Low Emulsifier Concentrations Research Articles

A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs.

Almost 60% of oil and 40% of gas reserves worldwide are contained in carbonate reservoirs where acidizing stimulation is more challenging compared to sandstone reservoirs. Utilization of emulsified acids in matrix acidizing operations has been the most effective technique for more than half a century. This is due to the colloidal system's ability to generate deep, narrow conduits toward production zones under controlled retarded reactivity with the rock surface, along with the excellent sweep efficiency and corrosion inhibition of the well equipment. This Review attempts to review the various kinds of emulsified acids that are used for matrix acidizing of carbonate formations. The Review is trying to trace the innovations that have, gradually, been applied for enhancing the performance of emulsified acids for a variety of conditions, their limitations, and the developmental solutions such hybrid emulsifiers and pickering emulsions. In addition, the Review also discusses the parameters, characteristics, and measuring techniques required for the successful synthesis of a stable and quality emulsion while considering the environmental concerns raised toward the application of an emulsified acid system. From the reviewed publications, it can be summarized that macroemulsions are best suited for matrix acidizing applications over microemulsions due to low emulsifier concentrations and high acid volume retention; similarly, water in oil emulsions provide better retardation in a comparison to oil in water emulsions. The small droplet size of the emulsion yields high viscosity and stability. The compositional balance between each component present in the acidizing system is a crucial factor for optimum performance. Moreover, for future practice, much focus is required to design emulsified acids as ecofriendly systems that can leave the least amount of toxicity during and after implementation.

Eugenol emulsions stabilized by a natural-derived nonionic palmitate surfactant/polyacrylic acid complex

Eugenol emulsions based on a palmitate surfactant were prepared. The palmitate surfactant was synthesized via a simple esterification reaction of poly(ethylene glycol) ( M n 10,000 g mol −1 ) and palmitic acid. Subsequently, the surfactant was combined with poly(acrylic acid) (PAA) to give intermolecular complexes that served as the emulsions' stabilising agents. Different ratios of PAA/surfactant complexes were used for the preparation of emulsions. Emulsions with a PAA/surfactant complex ratio of 1/3 gave long-term stable emulsions with hydrodynamic diameters ranging from 62 to 89 nm and narrow size distributions at a quite low emulsifier concentration. The latter emulsions loaded eugenol up to 85%. Furthermore, eugenol emulsions successfully encapsulated the poor-water soluble compound curcumin, increasing its solubility up to 6 times. Eugenol emulsions based on a palmitate surfactant were prepared. Emulsions with a PAA/surfactant complex ratio of 1/3 gave long-term stable emulsions with hydrodynamic diameters ranging from 62 to 89 nm and narrow size distributions at a low emulsifier concentration, presenting up to 85% eugenol loading efficiency. Eugenol emulsions also encapsulated the poor-water soluble compound curcumin, increasing its solubility up to 6 times while at the same time retaining up to 55% curcumin.

Ionic liquid-containing non-aqueous Pickering emulsions prepared with sterically-stabilized polymer nanoparticles: A highly efficient platform for Knoevenagel reaction

Room temperature ionic liquids (RTILs)-containing Pickering emulsions exhibit promising application potentials because of the integration of the “green” quality and the tunable applications of RTILs with the advantages of Pickering emulsions, such as the high stability and adjustable droplet size. In the present study, sterically-stabilized polymer nanoparticles (SSPNs) were first prepared via the reversible addition-fragmentation chain transfer (RAFT)-mediated non-aqueous dispersion polymerization, in which poly(lauryl methacrylate) (PLMA) and poly(4-vinyl pyridine) (P4VP) acted as the stabilizer block and the core-forming block, respectively. Kinetically-trapped PLMA-b-P4VP spheres and mixed spherical/worm-like morphologies could be achieved at a target copolymer composition. Subsequently, core cross-linked SSPNs (CSSPNs) were obtained by means of chemical cross-linking of P4VP cores of SSPNs with 1,4-dibromobutane in a diluted solution of SSPNs in toluene (0.4 mg/mL). Stable 1-butyl-3-methylimidazolium tetrafluoroborate-in-toluene ([Bmim][BF4]-in-toluene) non-aqueous Pickering emulsions could be formed at a low emulsifier content of 0.005 wt% adopting CSSPNs with mixed spherical/worm-like morphologies as Pickering emulsifiers. Benefiting from large surface areas of Pickering emulsions and unique chemical/physical properties of RTILs, [Bmim][BF4]-in-toluene Pickering emulsions provided readily available platforms for many organic reactions. As a proof of the concept, proline catalyzed Knoevenagel reaction of 4-nitrobenzaldehyde with malononitrile was chosen as a model here. Both high reaction efficiency and good recyclability were observed.

Synthesis, characterization and stress-testing of a robust quillaja saponin stabilized oil-in-water phytocannabinoid nanoemulsion

BackgroundThis study describes the design, optimization, and stress-testing of a novel phytocannabinoid nanoemulsion generated using high-pressure homogenization. text {QNaturale}^{circledR }, a plant-derived commercial emulsifier containing quillaja saponin, was used to stabilize the lipid phase droplets in water. Stress-testing was performed on this nanoemulsion in order to evaluate its chemical and colloidal stability under the influence of different environmental factors, encompassing both physical and chemical stressors.MethodsExtensive optimization studies were conducted to arrive at an ideal nanoemulsion formulation. A coarse emulsion containing 16.6 wt% CBD-enriched cannabis distillate and 83.4 wt% carrier (soybean) oil dispersed in 10 wt% text {QNaturale}^{circledR } (1.5 wt% quillaja saponin) solution after 10 homogenization cycles at a pressure of 30,000 psi produced a stable nanoemulsion. This nanoemulsion was then subjected to the stress studies.ResultsThe optimized nanoemulsion had an average droplet diameter of ca. 120 nm and average droplet surface ζ potentials of ca. -30 mV. It was imaged and characterized by a variety of protocols. It proved to be stable to droplet agglomeration and phase separation upon storage under ambient conditions for 6 weeks, as well as under a variety of physical stressors such as heat, cold, dilution, and carbonation. pH values ≤2 and moderately high salt concentrations (> 100 mM), however, destabilized the nanoemulsion, eventually leading to phase separation. Cannabis potency, determined by HPLC, was detrimentally affected by any changes in the nanoemulsion phase stability.ConclusionsQuillaja saponin stabilized cannabidiol(CBD)-enriched nanoemulsions are stable, robust systems even at low emulsifier concentrations, and are therefore significant from both a scientific as well as a commercial perspective.

Surfactin from Bacillus subtilis displays promising characteristics as O/W-emulsifier for food formulations

BackgroundBiosurfactants are surface-active molecules produced by different microorganisms and display a promising alternative to synthetically derived food emulsifiers. One of these biosurfactants, synthesized by Bacillus subtilis, is the lipopeptide surfactin, which composes a linear fatty acid and cyclic peptide moiety. This study explores the interfacial and emulsion forming properties of surfactin to further characterize its suitability as an O/W emulsifier in food formulations. ResultsSurfactin revealed a high interfacial activity with a reduction of interfacial tension of 83.26 % to 4.21 ± 0.11 mN/m. O/W emulsions (coil = 10 % w/w) were prepared by high-pressure homogenization, which yielded volume-based mean particle sizes below 1 μm already at low emulsifier concentrations of 0.01 % (w/w). Environmental stress experiments revealed that emulsions were stable between pH 6 to pH 9. Furthermore, neither phase separation nor extensive emulsion instability was observed with NaCl addition up to 0.5 M. However, CaCl2 addition (> 3 mM) destabilized surfactin mediated emulsions. Finally, the main emulsion forming and stabilization effect of surfactin was related to its high interfacial activity and the high degree of electrostatic repulsion between the oil droplets (i.e. zeta-potential of up to −100 mV). ConclusionIn comparison to other natural and synthetic emulsifiers, the results showed that surfactin is a strong candidate to form and stabilize O/W emulsions under the reported conditions.

Margarine‐Like Emulsions Prepared with Coconut and Palm Oils: Analysis of Microstructure and Freeze–Thaw Stability by Differential Scanning Calorimetry

AbstractThe objective was to study the microstructure and freeze–thaw stability of margarine‐like emulsions formulated with vegetable fats using differential scanning calorimetry. Emulsions were prepared with 20% w/w dispersed aqueous phase and a continuous lipid phase composed by coconut oil (CO) and/or palm oil (PO) plus polyglycerol polyricinoleate (PGPR) as emulsifier. Mean temperature (TM) and crystallization enthalpy (ΔHc) were obtained from the exothermic peaks corresponding to freezing of aqueous phase. Successive cooling–heating–cooling cycles were applied to analyze changes in the exothermic peak. The emulsion prepared with CO (without PO) and 1% w/w PGPR in lipid phase showed higher water droplets size (TM = −44.8 ± 0.1 °C) and lower quantity of stabilized aqueous phase (ΔHc = 28.9 ± 1.2 J g−1) prior to application of temperature cycles, while coalescence and (presumably) water transfer processes occurred during the treatment. The use of 2% w/w PGPR was sufficient to accomplish full stabilization of aqueous phase (TM = −45.9 ± 0.1 °C; ΔHc = 42.6 ± 0.3 J g−1) before and after the freeze–thaw treatment. The total or partial (50%) substitution of CO by PO in emulsions with 1% w/w PGPR also improved the stability of the system, exhibiting slight microstructural changes. This enhanced stability would be linked to reduced water droplets size because of more rapid crystallization of lipid phase and immobilization of aqueous phase after emulsion preparation. In conclusion, it is possible to obtain margarine‐like emulsions prepared with CO and/or PO using relatively low emulsifier concentration and maintaining a desired microstructure after freeze‐thawing if the percentage ratio of both fats is controlled.

Adsorption behavior at interface of oil-in-water emulsions prepared with mixtures of milk fat globule membrane proteins and polar lipids

The milk fat globule membrane (MFGM) contains proteins and polar lipids making this complex mixture a good emulsifier. In this study, MFGM material was isolated from reconstituted buttermilk using microfiltration and further separated into MFGM protein concentrate and polar lipid concentrate using solvent fractionation. The emulsifying properties of those two emulsifier fractions, separately or in combination, at various concentrations of proteins (0.3; 1.3 and 2.3 w%) and polar lipids (0.3; 1.3 and 2.3 w%), were investigated. The results showed that at low emulsifier concentrations (< 2.3%), the combination of both proteins and polar lipids resulting in the formation of emulsions with a small droplets size and low apparent viscosity. The addition of polar lipids did not replace the adsorbed proteins. Between the two emulsifier fractions, MFGM protein concentrate had greater emulsifying properties compared to the polar lipid concentrate.

Effect of pH and ionic strength on the emulsifying properties of two Octenylsuccinate starches in comparison with gum Arabic

Octenylsuccinate starches were obtained by combining esterification reaction and β-amylase hydrolysis treatment with (HOSE) and without (OSE) acid pretreatment. In the present study, the emulsions stabilized by gum Arabic (GA), OSE and HOSE starches were systematically compared in terms of molecular structure and emulsion properties. The molecular structure of three emulsifiers was analyzed using size exclusion chromatography, showing that the GA had a relative smaller molecular size distribution compared to OSE and HOSE starches. Emulsifying activity index (EAI), emulsifying stability index (ESI), droplet size (d4,3) of emulsions at different emulsifier to oil ratios were determined to evaluate the emulsion properties of three emulsifiers under a wide range of pH and NaCl concentration. The GA stabilized emulsion showed the lowest droplet size at high emulsifier concentrations, but clear phase separation was observed after 7 days of storage at relatively low emulsifier concentrations (1:9 and 0.5:9.5). The emulsions stabilized by the HOSE starch showed excellent emulsion stability under a wide range of pH and NaCl concentration, and produced the small droplets with better storage stability, particularly at relatively low emulsifier concentrations (1:9 and 0.5:9.5).

Determination of the latex particle size in emulsion polymerization of methyl methacrylate with low emulsifier concentrations

The mean size of the latex particles formed in emulsion polymerization of methyl methacrylate under definite conditions (water: monomer volume ratio 15: 1, 80°C, potassium persulfate concentration 0.07 wt %) decreases from 200 to 9–10 nm as the concentration of an ionic surfactant (anionic Disponil AES 60, SDS, cationic C19H42BrN) is increased from 0.0 to 1.0 wt %. The nonionic surfactants studied influence the size of the latex particles formed differently: with ALM-10, the particle size decreases from 200 to 150–190 nm, whereas with ALM-7 and ALM-2 it increases from 200 to 320 nm as the surfactant concentration is increased from 0.0 to 1.0 wt %. An increase in the concentration of F127 amphiphilic ternary block copolymer from 0.0 to 1.0 wt % leads to a monotonic decrease in the size of the poly(methyl methacrylate) latex particles formed from 200 to 53 nm.

Preparation and in vitro evaluation of 5-fluorouracil-loaded PCL nanoparticles for colon cancer treatment

Nanoparticles loaded with 5-fluorouracil (5-FU) for colon cancer therapies were prepared using the solvent evaporation technique, which involved lyophilization by freeze-drying. Formulations produced a substantially high encapsulation efficiency of approximately 93%. A positive correlation was seen when increasing polycaprolactone (PCL) and/or PVA concentrations and the size of nanoparticles produced. Increasing PCL concentration had a considerable influence on PDI while increasing PVA concentration had a lesser effect. All nanoparticles possessed a negative zeta potential, particularly in formulations with low polymer and polymer emulsifier concentrations. The formulation with the lowest PCL and PVA concentration was characterized by the most optimal properties; which accounts for the desirable delayed release profile of the active drug in dissolution testing indicating an improved targeting capability and enhanced bioavailability at the action site. Cytotoxicity studies showed that 5-FU loaded PCL nanoparticles had higher antiproliferative effect than free 5-FU on Caco-2 cell line (p < 0.05). The encouraging results obtained offer reasons for optimism regarding the future of 5-FU nanoparticles as a promising drug delivery system which could be further improved by including either enteric coating or encapsulating the nanoparticles onto microparticles to overcome unanticipated degradation.

Development of an efficient emulsification process using miniaturized process engineering equipment

In many cases, emulsification with highly viscous materials is performed batchwise using CSTR systems being heated in a conventional way. A more efficient process may be continuous emulsification using miniaturized equipment like micro heat exchangers and micro mixers. The advantages of such systems like reduced diffusion length and increased heat transfer capacities are widely known, as well as the disadvantages, namely increased pressure losses. The present study describes the development of a continuous oil-in-water emulsification process using microstructured devices. Based on the analysis on the rheological properties, several suitable micro mixer systems were developed and tested. Some experiments under different conditions have been carried out to study the influence of different parameters to the emulsification quality referred to the droplet size. The studied range of the total mass flow rates was from roughly 4 to 9kg/h. The oil content varied from 52 to 72%. The oil passage was heated to 120°C and the water passage to 88°C. Characterized droplet sizes such as Sauter diameter were used as the main quality criteria. Results show that the higher the flow velocities are, the smaller the Sauter diameter of the emulsion droplets becomes. However, the pH of the products needed to be limited between 7 and 8. In this study, two water solutions were prepared, 1% (for S2–S9) or 2% (for S1) ammonia solution (25vol.%) was added to the water phase. Large Sauter diameters or phase separation may be faced if the pH is not adjusted correctly. A high oil content or low emulsifier content may also reduce the quality of emulsions.The combination of micro mixer emulsification units and micro heat exchangers was tested. Two micro heat exchanger devices have been tested to heat the water and to quench the emulsion and, therefore, to stabilize the emulsion. Both are 8cm3 active volume cross flow heat exchangers (each passage has a section area of 200×200μm2/channel×68 channels/foil×34 foils). The viscosity of the generated emulsions was around 74mPas at 25°C, measured at a shear rate of 100s−1. It shows only a weak temperature dependence. For example, it was reduced by 5mPas by increasing the temperature from 25 to 45°C.The quenching shows positive effects to the emulsion stability by preventing droplet collapses, which, thus, normally take place at higher temperature. The integration of miniaturized heat exchanger and mixer devices into a system led to a very efficient emulsification unit reducing the total energy consumption of the process considerably.

Combined effects of milk fat globule membrane polar lipids and protein concentrate on the stability of oil-in-water emulsions

Milk fat globule membrane (MFGM) material isolated from reconstituted buttermilk by microfiltration (i.e., whole MFGM) contains two major fractions, namely proteins (consisting mainly of MFGM-specific proteins and serum proteins) and lipids (original membrane polar lipids and contaminating triglycerides from the globule core). In this study, MFGM proteins and polar lipid (PL) concentrate were separated from whole MFGM material using solvent extraction. The particle size distribution, stability, surface protein and polar lipid load of oil-in-water emulsions prepared with protein or PL concentrate, individually or in combination, at various concentrations were examined. At low emulsifier concentrations (<2.3%), there was an interacting effect between proteins and PLs on the droplet size. The phase separation of emulsions prepared with a combination of 0.3% proteins and 0.3% PLs was similar to that of emulsions containing 0.3% proteins. The proteins were more preferentially adsorbed at the emulsion droplet surface compared with PLs.

Formation and stabilization of nanoemulsion-based vitamin E delivery systems using natural biopolymers: Whey protein isolate and gum arabic

Natural biopolymers, whey protein isolate (WPI) and gum arabic (GA), were used to fabricate emulsion-based delivery systems for vitamin E-acetate. Stable delivery systems could be formed when vitamin E-acetate was mixed with sufficient orange oil prior to high pressure homogenization. WPI (d32=0.11μm, 1% emulsifier) was better than GA (d32=0.38μm, 10% emulsifier) at producing small droplets at low emulsifier concentrations. However, WPI-stabilized nanoemulsions were unstable to flocculation near the protein isoelectric point (pH 5.0), at high ionic strength (>100mM), and at elevated temperatures (>60°C), whereas GA-stabilized emulsions were stable. This difference was attributed to differences in emulsifier stabilization mechanisms: WPI by electrostatic repulsion; GA by steric repulsion. These results provide useful information about the emulsifying and stabilizing capacities of natural biopolymers for forming food-grade vitamin-enriched delivery systems.

Biodegradable salicylate‐based poly(anhydride‐ester) microspheres for controlled insulin delivery

Salicylate-based poly(anhydride-esters) (PAEs) chemically incorporate salicylic acid (SA) into the polymer backbone, which is then delivered in a controlled manner upon polymer hydrolysis. In this work, a salicylate-based PAE is a carrier to encapsulate and deliver insulin. Polymer microspheres were formulated using a water/oil/water double-emulsion solvent evaporation technique. The microspheres obtained had a smooth surface, high protein encapsulation efficiency, and relatively low emulsifier content. Insulin was released in vitro for 15 days, with no signs of aggregation or unfolding of the secondary structure. The released insulin also retained bioactivity in vitro. Concurrently, SA was released from the microspheres with polymer degradation and anti-inflammatory activity was observed. Based upon these results, the formulated microspheres enable simultaneous delivery of insulin and SA, both retaining bioactivity following processing.

A hybrid polyacrylate/OMMT nanocomposite latex: Synthesis, characterization and its application as a coating binder

Hybrid latex particles have an increasing importance in industrial applications especially for high performance waterborne coatings. They provide combined properties of different phase compositions for the final polymer which can also be enhanced by additives such as nanoclays. The present study describes the preparation of a hybrid polyacrylate/OMMT nanocomposite latex via two stage in situ emulsion polymerization with a low emulsifier content (1wt%) which is usually a challenge for the preparation of stable polymer/OMMT nanocomposite latexes. The obtained nanocomposite latex was stable and had a fine average size diameter of 151nm with a very narrow size distribution. The copolymer films exhibited a well exfoliated structure observed by WAXD and TEM. Other polymer properties were investigated by FTIR, DSC, TGA, DMTA and rheological measurements. The results indicated that the addition of clay even in low amount (2wt%) yielded significantly improved mechanical and thermal properties of the final polymer. In addition, the nanocomposite latex was also applied on leathers as coating binder in a finishing formulation and the results of the performance tests revealed substantially increased rubbing and heat resistance whereas a slight decrease was observed at water vapor permeability of the coated leathers.

Physicochemical Characterization and in vivo Skin Performance of a Novel Alkyl Polyglucoside Emulsifier in Natural Cosmetic Cream-Bases

Abstract Alkyl polyglucosides (APGs) are a perfect amphiphilic structure, with excellent surface activity and solubility feature. The aim of this study is to develop a simple system, with a relatively low emulsifier content, composed of materials mainly naturally based and with no additional fatty alcohol. Hydroxystearyl alcohol and Hydroxystearyl glucoside, prepared with Jojoba and Hazelnut oil, medium chain triglycerides with or without Xylitylglucoside and Anhydroxylitol and Xylitol, have been investigated by using microscopy, rheology, thermal analysis, pH and conductimetry. Cyclic stress and in vivo skin irritation tests were also conducted. The investigated natural APG emulsifier has a capacity to form simple and stable emulsions of desirable rheological profile with improved hydration potential and to renew damaged skin, thus it can be safely applied as stabilizer in cosmetic and prospective pharmaceutical cream-bases.

Reaction of Emulsified Acids With Dolomite

Summary Emulsified acids have been used in the oil field for many years. They are retarded systems that can be used effectively in stimulation of carbonate reservoirs. Emulsified acids have been used primarily in acid fracturing and matrix acidizing. The delayed nature of emulsified acids is useful in generating longer etched fractures or deeper wormholes. To predict the penetration depth of the wormholes or the length obtained from an acid-fracturing treatment, diffusion-coefficient values need to be estimated. This paper discusses the reaction kinetics of dolomite disks with emulsified acids formulated using a cationic emulsifier. The emulsified acid systems were prepared using 15 wt% HCl and 0.7 acid volume fraction. The emulsifier concentration was varied from 0.5 to 2.0 vol%. Emulsified-acid reaction rates and, hence, acid diffusivity were measured using a rotating disk apparatus at 230°F. Disk-rotational speed was varied from 100 to 1,500 rev/min. Samples of the reacted acid were collected and analyzed using the inductively coupled plasma (ICP) mass spectrometry to measure calcium and magnesium concentrations. The dolomite core samples reacted slowly with emulsified acid. Emulsions with low emulsifier concentrations (0.5 vol%) had average droplet sizes of 8.118 lm and achieved a diffusion coefficient of 1.413x10-8 m2/s. While emulsions prepared with higher emulsifier concentration (2.0 vol%) had a smaller droplet size (2.82 lm), they achieved a diffusion coefficient of 8.367x10-10 cm2/s. Reaction of dolomite with emulsified acid at 230°F was found to be mass-transfer limited. Compared with calcite, the dissolution rate of dolomite in emulsified acids was lower by one order of magnitude, and the diffusion coefficient of acid was lower by two orders of magnitude.

On the stability and properties of the polyacrylate/Na-MMT nanocomposite obtained by seeded emulsion polymerization

For high performance waterborne coatings usually polymer latexes with low emulsifier content are more preferred. Although polymer/clay nanocomposites offer improved properties, it is difficult to produce clay based nanocomposite latexes containing low emulsifier due to the stabilization problems especially caused by organoclays. Present study deals with the preparation of a tBA/BA/MAA ternary copolymer/clay nanocomposite containing 3wt.% sodium montmorillonite (Na+-MMT) via seeded emulsion polymerization. Experimentally it was observed that even the usage of hydrophilic clay caused stabilization problem and a certain amount of emulsifier (>1wt.%) was necessary to obtain stable latexes. In addition, the usage of a low molecular weight water soluble polymer as steric barrier was found to increase the stability of system. Obtained nanocomposite latex showed fine particle size diameter (127nm) and very narrow size distribution (PDI=0.06). The WAXD and TEM investigations indicated that a mostly exfoliated nanocomposite was obtained. Thermal analyses (DSC, DMTA and TGA) showed that there was no change at Tg of the copolymer while very high improvement was obtained for elastic modulus and a slight increase in thermal stability. According to the rheological measurements, the nanocomposite latex showed a higher low shear viscosity, a stronger shear thinning behavior and an improved physical stability in comparison to the reference latex.

Effects of acidity and emulsifier concentration on the distribution of vitamin C in a model food emulsion

We have analyzed the effects of acidity and emulsifier concentration on the distribution of ascorbic acid or vitamin C (VC) in a model emulsion prepared by mixing octane, acidic (HCl) water and the non‐ionic surfactant hexaethyleneglycol monododecyl ether (C12E6). VC is oil insoluble, and only the partition constant between the interfacial and aqueous regions (PWI) is needed to describe its distribution within the emulsion. The PWI values are calculated from the kinetic analyses of the variation of the observed rate constant (kobs) determined electrochemically for the reaction between the hydrophobic 4‐hexadecylbenzenediazonium (16‐ArN2+) ions and VC with the emulsifier concentration. The determined PWI values (PWI = 4–25) are low in comparison with those obtained for more hydrophobic antioxidants like vitamin E, and pH dependent, decreasing upon decreasing the acidity of the medium. These low values are reflected in the distribution of VC so that a large fraction (70%) is located in the aqueous region at low emulsifier concentrations. At a given pH, the %VC in the aqueous region decreases upon increasing the emulsifier concentration; meanwhile, at a given emulsifier concentration %VC increases upon lowering the acidity. The intrinsic rate constants in the interfacial region kI for the reaction between 16‐ArN2+ and VC have also been determined at different acidities. Their variation with the pH follows an upward bend curve, suggesting an inverse dependence of kI with the acidity of the medium, in keeping with the proposed mechanism for the reaction. The results may be of some interest to the food and pharmaceutical industries because of the extensive use of VC as antioxidant or preservative and because of the health benefits of VC. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Synthesis of waterborne acrylic/clay nanocomposites by controlled surface initiation from macroinitiator modified montmorillonite

The nitroxide mediated controlled surface initiated polymerization of methyl methacrylate (MMA)/butyl acrylate (n-BA) was carried out with a macroinitiator modified montmorillonite. The macroinitiator was synthesized by the nitroxide mediated polymerization of vinylbenzyl trimethylammonium chloride (VBTMACl), methylmethacrylate (MMA) and styrene (S) at 90°C using BlocBuilder®. The macroinitiator was exchanged with the sodium cations of the montmorillonite, to yield surface modified reactive montmorillonite. The bulk polymerizations of BA/MMA from the clay surface produced controlled molecular weight polymers that were able to exfoliate the clay. This controlled polymer/clay nanocomposite was used as masterbatch and further dispersed in monomers and miniemulsified to perform miniemulsion polymerization of BA/MMA (90/10wt.%) at 30wt.% solids content at low emulsifier concentration. The adhesive properties of the nanocomposites prepared with the masterbatch were proved to be better than those prepared with an organically modified clay.