Influence of Aqueous/Solid Interactions on Organic Droplet Shape in Liquid/Liquid/Solid Systems

Abstract

We report the results of a theoretical study of the complex phenomena relating to contact angle changes for hexadecane droplets on a gold surface in aqueous ionic surfactant solutions. This approach integrates changes in the nature of the solid absorbed surfactant phase through use of the quasi‐chemical approximation. This improvement is accomplished with minimal additional model complexity and provides evidence for changes in adsorbate structure as aqueous surfactant concentration is increased. The theoretical predictions are tested using previously published data regarding the contact angle of hexadecane on gold in sodium dodecyl sulfate and cetyl‐trimethylammonium bromide solutions.     

Contact angle of surfactant solutions on precipitated surfactant surfaces. II. Effects of surfactant structure,presence of a subsaturated surfactant,pH, and counterion/surfactant ratio

The contact angle of a saturated aqueous surfactant solution on the precipitate of that surfactant was measured by using the sessile drop method. The sodium and calcium salts of alkyl sulfates (C₁₂, C₁₄, and C₁₈) had advancing contact angles higher than those of alkyl trimethylammonium bromides (C₁₄, C₁₆, and C₁₈). The measured advancing contact angles for several surfactant solutions did not substantially change with varying surfactant/counterion ratios; therefore, the precipitating counterion concentration (e.g., water hardness) had little effect on the wettability. The contact angles of fatty acid (C₁₂ and C₁₆) solutions did not show any dependence on pH between a pH of 4 and 10. The contact angles of saturated calcium dodecanoate (CaC₁₂) solutions containing a second subsaturated surfactant (sodium dodecyl sulfate: NaDS) decreased with increasing NaDS concentrations until reaching the critical micelle concentration of the surfactant mixture. These results show that the second suractant can act as a wetting agent in this saturated surfactant system. Application of Young’s equation to contact angles showed that the solid/liquid surface tension can change substantially with surfactant concentration and be important in addition to the liquid/vapor surface tension in reducing contact angles. Application of the Zisman equation results in a “critical” surface tension for the CaC₁₂ or soap scum of 25.5 mN/m, which is comparable to difluoroethene.     

Effects of Electrolyte Concentration on Surfactant Adsorption to a QCM Immersed in Surfactant + Electrolyte Solutions

Abstract

Surfactant adsorption from aqueous electrolyte solutions onto metal surfaces was characterized through the use of a Quartz Crystal Microbalance (QCM). The need for a better understanding of the surfactant adsorption process became apparent in previous studies by Morton et al., directed toward the development of a thermodynamically-based model of oil removal from metal surfaces. These modeling efforts utilized existing data on surfactant adsorption data, yet required the estimation of surfactant adsorption phenomena, such as the transition between monolayer adsorption and multi-layer adsorption and the location of the critical micelle concentration (CMC). Experimental techniques utilizing the quartz crystal microbalance (QCM) have been shown to be highly reliable for measuring slight changes, on the order of a nanogram, in the adsorption behavior of surfactants from aqueous solutions. The current study demonstrates that the addition of low concentrations (< 100 mM) of sodium chloride to aqueous solutions of ionic surfactant can have a significant effect on the adsorption of the surfactant to a gold surface. An analysis of the QCM measurements as well as a discussion of the effects of salt addition on various solution properties will be presented. Impacts of the current results to previously published work as well as potential applications will be discussed.     

Effect of Ionic Strength on Oil Removal from Stainless Steel in the Presence of Ionic Surfactant

Abstract

Contact angles of oil droplets on solid surfaces provide useful insight into surfactant cleaning behavior. Contact angles of hexadecane and MAR‐TEMP^® 355, an industrial quench oil, on stainless steel were measured for ionic surfactant solutions as a function of ionic strength. The ionic strength of sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) solutions was modified by the addition of sodium chloride. Increases in the contact angle with additions of 1.0 mM and 2.5 mM NaCl were observed for the two oils in SDS and for hexadecane in CTAB. For the industrial quench oil, detachment occurred in CTAB concentrations above the critical micelle concentration; as a result, the equilibrium contact angle measurements were not measured. The critical concentration of CTAB decreased with increasing NaCl concentration. Oil‐removal studies indicate that increasing ionic strength by as little as 2.5 mM can result in improved cleaning. A theoretical insight previously used to explain contact‐angle behavior for a hexadecane‐gold system is used to describe the results obtained with the current system.     

Synthesis and aqueous solution properties of hydrophobically modified graft copolymer of sodium carboxymethylcellulose with acrylamide and dimethyloctyl(2‐methacryloxyethyl)ammonium bromide

The hydrophobically modified water‐soluble graft copolymer of sodium carboxymethylcellulose with acrylamide and dimethyloctyl(2‐methacryloxyethyl)ammonium bromide has been synthesized using potassium persulfate and dimethylaminoethyl methacrylate as initiators in aqueous solution. The structure and composition of the graft copolymer were characterized by infrared spectrum and elementary analysis. Molecular weight was determined by gel permeation chromatography. The solubility and viscosity of the graft copolymers in aqueous solution were investigated, as a function of copolymer concentration, added salt, temperature, shear rate, and surfactant. In addition, the intermolecular hydrophobic association in aqueous solutions in the presence of added salt and surfactant was demonstrated through the retention time from gel permeation chromatography measurement. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 537–542, 2000     

Contact Angle of Ethanol and n‐Propanol Aqueous Solutions on Metal Surfaces

The contact angles of the aqueous solution of ethanol and that of n‐propanol on copper, aluminum, and stainless steel surfaces are reported. The contact angles were measured under atmospheric conditions, and then under vapor‐liquid equilibrium conditions at 1 atm and different temperatures. The results showed the variations of the contact angles with the concentrations of aqueous solutions on different metal material surfaces with different roughness. Some unstable behavior of the wetting ability around the azeotropic point of a binary solution is reported. Influences of concentration, kind of materials, and the surface roughness on the wetting ability are discussed. The model for predicting the contact angle of alcohol aqueous solutions on metal surfaces under atmospheric and vapor‐liquid two‐phase equilibrium conditions at 1 atm is derived from the Young equation.     

Limitation of the Young-Dupré Equation in the Analysis of Adhesion Forces Involving Surfactant Solutions

The atomic force microscope was used to measure adhesion forces between polyethylene particles, serving as model oil droplets, and mineral substrates (fluorite and quartz) in aqueous solutions of ethoxylated alcohols. Also, contact angles were measured in the kerosene–ethoxylated alcohol solution–mineral systems. Correlations obtained between adhesion and surfactant concentration for the polyethylene–aqueous solution–quartz system differs significantly from those predicted by the Young-Dupré equation for the kerosene–aqueous solution–quartz system. Interactions, characteristic for such aqueous systems, which contribute to the pull-off forces measured by atomic force microscopy are not included in the Young-Dupré equation, and are primarily responsible for the inconsistency in the adhesion versus surfactant concentration relationship obtained from contact angle measurements.     

Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with 1‐Octanol

Abstract

Pseudohydroxide extraction (PHE) was investigated for recovering sodium hydroxide (NaOH) from alkaline process solutions. PHE relies on the deprotonation of a lipophilic weak acid by hydroxide ion with concomitant transfer of sodium ion into an organic phase. Contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and NaOH in the aqueous phase, thus leading to a process in which NaOH equivalents are transferred from an alkaline feed solution to an aqueous stripping solution. In this work, we investigated PHE using a process‐friendly diluent—Isopar^® L. The lipophilic cation exchanger 3,5‐di‐tert‐butylphenol (35‐DTBP) was used as the extractant. The Isopar^® L diluent was modified with 1‐octanol to improve its solvation properties and the solubility of 35‐DTBP so that practical Na⁺ concentrations could be achieved in the process solvent. The PHE mechanism at process‐relevant conditions was explored by Raman and Fourier transform infrared spectroscopic measurements. Complementary electrospray ionization mass spectrometry studies were also performed. Equilibrium computer modeling suggested that the Na⁺ extraction behavior can be largely explained by the formation of 1∶1 and 1∶2 Na/35‐DTBP species in the organic phase. Extraction isotherms obtained using simulated caustic leaching solutions indicate the potential utility of this approach for recycling NaOH from complex alkaline mixtures.     

Whitening regenerated cellulose fibers using fluorescent agent,surfactants, and salt—color indices measurements

The whitening efficiency of regenerated cellulose fibers using sodium 4,4′‐distyrylbiphenyl sulfonate in the presence of an anionic surfactant (sodium dodecylsulfate) and a cationic surfactant (dodecyl trimethyl ammonium chloride) and salt (NaCl) was determined by fluorescence spectroscopy and color index values (brightness, whiteness, and yellowness). Epifluorescence images gave an intense blue color with an apparent uniform emission distribution. In absence of salt, the whitening efficiency was higher for aqueous solutions containing cationic surfactant below critical micellar concentration (cmc). In presence of salt, whitening efficiency was higher for anionic surfactant and more important. The concentration of surfactant required for greater brightness, whiteness, and yellowness was lower than that required in absence of salt. These data were discussed by the decrease of the cmc and by the screening of the modified cellulose fibers by counter ions coming from the salt. The role of surfactants was explained by the admicelization during the sorption process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Salt Effects on the Recovery of Phenol by Liquid‐Liquid Extraction with Cyanex 923

Abstract

In this work, the effect of salt addition on the recovery of phenol from a 46 g/L aqueous solution simulating a phenolic resin plant effluent by liquid‐liquid extraction at 298 K has been studied by using an organic phase containing 0.6 M Cyanex 923 extractant in ShellSol T. Addition of sodium sulfate, potassium nitrate, and sodium chloride to the aqueous phase was tested and sodium chloride was selected. Based on the obtained results, a study of phenol recovery process was undergone by taking advantage of the salting‐out effect. Equilibrium curves are presented for liquid‐liquid extraction with and without salt addition to the aqueous phase. An integrated process involving salting‐out and liquid‐liquid extraction was proposed. The stripping concentrates can be reused for phenolic resin production.     

Colloid‐Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part IV. Effect of Added Salt on the Surfactant Leakage in Surfactant Solutions and Surfactant–Polymer Mixtures

Abstract

The critical aggregation concentration (cac) in surfactant–polymer mixtures approximates a lower limit to the surfactant concentration in the permeate (surfactant leakage) in polyelectrolyte micellar‐enhanced ultrafiltration. Here, the cac was measured at different salinities by using surface tension measurements. It was found that the cac increases slightly with the addition of simple salt, then the cac value decreases at higher salt concentration. The critical micelle concentration (CMC), which approximates surfactant leakage in micellar systems (no polymer), decreases monotonically with increasing salinity for ionic surfactants. The surfactant leakage in colloid‐enhanced ultrafiltration (CEUF) processes is investigated by using a dialysis method in the presence of three phenolic solutes with various degrees of chlorination: 2‐monochlorophenol (MCP), 2,4‐dichlorophenol (DCP), and 2,4,6‐trichlorophenol (TCP). Cetylpyridinium chloride (CPC) or n‐hexadecylpyridinium chloride is used as a cationic surfactant; and sodium poly(styrenesulfonate) (PSS) is used as an anionic polyelectrolyte. The effect of salinity and type of colloid is focused on here. In the absence of added salt, the cac can be over an order of magnitude less than the CMC, as can be surfactant leakage with added polymer. The added salt reduces the surfactant leakage in the micellar solution due to CMC reduction in the presence of electrolyte. In the surfactant–polymer mixture, the surfactant leakage is dramatically affected by salinity.     

Wetting Behavior of Aqueous Solutions of Binary Surfactant Mixtures to Poly(tetrafluoroethylene)

Measurements of the surface tension (γ _LV) and advancing contact angle () on poly(tetrafluoroethylene) (PTFE) were carried out for aqueous solutions of cetyltrimethylammonium bromide (CTAB), cetylpyridynium bromide (CPyB), sodium decylsulfate (SDS), sodium dodecylsulfate (SDDS), p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol)s, Triton X-100 (TX100) and Triton X-165 (TX165) and their mixtures. The results obtained indicate that the values of the surface tension and wettability of PTFE depend on the concentration and composition of the surfactants mixture. In contrast to Zisman finding, there was no linear dependence between cos and the surface tension of aqueous solutions of surfactants and their mixtures for all studied systems, but a linear dependence existed between the adhesional tension and solution surface tension for PTFE in the whole concentration range, the slope of which was –1, indicating that the surface excess concentration of surfactant at the PTFE–solution interface was the same as that at the solution–air interface for a given bulk concentration. It was also found that the work of adhesion of aqueous solutions of surfactants and their mixtures to PTFE surface did not depend on the type of surfactant, its concentration and composition of the mixture. This means that for the studied systems the interaction across PTFE–solution interface was constant, and it was largely of Lifshitz–van der Waals type. On the basis of the surface tension of PTFE and the Young equation and thermodynamic analysis of the work of adhesion of aqueous solutions of surfactants to the polymer surface it was found that in the case of PTFE the changes of the contact angle as a function of the total mixture concentration in the bulk phase resulted only from changes of the polar component of the solution surface tension.     

Contact angle of surfactant solutions on precipitated surfactant surfaces

In this study, the contact angle of a saturated aqueous surfactant solution onto the surface of a precipitate of that surfactant is investigated. Those precipitates include fatty acids (C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈), sodium salts of fatty acids (C₁₄, C₁₆, and C₁₈), calcium salts of fatty acids (C₈, C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈). On virgin surfaces, free fatty acids and calcium salts of fatty acids have advancing contact angles (θ_A) between 77 and 92°, with little dependence on alkyl chain length for C₁₂ and higher alkyl chains. The sodium salt of a fatty acid has a lower θ_A than the free fatty or the calcium salt of the soap. The calcium salt of dodecyl sulfate has a lower θ_A than the calcium salt of dodecanoic acid (θ_A = 46 vs. 82°), but the calcium salt of the 18-carbon hydrophobes showed nearly the same contact angle for the soap and the alkyl sulfate. Greasiness, or slipperyness, or a scummy feel of a precipitated surfactant does not necessarily correspond to a hydrophobic surface.     

Partition Coefficients of Alkyl Parabens and Ibuprofen in Micellar Systems

The partitioning of alkyl parabens and ibuprofen in aqueous solutions of nonionic and ionic surfactants is studied experimentally and via a priori predictions using the COSMO‐RS model. The effects of organic (Bu₄NBr) and inorganic (NaCl) electrolytes are examined. Addition of NaCl results in a slight increase in the partition coefficients of parabens in solutions of octylphenolpoly(ethyleneglycolether) and a more pronounced increase in the sodium dodecyl sulfate (SDS) system. The partition coefficients of ibuprofen increase on addition of NaCl to aqueous solutions of SDS and decrease if Bu₄NBr is added to dodecyl trimethyl ammonium bromide (DTAB) solutions. Good agreement between experimental and calculated data shows a high potential of COSMO‐RS in the prediction of micelle/water partition coefficients in the presence of electrolytes and makes it a valuable tool in drug and drug‐carrier design as well as in optimizing micellar reactions or micelle‐enhanced separation processes.     

Sorption of Azo Dyes onto a Mexican Surfactant‐Modified Clinoptilolite‐Rich Tuff

Abstract

The selectivity of a Mexican surfactant‐modified clinoptilolite‐rich tuff to retain azo dyes (red‐40, yellow‐5 and a mixture of them) from aqueous solutions has been investigated. The zeolitic material was modified with hexadecyltrimethylammonium bromide and then left in contact with azo dyes. The uptake was determined at different contact times and concentrations of dyes solutions. First order Elovich, and pseudo second order models as well as the lineal, Langmuir, and Freundlich isotherms were used to describe the experimental data. It was found that in single and binary solutions, under the experimental conditions, the modified zeolitic material retain preferentially the dye red‐40 in comparison to yellow‐5. The best models to describe the reaction rate and the sorption of azo dyes red‐40 and yellow‐5 by Mexican surfactant modified clinoptilolite‐rich tuff were pseudo‐second order and Langmuir models, respectively. These results show that surfactant modified clinoptilolite‐rich tuff from Villa de Reyes (San Luis Potosi, Mexico) could be considered as a potential adsorbent of azo dyes from aqueous solutions.     

Flowsheet Modeling and Testing of Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with Exxal® 8

Abstract

A conceptual counter‐current process flowsheet was developed for sodium hydroxide recovery from alkaline solutions via pseudohydroxide extraction (PHE). PHE relies on a simple sodium ion/proton exchange mechanism at elevated pH using a weak organic acid extractant. The contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and sodium hydroxide in the aqueous phase. In this work, the 3,5‐di‐tert‐butylphenol (35‐DTBP) cation exchanger was used in the Isopar^® L diluent modified with isooctyl alcohol Exxal^® 8. Equilibrium isotherms determined for PHE from pure sodium hydroxide solutions and simulated radioactive waste leachate were used to develop a semi‐empirical model that could be used for designing PHE process flowsheets. Using this model, a conceptual PHE flowsheet was developed for recovering NaOH from solutions generated by caustic leaching of radioactive tank sludges. The flowsheet consists of the extraction, scrub, and strip processes, each employing four equilibrium stages. The modeling of this flowsheet indicates 97% recovery of the sodium hydroxide from the waste leachate feed solution. An experimental demonstration, performed with a simulated radioactive waste leachate using batch contacts in a co‐current analog of the counter‐current flowsheet, confirmed the potential for practical application of PHE technology.     

Soil Clean Up by in-situ Surfactant Flushing. III. Laboratory Results

Abstract

Data on the solubilization of p-dichlorobenzene (DCB), naphthalene, and biphenyl in aqueous solutions of sodium dodecylsulfate (SDS) (0-100 mM concentration) indicate increases in effective solubilities of these hydrophobic compounds by factors of roughly 20 to 100. DCB is effectively removed from spiked clay-sand mixtures by leaching with SDS solutions in laboratory columns. Surfactant solutions loaded with DCB are satisfactorily treated by gentle extraction with hexane, and the recovered surfactant solution satisfactorily solubilizes biphenyl. A simple model for predicting the solubilization behavior of surfactants is developed and tested experimentally.     

Dynamic Analysis of the Removal of Fatty Acid from a Pet Surface Using a Quartz Crystal Microbalance

A quartz crystal microbalance (QCM) was used to study the removal of stearic acid from poly(ethylene terephthalate) (PET) substrate in aqueous alkali and surfactant solutions. The PET substrate was prepared on a QCM gold electrode by spin‐coating; its properties were examined by scanning electron microscopy, X‐ray photoelectron spectroscopy, and water contact angle measurements. As a result, the QCM electrode was found to be completely covered with a smooth PET film. To investigate the effect of soil deposition state on its removal, stearic acid (an oily soil model) was deposited onto the PET substrate with the Langmuir–Blodgett (LB) technique or by spraying. The QCM frequency was recorded during the removal of stearic acid from the PET substrate in aqueous solutions. In NaOH solution, stearic acid deposited by the LB method was more rapidly removed than when deposited by the spraying method. However, the LB films of stearic acid were difficult to be removed in surfactant solutions. With respect to removal behavior of spray‐deposited stearic acid in surfactant solutions, the results determined by the QCM method were compared with those from microscopic image analysis. The removal efficiencies in the sodium dodecyl sulfate solution were in good agreement between the two methods. However, in the alkyl ethoxylate solution, the removal efficiencies obtained by the QCM method were larger than those from microscopic image analysis. These experimental results were explained by the removal mechanism of stearic acid by the alkali and surfactant solutions.     

Reverse Micellar Extraction and Backextraction of l-Lysine with Three Dialkyl Sodium Phosphinates in Pentanol/Isooctane Mixtures

Abstract

The effects of pH, salt concentration, and structure of the surfactant head on the reverse micellar extraction and backextraction of l-lysine in pentanol/isooctane mixtures have been comparatively studied. The surfactants used were bis(2,4,4-trimethylpentyl) sodium phosphinate (NaPOO), bis(2,4,4-trimethylpentyl) sodium monothiophosphinate (NaPSO), and bis(2,4,4-trimethylpentyl) sodium dithiophosphinate (NaPSS). Since all three surfactants have the same two hydrocarbon tails and differ only in their polar heads, their comparative study gives some insight into the effect of the surfactant head group on the reverse micellar extraction and backextraction of amino acids. The results show that the nature of the surfactant head, the pH, and the salt concentration have a major effect on the reverse micellar extraction of l-lysine. The percent of l-lysine extracted to the organic phase, at fixed surfactant and pentanol concentrations, decreased in the order NaPSS > NaPSO > NaPOO. The exchange with the three surfactants can be easily reversed for the backextraction of amino acids into a new surfactantfree aqueous solution.     

Interaction Between Ionic Liquids and Gemini Surfactant: A Detailed Investigation into the Role of Ionic Liquids in Modifying Properties of Aqueous Gemini Surfactant

Tuning physicochemical properties of aqueous surfactant solutions comprised of normal or reverse micelles by external additives is of utmost importance due to the enormous application potential of surfactant‐based systems. Unusual and interesting properties of environmentally benign ionic liquids (IL) make them suitable candidates for this purpose. To understand and establish the role of IL in modifying properties of aqueous gemini surfactants, we studied the effect of the IL, 1‐hexyl‐3‐methylimidazolium bromide ([Hmim][Br]) and 1‐octyl‐3‐methylimidazolium bromide ([Omim][Br]) on the properties of the aqueous cationic gemini surfactant 1,6‐hexanediyl‐α,ω‐bis(dimethyltetradecyl)ammonium bromide (14‐6‐14,2Br^?). The behavioral changes were investigated by measuring the critical micelle concentration (CMC) using electrical conductance, surface tension, dye solubilization and fluorescence probe measurements at 298.15 K. It was observed that the CMC of 14‐6‐14,2Br^? gemini surfactant decreases with addition of IL, thus favoring the micellization process. An increase in micellar size was observed at lower IL concentration using dynamic light scattering, with a decrease in aggregation number (N_agg) determined from fluorescence probe quenching measurements. It is noteworthy that the extent of modulation of the micellar properties is different for both the IL due to their structural differences. IL behave like electrolytes at lower concentrations and cosurfactants at higher concentrations and form mixed micelles with the cationic gemini surfactant showing an increase in N_agg.