Synthetic branched-chain glycolipids are suitable as model systems in understanding biological cell membranes, particularly because certain natural lipids possess chain branching. Herein, four branched-chain glycopyranosides, namely, 2-hexyl-decyl-α-D-glucopyranoside (α-Glc-OC10C6), 2-hexyl-decyl-β-D-glucopyranoside (β-Glc-OC10C6), 2-hexyl-decyl-α-D-galactopyranoside (α-Gal-OC10C6), and 2-hexyl-decyl-β-D-galactopyranoside (β-Gal-OC10C6), with a total alkyl chain length of 16 carbon atoms have been synthesized, and their phase behavior has been studied. The partial binary phase diagrams of these nonionic surfactants in water were investigated by optical polarizing microscopy (OPM) and small-angle X-ray scattering (SAXS). The introduction of chain branching in the hydrocarbon chain region is shown to result in the formation of inverse structures such as inverse hexagonal and inverse bicontinuous cubic phases. A comparison of the four compounds showed that they exhibited different polymorphism, especially in the thermotropic state, as a result of contributions from anomeric and epimeric effects according to their stereochemistry. The neat α-Glc-OC10C6 compound exhibited a lamellar (Lα) phase whereas dry α-Gal-OC10C6 formed an inverse bicontinuous cubic Ia3d (QII(G)) phase. Both β-anomers of glucoside and galactoside adopted the inverse hexagonal phase (HII) in the dry state. Generally, in the presence of water, all four glycolipids formed inverse bicontinuous cubic Ia3d (QII(G)) and Pn3m (QII(D)) phases over wide temperature and concentration ranges. The formation of inverse nonlamellar phases by these Guerbet branched-chain glycosides confirms their potential as materials for novel biotechnological applications such as drug delivery and crystallization of membrane proteins.
Water-driven self-assembly of lipids displays a variety of liquid crystalline phases that are crucial for membrane functions. Herein, we characterize the temperature-induced phase transitions in two compositions of an aqueous self-assembly system of the octyl β-D-glucoside (βGlcOC(8)) system, using steady-state and time-resolved fluorescence measurements. The phase transitions hexagonal ↔ micellar and cubic ↔ lamellar were investigated using tryptophan (Trp) and two of its ester derivatives (Trp-C(4) and Trp-C(8)) to probe the polar headgroup region and pyrene to probe the hydrophobic tail region. The polarity of the headgroup region was estimated to be close to that of simple alcohols (methanol and ethanol) for all phases. The pyrene fluorescence indicates that the pyrene molecules are dispersed among the tails of the hydrophobic region, yet remain in close proximity to the polar head groups. Comparing the present results with our previously reported one for βMaltoOC(12), increasing the tail length of the hexagonal phase from C(8) to C(12) leads to less interaction with pyrene, which is attributed to the more random and wobbling motion of the longer alkyl tail. We measured a reduction (more hydrophobic) in the ratio of the vibronic peak intensities of pyrene (I(1)/I(3)) for the lamellar phase compared to that of the cubic phase. The higher polarity in the cubic phase can be correlated to the nature of its interface, which curves toward the bulk water. This geometry also explains the slight reduction in polarity of the headgroup region compared to the other phases. Upon the addition of Trp-C(8), the fluorescence lifetime of pyrene is reduced by 28% in the lamellar and cubic phases, whereas the I(1)/I(3) value is only slightly reduced. The results reflect the dominant role of dynamic interaction mechanism between the C(8) chain of Trp-C(8) and pyrene. This mechanism may be important for these two phases since they participate in the process of membrane fusion. Both lipid compositions show completely reversible temperature-induced phase transitions, reflecting the thermodynamic equilibrium structures of their mesophases. Probing both regions of the different lipid phases reveals a large degree of heterogeneity and flexibility of the lipid self-assembly. These properties are crucial for carrying out different biological functions such as the ability to accommodate various molecular sizes.
New designer biofluorophores are being increasingly used in the investigation of complex cellular processes. In this study, we utilized new derivatives of pyrene (Py), i.e., 2-n-alkyl-pyrenes (Py-C4 and Py-C8), in order to probe different regions inside the hydrophobic tail of n-dodecyl β-d-maltoside (βMal-C12) in two different phases (cubic ↔ lamellar). Although the sensitivity to the local environment is reduced compared to that of Py, attaching C4 and C8 at the 2-position of Py can provide a possible means to probe the local hydrophobicity in different parts of the tail region. The absence of excimer fluorescence and the ratio of the vibronic fluorescence peak intensities (I1/I3) in a lipid environment indicate the existence of Py as monomers in the hydrophobic region, similar to hydrophobic solvation, yet close to the headgroup region. When Py is replaced by Py-C4 and Py-C8, there is a small increase in hydrophobicity (reduction in I1/I3) as the Py moiety is pulled deeper inside the tail region of both cubic and lamellar phases. The larger space of the tail region in the lamellar phase is reflected as more local hydrophobicity measured by the probes which can penetrate deep inside, whereas the curved structure of the cubic phase limits the available space for the probes. Three fluorescence lifetime components were measured in lipid, indicating the heterogeneous nature of the hydrophobic region. In the lamellar phase, a large reduction in the average lifetime value, led by the long decay component, was measured for Py-C4 (reduction by 25%) and Py-C8 (45%) compared to that of the parent Py. This observation suggests the presence of a mechanism of interaction more collisional than static between the Py moiety and the tail region of the bilayer unit due to the ample space provided by the lamellar phase as the probe is buried deeper inside the hydrophobic region. A much smaller effect was observed in the cubic phase and was correlated with the tight environment around the probes, which stems from the increased curvature of the cubic phase. The current results provide a deeper understanding of the hydrophobic region during phase transition of lipid self-assembly which is important for better control during the process of membrane-protein crystallization.
Pseudo-first-order rate constants (k(obs)) for the nucleophilic substitution reaction of piperidine (Pip) with ionized phenyl salicylate (PS(-)), obtained at a constant [Pip](T) (= 0.1 M), [PS(-)](T) (= 2 x 10(-4) M), [CTABr](T) (cetyltrimethylammonium bromide), < or = 0.06 M NaOH, and a varying concentration of MX (= 3-FC(6)H(4)CO(2)Na, 3-FBzNa and 4-FC(6)H(4)CO(2)Na, 4-FBzNa), follow the kinetic relationship k(obs) = (k(0) + thetaK(X/S)[MX])/(1 + K(X/S)[MX]) which is derived by the use of the pseudophase micellar (PM) model coupled with an empirical equation. The empirical equation explains the effects of [MX] on CTABr micellar binding constant (K(S)) of PS(-) that occur through X(-)/PS(-) ion exchange. Empirical constants theta and K(X/S) give the parameters F(X/S) and K(X/S), respectively. The magnitude of F(X/S) gives the measure of the fraction of micellized PS(-) transferred to the aqueous phase by the limiting concentration of X(-) through X(-)/PS(-) ion exchange. The values of F(X/S) and K(X/S) have been used to determine the usual thermodynamic ion exchange constant (K(X)(Y)) for ion exchange process X(-)/Y(-) on the CTABr micellar surface. The values of K(X)(Br) (where Br = Y) have been calculated for X = 3-FBzNa and 4-FBzNa. The mean values of K(X)(Br) are 12.8 +/- 0.9 and 13.4 +/- 0.6 for X(-) = 3-FBz(-) and 4-FBz(-), respectively. Nearly 3-fold-larger values of K(X)(Br) for X = 3-FBz(-) and 4-FBz(-) than those for X = Bz(-), 2-ClBz(-), 2-CH(3)Bz(-), and the 2,6-dichlorobenzoate ion (2,6-Cl(2)Bz(-)) are attributed to the presence of wormlike micelles in the presence of > 50 mM 3-FBz(-) and 4-FBz(-) in the [CTABr](T) range of 5-15 mM. Rheological properties such as shear thinning behavior of plots of shear viscosity versus the shear rate at a constant [3-FBz(-)] or [4-FBz(-)] as well as shear viscosity (at a constant shear rate) maxima as a function of the concentrations of 3-FBz(-) and 4-FBz(-) support the conclusion, derived from the values of K(X)(Br), for the probable presence of wormlike/viscoelastic micellar solutions under the conditions of the present study.
The search for high-performance catalysts to improve the catalytic activity for an oxygen reduction reaction (ORR) is crucial for developing a proton exchange membrane fuel cell. Using the first-principles method, we have performed computational screening on a series of transition metal (TM) atoms embedded in monolayer Nb2S2C to enhance the ORR activity. Through the scaling relationship and volcano plot, our results reveal that the introduction of a single Ni or Rh atom through substitutional doping into monolayer Nb2S2C yields promising ORR catalysts with low overpotentials of 0.52 and 0.42 V, respectively. These doped atoms remain intact on the monolayer Nb2S2C even at elevated temperatures. Importantly, the catalytic activity of the Nb2S2C doped with a TM atom can be effectively correlated with an intrinsic descriptor, which can be computed based on the number of d orbital electrons and the electronegativity of TM and O atoms.
A detailed study on the conflicting role that colloid stability plays in magnetophoresis is presented. Magnetic iron oxide particles (MIOPs) that were sterically stabilized via surface modification with poly(sodium 4-styrene sulfonate) of different molecular weights (i.e., 70 and 1000 kDa) were employed as our model system. Both sedimentation kinetics and quartz crystal microbalance with dissipation (QCM-D) measurements suggested that PSS 70 kDa is a better stabilizer as compared to PSS 1000 kDa. This observation is mostly attributed to the bridging flocculation of PSS 1000 kDa decorated MIOPs originated from the extended polymeric conformation layer. Later, a lab-scale high gradient magnetic separation (HGMS) device was designed to study the magnetophoretic collection of MIOPs. Our experimental results revealed that the more colloidally stable the MIOP suspension is, the harder it is to be magnetically isolated by HGMS. At 50 mg/L, naked MIOPs without coating can be easily captured by HGMS at separation efficiency up to 96.9 ± 2.6%. However, the degree of separation dropped quite drastically to 83.1 ± 1.2% and 67.7 ± 4.6%, for MIOPs with PSS 1000k and PSS 70k coating, respectively. This observation clearly implies that polyelectrolyte coating that was usually employed to electrosterically stabilize a colloidal system in turn compromises the magnetic isolation efficiency. By artificially destroying the colloidal stability of the MIOPs with ionic strength increment, the ability for HGMS to recover the most stable suspension (i.e., PSS 70k-coated MIOPs) increased to >86% at 100 mM monovalent ion (Na(+)) or at 10 mM divalent ion (Ca(2+)). This observation has verified the conflicting role of colloidal stability in magnetophoretic separation.
We describe a new laboratory synthesis of the α-methyl ester sulfonates based on direct sulfonation of the methyl ester by SO3 introduced from the vapor phase. This was used to synthesize a chain deuterated sample of αC14MES, which was then used to measure the surface excess of αC14MES directly at the air/water interface over a wide range of concentration using neutron reflection. The adsorption isotherm could be fitted to an empirical equation close to a Langmuir isotherm and gave a limiting surface excess of (3.4 ± 0.1) × 10-6 mol m-2 in the absence of added electrolyte. The neutron-measured surface excesses were combined with the integrated Gibbs equation to fit the variation in surface tension with concentration (σ-ln C curve). The fit was exact provided that we used a prefactor consistent with the counterion at the surface being an impurity divalent ion, as has previously been found for sodium diethylhexylsulfosuccinate (aerosol OT or AOT) and various perfluorooctanoates. The critical micelle concentration (CMC) was determined from this fit to be 2.4 ± 0.3 mM in the absence of electrolyte. In the presence of 100 mM NaCl, this contamination was suppressed and the σ-ln C curve could be fitted using the integrated Gibbs equation with the expected prefactor of 1. The new data were used to reinterpret measurements by Danov et al. on an unpurified sample of αC14MES for which computer refinement was used to try to eliminate the effects of the impurities.
Monodispersed iron oxide nanoparticles (IONPs) coated with polystyrenesulfonate (PSS) and cetrimonium bromide (CTAB) have been used to stabilize magnetic Pickering emulsions (MPEs). Magnetophoresis of MPEs under the influence of a low gradient magnetic field (∇B < 100 T/m) was investigated at the macroscopic and microscopic scale. At the macroscopic scale, for the case of pH 7, the MPE achieved a magnetophoretic velocity of 70.9 μm/s under the influence of ∇B at 93.8 T/m. The magnetic separation efficiency of the MPE at 90% was achieved within 30 min for pH 3, 7, and 10. At pH 10, the colloidal stability of the MPE was the lowest compared to that for pH 3 and 7. Thus, MPE at pH 10 required the shortest time for achieving the highest separation efficiency, as the MPE experienced cooperative magnetophoresis at alkaline pH. The creaming rate of the MPE at all conditions was still lower compared to magnetophoresis and was negligible in influencing its separation kinetics profiles. At the microscopic scale, the migration pathways of the MPEs (with diameters between 2.5 and 7.5 μm) undergoing magnetophoresis at ∇B ∼ 13.0 T/m were recorded by an optical microscope. From these experiments, and taking into consideration the MPE size distribution from the dynamic light scattering (DLS) measurement, we determined the averaged microscopic magnetophoretic velocity to be 7.8 ± 5.5 μm/s. By making noncooperative magnetophoresis assumptions (with negligible interactions between the MPEs along their migration pathways), the calculated velocity of individual MPEs was 9.8 μm/s. Such a value was within the percentage error of the experimental result of 7.8 ± 5.5 μm/s. This finding allows for an easy and quick estimation of the magnetophoretic velocity of MPEs at the microscale by using macroscopic separation kinetics data.
The changes in the transport behavior of a microswimmer before and after cargo loading are crucial to understanding and control of the motion of a biohybrid microbot. In this work, we show the change in swimming behavior of biflagellated microalgae Chlamydomonas reinhardtii picking up a 4.5 μm polystyrene microbead upon collision. The microswimmer changed from linear forward motion into helical motion upon the attachment of the cargo and swam with a decreased swimming velocity. We revealed the helical motion of the microswimmer upon cargo loading due to suppression of flagella by image analysis of magnified time-lapse images of C. reinhardtii with one microbead attached at the anterior end (between the flagella). Furthered suppression on the flagellum imposed by the loading of the second cargo has led to increased oscillation per displacement traveled and decreased swimming velocity. Moreover, the microswimmer with a microbead attached at the posterior end swam with swimming velocity close to free swimming microalgae and did not exhibit helical swimming behavior. The experimental results and analysis showed that the loading location of the cargo has a great influence over the swimming behavior of the microswimmer. Furthermore, the work balance calculation and mathematical analysis based on Lighthill's model are well consistent with our experimental findings.
Inverse bicontinuous cubic phases of lyotropic liquid crystal self-assembly have received much attention in biomedical, biosensing, and nanotechnology applications. An Ia3d bicontinuous cubic based on the gyroid G-surface can be formed by the Guerbet synthetic glucolipid 2-hexyl-decyl-β-d-glucopyranoside (β-Glc-OC6C10) in excess water. The small water channel diameter of this cubic phase could provide nanoscale constraints in encapsulation of large molecules and crystallization of membrane proteins, hence stresses the importance of water channel tuning ability. This work investigates the swelling behavior of lyotropic self-assembly of β-Glc-OC6C10 which could be controlled and modulated by different surfactants as a hydration-modulating agent. Our results demonstrate that addition of nonionic glycolipid octyl-β-d-glucopyranoside (β-Glc-OC8) at 20 and 25 mol % gives the largest attainable cubic water channel diameter of ca. 62 Å, and formation of coacervates which may be attributed to a sponge phase were seen at 20 mol % octyl-β-d-maltopyranoside (β-Mal-OC8). Swelling of the cubic water channel can also be attained in charged surfactant-doped systems dioctyl sodium sulfosuccinate (AOT) and hexadecyltrimethylammonium bromide (CTAB), of which phase transition occurred from cubic to a lamellar phase. Destabilization of the cubic phase to an inverse hexagonal phase was observed when a high amount of charged lecithin (LEC) and stearylamine (SA) was added to the lipid self-assembly.
Nanostructures play an important role in targeting sparingly water-soluble drugs to specific sites. Because of the structural flexibility and stability, the use of template microemulsions (μEs) can produce functional nanopharmaceuticals of different sizes, shapes, and chemical properties. In this article, we report a new volatile oil-in-water (o/w) μE formulation comprising ethyl acetate/ethanol/brij-35/water to obtain the highly water-dispersible nanoparticles of an antihyperlipidemic agent, ezetimibe (EZM-NPs), to enhance its dissolution profile. A pseudoternary phase diagram was delineated in a specified brij-35/ethanol ratio (1:1) to describe the transparent, optically isotropic domain of the as-formulated μE. The water-dilutable μE formulation, comprising an optimum composition of ethyl acetate (18.0%), ethanol (25.0%), brij-35 (25.0%), and water (32.0%), showed a good dissolvability of EZM around 4.8 wt % at pH 5.2. Electron micrographs showed a fine monomodal collection of EZM-loaded μE droplets (∼45 nm) that did not coalesce even after lyophilization, forming small spherical EZM-NPs (∼60 nm). However, the maturity of nanodrug droplets observed through dynamic light scattering suggests the affinity of EZM to the nonpolar microenvironment, which was further supported through peak-to-peak correlation of infrared analysis and fluorescence measurements. Moreover, the release profile of the as-obtained EZM-nanopowder increased significantly >98% in 30 min, which indicates that a reduced drug concentration will be needed for capsules or tablets in the future and can be simply incorporated into the multidosage formulation of EZM.
Five synthetic β-d-maltosides derived from Guerbet branched alcohols, whose total hydrocarbon chain length ranged from C8 to C24, were synthesized to a high anomeric purity, and their thermal properties, liquid-crystalline phases, and structures were characterized using differential scanning calorimetry, optical polarizing microscopy, and small-angle X-ray scattering. Thermal investigations of all anhydrous Guerbet maltosides showed that they do not form solid crystals but undergo a glass transition upon temperature change in the range of 35-53 °C. The glassy crystalline structure turns into the liquid-crystalline structure upon heating or addition of water. In thermotropic studies, the lamellar phase formation is prominent in shorter-chain-length analogues, whereas the longer-chain compounds exhibit a more frustrated form of self-assembly in the formation of a metastable state, polymorphism, and inverse bicontinuous cubic structure ( Ia3 d). The excess water conditions show that the phase formation is dominated by the lamellar phase for the longer-chain compounds. Normal micellar solution was observed in the shortest-chain-length maltosides because of the enlargement of hydrated maltose headgroups. The self-assembly of both dry and fully hydrated Guerbet maltosides, which exhibited glass-forming abilities and showed surface activity and also the ability to act as membrane-stabilizing compounds, makes them ideal candidates for practical use in industry as well as biomedical research.
For equivalent micellar volume fraction (ϕ), systems containing anisotropic micelles are generally more viscous than those comprising spherical micelles. Many surfactants used in water-in-CO2 (w/c) microemulsions are fluorinated analogues of sodium bis(2-ethylhexyl) sulfosuccinate (AOT): here it is proposed that mixtures of CO2-philic surfactants with hydrotropes and cosurfactants may generate elongated micelles in w/c systems at high-pressures (e.g., 100-400 bar). A range of novel w/c microemulsions, stabilized by new custom-synthesized CO2-phillic, partially fluorinated surfactants, were formulated with hydrotropes and cosurfactant. The effects of water content (w = [water]/[surfactant]), surfactant structure, and hydrotrope tail length were all investigated. Dispersed water domains were probed using high pressure small-angle neutron scattering (HP-SANS), which provided evidence for elongated reversed micelles in supercritical CO2. These new micelles have significantly lower fluorination levels than previously reported (6-29 wt % cf. 14-52 wt %), and furthermore, they support higher water dispersion levels than other related systems (w = 15 cf. w = 5). The intrinsic viscosities of these w/c microemulsions were estimated based on micelle aspect ratio; from this value a relative viscosity value can be estimated through combination with the micellar volume fraction (ϕ). Combining these new results with those for all other reported systems, it has been possible to "map" predicted viscosity increases in CO2 arising from elongated reversed micelles, as a function of surfactant fluorination and micellar aspect ratio.
This study investigates the effect of DNA hairpins on the stabilization of gold nanoparticles (AuNPs) against salt-induced aggregation (SIA) in label-free colorimetric biosensors. AuNPs were incubated with DNA hairpins of varying stem lengths and toehold sequences, followed by the addition of NaCl, before being subjected to ultraviolet-visible (UV-vis) measurement. Results showed that hairpins with longer stems generally provide better stabilization of AuNPs (18-bp >14-bp >10-bp). No improvement was observed for 14- and 18-bp hairpins with a toehold beyond 8A, which may be attributed to saturated adsorption of hairpins on the gold surface. For 14-bp hairpins with an 8-mer homopolymeric toehold, we observed a stabilization trend of A > C > G > T, similar to the reported trend of ssDNA. For variants containing ≥50% adenine as terminal bases, introducing cytosine or guanine as preceding bases could also result in strong stabilization. As the proportion of adenine decreases, variants with guanine or thymine provide less protection against SIA, especially for guanine-rich hairpins (≥6G) that could form G-quadruplexes. Such findings could serve as guidelines for researchers to design suitable DNA hairpins for label-free AuNP-based biosensors.
An artificial magnetotactic microbot was created by integrating the microalgal cell with magnetic microbead for its potential application as biomotor in microscale environment. Here, we demonstrate the remote magnetotactic control of the microbot under a low gradient magnetic field (<100 T/m). We characterize the kinematic behavior of the microbots carrying magnetic microbeads of two different sizes, with diameter of 2 and 4.5 μm, in the absence and presence of magnetic field. In the absence of magnetic field, we observed the microbot showed a helical motion as a result of the misalignment between the thrust force and the symmetry axis after the attachment. The microbot bound with a larger magnetic microbead moved with higher translational velocity but rotated slower about its axis of rotation. The viscous force was balanced by the thrust force of the microbot, resulting in a randomized swimming behavior of the microbot at its terminal velocity. Meanwhile, under the influence of a low gradient magnetic field, we demonstrated that the directional control of the microbot was based on following principles: (1) magnetophoretic force was insignificant on influencing its perpendicular motion and (2) its parallel motion was dependent on both self-swimming and magnetophoresis, in which this cooperative effect was a function of separation distance from the magnet. As the microbot approached the magnet, the magnetophoretic force suppressed its self-swimming behavior, leading to a positive magnetotaxis of the microbot toward the source of magnetic field. Our experimental results and kinematic analysis revealed the contribution of mass density variation of particle-and-cell system on influencing its dynamical behavior.
A detailed study of the sedimentation kinetics of iron oxide nanoparticle (IONP) clusters composed of nanospheres and nanorods is presented. Measurements were performed to determine the absorbance of an IONP suspension undergoing sedimentation over time by using a UV-vis spectrophotometer with simultaneous monitoring of the hydrodynamic diameter of the clusters formed with dynamic light scattering (DLS). Mathematical analysis based on Happel's spherical and cylindrical models was conducted to reveal the relationship between the settling velocity of the IONP clusters and their packing density. For the case of IONP clusters composed of rodlike particles, two distinctive phases of sedimentation were recorded, with the occurrence of rapid sedimentation at the beginning of the process (phase I) followed by a slower settling rate (phase II). In sedimentation phase II, even though the nanorod clusters had a hydrodynamic size of >500 nm, which was much larger than that of the nanosphere clusters (∼200 nm), their settling velocity of 0.0038 mm/min was still slower than that of the nanosphere clusters. Such observations were mainly a result of the packing density differences between the formed clusters; due to the end-to-end particle interactions of nanorods, the nanorod clusters were less tightly packed and more permeable. In addition to the mathematical analysis, quartz crystal microbalance with dissipation (QCM-D) was employed to measure the "softness" of the IONP clusters formed, and this physical property can be further related to their packing density. This study illustrated that for a rapidly aggregating system, such as magnetic IONPs, not only do the particle shape and size uniformity contribute to the physical properties of the particle clusters formed but also the nature of the aggregation, either end-to-end and/or side-to-side, should be carefully considered when designing a colloidally stable IONP suspension.
This study provides a systematic analysis of the transport and magnetophoretic behavior of nanoscale zerovalent iron (nZVI) particles, both bare and surface functionalized by poly(ethylene glycol) (PEG) and carboxymethyl cellulose (CMC), after undergoing a chemical reaction. Here, a simple and well-investigated chemical reaction of methyl orange (MO) degradation by nZVI was used as a model reaction system, and the sand column transport and low-gradient magnetophoretic profiles of the nanoparticles were measured before and after the reaction. The results were compared over time and analyzed in the context of extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to understand the particle interactions involved. The colloidal stability of both bare and functionalized nZVI particles was enhanced after the reaction due to the consumption of metallic Fe content, resulting in a significant drop in their magnetic properties. As a result, they exhibited improved mobility across the sand column and a slower magnetophoretic collection rate compared to the unreacted particles. Here, the colloidal filtration theory (CFT) was employed to analyze the transport behavior of nZVI particles across the packed sand column. It has been observed that the surface properties of the reacted functionalized particles changed, possibly due to the entrapment of degraded products within the polymer adlayer. Moreover, quartz crystal microbalance with dissipation (QCM-D) measurements were performed to reveal the viscoelastic contribution of the adlayer formed by both bare and functionalized nZVI particles after the reaction on influencing their transport behavior across the sand column. Finally, we proposed the implementation of a high-gradient magnetic trap (HGMT) to reduce the transport distance of the colloidally stable CMC-nZVI, both before and after the reaction. This study sheds light on the behavioral changes of iron nanoparticles after the reaction and highlights environmental concerns regarding the presence of reacted nanoparticles.
To overcome the increased disease rate, utilization of the versatile broad spectrum antibiotic drugs in controlled drug-delivery systems has been a challenging and complex consignment. However, with the development of microemulsion (μE)-based formulations, drugs can be effectively encapsulated and transferred to the target source. Herein, two biocompatible oil-in-water (o/w) μE formulations comprising clove oil/Tween 20/ethylene glycol/water (formulation A) and clove oil/Tween 20/1-butanol/water (formulation B) were developed for encapsulating the gatifloxacin (GTF), a fourth-generation antibiotic. The pseudoternary phase diagrams were mapped at a constant surfactant/co-surfactant (1:1) ratio to bound the existence of a monophasic isotropic region for as-formulated μEs. Multiple complementary characterization techniques, namely, conductivity (σ), viscosity (η), and optical microscopy analyses, were used to study the gradual changes that occurred in the microstructure of the as-formulated μEs, indicating the presence of a percolation transformation to a bicontinuous permeate flow. GTF showed good solubility, 3.2 wt % at pH 6.2 and 4.0 wt % at pH 6.8, in optimum μE of formulation A and formulation B, respectively. Each loaded μE formulation showed long-term stability over 8 months of storage. Moreover, no observable aggregation of GTF was found, as revealed by scanning transmission electron microscopy and peak-to-peak correlation of IR analysis, indicating the stability of GTF inside the formulation. The average particle size of each μE, measured by dynamic light scattering, increased upon loading GTF, intending the accretion of drug in the interfacial layers of microdomains. Likewise, fluorescence probing sense an interfacial hydrophobic environment to GTF molecules in any of the examined formulations, which may be of significant interest for understanding the kinetics of drug release.
In situ rheological measurements for clathrate hydrate slurries were performed using a high pressure rheometer to determine the effect of hydrate particles on the viscosity and transportability of these slurries. These measurements were conducted using a well-characterized model water-in-oil emulsion ( Delgado-Linares et al. Model Water in-Oil Emulsions for Gas Hydrate Studies in Oil Continuous Systems . Energy Fuels 2013 , 27 , 4564 - 4573 ). The emulsion consists of a model liquid hydrocarbon, water, and a surfactant mixture of sorbitane monooleate 80 (Span 80) and sodium di-2-ethylhexylsulfosuccinate (Aerosol OT, AOT). This emulsion was used as an analog to water-in-crude oil (w/o) emulsions and provides reproducible results. The flow properties of the model w/o emulsion prior to hydrate formation were investigated in terms of several parameters including water percentage, temperature and pressure. A general equation that describes the viscosity of the emulsion as a function of the aforementioned parameters was developed. This general equation was able to predict the viscosity of a saturated emulsion at various temperatures and water percentages to within ±13% error. The general equation was then used to analyze the effect of hydrate formation on the transportability of gas hydrate slurries. As for hydrate slurries investigation, measurements were performed using methane gas as the hydrate former and a straight vane impeller as a stirring system. Tests were conducted at constant temperature and pressure (1 °C and 1500 psig of methane) and water percentages ranging from 5 to 30 vol %. Results of this work were analyzed and presented in terms of relative values, i.e., viscosities of the slurries relative to the viscosities of the continuous phase at similar temperature and pressure. In this work, a correlation to predict the relative viscosity of a hydrate slurry at various hydrate volume fractions was developed. Analysis of the developed correlation showed that the model was able to predict the relative viscosity of a hydrate slurry to within ±17% error.
When two or more droplets coalesce on a superhydrophobic surface, the merged droplet can jump spontaneously from the surface without requiring any external energy. This phenomenon is defined as coalescence-induced droplet jumping and has received significant attention due to its potential applications in a variety of self-cleaning, anti-icing, antifrosting, and condensation heat-transfer enhancement uses. This article reviews the research and applications of coalescence-induced droplet jumping behavior in recent years, including the influence of droplet parameters on coalescence-induced droplet jumping, such as the droplet size, number, and initial velocity, to name a few. The main structure types and influence mechanism of the superhydrophobic substrates for coalescence-induced droplet jumping are described, and the potential application areas of coalescence-induced droplet jumping are summarized and forecasted.