the hole formation of nanodroplets is triggered by a nucleated vapor bubble due to thermodynamic instability, whereas it is initiated by air bubble entrapment during impact due to hydrodynamic instability for millimeter-sized droplets. The hole formation of nanodroplets relies heavily on the surface temperature and surface wettability, because the nucleated vapor bubble more easily occurs and grows on the surface with high initial temperatures and hydrophobic surfaces. Based on the thermal stability analysis, a criterion is developed to predict the hole formation of nanodroplets, which verifies the dependence of hole formation on the surface temperature and wettability. Furthermore, we show that the ring-bouncing of nanodroplets is triggered by the nucleated vapor bubble. We clarify the reasons for the reduced contact time of nanodroplets caused by the ring-bouncing.

Electrochemical-Shock Synthesis of Nanoparticles from Sub-femtoliter Nanodroplets

ConspectusNanoparticles have witnessed immense development in the past several decades due to their intriguing physicochemical properties. The modern chemist is interested not only in methods of synthesizing nanoparticles with tunable properties but also in the chemistry that nanoparticles can drive. While several methods exist to synthesize nanoparticles, it is often advantageous to put nanoparticles on a variety of conductive substrates for multiple applications (such as energy storage and conversion). Despite enjoying over 200 years of development, electrodeposition of nanoparticles suffers from a lack of control over nanoparticle size and morphology. There have been heroic efforts to address these issues over time. With an understanding that structure-function studies are imperative to understand the chemistry of nanoparticles, new methods are necessary to electrodeposit a variety of nanoparticles with control over macromorphology and also microstructure.This Account details our group's efforts in overcoming challenges of classical nanoparticle electrodeposition by electrodepositing nanoparticles from water nanodroplets. When a nanodroplet full of metal salt precursor is incident on the electrode biased sufficiently negative to drive electroplating, nanoparticles form at a fast rate (on the order of microseconds to milliseconds). We start with the general nuts-and-bolts of the experiment (nanodroplet formation and methods for electrodeposition). The deposition of new nanomaterials often requires one to develop new methods of measurement, and we detail new measurement tools for quantifying nanoparticle porosity and nanopore tortuosity within single nanoparticles. We achieve nanopore characterization by using Focused Ion Beam milling and Scanning Electron Microscopy. Owing to the small size of the nanodroplets and fast mass transfer (the contents of a femtoliter droplet can be electrolyzed in only a few milliseconds), the use of nanodroplets also allows the electrodeposition of high entropy alloy nanoparticles at room temperature.We detail how a deep understanding of ion transfer mechanisms can be used to expand the library of possible metals that can be deposited. Furthermore, simple ion changes in the dispersed droplet phase can decrease the cost per experiment by orders of magnitude. Finally, electrodeposition in aqueous nanodroplets can also be combined with stochastic electrochemistry for a variety of interesting studies. We detail the quantification of the growth kinetics of single nanoparticles in single aqueous nanodroplets. Nanodroplets can also be used as tiny reactors to trap only a few molecules of a metal salt precursor. Upon reduction to the zerovalent metal, electrocatalysis at very small metal clusters can be probed and evaluated with time using steady-state electrochemical measurements. Overall, this burgeoning synthetic tool is providing unexpected avenues of tunability of metal nanoparticles on conductive substrates.

Microfluidic formation of surface nanodroplets using green deep eutectic solvents for liquid–liquid nanoextraction and controlled precipitation

HypothesisSurface nanodroplets have recently been employed for in situ chemical analysis leveraging their low volume, e.g. O(10−15 L), that enables rapid analyte extraction and pre-concentration. So far, most surface nanodroplets have been formed using single organic solvents such as 1-octanol, toluene, among others. Designing multicomponent surface nanodroplet with controllable composition is highly desirable for extending their application as extractant. ExperimentHere, we formed surface nanodroplets using green deep eutectic solvent (gDES) composed of thymol and decanoic acid, both of which are naturally occurring chemicals. The influence of parameters such as flowrate and the composition of deep eutectic solvent on the surface nanodroplet formation were studied. As proof-of-concept, the gDES surface nanodroplets were further used to extract and detect trace amounts of fluorescent rhodamine 6G dye and copper ions from water. FindingsThe formation of gDES surface nanodroplets follows the theoretical model which states that the final droplet volume (Vf) scales with the Peclét number (Pe) of the flow during formation by the solvent exchange process, that is Vf ∼ Pe3/4, and the nanodroplets demonstrate excellent ability as extractant for rhodamine 6G and copper ions from water. Surprisingly, the confined volume of gDES surface nanodroplets enables fast and controlled formation of Cu (II)-decanoate crystal.

Computational module of nanodroplet formation en route to fibrillization of amyloid peptides with designed flanking sequences.

Soluble oligomers populating early amyloid aggregation can be regarded as nanodroplets of liquid-liquid phase separation (LLPS). Amyloid peptides typically contain hydrophobic aggregation-prone regions connected by hydrophilic linkers and flanking sequences, and such sequence hydropathy pattern drives the formation of supramolecular structures in the nanodroplets and modulates subsequent fibrillization. Here, we studied LLPS and fibrillization of coarse-grained amyloid peptides with increasing flanking sequences. Nanodroplets assumed lamellar, cylindrical micellar and spherical micellar structures with increasing peptide hydrophilic/hydrophobic ratios, and such morphologies governed subsequent fibrillization processes. Adding glycine-serine repeats as flanking sequences to Aβ16-22, the amyloidogenic core of amyloid-β, our computational predictions of morphological transitions were corroborated experimentally. The uncovered inter-relationships between peptide sequence pattern, oligomer/nanodroplet morphology, and fibrillization pathway, kinetics and structure may contribute to our understanding of pathogenic amyloidosis in ageing, facilitate future efforts ameliorating amyloidosis through peptide engineering, and aid in the design of novel amyloid-based functional nano-biomaterials and nanocomposites.

Phase-Separated Nanodroplets Formed below the Cloud Point for the Aqueous Solution of Stereo-Controlled Poly(N-isopropylacrylamide).

The relationship between dehydration of polymer chains and the nanodroplet formation through the macroscopic liquid-liquid phase separation (LLPS) has been investigated for the aqueous solution of stereocontrolled poly(N-isopropylacrylamide) (PNiPAm) and poly(N-diethylacrylamide) (PNdEAm). The fluorescent probe method reveals that the temperature range of dehydration for PNiPAm chains is much narrower than that for PNdEAm. The sharp dehydration of polymer chains may give rise to the characteristic thermoresponsive behavior of PNiPAm in water. For meso-rich PNiPAms, the dehydration point (Tdh), which is defined as the temperature where the single chains start assembling in the solution, locates far from the cloud point (Tc). That is, the dehydration of the chain occurs antecedently before the system undergoes a macroscopic LLPS. For PNdEAm, however, the dissociation between Tdh and Tc is not found. For the aqueous solution of PNiPAm with 52% of the meso content, the fluorescence correlation spectroscopy has revealed that nano-order droplets (ca. 45 nm of the hydration radius) are stabilized in the intermediate state between Tdh and Tc. The sharp dehydration of PNiPAm chains may enable an acute condensation of polymers in droplets, causing a viscoelastic hindrance in the coalescence of droplets.

Modulating Nanodroplet Formation En Route to Fibrillization of Amyloid Peptides with Designed Flanking Sequences.

Soluble oligomers populating early amyloid aggregation can be regarded as nanodroplets of liquid-liquid phase separation (LLPS). Amyloid peptides typically contain hydrophobic aggregation-prone regions connected by hydrophilic linkers and flanking sequences, and such a sequence hydropathy pattern drives the formation of supramolecular structures in the nanodroplets and modulates subsequent fibrillization. Here, we studied LLPS and fibrillization of coarse-grained amyloid peptides with increasing flanking sequences. Nanodroplets assumed lamellar, cylindrical micellar, and spherical micellar structures with increasing peptide hydrophilic/hydrophobic ratios, and such morphologies governed subsequent fibrillization processes. Adding glycine-serine repeats as flanking sequences to Aβ16-22, the amyloidogenic core of amyloid-β, our computational predictions of morphological transitions were corroborated experimentally. The uncovered inter-relationships between the peptide sequence pattern, oligomer/nanodroplet morphology, and fibrillization pathway, kinetics, and structure may contribute to our understanding of pathogenic amyloidosis in aging, facilitate future efforts ameliorating amyloidosis through peptide engineering, and aid in the design of novel amyloid-based functional nanobiomaterials and nanocomposites.

Explaining the Release Mechanism of Ritonavir/PVPVA Amorphous Solid Dispersions.

In amorphous solid dispersions (ASDs), an active pharmaceutical ingredient (API) is dissolved on a molecular level in a polymeric matrix. The API is expected to be released from the ASD upon dissolution in aqueous media. However, a series of earlier works observed a drastic collapse of the API release for ASDs with high drug loads (DLs) compared to those with low DLs. This work provides a thermodynamic analysis of the release mechanism of ASDs composed of ritonavir (RIT) and poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA). The observed release behavior is, for the first time, explained based on the quantitative thermodynamic phase diagram predicted by PC-SAFT. Both liquid–liquid phase separation in the dissolution medium, as well as amorphous phase separation in the ASD, could be linked back to the same thermodynamic origin, whereas they had been understood as different phenomena so far in the literature. Furthermore, it is illustrated that upon release, independent of DL, both phenomena occur simultaneously for the investigated system. It could be shown that the non-congruent release of the drug and polymer is observed when amorphous phase separation within the ASD has taken place to some degree prior to dissolution. Nanodroplet formation in the dissolution medium could be explained as the liquid–liquid phase separation, as predicted by PC-SAFT.

3D Printing of Largescale Functional Nanofilm using Electrically assisted Direct Ink Deposition

Functional nanofilms show significant importance for various applications in different fields, such as sustainable energy, biomedicine, electronics, and optics. However, there are still many challenges in the fabrication of nanostructured films with tailored properties using traditional manufacturing technologies. A novel 3D printing approach called electrical field-assisted direct ink deposition (EF-DID) was developed to produce large-scale nanofilms with controllable nanostructures and patternable features. In the proposed method, the formation of nanodroplets in the direct ink deposition was investigated under an electrostatic field with high voltage. Critical printing parameters, including solution concentration, deposition height, applied voltage, and ink flow rate, were studied systematically to understand fundamental mechanisms of the nanostructures generation during the printing. In addition, the scientific relationship between deposition parameters and nanofilm properties, including film thickness, electrical conductivity, and contact angle, were explored. Finally, patterned nanofilms with well-organized nanostructures were fabricated to demonstrate potential application prospects in the field of nanotechnology.

A new insight into the interaction of hydroxyl radical with supercooled nanodroplet in the atmosphere

• The interaction between OH* and supercooled nanodroplet led to delocalized states caused by surface effects. • The OH* shows a high tendency for accepting H-bond from neighboring water molecules around (1.77 Å, 122°). • RDF and ring analysis results confirmed the LDA ice for OH*-supercooled nanodroplet. • The preference of six-membered rings in supercooled nanodroplet based on ring analysis. • The 3-fold and 4-fold coordination were revealed as dominant structures. Fallstreak clouds are types of clouds with supercooled water droplets, meaning that they are still liquid at sub-freezing temperatures. In the atmosphere, hydroxyl radicals serve as an important source of oxidants. The reactivity of the hydroxyl radicals in ice environments is significant, affecting other atmospheric reactions. However, the interaction between OH radical with supercooled water nanodroplet remains unknown. This work presents a comprehensive computational study of OH radicals at the air-ice interface. Ab initio molecular dynamics simulation showed that despite previous assumptions, the hemibond could also exist in large OH*-nanodroplet systems under supercooling process. Two hydrogen-bonded water molecules along with the hemibond have been found to be the reason for OH* stability. There is a significant correlation between our RDF and ring analysis results and the structural information from X-ray crystallography, confirming LDA ice for supercooled nanodroplets. The hydrogen bond analysis revealed that there is no radical effect on the hydrogen bond formation of water nanodroplets at 250 K. Moreover, the time evolution of critical bonds based on distances revealed that the OH* could be a movable and reactive radical during the supercooling process. Results from this research contribute to a better understanding of natural phenomena and rational design of anti-icing systems for aviation, wind energy, and infrastructures along with cryopreservation.

Multiscale Analysis of Segmental Relaxation in PC/PETg Multilayers: Evidence of Immiscible Nanodroplets

This work highlights the influence of layer thicknesses on glass transition and molecular mobility in polycarbonate (PC) and poly(ethylene terephthalate glycol) (PETg) multilayered films obtained by the layer-multiplying coextrusion process. By combining modulated temperature scanning calorimetry (MT-DSC) and dielectric relaxation spectroscopy (DRS) measurements, the average values of the cooperative rearranging region (CRR) size in a wide range of relaxation times and temperatures have been calculated. The size reduction from micro- to nanoscale is accompanied by a significant deviation of the structural and dynamical properties compared to the bulk. Furthermore, we have evidenced significant differences in PETg and PC behaviors: PETg plays the role of a “hard-confined” polymer, while PC behaves as a “free-confined” polymer, implying opposite variations of the glass transition temperature. The determination of the relaxation parameters for each individual polymer has been possible even for very low layer thicknesses (below 10 nm), for which the multilayer structure is not observed. This result shows that even when PETg and PC are brought into very intimate contact, they maintain their own structural behavior and segmental relaxation, suggesting the formation of immiscible nanodroplets when the multilayer structure disappears.

Controlling size, shape, and charge of nanoparticles via low-energy miniemulsion and heterogeneous RAFT polymerization

Size, shape, and charge are key parameters of nanoparticles, and variations in these parameters can significantly impact their properties and applications. Among various nanoparticle synthesis methods, the combination of low-energy miniemulsions with reversible addition-fragmentation chain-transfer (RAFT) polymerization allows for the facile, rapid, and environmentally friendly preparation of uniform nanoparticles. However, this method cannot, yet, simultaneously control the size, shape, and charge of nanoparticles, thereby limiting its potential applications. Here we report the synthesis of polymeric nanoparticles with concurrent control over particle size, shape, and charge via low-energy miniemulsion and heterogeneous RAFT polymerization. Key to our approach is the combination of (i) a macromolecular surface-active agent to facilitate the formation of nanodroplets, (ii) various small-molecule surfactants with different charges to control the size and charge of nanodroplets, and (iii) a molecular transformer to control the morphology of the final polymeric nanoparticles. In particular, negatively charged polystyrene nanoparticles of different sizes (from ∼100 to ∼500 nm) and shapes (sphere, worm, and vesicle) were obtained by simply tuning the amount of added sodium dodecyl sulfate (SDS) and toluene. The nanoparticle charge was then switched from negative to positive by replacing SDS with cetyltrimethylammonium bromide (CTAB), a positively charged surfactant. In addition, biocompatible and neutral surfactants (including Tweens and Span 80) were employed to tune the nanoparticle size yielding challenging-to-synthesize nanoworms. This work provides a simple but powerful approach to produce nanoparticles of different properties, thus expanding the scope of nanomaterials made by RAFT low-energy miniemulsion polymerization.

Excited state intramolecular proton transfer of 2-Aryl,3-Hydroxybenzo[g]quinolones in surfactant supramolecular assemblies

The 2-Aryl 3-Hydroxybenzo[g]quinolones (2Ar3HBQ) are a relatively new family of ESIPT fluorophores distinguished by their visible absorption spectra, which makes them potential ratiometric probes for biological media. In the present work, we found that 2Ar3HBQ residing as guest fluorophores inside biomimetic host systems like surfactant supramolecular assemblies like micelles and reverse micelles, exhibit dual emission attributable to ESIPT. Ratiometric analysis of the two emission peaks corresponding to the normal (N*) and tautomer (T*) species indicated that the ESIPT rates depend strongly on the nature of the host supramolecular assembly. For example, the ESIPT rate in reverse micelles containing no water was found to be similar to that in weak H-bonding and low polar solvents like acetonitrile. However, addition of water leads to the formation of water nano-droplets inside the reverse micelles, with concomitant sharp decrease of ESIPT rates. In each of the cases studied, the major factor determining the ESIPT rate appears to be the competition between intramolecular H-bonding within the guest fluorophore on the one hand, and intermolecular H-bonding involving the guest fluorophore and water molecules in its local environment, on the other hand.

In-situ fabrication of metal oxide nanocaps based on biphasic reactions with surface nanodroplets

HypothesisSurface-bound nanomaterials are widely used in clean energy techniques from solar-driven evaporation in desalination to hydrogen production by photocatalytic electrolysis. Reactive surface nanodroplets may potentially streamline the process of fabrication of a range of surface-bound nanomaterials invoking biphasic reactions at interfaces. ExperimentsIn this work, we demonstrate the feasibility of reactive surface nanodroplets for in situ synthesis and anchoring of nanocaps of metal oxides with tailored porous structures. FindingsSpatial arrangement and surface coverage of nanocaps are predetermined during the formation of nanodroplets, while the crystalline structures of metal oxides can be controlled by thermal treatment of organometallic nanodroplets produced from the biphasic reactions. Notably, tuning the ratio of reactive and nonreactive components in surface nanodroplets enables the formation of porous nanocaps that can double photocatalytic efficiency in the degradation of organic contaminants in water, compared to smooth nanocaps. In total, we demonstrate in situ fabrication of four types of metal oxides in the shape of nanocaps. Our work shows that reactive surface nanodroplets may open the door to a general, fast and tuneable route for preparing surface-bound materials. This fabrication approach may develop new nanomaterials needed for photocatalytic reactions, wastewater treatment, optical focusing, solar energy conversion and other clean energy techniques.