H3PO4-induced micellization of styrene-ethylene oxide block copolymers in toluene solutions

In toluene/dimethoxyethane (80/20)_v solution, copolymers containing 11, 33, and 51 mol% of oxyethylene residues and having a fixed PS-segment molecular weight of ~60,000 g/mol, are dissolved molecularly. Doping with 10, 20, and 50 mol% of H₃PO₄ based on the oxyethylene content, induces varying degrees, of micellization in the respective block copolymer solutions. Light scattering and viscometry were used to evaluate the relationship between block-copolymer composition and the state of aggregation for solutions of styrene/ethylene oxide block copolymers as a function of solution concentration and level of doping with phosphoric acid. Specifically, diffusion coefficients, hydrodynamic radii, and critical micelle concentration were evaluated by dynamic light scattering. Radii of gyration were obtained by complementary static light scattering measurements. In all three block copolymers, complete micellization is realized at the 50 mol% H₃PO₄ doping level. At the 20 mol% H₃PO₄ doping level, complete micellization is induced with the copolymers containing 11 and 33 mol% of oxyethylene residues.     

Correlation of nonionic surfactant structure and solubility with textile wetting

The effect of nonionic surfactant structure with respect to textile wetting efficiency has been studied. A correlation has been shown to exist between wetting speed and molecular diffusion rate, critical micelle concentration, area per molecule (as deduced from surface tension versus concentration measurements), extent of adsorption and temperature. The slope of the log wetting time versus log concentration curve is dependent upon temperature, cloud point, critical micelle concentration and area per molecule. Log concentration for ten-second wetting is shown to be inversely proportional to the diffusion constant which in turn is a function of the critical micelle concentration. Concentration coefficients of wetting indicate that the most efficient wetting is obtained at or very near to the critical micelle concentration. Presented at the AOCS Meeting, Cincinnati, October 1965.     

Surfactant properties of purified polyglycerol monolaurates

A series of purified polyglycerol monolaurates (PGML), such as di-, tri-, tetra-, and pentaglycerol monolaurates, were synthesized, and their surfactant properties in aqueous solutions were examined. The surfactant properties of PGML were compared with those of n-dodecyl polyoxyethylene monoethers (C₁₂EO_n) to examine the function of the hydrophilic part of these compounds. The critical micelle concentration (CMC) values and the surface tension at CMC of PGML and C₁₂EO_n increased linearly with an increase in the number of glycerol and oxyethylene units, respectively; the slope of the increase was greater for PGML than C₁₂EO_n. The minimum surface area per molecule of PGML was smaller than that of C₁₂EO_n at the air/aqueous solution interface. The initial foam heights of the surfactants at the CMC increased with an increase in the number of glycerol or oxyethylene units, and the foam heights of PGML were consistently higher and more stable than those of C₁₂EO_n. Detergency depended on a reduction in interfacial tension. Triglycerol monolaurate showed the lowest interfacial tension and the highest detergency among all the surfactants tested. Overall, the PGML showed better performance in all the surfactant properties tested than C₁₂EO_n. It is noteworthy that the surfactant properties of PGML having few glycerol units (di- to tetraglycerol monolaurates) are on par with those of C₁₂EO_n having many oxyethylene units (hexa- and octaoxyethylene). These results suggest that PGML having a secondary hydroxyl group on every glycerol unit of the hydrophilic part could be more hydrophilic than C₁₂EO_n; this characteristic feature guaranteed the superior surfactant properties of PGML.     

Molecular weight distribution of nonionic surfactants. III. Foam,wetting, detergency,emulsification and solubility properties of normal distribution and homogeneous p,t-octylphenoxyethoxyethanols

The effect of mol wt distribution on the foaming, wetting, detergency, emulsification and solubility properties of p,t-octylphenoxyethoxy-ethanols (OPE's) has been studied by comparing normal distribution and homogeneous compounds: Ross-Miles foam studies indicate that, although homogeneous OPE_7-10 are higher in initial foam height than normal distribution OPE_7-10, their foam stability is poorer. Hard surface and textile wetting were studied by contact angle determinations and the Draves' skein test, respectively. An exact correlation exists between hard surface wetting by solutions of OPE's of a Teflon surface and surface tension lowering. Normal distribution OPE's are, in general, better hard surface wetting agents than the corresponding homogeneous compounds. In textile wetting, normal distribution OPE_5-10 are approximately equivalent in performance and by implication are probably equivalent in wetting performance to the corresponding homogeneous compounds. Hard surface detergency studies show that normal distribution OPE's are generally slightly superior in detersive power to homogeneous OPE's at corresponding ethylene oxide chain lengths. OPE₁₀ is the best hard surface detergent of the OPE series, there being no distinguishable difference in performance between homogeneous and normal distribution OPE₁₀. Emulsification studies on the system, water-isooctane, show that only normal distribution OPE₅ is capable of forming stable o/w emulsions. Both homogeneous and normal distribution OPE₃ and OPE₄ form stable w/o (invert) emulsions. Solubility studies in isooctane and Ultrasene show that homogeneous OPE₄ is soluble at lower temp than the corresponding normal distribution compound. Studies of aqueous OPE solutions at temp above their cloud points show that solubility of both homogeneous and normal distribution materials is of the same order of magnitude as their critical micelle concn and that homogeneous OPE₄ is more soluble than normal distribution OPE₄.     

α-Sulfonato palmitic acid methyl ester-hexaoxyethylene monododecyl ether mixed surfactant system: Interfacial,thermodynamic, and performance property study

Interfacial, thermodynamic, and performance properties of aqueous binary mixtures of α-sulfonato palmitic acid methyl ester, C₁₄H₂₉CH(SO₃Na)COOCH₃(PES), and hexaoxyethylene monododecyl ether, CH₃(CH₂)₁₁(OCH₂CH₂)₆OH (C₁₂E₆), were investigated with tensiometric, conductometric, fluorimetric, and viscometric techniques. The critical micelle concentration (CMC), maximum surface excess, minimum area per molecule of surfactant at the air/water interface, and the thermodynamics of micellization and adsorption were determined. The CMC was very low for mixed systems, indicating probable use as a detergent with less effect on the environment because of surfactant biodegradability and less amount in the environment. The interaction parameter β^m, computed by using the theory of Rubingh and Maeda, indicated an attractive interaction (synergism) between the surfactant molecules, which was also confirmed by proton nuclear magnetic resonance studies in the mixed micelle. The micellar aggregation number (N _agg), determined by using a steady-state fluorescence quenching method at a total surfactant concentration of about ∼10 mM at 25°C, was almost independent of the surfactant mixture composition. The micropolarity and the binding constant (K _sv) for the C₁₂E₆/PES mixed system were determined by the ratio of the intensities (I ₁/I ₃) of the pyrene fluorescence emission spectrum, and the local microenvironment inside the micelle was found to be polar. The viscosity of the mixed system at all mole fractions suggested that mixed micelles are nonspherical in nature. The cloud point of oxyethylene group-containing surfactants was increased by the addition of PES. Foaming was temperature dependent, and a 1∶1 mixed system showed minimum foaming. All performance properties were composition dependent.     

Synthesis and surface measurements of surfactants derived from dehydroabietic acid

Dehydroabietates with poly(ethylene oxide) chains of average m=12, 17, and 45 units [DeHab(E) _m ] were synthesized. The adsorption at the liquid-vapor interface was measured, and the adsorbed amount and critical micelle concentrations (CMC) were determined. The foamability, the foam stability, wetting properties, and cloud points, with and without salt content, were studied. The results were compared with common linear alkyl ethoxylates, nonylphenol ethoxylates, and cholesterol ethoxylates. The dehydroabietic acid as hydrophobe was found to result in the same CMC as a linear dodecyl chain. DeHab(E)₄₅ was found to be insoluble above 400 mg/L, but the surface tensions at lower concentrations were similar to those of the C_11–13E_38–40 surfactants, which exhibit CMC in aqueous media. The foaming behavior of the DeHab(E)₁₂ and DeHab(E)₁₇ surfactants was about the same as for common linear C _n E _m surfactants. The foamability as well as the foam stability increased with ethylene oxide (EO) chain length. The cloud point was depressed by increased salt concentration and increased with the number of EO units in the head group. The cloud point was significantly lower than for the corresponding surfactant with a dodecyl chain with similar EO chain length. The wetting results, obtained by measuring the contact angle at similar surface tensions, indicate that surfactants of the DeHab(E) _m type are more efficient wetting agents than both disaccharide sugar surfactants and C _n E _m type surfactants.     

Contact angle of surfactant solutions on precipitated surfactant surfaces. III. Effects of subsaturated anionic and nonionic surfactants and NaCl

The contact angles of saturated calcium dodecanoate (CaC₁₂) solutions containing a second subsaturated surfactant on a precipitated CaC₁₂ surface were measured by using the drop shape analysis technique. The subsaturated surfactants used were anionic sodium dodecylsulfate (NaDS), anionic sodium octanoate (NaC₈), and nonionic nonylphenol polyethoxylate (NPE). Comparing at the critical micelle concentration (CMC) for each surfactant, NaC₈ was the best wetting agent, followed by NaDS, with NPE as the poorest wetter (contact angles of 32⁰, 42⁰, and 62⁰, respectively). Surface tension at the CMC increased in the order NaC₈<NPE<NaDS, and subsaturated surfactant adsorption increased in the order NPE≪NaDS (1.4 vs. 84 μmole/g); adsorption of the NaC₈ was not measurable. Interfacial tension (IFT) reduction at the solid-liquid interface due to subsaturated surfactant adsorption is an important contribution to contact angle reduction, in addition to surface tension reduction at the air-water interface. Surfactant adsorption onto the soap scum solid is crucial to solid-liquid IFT reduction and to good wetting. The fatty acid was the best wetting agent of the three surfactants studied, probably because calcium bridging with the carboxylate group synergizes surfactant adsorption onto the solid of the higher molecular weight soap. NaCl added to NaDS surfactant results in depressed CMC, lower surface tension at the CMC, decreased NaDS adsorption onto the solid, and decreased reduction in solid-liquid IFT. The contact angle is not dependent on the NaCl concentration for NaDS. The NaCl causes an increased tendency to form monolayers, which decrease air-water surface tension, but a decreased tendency to form adsorbed aggregates on the solid; the two trends offset each other, so wettability is not affected by added salt. The Zisman equation does not describe the wetting data for these systems well except for NaDS, further emphasizing the danger of ignoring solid-liquid IFT reduction in interpreting wetting data in these systems.     

Surface active block copolymers: I. The preparation and some surface active properties of block copolymers of tetrahydrofuran and ethylene oxide

A new type of surface active block copolymer (TE type) having the general formula HO(C₂H₄O)_x(CH₂. CH₂CH₂CH₂O)_y-(C₂H₄O)_zH, was obtained by addition of ethylene oxide to polyoxytetramethylene glycols with molecular weight of 1000-3400. TE types in which the polyoxyethylene sections comprised more than 20–25% of the total weight are soluble in water, and the relation between cloud point and oxyethylene content for TE types was similar to that for propylene oxide-ethylene oxide block copolymers (Pluronics). Some surface active properties of TE types were examined in comparison with those of Pluronics and some other surfactants. The surface tension, foaming and antifoaming properties of TE types were comparable to those of Pluronics. Although the wetting power of TE types was poor, their suspending power (for carbon black) was superior to that of Pluronics in both aqueous and nonaqeuous media. The addition of TE types to some conventional detergents enhanced significantly their detergency. TE types showed a remarkable demulsifying action, on addition to some W/O emulsions.     

An optimization and modeling approach for H2O2/UV‐C oxidation of a commercial non‐ionic textile surfactant using central composite design

BACKGROUND: Industrial surfactants are biologically complex organics that are difficult to degrade and may cause ecotoxicological risks in the environment. Until now, many scientific reports have been devoted to the effective treatment of surfactants employing advanced oxidation processes, but there is no available experimental study dealing with the optimization and statistical design of surfactant oxidation with the well‐established H₂O₂/UV‐C process. RESULTS: Considering the major factors influencing H₂O₂/UV‐C performance as well as their interactions, the reaction conditions required for the complete oxidation of a commercial non‐ionic textile surfactant, an alkyl ethoxylate, were modeled and optimized using central composite design‐response surface methodology (CCD‐RSM). Experimental results revealed that for an aqueous non‐ionic surfactant solution at an initial chemical oxygen demand (COD) of 450 mg L^?1, the most appropriate H₂O₂/UV‐C treatment conditions to achieve full mineralization at an initial pH of 10.5 were 47 mmol L^?1 H₂O₂ and a reaction time of 86 min (corresponding to a UV dose of 30 kWh m^?3). CONCLUSION: CCD allowed the development of empirical polynomial equations (quadratic models) that successfully predicted COD and TOC removal efficiencies under all experimental conditions employed in the present work. The process variable treatment time, followed by the initial COD content of the aqueous surfactant solution were found to be the main parameters affecting treatment performance, whereas the initial H₂O₂ concentration had the least influence on advanced oxidation efficiencies. The H₂O₂ concentration and surfactant COD were found to be more important for TOC abatement compared with COD abatement. Copyright © 2009 Society of Chemical Industry     

Nonionic surfactants derived from a new hydrophobic base

Summary A versatile new class of nonionic surfactants has been prepared essentially from ethylene and propylene oxides. The new products are based upon the discovery that a polyoxypropylene glycol having a molecular weight of approximately 900 or higher will function as the hydrophobic unit of a nonionic surfactant which may presumably be represented as HO (C₂H₄O)_a (C₃H₆O)_b (CH₂O₄)_cH. By selection of a polyoxypropylene glycol having a suitable molecular weight and by adjusting the weight ratio of oxypropylene to oxyethylene units in the product, nonionics have been prepared which range in physical form from liquids to solids which are sufficiently hard that they may be flaked. The possibility of wide variation in the molecular weight of the hydrophobic unit and in the weight ratio of the hydrophobic to hydrophilic units in the molecules allows extensive tailoring of the products to give specific control of properties such as solubility in water, detergency, wetting action, and surface tension lowering. Presented at 25th annual fall meeting, American Oil Chemists' Society, Chicago, Ill., Oct. 8–10, 1951.     

Waterborne latex coatings of color: II. Surfactant influences on color development and viscosity

A matrix of coating variables, nonassociative versus associative thickeners, different latex median particle sizes, individual surfactants and colorants [carbon black (CB), red, and yellow pigments], was examined for their influence on variances in coatings rheology and color development. Within the different coating groups, the variable of interest in this study was the surfactant added to the colorant formulation. In all three colorant formulations, sodium dodecyl sulfate (an anionic surfactant) provided poorer color development (CD) than in applied formulations containing an equivalent nonylphenol oxyethylene (EO) surfactant. In CB formulations, nonionic surfactants with higher EO content provide improved color development at low (2 mM) concentrations, but near equality in CD is achieved with low EO surfactants at higher concentrations. In contrast to CB formulations, red and yellow colorants exhibit good color development with high EO content nonionic surfactants only at low nonionic surfactants concentrations. This variance appears to be related to the interactions of surfactants with inorganic pigments (talc and laponite) in the colorant formulation. The coating’s rheology is related to latex, thickeners, and surfactant components of the paint, as has been noted in previous studies, but not to the nature of the color pigment. The viscosity of the hydroxyethyl cellulose (nonassociative type) and HEUR (associative type) thickened paint decreased with colorant addition due to dilution effects. There were no unusual deviations with the NP(EO)_x surfactants, except when a large hydrophobe nonionic surfactant [e.g., C₁₈H₃₇(EO)₁₀₀] is added. In HEC thickened coatings, the viscosity decreases when C₁₈H₃₇-(EO)₁₀₀ is in the colorant due to that surfactant inhibiting depletion flocculation. In the C₁₈H₃₇(EO)₁₀₀ coatings containing the HEUR thickener, significant increases in viscosity were observed, above the dilution values observed with the colorant addition. This is related to the viscosity maximum in the low concentration of HEUR with the C₁₈H₃₇(EO)₁₀₀ surfactant. Color development is independent of the viscosity profile of the coating. Presented in part at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2003 in Philadelphia, PA.     

Effect of the octadecyl acrylate concentration on the phase behavior of poly(octadecyl acrylate)/supercritical CO2 and C2H4 at high pressures

Pressure–composition isotherms were measured for the CO₂/octadecyl acrylate system at 45.0, 80.0, and 100.0°C and at pressures up to 307 bar. This system exhibited type I phase behavior with a continuous mixture‐critical curve. The solubility of octadecyl acrylate for the CO₂/octadecyl acrylate system increased as the temperature increased at a constant pressure. The experimental results for the CO₂/octadecyl acrylate system were modeled with the Peng–Robinson equation of state. A good fit of the data was obtained with the Peng–Robinson equation of state with one adjustable parameter for the CO₂/octadecyl acrylate system. Experimental cloud‐point data for the poly(octadecyl acrylate)/CO₂/octadecyl acrylate system were measured from 36 to 193°C and at pressures up to 2100 bar, and the added octadecyl acrylate concentrations were 11.9, 25.9, 28.0, 35.0, and 40.0 wt %. Poly(octadecyl acrylate) dissolved in pure CO₂ up to 250°C and 2100 bar. Also, adding 45.0 wt % octadecyl acrylate to the poly(octadecyl acrylate)/CO₂ solution significantly changed the phase behavior. This system changed the pressure–temperature slope of the phase‐behavior curves from an upper critical solution temperature (UCST) region to a lower critical solution temperature region as the octadecyl acrylate concentration increased. Cloud‐point data to 150°C and 750 bar were examined for poly(octadecyl acrylate)/C₂H₄/octadecyl acrylate mixtures at octadecyl acrylate concentrations of 0.0, 15.0, and 45.0 wt %. The cloud‐point curve of the poly(octadecyl acrylate)/C₂H₄ system was relatively flat at 730 bar between 41 and 150°C. The cloud‐point curves of 15.0 and 45.0 wt % octadecyl acrylate exhibited positive slopes extending to 35°C and approximately 180 bar. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 372–380, 2002     

Effects of Surfactant Hydrophilicity on the Oil Solubilization and Rheological Behavior of a Nonionic Hexagonal Phase

The effects of surfactant hydrophilicity on the phase behavior and rheology of a hexagonal phase (H₁) and related O/H₁ emulsions in a water/C₁₂EO _n /isohexadecane system (n = 7, 9) have been investigated. In this phase behavior study, a variety of surfactant aggregates (micellar, W_m; hexagonal, H₁; bicontinuous cubic, V₁; lamellar, L_α; inverse micellar, O_m) have been observed in water-C₁₂EO _n binary systems. The oil solubility of different surfactant aggregates was strongly affected by the surfactant hydrophilicity, i.e., surfactant aggregates in the C₁₂EO₇ system could solubilize a larger amount of oil than those in the C₁₂EO₉ system. It can be inferred that the surfactant with long hydrophilic head groups could be closely packed in the interface, leading to a reduction in the oil solubility in the micellar core due to the strong head group interaction. Interestingly, the rheology of the H₁ phase also exhibits behavior that is dependent on the surfactant hydrophilicity, i.e., high values of the elastic modulus G′ and complex viscosity |η*| have been observed in the C₁₂EO₉ system, possibly due to the strong neighboring head group interaction. Hexagon structure of the H₁ phase was calculated by using the Bohlin model. The viscosity of the O/H₁ emulsions decreases with increasing oil concentration, possibly due to the low volume fraction of the continuous phase (the H₁ phase).     

Removal of Copper(II) from a Concentrated Sulphate Medium by Cloud Point Extraction Using an N,N′-Bis(salicylaldehyde)Ethylenediimine Di-Schiff Base Chelating Ligand

Various chelating ligands have been investigated for the cloud point extraction of several metal ions. However, limited studies on the use of the Schiff base ligands have been reported. In this work, cloud point extraction behavior of copper(II) with N,N′‐bis(salicylaldehyde)Ethylenediimine Schiff base chelating ligand, (H₂SALEN), was investigated in aqueous concentrated sulphate medium. The extraction process used is based on the formation of hydrophobic H₂SALEN–copper(II) complexes that are solubilized in the micellar phase of a non‐ionic surfactant, i.e. ethoxylated (9.5EO) tert‐butylphenol. The copper(II) complexes are then extracted into the surfactant‐rich phase above cloud point temperature. Different parameters affecting the extraction process of Cu(II), such as equilibrium pH, extractant concentration, and non‐ionic surfactant concentration were explored. The extraction of Cu(II) was studied in the pH range of 2–11. The results obtained showed that it was profoundly influenced by the pH of the aqueous medium. The concentration factor, C_f, of about 17 with extraction efficiency of E % ≈100 was achieved. The stoichiometry of the extracted complex of copper(II) was ascertained by the Yoe–Jones method to give a composition of 1:1 (Cu:H₂L). The optimum conditions of the extraction‐removal have been established as the following: (1) 1.86 × 10^?3 mol/L ligand; (2) 3 wt% surfactant; (3) pH of 8 (4) 0.5 mol/L Na₂SO₄ and (5) temperature of 60 °C.     

Continuous and scale‐up synthesis of high purity H2O2 by safe gas‐phase H2/O2 plasma reaction

A new generation of double dielectric barrier discharge (DDBD) reactor featured by a metal powder (MP) high voltage electrode is presented. The MP high voltage electrode not only has excellent homogeneous discharge performance but also has the advantage of without regular maintenance. Therefore, the MP‐DDBD reactor was proved to be suitable for the uninterrupted and safe synthesis of high purity H₂O₂ aqueous solution with up to 65 wt % concentration from the H₂/O₂ mixture. The scale‐up synthesis of H₂O₂ was successfully attempted in an integrated device based on the MP‐DDBD reactor. The future practical H₂O₂ synthesizer based on the MP‐DDBD reactor will be small and movable, and therefore, be convenient to supply high purity H₂O₂ on site for small scale users like semiconductor industry. © 2013 American Institute of Chemical Engineers AIChE J 60: 415–419, 2014     

Single step room temperature oxidation of poly(ethylene glycol) to poly(oxyethylene)-dicarboxylic acid

Poly(oxyethylene)-dicarboxylic acids were obtained in high yields by room temperature oxidation of poly(ethylene glycol)s of molecular weights in the 4000–100,000 range using Jone's reagent (CrO₃ and H₂SO₄) as the oxidizing agent. Oxidation by-products from the reaction mixture were eliminated by adsorbing chromium salts onto activated charcoal. The acid values of poly(oxyethylene)-dicarboxylic acids so synthesized were in agreement with the theoretical values. Poly(oxyethylene)-dicarboxylic acids were characterized by ¹H-NMR, IR spectroscopy. Spectral data were in agreement with the proposed structures of products. In summary, a convenient, one pot method for the synthesis of a wide range of poly(oxyethylene)-dicarboxylic acids was developed. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 883–890, 1998     

Effect of electrolytes on foaming of nonionic surfactant solutions

The effect of electrolytes and other additives on the foaming of solutions of the nonionic surfactant octoxynol 9 (Triton X-100) was investigated and correlated with their effect on the cloud point. Foams were generated by pouring solutions as a thin stream into a vertical tube. The height of the generally fast-draining foam columns was measured as a function of time, and their stability was rated according to the damage sustained within 13 min. The surfactant concentrations used, 0.050, 0.100 and 2.00%, were above the critical micelle concentration. Increasing concentrations increased foam height but not foam stability. The electrolytes NaCl and Na₂SO₄ salted the surfactant out. They reduced its cloud point in proportion to their concentration. They also reduced the foam height, albeit to a lesser extent than the cloud point, but hardly reduced the foam stability below the cloud point.     

Synthesis and Surface Properties Characterization of Perfluoroalkylated Oligo(oxyethylene)glycols

A series of perfluoroalkylated oligo(oxyethylene) glycols as non-ionic fluorinated surfactants was prepared. The synthesis was performed by adding a molecule of a oligo(oxyethylene)glycol of the general formula HO(CH₂CH₂O)_nOH (n = 1, 2, 4, 6.4, 22.3) to 2-(perfluorooctylmethyl) oxirane in the presence of catalytic amounts of a Lewis acid. This procedure led to the formation of an amphiphilic molecule characterized by an hydrophobic lipophobic perfluorinated tail and hydrophilic non-ionic oligo(oxyethylene)chain. Infra red spectroscopy, mass spectroscopy and multinuclear NMR spectroscopy allowed the chemical characterization of the synthesized compounds to be made. Critical micellar concentration, surface tension, interfacial tension and cloud point measurements carries out on aqueous solutions allowed us to evaluate the surface and interfacial properties of the perfluoroalkylated oligo(oxyethylene)glycols. In addition, surface pressure-area (π, A) diagrams allowed us to determine the principal parameters characterizing the state of their monolayers. The aim of the work was to investigate the effect of the hydrophilic chain length on physical and surface properties.     

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.     

Analysis of the wetting behaviour of pigments and the effectiveness of surfactants

A new test method is introduced to analyse the wetting behaviour of pigments and the effectiveness of surfactants. The method involves the study of torque vs time curves obtained during the wetting of pigments by surfactant solutions. These curves provide valuable information regarding the wetting behaviour of pigments and the ability of the surfactant to wet the pigment. To study the wetting behaviour, two pigments which varied widely in their surface character are studied with the same surfactant, while, to study the effectiveness of the surfactant, different surfactants with differing polarity are studied using the same pigment. The results are found to be consistent with the theoretical expectations.