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.     

Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry,surface tensiometry and circular dichroism studies

Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25 °C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (ΔG_agg) and micellization (ΔG_mic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity – [IMP] plots.     

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.     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

Interfacial and Thermodynamic Properties of Anionic‐Nonionic Mixed Surfactant System: Influence of Hydrophobic Chain Length of the Nonionic Surfactant

The influence of hydrophobic chain length in nonionic surfactants on interfacial and thermodynamics properties of a binary anionic‐nonionic mixed surfactant was investigated. In this study, nonionic surfactants lauric‐monoethanolamide (C₁₂ MEA) and myrisitic‐monoethanolamide (C₁₄ MEA) were mixed with an anionic surfactant, α‐olefin sulfonate (AOS). The critical micelle concentration (cmc), maximum surface excess (Γ_max), and minimum area per molecule (A_min) were obtained from surface tension isotherms at various temperatures. The thermodynamic parameters of micellization and adsorption were also computed. Micellar aggregation number (N_agg), micropolarity, and binding constant (K_sv) of pure and mixed surfactant system was calculated by fluorescence measurements. Rubingh's method was applied to calculate interaction parameters for the mixed surfactant systems.     

Thermodynamics of micellization of alkylimidazolium surfactants in aqueous solution

Alkylimidazolium salts are a very important class of compounds. So far, calorimetry has hardly been used to characterize their solution behaviour. The enthalpies obtained from indirect methods have an intrinsic large uncertainty, and nowadays it is clear that calorimetry is the most sensitive technique for directly measuring the thermodynamic properties of aggregation.In this work, isothermal titration calorimetry (ITC) was used along with conductivity to determine the thermodynamics of aggregation of 1-alkyl-3-methylimidazolium chlorides ([C_nmim]Cl, n = 8, 10, 12, and 14) in aqueous solution. The critical micelle concentrations, cmc, were obtained from conductivity and calorimetry, and the enthalpies of micelle formation, ΔH_mic, were derived from the calorimetric titrations. From conductivity, we could also derive the values for the degree of ionisation of the micelles (α), the molar conductivity (Λ^M) of the [C_nmim]Cl micellar species and the molar conductivity at infinite dilution (Λ^∞) for the [C_nmim]⁺ cations.Values are therefore reported for the enthalpy (ΔH_mic), the Gibbs free energy (ΔG_mic) and entropy (ΔS_mic) changes for micelle formation. Further, the aggregate sizes and aggregation numbers were obtained by light scattering (LS) measurements.The observed variation of the thermodynamic properties with the alkyl chain length is discussed in detail and compared with the traditional cationic surfactants 1-alkyl-trimethylammonium chlorides, [C_nTA]Cl. The difference in the values of the thermodynamic parameters for both types of surfactants is here related to the structure of their head groups.     

Effect of gelatin on micellization and microstructural behavior of amphiphilic amitriptyline hydrochloride drug solution: A detailed study

Herein we have investigated the dealings between amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) and gelatin interaction using different proposed techniques. AMT is used for the treatment of mental/mood problems such as depression. Gelatin interacts with this drug alike fashions to the interaction of polymers and surfactants i.e., critical aggregation concentration (cac) and polymer saturation point (psp) were together achieved significantly. AMT and gelatin interaction starts due to the highly surface active complex formation as disclosed by decreasing of surface tension of gelatin solution by adding of AMT. It was uncovered from results that cac decreases on increasing the gelatin concentrations, whereas psp increases which is a sign of the attraction between AMT and gelatin. Thermodynamic parameters were also evaluated and discussed in detail. Fluorescence measurements were used to find the values of average aggregation numbers (N_agg) and various other parameters like Stern–Volmer constant (K_sv) and micropolarity. The nuclear magnetic resonance (¹H NMR) data suggested that AMT interacts with gelatin by the means of hydrophobic interaction. The ¹H NMR experiments explain that the extent of chemical shifts (δ) and line width (lw) increases with the increase in gelatin concentration. Secondary structure of gelatin was also examined via circular dichroism (CD) technique at different concentration of AMT. CD results confirmed that with increasing drug concentration the random coil portion of gelatin enhances. Field emission scanning electron microscope (FESEM) provided clear pictures of (drug + gelatin) interaction.     

BINDING OF IONIC SURFACTANTS ON OPPOSITELY CHARGED POLYELECTROLYTES OBSERVED BY FLUORESCENCE METHODS

Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C_(12)E_8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity I_E/I_M of a cationic probe l-pyrenemethylamine hydrochloride(PyMeA·HCl) and the non-radiative energy transfer (NRET) I_(Py)/I_(Np) of naphthalene to pyrene for labeled polyelectrolyteswere chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes. The 1:1aggregation of polyelectrolyte-CTAB with respect to the charge was found as long as the CTAB concentration was slightlyhigher than its critical aggregation concentration (CAC). The intermolecular NRET indicated that the CTAB-boundpolyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails. However, neither 1:1polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to itsweaker hydrophobicity of 12 carbon atoms in the tail, which is shorter than that of CTAB. As known from the fluorescenceresults, nonionic surfactant C_(12)E_8 did not bind on the anionic polyelectrolytes, but the presence of PAMPS promoted themicelle formation for C_(12)E_8 at the CAC slightly below its critical micelle concentration (CMC). The solid complex of dansyllabeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of thepolyelectrolyte or with alkane tail length of the surfactant. SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC, respectively.     

Spectrophotometric studies on the interactions of C.I. Basic Red 9 and C.I. Acid Blue 25 with hexadecyltrimethylammonium bromide in cationic surfactant micelles

Interactions between cationic dye-cationic surfactant and anionic dye-cationic surfactant systems were investigated in aqueous solutions using spectrophotometric method at 288.15, 298.15, 308.15 and 318.15 K. C.I. Basic Red 9 (BR9) and C.I. Acid Blue 25 (AB25) were used as cationic and anionic dyes, respectively, and hexadecyltrimethylammonium bromide (HDTMABr) was selected as cationic surfactant in this study. Although there was an interaction between the AB25 and the HDTMABr molecules, an interaction between the BR9 and HDTMABr did not occur due to the electrostatic repulsion forces. Binding constants and partition coefficients between the micellar and the bulk water phases for the AB25-HDTMABr system were calculated from the changes in absorbance values and the critical micelle concentrations at different temperatures. It was found that the values of binding constant and partition coefficient decreased with increasing temperature. Thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) were determined for the binding and partition processes of AB25-HDTMABr system. It was concluded from ΔG⁰ values that the binding of AB25 to HDTMABr occurred spontaneously. In addition, the binding and partition processes were exothermic.     

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.     

Interaction of Anionic Gemini Surfactants with Other Surfactants

The interaction of anionic gemini surfactants with other surfactants (such as anionic, cationic, nonionic) was systematically overviewed, paying attention to synergism observed in various properties. These mixed systems were found to show remarkable synergism in micelle formation. The critical micelle formation values being lower than the individual gemini surfactants indicate that the mixed micellization is due to attractive interaction between the two components. Almost all combinations were discussed in terms of respective surface tension reduction effectiveness and surface tension reduction efficiency and aggregation number for evaluation of synergism.     

Aggregation Number of Ionic Surfactants and its Application for Alkyltrimethyl Ammonium Bromides and Sodium Tetradecyl Sulfate by Potentiometric Technique

A potentiometric technique based on surfactant ion selective electrode has been used for various cationic and anionic surfactants. The data obtained contain m ₁ (surfactant monomer concentration); m ₂ (free counterion concentration) and α (degree of dissociation of micelle) were used for determination of aggregation number at and above cmc (critical micelle concentration). Data fitting show a relationship between aggregation number with such parameters. The correlation equation obtained shows that size of ionic micelle vary sharply after cmc. Also, the equation obtained shows size of micelle growth with increase in counterion concentration.     

Microstructure of un-neutralized hydrophobically modified alkali-soluble emulsion latex in different surfactant solutions

At low pH conditions and in the presence of anionic, cationic, and nonionic surfactants, hydrophobically modified alkali-soluble emulsions (HASE) exhibit pronounced interaction that results in the solubilization of the latex. The interaction between HASE latex and surfactant was studied using various techniques, such as light transmittance, isothermal titration calorimetry, laser light scattering, and electrophoresis. For anionic surfactant, noncooperative hydrophobic binding dominates the interaction at concentrations lower than the critical aggregation concentration (CAC) (C < CAC). However, cooperative hydrophobic binding controls the formation of mixed micelles at high surfactant concentrations (C > or = CAC), where the cloudy solution becomes clear. For cross-linked HASE latex, anionic surfactant binds only noncooperatively to the latex and causes it to swell. For cationic surfactant, electrostatic interaction occurs at very low surfactant concentrations, resulting in phase separation. With further increase in surfactant concentration, noncooperative hydrophobic and cooperative hydrophobic interactions dominate the binding at low and high surfactant concentrations, respectively. For anionic and cationic surfactant systems, the CAC is lower than the critical micelle concentration (CMC) of surfactants in water. In addition, counterion condensation plays an important role during the binding interaction between HASE latex and ionic surfactants. In the case of nonionic surfactants, free surfactant micelles are formed in solution due to their relatively low CMC values, and HASE latexes are directly solubilized into the micellar core of nonionic surfactants.     

Synergistic Behavior of Binary Mixed Micellar Solution

Conductivity measurement has been used to study the properties of aqueous solutions of the nonionic polyoxyethylene sorbitan(20)monooleate (T₈₀) and the cationic 1,1′ lauryl amido propyl ammonium chloride (LAPACl) and their mixtures in the presence of 0.1 M HCl and at 303 K. The values of the critical micelle concentration (CMC) of the individual surfactants and their mixtures were determined from the conductometric measurements. Based on Rubingh's theory (approximation of the theory of regular solutions), the compositions of micelles (X₁), and the parameters of interaction between the molecules of cationic and nonionic surfactants (β) were calculated for mixture of systems LAPACl+α T₈₀ and T₈₀+α LAPACl. The mixture LAPACl+α T₈₀ showed synergistic interactions up to α=0.2 whereas those of T₈₀+α LAPACl registered antagonistic behavior. The study disclosed that for cationic/nonionic surfactants mixtures, the priority is for mixtures of cationic base with small mole fraction of nonionic surfactant and not the reverse.     

Mixed micellization of gemini surfactant with nonionic surfactant in aqueous media: a fluorometric study

Herein we report on the study of the interactions between alkanediyl-α,ω-type cationic dimeric (gemini) surfactant and the nonionic Triton X-100 in aqueous medium. The critical micelle concentrations of binary mixtures were determined by fluorometric study. Using the regular solution theory for the analysis of the experimental data, the attractive nature of interactions and synergistic behavior of gemini surfactant and Triton X-100 mixture were demonstrated. The micelle aggregation number was measured using steady state fluorescence quenching method. The micropolarity, binding constant and dielectric constant of mixed systems were determined from the ratio of peak’s intensity (I ₁/I ₃) in the pyrene fluorescence emission spectrum.     

Interaction of the Amphiphilic Drug Amitriptyline Hydrochloride with Gemini and Conventional Surfactants: A Physicochemical Approach

Pyrene fluorescence measurements were carried out on various binary mixtures of the antidepressant amphiphilic drug amitriptyline hydrochloride (AMT) with conventional (TTAB and CTAB) and gemini surfactants (14-4-14 and 16-4-16). In all cases mixed micellar aggregates were formed and the mixed critical micelle concentration (cmc) of various mixtures was computed from the I ₁/I ₃ versus total surfactant concentration plots. In the region where mixed micelles are formed, the interaction of the amphiphlic drug and four surfactants showed synergistic behavior. The results were analyzed using an interaction parameter, β, which characterize the interaction in the mixed micelle and is introduced by a regular solution theory. The β values are negative in all binary mixtures, and their magnitudes increase with increasing hydrophobicity of the amphiphile. The micellar mole fraction of AMT in the mixed micelle (x ₁) and in the ideal sate (x _ideal) were evaluated and their values (x ₁ > x _ideal) suggest that the contribution of the AMT component is greater in binary mixtures as compared to that in the ideal state. Activity coefficients (f ₁ and f ₂) and excess Gibbs energy (G _ex) were also calculated. The values of micelle aggregation numbers (N _agg) and various other parameters like the Stern–Volmer constant (K _sv), micropolarity and dielectric constant of mixed systems have also been evaluated from the ratios of respective peak intensities (I ₁/I ₃ or I ₀/I ₁).     

Mixed Micellization and Interfacial Properties of Nonionic Surfactants with the Phenothiazine Drug Promazine Hydrochloride at 30 °C

In the present work, the micellization and adsorption behaviors of mixed systems containing an amphiphilic phenothiazine drug, promazine hydrochloride (PMZ) and nonionic surfactants in aqueous media at different mole fractions of nonionic surfactants (?? ₁) were investigated at 30?°C by surface tension measurements. The critical micelle concentrations of the mixtures fall between the values of the individual components, which indicates nonideal mixing. With Tritons the interactions are repulsive at low mole fractions. At high ?? ₁ the mixing becomes almost ideal. On the basis of regular solution theory, the micellar mole fractions of surfactants ( $X_{1}^{m}$ ) and interaction parameter (?? ^m ) were evaluated, while their interfacial mole fractions ( $X_{1}^{\sigma} $ ) and interaction parameters at the interface (?? ^?? ) were calculated using Rosen??s model. The results indicate that the surfactant??s contribution is greater than that of the drug both at the interface and in micelles. The short and rigid hydrophobic structure of the drug resists its participation in micelle formation more than in the monolayer, leading to $X_{1}^{m}<X_{1}^{\sigma}$ . Values of the surface excess (?? _max) and minimum area per head group (A _min) indicate attractive interactions. ?? _max increases and A _min decreases as the surfactant mole fraction increases.     

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.     

Transition from antagonistic to synergistic interaction in mixed micellar system by increase in alkyl chain length of alkyl trimethylammonium bromide

Herein, the electrical conductivity technique used to measure the critical micelle concentration (cmc) for pure cationic surfactants (Dodecyl/cetyltrimethylammonium bromides) and phenothiazine drug (Promethazine hydrochloride), as well as their different mole fractions in 10^?3 ?mol/kg 1-methyl-3-octylimidazolium chloride (C₈mim.Cl) at different temperatures. By using the cmc values the regular solution theory used to evaluate the micellar mole fraction for DTAB/CTAB-PMT mixed systems. The clint's model used to calculate the ideal critical micelle concentration (cmc1) that helps to evaluate the ideal micellar mole fraction for studied mixed systems, both explain the deviation from ideality. In addition, interaction parameter β^m helps to confirm the nature of interaction (either antagonistic or synergistic) for the studied systems. The calculated parameters confirm a transition in the binding nature from antagonistic to synergistic with the increase in alkyl chain length of cationic surfactant i.e., component of the binary mixed system. The ease of micellization for the studied systems discussed by the standard Gibb's energy of micellization ($\Delta G_m^0$), as well as the standard enthalpy and standard entropy of micellization were ($\Delta H_m^0$) and ($\Delta S_m^0$), respectively to discuss the stability of the studied systems.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.