The Characteristic Curvature (Cc) of Ionic Surfactants Assessed via Small-Angle X-ray Scattering.

The characteristic curvature (Cc), within the hydrophilic-lipophilic difference + net (Hn) - average (Ha) curvature (HLD-NAC) framework, is the dimensionless net curvature, -Hn·L (L is the surfactant's tail length parameter), that a surfactant acquires at the characteristic condition (T = 25 °C, no added cosurfactants, oil with an equivalent alkane carbon number (EACN) of zero and for ionic surfactants, a total salinity (S) of 1 g NaCl/100 mL). A recent article demonstrated the validity of the Cc concept, where Hn was assessed via oil and water solubilization radii. Here, we assess Hn from the characteristic length (ξ) obtained from the analysis of SAXS profiles of microemulsions produced at semicharacteristic conditions (characteristic condition but varying S). The predicted relationship, -L·Hn,semicharacteristic = Ccbi + bi·ln(S), was confirmed with the five ionic surfactants explored. The SAXS-assessed Cc (Cc = Ccbi/bi) values are consistent with those obtained from solubilization studies and phase inversion scans. The Cc-SAXS method provides a way to assess the hydrophobicity of ionic surfactants directly, avoiding the bias that could be introduced by cosurfactants in phase inversion studies and minimizing the impact of potential uncertainties in the surfactant volume to area ratio (vs/as) required to calculate the solubilization radii in the solubilization method.

HLD-NAC design and evaluation of a fully dilutable lecithin-linker SMEDDS for ibuprofen.

Lecithin-linker microemulsions have been previously proposed as a platform for designing a fully dilutable self-microemulsifying drug delivery system (SMEDDS). This SMEDDS formulation, composed of ethyl caprate (oil), lecithin (Le), glycerol monooleate (lipophilic linker, LL) and polyglycerol caprylate (hydrophilic linker, HL), produced a ternary phase diagram (TPD) that had a fully dilutable path suitable for oral drug delivery. However, introducing ibuprofen as an active pharmaceutical ingredient (API) resulted in TPD phase boundaries that eliminated the fully dilutable path. The purpose of this work was to understand the origin of the changes in the TPD, use that understanding to restore the fully dilutable path with an ibuprofen-loaded SMEDDS, and finally to evaluate the absorption of ibuprofen in vivo. The effect of ibuprofen on the HLD (hydrophilic-lipophilic difference, interpreted as normalized net interfacial curvature) of the system was evaluated via a polar oil model, showing that ibuprofen played a surfactant-like role, having a characteristic curvature (Cc) value of +5 (highly hydrophobic). The net-average curvature (NAC) framework used the HLD calculated with Le, LL, HL and ibuprofen Cc to generate TPDs in ibuprofen lecithin-linker systems. The HLD-NAC simulations show that restoring full dilutability required a highly hydrophilic linker (HL-) with a Cc of -5 or more negative. The fully dilutable path was restored after introducing a hexaglycerol caprylate as HL- (Cc = -6). Plasma concentration profiles obtained with this ibuprofen-loaded SMEDDS showed a more than three-fold increase in the area under the curve (AUC) of rat plasma concentration profiles compared to the same 25 mg/kg ibuprofen dose in suspension.

Separation of Emulsions with Fibrous Filter-Coalescers.

During froth treatment, a water-in-diluted bitumen emulsion is obtained. The emulsified water contains chloride ions that form hydrochloric acid in downstream oil processing, leading to catalyst deactivation and equipment corrosion. Emulsified water, drops smaller than 10 µm, cannot be effectively removed by gravity settling and centrifugation to below 2 wt %. In this work, a filter-coalescer was used to promote the coalescence and separation of water-in-bitumen emulsion. The larger water drops (>300 µm) exiting the coalescer undergo gravity settling, reducing the water content in diluted bitumen emulsions to values lower than 0.1 vol %. The performance of the coalescer was interpreted via the colloid filtration theory of Rajagopalan and Tien (RT), improved in this work with a coalescence probability (CP) prefactor. This new RTCP framework was able to reproduce the experimental data, allowing its potential use as a predictive model for emulsion filtration and the operation of filter-coalescers. A capillary number analysis was used to account for the detachment of coalesced drops and interpret the drop sizes with different superficial velocities and bed porosities.

Estado nutricional, síndrome metabólico e inflamación en pacientes con enfermedad de Chagas / Nutritional condition, metabolic syndrome and inflammation in patients with Chagas disease

El propósito de este estudio fue describir la asociación entre el estado nutricional, la presencia de síndrome metabólico (SM), y el estado inflamatorio, en pacientes con Enfermedad de Chagas (ECh), atendidos en la consulta externa del Instituto de Medicina Tropical en Caracas. El estudio fue de tipo transversal y correlacional, en el cual se seleccionaron 34 pacientes a los cuales se les realizó un diagnóstico parasitológico, inmunológico y molecular de la ECh. Se evaluaron variables antropométricas, clínicas y bioquímicas, así como el SM el cual fue determinado por los criterios del III Panel estadounidense para el Tratamiento de Adultos del Programa Nacional de Educación sobre el Colesterol (ATP-III, por sus siglas en inglés). Se encontró que la mayoría de los pacientes presentaron sobrepeso u obesidad (73,5%), un porcentaje de grasa corporal (% GC) alto o muy alto (82,3%), y obesidad abdominal (61,8 %). La frecuencia de SM fue de 29,4% y más del 90% mostraron valores elevados de Proteína C Reactiva ultrasensible (PCRus). Valores más elevados del IMC se asociaron con un estadio más avanzado de la ECh. Los sujetos con presencia de ADN de Tripanosoma cruzi (T. cruzi) circulante en sangre, presentaron mayor % GC, y en su mayoría, fueron diagnosticados con SM. En conclusión, los pacientes evaluados mostraron un exceso de adiposidad, que puede favorecer el estado inflamatorio, el desarrollo de SM y la progresión de la ECh(AU)

The purpose of the study was to describe the association between nutritional and inflammatory status and the presence of metabolic syndrome (MS) on patients with Chagas disease (CD) treated at the Outpatient Services of the Tropical Medicine Institute in Caracas, Venezuela. The study was cross-sectional and correlational. Thirty-four (34) patients were selected and a molecular, immunological, and parasitological diagnostic test was ran for Chagas disease. Anthropometric, clinic, and biochemical variables were evaluated, and the MS was determined using National Cholesterol Education Program Expert/Adult Treatment Panel III (ATP-III) criteria. The results showed a high percentage of patients overweight or presenting obesity (73.5%), a high and very high percentage of body fat (82.3%), and abdominal obesity (61.8%). The prevalence of MS was 29,4% and more than 90% of patients showed elevated values of high sensitivity C-reactive protein (hsCRP). Higher body-mass index values were associated with advanced stages of the CD. Subjects in the presence of T. cruzi DNA in the blood showed a greater percentage of body fat and, most of them, were diagnosed with MS. In conclusion, the evaluated patients showed an excess of adiposity which may favor an inflammatory status, the development of the MS, and the progress of the CD(AU)

Predicting the effect of additives on wormlike micelle and liquid crystal formation and rheology with phase inversion phenomena.

HYPOTHESIS: Surfactant-based viscoelastic fluids are used in consumer products such as body wash, cosmetics, and in hydraulic fracturing fluids to suspend proppant, among others. The solubilization of oil within these fluids changes the curvature of the surfactant and their nanostructure and rheological properties. The curvature-based hydrophilic-lipophilic-difference + net-average-curvature (HLD-NAC) framework may be able to quantify curvature changes and predict the formulation conditions required to obtain viscoelasticity. EXPERIMENTS: Phase inversion experiments were conducted for combinations of commercial-grade C8, C10 and C12 tetrapropylene glycol ether sulfate (extended) surfactant and sodium dihexyl sulfosuccinate with oil to obtain the HLD-NAC parameters. Wormlike micelles (WLMs) and liquid crystals (LCs) were then formulated and characterized. The transition from spherical micelles to WLMs/LCs at different oil contents was identified and compared with phase transitions predicted via the HLD-NAC model. FINDINGS: The spherical micelle to branched WLM/LC transition in surfactant + oil systems coincided with the water-continuous (Type I) to bicontinuous (Type III) microemulsion phase transition predicted with the HLD-NAC model. Using this finding, the transition of commercial-grade sodium laureth sulfate (SLES) micelles to viscoelastic LCs containing various oils was predicted using the HLD-NAC. The HLD-NAC also predicted the presence of a secondary peak in viscosity obtained in "salt curves" experiments associated with branched WLMs and LCs.

Formulating and Retaining the Structure of Polymerized Surfactant Phases Using a Microemulsion Curvature Framework.

Nanostructured polymers contain features smaller than 100 nm that are useful in a wide range of areas, including photonics, biomedical materials, and environmental applications. Out of the myriad of nanostructured polymers, surfactant-templated polymers are versatile because of their ability to have tunable domain sizes, structure, and composition. This work addresses the gap between the formulation with industrial-grade polymerizable surfactants and the final structure of the polymer, using the hydrophilic-lipophilic difference (HLD) and net-average curvature (NAC) frameworks. HLD indicates the proximity of the formulation (surfactant and oil monomer selection, temperature, electrolyte concentration) to the phase inversion point, where HLD = 0. NAC uses the HLD to determine the curvature of the surfactant-oil-water interface, leading not only to the size and shape of micelles and bicontinuous isotropic (L3) systems but also to defining the most likely regions for lyotropic liquid crystal (LLC) existence and phase separation in ternary phase diagrams. Polymerizing LLC fluids produced nanostructured polymers with similar LLC structures that were highly swellable, but with low compressive strength. Polymerizing L3 fluids produced strong, but less water-swellable nanostructured polymers with a similar characteristic length to the parent L3 microemulsion. The relatively small scale of the parent LLC (∼6-8 nm) or L3 (∼3-4 nm) systems is consistent with the translucent nature of the polymers produced and the HLD-NAC predicted sizes.

Interfacial Tension of the Water-Diluted Bitumen Interface at High Bitumen Concentrations Measured Using a Microfluidic Technique.

The interfacial tension (IFT) is a critical parameter to inform our understanding of the phenomena of drop breakup and droplet-droplet coalescence in sheared water-in-diluted bitumen (dilbit) emulsions. A microfluidic extensional flow device (MEFD) was used to determine the IFT of the dilbit-water emulsion system for bitumen concentrations of 33%, 50%, and 67% by weight (solvent to bitumen ratio (S/B) = 2, 1, and 0.5, respectively) and two different pH values of water: 8.3 and 9.9. The IFT was observed to increase with the bitumen concentration and decrease significantly upon lowering the water pH. The time scale for achieving the steady state IFT increased with bitumen concentration and was less sensitive to the water pH. But the most important feature of our measurements is that the IFTs recorded were significantly smaller than the values reported in the literature. We recognized two important differences between our studies and prior investigations: measurement of the IFT of water drops in dilbit as opposed to dilbit drops in water in earlier studies, and time scales of measurement of IFT that ranged from hundreds of milliseconds to a few seconds, as compared to a minute or longer in past investigations. These differences were examined carefully, but neither was found to explain the low IFTs measured in our studies. Our work leads to the following hypothesis: the mechanical properties of the interface of a sheared water drop in bitumen are significantly different from a stagnant one.

Characterizing the Oil-like and Surfactant-like Behavior of Polar Oils.

In this work, a bifunctional model was developed to fit and predict the phase inversion point (PIP) of microemulsions containing polar oils. This model incorporated the hydrophilic-lipophilic difference (HLD) equations, where HLD = 0 at the PIP. The model uses a Langmuir isotherm to account for the interfacial segregation of polar oils as a function of their concentration in the bulk oil phase. The segregated polar oil was treated as being surfactant-like, having a characteristic curvature (Cc). The polar oil in the bulk oil phase was characterized via an equivalent alkane carbon number (EACN). The Cc value was obtained considering deviations in the PIP at low polar oil concentrations. The EACN was determined considering PIP deviations at high polar oil concentrations. Naphthenic acid and dodecanol were used as model polar oils mixed with ionic and nonionic surfactants and nonpolar oils. The EACN of the polar oil was shown to be independent of the EACN of the nonpolar oil and likely independent of the surfactant. The Cc for dodecanol was likely independent of the surfactant used. For naphthenic acid, the Cc was independent of the nonpolar oil, and within a certain surfactant type (ionic, nonionic, or extended ionic), it was likely independent of the surfactant. For the naphthenic acid systems, the segregation predicted via the bifunctional model was consistent with experimental measurements of this segregation. Given that the bifunctional model only involves phase inversion experiments, it is a convenient method to determine the oil-like and surfactant-like nature of polar oils.

Percepción de la imagen corporal en adolescentes universitarios / Body image perception among university adolescents

Los adolescentes son vulnerables a la insatisfacción corporal (IC) por los cambios que experimentan. Se evaluó la percepción de la imagen corporal (PIC) y su relación con estrato socioeconómico (ESE), estado nutricional (EN), actividad física (AF), condición física (CF) y calidad de la dieta en adolescentes. El estudio fue descriptivo, correlacional, de campo y corte transversal en 143 adolescentes. Se evaluó la PIC y se midieron variables nutricionales, socioeconómicas, AF y CF. La mayoría de los adolescentes pertenecieron al ESE III (37,6%), normopeso (87,4%), inactivos (55,2%) y con adherencia media a la dieta Mediterránea (67,1%). Los componentes de la CF y la CF general fueron superiores en el sexo masculino (p< 0,05). Los sujetos con deseo de un mayor volumen corporal fueron mayores en el sexo masculino, mientras que los que deseaban un menor volumen corporal fueron más frecuentes en el sexo femenino (p< 0,05). El IIC correlacionó con el IMC, los componentes de la CF y la CFg. En conclusión, en esta investigación fue posible relacionar la IC con componentes de la condición física y la condición física general en todos los sujetos y por sexo.

Adolescents are considered vulnerable to body dissatisfaction (BD) because of the changes they experience. Body image perception and its relationship with socioeconomic stratum (SES), nutritional status (NS), physical activity (PA), physical condition (PC) and diet quality among adolescents was evaluated. The study was descriptive, correlational, and cross sectional; 143 adolescents participated. Perception of body image was evaluated and nutritional, socioeconomic, AF and CF variables were measured. The majority of the adolescents were to the third SES level (37.6%), normal weight (87.4%), inactive (55.2%) and with average adherence to the Mediterranean diet (67.1%). The components of PC and general PC were higher among males (p <0.05). Male subjects had a stronger desire for a greater body volume, while female subjects had a stronger desire for a lower body volume (p< 0.05). BD index correlated with body mass index, components of the CF and the CFg. In conclusion, CI was related to components of PC and general PC in all subjects.

Consumo de calcio y otros predictores de la densidad mineral ósea en adolescentes venezolanos / Calcium consumption and other predictors of bone mineral density in Venezuelan adolescents

La acumulación adecuada de masa ósea durante la adolescencia es un factor protector para osteoporosis y otras afecciones óseas, por tanto, resulta relevante la evaluación del consumo de calcio y de otros determinantes de la densidad mineral ósea (DMO), en adolescentes. Se evaluó el consumo de calcio, otros factores biológicos y de estilo de vida, como predictores de la DMO en adolescentes venezolanos. Se realizó un estudio transversal, correlacional en 60 adolescentes (15 a 18 años), de la cohorte 2011-2012 del Programa Igualdad de Oportunidades de la Universidad Simón Bolívar (USB). La DMO, y el consumo de calcio y bebidas antagonistas del metabolismo del calcio, se determinaron mediante un cuestionario semicuantitativo de frecuencia de alimentos; También se evaluó el estado nutricional (por índice de masa corporal) y el nivel de actividad física. En promedio, la ingesta de calcio fue adecuada (1183 mujeres y 1315 mg/d hombres) y las principales fuente de calcio fueron la leche y sus derivados. Sin embargo, el 42% de los individuos presentó un consumo de calcio por debajo de lo recomendado. Los niveles de actividad física fueron entre bajos y moderados. El 95% de los adolescentes presentaron una DMO adecuada para su edad, siendo el sexo y el consumo de calcio los principales predictores. El consumo de calcio es un determinante importante de la DMO, siendo necesario para garantizar una contribución dietética adecuada durante la adolescencia, con el fin de prevenir un riesgo de deficiencia nutricional que pueda afectar la salud ósea(AU)

The adequate accumulation of bone mass during adolescence is a protective factor against the development of osteoporosis and other bone conditions. Therefore, evaluation of the consumption of calcium and other determinants of bone mineral density (BMD) in adolescents is relevant. The consumption of calcium and other biological and lifestyle factors were evaluated as predictors of BMD in Venezuelan adolescents. A correlational cross-sectional study was conducted in a group of 60 adolescents (15-18 years old), of the 2011-2012 cohort of the Equal Opportunities Program of the Simón Bolívar University (USB). BMD, and the consumption of calcium and drinks antagonistic to calcium metabolism, were determined through a semi-quantitative food frequency questionnaire; the nutritional status (by body mass index) and the level of physical activity were also evaluated. On average, calcium intake was adequate (1183 women and 1315 mg/d men) and the main sources of calcium were milk and its derivatives. However, 42% of individuals had a calcium intake below recommended. The majority of adolescents presented BMI within normal values (78.4% women and 69.6% men). Physical activity levels were between low and moderate. 95% of adolescents presented an adequate BMD for their age, being sex and calcium consumption the main predictors. The calcium consumption is an important determinant of BMD, being necessary to ensure an adequate dietary contribution during adolescence, with the purpose of preventing a risk of nutritional deficiency that may affects bone health(AU)

Solid-Liquid-Liquid Wettability of Surfactant-Oil-Water Systems and Its Prediction around the Phase Inversion Point.

Surfactant-oil-water (SOW) systems are important for numerous applications, including hard surface cleaning, detergency, and enhanced oil-recovery applications. There is limited literature on the wettability of solid-liquid-liquid (SLL) systems around the surfactant phase inversion point (PIP), and the few references that exist point to wettability inversion accompanying the microemulsion (µE) phase inversion. Despite the significance of this phenomenon and the extreme changes in contact angles, there are no models to predict SLL wettability as a function of proximity to the PIP. Recent works on SLL wettability in surfactant-free systems suggest that SLL contact angles can be predicted with an extension of Neumann's equation of state (e-EQS) if the interfacial tension (IFT or γo-w) is known and if there is a good estimate for the interfacial energy between the wetting phase and the surface (γS-wetting liquid). In this work, IFT predictions for SOW systems around the PIP were obtained via the combined hydrophilic-lipophilic difference (HLD) and net-average-curvature (NAC) framework. To test the hypothesis that the combined HLD-NAC + e-EQS can predict wettability inversion around the PIP, with a given γS-µE, the contact angles (measured through the light oil phase, θO) for the µE of sodium dihexyl sulfosuccinate-toluene-saline water system were measured on high surface free energy (SFE) materials (glass, stainless steel, and mica) and on polytetrafluoroethylene (low SFE) around the PIP. Considering that at the PIP, most systems have a contact angle of 90°, an estimated γS-µE = 1/4γo-w@PIP was found to be suitable for the systems considered in this work and for systems presented in the literature. The largest deviations between the predictions and the experimental values were found in the positive HLD range (surfactant in the light oil phase). Although there is room for improvement, this framework can estimate the wetting behavior of SOW systems starting solely from formulation parameters.

Oil-induced formation of branched wormlike micelles in an alcohol propoxysulfate extended surfactant system.

The addition of oil to an extended surfactant-water system (sodium tetrapropylene glycol (2-ethyl)octyl ether sulfate, C10PO4SO4Na) induces the elongation of spherical micelles into oil-swollen branched wormlike micelles (WLMs) near the phase inversion point of the surfactant-oil-water (SOW) system. The hydrophilic-lipophilic-difference (HLD) framework, which has been associated with surfactant curvature, was successfully used to predict the conditions under which WLMs are produced for both polar and non-polar oils. At HLD = 0, the formation of low-curvature surfactant structures including WLMs and liquid crystals are favored in water-rich systems. Micellar growth begins around HLD = -0.5, and reaches a plateau upon the formation of a branched WLM network at HLD = 0. Above the entanglement concentration, the branched WLMs exhibit Maxwell and shear thinning behavior which is suitable for the suspension of nanoparticles, among others.

El engranaje institucional como elemento del enfoque sistemático de la innovación en Latinoamérica / The institutional gear as an element of systemic approach to innovation in Latin America

Resumen El enfoque sistémico de la innovación resalta la interrelación de los agentes e instituciónes, sin embargo, no reconoce la complementariedad institucional. El presente trabajo tuvo como objetivo diseñar y evaluar un indicador del constructo de "engranaje institucional" como un elemento que reconoce el impacto que una institución tiene sobre otra en los procesos de innovación, así como examinar la relación existente entre el índice de engranaje institucional y el crecimiento económico. Se utilizó el método de regresión lineal, considerando el PIB per cápita de 17 países de América Latina en el periodo de 1980 a 2014. Se usaron variables como la tasa de actividades empresariales (TAE), que mide la población involucrada; el porcentaje de la TAE, que tiene un producto o servicio nuevo; gobierno efectivo, Estado de derecho, leyes estables; y vínculos entre universidad-empresa, siendo clasificados como productos e insumos. El diseño del indicador de engranaje institucional resultó adecuado para reconocer la complementariedad en las instituciones y su papel en los procesos de innovación, además de confirmar que los países en donde se tiene un mayor índice de engranaje institucional presentan un crecimiento económico superior. Los resultados muestran que los países latinoamericanos deben impulsar el engranaje institucional para fortalecer su sistema nacional de innovación, y así lograr un progreso económico sostenido, como el que presentan la mayoría de los países desarrollados (Unión Europea y los Estados Unidos).

Abstract The systemic approach to innovation highlights the interrelationship between actors and institutions, but does not recognize the institutional complementarity. For that, this paper aims to design and assess an indicator of institutional gear as an element that recognizes the impact that an institution has over another in the innovation process, and the relationship between institutional gear index and economic growth. Linear regression was used by considering GDP per cápita of 17 Latin American economies for the 1980 to 2014 period. Variables such as the rate of entrepreneurial activity (REA) which measures population involved, the percentage of REA that a new product or service has, effective government, state rights, laws and stable links between university-companies were used. These were classified as outputs and inputs. The institutional gear design was suitable for recognizing the complementary between the institutions and their role in innovation processes, as well as establishing that the countries where they have greater institutional gear have higher economie growth. The results show that the Latin American countries must boost the institutional gear to strengthen their national innovation systems and thus achieve sustained economie growth, as that shown by most of the developed countries (European Union and the United States).

Risk Factors for Unfavorable Outcomes in Surgically Treated Brainstem Cavernous Malformations.

OBJECTIVE: Brainstem cavernous malformations (BSCMs) account for up to 18% of all intracranial cavernous malformations. Due to their complex anatomic location, they represent a significant challenge for neurosurgeons. As such, the identification of risk factors associated with negative outcomes is of significant importance. We analyze a series of 50 cases of BSCMs treated surgically in order to identify risk factors for unfavorable outcomes. METHODS: Patients who underwent surgical resection of BSCM at our institution between 2000 and 2015 were retrospectively reviewed. Univariate and multivariable logistic regression models were used to identify predictors of unfavorable outcomes, defined as those with a modified Rankin score (mRs) of >2. RESULTS: Fifty Latin American patients, with a mean age of 35.85 ± 13.06 years, consisting of 29 females (58%) and 21 males (42%), underwent surgical resection. Mean modified Rankin Scale (mRs) score at admission was 2.6 ± 1.05, and the mean BCSM size was 18.00 ± 7.19 mm. The rate of gross total resection was 92%. Overall, 80% of patients showed improved or unchanged clinical status at the last follow-up period; however, only 58% of patients had a favorable outcome with a mean mRs of 2.33 ± 1.136. Multivariable logistic binary regression identified hemorrhagic recurrence (P = 0.040), lower cranial nerve deficit (P = 0.019), and BSCMs >15 mm in diameter (P = 0.006) as predictive factors for unfavorable surgical outcomes. CONCLUSION: BSCM size, compromise of lower cranial nerves, and hemorrhagic recurrence before surgery were identified as risk factors associated with unfavorable outcomes of surgically treated BSCMs in this cohort.

Acid-Base Polymeric Foams for the Adsorption of Micro-oil Droplets from Industrial Effluents.

Separation of toxic organic pollutants from industrial effluents is a great environmental challenge. Herein, an acid-base engineered foam is employed for separation of micro-oil droplets from an aqueous solution. In acidic or basic environments, acid-base polymers acquire surface charge due to protonation or dissociation of surface active functional groups. This property is invoked to adsorb crude oil microdroplets from water using polyester polyurethane (PESPU) foam. The physicochemical surface properties of the foam were characterized using X-ray photoelectron spectroscopy, inverse gas chromatography, electrokinetic analysis, and micro-computed tomography. Using the surface charge of the foam and oil droplets, the solution pH (5.6) for maximum separation efficacy was predicted. This optimal pH was verified through underwater wetting behavior and adsorption experiments. The droplet adsorption onto the foam was governed by physisorption, and the driving forces were attributed to electrostatic attraction and Lifshitz-van der Waals forces. The foam was regenerated and reused multiple times by simple compression. The lowest trace oil content in the retentate was 3.6 mg L-1, and all oil droplets larger than 140 nm were removed. This work lays the foundation for the development of a new class of engineered foam adsorbents with the potential to revolutionize water treatment technologies.

Design of nonionic micelle-laden polysaccharide hydrogels for controlled delivery of hydrophobic drugs.

The incorporation of micelle self-assembly in hydrogels has been used to produce self-healing materials, materials with tunable mechanical properties, and hydrophilic or hydrophobic drug delivery systems. However, little is known about the connection among formulation - structure - properties (particularly transport) in these systems. This connection is explored in alkyl ethoxylate micelle-laden gellan gum hydrogels used as delivery system for the hydrophobic drug dexamethasone. Phase behavior maps and rheological characterization of the micelle-laden hydrogels indicate that their properties are largely dominated by the concentration and cloud point (CP) of the alkyl ethoxylate nonionic surfactant. The sol-gel temperature of the hybrid hydrogels was found to be close to the CP of the surfactant, and their storage modulus (G') was found to increase with increasing surfactant concentration. A detailed analysis of the phase behavior maps, and evaluations of the mesh size of the hybrid hydrogels suggest a novel mechanism whereby micelles associate with gellan gum strands during high temperature hydration, hindering the double-helix assembly of the strands upon cooling. This increases the number of single strands and the density of physical cross-links, reducing the mesh size of the hydrogel. This mesh size reduction led to a decrease in the effective diffusion coefficient of micelles in the gel, and extended the release time of dexamethasone from 2h in surfactant-free hydrogel to more than 2days in the micelle-laden hydrogel.

Predicting solubilisation features of ternary phase diagrams of fully dilutable lecithin linker microemulsions.

Fully dilutable microemulsions (µEs), used to design self-microemulsifying delivery system (SMEDS), are formulated as concentrate solutions containing oil and surfactants, without water. As water is added to dilute these systems, various µEs are produced (water-swollen reverse micelles, bicontinuous systems, and oil-swollen micelles), without the onset of phase separation. Currently, the formulation dilutable µEs follows a trial and error approach that has had a limited success. The objective of this work is to introduce the use of the hydrophilic-lipophilic-difference (HLD) and net-average-curvature (NAC) frameworks to predict the solubilisation features of ternary phase diagrams of lecithin-linker µEs and the use of these predictions to guide the formulation of dilutable µEs. To this end, the characteristic curvatures (Cc) of soybean lecithin (surfactant), glycerol monooleate (lipophilic linker) and polyglycerol caprylate (hydrophilic linker) and the equivalent alkane carbon number (EACN) of ethyl caprate (oil) were obtained via phase scans with reference surfactant-oil systems. These parameters were then used to calculate the HLD of lecithin-linkers-ethyl caprate microemulsions. The calculated HLDs were able to predict the phase transitions observed in the phase scans. The NAC was then used to fit and predict phase volumes obtained from salinity phase scans, and to predict the solubilisation features of ternary phase diagrams of the lecithin-linker formulations. The HLD-NAC predictions were reasonably accurate, and indicated that the largest region for dilutable µEs was obtained with slightly negative HLD values. The NAC framework also predicted, and explained, the changes in microemulsion properties along dilution lines.

Integrated Free Energy Model (IFEM) for microemulsions.

The Integrated Free Energy Model (IFEM) is a platform used to predict the solubilization of nonpolar oils in nonionic alkyl-polyethylene oxide (C(X)EO(Y)) micelles starting from a free energy balance of costs and gains when surfactants from empty micelles and oil from a continuous oil phase assemble to form an oil-swollen micelle. IFEM considers lipophilic interactions between surfactant tails and oil solubilized in the core of micelles, and the interaction between surfactant tails and the oil solubilized in the surfactant tail domain, as well as oil-oil and surfactant-surfactant tail interactions. Expressions to calculate these lipophilic interactions from van der Waals (VDW) interaction potential were introduced in a previous publication. In this article, two new surfactant-water interactions are considered, surfactant headgroup dehydration during solubilization, and surfactant tail group dehydration. These six interaction terms, in addition to two entropy of mixing contributions (in the lipophilic and in the hydrophilic domains) make up the eight terms of the IFEM platform. Of these terms, only the headgroup dehydration requires a calibrated parameter. After calibrating this parameter, the model is capable of predicting experimental solubilization data, and the experimental trends reflected by a semi-empirical model, the Hydrophilic-Lipophilic-Difference+Net-Average-Curvature (HLD-NAC). Although there are numerous approaches to predict the surfactant-oil-water (SOW) phase behavior, the IFEM platform is the only one, to the knowledge of the authors that produces an explicit connection between molecular interactions and experimental data for real SOW systems. The IFEM platform can be programmed in a personal computer using relatively inexpensive software and its explicit nature opens the possibility to introduce additional interaction terms for more complex SOW systems.

The Cloud Point of Alkyl Ethoxylates and Its Prediction with the Hydrophilic-Lipophilic Difference (HLD) Framework.

The hydrophobicity of surfactants has been described through different concepts used to guide the formulation of surfactant-water (SW) and surfactant-oil-water (SOW) systems. An integrated framework of hydrophobicity indicators could provide a complete tool for surfactant characterization, and insights on how their relationship may influence the overall phase behavior of the system. The hydrophilic-lipophilic difference (HLD) and the characteristic curvature (Cc) parameter, included in the HLD, have been shown to correlate with different hydrophobicity indicators including the hydrophilic-lipophilic balance (HLB), packing factor (Pf), phase inversion temperature (PIT), spontaneous curvature (Ho), surfactant partition (K(o-w)), and the critical micelle concentration (CMC). This work aims to investigate whether the HLD can further describe a concomitant hydrophobicity parameter, the cloud point (CP) of alkyl ethoxylates. After applying group contribution models to calculate the Cc of monodisperse (pure) nonionic alkyl ethoxylates, a linear correlation between the calculated Cc and the CP was observed for pure surfactants with 8 ethylene oxide (EO) units or less. Furthermore, using an apparent equivalent alkane carbon number (EACN) to represent the hydrophobicity of the micelle core, the HLD equation was capable of predicting cloud point temperatures of pure alkyl ethoxylates, typically within 5 °C. Polydisperse surfactants did not follow the linear CP-Cc correlation found for pure surfactants. After treating polydisperse samples using a liquid-liquid extraction procedure used to remove the most hydrophobic components in the mixture, the resulting treated surfactants fell in the correlation line of pure alkyl ethoxylates. A closer look at the partition behavior of these treated surfactants showed that their partition, Cc and cloud point are dominated by the most abundant ethoxymers in the treated surfactant. The HLD also predicted the cloud point depression of treated surfactants with increasing sodium chloride concentration. This work shows how the HLD framework could be extended to predict the behavior of SW systems.