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.     

Micellar parameters of diblock copolymers and their interactions with ionic surfactants

The interactions of non-ionic amphiphilic diblock copolymer poly（oxyethylene/oxybutylene）(E₃₉B₁₈) with anionic surfactant sodium dodecyl sulphate（SDS） and cationic surfactant hexadecyltrimethylammonium bromide（CTAB） were studied by using various techniques such as surface tension,conductivity,steady-state fluorescence and dynamic light scattering.Surface tension measurements were used to determine the critical micelle concentration（CMC） and thereby the free energy of micellization(△G_mic),free energy of adsorption(△G_ads),surface excess concentration（Γ） and minimum area per molecule（A）.Conductivity measurements were used to determine the critical micelle concentration（CMC）,critical aggregation concentration（CAC）,polymer saturation point（PSP）,degree of ionization（α） and counter ion binding（β）. Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles taken place due to the interactions of diblock copolymers with ionic surfactants.The ratio of the first and third vibronic peaks（I₁/I₃） indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant interactions.Aggregation number（N）,number of binding sites（n） and free energy of binding （△G_b） for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching method.     

Surface activity and thermodynamic properties of water‐soluble polyester surfactants based on 1,3‐dicarboxymethoxybenzene used for enhanced oil recovery

The surface activity and thermodynamic properties for eight low molecular weight nonionic co‐polyester (PE) surfactants have been investigated. Surface and interfacial tensions (IFT) of surfactants in aqueous solutions were measured using the spinning drop technique. From these measurements, the critical micelle concentration (CMC), the surface pressure at CMC (Y_CMC), the maximum surface concentration (Γ_max), the minimum area/molecule at the aqueous solution/air interface (A_min), the effectiveness of surface tension reduction (Π_CMC), the alkane carbon number (n_min) and the IFT at n_min (Y_min) were determined. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic and ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad and ΔS_ad) for these polymeric surfactants were also calculated. Structural effects on micellization and adsorption are discussed in terms of these parameters. The results show that the ΔG_ad values were more negative than ΔG_mic values for these compounds, so that they favored adsorption before the micellization process. They exhibited IFT in the order of 10⁻³ to 10⁻⁴ mN/m against the thin alkane carbon number range 6–9. This range seemed to be prefered for enhanced oil recovery. Copyright © 2000 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

Conductometric studies of hexadecyltrimethylammonium bromide in aqueous solutions of ethanol and ethylene glycol

The effect of cosolvent on micellization of hexadecyltrimethyl ammonium bromide (CTAB) in aqueous solutions was studied. The conductivity of a mixture (cosolvent + water) as function of CTAB concentration was measured at different temperatures. Ethylene glycol and ethanol were used as a cosolvent. The conductivity data were used to determine the critical micelle concentration (CMC) and the effective degree of counterion dissociation of micelle in the temperature range 303.2 to 313.2 K. In all the cases studied, a linear relationship between log([CMC]_mix/mol dm⁻³) and the mass fraction of cosolvent in solvent mixture has been observed. The free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of micellization were determined using the temperature dependence of CMC. The dependence of these thermodynamic parameters on solvent composition was determined. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the cosolvent content increases. The enthalpy and entropy of micellization are independent of temperature in pure water, while ΔH _mic ⁰ and ΔS _mic ⁰ decrease dramatically with temperature in mixed cosolvents. Furthermore, the entropic contribution is larger than the enthalpic one in pure water, while in the mixed solvents, the enthalpic contribution predominates. The text was submitted by the authors in English.     

Investigation of the Thermodynamic Properties of the Cationic Surfactant CTAC in EG + Water Binary Mixtures

To understand the thermodynamic characteristics of cationic surfactants in binary mixtures, the aggregation behavior of hexadecyltrimethylammonium chloride (CTAC) has been investigated in ethylene glycol (EG) + water solvent mixtures at different temperatures and EG to water ratios. The critical micelle concentration (CMC) and degree of counter ion bonding (β) were calculated from electrical conductivity measurements. An equilibrium model for micelle formation was applied to obtain the thermodynamic parameters for micellization, including the standard Gibbs energies of micellization (DG_mic^o)\Delta G_{\mathrm{mic}}^{\mathrm{o}}), standard enthalpies of micelle formation (DH_mic^o)\Delta H_{\mathrm{mic}}^{\mathrm{o}}) and standard entropies of micellization (DS_mic^o)\Delta S_{\mathrm{mic}}^{\mathrm{o}}). Our results show that DG_mic^o\Delta G_{\mathrm{mic}}^{\mathrm{o}} is always negative and slightly dependent on temperature. The process of micellization is entropy driven in pure water, whereas in EG + water mixtures the micellization is enthalpy driven.     

Studies on Thermodynamics of Micellization and Solvophobic Interactions of Novel Surfactant–Cr(III) Complexes in Non-aqueous Solvents

The critical micelle concentration (CMC) of surfactant–Cr(III)–dodecylamine complexes of the type cis-α-[Cr(trien)(C₁₂H₂₅NH₂)X]²⁺ (where trien = triethylenetetramine; X = F⁻, Cl⁻, Br⁻) has been studied in n-alcohol and in formamide at different temperatures, by electrical conductivity measurements. From the CMC values as a function of temperature, various thermodynamic properties have been evaluated: standard Gibbs energy changes (Δ_mic G ⁰), standard enthalpy changes (Δ_mic H ⁰) and standard entropy changes (Δ_mic S ⁰) for micellization. Critical micelle concentrations have also been measured as a function of the percentage composition of alcohol added. The solvent composition dependences of these thermodynamic parameters were determined. It is suggested that alcohol addition leads to an increase in formamide penetration into the micellar interface that depends on the alcohol’s chain length. The results are discussed in terms of an increased hydrophobic effect, dielectric constant of the medium, the chain length of the alcohols, and the surfactant in the solvent mixture.     

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.     

Physicochemical Investigation of the Micellar Behavior of a Diblock (PEO)62-b-(PBO)33 Copolymer in Water and its Interaction with Ionic Surfactants

The physicochemical investigations on the associative, micellar, and thermodynamic properties of a diblock (PEO)₆₂-b-(PBO)₃₃ copolymer in aqueous medium and its interaction with ionic surfactants were carried out by using surface tensiometry, laser light scattering, and steady-state fluorescence spectroscopy. Surface tension and fluorescence measurements were used to find out the critical micelle concentration (CMC) and related thermodynamic parameters of micellization copolymer at various temperatures. The data from dynamic light scattering (DLS) were helpful to obtain the values of hydrodynamic radii (R_h), volume (υ_h), and hydrodynamic expansion parameter (δ_h) of the copolymer micelle. Likewise, the measurements from static light scattering (SLS) were employed to determine weight-average molar (M_w), association number (N_w), thermodynamic radius (R_t), thermodynamic volume (υ_t), anhydrous volume (υ_a), and thermodynamic expansion parameter (δ_t) of the copolymer micelles in the temperature range of 20–50°C. Similarly, the interactions between (PEO)₆₂-b-(PBO)₃₃ and two ionic surfactants, sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB), have also been investigated by fluorescence spectroscopy and DLS at 30°C. Similarly, the interactions between (PEO)₆₂-b-(PBO)₃₃ and two ionic surfactants, sodium dodecyl sulfate and hexadecyl trimethylammonium bromide, have also been investigated by fluorescence spectroscopy and DLS in detail.     

Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

The aggregation behavior of metal dodecyl sulfates (MDS), [Na¹⁺, Mg²⁺, Mn²⁺, Co²⁺, and Ni²⁺] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔG_m ⁰), enthalpy (ΔH_m ⁰), and entropy (ΔS_m ⁰) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) _T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.     

Thermodynamic studies of interaction between cetylpyridinium bromide and lysozyme by means of calorimetric titrations

In this study, we have investigated the micellization characteristics of n-cetylpyridinium bromide (CPB) and lysozyme–CPB system using isothermal titration calorimetry (ITC) technique. The ITC operates in a stepwise addition mode, providing an excellent method of determination of critical micelle concentration (CMC) and enthalpy of demicellization (and hence micellization). The micellization characteristics of CPB have been investigated by microcalorimetric technique at 25, 30, 35, and 40 °C in a buffer solution of Tris(hydroxymethyl)aminomethane and pH of 7.3. A scheme to describe lysozyme–CPB interaction has also been proposed on the basis of ITC technique in a buffer solution of Tris(hydroxymethyl)aminomethane at 30 °C, pH of 7.3, 0 mM NaCl, and 1 mM NaCl. The enthalpy changes associated with micelle dissociation were temperature and lysozyme concentration dependent, indicating the importance of hydrophobic interactions. The ΔG _mic was found to be negative, implying that, micellization, as expected, occurs spontaneously once the CMC has been reached. The values of ΔG _mic were found to become more negative with increasing temperature (in case of micellization of CPB) and with increasing the lysozyme concentration (in the case of lysozyme–CPB). The ΔS _mic was also found to decrease with increasing temperature in both cases. The presence of NaCl (1 mM) in the solutions decreased the CMC of CPB.     

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.     

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.     

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.     

Micellization of dodecylpyridinium chloride in water-ethanol solutions

Micellar properties of dodecylpyridinium chloride (DPC) were investigated by means of electrical conductometry with emphasis on the influences of cosolvent-water content and temperature. Ethanol was used as a cosolvent. Conductivity measurements gave information about critical micelle concentration and micellar ionization degree of the water-ethanol micellar solutions at different temperatures. In all solvent mixtures, it was observed that the critical micelle concentration of DPC and the degree of the counterion dissociation increase with an increasing concentration of ethanol and increasing temperature. Micellar and thermodynamics data were obtained from the temperature dependence of critical micelle concentrations in various aqueous mixtures of ethanol. In order to explain the effect of the cosolvent, the differences in the Gibbs energies of micellization of DPC between water and binary cosolvent were determined. The standard free energy (ΔG°_mic) of micellization was found to be negative as the concentration of the solvent increases, but it is roughly independent of temperature. Although the enthalpic contribution was found to be larger than the entropic one, in particular at lower temperatures, an entropy-enthalpy compensation effect was observed for all systems. Also, enthalpy (ΔH°_mic) and entropy (ΔS°_mic) of micellization are strongly temperature dependent and decrease with increasing temperature and cosolvent content. The text was submitted by the authors in English.     

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.     

Mixing behaviour of a conjugated molecular wire candidate and an insulating fatty acid within Langmuir–Blodgett films

The conductivity, weight loss and A.C. impedance studies were carried out to establish the influence the presence of neutral copolymer (Vinyl pyrrodlidone/Vinyl acetate copolymer) with anionic surfactant (Disodium laurethsulfosuccinate) in cyclohexane propionic acid (CHPA) on the corrosion behaviour of carbon steel. The protection efficiency (P%) of AS in the absence and presence of polymer increases with increase in AS concentration until it reaches a maximum constant value near the CMC of AS and decreases with increase in solution temperature. The protective efficiency of AS can be enhanced and its critical micelle concentration shifts to low value by adding of 0.05 g/l of polymer. The critical micelle concentration of AS in the absence and presence of polymer increases with increase in temperature. The calculated thermodynamic parameters of micellization (ΔG_mic), (ΔH_mic) and (ΔS_mic) in the presence of neutral copolymer molecules with AS show that these processes are spontaneous and exothermic in nature and indicate the association between AS and neutral copolymer molecules.