Influence of Surfactants on Sodium Chloride Crystallization in Confinement

Exploring the cationic surfactant adsorption efficiency at concentrations relative to the critical micelle concentration by SA/SiO2 microspheres

Studying the adsorption behavior of cationic surfactants can help to develop more effective strategies to limit their dispersion in the environment. However, there have few studies on the adsorption of cationic surfactants from the perspective of critical micelle concentration (CMC). In this study, with cetyltrimethylammonium bromide (CTAB) and octadecyl trimethylammonium bromide (OTAB) serving as the model cationic surfactants, the effect of CMC on the adsorption behavior of cationic surfactant onto the surface of sodium alginate/silica (SA/SiO2) microspheres was systematically revealed. The adsorption mechanism relative to CMC was investigated under different conditions, including surfactant concentration, pH, temperature, and adsorption time. The results suggest that at identical concentrations, the smaller the CMC value of the cationic surfactants, the greater the adsorption amount (qt). qt for CTAB and OTAB were 583.2 and 678.0 mg/g respectively, with the concentration higher than their CMC value. When the concentration was lower than the CMC value of the cationic surfactants, qt for CTAB and OTAB were 123.2 and 138.7 mg/g, respectively. The CMC value of CTAB was lower than that of OTAB under identical conditions, suggesting that the adsorption of cationic surfactants is related to their CMC. These results are beneficial for the removal of cationic surfactants by adsorption methods.

Formulation and Optimization of Effective Oil Spill Dispersants Composed of Surface-Active Ionic Liquids and Nonionic Surfactants

The use of chemical dispersants to remove oil spills in aquatic environments raises serious concerns, including heightened toxicity and limited biodegradability, which diminish their effectiveness. This study aimed to develop an environmentally friendly formulation by combining two nonionic surfactants (Tween 80, Span 80) with two surface-active ionic liquids (SAILs): 1-butyl-3-methylimidazolium lauroyl sarcosinate [Bmim][Lausar] and choline myristate [Cho][Mys], to remediate crude oil spill. The performance of the formulation was evaluated by its emulsion stability, surface tension, interfacial tension (IFT), and effectiveness. The toxicity and biodegradability of the formulation were also assessed to ensure their safe application in aquatic environments. The formulation (F9) exhibited the most stable emulsion, maintaining stability even after 5 h with a critical micelle concentration (CMC) of 3.52 mM. The efficiency of the formulation in dispersing various crude oils (Arab, Ratawi, and Doba) ranged from 70.12 to 93.72%. Acute toxicity tests conducted on zebrafish demonstrated that the formulation, with an LC50 value of 450 mg L-1, exhibited practically nontoxicity after 96 h. The formulation showed rapid biodegradability, exceeding 60% within a 28-day testing period. This research presents a promising approach for synthesizing the green formulation which can contribute to mitigating the environmental impacts of oil spills and enhancing the efficiency of cleanup operations.

Crystallization-induced thickness tuning of carbon nanosheets for fast potassium storage

Carbon nanosheets (CNS) have garnered significant interest as anode materials for potassium-ion batteries (PIBs) due to the excellent potassium storage kinetics and rate performance. Moreover, tuning the thickness of CNS can enhance the potassium storage performance by exposing abundant surface active sites and shortening the K+ migration path. Herein, crystallization-induced thickness tuning of carbon nanosheets in polyvinyl pyrrolidone-potassium chloride (PVP-KCl) solution is reported to enhance the fast potassium storage. PVP with varying molecular weights is employed to induce the crystallization behavior of KCl, leading to the formation of KCl grains with controllable sizes. Concurrently, these KCl grains act as hard templates for dispersing the PVP molecules to fabricate carbon nanosheets on the surface during annealing. PVP with high molecular weight is beneficial for hindering ion migration to reduce crystal sizes, which can decrease the thickness of carbon nanosheets. The ultrathin structure exposes abundant potassium storage sites, endowing CNS with high reversible capacity (359.0 mAh/g at 100 mA/g). The reduction in the migration path of K+ ions facilitate rapid ion and electron transport kinetics, resulting in rate performance with a capacity of 181.9 mAh/g at 1 A/g. Our work extends the application of the crystallization-induced strategy for controllable designing carbon nanosheets, and puts forward some conceptions on improving the potassium storage performance of carbon anode materials.

Capillary Forces Lead to Pendant Crystals at the Liquid-Air Interface of Evaporating Salt Solutions

We investigated the nucleation and growth processes of individual NaCl crystals from an evaporating salt solution that is supersaturated. We find that crystals nucleate at the liquid/vapor interface, resulting in distinct "pendant" crystals, which reach millimeter dimensions. The substantial size of the crystals induces deformation of the interface. This process and the evaporation rate, in turn, determine the final crystal shape, which features a deep central cavity. Our findings reveal that a delicate balance exists between gravity, buoyancy, and the surface tension of the liquid/vapor interface that allows the crystal to remain pendant. When the contact angle of the crystal with the meniscus reaches 90°, the crystal disconnects from the interface and falls into the solution. We quantitatively predict the critical mass at which this occurs.

CNT effective interfacial energy and pre-exponential kinetic factor from measured NaCl crystal nucleation time distributions in contracting microdroplets

Nucleation, the birth of a stable cluster from a disorder, is inherently stochastic. Yet up to date, there are no quantitative studies on NaCl nucleation that accounts for its stochastic nature. Here, we report the first stochastic treatment of NaCl-water nucleation kinetics. Using a recently developed microfluidic system and evaporation model, our measured interfacial energies extracted from a modified Poisson distribution of nucleation time show an excellent agreement with theoretical predictions. Furthermore, analysis of nucleation parameters in 0.5, 1.5, and 5.5 pl microdroplets reveals an interesting interplay between confinement effects and shifting of nucleation mechanisms. Overall, our findings highlight the need to treat nucleation stochastically rather than deterministically to bridge the gap between theory and experiment.

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.

Patterns during Evaporative Crystallization of a Saline Droplet

In the present work, we investigate the influence of substrate wettability and crystal morphology on the evaporative crystallization of saline droplets. On a superhydrophilic substrate, the evaporative crystals formed during the drying of a saline droplet of aqueous potassium nitrate are observed to be long and needle-shaped, oriented along the substrate. The crystal deposits form a flower-shaped pattern when the initial contact angle of the droplet increases to ∼72°. The orientation of the crystals along the triple contact line of the droplet controls the self-amplifying creeping growth of the salt crystals that eventually determines the overall evaporative patterns. The crystals change from being needle-shaped to globular salt deposits as the volume of liquid available for crystallization reduces. We demonstrate that the arrangement of the crystal with respect to the substrate and the droplet-air interface governs the rate of evaporation, growth, and morphology of the crystals.

Hierarchical Exploration of Drying Patterns Formed in Drops Containing Lysozyme, PBS, and Liquid Crystals

Biological systems, by nature, are highly complex. These systems exhibit diverse hierarchical spatial and temporal features when driven far from equilibrium. The generated features are susceptible to the initial conditions that largely depend on vast parameter space. Extracting information on their properties and behavior thus becomes far too complex. This work seeks to examine the drying kinetics of the drops containing a globular protein (xlysozyme (Lys)), phosphate buffer saline (PBS), and thermotropic liquid crystal (LCs). The drying evolution and the morphological crack patterns of these drops are examined using high-resolution microscopy, textural image analysis, and statistical methods. This study observes that the textural parameters can identify the (i) phase separation of the salts present in the PBS and (ii) the LCs’ birefringence during the drying evolution. This birefringence activities of the LCs slow down when the initial PBS concentration is increased from 0.25 to 1× despite using a fixed volume of LCs. To comprehend such a surprising effect, the combinations of (i) Lys+PBS and (ii) PBS+LCs are thoroughly examined. A phase diagram is established as a function of initial concentrations of Lys and PBS. The scanning electron microscopic images of Lys+PBS reveal that the tuning between lysozyme and salt concentrations in PBS plays a significant role in determining the morphological patterns. The Lys drops with and without LCs exhibit two distinct regions: the peripheral ring (“coffee-ring”) and the central ones. This phase-separated ring formation indicates that the film containing Lys and salts might have formed on top of these LCs in the central region, which reduces the optical response (birefringence) of LCs. A physical mechanism is proposed in this paper to anticipate the redistributions of LCs in a multi-component system such as Lys+PBS+LCs.

Cationic surfactant-directed structural control of NaCl crystals from evaporating sessile droplets

We report morphological regulation of NaCl (sodium chloride) crystals through the evaporative crystallisation process of microdroplets containing a cationic surfactant CTAB (cetyltrimethylammonium bromide). Various fascinating evaporative salt morphologies are observed using different combinations of salt (C_NaCl) and surfactant (C_CTAB) concentrations. Each observed morphology is carefully explained by the interplaying physical phenomena, such as crystallisation, micellisation, evaporative dewetting, and surface adsorption of anionic couneterions. Salt morphologies are investigated for low (C_NaCl = 0.1 (M)), intermediate (C_NaCl = 0.5 (M)) and high (C_NaCl = 2 (M)) concentrations, whereas surfactant concentrations are varied four orders of magnitudes (from 0.0001 (M) to 0.1 (M)). Interestingly, we observe a threshold in C_CTAB at 0.001 (M), beyond which the peripheral rings of dried deposits are found to be composed of CTAB for C_NaCl = 0.1 (M), while the same is seen to be made up of NaCl for C_NaCl = 2 (M). We have explained the morphological evolution by the process of competitive surface adsorption phenomenon between Cl^- and Br^- counter ions. Such a detailed study of saline droplet crystallisation in the presence of a cationic surfactant underpins the fundamental understanding of the crystallisation process. In addition, it may further impact application sectors where crystallisation of saline solution plays an important role, especially in the presence of additives.

Effects of salinity and shear stress on clay deformation: A molecular dynamics study

The deformation of clay minerals is an important phenomenon that is relevant to many problems, particularly those that occur in subsurface geological formations. The salinity of the formations and external shear stress applied to them are two important factors that contribute to the deformation of such porous media. To gain a deeper understanding of such phenomena, we have carried out extensive molecular dynamics simulations using the Na-montmorillonite (Na-MMT) structure as the model of clay minerals and have studied the effect of salt concentration on its swelling. As the NaCl concentration increases, so also does the basal spacing. We demonstrate the effect of the coupling between the applied shear stress and NaCl salinity on the swelling behavior of Na-MMT, namely, deformation of the interlayer space that results in swelling. According to the results, the extent of Na-MMT deformation depends on both the brine salinity and the shear rate.

Controllable light-induced droplet evaporative crystallization

Droplet evaporative crystallization is one of the practical tools for clinical diagnosis, environmental monitoring, and pharmaceutical synthesis. Herein, we proposed a controllable and flexible light strategy to manipulate the droplet evaporative crystallization, in which the photothermal effect of a focused infrared laser actuated intense evaporation to attain the droplet evaporative crystallization. Due to the localized heating effect, not only the droplet evaporative crystallization could be promoted, but also the resultant Marangoni-flow enabled the crystals to be concentrated, exhibiting excellent controllability. Besides, a relationship between the crystallization starting time and the solution concentration/laser power was achieved, which benefited the manipulation of the droplet evaporative crystallization. The light strategy proposed in the present study possesses promising potential for future applications.

Surfactant-guided spatial assembly of nano-architectures for molecular profiling of extracellular vesicles

The controlled assembly of nanomaterials into desired architectures presents many opportunities; however, current preparations lack spatial precision and versatility in developing complex nano-architectures. Inspired by the amphiphilic nature of surfactants, we develop a facile approach to guide nanomaterial integration – spatial organization and distribution – in metal-organic frameworks (MOFs). Named surfactant tunable spatial architecture (STAR), the technology leverages the varied interactions of surfactants with nanoparticles and MOF constituents, respectively, to direct nanoparticle arrangement while molding the growing framework. By surfactant matching, the approach achieves not only tunable and precise integration of diverse nanomaterials in different MOF structures, but also fast and aqueous synthesis, in solution and on solid substrates. Employing the approach, we develop a dual-probe STAR that comprises peripheral working probes and central reference probes to achieve differential responsiveness to biomarkers. When applied for the direct profiling of clinical ascites, STAR reveals glycosylation signatures of extracellular vesicles and differentiates cancer patient prognosis.

Current methods for controlled assembly of nanomaterials into desired architectures often lack the precision and versatility to develop complex architectures. Here the authors report STAR, surfactant tunable spatial architecture, to guide nanomaterial integration in metal-organic frameworks.

A Novel Hydrate Form of Sodium Dodecyl Sulfate and Its Crystallization Process

A novel hydrate form of sodium dodecyl sulfate (SDS) was firstly discovered through a hydrate screening with the use of organic solvents, while SDS is generally prepared solely in aqueous media. Surprisingly, a novel SDS hydrate form with needle-shaped crystals produced by adding acetonitrile to a 20 wt % SDS aqueous solution at a ratio of 3:1 (v/v) and further cooling to around 5 °C could be found with a trace amount in one of the two purchased SDS products that we examined. After comprehensive solid-state characterizations by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Raman spectroscopy, dynamic vapor sorption (DVS), and elemental analysis (EA), it is also successfully made directly from the synthesis of SDS through esterification and saponification. Four times the equal proportion of acetone was added into the reaction solution at an interval of 5 min to separate the side product, sodium sulfate, from the mother liquor. The desired novel hydrate form of SDS was then obtained by cooling the filtered mother liquor to 5 °C and aged for 8 h for a preferential growth.

Influence of Lactobacillus Biosurfactants on Skin Permeation of Hydrocortisone

One of the most widely used strategies to improve drug diffusion through the skin is the use of permeation enhancers. The aim of this work was to investigate the effect of two biosurfactants (BS), produced by Lactobacillus crispatus BC1 and Lactobacillus gasseri BC9, on the skin permeation profile of hydrocortisone (HC, model drug). HC aqueous solubility and in vitro diffusion studies through porcine skin were performed in the presence of BC1-BS and BC9-BS at concentrations below and above critical micellar concentrations (CMC). Moreover, skin hydration tests and differential scanning calorimetry (DSC) analysis were performed to further investigate BS interaction with the outermost layer of the skin. Both BS increased HC solubility, especially at concentrations above their CMC. At concentrations below the CMC, drug permeation through the skin was improved, as the result of a dual effect: a) the formation of a superficial lipophilic environment, as confirmed by the reduction in skin hydration and b) the interaction between BS and the stratum corneum (SC), as demonstrated by the DSC curves. From the obtained data, it appears that BC1-BS and BC9-BS could represent new promising green excipients for drug permeation enhancement through the skin.

Unraveling driving regimes for destabilizing concentrated emulsions within microchannels

Coalescence is the most widely demonstrated mechanism for destabilizing emulsion droplets in microfluidic chambers. However, we find that depending on the channel wall surface functionalization, surface zeta potential, type of surfactant, characteristics of the oil as a dispersed phase, or even the presence of externally-induced stress, other different destabilization mechanisms can occur in subtle ways. In general, we observe four regimes leading to destabilization of concentrated emulsions: (i) coalescence, (ii) emulsion bursts, (iii) a combination of the two first mechanisms, attributed to the simultaneous occurrence of coalescence and emulsion bursts; and (iv) compaction of the droplet network that eventually destabilizes to fracture-like behavior. We correlate various physico-chemical properties (zeta potential, contact angle, interfacial tension) to understand their respective influence on the destabilization mechanisms. This work provides insights into possible ways to control or inflict emulsion droplet destabilization for different applications.

Self-Lifting NaCl Crystals

We show that macroscopic crystals of NaCl that form from evaporating drops of aqueous salt solutions can spontaneously lift themselves up and away from a hydrophobic surface. At the end of the evaporation process, tiny crystals of NaCl grow onto larger ones and form "legs" that push the large crystals away from the surface. The temperature dependence of the lifting speed is found to exhibit Arrhenius behavior with an activation energy similar to that of crystals growing in solution: the crystal growth itself determines the lifting speed that can be up to half a centimeter per minute. We show that surface hydrophobicity is a necessary but not a sufficient condition to obtain this "self-lifting" behavior.

Crystallization in Confinement

Many crystallization processes of great importance, including frost heave, biomineralization, the synthesis of nanomaterials, and scale formation, occur in small volumes rather than bulk solution. Here, the influence of confinement on crystallization processes is described, drawing together information from fields as diverse as bioinspired mineralization, templating, pharmaceuticals, colloidal crystallization, and geochemistry. Experiments are principally conducted within confining systems that offer well-defined environments, varying from droplets in microfluidic devices, to cylindrical pores in filtration membranes, to nanoporous glasses and carbon nanotubes. Dramatic effects are observed, including a stabilization of metastable polymorphs, a depression of freezing points, and the formation of crystals with preferred orientations, modified morphologies, and even structures not seen in bulk. Confinement is also shown to influence crystallization processes over length scales ranging from the atomic to hundreds of micrometers, and to originate from a wide range of mechanisms. The development of an enhanced understanding of the influence of confinement on crystal nucleation and growth will not only provide superior insight into crystallization processes in many real-world environments, but will also enable this phenomenon to be used to control crystallization in applications including nanomaterial synthesis, heavy metal remediation, and the prevention of weathering.

Micellar liquid chromatographic green enantioseparation of racemic amino alcohols and determination of elution order

A micellar liquid chromatographic method was developed for the green enantioseparation of racemic amino alcohols using an aqueous solution of the mixed surfactants as an alternative for organic solvents. In this study, the derivatives of the amino alcohols were synthesized using highly reactive chiral esters of (S)-levofloxacin (Lfx) under microwave conditions, and an aqueous solution of the surfactants (Brij-35 and SDS) was used for the enantioseparation of the synthesized diastereomeric derivatives (DDs) of amino alcohols using reversed-phase HPLC. The activated ester of Lfx was synthesized by reacting with N-hydroxybenzotriazole and characterized using UV, IR, ¹ H NMR, high-resolution mass spectrometry, and elemental analysis. The DDs of racemic amino alcohols were separated on a C₁₈ column using micellar LC. Chromatographic conditions were optimized by varying the concentration of the surfactants in aqueous solution and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (score: 82, an excellent green method). In addition, the density functional theory calculations were performed to develop the lowest energy-optimized structures of DDs. The method was validated according to the International Conference of Harmonization guidelines, and the retention factor (k), selectivity factor (α), resolution factor (R_S ), limit of detection (0.198 ng mL^-1 or 0.291 pM mL^-1 ), and limit of quantification (0.594 ng mL^-1 or 0.873 pM mL^-1 ) were calculated.

Dynamic Surface Tension of Surfactants in the Presence of High Salt Concentrations

We study the influence of high NaCl concentrations on the equilibrium and dynamic surface tensions of ionic (CTAB) and nonionic (Tween 80) surfactant solutions. Equilibrium surface tension measurements show that NaCl significantly reduces the critical micellar concentration (CMC) of CTAB but has no effect on the CMC of Tween 80. Dynamic surface tension measurements allow comparing the surface tension as a function of time for pure surfactant solutions and in the presence of NaCl. For the ionic surfactant, the dynamics agree with the usual diffusion-limited interfacial adsorption kinetics; however, the kinetics become orders of magnitude slower when NaCl is present. Sum-frequency generation spectroscopy experiments and the equilibrium adsorption measurements show that the presence of NaCl in CTAB solution leads to the formation of ion pairs at the surface, thereby neutralizing the charge of the head group of CTAB. This change, however, is not able to account for the slowing down of adsorption dynamics; we find that it is rather the decreases in the monomer concentration (CMC) in the presence of salt which has the major influence. For the nonionic surfactant, the kinetics of interfacial tension is seen to be already very slow, and the addition of salt does not influence it further. This also correlates very well to the very low CMC of Tween 80.

An efficient method for the determination of enantiomeric purity of racemic amino acids using micellar chromatography, a green approach

A simple, sensitive and green micellar liquid chromatographic method (RP-HPLC) was developed for enantioseparation of four racemic amino acids, namely, (RS)-selenomethionine, (RS)-methionine, (RS)-cysteine and (RS)-penicillamine. An aqueous solution of sodium dodecyl sulfate and Brij-35 was prepared and used as mobile phase for HPLC analysis. Activated esters of (S)-ibuprofen, (S)-ketoprofen and (S)-levofloxacin were synthesized by reacting them with N-hydroxybenzotriazole. These esters were characterized by UV, IR, ¹ HNMR, HRMS and elemental analysis. These chiral reagents (activated esters) were used for the synthesis of diastereomeric derivatives of the chosen amino acids. The diastereomeric derivatives were separated on a C₁₈ column by micellar liquid chromatography. Chromatographic conditions were optimized by varying concentration of surfactant in aqueous solution, and by varying the concentration and pH of the buffer. The green assessment score was calculated for the developed method (78, an excellent green method score). In addition, density functional theory calculations were performed, using Gaussian 09 rev. A.02 and hybrid density functional B3LYP with a 6-31G* basis set program, in order to develop lowest energy optimized structures of diastereomeric derivatives. The method was validated according to International Conference on Harmonization guidelines and the retention factor (k), selectivity factor (α), resolution factor (R_S ) and limit of detection (0.295 ng ml^-1 ) and limit of quantification (0.896 ng ml^-1 ) were calculated.

Mechanistic understanding of salt-induced drug encapsulation in nanosuspension via acid-base neutralization as a nanonization platform technology to enhance dissolution rate of pH-dependent poorly water-soluble drugs

An acid-base neutralization technique has generated interest for the ability to achieve an enhanced dissolution of pH-dependent weakly basic or acidic poorly water-soluble drugs. However, the underlying nanonization mechanism, following acid-base neutralization, requires further elucidation. We hypothesized that the nanosuspensions (NSPs) via nanonization of drug particles could be attributed to the "salt-induced effect" and surfactant-driven micellization after acid-base neutralization. Rebamipide (RBM) and valsartan (VAL) were chosen as model drugs owing to poor water solubility and pH-dependent aqueous solubility. The drug NSP was rapidly obtained via salt formation (NaCl) after neutralization of the drug in basic NaOH solution and poloxamer 407 (POX 407) in acidic HCl solution. The NSP surrounded by NaCl salt was further stabilized by POX 407. The resulting NaCl salt modulated the critical micelle aggregation of POX 407, stabilizing the drug-loaded NSP in a cage of salt and micellar surfactant. In non-assisted homogenization, size analysis indicated the relationship between salt concentration and size reduction. Fourier transform infrared (FTIR) spectra revealed that the existence of hydrogen bonding between the drug and surfactant after neutralization, attributed to NSP size reduction. Changes in drug crystallinity to the nano-amorphous state were confirmed by powder X-ray diffraction (PXRD). Overall, the salt-induced drug NSP synergistically enhanced the dissolution rate, narrowing a gap between drug dissolution profiles in different pH environments.

Development, formulation and optimization of a novel biocompatible ionic liquids dispersant for the effective oil spill remediation

The application of chemical dispersants in marine oil spill remediation is comprehensively reported across the globe. But, the augmented toxicity and poor biodegradability of reported chemical dispersants have created necessity for their replacement with the bio-based green dispersants. Therefore, in the present study, we have synthesized five ionic liquids (ILs) namely 1-butyl-3-methylimidazolium lauroylsarcosinate, 1,1'-(1,4-butanediyl)bis(1-H-pyrrolidinium) dodecylbenzenesulfonate, tetrabutylammonium citrate, tetrabutylammonium polyphosphate and tetrabutylammonium ethoxylate oleyl ether glycolate, and formulated a water based ILs dispersant combining the synthesized ILs at specified compositions. The effectiveness of formulated ILs dispersant was found between 70.75% and 94.71% for the dispersion of various crude oils ranging from light to heavy. Further, the acute toxicity tests against zebra fish and grouper fish have revealed the practically non-toxic behaviour of formulated ILs dispersant with LC₅₀ value greater than 100 ppm after 96 h. In addition, the formulated ILs dispersant has provided excellent biodegradability throughout the test period. Overall, the formulated new ILs dispersant is deemed to facilitate environmentally benign oil spill remediation and could effectively substitute the use of hazardous chemical dispersants in immediate future.

Salt creeping as a self-amplifying crystallization process

Salt creeping is a ubiquitous phenomenon in which crystals precipitate far from an evaporating salt solution boundary, which constitutes a major problem in outdoor electronics, civil engineering, artworks, and agriculture. We report a novel experimental approach that allows to quantitatively describe the creeping mechanism and demonstrate its universality with respect to different salts. We show that there exists a critical contact angle below which salt creeping occurs, provided also the nucleation of multiple crystals is favored. The precipitation of new crystals happens ahead of the contact line by the meniscus that progressively advances over the crystals forming also nanometric precursor films. This enlarges the evaporative area, causing an exponential increase in the crystal mass in time. The self-amplifying process then results in a spectacular three-dimensional crystal network at macroscopic distances from the solution reservoir. These findings also allow us to control the creeping by using crystallization modifiers.

Fundamental Study on the Salt Tolerance of Oregano Essential Oil-in-Water Nanoemulsions Containing Tween 80

This study provides fundamental information about the influence of salt on the physicochemical stability of oregano essential oil (EO) and its main components incorporated in a nanoemulsion delivery system containing Tween 80 (T80) emulsifier. The emulsion stability was found to be strongly correlated with the lipid phase composition and the type of salts. The oregano essential oil nanoemulsions remained stable for several weeks in the absence of salts. Moreover, they were insensitive to tetrabutylammonium bromide, whereas similar to carvacrol emulsions, they exhibited a rapid phase separation and oiling-off in the presence of sodium chloride. On the other hand, high oleic sunflower oil (HOSO) and p-cymene emulsions remained stable in the presence of NaCl. Addition of 70 and 80% HOSO to the lipid phase of oregano EO and carvacrol, respectively, was found to be sufficient for the formation of emulsions with a high stability to 1.7 M NaCl. Hereby, the morphology of the oregano EO emulsions after 30 days of storage in the presence of NaCl was visualized using a transmission electron microscope. The determination of the surface load and area per surfactant molecule by interfacial tension (IFT) measurements and quartz crystal microbalance with dissipation revealed the dehydration of the polyoxyethylene groups of T80 in the presence of salt. The thickness of the T80 adsorbed layer onto solid hydrophobic and hydrophilic surfaces was significantly lower (p < 0.05) in the presence of sodium chloride. It is hypothesized that a combination of Ostwald ripening and coalescence due to an IFT increase and dehydration was responsible for the instability of the emulsions containing the more polar oregano EO and carvacrol in the presence of salt. The results obtained in this study could be useful for the formulation of essential oil nanoemulsions in the presence of salts applicable in food, pharmaceutical, and personal care products.

Dissolution-Crystallization Transition within a Polymer Hydrogel for a Processable Ultratough Electrolyte

Although nonliquid electrolytes have been developed rapidly under the condition of safe demand of energy storage devices, the inherent weaknesses in ionic conductivity, mechanical properties, or interfacial compatibility severely hinder their application under a harsh environment. Inspired by the hybridized characteristics of composite materials and the potential advantages of hydrated crystals, a processable crystal-type gel electrolyte with good comprehensive performance via the dissolution-crystallization transition of NaAc within hydrogel is creatively prepared. The use of NaAc crystal within a hydrogel leads to nearly 26 000 times greater modulus (474.24 MPa) and higher operating voltage (2.0 V) than the hydrogel without the crystal. The reliable supercapacitor using this electrolyte can work in extreme environment (-40 to 80 °C, even in the fire or in liquid nitrogen within a short time) benefiting from its phase-transition capacity. This investigation offers a facile and versatile way to construct an ideal gel electrolyte for next-generation energy storage devices.

Solubilization of Carbamazepine in TPGS Micelles: Effect of Temperature and Electrolyte Addition

D-α-Tocopheryl polyethylene glycol succinate (TPGS), a polyethylene glycol condensate, is a biologically important nonionic amphiphile. In this study, we report on aqueous solution behavior of TPGS with a focus on its clouding, surface activity, micellar characteristics, and solubilization capacity for a model hydrophobic drug, carbamazepine (CBZ). Micelles were characterized by dynamic light and small-angle neutron scattering studies as a function of temperature, salt addition, and CBZ solubilization. TPGS showed a cloud point of 78°C and possessed good surface activity (as observed from surface tension reduction and adsorption parameters). The critical micelle concentration (CMC), obtained from surface tension and fluorescence studies, was 0.02 mM. Scattering studies showed formation of stable micelles (average diameter-12 nm), exhibiting no significant changes in size upon salt addition (up to 1 M NaCl), CBZ incorporation (up to 5 mM), and temperature increase (40°C). Micelles in 5 wt% TPGS showed about twentyfold enhancement in CBZ solubility. Considering the remarkable CBZ solubilization and its positioning in the core, we suggest that the formulation can be exploited as a sustained delivery vehicle.

Exploring Physicochemical Interactions of Different Salts with Sodium N-Dodecanoyl Sarcosinate in Aqueous Solution

Amino acid-based surfactants are used in academics and industry. Sodium N-dodecanoyl sarcosinate (SDDS) is such an amino acid-based surfactant having applications in pharmaceutical, food, and cosmetic formulations. Although the surface properties of this surfactant have been studied in the presence of univalent cationic and anionic salts, there is no report on such solution in the presence of higher valencies. In this experiment, critical micelle concentration (CMC) of SDDS from tensiometry, conductometry, and fluorimetry has been determined. In each case, CMC decreases with increasing salt concentration. Counterion binding of micelles (β), diffusion coefficient (D ₀), and surface properties, e.g., Gibbs free energy for micellization (ΔG _m ⁰), Gibbs surface excess (Γ_max), area of exclusion per surfactant monomer (A _min), surface pressure at CMC (π_cmc), etc., have been evaluated using methods such as tensiometry, conductometry, and fluorimetry. The hydrodynamic radius of SDDS in the presence of different salts was measured by the light scattering method. Aggregation number and shape of micelle have been determined by small-angle neutron scattering experiment. The nature of amphiphilic packing and the aggregation numbers of the assemblies have also been explored. The results from different experiments have been rationalized and represented systematically.

New Electrochemical Flow-Cell Configuration Integrated into a Three-Dimensional Microfluidic Platform: Improving Analytical Application in the Presence of Air Bubbles

A newly configured electrochemical flow cell to be used for (end-channel) amperometric detection in a microfluidic device is presented. The design was assembled to place the reference electrode in a separated compartment, isolated from the flow in the microchannel, while the working and counter electrodes remain in direct contact with both compartments. Moreover, a three-dimensional coil-shaped microfluidic device was fabricated using a nonconventional protocol. Both devices working in association enabled us to solve the drawback caused by the discrete injection when the automatic micropipette was used. The high performance of the proposed electrochemical flow cell was demonstrated after in situ modifying the surface of the platinum working electrode with surfactant (e.g., using Tween 20 at 0.10%). As the reference electrode remained out of contact with the flowing solution, there was no trouble by air bubble formation (generated by accidental insertion or by presence of surfactants) throughout the measurements. This device was characterized regarding its analytical performance by evaluating the amperometric detection of acetaminophen, enabling determination from 6.60 to 66.0 μmol L^-1. This issue is important since at high concentration (e.g., as assessed in clinical analysis) the acetaminophen is known to passivate the working electrode surfaces by electrogenerated products, impairing the accuracy of the electrochemical measurements.

Hopper Growth of Salt Crystals

The growth of hopper crystals is observed for many substances, but the mechanism of their formation remains ill understood. Here we investigate their growth by performing evaporation experiments on small volumes of salt solutions. We show that sodium chloride crystals that grow very fast from a highly supersaturated solution form a peculiar form of hopper crystal consisting of a series of connected miniature versions of the original cubic crystal. The transition between cubic and such hopper growth happens at a well-defined supersaturation where the growth rate of the cubic crystal reaches a maximum (∼6.5 ± 1.8 μm/s). Above this threshold, the growth rate varies as the third power of supersaturation, showing that a new mechanism, controlled by the maximum speed of surface integration of new molecules, induces the hopper growth of cubic crystals in cascade.

Evaporation of a sessile water drop and a drop of aqueous salt solution

The influence of various factors on the evaporation of drops of water and aqueous salt solution has been experimentally studied. Typically, in the studies of drop evaporation, only the diffusive vapor transfer, radiation and the molecular heat conduction are taken into account. However, vapor-gas convection plays an important role at droplet evaporation. In the absence of droplet boiling, the influence of gas convection turns out to be the prevailing factor. At nucleate boiling, a prevailing role is played by bubbles generation and vapor jet discharge at a bubble collapse. The gas convection behavior for water and aqueous salt solution is substantially different. With a growth of salt concentration over time, the influence of the convective component first increases, reaches an extremum and then significantly decreases. At nucleate boiling in a salt solution it is incorrect to simulate the droplet evaporation and the heat transfer in quasi-stationary approximation. The evaporation at nucleate boiling in a liquid drop is divided into several characteristic time intervals. Each of these intervals is characterized by a noticeable change in both the evaporation rate and the convection role.