Hydrophile-lipophile Balance Number Research Articles

Application of hydrophilic–lipophilic balance (HLB) number to optimize a compatible non-ionic surfactant for dried aerial conidia of Beauveria bassiana

The hydrophilic–lipophilic balance (HLB) number system was used to optimize a compatible non-ionic surfactant, TDA (polyoxyethylene tridecyl ether) in formulations for two Beauveria bassiana strains, NI8 and GHA. The optimal HLB number for TDA was determined on the basis of wetting times for conidial powders. The results indicated that optimal HLB number of TDA for B. bassiana strain NI8 was 8, while the optimum HLB number for strain GHA was 10. The optimized TDA surfactants required significantly less wetting times than the commonly used laboratory surfactants, Triton X-100, Span 80, and Tween 80. These optimized TDA surfactants were further characterized on their ability to produce conidial suspensions of the two strains after 5 min of mixing, TDA HLB 8 and TDA HLB 10 produced suspensions of 1.8 × 10 8 and 1.6 × 10 8 conidia/ml for NI8 and GHA, respectively. These conidial levels were significantly higher than those in Triton X-100, Span 80, and Tween 80 suspensions after the same mixing time. Germination assays showed that TDA HLB 8 promoted significantly higher germination rates of strain NI8 than those observed in other commonly used laboratory surfactants. However, the germination rates of the GHA strain were unaffected by any of the surfactants tested. The efficacy of the conidial suspensions was confirmed with assays against Lygus lineolaris. Bioassay results indicated that there were no significant differences in mortalities because of surfactants. These results suggest optimization based upon HLB number will not negatively impact parameters associated with efficacy, while providing desirable physical properties.

Phase behavior of the mixtures of poly(oxyethylene) (10) stearyl ether (Brij-76), 1-butanol, isooctane, and mixed polar solvents: II. Water and ethylene glycol (EG) or tetraethylene glycol (TEG)

The phase diagrams of the pseudo-quaternary systems poly(oxyethylene) (10) stearyl ether (Brij-76)/1-butanol/isooctane/water (with equal amounts of oil and water in the presence of two nonaqueous polar solvents (NPS), ethylene glycol (EG), and tetraethylene glycol (TEG)), have been constructed at 30 °C. Regular fish-tail diagrams were obtained up to ψ (weight fraction of EG or TEG in the mixture of polar solvents) equal to 0.5, confirming the establishment of hydrophile–lipophile balance (HLB) of the systems. The maximum solubilization capacity passed through a minimum at ψ = 0.2 . No HLB was obtained at higher ψ. The usual fish-tail diagrams were also obtained in temperature-induced phase mapping at fixed W 1 (weight fraction of 1-butanol in total amphiphile). Solubilization capacity and HLB temperature ( T HLB ) decreased with increasing ψ at a fixed W 1 , the effect being more pronounced for TEG than EG. A correlation between HLB temperature ( T HLB ) and HLB number ( N HLB ) of mixed amphiphiles (Brij-76 + Bu) in pseudo-quaternary systems (in the presence of water and partial substitution of water with both NPS) has been established. The novelty of the work with respect to possible applications has been discussed.

HLB number of Vitamins C, E, coenzyme Q 10 derivatives and their transportation efficiency into skin

We have been proposing a new delivery system of medicines and supplements. Derivatives of vitamin C, E and coenzyme Q 10 were examined regarding the relationship between the hydrophile-lipophile balance (HLB) number and the transdermal transportation efficiency into the skin. Non-invasive vibrational spectroscopies, infrared attenuated total reflection (IR-ATR) and near-infrared diffusive reflection (NIR-DR) methods were used in order to evaluate transported materials in the skin. Vitamin C derivatives of sodium l-ascorbyl-2-phosphate (hereafter abbreviated as APS) and sodium l-ascorbyl-2-phosphate-6-palmitate (APPS) were examined. APPS contains both a hydrophilic group and a hydrophobic group, since APS has been modified to APPS by deriving palmitic acid ester in the 6-OH position. APPS has the value of HLB around 9.0, while APS has that of 20. The iontophoretic efficiency of APPS is higher than APS. Vitamin E derivatives of DL-α-tocopheryl N, N-dimethylglycinate (TDMG) and α-tocopheryl acetate (TA) were examined regarding the transdermal transportation effect. Those HLB numbers are 2.3 and 0, respectively. TA is hydrophobic, while TDMG has a hydrophilic terminal group of dimethylglycine HCl materials. Coenzyme Q 10 (CoQ 10) is hydrophobic and a portion of benzoquinone is also hydrophobic, thus, HLB = 0. CoQ 10 has been modified to a reduced form of CoQ 10 (CoH 2Q 10) by NaBH 4. CoH 2Q 10 has a hydroquinone structure of hydrophilic property and HLB = 3.9. Supersonic perforation transported a greater amount of CoH 2Q 10 into the skin than CoQ 10. The balance of the hydrophilic group and the hydrophobic group in the transported material is an important factor for the effective transportation into the skin.

Virucidal activities of medium‐ and long‐chain fatty alcohols, fatty acids and monoglycerides against herpes simplex virus types 1 and 2: comparison at different pH levels

Previous studies have shown that certain lipids and fatty alcohols have microbicidal activities against a number of pathogens. In this study, virucidal activities of fatty alcohols and lipids were tested against HSV types 1 and 2 at various concentrations, times, and pH levels. The aim was first, to determine which compounds are most virucidal against HSV and could possibly be used as active ingredients in topical drug formulations and second, to attempt to throw light on the mode of action of virucidal lipids. Good agreement was found between the activities for HSV-1 and HSV-2. The activity of a compound depends on the concentration and time of contact and most of the compounds are more active at pH 4.2 than at pH 7. This information may be helpful in the formulation of pharmaceutical dosage forms for treatment of herpes lesions in skin and mucosa. The difference between the polar groups of alcohols and fatty acids, i.e. hydroxyl group versus carboxyl group, and the corresponding difference in their hydrophile-lipophile balance (HLB) may explain their different virucidal activities against HSV. However, in most cases HLB numbers cannot explain the different virucidal activities of fatty alcohols and lipids, particularly not their increased activity at low pH. It is more likely that the acidic environment makes HSV more sensitive, possibly by ionic changes in the envelope proteins.

Neutron and X-ray Reflectivity from Polyisobutylene-Based Amphiphiles at the Air−Water Interface

We have performed X-ray and neutron reflectivity experiments on amphiphile films spread at the air−water and air-saturated ammonium nitrate solution interfaces as a function of film compression. We have examined ca. 750, 1100, and 1700 molecular weight monodisperse polyisobutylene amide (PIBSA), 1100 imide (PIBSIM), and also palmitic acid for the pure amphiphiles and binary mixtures. We have used deuterated and hydrogenous components so that a given film may be examined in up to seven contrasts. All of the films form a monolayer, with molecular area determined by tail group size, which increases slightly in thickness on compression for PIB derivatives. There are differences in film thicknesses as shown by a dependence on compression and substructure; this is understood in terms of the increasing tendency of the tail to adopt a coiled conformation as molecular weight increases. PIBSA films consist of packed micrometer scale disks containing up to 10% open water (polynya) area. Palmitic acid-containing films contain a greater polynya area. All films lose up to half of the original amount of amphiphile from the monolayer when compressed. The almost reversible loss of material followed the trend palmitic acid < 750 amide < 1100 amide < 1100 imide, empirically in order of hydrophile−lipophile balance (HLB) number. This pattern suggests an amphiphile loss into submicrometer aggregates at the interface, rather than dispersion into the aqueous phase. Binary mixtures exhibit differential competition of the components to remain in the monolayer with the trend: palmitic acid >750 amide > 1100 amide > 1100 imide, opposite to the aggregation tendency as expected. The preference to remain at the surface may be physically related to more effective packing of the headgroup molecules on the surface when head and tail areas are better matched in size. Mixtures also spontaneously segregate laterally and form micrometer scale domains. This tendency also follows the HLB number, with better mixing for those components with similar HLB values. Lateral segregation is encouraged by film compression. Surprisingly, properties of films on water and 50 wt % ammonium nitrate subphase show little difference with respect to these trends.

A simple method for the selection of a suitable emulsifier based on color difference.

The purpose of this study was to establish a simple and rapid method for selecting a nonionic surfactant to prepare an emulsion that can maintain a stable emulsification phase. As an index of the degree of emulsification, the white chromaticity of the prepared sample was measured using a color difference meter. When liquid paraffin was used as an oil, the color difference (dE(H)) was shown as a change in a V-shaped curve depending on changes in the hydrophile-lipophile balance (HLB) number of sorbitan ester, polyoxyethylene sorbitan ester, or polyethyleneglycol ester. Although there was a difference in the minimal value of dE(H) in these experiments, the dE(H) was similar to the required HLB of liquid paraffin (HLB=10). On the other hand, no relationship was found between the HLB number and color difference when polyglycerol ester was used. It seems that there was possibility of the effect by the lowering of apparent HLB with a collapse of the hydration. These results indicate that color difference could be utilized for the selection of surfactants, except for polyglycerol ester.

The Effects of Pressure-Sensitive Adhesives and Solubilizers on the Skin Permeation of Testosterone from a Matrix-Type Transdermal Delivery System

ABSTRACTMatrix-type transdermal delivery systems of testosterone (TS) were formulated with three different pressure-sensitive adhesives (PSA). The effects of PSA, skin permeation enhancers, and solubilizers on the rat skin permeation rate of TS were systematically investigated. Without a solubilizer, the skin permeation rate of TS reached its maximum value when only 2% of TS was loaded in the matrix and the crystal formation in the matrix was very rapid and severe. Two surfactants differing in their hydrophile–lipophile balance (HLB) number were, therefore, considered. Span 80, which was of the lower HLB number, was more effective than Tween 80 in increasing the solubility, and thereby increasing the permeation rate of TS. Moreover, the concentrations of both the solubilizer and the skin permeation enhancer affected the skin permeation rate. Thus, the highest skin permeation rate (4.14 µg/cm2/hr) was achieved when 2% TS was loaded in DuroTak® 87-2516 together with 10% Span 80 and 3% dodecylamine, the permeation enhancer. In vivo study showed that the application of an experimental patch on rat abdominal skin resulted in a prompt and significantly higher plasma concentration of TS than that of a commercial product (Testoderm®) designed to apply on the scrotal skin. The area under the curve (AUC) increased linearly as the loading dose of TS increased up to 6%. Thus, based on these results, a non-scrotal matrix-type transdermal delivery system of TS could be developed.

Dissolution and partitioning behavior of hydrophobic ion-paired compounds.

This study was conducted to determine the effects of counterion hydrophobicity on organic/aqueous partition coefficients for hydrophobic ion paired (HIP) complexes. Furthermore, the coupled dissolution and reverse ion-exchange kinetics for dissolution of HIP complexes into aqueous electrolyte solutions were measured and mathematically modeled. HIP complexes of model drugs tacrine and l-phenylephrine were formed using linear sodium alkylsulfates and bis (2-ethylhexyl sodium sulfosuccinate). Equilibrium partition coefficients between chloroform and aqueous solutions for the complexes and the kinetics of dissolution of the complexes in buffered aqueous solutions were measured. The chloroform/aqueous partition coefficients for l-phenylephrine/bis (2-ethylhexyl sodium sulfosuccinate) complexes decrease with increasing molar surface tension increment of salts added to the aqueous solution. The logarithm of the partition coefficient for a homologous series of alkyl sulfate complexes decreases as the hydrophilic-lipophilic balance number increases. Dissolution of HIP complexes in deionized water shows first order kinetics, whereas dissolution in aqueous electrolyte solutions shows biphasic kinetics. A kinetic model explains these dissolution rates. Solubility and dissolution rates for HIP complexes depend on the hydrophobic-lipophilic balance number of the organic counter ion as well as on the electrolyte composition of aqueous solutions. Reverse ion-exchange kinetics are sufficiently slow to allow HIP complexes to be considered simple prodrugs.

Removal of nonylphenol ethoxylates by electrochemically-generated coagulants

This study investigated the behaviour of aluminium and carbon steel electrodes in the presence and absence of nonylphenol ethoxylates (NPnEO, where n is the number of ethoxylate groups in the molecule) and NPnEO removal by electrochemically-generated coagulants. The electrode processes were studied by potentiodynamic polarization measurements to determine the influence of surfactant addition (ethylene oxide units and organic load), inorganic composition and pH. The polarization curves showed the extent of the involvement of NPnEO in the electrode processes. Their influence appeared clearly in the range of anodic activation, depending on the number of ethoxylate groups. Removal of NPnEO from simulated wastewaters was carried out in two electrocoagulation cells with vertical and horizontal electrodes, respectively. The removal efficiencies calculated from the chemical oxygen demand before and after treatment were 30–50% for NP16EO and NP40EO, and 40–80% for NP4EO. The hydrophilic-lipophilic balance number for NP4EO indicated a relative ratio of polar and non-polar groups lower than for the other two surfactants, which was in favour of better NP4EO removal. The experiments showed the processes in the bulk (bridging of electrochemically-generated polymeric species and adsorption of surfactants) were predominant over the involvement of NPnEO in the electrode processes, which were only responsible for the electrogeneration of coagulants.

Physicochemical Properties of a Ternary System Based on Medium Chain Triglycerides/Water/Mixed Nonionic Sugar-Based Surfactants

Equal ratios of medium chainlength triglycerides and water were emulsified with 5% w/w of mixed nonionic surfactants with various hydrophilic-lipophilic balance (HLB) values. The HLB numbers ranged from 15 to 6.6. Emulsifiers with HLB numbers 15, 14.2, 13.3, and 12.5 produced low viscosity milk-like liquid, 11.6, 10.8, 10, and 9.1 produced cream, 8.3 and 7.4 produced paste like consistency, and 6.6 produced a coarse emulsion. The effects of HLB on stability, particle size, and rheological properties were studied. Emulsifiers with intermediate HLB numbers produced emulsions that are stable for 30 days at room temperature but a thin layer of oil on top of the emulsion was observed at 45°C. The thin oil layer can be redispersed with mild agitation without loss of stability. Emulsifiers with high and low HLB number (15, 14.2, 13.3, 6.6) produced emulsions that were unstable at both storage conditions. The stability of the emulsions correlate well with the particle size. The curve flow plot for most of the emulsions fit the Herschel Bulkley model. They exhibit a pseudoplastic type behavior. Emulsifiers with different HLB numbers also affect the shear stress at zero shear, τ0, and the yield value, τ.

Laboratory Evaluation of the Use of Surfactants for Ground Water Remediation and the Potential for Recycling Them

AbstractThe primary goal of this study was to develop a suitable experimental and laboratory methodology for investigating the efficiency of surfactants in removing hydrophobic contaminants from sand and the efficient recovery of used surfactant solutions for reuse. One of the goals of this study was to test the use of a hydrophile‐lipophile balance (HLB) number as a suitable selection criterion. We used toluene as a model contaminant, Ottawa sand as a model porous medium, and six nontoxic, water‐soluble anionic or nonionic surfactants with HLB numbers ranging from 12 to greater than 25.Four of the six surfactants were judged to be less suitable on the basis of their properties (less suitable HLB and surface tension), and on batch experiments using separatory funnel, shaker table, and centrifugation methods. The two most suitable surfactants were trideceth‐19‐carboxylic acid (TDCA), an anionic surfactant, and polyoxypropylene‐polyoxyethylene block copolymer (POP‐POE), a nonionic surfactant. These two surfactants were then used for sand column leach experiments, and two of the less suitable surfactants were also investigated to determine if HLB number and batch experiments satisfactorily predicted leaching effectiveness.In sand column experiments, an aqueous surfactant solution containing a mixture of 1% anionic and 1% nonionic surfactant in a 1.6% NaOH solution was the most effective in removing the toluene. Removal efficiency of alkylaryl ethoxylate carboxylic acid (AECA), which has an HLB number of 19, was only slightly less than for the chemically similar TDCA, but that of dioctyl sulfosuccinate (DOSS) with an HLB greater than 25 was much less effective. These results indicate that HLB number alone is not a perfect indicator of surfactant effectiveness for leaching hydrophobic contaminants because the chemical structure of the surfactant is also important. In the counter‐current solvent extraction experiments designed to allow reuse of surfactants, the anionic surfactant solution (2% TDCA) was the most effectively recycled.

Relation between antigen release and immune response of oil adjuvanted vaccines in chickens.

The relationship between release properties of the model antigen, bovine serum albumin (BSA), from formulations in vitro and immune response after administration of various oil adjuvanted vaccines containing liquid paraffin was examined in chickens. The vaccine prepared at an hydrophile-lipophile-balance (HLB) number of 4.8 showed slower release of BSA and higher immune response on injected chickens than that with an HLB number of 6.0. Decreases of aqueous volume ratio in the formulation also led to slower release of BSA and higher immune response. The slower release rate of BSA showed higher ELISA antibody titer even at 20 weeks after vaccination. The ELISA antibody titer inversely was related to the constant release rate, k, calculated from the in vitro release test. The correlation coefficient was 0.863. The immune response of oil adjuvanted vaccines containing Haemophilus paragallinarum agreed well with these results with BSA. Our results indicated that a stronger and more prolonged immune response of oil adjuvanted vaccines was achieved by slower release rate of antigen from the formulation. In addition, there was a good correlation between immune response and the value of k.

Modification of ceftibuten transport by the addition of non-ionic surfactants

The effects of non-ionic surfactants on the carrier-mediated transport of ceftibuten by rat intestinal brush-border membrane vesicles (BBMVs) were investigated. Ceftibuten uptake by BBMVs was measured by a rapid filtration technique. The concentration of surfactants for the uptake experiments was determined by a decrease in the turbidity of BBMV suspension and by the release of an impermeable probe, 2′,7′-bis(carboxyethyl)-4(5)-carboxyfluorescein, from the vesicle inside. In fact, the surfactant concentration of 0.03% (w/v) was selected to maintain the stability of BBMVs. The extent of ceftibuten uptake by BBMVs with various surfactants was correlated with their physicochemical properties, i.e. hydrophile–lipophile balance (HLB), critical micelle concentration (c.m.c.), average diameter of micelle colloid, and polydispersity determined by particle size distribution. The surfactants used were divided into two groups on the basis of polydispersity index ( d w/ d n), i.e. low polydispersity ( d w/ d n≅1) and high polydispersity d w/ d n>2). The ceftibuten uptake due to the addition of surfactants with low polydispersity increased with a decrease in the HLB number. These results indicate that the ceftibuten transport is modulated by the size distribution and hydrophobicity of surfactants. In addition, the effects of surfactants on the membrane lipid fluidity monitored by diphenylhexatriene (DPH) and trimethylammonium diphenylhexatriene (TMA-DPH) were investigated. There was significant correlation between ceftibuten uptake and the fluorescence anisotropy of TMA-DPH-labeled membranes due to the addition of surfactants with low polydispersity ( r=−0.81, P<0.0001). These results suggest that surfactants with low polydispersity, in part, increase or decrease the outer membrane leaflet, thereby enhancing or suppressing the ceftibuten transport by BBMVs, and that ceftibuten transport caused by surfactants with low polydispersity may be strongly dependent on the hydrophobic interaction.

Partitioning of Ethoxylated Nonionic Surfactants into Nonaqueous-Phase Organic Liquids: Influence on Solubilization Behavior

The ability of surfactants to enhance the apparent aqueous solubilities of nonaqueous-phase liquid (NAPL) contaminants has increased interest in surfactant-enhanced aquifer remediation (SEAR) applications. This study examines the effect of surfactant partitioning on surfactant solubilization efficiency by analyzing the solubilization of several chlorinated NAPLs by a homologous series of linear alcohol ethoxylate nonionic surfactants. In general, it is found that the partitioning of surfactants can, especially in the cases of polar NAPLs, lead to substantial losses of surfactant, leaving little surfactant remaining in aqueous solution for solubilization. More importantly, it is found that neglecting surfactant partitioning can produce artifacts in the measured solubilization capacities of surfactants for NAPLs. For example, when surfactant partitioning is neglected, measurements of the solubilization capacity for homologous series of surfactants are often observed to produce a maximum solubilization capacity as a function of the surfactant hydrophile--lipophile balance number (HLB). The work described here demonstrates that the observed maximum solubilization capacity can result from neglecting partitioning of the surfactant into the NAPL. When solubilization capacity is calculated based on the amount of aqueous surfactant present after partitioning losses, no maximum is observed. The implications of this work for aquifer remediation are discussed.

A lattice fluid approach to the concept of hydrophile lipophile balance: alkylethoxylated surfactants

The relation between hydrophile lipophile balance (HLB) and the parameters of a lattice fluid equation of state (Sanchez–Lacombe) are studied. The observed linear relation between the characteristic pressure ( P*) and the HLB number, probably results from the fact that both parameters are connected to the cohesive energy density (CED). The relation between the HLB number and the number of lattice sites occupied by the alkylethoxylated surfactans in the lattice fluid model are also studied.

Self-Organizing Structures in Poly(oxyethylene) Oleyl Ether−Water System

A phase diagram of a water−poly(oxyethylene) oleyl ether (POlE) system was constructed as a function of poly(oxyethylene) chain length at 25 °C. The POlEs contain a highly pure oleyl group, whose purity is above 99.7%. The POlEs are in a liquid state over a wide range of composition. The increase in the poly(oxyethylene) (EO) chain of POlE corresponds to the increase in the curvature of surfactant layer toward water or the increase in HLB (hydrophile−lipophile balance) number of the surfactant. Various self-organizing structures were found: hexagonal and lamellar lquid crystals, four kinds of isotropic liquid crystals, a sponge phase, and reverse hexagonal liquid crystal. The phase transition between normal hexagonal and lamellar liquid crystals were investigated at constant volume fraction of the oleyl group in system by means of small-angle X-ray scattering. Correlation among the phase behavior, the packing of oleyl chain in self-organizing structures, and the HLB of POlE is discussed. The effect of temperature on the phase behavior in the present system is also discussed.

Alterations in Phospholipid Bilayers Caused by Oxyethylenated Nonylphenol Surfactants

The interactions of oxyethylenated nonylphenols [ethylene oxide units (EO) averaging between 5 and 30] with phosphatidylcholine liposomes were investigated. Three parameters were regarded as corresponding to the effective surfactant/lipid molar ratios at which the surfactant system (a) resulted in the transient liposome reorganization for the release of 50% of 5(6)-carboxyfluorescein (CF) trapped in the liposomes,R50%CF; (b) saturated the liposomes,RSAT; and (c) led to a complete liposome solubilization,RSOL. From these parameters the surfactant partition coefficientsK50%CF,KSAT, andKSOLwere determined. Permeability alterations were determined as a change in CF released from the interior of vesicles and solubilization as a decrease in the static light scattering of liposome suspensions.RSATandRSOLshowed the lowest values in the critical micellar concentration (CMC) range between 0.040 and 0.087 mMand 0.050 and 0.075 mM,respectively [hydrophilic–lipophilic balance (HLB) number ranging between 13 and 16 and 14 and 15], which corresponded approximately to the nonylphenols with 10–20 and 15 EO units, respectively. However,K50%CF,KSAT, andKSOLdrastically decreased as the number of EO units increased, especially in the EO range between 5 and 15. Thus, the highest surfactant affinity with bilayers (maximumKvalues) and its maximum ability to alter these structures (minimumRvalues) were governed by the CMC surfactants and their HLB numbers and, consequently, by the EO units present in the surfactant structure. The free surfactant concentrations were lower than their CMCs at sublytic level, whereas they remained similar to these values during bilayer saturation and solubilization. The nonylphenols investigated showed higher activity versus liposomes than that reported for Triton X-100, the oxyethylenated nonylphenol with an average of 10 ethylene oxide units showing low toxicity in biological tests.

Phase behaviour of polyoxyethylene hydrogenated castor oil in oil/water system

The phase behavior of oxyethylene hydrogenated castor oil (HCO10) in the oil/water system has been studied with three different oils, a polar oil, glycerol tris(2-ethyl hexanoic) ester (TEH) and two hydrocarbons, hexadecane and n-octane. For the TEH system, the triangular phase diagram is found to be dominated by a liquid crystalline phase at 25°C whereas a large portion of this phase melts to give a single-phase microemulsion at 35°C. For the hexadecane system, the single phase region in the triangular phase diagram is much smaller than that for TEH. These single-phase regions are almost isolated from the water/surfactant or oil/surfactant axes for both the oils. Since the surfactant is a commercial surfactant and contains many components with different polyoxyethylene chains, the theory for multisurfactant systems was applied to evaluate the hydrophilic-lipophilic balance (HLB) of HCO10. The HLB number of this surfactant is calculated by mixing it with a pure polyoxyethylene-type surfactant, C12EO6, whose HLB number is known. HLB numbers calculated from different oils agree well with each other.

Factors determining emulsion type: Hydrophile—lipophile balance and beyond

Bancroft's rule of thumb that a surfactant which preferentially partitions into water favors the formation of oil-in-water (O/W) emulsions and that a surfactant which preferentially partitions into oil favors the formation of water-in-oil (W/O) emulsions has been known for some 80 years. Although by judicious control of the emulsification process one can generate exceptions, the rule of thumb often works well. It was not, however, until Griffin's famous paper of 1949 that an attempt was made to quantify the emulsifying tendency of a surfactant. Griffin observed that certain combinations of the surfactant hydrocarbon and ethylene oxide chain lengths favored O/W or W/O emulsions. In the paper he noted that the emulsion chemist will choose a water-soluble surfactant to make an O/W emulsion and an oil-soluble one to make a W/O emulsion. To try to put this principle of hydrophile—lipophile balance (HLB) on a quantitative footing, he introduced the concept of an HLB number. According to Griffin, the HLB is the balance of the size and strength of the hydrophilic and lipophilic moieties of a surfactant molecule. The HLB number was based on the molecular groups composing the surfactant. According to this concept, the optimal surfactant for a desired emulsion of a given oil can be chosen by a simple calculation from a look-up table. A problem with the HLB concept was that the HLB numbers were based on ambient temperature data. A given ethoxylated hydrocarbon can form in O/W emulsions at room temperature while it gives W/O emulsions at higher temperatures. Thus the HLB cannot be related solely to the molecular groups of the surfactant. Temperature and interactions with the aqueous and oil phases have to be incorporated into the HLB number if it is to be a predictive tool. There is a strong correlation between whether an O/W emulsion or a W/O emulsion is formed and whether the surfactant tends to form an aqueous micellar phase or an oil-rich inverted micellar phase. Thus, as preferred by Becher, relating the HLB number to the free energies of micellization in water and oil phases ought to result in a more predictive tool. Shinoda and co-workers assert that it is preferable to introduce an HLB temperature based on the phase inversion temperature (PIT). This temperature is a property of the surfactant—oil—water phase diagram. For non-ionics, the PIT is the temperature below which a surfactant partitions preferentially into the water phase as oil-swollen micelles and above which it partitions preferentially into the oil phase as water-swollen inverted micelles. The advantage of basing the HLB on the PIT is that the surfactant—oil—water interactions are automatically incorporated into the HLB criterion. Similarly, the effect of cosurfactants, frequently needed for stable emulsions, is accounted for as a shift in the PIT. Finally, basing the HLB temperature on the PIT admits the strong correlation between emulsion type and ternary or pseudoternary phase behavior. We explore here the connection between the generic ternary phase behavior and emulsification tendencies and arrive at a generalization of Shinoda's PIT criterion. The trend from preferential partitioning of surfactant into the aqueous phase to a balanced or optimal microemulsion (equal uptake of oil and water) to preferential partitioning into the oil phase can be accomplished by a large number of variables (e.g. the field variables temperature, salinity and alcohol activity, and the extended field variables such as the average carbon number of the oil, the average carbon number of the hydrophobic moiety of the surfactant, the average number of ethylene oxide groups of the hydrophilic moiety of the surfactant, etc.) for the various types of surfactant. The field variable at which the optimal microemulsion occurs provides an optimal point (OP) that can serve as the HLB for a given system. If the field variable is set on one side (above or below depending on the variable) of the OP for a system, the surfactant serves as a hydrophilic agent (favors O/W emulsions) and if it is set on the other side of the OP, the surfactant serves as a hydrophobic agent (favors W/O emulsions). Since an optimal point can be achieved by variation of many parameters and field variables, the optimal microemulsion, and thus the HLB, is defined by a hypersurface in the space spanned by these variables. We also discuss the relationship between generic phase behavior of surfactant, oil and water systems and the curvature properties of surfactant interfacial films in association colloids.

Predispersed solvent extraction of dilute products using colloidal gas aphrons and colloidal liquid aphrons: Aphron preparation, stability and size

Early work on colloidal gas aphrons (CGAs) and Colloidal liquid aphrons (CLAs) has shown that they have considerable potential in the field of predispersed solvent extraction (PDSE). While their area of application is potentially very broad, their most promising use is in downstream separation in biotechnology where products are very dilute and occur in complex mixtures. Since little work has been done in this area, this preliminary study examined the influence of a range or solvents, varying from non-polar to mildly polar, and a variety of ionic and non-ionic surfactants, on CLA size, stability and phase volume ratio (PVR, volume ratio of the dispersed oil phase to the continuous aqueous phase). In addition, the effect of surfactant type, stirring speed and time, on the formation of CGAs was also studied. The results show that CLAs can be formulated with quite polar solvents (e.g. pentanol), and their stability increases as the HLB (hydrophilic/lipophilic balance) number of the non-ionic surfactant increases. CLAs could be formulated with PVRs as high as 20 without coalescence, which is markedly higher than with microemulsions, and seems to indicate that the liquid aphrons are stabilised by more than a surfactant monolayer. Finally, it was found that CGAs could be formulated as a foam with a half-life of 6 min, and that they could be used to separate dispersed CLAs effectively from a bulk solution.