Surface activity—thermodynamic properties and light scattering studies for some novel aliphatic polyester surfactants

The preparation of 12 new polyester surfactants based on aliphatic amines and different ethylene oxide content is described. These surfactants were characterized by determining their molecular weights and polydispersity by gel permeation chromatography (GPC) and nitrogen content. Drop volume tensiometry (DVT) was used to measure the surface tension at 25, 35, 45 and 55°C. The surface tension isotherms were used to determine critical micelle concentration (CMC), maximum Gibb's adsorption (Γ_max), minimum area per molecule (A_min), the effectiveness of surface tension reduction (π_cmc) and the efficiency (pC₂₀). The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad, ΔS_ad) were calculated and the data showed that these surfactants favor micellization to adsorption. The static scattered light intensity measurements provide the calculation of the molecular weight of micelle and the aggregation number (N°), while the dynamic light scattering provide the hydrodynamic radius of micelle (R_H) and the diffusion coefficient at different surfactant concentrations. The hydrodynamic radius of micelle (R_H) at different surfactant concentrations could be used also to determine the CMC giving results that are comparable to those obtained by surface tension measurements. All the data are discussed regarding the chemical structure of the polymeric surfactants. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of Some Novel Nonionic Ethoxylated Surfactants Based on α-Amino Acids and Investigation of Their Surface Active Properties

Eight novel ethoxylated nonionic surfactants were prepared based on oil soluble α-amino acids. The L-phenylalanine and L-leucine were esterified and amidated with cetyl alcohol and palamitic acid, respectively; two amides and two esters of α-amino acids were obtained. The ethylene oxide was condensed with the prepared amides and esters to get three different polyethylene oxide units (40, 60, and 100) as phenylalanine derivatives. The amide and ester of α-L-leucine were ethoxylated at (60 ethylene oxides units). The analytical micro analysise, FTIR, ¹H NMR, ¹³C NMR, mass spectra were carried out to confirm the chemical structures. The surface tension of the water soluble prepared compounds was measured at 25°C, further the surface active properties were determined and calculated. Such that critical micelle concentration (CMC), surface excess (Γ_max); area per molecule (A_min), effectiveness (γ_CMC) free energy of micellization and adsorption (ΔG_mic, ΔG_ad). From the data obtained it was found that the CMC of phenylalanine esters is greater than that obtained for the amide derivatives. The Γ_max decreased as the ethylene oxide units (EO) increased. It was found also that the ΔG_ad was greater than the ΔG_mic. The obtained data and discrepancy were discussed on the light of surfactant chemical structure.     

Effect of Organic Counterions on the Properties of N-Lauryl Diisopropanolamine Surfactants

The influence of counterions on the surface properties of N-lauryl diisopropanolamine surfactants is delineated using conductometry and surface tension measurements. Twelve types of organic counterions have been studied: C₁–C₁₂ monocarboxylic acids anions. The surface properties of the synthesized surfactants, including surface tension, critical micelle concentration (CMC), effectiveness (π_CMC), efficiency (pC₂₀), maximum surface excess (Γ_max), minimum surface area (A_min), Gibbs energy of micellization (ΔG_mic), and adsorption (ΔG_ad) processes in the aqueous. The biodegradability of the prepared surfactants was tested in river water using the die-away method. Petroleum-collecting and petroleum-dispersing capacities of the synthesized compounds on the surface of water of varying mineralization degree have been studied.     

Surface-active properties of new cationic gemini surfactants with cyclic spacer

Three cationic gemini surface active compounds of the type (1r,4r)-1,4-dialkyl-1,4-dimethy-l-piperazine-1,4-diium bromide (Ia, Ib, and Ic), were synthesized. They were characterized using elemental analysis and ¹H-NMR spectra. Their surface-active properties were measured in aqueous solutions with different concentrations at different temperatures (25, 40, and 55°C). Various surface measurements of these gemini surfactants, (compared to the conventional one, 1-Dodecyl-1-methylpiperidinium bromide (a)) were estimated, specifically critical micelle concentration (CMC), effectiveness (π_CMC), efficiency (P_C20) as well as maximum surface excess (Γ_max) and minimum surface area (A_min). The measurements of the gemini compounds gave low CMC, high efficiency in reducing the surface tension, and intense adsorption at air/water interface. These surfactants have lower Krafft points and thus better solubility. Thermodynamic data, free energy, entropy, and enthalpy changes (ΔG°, ΔS°, and ΔH°) for micellization at the air/water interface and also for adsorption in the bulk of surface-active solutions were calculated.     

Synthesis and Evaluation of Surface Activity of Gemini Borate Surfactants Based on Glucose Moiety

A series of Gemini borate surfactants were synthesized based on glucose molecule. Their chemical structures were confirmed using ¹H-NMR,¹³C nuclear magnetic resonance (NMR), and mass spectroscopy. The surface activities of these Gemini amphiphiles were measured, including surface tension (γ), critical micelle concentration (CMC), effectiveness (II_cmc), efficiency (pC₂₀), maximum surface excess (Γ_max), and minimum surface area (A_min) at different temperatures 25, 35, and 45°C either in pure water or in water–ethanol mixture (10%). Also, thermodynamic data including free energy, entropy, and enthalpy changes (ΔS, TΔS, ΔH) for adsorption at the air–water interface and also for micellization in surfactant solutions were calculated.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

Synthesis,micellization properties,and cytotoxicity trends of N-hydroxyethyl-3-alkyloxypyridinium surfactants

N-hydroxyethyl-3-alkyloxypyridinium amphiphiles have been synthesized and characterized by various spectroscopic techniques. Self-assembling properties of these amphiphiles have been studied by surface tension, conductivity, and fluorescence measurements. Basic micellization parameters like critical micelle concentration (cmc), surface tension at the cmc (γ _cmc), adsorption efficiency (pC₂₀), effectiveness of surface tension reduction (Π _cmc), maximum surface excess concentration (Γ _max) and minimum surface area/molecule (A _min), and Gibbs free energy of the micellization (ΔG⁰ _mic) have also been determined. The micellization of these 3-alkyloxypyridinium halides in aqueous phase have been found to be exothermic and entropy-driven as assessed by conductivity measurements at different temperatures. Thermal degradation of these surfactants has also been assessed by thermal gravimetric analysis under nitrogen atmosphere. Further, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay of these surfactants on C6 glioma cells show them to be less toxic than conventional cationic surfactants.     

Study on the Interfacial Tensions Between Oils and Alkylbenzene Sulfonate Gemini Surfactant Solutions

Interfacial tensions (IFT) of five alkylbenzene sulfonate Gemini surfactants Ia, Ib, Ic, Id, and Ie at different oils/water systems were measured by a spinning drop interfacial tensiometer. And critical micelle concentration (CMC), the interfacial tension at CMC (γ_CMC), maximum interfacial excess concentration (Γ _max) and the surface area per molecule (A_min) were calculated. The results indicated that the CMC values determined with interfacial tension method were lower than those determined with surface tension method. And γ_CMC for Ie is larger than that for Ia, Ib, Ic, and Id. In addition, the effects of temperature and hydrophobic chains on dynamic IFT were also studied. With the increment of temperature, dynamic IFT is easier to reach a stable value. However, with the increment of hydrophobic chains, dynamic IFT is more difficult to reach a stable value. Each Gemini surfactant produces a minimum IFT when measured against a different n-alkane.     

Anionic–Nonionic Mixed Surfactant Systems: Micellar Interaction and Thermodynamic Behavior

The interactions between an anionic surfactant, viz., sodium dodecylbenzenesulfonate and nonionic surfactants with different secondary ethoxylated chain length, viz., Tergitol 15-S-12, Tergitol 15-S-9, and Tergitol 15-S-7 have been studied in the present article. An attempt has also been made to investigate the effect of ethoxylated chain length on the micellar and the thermodynamic properties of the mixed surfactant systems. The micellar properties like critical micelle concentration (CMC), micellar composition (X_A), interaction parameter (β), and the activity coefficients (f_A and f_NI) have been evaluated using Rubingh's regular solution theory. In addition to micellar studies, thermodynamic parameters like the surface pressure (Π_CMC), surface excess values (Γ_CMC), average area of the monomers at the air–water interface (A_avg), free energy of micellization (ΔG_m), minimum energy at the air–water interface (G_min), etc., have also been calculated. It has been found that in mixtures of anionic and nonionic secondary ethoxylated surfactants, a surfactant containing a smaller ethoxylated chain is favored thermodynamically. Additionally, the adsorption of nonionic species on air/water interface and micelle increases with decreasing secondary ethoxylated chain length. Dynamic light scattering and viscometric studies have also been performed to study the interactions between anionic and nonionic surfactants used.     

Adsorption and aggregation properties of novel star-shaped gluconamide-type cationic surfactants in aqueous solution

The adsorption and aggregation behavior of novel star-shaped gluconamide-type cationic surfactants N-dodecyl-N,N-bis[(3-D-gluconylamido)propyl]-N-alkylammonium bromide (C_nDBGB, where n represents hydrocarbon chain lengths of 10, 12, and 14) has been studied on the basis of static/dynamic surface tension, conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM) data. The static surface tension of the C_nDBGB aqueous solution measured at the critical micelle concentration (CMC) is observed to be significantly lower than that of the corresponding monomeric surfactants. The dynamic surface tension results indicate that adsorption process of above CMC is a mixed diffusion–kinetic adsorption mechanism. From the results of temperature dependent conductivity measurements, we could obtain the degree of counterion binding (β) and the thermodynamic parameters such as standard free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of aggregation. With a combination of the DLS and TEM data, a size transformation of the micelles is suggested to occur with an increase in the concentration.     

Effect of Hydrophilic/Hydrophobic Block Ratio and Temperature on the Surface and Associative Properties of Oxyethylene and Oxybutylene Diblock Copolymers in Aqueous Media

Recent development in dispersion science and technology demands block copolymers with a variable block length and composition. To highlight that purpose, the surface active, associative, colloidal, and thermodynamic behavior of three diblock copolymers having different hydrophilic to hydrophobic ratio is reported here. Using surface tension and light scattering measurements, the micellization and adsorption behavior of polyoxyethylene and polyoxybutylene diblock copolymers of the type E_mB_n have been analyzed. Critical micelle concentration (CMC) and related thermodynamic parameters like free energy (ΔG_mic), enthalpy (ΔH_mic), and entropy (ΔS_mic) of micellization were calculated from CMC value using the closed association model. Likewise, the surface active parameters, like surface excess concentration (Γ₂), area per molecule (A₂), and thermodynamic parameters such as free energy (ΔG_ads), enthalpy (ΔH_ads), and entropy (ΔS_ads) of adsorption of polymer at the air/water interface, were also calculated at various temperatures. Static and dynamic light scattering techniques were employed for the determination of the weight-average molar (M_w), association number (N_w), polymer–water interaction (A₂), and micellar size in terms of hydrodynamic radii (R_h) of copolymer micelles. The effect of block length and solution temperature on the surface and micellar properties of these copolymers was also investigated.     

Solubilization Behaviors of Nonpolar Substrates Using Double Tailed Cationic Surfactants

A series of double hydrophobic tails of N-methyl diethanolammonium bromide cationic surface active agents were synthesized. Their chemical structures were elucidated using different analytical tools including elemental analyses, FTIR, mass fragmentation, and ¹H-NMR spectroscopy. Their surface parameters including critical micelle concentration (CMC), effectiveness (π _CMC ), efficiency (Pc ₂₀), maximum surface excess (Γ _max ), and minimum surface area (A _min ) were calculated. The behaviors of the synthesized molecules in their solutions were discussed based on the data of surface parameters, micellization and adsorption thermodynamics at 25°, 40°, and 55°C. The experimental data of surface activity showed that these molecules are tends to form micelles in the bulk of their solutions at lower temperatures. On contrarily, they prefer to adsorb at higher temperatures. The synthesized cationic surfactants were used as solubilizing agent for nonpolar substrate (paraffin oil) at 25°C. The results of solubilization measurements showed good ability for the used surfactants towards solubilizing paraffin oil in aqueous medium. The results showed that the chemical structure of the solubilizate plays an important rule in its solubilization. Several factors were found to influence the extent of solubilization including: number of alkyl chains within surfactant molecule, symmetry of molecules and chain length of hydrophobic parts. The results were rationalized by the Kraft point and HLB values of the used surfactants. Furthermore, solubilization curves showed the steady state solubilization of each surfactant used.     

Thermodynamic parameters of some partially fluorinated and hydrogenated amphiphilic enantiomers and their racemates in aqueous solution

Micellization properties of aqueous solutions of four enantiomeric/racemic pairs obtained from partially fluorinated octylesters (PFOEs) and hydrogenated dodecylesters (DDEs) of alanine and serine were investigated by electrical conductivity, surface tension and density measurements over the temperature range of (15 to 35) °C. The Krafft temperatures (T_Ks) of most of the esters were found to be below or near zero temperature. The critical micelle concentrations (cmcs) of the PFOEs were found to be larger than those of the DDEs from which it was calculated that a CF₂ group in the partially fluorinated chain is approximately equivalent to 1.8 CH₂ group in the hydrogenated dodecyl chain and there were no noteworthy differences in the cmcs of the L- and DL-forms of the studied amphiphiles. The thermodynamic quantities of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and adsorption (ΔG_ad), and the adsorption parameters at the air/water interface, the surface excess concentration (Γ_max), the minimum area per head group of a molecule (A_min) and the efficiency in the surface tension reduction (pC₂₀), were also calculated. It was found that the micellization for DDE of alanine and the adsorption for PFOE of serine were more favoured than the other L-and DL-forms where the latter was in part as dimer at the air/water interface. Furthermore, except for the ΔH_mic values, there were no significant differences in these quantities for the L-and DL-forms of the studied systems. The mass density measurements showed that the apparent molal volumes ($V_{\phi }^{\text{cmc}}\text{,}{V}_{\phi }^{\text{mic}}$) of the hydrogenated esters were strikingly larger than those of the partially fluorinated ones, whereas the change of the apparent molal volume upon micellization ($\mathrm{\Delta }{V}_{\phi }^{\text{mic}}$) exhibited reverse behaviour, from which it was concluded that the micelles of the partially fluorinated esters were larger than those of the hydrogenated ones.     

Role played by the head size of some non‐ionic surfactants on their adsorption onto montmorillonite clay

Sorption behavior of polyoxethylene(n)monooleate series [Ol(EO)_n] onto montmorillonite clay was studied at 25°C to investigate the influence of the surfactant's head size on the sorption process. All the tested surfactants exhibited L‐shaped isotherms that means a strong interaction between the adsorbent and the adsorbate. Also, all the obtained isotherms ended with a drastic increase in the isotherm slope at nearly constant equilibrium concentration. This abrupt increase reflected the fairly high affinity of the tested surfactants to the clay surface at high bulk concentration region. The maximum amount adsorbed at the plateau region, Γ_max, was calculated according to the Langmuir adsorption theory and followed the order: Ol(EO)₁₄ > Ol(EO)₂₀ < Ol(EO)₄₀ < Ol(EO)₈₀. In case of short ethylene oxide (EO) chain, Γ_max decreased with the increase in the chain length; but a reverse result was obtained in case of surfactants with longer EO chain length (20 to 80 units). The free energy of adsorption, ΔG°_ad, had negative values indicating the spontaneous adsorption of surfactant molecules onto clay. The values of ΔG°_ad increased with increasing EO units from 14 to 20 units and decreased with further elongation in the EO chain from 20 to 80 units. Copyright © 2004 John Wiley & Sons, Ltd.     

Mixed micellization and surface properties of non-ionic/cationic surfactants

We investigate the surface properties of aqueous binary mixtures of our cationic surfactant O-dodecyl-N,N′-diisopropylisourea hydrochloride (ISO-DIC C₁₂) with commercially available nonionic surfactant polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether (TritonX-100) at different temperatures (288 to 303?K). The micellization behavior of the binary systems is studied by determining the surface tension and other important physicochemical parameters, such as the critical micelle concentration (CMC), surface tension at the CMC(γ_cmc), Krafft Temperature (T_K), maximum excess concentration (Γ_max), minimum surface area per molecule (A_min), surface pressure at the CMC (П_cmc), and the adsorption efficiency (pC20) at the air/water interface. The study has additionally covered the calculation of thermodynamic parameters of micellization, including the standard Gibbs free energy, the standard enthalpy, the standard entropy, the free energy, and the Gibbs free energy of adsorption at air/water interface. The CMC values of the binary systems determined by experimental data are used to evaluate the micellar composition in the mixed micelle, the interaction parameter β and the activity coefficients f₁(ISO-DIC C₁₂) and f₂ (polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether) using the theoretical treatment proposed by Clint and Rubingh. Our results reveal that the proposed binary systems possess enhanced surface activity compared to those of the individual surfactants.     

Physicochemical Properties and Surface Tension Prediction of Mixed Surfactant Systems: Triton X‐100 with Dodecylpyridinium Bromide and Triton X‐100 with Sodium Dodecylsulfonate

Dependences of the surface tension of aqueous solutions of ionic (dodecylpyridinium bromide, sodium dodecylsulfonate) and nonionic (Triton X‐100) surfactants and their mixtures on total surfactant concentration and solution composition were studied, and the surface tension of the mixed systems were predicted using different Miller's model. It was found that how to select the model for calculation of ω is corresponding to the degree of the deviation from the ideality during the adsorption of mixed surfactants. The compositions of micelles and adsorption layers at air‐solution interface as well as parameters (β^m, β^ads) of headgroup‐headgroup interaction between the molecules of ionic and nonionic surfactants were calculated based on Rubingh model. The parameters (B₁) of chain‐chain interaction between the molecules of ionic and nonionic surfactants were calculated based on Maeda model. The free energy of micellization calculated from the phase separation model (ΔG ₂ ^m ), and by Maeda's method (ΔG ₁ ^m ) agree reasonably well at high content of nonionic surfactant. The excess free energy ΔG _ads ^E and ΔG _m ^E (except α=0.4) for TX‐100/SDSn system are more negative than that TX‐100/DDPB system. These can be probably explained with the EO groups of TX‐100 surfactant carrying partial positive charge.     

Aggregation behavior of silicone surfactants in ethylammonium nitrate ionic liquid

The aggregation behavior of two silicone surfactants (monomeric and Gemini) was studied by surface tension measurements in a room temperature ionic liquid, ethylammonium nitrate (EAN), at various temperatures. A series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ _CMC), adsorption efficiency (pC ₂₀), and effectiveness of surface tension reduction (Π _CMC), were obtained. By comparing the silicone surfactants with traditional surfactants, we deduced that the surface activity of the silicone surfactants in EAN was superior to the activity of other surfactants. In addition, from the CMC values and their temperature dependence, we estimated the thermodynamic parameters of the micelle formation, $ \Delta G_m^0 $ , $ \Delta H_m^0 $ , and $ \Delta S_m^0 $ . It was revealed that the micellization of the silicone surfactants is entropy driven at low temperature and enthalpy driven at high temperature. Isothermal titration calorimetry measurements were also carried out to study the micellization of Gemini silicone surfactant. ¹H NMR was performed to study the silicone surfactant micelle formation mechanism in EAN.     

Thermodynamics of Adsorption and Micellization of Triblock Copolymers of Oxyethylene and Oxybutylene in Aqueous Medium Using Surface Tensiometry

The aqueous solutions of three triblock copolymers based on polyoxyethylene and polyoxybutylene of the type E_mB₁₀E_m have been analyzed by surface tension measurements. Surface activity of these triblock copolymers was studied by measuring surface parameters, like surface excess concentration, Γ₂, area per molecule of polymer and standard Gibb's free energy of adsorption, Δ^oG_ads, at various temperatures in the range of 20 to 50°C. The Effect of block length of hydrophilic portion of triblock copolymers on surface activity was investigated in this work. Miceller behavior of these triblock copolymers was also investigated using above technique. Critical micelle concentration (CMC) was determined from the plot of surface tension versus log of concentration in the range of temperature of 20–50°C. Thermodynamic parameters, standard free energy of micellization, Δ^oG_mic, standard enthalpy of micellization, Δ^oH_mic, and standard entropy of micellization, Δ^oS_mic were calculated from CMC value using closed association model in this range of temperature. Self assembly behavior of triblock copolymer E₂₀B₁₀E₂₀ was compared with E₃₀B₁₀E₃₀ and E₄₈B₁₀E₄₈ triblock copolymer. Effect of temperature on surface and miceller properties of the triblock copolymers was also studied.     

Characterization of Surfactant-Diblock Copolymer Interactions and Its Thermodynamic Studies

The interaction of nonionic diblock copolymer poly(ethylene oxide butylene oxide) (E₆₂B₂₂) with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) were studied using surface tension, conductivity, and dynamic laser light scattering techniques. Surface tension measurements were used to determine critical micelle concentration and thereby its free energy of adsorption (ΔG_ads), free energy of micellization (ΔG_m), surface excess concentration (Γ), and minimum area per molecule (A). Conductivity measurements were used to determine critical micelle concentration (CMC) critical aggregation concentration (CAC) at different temperatures, enthalpy of micellization (ΔH_m), free energy of micellization and entropy of micellization (ΔS_m). Changes in physicochemical properties of the micellized block copolymer were studied by using dynamic laser light scattering. The effect of surfactant on the size and properties of block copolymer has also been discussed.     

Synthesis and surface activity of novel glucose ester surfactants containing carbohydrate and hydrocarbon chain

A series of glucosyl esters surfactants were synthesized based on glucose molecule by enzymatic catalysis. It could reach the highest esterification yield of 83.4% at the optimal condition, molar ratio of D-glucose and fatty acyl amino acid as 3:2 using 11% (w/w) enzyme catalyst Lipozyme 435 as catalyst in t-butanol at 40°C. The surface activities were studied, such as the critical micelle concentration (CMC), surface tension (γ_cmc), maximum excess concentration (Γ_max), minimum surface area/molecule (A_min), and the adsorption efficiency (pC₂₀); values of these were obtained by surface tension test. The results show that the longer the hydrophobic chain length, the lower the CMC and γ_cmc. The CMCs of novel glucosyl esters were between 4.4 and 1.5 mM. Further, the micellization physiochemical parameters, including Gibbs free energy of micellization (ΔG), standard enthalpy change (ΔH), and standard entropy change (ΔS) were calculated. It was indicated the micellization of glucosyl esters 9–16 was driven by entropy and deduced at different temperature.