Hydrophobic Media Research Articles

Mixed surfactant (altering chain length and head group) aggregates as an effective carrier for tuberculosis drug

Surface properties and aggregation behavior of cationic-cationic and cationic-non-ionic mixed surfactant systems viz. Dodecylethyldimethylammonium bromide (DDAB) with a series of double chain cationic surfactants (DiDDAB, DMDTAB, and DODAB) and non-ionic surfactants (Brij 96, Tyloxapol and Tween 80) were analysed using surface tension and transmission electron microscopy (TEM). The effect of chain length of cationic surfactant and hydrophilic-lypophilic balance (HLB) prominently observed in critical aggregation (cac) value. The aqueous solubility of anti-tuberculosis drug: rifampicin (RIF) was comparatively studied by UV–vis spectroscopy in presence of formulated micelles and vesicles. RIF was significantly solubilised in aqueous medium using all the formulated aggregates. RIF is very unstable in basic medium (above pH-7) and in oxidizing media. Therefore, stability at pH-13 as well as in strong oxidising environment was monitored using UV–vis spectroscopy. To trace the locus of the drug encapsulation in the micelles/vesicles, fluorescence spectroscopy and TEM studies were carried out. Both the techniques stemmed in complimentary results and confirmed that, RIF is majorly populated at polar medium in cationic-cationic vesicles and favour to reside at hydrophobic medium of the nonionic-cationic micelles.

Influence of hydrophobic nanosilica and hydrophobic medium on water bound in hydrophilic components of complex systems

The temperature behavior of water bound to compacted nanosilica cA-300 alone or in mixture with hydrophobic nanosilica AM1 alone or with addition of human serum albumin (HSA) or tannin was compared for different dispersion media (air, CDCl3 alone or with addition of HCl or trifluoroacetic acid, TFAA) using low-temperature 1H NMR spectroscopy and cryoporometry. There is overlapping of the confined space effects for water bound in voids between silica nanoparticles with the effects caused by the colligative properties of aqueous solutions of TFAA or HCl. These phenomena determine the temperature behavior of bound water unfrozen at T <273 K upon changes of the dispersion media. Typically, the contact area between unfrozen water and a surface of nanosilicas is smaller than the specific surface area of the solids due incomplete filling of voids between nanoparticles by bound water. Bound water tends to be in a clustered state upon the adsorption. In composites with cA-300/AM1, there is a tendency of diminution of the contact area of water with hydrophobic nanosilica AM1 and hydrophobic liquid CDCl3 immiscible with water. This effect changes the temperature behavior of water bound to hydrophilic silica or polar biomolecules. The observed effects can be of importance upon practical applications of nanosilica based composites.

Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface

An extensive structural characterization of the 2D-HB-Network formed by water molecules at the air-water interface has been carried out by means of DFT-based and classical molecular dynamics simulations. SPC/E and SPC/Fw force fields commonly used for modelling liquid water are shown to correctly reproduce the 2D-HB-Network structure obtained from the reference ab-initio simulation. For both DFT-MD and classical MD representations, identical results have been obtained by increasing the size and time-scale of the simulations, starting from a simulation box of 256 water molecules in the liquid phase, simulated for 20 ps up to 25 ns. One pivotal result is that ∼90% of the water molecules in the interfacial layer are connected by a collective and extended net of HBs oriented parallel to the surface, and this 2D-HB-Network is built upon adjacent water rings mostly formed by 4, 5 or 6 water molecules. This finding in particular rationalizes previous non linear SFG spectroscopic results suggesting that liquid water at the interface with hydrophobic media could arrange in rings.

Nanospikes functionalization as a universal strategy to disperse hydrophilic particles in non-polar media

Dispersion of hydrophilic particles in non-polar media has many important applications yet remains difficult. Surfactant or amphiphilic functionalization was conventionally applied to disperse particles but is highly dependent on the particle/solvent system and may induce unfavorable effects and impact particle hydrophilic nature. Recently 2 μm size polystyrene microbeads coated with ZnO nanospikes have been reported to display anomalous dispersity in phobic media without using surfactant or amphiphilic functionalization. However, due to the lack of understanding whether this phenomenon was applicable to a wider range of conditions, little application has been derived from it. Here the anomalous dispersity phenomenons of hydrophilic microparticles covered with nanospikes were systematically assessed at various conditions including different particle sizes, material compositions, particle morphologies, solvent hydrophobicities, and surface polar groups. Microparticles were functionalized with nanospikes through hydrothermal route, followed by dispersity test in hydrophobic media. The results suggest nanospikes consistently prevent particle aggregation in various particle or solvent conditions, indicating the universal applicability of the anomalous dispersion phenomenons. This work provides insight on the anomalous dispersity of hydrophilic particles in various systems and offers potential application to use this method for surfactant-free dispersions.

Polymerization induced shape-tuning and multi-triggered switchability of gold nanostructures

Near-IR absorbing gold nanostructures were prepared by a novel approach in the absence of any extra reducing agent, stabilizer or surface modification step through in-situ polymerization of an amine-containing monomer. Such nanoparticles can reversibly switch between hydrophilic and hydrophobic media using several triggers like temperature, pH and CO2/N2 bubbling.

Computational and experimental validation of antioxidant properties of synthesized bioactive ferulic acid derivatives

ABSTRACTFerulic acid, a well-known natural phenolic compound, is considerably reported for its hydroxyl and peroxyl radical scavenging activities. However, the antioxidant capacity of ferulic acid is limited by its relatively low solubility in hydrophobic media thereby preventing its application for autoxidation of fats and oils. To this end, several research efforts are being made to maximize the therapeutic benefits of ferulic acid and these efforts included but not limited to structural modification of ferulic acid to produce its derivatives. In this study, we synthesized ester and amide derivatives of ferulic acid and evaluated them for in vitro antioxidant potential as well as molecular docking properties. Data revealed that ferulic ester and amide derivatives had excellent antioxidant capacity and demonstrated strong inhibitory potential. Analysis of molecular docking indicated ferulic ester as potent inhibitor of target proteins in breast cancer as well as in oxidative stress. Taken together, the findings support potent antioxidant properties by these ferulic derivatives. Findings may become relevant where structural modification to enhance physico-chemical properties without compromising the antioxidant and/or medicinal potential are desirable.

Tunable interlayer hydrophobicity in a nanostructured high charge organo-mica

A tunable hydrophobicity, from a fully hydrophobic medium to an amphiphilic quasi-solution, has been obtained in the interlayer space of a synthetic high charged mica by ion exchange reaction with amine cations. The structural and intercalation properties of the hybrids after the exchange with the n-alkylammonium cations: [RNH3]+, [RNH(CH3)2]+ and [RN(CH3]3+ with C16 alkyl chain length have been determined by termogravimetric/differential scanning calorimetry analysis (TGA-DSC) and mass spectrometry (MS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) has been used as a complementary technique to provide new insights into the morphology of the exchanged products. Coverage and cation distribution have been correlated with layer charge and steric effects. Thus, a full organo-clay is obtained when the primary amine cations are adsorbed between the layers. However, a homogenous single phase of mixed organic/inorganic cations is formed in the same interlayer with the tertiary amine cations. Mixed ion clays combining both exchangeable inorganic and adsorbent organic ions in their interlayer space can be potential materials to be used as adsorbents for water decontamination, independently of the hydrophilic/hydrophobic nature of the pollutants. For the quaternary amine cations steric effects preclude the coexistence of both organic and inorganic species in the same interlayer of the clay so phase segregation together with a heterogeneous phase of organic and inorganic galleries in the same particle can be observed.

Electromagnetic, magnetorheological and stability properties of polysiloxane elastomers based on silane–modified carbonyl iron particles with enhanced wettability

Soft carbonyl iron (CI) particles were successfully modified with a thin layer of tetraethoxysilane (TEOS) to enhance the wettability of their surface in hydrophobic media. The contact angle investigations and tensiometric analysis revealed and helped quantify the significantly enhanced wettability and, thus, the better interfacial adhesion of the TEOS–coated CI particles (CI–TEOS) with the non–polar siloxane–based materials. Therefore, stable magnetorheological elastomers (MREs) based on CI–TEOS particles and polydimethyl siloxane matrix were fabricated. The prepared composites had different particle loadings and microstructural characteristics: isotropic and anisotropic. These structural differences were confirmed by scanning electron microscopy and were found to considerably affect dielectric properties of the MREs due to various charge transport mechanisms within the particle clusters. Furthermore, the magnetorheological (MR) performances of isotropic MRE variants were analysed before and after exposure to acidic environment. After the corrosion test, the MRE based on bare CI particles exhibited dramatically decreased relative MR effect and mechanical properties when compared with its analogue containing CI–TEOS.

Patterned polycaprolactone-filled glass microfiber microfluidic devices for total protein content analysis

Membrane based microfluidic devices have gained much popularity in recent years, as they make possible rapid, inexpensive analytical techniques that can be applied to a wide variety of areas. The ability to modify device hydrophilicity and hydrophobicity is critically important in fabricating membrane based microfluidic devices. Polar hydrophilic membranes, such as glass microfiber (GMF) membranes, hold great potential as they are inexpensive, chemically inert, and stable. Filling of these membranes with non-polar polymers such as polycaprolactone (PCL) converts the hydrophilic GMF into a hydrophobic medium. Controlled alteration of the surface chemistry of PCL/GMF substrates allows for the fabrication of microfluidic patterns on the surface. Using this approach, we have developed a simple and rapid technique for fabrication of highly adaptable complex multidimensional (2D and 3D) microfluidic pathways on a single membrane. PCL-filled GMF media were masked and selectively exposed to oxygen radicals so that the exposed surface became permanently superhydrophilic in its behavior. The desired microfluidic pattern was cut into the mask prior to assembly and exposure, and the mask was removed after exposure to reveal the ready-to-use microfluidic device. To verify and demonstrate the performance of this novel fabrication method, a colorimetric total protein assay was applied to the determination of protein concentrations in real samples.

Mechanistic modeling of hydrophobic interaction chromatography for monoclonal antibody purification: process optimization in the quality by design paradigm

AbstractBACKGROUNDA mechanistic model has been developed for hydrophobic interaction chromatography (HIC) based purification of monoclonal antibodies (mAbs). The model has been used to gain thorough process understanding as desired by the quality by design paradigm. The model is based on the general rate model coupled with an exponentially modified Langmuir adsorption model. The latter has been modeled by using the solvophobic theory for correlating protein adsorption equilibrium on the hydrophobic media with the mobile phase salt concentration.RESULTSThe proposed model satisfactorily predicts the elution profile of the monoclonal antibody product under consideration and its aggregates on a HIC column (Phenyl Sepharose 6 Fast FlowTM low sub) operated in linear gradient mode. The model has been used to elucidate the underlying mechanism behind separation of monomer and aggregate species. A comparison of the relative time scales for the various mass transfer events for mAb and aggregate species indicates that the intra‐particle (pore) diffusion transport of these molecules to their respective binding sites within the porous HIC resin is the rate limiting step whereas convection, film diffusion, and binding kinetics are relatively faster (time scales are 10−1 to 10−3 order of magnitude times the time scale of intra‐particle pore diffusion).CONCLUSIONSThe proposed methodology for modeling can be successfully implemented to achieve efficient aggregate removal by HIC using minimal experimentation compared with the traditional experimentally extensive approaches. © 2017 Society of Chemical Industry

Convective drying in thin hydrophobic porous media

A pore network (PN) model is developed to explore drying of a thin hydrophobic porous medium bounded with a gas purge channel. The PN is composed of cubic pore bodies connected by cylindrical pore throats. At the interface between a pore throat and body, a sudden geometrical expansion exists. When a meniscus advances to this interface, it will be pinned first until the pressure across the meniscus increases to a critical value. This phenomenon is called the capillary valve effect. Because of this effect, two types of invasion into pore bodies are discerned, i.e. bursting and merging invasion. The developed PN model with the capillary valve effect is validated against the experimental results. For the drying case of dominant merging invasion, a drying front of finite width is stably receded. But when bursting invasion dominates, gas invasion is a random process; the drying process can be characterized by three regimes: a surface evaporation period, a constant rate period, and a falling rate period. The total liquid saturation for transition from the constant to falling rate period is close to that at which the total area for vapor transport is maximal between the partially filled pores and their neighboring empty pores.

Electrochemical preparation of standard solutions of Pb(II) ions in ionic liquid for analysis of hydrophobic samples: The olive oil case

In this paper we present an electrochemical approach to prepare standard solutions of metal ions in a room temperature ionic liquid (IL), which can find useful application for analysis in hydrophobic matrices. The method, developed here for the case of lead ions, is based on the galvanostatic dissolution of a lead anode dipped directly in a suitable IL, namely tri-hexyl(tetradecyl)phosphonium bis (trifluoromethylsulfonyl) imide ([P14,6,6,6]+[NTf2]-). After each oxidation step, the metal dissolution process in the IL solutions was monitored by cyclic voltammetric measurements at a glassy carbon disk electrode. The results indicated that the peak current relevant to the reduction of the electro-generated Pb(II) increased linearly while increasing the oxidation time. By varying the oxidation time from 200 to 6000s, a set of Pb(II)/[P14,6,6,6]+[NTf2]- solutions at concentrations ranging between 10 and 300μgg−1 was prepared. To validate the efficiency of the electrochemical procedure to produce metal ion standard solutions, the Pb content was quantified by developing a microwave digestion procedure specifically suitable for the IL medium, followed by ICP-QMS analysis in the digested standards. The results indicated a satisfactory agreement between concentrations found by ICP-QMS and calculated from electrochemical data, with a coulometric efficiency of Pb(II) generation in ionic liquid ≥95.6%. Finally, the applicability of the Pb(II)/IL solutions as standards for analyses in hydrophobic media was tested by determining, by ICP-QMS, the Pb content in an extra-virgin olive oil spiked with known amounts of a Pb(II)/IL standard. Satisfactory Pb recoveries, ≥96%, were measured.

Effect of mass overloading on binding and elution of unstable proteins in hydrophobic interaction chromatography

Adsorption behavior of unstable proteins, i.e., bovine serum albumin and α-lactalbumin, has been studied on a hydrophobic interaction chromatography medium under mass overloading conditions at different kosmotropic salt concentrations in the mobile phase. A mechanistic model has been formulated and used to describe kinetics and thermodynamics of protein interactions with the adsorbent surface. The model assumed two-site binding adsorption and reversible protein unfolding, which allowed predicting the inhibition of protein unfolding at high column loadings. A simplified procedure for the determination of model parameters has been developed, which was based on the inverse method. The model was successfully used to reproduce the pattern of chromatographic elution as well as the course of breakthrough curves. The model formulation was supported by Nano Differential Scanning Fluorimetry measurements, which were exploited to determine the protein stability in the liquid and adsorbed phases at different column loadings and salt concentrations.

Predicting hydrophobic solvation by molecular simulation: 2. New united-atom model for alkanes, alkenes, and alkynes.

Existing united-atom models for non-polar hydrocarbons lead to systematic deviations in predicted solvation free energies in hydrophobic solvents. In this article, an improved set of parameters is proposed for alkane molecules that corrects this systematic deviation and accurately predicts solvation free energies in hydrophobic media, while simultaneously providing a very good description of pure liquid densities. The model is then extended to alkenes and alkynes, again yielding very accurate predictions of solvation free energies and densities for these classes of compounds. For alkynes in particular, this work represents the first attempt at a systematic parameterization using the united-atom approach. Averaging over all 95 solute/solvent pairs tested, the mean signed deviation from experimental data is very close to zero, indicating no systematic error in the predictions. The fact that predictions are robust even for relatively large molecules suggests that the new model may be applicable to solvation of non-polar macromolecules without accumulation of errors. The root mean squared deviation of the simulations is only 0.6 kJ/mol, which is lower than the estimated uncertainty in the experimental measurements. This excellent performance constitutes a solid basis on which a more general model can be parameterized to describe solvation in both polar and non-polar environments. © 2016 Wiley Periodicals, Inc.

Benchmarking Uranyl Peroxide Capsule Chemistry in Organic Media

Uranyl peroxide capsules are a recent addition to polyoxometalate (POM) chemistry. Ten years of development has ensued only in water, while transition metal POMs are commonly exploited in aqueous and organic media, controlled by counterions or ligation to render the clusters hydrophilic or hydrophobic. Here, new uranyl POM behavior is recognized in organic media, including (1) stabilization and immobilization of encapsulated hydrophilic countercations, identified by Li nuclear magnetic resonance (NMR) spectroscopy, (2) formation of new cluster species upon phase transfer, (3) extraction of uranyl clusters from different starting materials including simulated spent nuclear fuel, (4) selective phase transfer of one cluster type from a mixture, and (5) phase transfer of clusters from both acidic and alkaline media. The capsule morphology of the uranyl POMs renders accurate characterization by X‐ray scattering, including the distinction of geometrically similar clusters. Compositional analysis of the aqueous phase post‐extraction provided a quantitative determination of the ion exchange process that enables transfer of the clusters into the organic phase. Preferential partitioning of uranyl POMs into organic media presents new frontiers in metal ion behavior and chemical reactions in the confined space of the cluster capsules in hydrophobic media, as well as the reactivity of clusters at the organic/aqueous interface.

A new method for ultra-fast concentration of hydrophobic particles

In froth flotation, fine hydrophobic particles selectively attach to the surface of air bubbles, in turn rising through the liquid and then more slowly as part of the foam that emerges from the system. This paper proposes a paradigm shift from the traditional use of air bubbles as the hydrophobic separation medium to potentially a far more powerful version that utilises a novel hydrophobic binder, a concentrated water in oil emulsion. We show empirically the oil consumption increases linearly with the specific surface area of the particles, with an average oil film thickness of 178nm for fine coal particles, well below the level required for conventional oil agglomeration. The new approach is ultrafast, achieving agglomeration within seconds under batch conditions, with strong selectivity. We also show for the first time continuous steady state agglomeration can be achieved by simply passing the feed and binder suspensions through a partially closed ball valve. Here the residence time through the valve is less than 0.1s. And, by subjecting the agglomerated product to further shear, the emulsion is inverted, releasing bound water. Pressure driven filtration then delivers remarkably low product moistures. Operational aspects of this new technology are discussed.

Silane functionalization of nanodiamond for polymer nanocomposites-effect of degree of silanization

The silanization of nanodiamond (ND) was successfully carried out by using the esterification reaction of hydrolyzed vinyltrimethoxysilane (VTS) in alcoholic solution. The surface carboxylic group of ND was first enhanced by thermal oxidation to increase the degree of esterification reaction. The extent of silane functionalization of ND was controlled by varying the weight ratio of VTS and oxidized ND (oxND), from 2:1 to 10:1 (w/w) in the functionalization reaction medium. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) revealed that the highest degree of silanization occurred at VTS/oxND of 5:1 (w/w), while more silane concentrations resulted in self-condensation of silane molecules and formation of polysiloxane layers around nanoparticles leading to agglomeration of nanoparticles. Silanized ND (sND) exhibited more stable suspension in hydrophobic medium compared to as-received ND and oxND. To investigate the influence of silane functionality on the polymer-filler interactions, the rheological properties of polydimethylsiloxane (PDMS)/ND suspensions were also investigated and the results discussed accordingly.

Materials Study for Optimization of Redox-Magnetohydrodynamics (R-MHD) for Pumping in Microfluidics Systems

Magnetohydrodynamics (MHD) is a unique pumping approach that can be used in Lab-On-A-Chip microfluidics and offers several features that either complement or improve upon other microfluidic pumping methods, including a flat flow profile, low voltage requirements, portability and programmability, and rotational flow. 1 MHD generates a body force (FB ) from the interaction of net ionic current in the solution (j) in the presence of magnetic flux density (B), by following the equation FB = j X B. 2, 3 Ionic current can be generated between electrodes in a solution by passing electronic current through the electrodes in the external circuit to oxidize or reduce electroactive species called redox species. Redox species can be confined onto the electrode surface or mixed with electrolyte solution. The latter may produce a larger interference with analytes. In addition to improved compatibility with analysis, the advantage of immobilized redox species is that of easily-accessible, high concentration of charge at the electrodes that offers high currents, and therefore high fluid velocities. Immobilization through electropolymerization allows controlled deposition of redox species onto the electrode surfaces. The conducting polymer polyethylene dioxythiophene (PEDOT) has been used successfully for this purpose, and has generated MHD flow while maintaining good chemical stability, reversible doping states, and low redox potential, and the monomer (EDOT) is commercially available. 4, 5 The pumping efficiency of MHD can be expressed as how fast and how far fluid will flow; and those features depend on the ionic current density and charge density generated from the polymer film, respectively. Both can be enhanced by optimizing the factors that affect the film morphology such as electrodeposition conditions (cycled or stepped potential, scan rate, and deposition cycles), solvents, electrolytes, and monomer concentrations. 6, 7 Solvent and electrolyte combinations for electrodeposition play an important role in PEDOT morphology. Organic solvents are particularly useful over aqueous solutions because EDOT dissolves more easily in them and produces polymer films with higher conductivity. Organic solvents also provide a hydrophobic medium that facilitates uniform and well-adherent thick films during deposition. 8, 9 In the studies that will be reported, propylene carbonate and acetonitrile were used as solvents and LiClO4 and TBAPF6 as electrolytes for electrochemical deposition at different numbers of deposition cycles and scan rates. The studies reveal the optimized current and charge density to maximize MHD pumping efficiency by comparing electrochemical responses of PEDOT films from different solvent/electrolyte combinations and deposition conditions. Chronoamperometry (CA) and chronocoulometry (CC) were used to determine charge and current densities in different electrolyte solutions. In a MHD fluidics application, the charge and current densities are good predictors of how far and how long the fluid will flow, respectively. The chip design for the MHD experiments contained four gold microband electrodes (each is 1.5 cm X 650 μm X 250 nm). A 2.14 mm polydimethylsiloxane gasket over the chip with a 3 cm x 1.8 cm rectangular opening used to define the cell dimensions. 1100 μL electrolyte solution pipetted into the cell with polystyrene beads as MHD solution. A glass coverslip (24 x 50 mm) placed over the gasket as a ceiling of the cell which also limit the vertical direction of fluid flow. MHD fluid flow obtained by applying current through anode and cathode (two adjacent PEDOT modified electrodes were chosen) and placing a 0.37 T DC magnet under the chip. Fluid flows by following FB = j X B in between the parallel electrodes and visualized and recorded by using a microscope interfaced with Sony Handycam camera. 1,10 Videos were analyzed by particle tracking velocimetry and particle tracking software to get bead velocities. For a fixed electrode geometry and cell height it was found that bead velocity is proportional to the current applied.

Carbocation-π interaction: evaluation of the stabilization by phenylalanine of a biochemical carbocation intermediate.

Computational analyses, using primarily density functional theory, have been used to determine the stabilization associated with the carbocation-π interaction of a biochemical carbocation intermediate binding to a phenylalanine residue in an enzyme active site. Studies of complexation between t-butyl cation and ethylbenzene, and of a model of a carbocation intermediate with a phenylalanine in the active site of geranyl diphosphate C-methyl transferase, have afforded the first quantitative evaluation of the stabilization that can be provided to a carbocation by an aromatic residue in an enzymatic reaction. Describing the hydrophobic surrounding medium using a dielectric constant between ε = 2 and ε = 4, the calculated carbocation-π stabilization energy lies in the range of 10-7.5 kcal mol-1.

Gelation-Stabilized Functional Composite-Modified Bitumen for Anti-icing Purposes

Ionic salts as anti-icing agents have been extensively used to eliminate accumulation of ice on asphalt surfaces. However, salt can be easily removed by rain or automobiles and requires frequent application on roads. Besides this economic consideration, anti-icing agents compromise the mechanical properties of asphalt and have a negative impact on living organisms and the environment when used in large amounts. Incorporation of hydrophilic salts into bitumen, a hydrophobic asphalt binder, and controlled release of specific molecules from this hydrophobic medium can provide an effective solution for reducing ice formation on pavements. Bitumen has previously been modified by various polymers, including styrene-butadiene-styrene (SBS) for improved strength and thermomechanical properties. However, an anti-icing function was not considered in those previous designs. In a previous study, we developed a functional polymer composite consisting of potassium formate (HCOOK) salt pockets dissolved in a hydrophilic...