Blend Of Nonionic Surfactants Research Articles

Nonionic Surfactant Blends for Enhanced Oil Recovery in High-Temperature Eagle Ford Reservoir

Summary Nonionic surfactants have proven successful and cost-effective in enhancing production from conventional and unconventional reservoirs. However, studies into the mechanism and performance of nonionic surfactants have been limited to reservoirs with temperatures below 200°F due to the temperature-dependent physiochemical properties, especially cloudpoint (CP). In this study, nonionic-ionic surfactant blends were designed to create nonionic systems with cloudpoint temperatures (CPTs) above 300°F for wettability alteration in high-temperature reservoirs like the Eagle Ford Shale in Texas, USA. Through CP, wettability, interfacial tension (IFT), and spontaneous imbibition experiments, 22 commercial surfactant samples (individual and blends) were investigated. Results showed that the amount of ionic cosurfactant affected thermal stability, with increasing concentration leading to increasing CPT. Wettability alteration was dependent not only on temperature but also on the class of ionic cosurfactant. Cationic cosurfactants were superior at improving nonionic surfactants’ thermal stability. However, they resulted in oil-wet contact angles (CAs) with increasing temperature. On the other hand, anionic cosurfactants displayed better synergy in terms of wettability alteration, creating strongly water-wet and intermediate-wet CAs at high temperatures. Therefore, the focus was placed on nonionic-anionic surfactant blends for the reservoir samples used in this study. Stable surfactant blends with CPTs from 316°F to 348°F were successfully created for enhanced oil recovery (EOR) applications at high-temperature conditions. Spontaneous imbibition studies using these blends indicated improved recovery by up to 173%. This work validates and builds upon previous studies of surfactant performance, wettability alteration, and IFT while providing new insight into nonionic surfactant blends at temperature conditions not currently available in the literature. It also serves as a template for the surfactant screening and selection process when considering nonionic surfactants.

Smooth scouringrush (Equisetum laevigatum) control with glyphosate is affected by surfactant choice and application time

AbstractSmooth scouringrush is a creeping perennial with a high silica content in stems that may impede herbicide uptake. Smooth scouringrush has become a troublesome weed in no-till cropping systems across eastern Washington. In previous field studies, glyphosate provided inconsistent control of smooth scouringrush. The objective of this study was to determine if the addition of an organosilicone surfactant to glyphosate would improve the efficacy and consistency of control through stomatal flooding. To test this hypothesis, glyphosate was applied at three field sites at 3.78 kg ae ha–1 alone, with an organosilicone surfactant (OS1 or OS2), an organosilicone plus nonionic surfactant blend, or an alcohol-based surfactant applied during the day or at night. Stem counts were recorded 1 yr after herbicide applications. Five of the six effective treatments observed across the three study sites included organosilicone surfactant or an organosilicone plus nonionic surfactant blend. At two sites, when there was a difference in efficacy between application times; daytime applications were more effective than nighttime applications. These results support the hypothesis of stomatal flooding as a likely mechanism for enhanced efficacy of glyphosate with the addition of an organosilicone surfactant. However, at one site, the treatments containing organosilicone surfactant were more efficacious when applied at night than during the day. At this site, high daytime temperatures and low relative humidity may have resulted in rapid evaporation of spray droplets. The addition of an organosilicone surfactant to glyphosate is recommended for smooth scouringrush control, and daytime treatments are preferred but should be applied when temperatures and humidity are not conducive to rapid droplet drying. Further research is necessary to confirm that stomatal flooding is responsible for improved glyphosate efficacy.

Influence of interfacial characteristics and antioxidant polarity on the chemical stability of β-carotene in emulsions prepared using non-ionic surfactant blends

To evaluate the effects of characteristics of the interfacial region and physical location of antioxidants on the chemical stability of β-carotene in emulsions, β-carotene-loaded emulsions were prepared with the blends of surfactants with different hydrophilic head sizes (ethylene oxide (EO) unit number). In addition, antioxidants having the different solubilities, tert-butylhydroquinone (TBHQ) and lauryl gallate as lipophilic and amphiphilic antioxidants, respectively, were incorporated into emulsions. Decrease in the average EO unit number at interfacial region by surfactant blending did not affect the stability of β-carotene in emulsions at neutral pH but it had a positive effect on the β-carotene stability at acidic pH. Decrease in the average EO unit number at interfacial region reduced the ability of antioxidants, regardless of their polarity, to protect β-carotene in emulsions at neutral and acidic pH. TBHQ was more effective in retarding β-carotene degradation than lauryl gallate, independent of the interfacial composition and surfactant concentration.

Analysis of ionic and nonionic surfactants blends used for the reverse micellar extraction of Lactoperoxidase from whey

AbstractBovine Lactoperoxidase (LP), a minor whey protein, is used as an antimicrobial in cosmetic, food, and pharmaceutical preparations. Industries are in pursuit of reliable, cheap, and scalable purification methods as the conventional techniques for LP purification like chromatography and membrane separation suffer from several drawbacks. The present work investigates the selective reverse micellar extraction of LP using the reverse micellar system formed by mixing food grade nonionic (Tween, Span, and Triton series) and ionic (AOT) surfactant blends. The analysis of LP extraction efficiency was performed by varying the concentration of nonionic surfactants with a constant AOT concentration of 100 mM and the initial pH of the system. Complete LP solubilization was achieved with reverse micelles formed by 100 mM AOT and 20 mM Tween 80 at pH 8. It was found that the extraction efficiency was dependent on the chain length or the number of ethylene oxide units in the Triton surfactant tail and the carbon–carbon double bond in Tween 80 tail, that is, on oleic acid. Span series however showed poor extraction in the organic phase substantiating the lesser water content. The forward extracted LP was successfully back‐extracted into a fresh aqueous phase containing 1 M KCl at pH 10.5. The aqueous phase (whey) from the forward transfer can be further used to fractionate other whey proteins.

Nonionic Surfactant Blends to Control the Size of Microgels and Their Catalytic Performance during Glycoside Hydrolyses

In a proof of concept study, a series of nonionic surfactant blends derived from Tween 80 and Span 80 were used to prepare catalytic microgels from stabilized droplets in miniemulsions. The goal of this study is to optimize the catalytic efficiency of microgels by decreasing their particle size with surfactants that are custom-made for the respective prepolymerization mixture. The effectiveness of the approach is examined by evaluating the catalytic efficiency of the resulting microgels in comparison to their counterparts made in the presence of ionic sodium dodecyl sulfate (SDS) solution. Spherical particles with hydrophilic–lipophilic balance (HLB) value dependent mean hydrodynamic diameters between 99 and 200 nm are obtained. Addition of Cu(II) ions and selected other transition metal ions activated the dormant catalysts for cleavage of glycosidic bonds in 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid (HEPES) buffer at pH 7.00 and 37 °C using a fluorescent model substrate. The highest proficiency for the catalytic hydrolysis was observed for Cu(II)-containing microgels (kcat/KM × knon = 870 000) with the lowest diameter indicating an almost twofold better stabilization of the transition state compared to a microgel prepared in the presence of ionic SDS solution. The study establishes a correlation of the HLB value of the nonionic surfactant blend used during material synthesis to the particle size and catalytic performance of the resulting microgels.

The mixing behaviour of anionic and nonionic surfactant blends in aqueous environment correlates in fatty acid ester medium

Mixtures of dissimilar surfactants can have superior properties compared to those of the individual surfactant components involved, which provide impetus for research on interactions between surfactants. It was also demonstrated that a change in the composition of external phase promotes remarkable changes in interfacial properties of reverse micelles (RMs), which are crucial to understand the system in order to use them as nanoreactors. Hence, it should be achievable to explore the influence of non-ionic Tween-85 on the properties of anionic AOT based micelle as well as RMs in fatty acid esters [e.g., ethyl myristate (EM), ethyl palmitate (EP) and ethyl oleate (EO)]. A comprehensive micellization behavior is studied at different mixed compositions (XTween-85) by surface tension method. Non-ideal mixing behaviors along with synergistic interaction between the constituent surfactants in the mixed micelles are evidenced. Mixed micelles illustrate favorable micellization behavior in terms of thermodynamic parameters. Further, fatty acid ester medium-based mixed RM shows synergism in water solubilization capacity. Microstructures of these systems are investigated by conductance, DLS, and FTIR studies. The solvation and rotational relaxation dynamics using picosecond time-resolved emission spectroscopy (TRES) is used to investigate the effect of XTween-85 as well as chemical architecture of fatty acid esters for the first time on the excited state dynamics of fluorophore. The solvation dynamics is found to be faster with an increase in XTween-85 and the average solvation time follows the order, EO<EP<EM, which collaborates well with droplet size and abundance of bulk-like water. Anisotropy studies reveal a decrease in the rotational restriction on the probe for EO based RMs. It is reasonable that this work have the potential to serve as good biomimicry models to study various processes occurring in biological molecules embedded in biomembranes.

Thermogravimetric Analysis of Target Inhibitors for the Spontaneous Self-Heating of Coal

ABSTRACTSelf-oxidation of coal can result in spontaneous combustion events at any time during mining, transporting, or processing causing environmental, economical, and safety concerns. Spontaneous coal combustion is a naturally occurring phenomenon that often causes damage to industrial and commercial facilities and freight, reduces the caloric value of coal, releases noxious gases and particulate matter, and increases pollution. As heat accumulates through self-oxidation, the internal temperature of the coal continues to rise over time and if left unaltered will lead to spontaneous coal fires. In this study, we investigated thermogravimetric properties of target compounds for the inhibition of the spontaneous self-heating of coal. Coal was treated with inorganic phosphate and sulfonate salts combined with anionic and non-ionic surfactant blends. Each ingredient was applied to the surface individually and systematically varied to reach a cost-effective and efficient formulation. Thermal and microscopic analyses were used to characterize these effects. Results showed that novel formulations can significantly increase the onset temperature for pyrolysis and oxidation of coal.

Effects of Surfactant Blend Formulation on Crude Oil-Brine Interaction and Wettability: An Experimental Study

Interfacial tension of reservoir fluids and wettability are important parameters in the process of enhanced oil recovery. These two parameters affect the fluid distribution within reservoir formation. The fluids distribution in the reservoir strongly affects the flow behavior and residual oil recovery. Interfacial tension plays an important role due to its relationship between foam surface energy and foam stability. The wettability by contact angle measurement provides a method for determining fluid interaction and is considered as a basic research than practical tool for analysis of reservoir formation. The main objective of this research study is to determine the effects of interfacial tension and wettability on foam surfactant blend formulations, brine and crude oil. Anionic and nonionic surfactant blend were selected. The interfacial tension test was performed at 85oC. Dynamic interfacial tension of blended surfactant formulations with Malaysian crude oil were measured in fixed brine salinity. The interfacial tension values of tested surfactant blends were found lower than the interfacial tension between brine and crude oil. Interracial tension between crude oil and foam forming surfactant was reduced by using different concentration of surfactant blend. Good values were obtained by the measurement of contact angle between solid and three foam surfactant blend formulations. The interfacial tension and contact angle experimental studies revealed that, the blend of Alpha Olefin Sulfonate and Sodium Dodecyl Sulfonate with Octylphenol Ethylene Oxide play an important role in reducing the interfacial tension at crude oil-brine interface. The reduced interfacial tension and more wetting surface effects indicated that, these foam surfactant formulations are of great importance in the process of residual oil recovery.

Influence of Lavander Essential Oil Addition on Passion Fruit Oil Nanoemulsions: Stability and In vivo Study

Nanoemulsions present droplets between 20 to 500 nm. It can be obtained by high-energy or low-energy methods. The aim of this study was to evaluate the influence of Lavander Essential Oil (LEO) in the formation of Passion Fruit Oil nanoemulsions, water and a blend of nonionic surfactants. The results show a reduction in droplet size with the addition of LEO, which can be explained by the possibility of essential oil molecules to penetrate into the interface and change their properties.

Improved cell infiltration of highly porous nanofibrous scaffolds formed by combined fiber-fiber charge repulsions and ultra-sonication.

A significant problem affecting electrospun nanofibrous tissue scaffolds is poor infiltration of cells into their three-dimensional (3D) structure. Environmental and physical manipulation, however, can enhance cellular infiltration into electrospun scaffolds. In this work, RGD-modified alginate mats with increased thickness and porosity were achieved by pairing high humidity electrospinning with post-processing ultra-sonication. RGD-modified alginate, polyethylene oxide (PEO), and an FDA-approved, nonionic surfactant blends were electrospun in 20 and 50% relative humidity conditions. Mats electrospun in high humidity conditions resulted in significantly increased mat thickness and decreased fiber diameters. The mats' alginate content was then isolated via ionic crosslinking and PEO/surfactant extraction. Finally, the alginate-only mat was post-processed by ultra-sonication to further enhance its cross-sectional thickness. Cell morphology, proliferation, and infiltration into the scaffolds were evaluated by seeding fibroblasts onto the alginate mat. Cell spreading, growth and infiltration improved with increased humidity and ultra-sonication. This approach shows great promise for the design of cell-permeable nanofibrous scaffolds for tissue-engineering applications.

Interfacing Multistage Mass Spectrometry with Liquid Chromatography or Ion Mobility Separation for Synthetic Polymer Analysis

Synthetic polymers are naturally mixtures of homologs, even in pure form. More complexity is introduced by the presence of different comonomers, end groups and/or macromolecular architectures. The analysis of such systems is substantially facilitated by interfacing mass spectrometry (MS), which disperses based on mass, with an additional level of separation involving either interactive liquid chromatography (LC) or ion mobility (IM) spectrometry, both of which are readily coupled online with electrospray ionization and MS detection. IM-MS separates in the gas phase, post-ionization and, therefore, is ideally suitable for labile and reactive polymers. Its usefulness is illustrated with the characterization of non-covalent siloxane-saccharide complexes, metallosupramolecular assemblies and an air- and moisture-sensitive inorganic polymer, poly(dichlorophosphazene). Conversely, LC-MS which separates in solution phase, before ionization, is most effective for the analysis of polymeric mixtures whose components differ in polarity. Interactive LC conditions can be optimized to disperse by the content of hydrophobic units, as is demonstrated for amphiphilic polyether copolymers and sugar-based nonionic surfactant blends. Both LC-MS and IM-MS can be extended into a third dimension by tandem mass spectrometry (MS(2)) studies on select oligomers, in order to obtain insight into individual end groups and isomeric architectures, comonomer sequences and degree of substitution, for example, by hydrophobic functionalities.

Relationship between Rheological Properties and One-Step W/O/W Multiple Emulsion Formation

Formation of a normal (not temporary) W/O/W multiple emulsion via the one-step method as a result of the simultaneous occurrence of catastrophic and transitional phase inversion processes has been recently reported. Critical features of this process include the emulsification temperature (corresponding to the ultralow surface tension point), the use of a specific nonionic surfactant blend and the surfactant blend/oil phase ratio, and the addition of the surfactant blend to the oil phase. The purpose of this study was to investigate physicochemical properties in an effort to gain a mechanistic understanding of the formation of these emulsions. Bulk, surface, and interfacial rheological properties of adsorbed nonionic surfactant (CremophorRH40 and Span80) films were investigated under conditions known to affect W/O/W emulsion formation. Bulk viscosity results demonstrated that CremophorRH40 has a higher mobility in oil compared than in water, explaining the significance of the solvent phase. In addition, the bulk viscosity profile of aqueous solutions containing CremophorRH40 indicated a phase transition at around 78 ± 2 °C, which is in agreement with cubic phase formation in the Winsor III region. The similarity in the interfacial elasticity values of CremophorRH40 and Span80 indicated that canola oil has a major effect on surface activity, showing the significance of vegetable oil. The highest interfacial shear elasticity and viscosity were observed when both surfactants were added to the oil phase, indicating the importance of the microstructural arrangement. CremophorRH40/Span80 complexes tended to desorb from the solution/solution interface with increasing temperature, indicating surfactant phase formation as is theoretically predicted in the Winsor III region. Together these interfacial and bulk rheology data demonstrate that one-step W/O/W emulsions form as a result of the simultaneous occurrence of phase-transition processes in the Winsor III region and explain the critical formulation and processing parameters necessary to achieve the formation of these normal W/O/W emulsions.

Development and Evaluation of Emulsions from Carapa guianensis (Andiroba) Oil

Carapa guianensis, a popular medicinal plant known as "Andiroba" in Brazil, has been used in traditional medicine as an insect repellent and anti-inflammatory product. Additionally, this seed oil has been reported in the literature as a repellent against Aedes aegypti. The aim of this work is to report on the emulsification of vegetable oils such as "Andiroba" oil by using a blend of nonionic surfactants (Span 80® and Tween 20®), using the critical hydrophilic-lipophilic balance (HLB) and pseudo-ternary diagram as tools to evaluate the system's stability. The emulsions were prepared by the inverse phase method. Several formulations were made according to a HLB spreadsheet design (from 4.3 to 16.7), and the products were stored at 25°C and 4°C. The emulsion stabilities were tested both long- and short-term, and the more stable one was used for the pseudo-ternary diagram study. The emulsions were successfully obtained by a couple of surfactants, and the HLB analysis showed that the required HLB of the oil was 16.7. To conclude, the pseudo-ternary diagram identified several characteristic regions such as emulsion, micro-emulsion, and separation of phases.

Ionic liquid-in-oil microemulsion as a potential carrier of sparingly soluble drug: Characterization and cytotoxicity evaluation

Pharmaceutical industries have posed challenges in the topical and transdermal administration of drugs which are poorly soluble or insoluble in water and most of organic solvents. In an approach to overcome this limitation, ionic liquid-in-oil (IL/o) microemulsions (MEs) were employed to increase the solubility of a sparingly soluble drug to enhance its topical and transdermal delivery. The formulation of MEs was composed of a blend of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80) and sorbitan laurate (Span-20), isopropyl myristate (IPM) as an oil phase, and IL [C 1mim] [(CH 3O) 2PO 2] (dimethylimidazolium dimethylphosphate) as a pseudophase. Among various weight ratios of Tween-80 to Span-20 investigated in the ME systems, the ratio 3:2 showed excellent solubility and skin permeation enhancing effect for acyclovir (ACV) used as a model sparingly soluble drug. The size and size distribution of the ME droplets with and without drug were determined by dynamic light scattering. The permeability study of ACV incorporated in IL droplets as well as other formulations was performed into and across the Yucatan micropig (YMP) porcine skin, and the use of IL/o MEs has been shown to dramatically increase ACV administration. Finally, the cytotoxicity of the new carrier was evaluated in vitro using the reconstructed human epidermal model LabCyte™ EPI-MODEL12. It was found that the cell viability of IL/o MEs containing 4 wt% IL was over 80% compared to Dulbecco's Phosphate-Buffered Salines, indicating low cytotoxicity of the carrier. Taken together these results, it can be assumed that IL-assisted nonaqueous ME could serve as a versatile and efficient nanodelivery system for insoluble or sparingly soluble drug molecules that require solubilizing agents for delivery.

Ionic liquid based microemulsion with pharmaceutically accepted components: Formulation and potential applications

In this paper, we report a novel ionic liquid-in-oil (IL/o) microemulsion which is able to dissolve pharmaceuticals that are insoluble or sparingly soluble in water and most of pharmaceutical grade organic liquids. Towards this approach, the nanometer-sized ionic liquid droplets in isopropyl myristate (IPM) were formed with a blend of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80), and sorbitan laurate (Span-20). A set of ionic liquids (ILs) was tested as a dispersed phase, and it was observed that ILs possessing coordinating anions which are strong hydrogen bond acceptor were most effective in forming microemulsion droplets. The possible formation mechanism was also studied. Ternary phase behavior study clearly indicated the formation of optically transparent and thermodynamically stable microemulsions with a wide range of IL content. The shape, size and size distribution of the aggregates in microemulsions were characterized using dynamic light scattering (DLS), which demonstrated the formation of spherical micelles in the range of 8-34nm. In order to explore the use of newly developed microemulsion as a potential drug carrier, we have investigated the solubility of some drug molecules (e.g., acyclovir, methotrexate and 1-[(5-(p-nitrophenyl) furfurylidene) amino] hydantoin sodium) that are insoluble or sparingly soluble in most of the conventional solvents. Very significantly, the solubility studies indicated a high degree of solubilization of such drugs in IL microemulsions. We believe that this microemulsion formed with ILs having the unique physical, chemical and biological properties may offer novel opportunities to develop a potential drug delivery carrier for poorly soluble drugs molecules.

Emulsification of Vegetable Oils using a Blend of Nonionic Surfactants for Cosmetic Applications

Sunflower oil and sesame oil contain fairly high percentage of tocopherols and tocotrienols. These oils were emulsified by using a combination of non‐ionic surface‐active agents viz. Span‐80 and Tween‐20 surfactants to get cosmetic emulsions. Stability of the emulsions was enhanced by using natural polymer additives. The effect of various parameters such as pH, oil content, emulsifier content, HLB of blend of emulsifier concentration of additives and temperature on the stability of cosmetic emulsion was studied. These emulsions are “skin compatible” being stable at neutral pH. Xanthan gum was found to be the most effective additive as compared to the other natural polymers. The emulsions showed a “pseudoplastic” flow behavior.

Effects of alcohols and diols on the phase behaviour of quaternary systems

The aim of the current study was to investigate the effect of different co-surfactants on the phase behaviour of the pseudoternary system water:ethyl oleate:nonionic surfactant blend (sorbitan monolaurate/polyoxyethylene 20 sorbitan mono-oleate). Four aliphatic alcohols (1-propanol, 1-butanol, 1-hexanol and 1-octanol) and four 1,2-alkanediols (1,2-propanediol, 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol) were used. The co-surfactant-free system forms two different colloidal structures, a water-in-oil microemulsion (w/o ME) and lamellar liquid crystals (LC) and two coarse dispersions, water-in-oil (w/o EM) and oil-in-water (o/w EM) emulsions. Microemulsion region area (%ME), liquid crystalline region area (%LC), amount of amphiphile blend required to produce a balanced microemulsion (%AMPH) and amount of water solubilised (%W) were used as assessment criteria to evaluate the co-surfactants. Seven calculated physico-chemical descriptors were used to represent the different co-surfactants. 1-butanol, 1,2-hexanediol and 1,2-octanediol produced balanced MEs capable of solubilising a high percentage of both oil and water. A similarity was observed between the descriptors attributed to 1-butanol and 1,2-hexanediol. The requirements of a co-surfactant molecule to produce a balanced microemulsion were: HLB value 7.0–8.0, a carbon backbone of 4–6 atoms, percentage carbon of 60–65%, percentage oxygen of 20–30%, logP value 0.2–0.9 and log 1/S (S: aqueous solubility) close to zero.

Influence of Adjuvants on Itchgrass (Rottboellia cochinchinensis) Control in Corn (Zea mays) with Nicosulfuron and Primisulfuron1

In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.Nomenclature: Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; primisulfuron, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; itchgrass, Rottboellia cochinchinensis (Lour.) W. Clayton #3 ROOEX; corn, Zea mays L. ‘DeKalb 689’.Additional index words: Crop oil concentrate, methylated seed oil, nonionic surfactant, organosilicone surfactant, ROOEX.Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence.

Experimental investigations on model emulsion systems stabilized with non-ionic surfactant blends

We have performed experimental research into model oil-in-water emulsion systems stabilized with non-ionic surfactant blends: thin aqueous films between oil phases and oil drops coalescing against their homophase. Xylene was chosen as the oil phase, and Tween 20 and Span 20, alone or in mixtures at different molar ratios, were used as stabilizers. The roles of the surfactant mole ratio, the electrolyte concentration and pH were studied. It was shown that there is considerable electrostatic repulsion within the aqueous films. The results obtained on thin film stability and on drop lifetime at constant electrolyte concentration indicate that Tween 20 (when present) is the emulsifier that predominantly determines the stability of the systems. This conclusion can be related to the higher surface activity and higher adsorption of Tween as deducted from interfacial tension data. Some evidence of synergism was observed only at an electrolyte concentration of 10 −3 M (NaCl). We also carried out stability tests on shaken and homogenized batch emulsion systems and the results show good correlation with the data from the model investigations.

Application of the cohesive energy ratio concept (CER) to the formation of polymerizable microemulsions

The cohesive energy ratio concept (CER) developed by Beerbower and Hill for the stabilization of emulsions has been extended to microemulsions. The CER concept allowed us to predict the most suitable emulsifiers and oils for the production of polymerizable microemulsions. For example, a blend of non-ionic surfactants (sorbitan sesqui-oleate and poly(oxyethylene) sorbitol hexaoleate) was found to be very efficient for the microemulsification of an aqueous solution of acrylamide in an isoparaffinic oil (Isopar M). Under these conditions, microemulsion polymerization leads to stable uniform polyacrylamide microlatexes ( d < 0.1 μm) which can be useful for industrial applications.