Aqueous Phase Volume Fraction Research Articles

Mechanical and Thermal Properties of Porous Nanocellulose/Polymer Composites: Influence of the Polymer Chemical Structure and Porosity.

The excellent emulsifying capacity of nanocellulose allows for the preparation of porous nanocellulose/polymer composites through the emulsion templating process. However, the effects of the polymer chemical structure and porosity on the material properties have not been extensively explored. Here, we discuss the effects of these two factors on the thermal and mechanical properties of the composites. Two types of porous nanocellulose/polymer composites were fabricated with styrene-divinylbenzene (poly(St-co-DVB)) or styrene-poly(ethylene glycol) dimethacrylate (poly(St-co-EGDMA)) copolymers as the polymer phases. The porosity of the composite was changed up to ∼50% v/v by varying the aqueous phase volume fraction in the original nanocellulose-stabilized w/o emulsions. As the porosity increased, the thermal conductivity of the composite decreased. The mechanical properties were strongly influenced by the polymer type; the nanocellulose/poly(St-co-DVB) composite showed stiff but brittle behavior, whereas the nanocellulose/poly(St-co-EGDMA) composite showed higher strength and toughness. In both types of composites, the nanocelluloses served as reinforcing agents, contributing to the improvement of the mechanical properties.

Water-in-oil oleogel with biphasic stabilization for fabrication of low-fat salad dressing

Salad dressing has become a popular condiment for consumers in many countries, especially for vegetarians. However, the rapid increase in the prevalence of obesity worldwide has been partially attributed to the overconsumption of fats. In this study, we constructed a water-in-oil oleogel with biphasic stabilization for fabrication of low-fat salad dressing. The oleogel was stabilized by adding beeswax to the external oil phase and curdlan to the internal aqueous phase. The oleogel exhibited shear thinning behavior and had a higher storage modulus than the loss modulus, which indicated good elastic behavior. The oleogel displayed high stability as the volume fraction of the internal aqueous phase was increased to 70% because of biphasic stabilization. Beeswax had a positive effect on the structure of the oil phase in the oleogel. When the concentration of beeswax reached 3%, the oleogel exhibited a uniform distribution, a small droplet size, and considerable freeze-thaw stability. In comparison with the oleogel where curdlan alone was used in the internal aqueous phase, the viscoelastic properties and stability could be improved by using a mixture of curdlan and pullulan or curdlan and β-cyclodextrin. Our study provides a green and sustainable method for fabrication of low-fat salad dressing.

1D magnetic resonance imaging and low-field nuclear magnetic resonance relaxometry of water-based silica nanofluids

The purpose of this research is to investigate 1-D Magnetic Resonance Imaging (MRI) and low-field Nuclear Magnetic Resonance (NMR) relaxation characteristics of silica nanofluids. The results show that presence of silica nanoparticles increases the MRI signal intensity and influences the NMR relaxation by shifting the relaxation peaks toward faster times compared to deionized water (DIW). Additionally, inversion recovery sequences show that nanoparticles reduce longitudinal relaxation time. For the tested nanofluid of EOR-12, signal intensity, longitudinal relaxation rate and transverse relaxation rate show a strong linear dependence on nanoparticle concentration with the highest enhancement of 1.75-fold, 2.57-fold and 3.20-fold, respectively compared to DIW. Additionally, investigation of the effect of nanoparticle size shows that below an optimal size, the MRI signal intensity and the NMR relaxation rates show a positive correlation with nanoparticle size but above the optimal size, the behavior reverses. For the nanoparticle with the optimal diameter, signal intensity, longitudinal relaxation rate and transverse relaxation rate enhancement was 2.21-fold, 4.44-fold and 4.45-fold, respectively compared to DIW. Application of the observed improvement in signal intensity to obtain the profile of the aqueous phase volume fraction in a Pickering emulsion shows a maximum error of 8% which indicates that the proposed technique can be applied for emulsion characterization with good accuracy.

Self-assembly and thermoreversible rheology of perfluorocarbon nanoemulsion-based gels with amphiphilic copolymers

Perfluorocarbon (PFC) nanoemulsions have great potential in biomedical applications due to their unique chemical stability, biocompatibility, and possibilities for enhanced oxygen supply. The addition of amphiphilic block copolymers promotes the formation and long-term stability of emulsion-based gels. In this work, we report the systematic study of the impact of adding amphiphilic triblock copolymers to water-in-perfluorocarbon nanoemulsions on their structure and viscoelasticity, utilizing small-angle neutron and X-ray scattering (SANS and SAXS) and rheology. We find that an intermediate concentration of copolymer yields the highest strength of attraction between droplets, corresponding to a maximum in the elasticity and storage modulus. The stability and viscoelastic moduli can be tuned via the amount of copolymer and surfactant along with the volume fraction of aqueous phase. SANS provides the detail on nanostructure and can be fit to a spherical core-shell form factor with a square-well hard sphere structure factor. The PFC nanoemulsion system displays thermoresponsive and thermoreversible properties in temperature sweeps.

Rheology and Catastrophic Phase Inversion of Emulsions in the Presence of Starch Nanoparticles

Emulsions stabilized by solid nanoparticles, referred to as Pickering emulsions, are becoming increasingly important in applications as they are free of surfactants. However, the bulk properties and stability of Pickering emulsions are far from being well understood. In this work, the rheological behavior and catastrophic phase inversion of emulsions in the presence of starch nanoparticles were studied using in-situ measurements of viscosity and electrical conductivity. The aqueous phase consisting of starch nanoparticles was added sequentially in increments of 5% vol. to the oil phase under agitation condition to prepare the emulsions. The emulsions were water-in-oil (W/O) type at low to moderate concentrations of aqueous phase. At a certain critical volume fraction of aqueous phase, catastrophic phase inversion of W/O emulsion to oil-in-water (O/W) emulsion took place accompanied a sharp jump in the electrical conductivity and a sharp drop in the emulsion viscosity. The W/O emulsions were nearly Newtonian at low concentrations of aqueous phase. At high concentrations of aqueous phase, prior to phase inversion, the W/O emulsions exhibited a shear-thickening behavior. The O/W emulsions produced after phase inversion were shear-thinning in nature. The comparison of the experimental viscosity data with the predictions of emulsion viscosity model revealed only partial coverage of droplet surfaces with nanoparticles. With the increase in the concentration of starch nanoparticles (SNPs) in the aqueous phase of the emulsions, the phase inversion of W/O emulsion to O/W emulsion was delayed to higher volume fraction of aqueous phase. Thus SNPs imparted some stability to W/O emulsions against coalescence and phase inversion.

Multi-site phase transfer catalyzed radical polymerization of methyl methacrylate in mixed aqueous\u2013organic medium: a kinetic study

This work establishes the kinetics of radical polymerization of methyl methacrylate in an aqueous–organic two-phase system using 1,4-bis (triethylmethylammonium) benzene dichloride (TEMABDC) as multi-site phase transfer catalyst and potassium peroxydisulphate (K2S2O8) as water-soluble initiator at 60 ± 1 °C under nitrogen atmosphere. The role of concentrations of monomer, initiator, catalyst, acid and ionic strength, temperature and volume fraction of aqueous phase on the rate of polymerization (Rp) was investigated. The rate of polymerization (Rp); Rp α [MMA]0.64, [TEMABDC]1.24 and [K2S2O8]1.50. The rate of polymerization increases with an increase in the concentration of monomer, initiator, catalyst and temperature. A generalized reaction model was developed to explain the phase transfer catalyzed polymerization reaction. Based on the kinetic results, radical mechanism has been derived. The activation energy and other thermodynamic parameters were calculated. The FT-IR spectroscopy validates a band of 1732 cm−1 of ester group of the obtained polymer. The viscosity average molecular weight of the PMMA was found 1.6955 × 104 g/mol.

Microencapsulation of insulin and its release using w/o/w double emulsion method

The present work is devoted to design of capsules with hydrophilic drugs such as insulin to preserve its stability and biological activity using the double emulsion technique and its subsequent entrapment into biodegradable microcapsules with shells made of Chitosan and Xanthan Gum complexes. Formulation parameters (type of biopolymer, type of oil and stabilizer and its concentration, volume fraction and content of internal aqueous phase, time and regime of mixing) were investigated.The effect of the complexes on the process of emulsion formation and on the stability and characteristics of the resulting emulsions was investigated by measurements of size distribution (DLS) and interfacial charge (Zeta-potential). The resulting capsules were characterized by microscopy, size distribution and Zeta-potential measurements. The release kinetics of insulin was monitored using UV–vis spectroscopy and showed the progressive enhancement of sustainability.

Influence of ultrasonic condition on phase transfer catalyzed radical polymerization of methyl methacrylate in two phase system – A kinetic study

An ultrasonic condition assisted phase transfer catalyzed radical polymerization of methyl methacrylate was investigated in an ethyl acetate/water two phase system at 60±1°C and 25kHz, 300W under inert atmosphere. The influence of monomer, initiator, catalyst and temperature, volume fraction of aqueous phase on the rate of polymerization was examined in detail. The reaction order was found to be unity for monomer, initiator and catalyst. Generally, the reaction rate was relatively fast in two phase system, when a catalytic amount of phase transfer catalyst was used. The combined approach, use of ultrasonic and PTC condition was significantly enhances the rate of polymerization. An ultrasonic and phase transfer catalyzed radical polymerization of methyl methacrylate has shown about three fold enhancements in the rate compared with silent polymerization of MMA using cetyltrimethylammonium bromide as PTC. The resultant kinetics was evaluated with silent polymerization and an important feature was discussed. The activation energy and other thermodynamic parameters were computed. Based on the obtained results an appropriate radical mechanism has been derived. TGA showed the polymer was stable up to 150°C. The FT-IR and DSC analysis validates the atactic nature of the obtained polymer. The XRD pattern reveals the amorphous nature of polymer was dominated.

Rheological properties of highly concentrated dense packed layer emulsions (w/o) stabilized by asphaltene

Abstract Dense packed layers (DPLs) were sedimented and removed from various asphaltene stabilized w/o emulsion batches, and contained aqueous phase volume fractions ( ϕ ) between 0.701 and 0.808. These values are close to the theoretical value of hexagonally close-packed spheres (0.74). Rheological properties of the DPLs were investigated using a rheometer equipped with plate–plate and cone–plate geometries. Flow curves and oscillatory shear measurements were obtained at 20 °C. Shear thinning and yield stress behaviour is observed. The measurements confirm the existence of a DPL yield stress which increases with the aqueous phase volume fraction. Hysteretic flow curve data show agreement with the Herschel–Bulkley relation. Oscillatory shear measurements within the linear viscoelastic regime are confirmed by strain-invariant values of G ′ (storage modulus) and G ″ (loss modulus). Beyond the linear viscoelastic regime, non-linear relaxation processes are observed. The rheometric results indicate weak gel-like behaviour and a dispersed-fraction dependent gel strength. Correlated UV–vis spectroscopy and NMR measurements indicate asphaltene adsorption amounts ( Γ ) of 1.95 mg m−2 to 2.15 mg m−2 and average surfaces areas per asphaltene molecule ( σ ) were in the range of 64–69 A2 in the DPL.

3D Surface Functionalization of Emulsion-Templated Polymeric Foams

We describe the preparation of porous polymeric scaffolds via polymerization of the oil phase in high internal phase water-in-oil-emulsions using amphiphilic block copolymers polystyrene-b-poly(ethylene oxide), polystyrene-b-poly(acrylic acid), poly(1,4-butadiene)-b-poly(ethylene oxide), and poly(1,4-butadiene)-b-poly(acrylic acid) as surfactants. We show that the block copolymers anchor to the polymerized oil phase via the lipophilic block, which can occur by chemical and/or physical entanglement and consequent presentation of the hydrophilic block on the pore surfaces. The in situ polymerization enables the full surface functionalization of the porous materials with the final surface chemistry dictated by the hydrophilic block. Furthermore, the foam physical architecture may be tailored through controlling emulsion parameters such as the initiator, shear rate, and aqueous phase volume fraction.

Influence of aqueous phase volume fraction, organoclay concentration and pressure on invert-emulsion oil muds rheology

This paper studies the effect that both aqueous phase fraction and organoclay concentration exert on the rheological properties of model suspoemulsions under pressure, commonly used in the formulation of invert oil muds for the drilling industry. These emulsions show a complex rheological behaviour that follows the Herschel–Bulkley's model. The yield stress shows a linear dependence with internal aqueous phase fraction for emulsions formulated with low organoclay concentration and power-law dependence for higher concentration. Barus’ model fits the pressure dependence of suspoemulsion viscosity, for different disperse phase volume fractions and organoclay concentration, fairly well.

AC field induced destabilization of water-in-oil emulsions based on North Sea acidic crude oil

The current work explores the effects of alternating current (AC) electric fields on coalescence of water droplets in crude oil. A North Sea crude oil emulsion with aqueous phase volume fraction of 0.3 and ∼2μm water droplets was used. The emulsions were prepared by an Ultra-Turrax disperser. Volume-specific energy input (Ev) has been calculated. Droplet collision frequency was enhanced by increasing the shear rate and initiating intense flow conditions. The flow conditions were verified to be within the valid flow regime for the specific rheometer geometry through calculations of the Taylor and Reynolds numbers. Viscosity alteration of water-in-oil emulsions as a result of electrocoalescence was investigated under the influence of electric fields in conjunction with variation of temperature, frequency, electric waveform, and duration of the applied electric field.

Water-in-Water Emulsions Based on Incompatible Polymers and Stabilized by Triblock Copolymers–Templated Polymersomes

Aqueous solutions containing a mixture of polyethylene glycol (PEG) and dextran homopolymers form an aqueous two-phase system which can be emulsified to give a water-in-water emulsion. We show how these emulsions can be stabilized using triblock polymers containing poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA), poly (n-butyl methacrylate) (BuMA), and poly[2-(dimethylamino) ethyl methacrylate] (DMAEMA) blocks of general structure Pp-Bb-Dd, in which the middle BuMA block is hydrophobic. Low-energy input stirring of mixtures containing equal volumes of PEG- and dex-rich aqueous phases plus 1 wt % of Pp-Bb-Dd stabilizer all form dex-in-PEG emulsions (for the range of Pp-Bb-Dd triblock polymers used here) which have a polymersome-like structure. In favorable cases, the emulsion drop (or templated polymersome) sizes are a few micrometers and are stable for periods in excess of 6 months. The emulsions can be inverted from dex-in-PEG to PEG-in-dex by increasing the volume fraction of dex-rich aqueous phase. We demonstrate that both high and low molecular weight fluorescent solutes "self-load" into either the dex- or PEG-rich regions and that solute mass transfer across the water-water interface occurs on a timescale of less than 1 min.

Flow properties of water-in-North Sea heavy crude oil emulsions

In the present research, rheological and pipeline flow properties of North Sea heavy crude oil emulsions (w/o) were investigated using a stress-controlled rheometer and lab scale flow rig. The rheological properties of the emulsions were studied at different aqueous phase volume fractions (ϕ) from 0.0 to 0.70, temperatures from 20°C to 50°C, and shear rates from 0.1s−1 to 1000s−1. The rheology measurements indicate the crude oil and emulsions exhibit strong shear thinning at low temperatures and the power law fits quite well the rheology data of the crude oil as well as emulsions. Viscosities of the emulsions were determined from the rheograms at different shear rates and temperatures and modeled successfully using the Pal and Rhodes viscosity equation. Droplet size distributions measured using the Nuclear Magnetic Resonance (NMR) and digital video microscopy (DVM) techniques indicate the emulsions have an average droplet size of around 3–4μm. The pipeline flow properties of the emulsions were investigated in a 3m horizontal test section of pipe with 0.0221m inner diameter using the lab scale flow rig at different aqueous phase volume fractions from 0.0 to 0.50 and flow rates from 0.10m/s to 0.70m/s for 50°C. The pipeline flow measurements indicate the pressure gradients (ΔP/L) in the pipeline increase as a function of aqueous phase volume fraction and flow rate and water and North Sea heavy crude oil flows are not fully dispersed at aqueous phase volume fractions above 0.10.

Solubilization of Azithromycin in Microemulsions Based on Mixed Nonionic Surfactants and Mixed Oils

Water/propylene glycol/sucrose laurate/ethoxylated mono-di-glyceride/isopropylmyristate/peppermint oil U-type microemulsions were used to solubilize azithromycin. Microemulsions dilution and interfacial factors contributing to the azithromycin solubilization were evaluated. Azithromycin solubilization capacity decreases with the increase in the aqueous phase volume fraction. Electrical conductivity of drug loaded and drug free microemulsions reveal the structural transition occurring in the microemulsion region. It was found that below 0.2 aqueous phase volume fraction the water–in-oil microemulsions are present. For aqueous phase volume fraction between 0.3 and 0.7 bicontinuous microemulsions are present. For aqueous phase volume fractions above 0.8 oil-in-water microemulsions are present. The hydrodynamic radius measured by dynamic light scattering of the oil-in-water drug loaded microemulsion decrease with temperature.

Characterization of cephalexin loaded nonionic microemulsions

Water/propylene glycol/sucrose laurate/ethoxylated mono-di-glyceride/isopropyl myristate/peppermint oil U-type microemulsions were used to solubilize cephalexin. Microemulsion dilution and interfacial factors contributing to the cephalexin solubilization were evaluated. Cephalexin solubilization capacity increases with the increase in the aqueous phase volume fraction (φ) up to 0.4 then decreases. Electrical conductivity of drug loaded and drug free microemulsions increases with φ. The hydrodynamic radius measured by dynamic light scattering of the oil-in-water loaded microemulsions decreases with temperature. The microemulsions were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity and isentropic compressibility. The microemulsion densities increase with φ up to 0.8 then decrease. The excess volume decreases with φ up to 0.8 then stabilizes. Ultrasonic velocities increase with the increase in φ while isentropic compressibility decreases. Analysis of the volumetric parameters enabled the characterization of structural transition along the microemulsion phase region. The presence of water-in-oil, bicontinuous and oil-in-water microemulsions, at aqueous phase volume fractions below 0.2, between 0.3 and 0.7 and above 0.8, respectively were found. Interfacial properties and dynamic structure of the monolayer for drug loaded and drug free microemulsions, were studied by electron paramagnetic resonance spectroscopy employing the nitroxide spin probe 5-doxylstearic acid. The rigidity of the interface was affected by the water content and also the presence of cephalexin.

KOH modified Nafion112 membrane for high performance alkaline direct ethanol fuel cell

A polymer electrolyte membrane for alkaline direct ethanol fuel cell (ADEFC) was prepared by dipping Nafion112 membrane into KOH solution for some time at room temperature. The obtained membrane (Nafion112/KOH) exhibited higher mechanical properties and thermal stability than Nafion112 membrane. The ionic conductivity of Nafion112/KOH in 1 M, 2 M and 6 M KOH solutions was 0.011 S/cm, 0.026 S/cm, 0.032 S/cm, respectively, depending on internal OH − concentration and the volume fraction of the internal aqueous phase. Single cell performance suggested that active ADEFC with Nafion112/KOH membrane can deliver a peak power density of 58.87 mW/cm 2 at 90 °C, meanwhile, it can stably run for at least 12 h above 0.2 V. On the other hand, Pt-free air breathing ADEFC with Nafion112/KOH can output a peak power density of 11.5 mW/cm 2 at 60 °C, and the corresponding lifetime was as long as 473 h above 0.3 V.

Kinetics of radical polymerization of glycidyl methacrylate initiated by multi‐site phase transfer catalyst–potassium peroxydisulfate in two‐phase system

AbstractThe kinetics of radical polymerization of glycidyl methacrylate, initiated by the free radicals formed in situ in the multi‐site phase transfer catalyst (PTC), 1,1,2,2‐tetramethyl‐1‐benzyl‐2‐n‐propylethylene‐1,2‐diammonium bromide chloride–potassium peroxydisulfate system was studied in an aqueous–organic two‐phase media at 60°C ± 1°C under inert and unstirred condition. The rate of polymerization (Rp) was determined at various concentrations of the monomer, initiator, catalyst, and volume fraction of aqueous phase. The effect of acid, ionic strength, and water‐immiscible organic solvents on the Rp was examined. The temperature dependence of the rate was studied, and activation parameters were calculated. Rp increased with an increase in the concentrations of monomer, initiator, multi‐site PTC, and increase in the polarity of solvent and temperature. The order with respect to monomer, initiator, and multi‐site PTC was found to be 0.50. A feasible free‐radical mechanism consistent with the experimental data has been proposed, and its significance was discussed. The synthesized polymer was confirmed by Fourier transform infrared spectral analysis. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Solubilization of Celecoxib in Microemulsions Based on Mixed Nonionic Surfactants and Peppermint Oil

U-type microemulsions formulated with water, mixed nonionic surfactants, and peppermint oil were used to solubilize celecoxib. Microemulsion dilution and interfacial factors contributing to the celecoxib solubilization were evaluated. Celecoxib solubilization capacity decreases with the increase in the water content. Electrical conductivity, dynamic viscosity, and SAXS measurements reveal the structural transition occurring in the microemulsion region. It was found that below 0.25 aqueous phase volume fraction the water-in-oil microemulsions are present, the transition between the water-in-oil to bicontinuous and then to oil-in water microemulsions occur at 0.30 and 0.8 aqueous phase volume fraction, respectively. The results demonstrate that the solubilized drug affects the transition from bicontinuous to water-in-oil microemulsions. The solubilized drug increases the hydrodynamic radius of the oil-in-water microemulsion droplets measured by dynamic light scattering.

MULTI-SITE PHASE TRANSFER CATALYZED RADICAL POLYMERIZATION OF n-BUTYL METHACRYLATE: A KINETIC STUDY

The kinetics and mechanism of radical polymerization of n-butyl methacrylate (n-BMA) using potassium peroxydisulfate (PDS) as a water-soluble initiator in the presence of 1,4-bis(tributyl methyl ammonium) benzene dichloride (TBMABDC) as a multi-site phase transfer catalyst (MPTC) were studied. The polymerization reactions were carried out under oxygen-free, unstirred conditions at a constant temperature of 60° ± 1°C in cyclohexane-water two-phase systems. The dependence of rate of polymerization (Rp) on concentrations of monomer, initiator, and catalyst, volume fraction of aqueous phase, solvent polarity, and temperature was determined. The reaction order with respect to monomer, initiator, and multi-site phase transfer catalyst was found to be 0.50, 1.0, and 0.52 respectively. Based on the experimental results, an appropriate reaction mechanism has been proposed and its significance discussed. The prepared polymer was characterized with spectral analysis.