Preparation,Characterization and Properties of Novel Cationic Gemini Surfactants with Rigid Amido Spacer Groups

A series of novel cationic gemini surfactants with rigid amido groups inserted as the spacers, named C ₁₂ ‐PPDA‐C ₁₂ , C ₁₄ ‐PPDA‐C ₁₄ and C ₁₆ ‐PPDA‐C ₁₆ , were synthesized by a two‐step reaction with dimethyl terephthalate, N,N‐dimethyl propylene diamine and alkyl bromide as raw materials. The chemical structures of the prepared compounds were confirmed by IR, ¹H and ¹³C NMR and element analysis. Surface activity properties of the synthesized compounds were investigated by surface tension, electrical conductivity and fluorescence. Increasing the number of carbon atoms in the hydrophobic alkyl chain, decreased the critical micelle concentration (CMC), surface tension at the CMC and the minimum surface area. Other relevant properties including foaming ability and emulsion stability were investigated. The results indicated that the synthesized gemini surfactants possess good surface properties, emulsifying properties and steady foam properties.     

Synthesis and Characterization of Glucosamide Surfactant

The synthesis and structural analysis of glucosamide surfactants of the general formula C_nH_2n+1NH(CH₂)₂NHCO(CHOH)₄CH₂OH (n = 8, 10, 12) are described, and the surface activity properties of the surfactants are studied. N‐alkylethylenediamines were synthesized by the alkylation of the ethylenediamine with alkyl bromide. The glucosamide surfactants, N‐alkyl‐N′‐glucosylethylenediamine (C_nGA), were prepared by amidation of the precursor diamine with d ‐gluconic acid δ‐lactone. They were structurally characterized by IR, ¹H NMR and MS. They reduced the surface tension of water to approximately 26–27 mN m^?1 at concentration levels of (0.5–1.6) × 10^?3 mol L^?1.     

Synthesis and Surface Properties of Novel Carboxylic Ester-Containing Imidazolium-Based Zwitterionic Surfactants: Monoalkyl 2-(3-Methylimidazolium-1-yl) Succinate Inner Salts

A series of carboxylic ester‐containing imidazolium‐based zwitterionic surfactants, namely, monoalkyl 2‐(3‐methylimidazolium‐1‐yl) succinate inner salts (C_nMimSU, n = 8, 10, 12 and 14), have been synthesized. Their structures were confirmed by ¹H NMR, ¹³C NMR and FTIR. The typical physicochemical properties parameters such as isoelectric point, critical micelle concentration (CMC), surface tension at CMC (γ_CMC), surface pressure at CMC (Π_CMC), adsorption efficiency (pC₂₀), the maximum surface excess (Γ_m), the minimum molecular cross‐sectional area (A_min) and the value of CMC/C₂₀ were determined. The effect of the long‐chain length on the important physicochemical properties of C_nMimSU was studied. It is found that the surface activity of C_nMimSU is enhanced with the long‐chain length increases.     

Synthesis and properties of novel alkyl sulfate gemini surfactants

Four anionic gemini surfactants of the sulfate type C₁₂C_nC₁₂, where n is the spacer chain length (n = 3, 4, 6, and 10) were synthesized. The structures of these surfactants were confirmed by FT‐IR, ¹H NMR, ESI mass spectra (ESI‐MS), and elemental analysis. The surface‐active properties of these compounds were investigated by means of surface tension, electrical conductivity, and fluorescence measurements. Premicellar aggregations were found for the four gemini surfactants, as revealed by the conductivity measurement. The formation of premicellar aggregates may account for the discrepancy between the critical micelle concentration (cmc) obtained by the surface tension and conductivity measurement. The cmc values of these gemini surfactants were much lower than that of sodium dodecylsulfate (SDS) and decreased monotonously with the increase of spacer chain length from 3 to 10. The effect of spacer chain length on the performance properties like foaming, emulsion stability, and lime soap dispersing ability were also studied and discussed. Practical applications : Alkyl sulfate surfactants are one of the most widely used surfactants. The new alkyl sulfate gemini surfactants synthesized in our study are more surface‐active than sodium dodecylsulfate. These gemini surfactants possess low critical micelle concentrations, high emulsion stability, and excellent lime soap dispersing ability. They have potential applications in the fields of cosmetics, detergents, etc.     

A Novel Alkyl Sulphobetaine Gemini Surfactant Based on S‐triazine: Synthesis and Properties

A series of alkyl sulphobetaine Gemini surfactants C_n‐GSBS (n = 8, 10, 12, 14, 16) was synthesized, using aliphatic amine, cyanuric chloride, ethylenediamine, N,N′‐dimethyl‐1,3‐propyldiamine and sodium 2‐chloroethane sulfonate as main raw materials. The chemical structures were confirmed by FT‐IR, ¹H NMR and elemental analysis. The Krafft points differ markedly with different carbon chain length, for C₈‐GSBS, C₁₀‐GSBS and C₁₂‐GSBS are considered to be below 0 °C and C₁₄‐GSBS, C₁₆‐GSBS are higher than 0 °C but lower than room temperature. Surface‐active properties were studied by surface tension and electrical conductivity. Critical micelle concentrations were much lower than dodecyl sulphobetaine (BS‐12) and decreased with increasing length of the carbon chain from 8 to 16, and can reach a minimum as low as 5 × 10^?5 mol L^?1 for C₁₆‐GSBS. Effects of carbon chain length and concentration of C_n‐GSBS on crude oil emulsion stability were also investigated and discussed.     

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.     

Synthesis and Properties of Novel Phenylenediamine Gemini Surfactants

In the present work, a two-step method was adopted to synthesize a series of novel Gemini surfactants using N,N-dimethylalkyl amines (alkyl length = C₁₂, C₁₆ and C₁₈), epichlorohydrin, and n-phenyllenediamine as starting materials. The products were characterized using mass spectroscopy (MS) and nuclear magnetic resonance spectroscopy (¹H NMR). Systematic experiments were conducted to evaluate their surface activity, foaming properties, and antibacterial performance. Results showed the critical micelle concentrations (CMC) of the C₁₂-based, C₁₆-based, and C₁₈-based phenylenediamine surfactants were 3.295 × 10⁻³, 2.532 × 10⁻⁴, and 3.140 × 10⁻⁴ mol L⁻¹ at 298 K, respectively, with corresponding surface tension (γ_cmc) values of 28.24, 31.95, and 35.06 mN m⁻¹ under the same conditions. The Gemini surfactants showed not only good surface activity and foaming properties, but also demonstrated good antimicrobial performance against Gram-positive and Gram-negative bacteria and fungi.     

Synthesis and Surface Properties of Disodium Monoalkyl Diphenyl Oxide Disulfonate

Disodium monoalkyl diphenyl oxide disulfonates (MADS) with different carbon chains (C_n‐MADS, n = 8, 12, 16) were synthesized through the steps of alkylation‐sulfonation‐neutralization using fatty alcohols (C₈, C₁₂, C₁₆), diphenyl oxide and fuming sulfuric acid (20 % free SO₃) as reagents. The structures of the products were identified by infrared spectroscopy and electrospray ionization‐mass spectrometry. The surface properties, emulsification, wettability alteration and salinity and hardness tolerance of the products were systematically investigated. The results show that the critical micelle concentration (CMC) of C₈MADS, C₁₂MADS and C₁₆MADS are 7.24 × 10^?3, 1.49 × 10^?3 and 2.09 × 10^?4 mol/L. The surface tensions at the CMC (γ_CMC) of each product are 37.5, 38.9 and 46.8 mN/m. The negative logarithm of the surfactant concentration in the bulk phase required to produce a 20 mN/m reduction in the surface tension of the solvent (pC₂₀) increases with the increase in the alkyl chain length. The emulsifying ability of C₁₂‐MADS is better than C₈‐MADS and C₁₆‐MADS, and the MADS showed less oil‐wet nature. The salinity and hardness tolerance of MADS is much stronger than that of conventional surfactants.     

Protocol for Studying Aqueous Foams Stabilized by Surfactant Mixtures

Even though foams have been the subject of intensive investigations over the last decades, many important questions related to their properties remain open. This concerns in particular foams which are stabilized by mixtures of surfactants. The present study deals with the fundamental question: which are the important parameters one needs to consider if one wants to characterize foams properly? We give an answer to this question by providing a measuring protocol which we apply to well‐known surfactant systems. The surfactants of choice are the two non‐ionic surfactants n‐dodecyl‐β‐d ‐maltoside (β‐C₁₂G₂) and hexaethyleneglycol monododecyl ether (C₁₂E₆) as well as their 1:1 mixture. Following the suggested protocol, we generated data which allow discussion of the influence of the surfactant structure and of the composition on the time evolution of the foam volume, the liquid fraction, the bubble size and the bubble size distribution. This paper shows that different foam properties can be assigned to different surfactant structures, which is the crucial point if one wants to tailor‐make surfactants for specific applications.     

Effect of aromatic ring in the alkyl chain on surface properties of arylalkyl surfactant solutions

Surface properties of two series of anionic arylalkyl surfactants, containing different aromatic rings in the straight aliphatic chain, sodium N-aryloleyl-N-methyl-2-aminoethanesulfonates and sodium N-aryloleyl p-methoxyanili-nesulfonates, were investigated. An increase of the aromatic ring size in the alkyl chain increases the critical micelle concentration (CMC) and surface tension at CMC. However, this also decreases the efficiency and effectiveness in reducing water surface tension. The dominant factor of the decrease of efficiency and effectiveness is attributed to the function of the hydrophilic segment and hydrophobic segment for arylalkyl surfactants, respectively. The same results are found in the standard free energy of adsorption (ΔG ^o _ads) and the standard free energy of micellization (ΔG ^o _mic) values. Moreover, with the increase of the aromatic ring size, the adsorption and micellization of arylalkyl surfactants begin to weaken. The data indicate that some parts of surface properties for arylalkyl surfactants are affected by the bulkiness of the arylalkyl chain. The results provide opportunities for further detailed examination of surface properties of arylalkyl surfactants with other branched alkyl chains.     

Comparative Study of Interfacial and Biological Properties in <Emphasis Type="SmallCaps">d</Emphasis>-Glycerate-Derived Surfactants

The effects of hydrophobic chain length on the interfacial and biological properties of diacyl d ‐glyceric acid (d ‐GA) sodium salts were evaluated based on interfacial tension analyses, dynamic light scattering (DLS), and antitrypsin activity. Of the four synthesized d ‐GA‐derived surfactants [dihexanoyl d ‐GA sodium salt (diC6GA‐Na), dioctanoyl d ‐GA sodium salt (diC8GA‐Na), didecanoyl d ‐GA sodium salt (diC10GA‐Na), and dilauroyl d ‐GA sodium salt (diC12GA‐Na)], only those with C6, C8, and C10 acyl chains were investigated because diC12GA‐Na were insoluble at room temperature. Together with our previous results, surface tensions at the critical micelle concentration (CMC) were 33.9 mN/m for diC6GA‐Na, 25.5 mN/m for diC8GA‐Na, and 27.9 mN/m for diC10GA‐Na. Evaluation of assembly size via DLS and optical microscopy revealed that diC8GA‐Na and diC10GA‐Na formed large associates with average sizes ranging from 50 to 200 μm at concentrations 4–5 times greater than their CMC, whereas diC6GA‐Na did not form such associates. In tryptic hydrolysis studies using N^α‐benzoyl‐dl ‐arginine‐4‐nitroanilide as a substrate, diC8GA‐Na exhibited an inhibitory effect on trypsin (trypsin specific activity: 0.26 ± 0.045 U/mg‐protein) greater than that of diC10GA‐Na (0.39 ± 0.10 U/mg‐protein), whereas diC6GA‐Na did not show antitrypsin activity. These results show that diC8GA‐Na was the most bioactive of the evaluated diacyl d ‐glycerate surfactants.     

Corrosion inhibition by N‐(alkyloxycarbonylmethyl)‐N‐triethanol ammonium chloride with respect to the surface and thermodynamic properties

N‐[(octyloxycarbonylmethyl)‐ N‐triethanol ammonium chloride] (C₈ ), N ‐[(dodecyl‐oxycarbonylmethyl)‐ N‐triethanol ammonium chloride] (C₁₂ ) and N ‐[(hexadecyloxycarbonylmethyl)‐N ‐triethanol ammonium chloride] (C₁₆ ) were synthesized. Surface tension was measured in aqueous solution for different concentrations at 28, 38 and 48°C. Various surface properties of the synthesized surfactants were evaluated, particularly critical micelle concentration (CMC), efficiency (Π_CMC) as well as maximum surface excess (Γ_max) and minimum surface area (A_min). Micellization and adsorption in both liquid/air and liquid/solid interfaces thermodynamics were investigated. These products have pronounced surface activity and satisfactory corrosion inhibition of C‐steel in hydrochloric acid at 28, 38 and 48°C. © 1999 Society of Chemical Industry     

Surface properties of linear alkyl benzene sulfonates in hard river water

Surface properties of a series of highly purified linear alkyl benzene sulfonates were extensively studied in hard river water. The effects of water hardness, alkyl chain length and position of the phenyl sulfonate group in the molecule on such surface properties as pC₂₀, critical micelle concentration (CMC), γ_CMC, CMC/C₂₀ ratio, and minimum area per molecule at the interface are discussed in detail. The position of phenyl sulfonate group in the molecule was found to have a pronounced effect on the CMC, γ_CMC value, CMC/C₂₀ ratio, and, to the contrary, a relatively small effect on the pC₂₀ value. The linear relationship between pC₂₀ or-log CMC, and m, the number of carbon atoms in the alkyl chain, was found for surfactants with the phenyl sulfonate group either at the terminal position or at the more central position in the molecule. γ_CMC decreases but the CMC value increases, when the position of phenyl sulfonate group moves from the terminal toward a more central position of the molecule, reflecting the “Hartley Effect” resulting from the branched alkyl chain.     

Surface Chemical Properties and Micellization of Disodium Hexadecyl Diphenyl Ether Disulfonate in Aqueous Solution

The surface tension of disodium hexadecyl diphenyl ether disulfonate (C₁₆‐MADS) was measured at different NaCl concentrations (0.00–0.50 mol L^?1) and temperatures (298.0–318.0 K) using the drop‐volume method. The results show that, with increasing temperature, the critical micelle concentration (CMC) of C₁₆‐MADS increases slightly, but the maximum surface adsorption capacity (Γ_max) at the air–water interface decreases. When the concentration of NaCl was increased from 0.00 to 0.50 mol L^?1, the CMC of C₁₆‐MADS decreased from 1.45 × 10^?4 to 4.10 × 10^?5 mol L^?1, but the surface tension at the CMC (γ_cmc) was not affected. When the concentration of NaCl was increased at 298.0 and 303.0 K, the Γ_max of C₁₆‐MADS increased. When the temperature was increased from 308.0 to 318.0 K, the surface excess concentration (Γ_max) of C₁₆‐MADS abnormally decreased from 2.26 to 1.41 μmol m^?2 with increasing NaCl concentration. The micellization free energy () decreased from ?63.98 to ?76.20 kJ mol^?1 with increase of temperature and NaCl concentration. The micellar aggregation number (N_m) of disodium hexadecyl diphenyl ether disulfonate (C₁₆‐MADS) was determined using the molecule fluorescence probe method with pyrene as probe and benzophenone as quencher. The results show that an appropriate N_m could be measured only at surfactant concentration above the CMC. The N_m increased with an increase in C₁₆‐MADS concentration, but the micropolarity in the micelle nucleus decreased. The temperature had little effect on N_m. Compared with typical single hydrophilic headgroup surfactants, aggregates of C₁₆‐MADS exhibit different properties.     

Synthesis and Surface Properties of a Novel Sodium 3‐(3‐Alkyloxy‐3‐oxopropoxy)‐3‐oxopropane‐1‐sulfonate at the Air–Water Interface

The present paper describes the synthesis and evaluation of surface properties of a novel series of anionic surfactant, namely sodium 3‐(3‐alkyloxy‐3‐oxopropoxy)‐3‐oxopropane‐1‐sulfonate with varying alkyl chain length (C8–C16). Synthesis involves initial formation of the 3‐alkyloxy‐3‐oxopropyl acrylate along with fatty acrylate during the direct esterification of fatty alcohol with acrylic acid in the presence of 0.5 % NaHSO₄ at 110 °C followed by sulfonation of the terminal double bond of the 3‐alkyloxy‐3‐oxopropyl acrylate. Synthesized compounds were evaluated for surface and thermodynamic properties such as critical micelle concentration (CMC), surface tension at CMC (γ_cmc), efficiency of surface adsorption (pC₂₀), surface excess (Γ_max), minimum area per molecule at the air–water interface (A_min), free energy of adsorption (?G°_ads), free energy of micellization (?G°_mic), wetting time, emulsifying properties, foaming power and calcium tolerance. Effect of chain length on CMC follows the classic trend, i.e. decrease in CMC with the increase in alkyl chain length. High pC₂₀ (>3) value indicates higher hydrophobic character of the surfactant. These surfactants showed very poor wetting time and calcium tolerance, but exhibited good emulsion stability and excellent foamability. Foaming power and foam stability of C14‐sulfonate were found to be the best among the studied compounds. Foam stability of C14‐sulfonate was also studied at different concentrations over time and excellent foam stability was obtained at a concentration of 0.075 %. Thus this novel class of surfactant may find applications as foam boosters in combination with other suitable surfactants.     

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.     

Effect of Chain Length on the Micellization,Antibacterial, DPPC Interaction and Antioxidant Activities of l‐3,4‐Dihydroxyphenylalanine (l‐DOPA) Esters

l ‐DOPA (l ‐3,4‐dihydroxyphenylalanine) has been widely used as a drug in the clinical treatment of Parkinson's disease. In this report, the systematic study of the effect of chain length on the critical micelle concentration (CMC), antibacterial and antioxidant activity of esters derived from the aromatic amino acid l ‐3,4‐dihydroxyphenylalanine as surfactants are accounted for the first time. The antibacterial activity displayed a cut‐off effect at C₁₂ with respect to both gram positive and gram negative bacteria (except for Pseudomonas aeruginosa where the cut‐off was displayed at C₁₀). Correlation of the CMC with the minimum inhibitory concentration (MIC) shows that the DOPA esters exist in micellar form at the MIC. An increase in chain length of the DOPA esters induces greater binding with phospholipid vesicles 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine. The C₁₂ ester possessed highest radical scavenging ability among the esters tested against both 2,2‐diphenyl‐1‐picrylhydrazyl and 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid) showing that antioxidant activity of the DOPA esters is also affected by chain length. This study showed that DOPA esters are promising candidates as antibacterial agents as well as good antioxidants.     

Synthesis, Surface and Thermodynamic Properties of Substituted Polytriethanolamine Nonionic Surfactants

Three series of nonionic surfactants derived from polytriethanolamine containing 8, 10, and 12 units of triethanolamine were synthesized. Structural assignment of the different compounds was made on the basis of FTIR and ¹H‐NMR spectroscopic data. The surface parameters of these surfactants included critical micelle concentration (CMC), surface tension at the CMC (γ_CMC), surfactant concentration required to reduce the surface tension of the solvent by 20 mN m^?1 (pC₂₀), maximum surface excess (Γ_max), and the interfacial area occupied by the surfactant molecules (A_min) using surface tension measurements. The micellization and adsorption free energies were calculated at 25 °C.     

Synthesis and Properties of Alkoxyethyl β‐d‐Xylopyranoside

In order to improve the water solubility of sugar‐based surfactants, alkyl β‐d‐ xylopyranosides, novel sugar‐based surfactants, 1,2‐trans alkoxyethyl β‐d‐ xylopyranosides, with alkyl chain length n = 6–12 were stereoselectively prepared by the trichloroacetimidate method. Their properties including hydrophilic–lipophilic balance (HLB) number, water solubility, surface tension, emulsification, foamability, thermotropic liquid crystal, and hygroscopicity were investigated. The results indicated that their HLB number decreased with increase of alkyl chain, the water solubility improved since the hydrophilic oxyethene (─OCH₂CH₂─) fragment was introduced. The dissolution process was entropy driven at 25–45 °C for alkyl chain length n = 6–10. Octyloxyethyl β‐d‐ xylopyranoside had the best foaming ability. Nonyloxyethyl β‐d‐ xylopyranoside had the best foam stability and the emulsifying ability was better in toluene/water system than in rapeseed oil/water system. The surface tension of in aqueous solution dropped to 27.8 mN m^?1 at the critical micelle concentration, and it also showed the most distinct thermotropic liquid phases with cross pattern texture upon heating and the fan schlieren texture on cooling. Hexyloxyethyl β‐d‐ xylopyranoside possessed the strongest hygroscopicity. Based on the effective improvement of water solubility, the prepared alkoxyethyl β‐d‐ xylopyranosides showed excellent surface activity and are expected to develop their practical application as a class of novel sugar‐based surfactants.     

Chemical structure/property relationships in surfactants. 17. N-substituted-N-acyl glycinates in pure and synthetic hard river water

The surface properties [effectiveness of surface tension reduction (γ_CMC), critical micelle concentration (CMC), efficiency of surface tension reduction (pC ₂₀), maximum surface excess concentration (Γ_CMC), minimum area/molecule at the interface (A _min), and the CMC/C ₂₀) ratio] of well-purified N-substituted glycine derivatives, having the structural formula RC(O)N(R′)CH₂COONa, where RC(O)=lauroyl, myristoyl, or oleoyl, and R′=Et, Pr, Bu, CH₂CH₂OH or CH₂CH₂CH₂OCH₃, were investigated at 25°C in hard river water and distilled water. These surfactants show greater surface activity in hard river water than in distilled water. The effect of both the main alkyl chain R and the N-substituent R′ on surface properties was elucidated, the oleoyl group showing properties equivalent to that of a C₁₆ saturated acyl group. A linear relationship was observed between the pC ₂₀ or CMC values and the number of carbon atoms in the alkyl chain R or in R′ when it was alkyl. With increase in the number of carbon atoms in either R or the N-substituent R′ when it is alkyl, both pC ₂₀ and micelle-forming ability increase, although the effect of R′ on the foregoing two surface properties is lower than that of R. When R′ is (CH₂)₃OCH₃, however, the results suggest that R′ is only partly removed from contact with the aqueous phase either upon adsorption at the water/air interface or upon micellization. It increases A _min, is equivalent only to an ethyl group in its effect on pC ₂₀ and to a methyl group in its effect on CMC, and, in contrast to the effect of R′ when it is alkyl, produces no increase in the CMC/C ₂₀ ratio. As a result, γ_CMC increases with R when R′ is alkyl and decreases with R when R′ is (CH₂)₃OCH₃.