Properties of Sodium Methyl Ester Alpha-Sulfo Alkylate/Trimethylammonium Bromide Mixtures

The surface properties of binary mixtures of anionic sodium methyl ester ??-sulfo alkylate (C _m MES) and cationic alkyl trimethylammonium bromide (C _n TAB) of different carbon chain length have been studied in the present work. The critical micelle concentration (CMC) that was obtained from the plots of surface tension (??) versus concentration showed that mixed surfactants have CMC values that were about 10 times lower than their single components. The large negative values for both interaction parameters suggest the existence of strong synergism between the oppositely charged surfactant molecules. The effect of hydrocarbon chain length of either surfactant was also compared and results showed that the effect of cationic surfactant chain length dominated that of the anionic surfactants. It was also discovered that certain mixed surfactant combinations behave differently from the expected trend.     

Emulsion polymerization of methyl methacrylate in concentration of emulsifiers below their CMCs—polymerization rate,particle size,and particle-size distribution

The emulsion polymerization of methyl methacrylate (MMA) in concentration of emulsifiers below their critical micelle concentrations (CMCs) initiated by K₂S₂O₈ (KPS) was studied. It was observed that the initiator concentration has little effect on both polymerization rate and particle size. However, the polymerization rate is faster and particle size is smaller obviously when decreasing the ratio of the water/monomer or increasing the temperature of polymerization or the amount of the emulsifier. In the range of a 200–400 rpm stirring speed, the polymerization rate is almost unchanged although the particle size become larger with increase in the stirring speed. The monodisperse particle (size about 100–200 nm) can be obtained using this process. The mechanism of emulsion polymerization of MMA in the emulsifier concentration below its CMC is discussed. © 1995 John Wiley & Sons, Inc.     

Experimental Study of CMC Evaluation in Single and Mixed Surfactant Systems, Using the UV–Vis Spectroscopic Method

In this study, the critical micellar concentration (CMC) of anionic, cationic and nonionic surfactants was determined using the UV–Vis spectroscopic method. Sodium lauryl sulfate (SDS) as anionic, hexadecyl-trimethyl-ammonium bromide as cationic, tert-octylphenol ethoxylates TOPEON (with N = 9.5, 7.5 and 35) and lauryl alcohol ethoxylate (23EO) as nonionic surfactants have been used. Concentration of surfactants varies both from below and above the CMC value in the pyrene solution. In addition, the amount of the CMC was determined using the values from the data obtained from the graph of absorbance versus concentration of surfactants. A comparative study was conducted between the results of the present study and the literature which shows a good agreement, in particular for TOPEO9.5 and LAEO23. Furthermore, the CMC value of SDS (as an ionic surfactant) in the presence of nonionic surfactants was also examined. The result reveals that with addition of small amount of nonionic surfactant to the anionic SDS surfactant, a decline in the CMC value of the anionic–nonionic system relative to the CMC of pure anionic surfactant was observed. In addition and for the first time, the effect of UV irradiation on the size of the micelle formations was studied. It was found that UV irradiation causes the formation of smaller micelles which is of prime concern in membrane technology.     

The study of Sunset Yellow anionic dye interaction with gemini and conventional cationic surfactants in aqueous solution

In the present study, the interaction of an anionic azo dye, Sunset Yellow, with two cationic gemini surfactants with different spacer lengths (s = 3, 6 methylene groups) and their monomeric counterpart, dodecyl trimethyl ammonium bromide (DTAB), was investigated by surface tension, UV–Vis spectroscopy, and zeta potential measurements. The critical micelle concentration (CMC) was determined from plots of the surface tension (γ) as a function of the logarithm of total surfactant concentration. Moreover, the values of binding constants (K_b) of dye-surfactant complexes were calculated by UV–Vis spectroscopy. The UV–Vis spectra showed that the dye–surfactant interaction occurred in the solution at concentrations far below the CMC of each surfactant. The gemini surfactant with a shorter spacer showed stronger interaction with dye in comparison to DTAB and the gemini with longer spacer. The effect of surfactant chemical structure on solubilization of dye-surfactant aggregates at surfactant concentration above CMC was investigated by zeta potential.     

Influence of Spacer Nature on the Aggregation Properties of Anionic Gemini Surfactants in Aqueous Solutions

A series of anionic gemini surfactants with the same structure except the spacer nature have been studied. Their solution properties were characterized by the equilibrium surface tension and intrinsic fluorescence quenching method. The critical micelle concentrations (CMC), surface tension at cmc, C₂₀, and the micelle aggregation number (N) were obtained. The surface tension measurements indicate that these gemini surfactants have much lower cmc values and great efficiency in lowering the surface tension of water compared with those of conventional monomeric surfactants. Furthermore, the standard free energy of micellization for anionic gemini surfactants was also determined. The results showed that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in aqueous solutions. The surfactant with a hydrophilic, flexible spacer was more readily able to form micelle compared with the surfactant with a hydrophobic, rigid spacer, which leads to a lower CMC value, larger N, more negative free energy of micellization, and a more closely packed micelle structure.     

Semi-continuous emulsion copolymerization of butyl methacrylate with polymerizable anionic surfactants

Two polymerizable anionic surfactants sodium 4-(ω-acryloyloxyalkyl)oxy benzene sulfonate (SABS-n, n=8 or 10) have been successfully used in the semi-continuous emulsion copolymerization with butyl methacrylate (BMA). After generating seeding particles in an emulsion consisting SABS-8 or SABS-10 and small amount of BMA using a redox initiator ammonium persulfate (APS)/tetramethylethylenediamine (TMEDA) at room temperature, most of BMA was added drop-wise to the polymerizing emulsion system during a period of 4-8 h. These emulsion copolymerizations produced nanosized latexes with high polymer/surfactant weight ratios up to about 12/1 and nearly monodisperse particles ranging from 18 to 33 nm in diameter. X-ray photoelectron spectroscopy results showed that SABS-n was significantly enriched on the surface of latex particles. The effects of concentrations of SABS-n, BMA, and APS/TMEDA and the latex characteristics during the continuous addition of monomer were studied. A possible polymerization mechanism was proposed.     

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C₁₂(EO)₅ and C₁₂(EO)₈] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.     

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.     

Study of the Interaction Between Methyl Orange and Mono and Bis-Quaternary Ammonium Surfactants

The solubilization and interaction of an azo-dye (methyl orange) with dodecyl trimethyl ammonium bromide and cationic gemini surfactants in the series of alkanediyl α,ω-bis[(dimethyl alkyl ammonium)bromide)] referred to as (m-s-m), m = 10, 12, 14 and s = 2, 3, 4 were investigated by means of UV–Vis spectroscopy. Aggregation with the anionic dye was reflected by a hypsochromic shift with a decrease in the intensity of the absorption band. The results also show a bathochromic shift followed by a sharp increase in the intensity of the maximum absorption band λ_max after the critical micellar concentration (CMC). This indicates that the dye solubility increased with increasing surfactant concentration. It was also observed that the aggregation of surfactant and dye takes place at a surfactant concentration far below the CMC of the individual surfactant. The effects of the chain length as well as the spacer length of gemini surfactants on the critical aggregation concentration and CMC were also examined. Moreover, the partition coefficients between the bulk water and surfactant micelles K _S and K _X as well as the Gibbs energies of distribution of dye between the bulk water and surfactant micelles were determined using the pseudo-phase model. The effect of the hydrophobic chain length and spacer of gemini surfactants on the distribution parameters is also reported.     

Critical micelle concentrations of ternary surfactant mixtures: Theoretical prediction with user-friendly computer programs and experimental design analysis

We studied the behavior of an aqueous ternary surfactant mixture composed of a nonionic surfactant and two anionic surfactants which differ in both surfactant hydrophobic tail length and surfactant hydrophilic head structure. We used an experimental design program to calculate the critical micelle concentrations (CMCs) of this ternary surfactant mixture over the entire range of solution compositions. As inputs, the experimental design methodology requires the values of the ternary surfactant mixture CMCs for a limited subset of solution compositions which is determined by the experimental design program. We showed that this subset of ternary surfactant mixture CMC values can either be measured experimentally or predicted theoretically. The theoretical CMCs were predicted by a series of userfriendly computer programs which are based on molecular-ther-modynamic theories describing single and mixed micelle formation. The experimental design program generated two surfaces describing the ternary surfactant mixture CMCs over the entire solution composition range—one based on the experimentally measured subset of CMC values, and the other based on the theoretically predicted CMC values for the same subset of solution compositions. We found that these two CMC surfaces agree very well, thus demonstrating the utility of the computerassisted molecular-thermodynamic modeling as a predictive tool in surfactant mixture characterization and design.     

Performance and Efficiency of Anionic Dishwashing Liquids with Amphoteric and Nonionic Surfactants

Performance and efficiency of anionic [sodium lauryl ether sulfate (SLES) and sodium α-olefin sulfonate (AOS)] and amphoteric [cocamidopropyl betaine (CAB)] as well as nonionic [cocodiethanol amide (DEA), various ethoxylated alcohols (C₁₂–C₁₅–7EO, C₁₀–7EO and C₉–C₁₁–7EO) and lauramine oxide (AO)] surfactants in various dishwashing liquid mixed micelle systems have been studied at different temperatures (17.0, 23.0 and 42.0 °C). The investigated parameters were critical micelle concentration (CMC), surface tension (γ), cleaning performance and, foaming, biodegradability and irritability of anionic (SLES/AOS) and anionic/amphoteric/nonionic (SLES/AOS/CAB/AO) as well as anionic/nonionic (SLES/AOS/DEA/AO, SLES/AOS/C₁₂-C₁₅-7EO/AO, SLES/AOS/C₁₀–7EO/AO and SLES/AOS/C₉–C₁₁–7EO/AO) dishwashing surfactant mixtures. In comparison to the starting binary SLES/AOS surfactant mixture, addition of various nonionic surfactants promoted CMC and γ lowering, enhanced cleaning performance and foaming, but did not significantly affect biodegradability and irritability of dishwashing formulations. The anionic/nonionic formulation SLES/AOS/C₉–C₁₁–7EO/AO shows both the lowest CMC and γ as well as the best cleaning performance, compared to the other examined dishwashing formulations. However, the results in this study reveal that synergistic behavior of anionic/nonionic SLES/AOS/ethoxylated alcohols/AO formulations significantly improves dishwashing performance and efficiency at both low and regular dishwashing temperatures (17.0 and 42.0 °C) and lead to better application properties.     

Surface and Biocidal Properties of Gemini Cationic Surfactants Based on Propoxylated 1,6-Diaminohexane and Alkyl Bromides

Two new classes of gemini cationic surfactants—hexanediyl-1,6-bis[(isopropylol) alkylammonium] dibromide {in the abbreviation form: C_nC₆C_n[iPr-OH] and C_nC₆C_n[iPr-OH]₂; alkyl: C_nH_{2n + 1} with n = 9, 10, 12 and 14}—have been synthesized by interaction of alkyl bromides with N,N′-di-(isopropylol)-1,6-diaminohexane and N,N,N′,N′-tetra-(isopropylol)-1,6-diaminohexane. The surface tension, electrical conductivity, and dynamic light scattering (DLS) techniques were used to investigate the aggregation properties of the gemini cationic surfactants in aqueous solution. The formation of critical aggregates at two concentrations in an aqueous solution from obtained gemini cationic surfactants were determined via the tensiometric method. Thus, these gemini cationic surfactants start to form aggregates at concentrations well below their critical micelle concentrations (CMC). The surface properties and the binding degree (β) of the opposite ion were tested against the length of the surfactant hydrocarbon chain and the number of the isopropylol groups in the head group. By applying the DLS technique, it was explored that how the number of isopropylol groups in gemini cationic surfactants with C₁₂H₂₅ chain affects the sizes of micelles at concentrations greater than CMC. It was discovered that the obtained gemini cationic surfactants have a biocidal character.     

Interaction between bisphenol A and micelles of ionic surfactants

Interactions between bisphenol A (BPA) and ionic surfactants—cationic hexadecyltrimethylammonium bromide (HTAB) and anionic sodium dodecylsulfate (SDS)—were studied by measuring interfacial tensions and the intensities of pyrene fluorescence. The critical micellar concentrations (CMC) decreased with an increase in the BPA concentration, and the degree of that decrease was greater in HTAB than in SDS. In those micelles, BPA interacted more strongly with HTAB than with SDS. Conversely, BPA adsorbed on the air-water interface cooperatively with the surfactants, even though almost no adsorption of BPA itself was observed. This cooperative adsorption was more enhanced with HTAB than with SDS. Thus, BPA worked on the surfactants to stabilize the micelles and interfacial adsorption. The stability gained by the addition of BPA was greater on the interface than in the micelle. This was evidence of decreased hydrophilicity of the head group of the ionic surfactant, which interacted with BPA, because this decrease acted on the surface activities of the surfactants more directly than on the micelle stabilities. Pyrene fluorescence measurements yielded identical results for the effect on micelle stabilities. It is noteworthy that the fluorescence intensity of peak 1, l ₁, decreased with an increase in BPA concentrations at constant concentrations of surfactant greater than the CMC, but the peak ratio, l ₁/l ₃, remained almost unchanged. This fact was also related to the interaction of BPA with the hydrophilic head groups in the surfactant micelle.     

Influence of ingredients in water-based polyurethane–acrylic hybrid latexes on latex properties

Polyurethane–acrylic (PU–AC) hybrid latexes were prepared. Main monomers for PU preparation were isophorone diisocyanate, DMPA (dimethylol propanic acid) and polypropylene oxides (PPO) of different molecular weights. Acrylic monomers included butyl acrylate, methyl methacrylate and a crosslinker, trihydroxymethyl propane triacrylates (TMPTA). Several important ingredients in PU–AC latex preparation, such as surfactants, initiator, DMPA and PU/AC ratio, etc., were varied, and their effects on latex properties studied. Compared with surfactant free latexes, a sharp increase in particle size was observed in latexes done with 0.1% of surfactant regardless of the nature of the surfactants used (anionic, nonionic and anionic with long chain of amphiphilic alkylphenyl polyethoxylate). Further increase in surfactant content, however, led to latexes with smaller particle size and narrower particle size distribution when compared between latexes prepared using a same surfactant. When amount of the oil soluble initiator, azobisisobutyronitrile, was increased, AC monomers conversion was increased. It is interesting to observe that PPO with long propylene oxides brought about larger particle size combined with broader size distribution and less charge on particle surface; whereas lower DMPA levels led to latexes also of larger size combined with broader size distribution but more charges on particle surface. AC monomer crosslinker, TMPTA, contributed to reduce particle size, narrower size distribution and lower particle surface charges. By increasing AC amount in PU–AC latex, latex particle size significantly increased accompanied by a remarkable increase in particle surface charges. Mechanisms of particle formation and of DMPA stabilization were discussed in order to understand the experimental results.     

Synthesis and Surface Properties of Anionic Gemini Surfactants having N-acylamide and Carboxylate Groups

A straightforward synthetic strategy to an anionic gemini surfactant having both N-acylamide and carboxylate groups in a molecule has been demonstrated. The surface properties of the anionic gemini surfactant, such as CMC (critical micelle concentration), C₂₀ (the concentration required to reduce the surface tension of the solvent by 20 mN/m), γ _CMC (the surface tension at the CMC), ∏ _CMC (the surface pressure at the CMC), Γ _max (the maximum surface excess concentration at the air/aqueous solution interface), A _min (the minimum area per surfactant molecule at the air/water interface), and the CMC/C₂₀ ratio (a measure of the tendency to form micelles relative to adsorbtion at the air/water interface), have been studied. The influence of the different concentrations of NaCl on the surface properties of the gemini surfactant has been discussed. The results have shown that the CMC values decreased with an increase in the concentration of NaCl indicating that the Na⁺ preferentially adsorbs onto the surface of the charged aggregate and facilitates the aggregate growth by suppressing the main impediment of electrostatic repulsion among head groups. Additionally, the values of Γ _max are always higher in salt solutions as compared to those in pure water due to their salting out effect. The larger pC₂₀ value indicates that the surfactant adsorbs more efficiently at the air/water interface and reduces surface tension more efficiently. In addition, the geminis in water show little or no break in their specific conductance versus surfactant molar concentration plots. This is attributable to protonation of the carboxylate group and strong Na⁺ release during micellization.     

Crosslinkable surfactants based on linoleic acid-functionalized block copolymers of ethylene oxide and ε-caprolactone for the preparation of stable PMMA latices

Amphiphilic diblock and triblock copolymers consisting of poly(ethylene oxide) (PEO) as (central) hydrophilic segment and poly(ε-caprolactone) (PCL) as hydrophobic segment(s) were prepared by ring opening polymerization. The length of the PEO segment was kept constant , whereas the length of the PCL block(s) was either 6 or 10 units for diblock copolymers and 3 or 5 units at each end for the triblock copolymers. These block copolymers were end-functionalized by esterification with linoleic acid (LA), which contains reactive double bonds. The autoxidative behavior of PEO₄₅-(CL₃-LA)₂ functionalized triblock copolymers was investigated by exposure of films to air at ambient conditions. Ninety percent of the double bonds had disappeared in 15 d and a crosslinked structure was obtained after 30 d. Critical micelle concentrations (CMC) of the crosslinkable surfactants were in the range of 0.08-0.19 mmol/l for the diblock copolymer and of 0.19-0.26 mmol/l for the triblock copolymer. The surface tension of aqueous surfactant solutions at the CMC (γ_CMC) (25 °C) varied from 47.1 to 51.4 mN/m for the diblock and from 45.6 to 48.1 mN/m for the triblock systems. For both systems CMC and γ_CMC increase with increasing HLB values. These surfactants were used in PMMA latex preparations. The latices of PMMA prepared with LA-functionalized diblock and triblock copolymers yielded narrow particle size distributions and particle sizes of 180 and 370 nm, respectively, whereas latices prepared with SDS had a particle size of 90 nm. After extraction of the latex particles with methanol, the amounts of the unextractable (either buried or copolymerized) LA-functionalized diblock and triblock copolymers found in extracted PMMA latex particles were 10 and 24% of the initial amount of surfactant added respectively. Control experiments with a stearic acid (SA) containing diblock copolymer showed that the amount of buried surfactant in PMMA latices was 6.5%. By comparing the overall latex characteristics and stability (shelf stability, freeze-thaw testing and addition of electrolyte solutions and ethanol) it was concluded that an LA-functionalized diblock copolymer (MPEO₄₅-CL₁₀-LA) gave better stabilization of PMMA latices than an LA-functionalized triblock copolymer of comparable composition and HLB value.     

Micellar Behavior of Anionic Surfactants with Sulfonate Function in Aqueous Solutions

Using different reaction conditions of photosulfochlorination of n-alkanes, various samples of anionic surfactants of sulfonates type have been obtained. Their micellar behavior was researched and the relationship between their isomeric distribution and so, their chemical structures and micellar behaviors were more thoroughly explored. Their critical micelle concentrations (CMC) were determined with surface tension measurements, the surface activities (γ_CMC) were obtained, the surface absorption amounts (Γm) and the molecular areas (Am) at the interface of air-water gained by using Gibbs’ equation. In addition, under the conditions of adding electrolyte NaCl, the critical micellar concentrations (CMCs) of two samples were also examined, and the effects of the addition of electrolyte on their micellar behaviors were studied. The experiment results show that the samples rich in secondary isomers have characteristic micellar behavior: CMC are higher, and the abilities to decrease surface tension are better, which well compared to common anionic surfactants, especially Hostapur 60, commercially available. Besides, the effects of addition of electrolyte on the micellar behaviors of the anionic surface-active agents are similar to common anionic surfactants.

Alkyl Xylosides: Physico‐Chemical Properties and Influence on Environmental Bacteria Cells

A group of four selected non‐ionic surfactants based on carbohydrates, namely octyl d ‐xyloside (C₈X), nonyl d ‐xyloside (C₉X), decyl d ‐xyloside (C₁₀X) and dodecyl d ‐xyloside (C₁₂X), have been investigated to accomplish a better understanding of their physico‐chemical properties as well as biological activities. The surface‐active properties, such as critical micelle concentration (CMC), emulsion and foam stability, the impact of the compounds on cell surface hydrophobicity and cell membrane permeability together with their toxicity on the selected bacterial strains have been determined as well. The studied group of surfactants showed high surface‐active properties allowing a decrease in the surface tension to values below 25 mN m^?1 for dodecyl d ‐xyloside at the CMC. The investigated compounds did not have any toxic influence on two Pseudomonas bacterial strains at concentrations below 25 mg L^?1. The studied long‐chain alkyl xylosides influenced both the cell inner membrane permeability and the cell surface hydrophobicity. Furthermore, the alkyl chain length, as well as the surfactant concentration, had a significant impact on the modifications of the cell surface properties. The tested non‐ionic surfactants exhibited strong surface‐active properties accompanied by the significant influence on growth and properties of Pseudomonas bacteria cells.     

Adsorption of Anionic–Cationic Surfactant Mixtures on Metal oxide Surfaces

This research evaluates the adsorption of anionic and cationic surfactant mixtures on charged metal oxide surfaces (i.e., alumina and silica). For an anionic-rich surfactant mixture below the CMC, the adsorption of anionic surfactant was found to substantially increase with the addition of low mole fractions of cationic surfactant. Two anionic surfactants (sodium dodecyl sulfate and sodium dihexyl sulfosuccinate) and two cationic surfactants (dodecyl pyridinium chloride and benzethonium chloride) were studied to evaluate the effect of surfactant tail branching. While cationic surfactants were observed to co-adsorb with anionic surfactants onto positively charged surfaces, the plateau level of anionic surfactant adsorption (i.e., at or above the CMC) did not change significantly for anionic–cationic surfactant mixtures. At the same time, the adsorption of anionic surfactants onto alumina was dramatically reduced when present in cationic-rich micelles and the adsorption of cationic surfactants on silica was substantially reduced in the presence of anionic-rich micelles. This demonstrates that mixed micelle formation can effectively reduce the activity of the highly adsorbing surfactant and thus inhibit the adsorption of the surfactant, especially when the highly adsorbing surfactant is present at a low mole fraction in the mixed surfactant system. Thus surfactant adsorption can be either enhanced or inhibited using mixed anionic–cationic surfactant systems by varying the concentration and composition.

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Emulsion polymerization of methyl methacrylate using the reverse iodine transfer polymerization (RITP) technique

The targeted molecular weight poly (methyl methacrylate) [PMMA] latex was successfully prepared in the presence of 4,4-azobis(4-cyanopentanoic acid) (ACPA) and various surfactants using the reversible iodine transfer polymerization (RITP)-emulsion polymerization at 85 °C for 7 h in the absence of light. The properties of PMMA particles upon the various ratios of ACPA to iodine within the concentration ranges of ACPA (1.0–2.0 mmol) and iodine (0.1–1.0 mmol) with various surfactants were investigated by means of GPC, SEM and particle analyzer. The weight-average molecular weight and the conversion increased with the ratio of [ACPA]/[I₂], but no correlation between the particle size and the [ACPA]/[I₂] ratio was obtained. The initiator, ACPA, was important in the formation of PMMA spherical particles, while molecular iodine dominated in controlling the molecular weight, inhibition period and the conversion. In overall, the appropriate concentration of ACPA, iodine and anionic or anionic with non-ionic surfactants controls the targeted molecular weight less than 100,000 g/mol and the enhanced conversion higher than 90% along with particle stability.