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Hard carbon is regarded as the most promising anode material for sodium-ion (Na-ion) batteries, owing to its advantages of high abundance, low cost, and low operating potential. However, the rate capability and cycle life span of hard carbon anodes are far from satisfactory, severely hindering its industrial applications. Here, we demonstrate that the desolvation process defines the Na-ion diffusion kinetics and the formation of a solid electrolyte interface (SEI). The 3A zeolite molecular sieve film on the hard carbon is proposed to develop a step-by-step desolvation pathway that effectively reduces the high activation energy of the direct desolvation process. Moreover, step-by-step desolvation yields a thin and inorganic-dominated SEI with a lower activation energy for Na+ transport. As a result, it contributes to greatly improved power density and cycling stability for both ester and ether electrolytes. When the above insights are applied, the hard carbon anode achieves the longest life span and minimum capacity fading rate at all evaluated current densities. Moreover, with the increase in current densities, an improved plateau capacity ratio is observed. This step-by-step desolvation strategy comprehensively enhances various properties of hard carbon anodes, which provides the possibility of building practical Na-ion batteries with high power density, high energy density, and durability. [ABSTRACT FROM AUTHOR]

We report the self-organization of universal branching patterns of oil nanodroplets under the Ouzo effect [Vitale S, Katz J (2003) Langmuir 19:4105-4110]--a phenomenon in which spontaneous droplet formation occurs upon dilution of an organic solution of oil with water. The mixing of the organic and aqueous phases is confined under a quasi-2D geometry. In a manner analogous to the ramification of ground stream networks [Devauchelle O, Petroff AP, Seybold HF, Rothman DH (2012) Proc Natl Acad Sci USA 109: 20832-20836 and Cohen Y, et al. (2015) Proc Natl Acad Sci USA 112:14132-14137] but on a scale 10 orders of magnitude smaller, the angles between the droplet branches are seen to exhibit remarkable universality, with a value around 74° ± 2°, independent of the various control parameters of the process. Numerical simulations reveal that these nanodroplet branching patterns are governed by the interplay between the local concentration gradient, diffusion, and collective interactions. We further demonstrate the ability of the local concentration gradient to drive autonomous motion of colloidal particles in the highly confined space, and the possibility of using the nucleated nanodroplets for nanoextraction of a hydrophobic solute. The understanding obtained from this work provides a basis for quantitatively understanding the complex dynamical aspects associated with the Ouzo effect. We expect that this will facilitate improved control in nanodroplet formation for many applications, spanning from the preparation of pharmaceutical polymeric carriers, to the formulation of cosmetics and insecticides, to the fabrication of nanostructured materials, to the concentration and separation of trace analytes in liquid-liquid microextraction. [ABSTRACT FROM AUTHOR]

Understanding the microwettability of anisotropic molybdenum disulfide crystal is critically important in separation and processing of this material in liquid. In this work, static microwetting properties of MoS2 face (MF) and MoS2 edge (ME) surfaces in water are revealed by the morphology of femtoliter interfacial droplets. The oil droplets with different size distribution were produced from heterogeneous nucleation and growth of nanodroplets during the solvent exchange under controlled flow and solution conditions, and were polymerized for droplet morphology characterization to reveal the relative wettability of the droplets on surfaces. We first demonstrate that the shape of the nanodroplets is responsive to the surface charges on a model pH sensitive substrate of gold coated with a self-assembled monolayer of two types of thiol. The experimental results on MoS2 substrates indicate that (1) oil contact angle of the droplets on ME surface is much larger than that on MF surface at pH 3.0, suggesting that the ME surface is more hydrophilic than MF; (2) the droplets are pinned by the layered nanostructure on MoS2 edge. The fundamental understanding of microwettability elucidated in this study may allow for an improved control of the interaction between anisotropic MoS2 surfaces and the surrounding liquid environment, which is critically important for many industrial applications such as flotation and catalysis systems. [ABSTRACT FROM AUTHOR]

Manipulating the way a droplet shrinks by evaporation or dissolution is an effective approach for assembling dissolved nanomaterials. In this work, we investigate the dissolution dynamics of a submicroliter sessile droplet of electrolyte aqueous solution and of graphene oxide suspension immersed in a binary mixture of solvents, among which one is miscible and the other is immiscible with water (i.e., an Ouzo system). Our measurements reveal an interesting two-stage dissolution of the droplet: a fast initial stage and a slow second stage. The duration of the first stage is longer at a lower temperature, leading to a counterintuitive result that the dissolution completes faster at reduced temperature. The presence of graphene oxide in the droplet dramatically alters the dissolution dynamics, possibly due to its enrichment at the droplet surface. The finding from this work provides useful guideline for designing conditions to pack nanomaterials by dissolving droplets, especially for those temperature sensitive components. [ABSTRACT FROM AUTHOR]

Solvent exchange is a simple process of forming surface nanodroplets on an immersed substrate. In this process, the droplets nucleate and grow in response to transient oversaturation when a good solvent of the droplet liquid is displaced by a poor solvent. Here we will show how the final droplet size is influenced by solution composition in the solvent exchange. To do this, we produced water droplets on a hydrophilic substrate and cyclohexane droplets on a hydrophobic substrate by using a tertiary system of cyclohexane, ethanol, and water. The composition of the good solvent was varied systematically in the one-phase region on the phase diagram. We found that the key feature closely related to the droplet size is the area (A) in the phase diagram defined by the phase boundary and the concentration ratio between the good solvent and the droplet liquid. This area reflects the excessive amount of droplet liquid in the tertiary mixture, which can be complicated by bulk droplet formation during solvent exchange. We will also show that the droplet volume per unit surface area also increases with A. The findings from this work will provide guideline for the selection of solution conditions to achieve a desirable droplet size and number density on the surface. [ABSTRACT FROM AUTHOR]

Solvent exchange is a simple process of forming surface nanodroplets on an immersed substrate. In this process, the droplets nucleate and grow in response to transient oversaturation when a good solvent of the droplet liquid is displaced by a poor solvent. Here we will show how the final droplet size is influenced by solution composition in the solvent exchange. To do this, we produced water droplets on a hydrophilic substrate and cyclohexane droplets on a hydrophobic substrate by using a tertiary system of cyclohexane, ethanol, and water. The composition of the good solvent was varied systematically in the one-phase region on the phase diagram. We found that the key feature closely related to the droplet size is the area (A) in the phase diagram defined by the phase boundary and the concentration ratio between the good solvent and the droplet liquid. This area reflects the excessive amount of droplet liquid in the tertiary mixture, which can be complicated by bulk droplet formation during solvent exchange. We will also show that the droplet volume per unit surface area also increases with A. The findings from this work will provide guideline for the selection of solution conditions to achieve a desirable droplet size and number density on the surface. [ABSTRACT FROM AUTHOR]

Nanoscale droplets at a solid–liquidinterface are of highrelevance for many fundamental phenomena and applied processes. Thesolvent exchange process is a simple approach to produce, e.g., oilnanodroplets over a large surface area on a substrate, by exchangeoil-saturated ethanol by oil-saturated water, which has a lower oilsolubility than ethanol. In this process, the size of the nanodropletsis closely related to the flow conditions. To achieve control of thedroplet size, it is essential to fully understand the nucleation andgrowth of nanodroplets under different flow conditions. In this work,we investigate the gravitational effect on the droplet formation bythe solvent exchange. We compared the droplet size as the substratewas placed on the upper or lower wall in a horizontal fluid channelor on the sides of a vertical channel with an upward or downward flow.We found significant difference in the droplet size for the threesubstrate positions in a wide channel with height h= 0.21 mm. The difference of droplet size was eliminated in a narrowchannel with height h= 0.07 mm. The relevant dimensionalcontrol parameter for the occurrence of the gravitational effectsis the Archimedes number Ar and these two heights correspond to Ar= 10 and Ar = 0.35, respectively. The gravitational effects lead toa nonsymmetric parabolic profile of the mixing front, with the velocitymaximum being off-center and thus with different distances α(Ar)hand (1 – α(Ar))hto thelower and upper wall, respectively. The ratio of the total dropletvolume on the lower and upper wall is theoretically found to be (α(Ar)/(1– α(Ar)))3. This study thus improves our understandingof the mechanism of the solvent exchange process, providing guidelinesfor tailoring the volume of surface nanodroplets. [ABSTRACT FROM AUTHOR]

Solvent exchangeis a simple process to form oil nanodroplets atsolid–liquid interfaces with well-defined location and morphology.In this process, a good solvent of the oil is displaced by a poorsolvent, leading to the nucleation and growth of oil droplets froma transient oversaturation at the mixing front. Our recent work hasshown that the final volume of the droplets is related to the flowconditions. In this work, we investigate the effects of the type andthe composition of solvents on the droplet formation under the sameflow conditions. Water nanodroplets were produced by ethanol/cyclohexane(solution A) and cyclohexane (solution B) on a hydrophilic substrate.We found that the droplet size increases first and then decreaseswith an increase of the initial ethanol concentration in solutionA. This is attributed to the phase separation of ethanol–cyclohexane–water;in particular, the composition of solution A on the phase boundaryabove the Ouzo region. The same reason also contributes to the lowerefficiency in droplet formation for a longer alkane. The importantimplication from this work is that the maximal droplet volume is limitedby the phase separation of the solvents used in the solvent exchange. [ABSTRACT FROM AUTHOR]

Nanodroplets on a solid surface (i.e., surface nanodroplets) have practical implications for high-throughput chemical and biological analysis, lubrications, laboratory-on-chip devices, and near-field imaging techniques. Oil nanodroplets can be produced on a solid-liquid interface in a simple step of solvent exchange in which a good solvent of oil is displaced by a poor solvent. In this work, we experimentally and theoretically investigate the formation of nanodroplets by the solvent exchange process under well-controlled flow conditions. We find significant effects from the flow rate and the flow geometry on the droplet size. We develop a theoretical framework to account for these effects. The main idea is that the droplet nuclei are exposed to an oil oversaturation pulse during the exchange process. The analysis shows that the volume of the nanodroplets increases with the Peclet number Pe of the flow as ∝ Pe3/4, which is in good agreement with our experimental results. In addition, at fixed flow rate and thus fixed Peclet number, larger and less homogeneously distributed droplets formed at less-narrow channels, due to convection effects originating from the density difference between the two solutions of the solvent exchange. The understanding from this work provides valuable guidelines for producing surface nanodroplets with desired sizes by controlling the flow conditions. [ABSTRACT FROM AUTHOR]

A facile method was developed to synthesize free-standingSi nanosheets by using graphene oxide as a template. The resultingSi nanosheets were well-crystallized and showed high and stable Liion storage performance compared with Si nanoparticles because ofthe dimensional feature. [ABSTRACT FROM AUTHOR]

Enhancing ion and electron transport kinetics together with improving cycle life are important issues to be considered when developing high-performance Li ion batteries. Here we demonstrate a three dimensional ordered macroporous conductive electrode concept by entrapping electrode active nanoparticles in an interpenetrating macroporous carbon inverse opal. The electrodes are featured with simultaneously enhanced ion and electron transport kinetics as well as geometrically constrained active nanoparticles. The electrode can deliver up to 94.17% of theoretical capacity over 1000 discharge/charge cycles at a current density of 2.0 A g-1, and exhibits good rate capability in the high current density range of 1.0-10.0 A g-1. We hope that our findings will help pave the way for tailored design of many other sophisticated electrode materials in electrochemistry. [ABSTRACT FROM AUTHOR]

In this work, we investigated the kinetic balance between ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and subsequent condensation over the growth of silica particles in the Stöber method. Our results reveal that, at the initial stage, the reaction is dictated by TEOS hydrolysis to form silanol monomers, which is denoted as pathway I and is responsible for nucleation and growth of small silica particles via condensation of neighboring silanol monomers and siloxane network clusters derived thereafter. Afterward, the reaction is dictated by condensation of newly formed silanol monomers onto the earlier formed silica particles, which is denoted as pathway II and is responsible for the enlargement in size of silica particles. When TEOS hydrolysis is significantly promoted, either at high ammonia concentration (≥0.95 M) or at low ammonia concentration in the presence of LiOH as secondary catalyst, temporal separation of pathways I and II makes the Stöber method reminiscent of in situ seeded growth. This knowledge advance enables us not only to reconcile the most prevailing aggregation-only and monomer-addition models in literature into one consistent framework to interpret the Stöber process but also to grow monodisperse silica particles with sizes in the range 15–230 nm simply but precisely regulated by the ammonia concentration with the aid of LiOH. [ABSTRACT FROM AUTHOR]