Dynamically Reconfigurable, Multifunctional Emulsions with Controllable Structure and Movement

Cholic Acid/Glutathione-Assembled Nanofibrils for Stabilizing Pickering Emulsion Biogels

Achieving the delicate balance required for both emulsion and gel characteristics, while also imparting biological functionality in gelled emulsions, poses a significant challenge. Herein, Pickering emulsion biogels stabilized is reported by novel biological nanofibrils assembled from natural glutathione (GSH) and a tripod cholic acid derivative (TCA) via electrostatic interactions. GSH, composed of tripeptides with carboxyl groups, facilitates the protonation and dissolution of TCA compounds in water and the electrostatic interactions between GSH and TCA trigger nanofibrillar assembly. Fibrous nuclei initially emerge, and the formed mature nanofibrils can generate a stable hydrogel at a low solid concentration. These nanofibrils exhibit efficient emulsifying capability, enabling the preparation of stable Pickering oil-in-water (O/W) emulsion gels with adjustable phase volume ratios. The entangled nanofibrils adsorbed at the oil-water interface restrict droplet movement, imparting viscoelasticity and injectability to the emulsions. Remarkably, the biocompatible nanofibrils and stabilized emulsion gels demonstrate promising scavenging properties against reactive oxygen species (ROS). This strategy may open new scenarios for the design of advanced emulsion gel materials using natural precursors and affordable building blocks for biomedical applications.

Nanoparticle Surfactants at Complex Emulsion Interfaces

Using nanoparticle surfactants to stabilize the liquid-liquid interface has attracted significant attention for developing all-liquid constructs including emulsions and liquid devices. Here, an efficient strategy is demonstrated to stabilize complex emulsions that consist of multiphase droplets by using the co-assembly between the cellulose nanocrystal and amine-functionalized polystyrene. Cellulose nanocrystal surfactants (CNCSs) form and assembly in situ at the specified area of emulsion interface, showing a unique pH responsiveness due to their dynamic nature and allowing the reconfiguration of complex emulsion from encapsulated to Janus structures. Such complex emulsions can be further used as the templates to fabricate polymeric particles with hollow, semi-spherical, and spherical shapes on large scale. These findings establish a promising platform for designing intelligent soft matter that can be used in microreactors, sensors, and anisotropic materials.

Stimuli-responsive nanoparticle self-assembly at complex fluid interfaces: a new insight into dynamic surface chemistry

The self-assembly of core/shell nanoparticles (NPs) at fluid interfaces is a rapidly evolving area with tremendous potential in various fields, including biomedicine, display devices, catalysts, and sensors. This review provides an in-depth exploration of the current state-of-the-art in the programmed design of stimuli-responsive NP assemblies, with a specific focus on inorganic core/organic shell NPs below 100 nm for their responsive adsorption properties at fluid and polymer interfaces. The interface properties, such as ligands, charge, and surface chemistry, play a significant role in dictating the forces and energies governing both NP-NP and NP-hosting matrix interactions. We highlight the fundamental principles governing the reversible surface chemistry of NPs and present detailed experimental examples in the following three key aspects of stimuli-responsive NP assembly: (i) stimuli-driven assembly of NPs at the air/liquid interface, (ii) reversible NP assembly at the liquid/liquid interface, including films and Pickering emulsions, and (iii) hybrid NP assemblies at the polymer/polymer and polymer/water interfaces that exhibit stimuli-responsive behaviors. Finally, we address current challenges in existing approaches and offer a new perspective on the advances in this field.

Formation Mechanism of Starch-Based Double Emulsions from the Interfacial Perspective

Double emulsions are of significant practical value in protecting the core material owing to their multicomponent structure and have thus been applied in various fields, such as food, cosmetics, and drugs. However, the mechanism of double emulsion formation by native starch is not well established. Herein, we demonstrate a facile route to develop type-A, type-B, and type-C double emulsions using native starch and develop an innovative design for a carrier. Interfacial interaction, enthalpy changes of starch, and interfacial properties are key factors governing the formation of double emulsions and controlling the type of double emulsions formed. Therefore, the results of this study provide a better understanding of how and what type of starch-based double emulsions are formed.

pH/magnetic dual responsive Pickering emulsion stabilized by Fe3O4@SiO2@chitosan nanoparticles

In recent years, Pickering emulsifiers have been widely used in various production fields due to their excellent structural stability, biocompatibility and environmental friendliness. For some applications, it is required that the emulsifier can quickly respond to environmental stimuli and control the transition between stable and unstable emulsions. In this paper, we report a novel composite Pickering emulsifier with Fe3O4 as the core and magnetic response recognition body, silica as the intermediate protective layer, and chitosan (CS) of different molecular weights to endow solid particles with surface activity and pH-responsive properties. This emulsifier can stabilize the emulsion in the emulsion system with deionized water as the aqueous phase and liquid paraffin as the oil phase and can control the demulsification of the formed emulsion under the dual pH/magnetic stimulation. The experimental results show that Fe3O4@SiO2@CS has good paramagnetism and pH responsiveness. The particle size of the composite emulsifier nanoparticles is between 90 nm and 120 nm, and the best stabilizing effect of the emulsion is achieved when the dosage is 0.5 wt%. In the pH range of 3-11, the emulsifier can rapidly demulsify a stable paraffin oil-water emulsion system under the action of a magnetic field of strength 0.4 T. The pH response of the emulsifier is as follows: when pH ≤ 2, the system can form a stable emulsion, which is composed of fully protonated chitosan as a free chain segment and Fe3O4@SiO2. Emulsion stabilization was achieved with monolithic Fe3O4@SiO2@CS as an emulsifier at pH > 2, and demulsification was achieved at pH ≈ pKb (CS) at 298 K. The research in this paper can provide a feasible idea and synthesis method for the preparation of organic-inorganic composite structure emulsifier.

Responsive Janus droplets as modular sensory layers for the optical detection of bacteria

The field of biosensor development is fueled by innovations in new functional transduction materials and technologies. Material innovations promise to extend current sensor hardware limitations, reduce analysis costs, and ensure broad application of sensor methods. Optical sensors are particularly attractive because they enable sensitive and noninvasive analyte detection in near real-time. Optical transducers convert physical, chemical, or biological events into detectable changes in fluorescence, refractive index, or spectroscopic shifts. Thus, in addition to sophisticated biochemical selector designs, smart transducers can improve signal transmission and amplification, thereby greatly facilitating the practical applicability of biosensors, which, to date, is often hampered by complications such as difficult replication of reproducible selector-analyte interactions within a uniform and consistent sensing area. In this context, stimuli-responsive and optically active Janus emulsions, which are dispersions of kinetically stabilized biphasic fluid droplets, have emerged as a novel triggerable material platform that provides as a versatile and cost-effective alternative for the generation of reproducible, highly sensitive, and modular optical sensing layers. The intrinsic and unprecedented chemical-morphological-optical coupling inside Janus droplets has facilitated optical signal transduction and amplification in various chemo- and biosensor paradigms, which include examples for the rapid and cost-effective detection of major foodborne pathogens. These initial demonstrations resulted in detection limits that rival the capabilities of current commercial platforms. This trend article aims to present a conceptual summary of these initial efforts and to provide a concise and comprehensive overview of the pivotal kinetic and thermodynamic principles that govern the ability of Janus droplets to sensitively and selectively respond to and interact with bacteria.

Recent advances in bioactive nanocrystal-stabilized Pickering emulsions: Fabrication, characterization, and biological assessment

Numerous literatures have shown the advantages of Pickering emulsion (PE) for the delivery of bioactive ingredients in the fields of food, medicine, and cosmetics, among others. On this basis, the multi-loading mode of bioactives (internal phase encapsulation and/or loading at the interface) in small molecular bioactives nanocrystal-stabilized PE (BNC-PE) enables them higher loading efficiencies, controlled release, and synergistic or superimposed effects. Therefore, BNC-PE offers an efficacious delivery system. In this review, we briefly summarize BNC-PE fabrication and characterization, with a focus on the processes of possible evolution and absorption of differentially applied BNC-PE when interacting with the body. In addition, methods of monitoring changes and absorption of BNC-PE in vivo, from the nanomaterial perspective, are also introduced. The purpose of this review is to provide an accessible and comprehensive methodology for the characterization and evaluation of BNC-PE after formulation and preparation, especially in relation to biological assessment and detailed mechanisms throughout the absorption process of BNC-PE in vivo.

Dynamic In Situ Monitoring of the Salt Counter-ion Effect on Surfactant Effectiveness Using Reconfigurable Janus Emulsions

A straightforward method for visualization and quantification of surfactant effectiveness within different electrolyte environments based on using reconfigurable Janus emulsions as novel optical probes is reported. More specifically, we investigated the effect of different types and concentrations of salt counter-ions on the surfactant surface excess of commercial ionic and non-ionic surfactants, namely sodium dodecyl sulfate (SDS) and Tween 80 via in situ monitoring the morphological reconfigurations of biphasic Janus emulsions comprising hydrocarbon and fluorocarbon oils. We find that significant variations in interfacial tensions of SDS-stabilized interfaces (up to 15 mN·m^-1) can be evoked by titrating mono-, di-, and trivalent cationic counter-ions, which is coherent with the lyotropic (Hofmeister) series. In contrast, the salt counter-ion effect on the surfactant effectiveness was less pronounced for the non-ionic surfactant Tween 80 (∼3 mN·m^-1). Our results reveal a facile in situ method for monitoring the central role of electrolyte type and concentration on surfactant effectiveness and, more broadly, illustrate that Janus emulsions serve as powerful optical probes to dynamically study the properties of surfactants at liquid interfaces. We demonstrate the utility of our findings for an electro-induced morphological reconfiguration of Janus droplet morphologies by dynamically tuning Cu²⁺ concentration in solution using an electrode setup. The latter provides a unique platform for liquid-phase, real-time, and continuous tuning of Janus droplet morphologies, e.g., for their application in sensing and dynamic optical device platforms.

Progress in the Application of Food-Grade Emulsions

The detailed investigation of food-grade emulsions, which possess considerable structural and functional advantages, remains ongoing to enhance our understanding of these dispersion systems and to expand their application scope. This work reviews the applications of food-grade emulsions on the dispersed phase, interface structure, and macroscopic scales; further, it discusses the corresponding factors of influence, the selection and design of food dispersion systems, and the expansion of their application scope. Specifically, applications on the dispersed-phase scale mainly include delivery by soft matter carriers and auxiliary extraction/separation, while applications on the scale of the interface structure involve biphasic systems for enzymatic catalysis and systems that can influence substance digestion/absorption, washing, and disinfection. Future research on these scales should therefore focus on surface-active substances, real interface structure compositions, and the design of interface layers with antioxidant properties. By contrast, applications on the macroscopic scale mainly include the design of soft materials for structured food, in addition to various material applications and other emerging uses. In this case, future research should focus on the interactions between emulsion systems and food ingredients, the effects of food process engineering, safety, nutrition, and metabolism. Considering the ongoing research in this field, we believe that this review will be useful for researchers aiming to explore the applications of food-grade emulsions.

Effect of Thermal History and Hydrocarbon Core Size on Perfluorocarbon Endoskeletal Droplet Vaporization

Vaporizable hydrocarbon-in-fluorocarbon endoskeletal droplets are a unique category of phase-change emulsions with interesting physical and thermodynamic features. Here, we show microfluidic fabrication of various morphologies, such as solid-in-liquid, liquid-in-solid, and Janus-type, of complex solid n-C₂₀H₄₂ or n-C₂₁H₄₄ and liquid n-C₅F₁₂ droplets. Furthermore, we investigated the vaporization behavior of these endoskeletal droplets, focusing on the effects of heat treatment and core size. Comparison of vaporization and differential scanning calorimetry results indicated that vaporization occurs prior to melting of the bulk hydrocarbon phase for C₂₀H₄₂/C₅F₁₀ droplets and near the rotator phase for C₂₁H₄₄/C₅F₁₀ droplets. We found that heat treatment of the droplets increased the fraction of droplets that vaporized and also increased the vaporization temperature of the droplets, although the effect was temporary. Furthermore, we found that changing the relative size of the solid hydrocarbon core compared to the surrounding liquid shell increased the vaporization temperature and the vaporizing fraction. Taken together, these data support the hypothesis that surface melting behavior exhibited by the linear alkane may trigger the fluorocarbon vaporization event. These results may aid in the understanding of the interfacial thermodynamics and transport and the engineering of novel vaporizable endoskeletal droplets for biomedical imaging and other applications.

Shape-Changing Particles: From Materials Design and Mechanisms to Implementation

Demands for next-generation soft and responsive materials have sparked recent interest in the development of shape-changing particles and particle assemblies. Over the last two decades, a variety of mechanisms that drive shape change have been explored and integrated into particulate systems. Through a combination of top-down fabrication and bottom-up synthesis techniques, shape-morphing capabilities extend from the microscale to the nanoscale. Consequently, shape-morphing particles are rapidly emerging in a variety of contexts, including photonics, microfluidics, microrobotics, and biomedicine. Herein, the key mechanisms and materials that facilitate shape changes of microscale and nanoscale particles are discussed. Recent progress in the applications made possible by these particles is summarized, and perspectives on their promise and key open challenges in the field are discussed.

Liquid-Based Adaptive Structural Materials

Structural materials are used to provide stable mechanical architectures and transmit or support forces, and they play an important role in materials science and technology. During the long process of the exploitation of structural materials, the functionality of structural materials has gained prominence. Adaptive structures responding to external stimuli have come to the fore with significant advantages in structural materials. However, many solid adaptive structural materials still suffer from their single function and the lack of dynamic performance, such as issue around fouling and energy consumption, defects present everywhere in materials at the microscale, etc. To meet the increasing demands, more and more researchers have started turning their attention to liquid-based materials owing to their intrinsic spontaneous, dynamic, and functional properties. Liquid-based adaptive structural materials (LASMs) have been proposed and developed. Building upon both dynamic liquids and fixed solids, LASMs have been demonstrated to possess both dynamic adaptivity (from the active liquid part) and stable mechanical structure (from the fixed solid part), which are desired in many applications such as 3D printing, droplet manipulation, omniphobic surfaces, microfluidics, mass separation, etc. A unifying view of the recent progress of LASMs is presented, including liquid with particles, liquid with surfaces, as well as liquid with membranes. In addition, the discussion of the prospects and challenges are provided for promoting the development of LASMs.

Tuning Supramolecular Polymers' Amphiphilicity via Host-Guest Interfacial Recognition for Stabilizing Multiple Pickering Emulsions

Supramolecular host-guest chemistry bridging the adjustable amphiphilicity and macromolecular self-assembly is well advanced in aqueous media. However, the interfacial self-assembled behaviors have not been further exploited. Herein, we designed a β-cyclodextrin-grafted alginate/azobenzene-functionalized dodecyl (Alg-β-CD/AzoC12) supra-amphiphilic system that possessed tunable amphiphilicity by host-guest interfacial self-assembly. Especially, supra-amphiphilic aggregates could be utilized as highly efficient soft colloidal emulsifiers for stabilizing water-in-oil-water (W/O/W) Pickering emulsions due to the excellent interfacial activity. Meanwhile, the assembled particle structures could be modulated by adjusting the oil-water ratio, resulting from the tunable aggregation behavior of supra-amphiphilic macromolecules. Additionally, the interfacial adsorption films could be partially destroyed/reconstructed upon ultraviolet/visible irradiation due to the stimuli-altering balance of amphiphilicity of Alg-β-CD/AzoC12 polymers, further constructing the stimulus-responsive Pickering emulsions. Therefore, the supramolecular interfacial self-assembly-mediated approach not only technologically advances the continued development of creative templates to construct multifunctional soft materials with anisotropic structures but also serves as a creative bridge between supramolecular host-guest chemistry, colloidal interface science, and soft material technology.

Stalagmites in karst cave inspired construction: lotus root-type adsorbent with porous surface derived from CO2-in-water Pickering emulsion for selective and ultrafast uranium extraction

Simultaneous construction of porous and hollow adsorbent, especially from gas-in-water Pickering emulsion (PE) reactor, is vital for improving mass transfer kinetics and uptake amount. Inspired by the formation process of stalagmites in karst cave, amino and amidoxime bifunctionalized lotus root-type microsphere with porous surface (NH₂@AO-PLRMS) is prepared by the silica nanoparticles (SPs)-stabilized CO₂-in-water Pickering emulsion reactor and subsequent two-step grafting polymerization. The important roles of SPs acting as Pickering emulsifier, surface pore-forming agent, and adjusting internal lotus root structure are confirmed. Lotus root-type pores are dependent on the interface intensity and the permeability for compressed CO₂ bubbles in PE droplets. Benefitting from the lotus root-type structure and abundant affinity sites, the maximum uranium adsorption capacity of NH₂@AO-PLRMS is 1214.5 mg·g^-1 at 298 k, and an ultrafast uptake process can be achieved in the first 30 min. Both thermodynamic and kinetic studies indicate a spontaneous, entropy increased, and exothermic chemisorption process, and the synergies of amidoxime and amino groups can enhance the adsorption selectivity. Remarkably, NH₂@AO-PLRMS displays a high uranium adsorption capacity and desorption efficiency after seven cycles. These findings provide a way to obtain adsorbents with enhanced uranium extraction performance from gas-in-water PE reactor.

Reconfigurable Pickering Emulsions with Functionalized Carbon Nanotubes

Pickering emulsions (PEs) achieve interfacial stabilization by colloidal particle surfactants and are commonly used in food, cosmetics, and pharmaceuticals. Carbon nanotubes (CNTs) have recently been used as stabilizing materials to create dynamic single emulsions. In this study, we used the formation of Meisenheimer complexes on functionalized CNTs to fabricate complex biphasic emulsions containing hydrocarbons (HCs) and fluorocarbons (FCs). The reversible nature of Meisenheimer complex formation allows for further functionalization at the droplet-water interface. The strong affinity of fluorofluorescent perylene bisimide (F-PBI) to the CNTs was used to enhance the assembly of CNTs on the FC-water interface. The combination of different concentrations of the functionalized CNTs and the pelene additive enables predictable complex emulsion morphologies. Reversible morphology reconfiguration was explored with the addition of molecular surfactants. Our results show that the interfacial properties of functionalized CNTs have considerable utility in the fabrication of complex dynamic emulsions.

Manipulating Dispersions of Magnetic Nanoparticles

Dispersions of magnetic nanoparticles (MNPs) can exhibit paramagnetic ferrofluid or ferromagnetic liquid behavior. By modifying the surface functionality of MNPs, ferrofluids have been used to fabricate novel magnetically actuated devices. If the surface-functionalized MNPs interact with complementary ligands at a fluid-fluid interface, MNP surfactants form and in situ assemble at the interface. When jammed interfacially, MNP surfactants give rise to ferromagnetic behavior of the liquid (droplet), which is endowed with permanent magnetic dipoles while maintaining all of the characteristics of a fluid system. Here, we give a brief overview of the developments in the dispersion of MNPs in liquids from ferrofluids to ferromagnetic liquid droplets, their responses to external fields, and the manipulation of these responses for end uses. The reversible room-temperature para-to-ferro transformation of magnetic liquids is highlighted. We discuss challenges in the synthesis and characterization of these unusual liquids along with potential technological applications.

Dynamic Coloration of Complex Emulsions by Localization of Gold Rings Near the Triphase Junction

Multiphase microscale emulsions are a material platform that can be tuned and dynamically configured by a variety of chemical and physical phenomena, rendering them inexpensive and broadly programmable optical transducers. Interface engineering underpins many of these sensing schemes but typically focuses on manipulating a single interface, while engineering of the multiphase junctions of complex emulsions remains underexplored. Herein, multiphilic triblock copolymer surfactants are synthesized and assembled at the triphase junction of a dynamically reconfigurable biphasic emulsion. Tailoring the linear structure and composition of the polymer surfactants provides affinity to each phase of the complex emulsion (hydrocarbon, fluorocarbon, and continuous water phase), yielding selective localization of polymers around the triphase junction. Conjugation of these polymers with gold nanoparticles, forming structured rings, affords a dynamic reflected isotropic structural color that tracks with emulsion morphology, demonstrating the uniquely enabling nature of a functionalized triphase interface. This color is the result of interference of light along the internal hydrocarbon/fluorocarbon interface, with the gold nanoparticles scattering and redirecting light into total internal reflection competent paths. Thus, the functionalization of the triphase junction renders complex emulsions colorimetric sensors, a powerful tool toward sensitive and simple sensing platforms.

Destabilization mechanism of (W1+W2)/O reverse Janus emulsions

HYPOTHESIS

Reverse Janus emulsion, with droplets composed by "two rooms" of water phases, is a novel multiple emulsion attributed to excellent integration capability and biocompatibility. However, significant instability compared with normal Janus emulsions renders the stability issue of great importance. Moreover, the ultra-low aqueous-aqueous inner interfacial tension, the anisotropic nature of the droplets with distinct lobe composition, and the random orientation in the continuous phase endow the complicated and various demulsification mechanisms.

EXPERIMENTS

Reverse Janus emulsion of (W₁+W₂)/O, employing typical salt-alcohol aqueous two-phase system (ATPS) as inner phases, is prepared in batch scale by conventional one-step vortex mixing. The demulsification process is detected by multiple light scattering technique, which provides real-time, in-situ, and quantitative information of emulsion evolution. Moreover, the fusion pattern of the anisotropic droplets is illustrated by the combination with light microscopy and size distribution measurement.

FINDINGS

Coalescence and sedimentation are found to be two main demulsification processes. Two salt "body" lobes of the "snowman" shaped Janus droplets combine first resulting in an intermediate Cerberus topology with two alcohol "heads" on one salt "body". Subsequently, two "head" lobes coalesce resulting in a larger Janus droplet. Ultimately, the Gibbs free energy leads to a final state with three separated liquids. In addition, the variation in lobe viscosity, density, and properties of interfacial film greatly affect the demulsification rate and fusion pattern. A critical alcohol/surfactant mass ratio of 2 is found, beyond which a completely different fusion pattern occurs. Two alcohol "body" lobes combine first resulting in an intermediate Cerberus topology with two salt "heads" on one alcohol "body". Subsequently, two "head" lobes coalesce resulting in a larger Janus droplet. The findings are instructive in the stability of aqueous based multiple emulsions with advanced morphologies and meanwhile, promote the future application of this novel emulsion in food science, pharmacy, and biomimetic compartmentalization.

Controlled Movement of Complex Double Emulsions via Interfacially Confined Magnetic Nanoparticles

Controlled, dynamic movement of materials through noncontacting forces provides interesting opportunities in systems design. Confinement of magnetic nanoparticles to the interfaces of double emulsions introduces exceptional control of double emulsion movement. We report the selective magnetic functionalization of emulsions by the in situ selective reactions of amine-functionalized magnetic nanoparticles and oil-soluble aldehydes at only one of the double emulsion's interfaces. We demonstrate morphology-dependent macroscopic ferromagnetic behavior of emulsions induced by the interfacial confinement of the magnetic nanoparticles. The attraction and repulsion of the emulsions to applied magnetic fields results in controlled orientation changes and rotational movement. Furthermore, incorporation of liquid crystals into the double emulsions adds additional templating capabilities for precision assembly of magnetic nanoparticles, both along the interface and at point defects. Applying a magnetic field to liquid crystal complex emulsions can produce movement as well as reorganization of the director field in the droplets. The combination of interfacial chemistry and precise assembly of magnetic particles creates new systems with potentially useful field-responsive properties.

Particle Stabilization of Oil-Fluorocarbon Interfaces and Effects on Multiphase Oil-in-Water Complex Emulsion Morphology and Reconfigurability

Stabilization of oil-oil interfaces is important for nonaqueous emulsions as well as for multiphase oil-in-water emulsions, with relevance to a variety of fields ranging from emulsion polymerization to sensors and optics. Here, we focus on examining the ability of functionalized silica particles to stabilize interfaces between fluorinated oils and other immiscible oils (such as hydrocarbons and silicones) in nonaqueous emulsions and also on the particles' ability to affect the morphology and reconfigurability of complex, biphasic oil-in-water emulsions. We compare the effectiveness of fluorophilic, lipophilic, and bifunctional fluorophilic-lipophilic coated nanoparticles to stabilize these oil-oil interfaces. Sequential bulk emulsification steps by vortex mixing, or emulsification by microfluidics, can be used to create complex droplets in which particles stabilize the oil-oil interfaces and surfactants stabilize the oil-water interfaces. We examine the influence of particles adsorbed at the internal oil-oil interface in complex droplets to hinder the reconfiguration of these complex emulsions upon addition of aqueous surfactants, creating "metastable" droplets that resist changes in morphology. Such metastable droplets can be triggered to reconfigure when heated above their upper critical solution temperature. Thus, not only do these bifunctional silica particles enable the stabilization of a broad array of oil-fluorocarbon nonaqueous emulsions, but the ability to address the oil-oil interface within complex O/O/W droplets expands the diversity of oil chemical choices available and the accessibility of droplet morphologies and sensitivity.