Fluorocarbon Nanodroplets: Their Formation and Stability in Complex Solution Systems.

Perfluorocarbon (PFC) nanodroplets (NDs) are expanding in a wide range of applications in biotechnology and nanotechnology. Their efficacy in biological systems is significantly influenced by their size uniformity and stability within bioelectrolyte contexts. Presently, methods for creating monodisperse, highly concentrated, and well-stabilized PFC NDs under harsh conditions using low energy consumption methods have not been thoroughly developed, and their stability has not been sufficiently explored. This gap restricts their applicability for advanced medical interventions in tissues with high pH levels and various electrolytic conditions. To tackle these challenges and to circumvent potential toxicity from surface stabilizers, we have conducted an in-depth investigation into the formation and stability of uncoated perfluorohexane (PFH) NDs, which were synthesized by using a low-energy consumption solvent exchange technique, across complex electrolyte compositions or a broad spectrum of pH levels. The results indicated that low concentrations of low-valent electrolyte ions facilitate the nucleation of NDs and consistently accelerate Ostwald ripening over an extended period. Conversely, high concentrations of highly valent electrolyte ions inhibit nucleation and decelerate the ripening process over time. Given the similarities between the properties of NDs and nanobubbles, we propose a potential stabilization mechanism. Electrolytes influence the Ostwald ripening of NDs by adjusting the adsorption and distribution of ions on the NDs' surface, modifying the thickness of the electric double layer, and fine-tuning the energy barrier between droplets. These insights enable precise control over the stability of PFC NDs through the meticulous adjustment of the surrounding electrolyte composition. This offers an effective preparation method and a theoretical foundation for employing bare PFC NDs in physiological settings.

Formation of Bulk Nanobubbles Induced by Accelerated Electrons Irradiation: Dependences on Dose Rates and Doses of Irradiation.

Radiation on aqueous solutions can induce water radiolysis with products of radicals, H2, H2O2, and so on, and their consequent biological effects have long been interested in radiation chemistry. Unlike the decomposition of water by electric current that produces a significant number of bubbles, the gas products from the radiolysis of water are normally invisible by bare eyes, little is known on whether nanosized bubbles can be produced and what their dynamics are upon irradiation. Here, we first presented the formation of nanoscale bulk bubbles by irradiating pure water with accelerated electrons and their concentration and size distribution changes with the dose and rate of irradiation. The nanoparticle tracking analysis showed that irradiation can actually produce a certain amount of bulk nanobubbles in pure water. They exhibited a dependence on the irradiation dose rates and irradiation doses. The results indicated that the concentration of formed bulk nanobubbles increased as the irradiation dose rates increased, but it will increase and then decrease with the increased irradiation doses. The formed bulk nanobubbles could maintain stability for several hours. Our findings will provide a new angle of view for the radiation chemistry of water, and the formed nanobubbles may help elucidate the biological effects of irradiated solutions.

Influence of the Dissolved Gas on the Interfacial Properties of Decane Surface Nanodroplets.

Surface nanodroplets have received extensive attention recently due to their potential in the fabrication of functional materials with nanostructures and chemical reactions at micro- and nanoscales. Although the effect of dissolved gas in water has been realized in some important processes such as spontaneous emulsification of oil droplets in water, its roles in the wetting behavior of surface nanodroplets at the hydrophobic interface have been largely neglected. Here, we focused on the influence of dissolved gas on the interfacial properties of surface nanodroplets and characterized their morphological evolution when exposed to different air-saturated water samples. Results indicated that the morphology of surface nanodroplets barely changed in air-oversaturated cold water. However, their contact angle first decreases gradually in deionized water, increases immediately after replacement with degassed water, and eventually decreases gradually with time. Furthermore, the surface tension of nanodroplets would change similarly after the injection of degassed water. We considered these changes to be caused by the removal or reduction of the enriched gas at the substrate interface, in which the surface hydrophobicity was changed. Our findings could shed some light on the wetting behavior of nanodroplets at the hydrophobic surface in different air-saturated water samples and inspire the microscale manipulation and reaction of surface nanodroplets.

Controllable generation of interfacial gas structures on the graphite surface by substrate hydrophobicity and gas oversaturation in water.

Spherical nanobubbles and flat micropancakes are two typical states of gas aggregation on solid-liquid surfaces. Micropancakes, which are quasi-two-dimensional gaseous structures, are often produced accompanied by surface nanobubbles. Compared with surface nanobubbles, the intrinsic properties of micropancakes are barely understood due to the challenge of the highly efficient preparation and characterization of such structures. The hydrophobicity of the substrate and gas saturation of solvents are two crucial factors for the nucleation and stability of interfacial gas domains. Herein, we investigated the synergistic effect of the surface hydrophobicity and gas saturation on the generation of interfacial gas structures. Different surface hydrophobicities were achieved by the aging process of highly oriented pyrolytic graphite (HOPG). The results indicated that higher surface hydrophobicity and gas oversaturation could create surface nanobubbles and micropancakes with higher efficiency. Strong surface hydrophobicity could promote nanobubble nucleation and higher gas saturation would induce bigger nanobubbles. Degassed experiments could remove most of these structures and prove that they are actually gaseous domains. Finally, we draw a region diagram to describe the formation conditions of nanobubbles, micropancakes based on observations. These results would be very helpful for further understanding the formation of interfacial gas structures on the hydrophobic surface under different gas saturation.

Controllable formation of bulk perfluorohexane nanodroplets by solvent exchange.

Perfluorocarbon (PFC) nanodroplets have rapidly developed into useful ultrasound imaging agents in modern medicine due to their non-toxic and stable chemical properties that facilitate disease diagnosis and targeted therapy. In addition, with the good capacity for carrying breathing gases and the anti-infection ability, they are employed as blood substitutes and are the most ideal liquid respirators. However, it is still a challenge to prepare stable PFC nanodroplets of uniform size and high concentration for their efficient use. Herein, we developed a simple and highly reproducible method, i.e., propanol-water exchange, to prepare highly homogeneous and stable perfluorohexane (PFH) bulk nanodroplets. Interestingly, the size distribution and concentration of formed nanodroplets could be regulated by controlling the volume fraction of PFH and percentage of propanol in the propanol-water mixture. We demonstrated good reproducibility in the formation of bulk nanodroplets with PFH volume fractions of 1/2000-1/200 and propanol percentage of 5-40%, with uniform particle size distribution and high droplet concentration. Also, the prepared nanodroplets were very stable and could survive for several hours. We constructed a ternary phase diagram to describe the relationship between the PFH volume ratio, propanol concentration, and the size distribution and concentration of the formed PFH nanodroplets. This study provides a very useful method to prepare uniform size, high concentration and stable PFC nanodroplets for their medical applications.

Mechanical Properties of Sub-Microbubbles with a Nanoparticle-Decorated Polymer Shell.

Nanoparticle-decorated polymer-coated sub-microbubbles (NP-P-coated SMBs), as proved, have shown promising application prospects in ultrasound imaging, magnetic resonance imaging, drug delivery, and so forth. However, the quantitative evaluation of the stability and mechanical properties of single NP-P-coated SMB is absent. Here, we first reported the stiffness and Young's modulus of single NP-P-coated SMB obtained by the PeakForce mode of atomic force microscopy. Such NP-P-coated SMBs could maintain perfect spherical shapes and have a thinner shell thickness (about 10 nm), as determined by characterization using a transmission electron microscope. Young's modulus of NP-P-coated SMBs is about 4.6 ± 1.2 GPa, and their stiffness is about 15.0 ± 3.1 N/m. Both modulus and stiffness are obtained from the linear region in the force-deformation curve and are nearly independent of their sizes. These results should be very useful to evaluate their stability, which plays a key role in maintaining the shell drug loading and acoustic capabilities.

Wetting Behavior of Surface Nanodroplets Regulated by Periodic Nanostructured Surfaces.

Surfaces with nanostructure patterning are broadly encountered in nature, and they play a significant role in regulating various phenomena such as phase transition at the liquid/solid interface. Here, we designed two kinds of template substrates with periodic nanostructure patterns [i.e., nanotrench (NT) and nanopore (NP)]. Surface nanodroplets produced on these nanostructure surfaces were characterized to acquire their morphology and wetting properties. We show that nanostructure patterning could effectively regulate the shape, contact radius, and nucleate site of nanodroplets. While nanodroplets on the NT structure are constrained in one dimension, nanodroplets on the NP structure have enhanced the wetting property with constraints from two dimensions. Further numerical analysis indicates that the morphology and contact angles of nanodroplets on the NT structure depend on the substrate wettability and the droplet volume. These observations demonstrate how physical geometry and chemical heterogeneity of a substrate surface affect the growth and spreading of surface nanodroplets, which deepens our understanding on nanoscale phase separation.

Oxygenation and synchronous control of nitrogen and phosphorus release at the sediment-water interface using oxygen nano-bubble modified material.

Synchronously controlling the nitrogen (N) and phosphorus (P) release from sediments is an important basis for eutrophication management in lakes, but it is still a technical challenge at present. Loading nano-bubbles on the surface of natural minerals to increase dissolved oxygen(DO) level at the sediment-water interface (SWI)provides a possible solution to this problem. In this study, oxygen nano-bubble modified mineral (ONBMM) technology was developed, and its efficiency of oxygenation at the SWI and effect on the removal of internal nutrient input were evaluated under simulated conditions. The results showed that ONBMM effectively improved DO levels near the SWI; the highest concentration reached 6.55 mgL-1. Meanwhile, adding ONBMM remarkably reduced the concentrations of total P(TP), total N(TN) and ammonia N(NH3-N) in the overlying water. Compared with the control group, the fluxes of TP, NH3-N, and TN loading from sediments in simulation cores treated with ONBMM reduced by 96.4%, 51.1%, and 24.9%, respectively. The high-resolution data obtained by DGT showed that ONBMM effectively inhibited the reduction and release of FeP through increasing the oxygen level at the SWI. The results of 16S rRNA high-throughput sequencing showed that adding ONBMM strengthened the role of nitrobacteria, denitrifying bacteria, and ammonia oxidation bacteria at the SWI. The ONBMM technology provides a new tool to achieve oxygenation at the SWI and in situ control of internal pollution in eutrophic lakes.