Standard Free Energy Of Adsorption Research Articles

Exploring Ginkgo biloba extract's green corrosion inhibition effects on Q235 steel in H2SO4 environments

The corrosion inhibition properties of Ginkgo biloba extract on Q235 steel in 0.5 M H2SO4 solution were comprehensively investigated using weight loss measurements, electrochemical techniques, surface characterization, and quantum chemical calculations. The results demonstrate that Ginkgo biloba extract acts as an effective green corrosion inhibitor, with inhibition efficiencies reaching up to 96.54% at a concentration of 0.7 g/L. The inhibition efficiency increased with increasing extract concentration and temperature. FTIR and LC/MS analyses revealed that the extract contains various phytochemical constituents, including flavonoids, terpenoids, and other polyphenolic compounds, which contribute to its corrosion inhibition properties. The adsorption of the extract compounds on the steel surface followed the Langmuir adsorption isotherm, with a negative value of the standard free energy of adsorption, indicating a spontaneous and stable adsorption process involving both physisorption and chemisorption. SEM and XPS analyses confirmed the formation of a protective film by the adsorbed extract compounds, which acts as a barrier, preventing the direct contact between the aggressive solution and the steel substrate. The film also alters the wettability of the metal surface, making it more hydrophobic and further enhancing the corrosion inhibition efficiency. Quantum chemical calculations showed that flavonoids, particularly quercetin, contribute significantly to the corrosion inhibition performance due to their high reactivity, strong dipole moment, and stable adsorption on the Fe(110) surface. These findings provide valuable insights into the development of sustainable and eco-friendly corrosion inhibitors for the protection of metal structures in acidic environments.

A novel corrosion inhibitor based on a Schiff base for mild steel in 1M HCl: synthesis and anticorrosion study

PurposeThe aim of this study was to investigate the activity of 4-((4-((2-hydroxyethyl)(methyl)amino)benzylidene) amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HEMAP), a Schiff base synthesized and characterized for the first time, to the authors’ knowledge, as a novel inhibitor against corrosion of mild steel (MS) in hydrochloric acid solution.Design/methodology/approachHEMAP was characterized by some spectroscopic methods including High-Resolution Mass Spectrometry (HRMS), Proton Nuclear Magnetic Resonance (1H NMR), Carbon-13 (C13) nuclear magnetic resonance (13C NMR) and Fourier Transform Infrared Spectroscopy (FT-IR). Then, the inhibition efficiency of HEMAP on MS in a hydrochloric acid solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). To explain the inhibition mechanism, the surface charge, adsorption isotherms and thermodynamic parameters of MS in the inhibitor solution were studied.FindingsEIS tests displayed that the highest inhibition efficiency was calculated approximately as 99.5% for 5 × 10−2 M HEMAP in 1 M HCl solution. The adsorption of HEMAP on the MS surface was found to be compatible with the Langmuir model isotherm. The thermodynamic parameter results showed that the standard free energy of adsorption of HEMAP on the MS surface was found to be more chemical than physical.Originality/valueThis study is important in terms of demonstrating the performance of the first synthesized HEMAP molecule as an inhibitor against the corrosion of MS in acidic media. EIS tests displayed that the highest inhibition efficiency was calculated approximately as 99.5% for 5 × 10−2 M HEMAP in 1 M HCl solution.

Synergistic interaction on quasi-binary mixture of amino sulfonate amphoteric surfactant with nonionic diethanolamide induced by glycerol and its concentration

Molecular interaction about a quasi-binary mixtures of an amino sulfonate surfactant, sodium 3-(N-dodecyl ethylenediamino)-2-hydroxypropyl sulfonate (DES), with a fatty acid diethanolamide derived from coconut oil (CDA) in aqueous solutions containing both the glycerol of 0.100 mol/L and 0.200 mol/L was investigated using the surface tension measurement. The interfacial parameters indicate that the mixing of DES with CDA can promote the formation of the more compact distribution of molecules adsorbed in the mixed monolayer, the mixing ratio of the mixture induces the difference in the adsorption behaviors at air–liquid interface, and the standard free energy of adsorption at air–liquid interface implies the benefit of adsorption and the change of adsorption behavior based on both the concentration of glycerol in solutions and the mixing ratio in the mixture. In the framework of pseudo-phase separation model, thermodynamic models including the Clint’s model, the Rubingh’s model and the Maeda’s model were employed to effectively estimate the related micellization and thermodynamic parameters. The nonideal mixing of DES with CDA and their synergistic interactions in the mixed micelle depend on both the mixing ratio of the mixture and the concentration of glycerol in solutions. The abundant amount of DES in mixed micelle will result in the absence of synergistic interaction in aqueous solutions containing the glycerol of 0.100 mol/L, and whereas the abnormal case does not again emerge on increasing the concentration of glycerol to 0.200 mol/L. The compatibility in molecular conformation, the steric hindrance, the electrostatic repulsion and the hydrogen-bond formation are adopted to theoretically explain the interaction behavior. Thermodynamic parameters obtained using the Maeda’s treatments also confirm the absence or the presence of synergistic interaction and the formation of stable mixed micelle. These findings will help with understanding the intermolecular behavior and the effect of alcohol concentration.

Wetting Behaviour of Water, Ethanol, Rhamnolipid, and Triton X-165 Mixture in the Polymer-Solution Drop-Air System.

Despite the fact that the wetting properties of multicomponent mixtures including the surface active compounds play a very important role in many practical applications, they are not sufficiently known. Thus, the wettability of polytetrafluoroethylene (PTFE) and poly (methyl methacrylate) (PMMA) by the water + ethanol (ET) solution of rhamnolipid (RL) with Triton X-165 (TX165) mixture was studied. The investigations involved measuring the advancing contact angles of this solution on PTFE and PMMA by varying the concentration of TX165 while maintaining a constant concentration of ET and RL. Additionally, a thermodynamic analysis was conducted to obtain the compositions and concentrations of the ET, RL, and TX165 mixtures at the different interfaces. The composition and concentration of the interface mixed layer were considered using two different approaches to the wetting process. From these considerations, it follows that, depending on the ET concentration, it is possible to form the TX165 + RL layer at the solid-water + ET mixed solvent, as well as the water + ET-air interfaces, but not at the solid-water and water-air ones. This conclusion is in accordance with the Gibbs standard free energy of adsorption of particular components of the studied mixture at the solution-air and solid-solution interfaces.

Investigations on the effect of 2-[(furan-3ylmethylene)-amino]-benzenethiol on corrosion in carbon steel

A Schiff base namely, 2-[(furan-3ylmethylene)-amino]-benzenethiol (2-FAB) was synthesized and its influence on the inhibition of corrosion in carbon steel immersed in 0.5 M H2SO4 was investigated by weight loss analysis, potentiodynamic polarization studies, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and FT-IR spectroscopy. The weight loss measurements showed that 2-FAB has an excellent inhibiting efficiency of 95.51% at a concentration of 250 ppm. The inhibitor efficiency was found to depend on both the concentration and molecular structure of the inhibitor. Potentiodynamic polarization curves revealed that the studied inhibitors represent a mixed-type, predominantly cathodic control. An equivalent circuit is suggested based on an analysis of EIS data. Surface analysis using scanning electron microscope (SEM) and atomic force microscopy (AFM) show a significant morphological improvement on the mild steel surface with the addition of 2-FAB. The negative value of standard free energy of adsorption in the presence of inhibitor suggests the spontaneous adsorption of inhibitors on the carbon steel surface. The Temkin and Langmuir adsorption isotherms were found to provide a accurate description of the adsorption behavior of the inhibitor. Taken as a whole, this work demonstrates that 2-FAB shows promising results in resisting the deterioration of carbon steel in 0.5 M H2SO4 environment. The inhibitor forms a protective film on the surface of the carbon steel, significantly reducing its corrosion rate.

A comparative analysis on the effects of sodium nitrate and hexamine on the corrosion of aluminium alloy in an acidic environment

Despite aluminium and its alloys being relatively resistant to corrosion reaction as a result of their passivating tendencies, aluminium alloys usually succumb to acidic attacks resulting in mostly pitting corrosion. This study is focused on comparing the efficiency of sodium nitrate with that of hexamine on the acid corrosion of aluminium when used individually as inhibitors in 1 M Hydrochloric acid. The gravimetric method was used for the corrosion study. Sodium nitrate was found to have higher inhibitor efficiency of 94% compared to that of hexamine (44%), positioning the former as a better inhibitor for aluminium alloy in 1 M HCl. ΔGadso was evaluated and the obtained Standard free energy of adsorption were in the range of −13 to −17 kJ/mol for NaNO3 and −6 to −12 kJ/mol for hexamine, signifying the physisorption mode of adsorption.

Optimization of the inhibition corrosion of carbon steel in an acidic medium by a novel eco-friendly inhibitor Asphodelus ramosus using response surface methodology

Ethyl acetate extract of Asphodelus ramosus (ARAE) was examined as an anti-corrosion agent for carbon steel (CS) in 1 M HCl acid medium using different techniques, namely weight loss method, potentiodynamic polarization, and electrochemical impedance spec­troscopy (EIS) at various temperatures and inhibitor concentrations. An inhibition efficiency of 89.81 % was obtained by the weight loss method at the inhibitor concentration of 700 ppm at 293 K. Increasing the temperature decreases the corrosion inhibition rate. Poten­tiodynamic polarization results showed that the extract is adsorbed on CS surface according to the Freundlich isotherm, while negative values of the standard free energy of adsorption (DG0ads) suggested the physical spontaneity of the adsorption reaction. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses were performed to examine the surface morphology of inhibited and uninhibited CS samples. Central composite design (CCD) based optimization was engaged to analyze factors and maximize inhibition efficiency by applying response surface methodology (RSM) using Design-Expert software.

The study on corrosion inhibition effect of 2-Phenylbenzimidazole for X70 steel in HCl solution at 308 K

The inhibition behavior of X70 steel with different concentrations of 2-Phenylbenzimidazole in 1 M HCl solution at 308 K was evaluated through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) curves and scanning electron microscopy (SEM). It was found that the inhibition efficiency increased with increasing of 2-Phenylbenzimidazole concentration, and the best inhibition efficiency was achieved at 5 mM. Analysis of the polarization curves showed that 2-Phenylbenzimidazole belonged to mixed type inhibitor, inhibiting concurrently cathode and anode, and the inhibition effect was more significant for cathode. Moreover, the adsorption isotherm study showed that the adsorption of 2-Phenylbenzimidazole inhibitors on the surface of X70 steel followed the Langmuir adsorption model, and the calculation of the standard free energy of adsorption (ΔG0ads) indicated the presence of both physical and chemical adsorption. Furthermore, molecular dynamics (MD) simulations were applied to display the mechanism of the strong anticorrosion effect of 2-Phenylbenzimidazole molecules.

Behavior of Auramine O in the Aqueous Solution of Two Kolliphors and Their Mixture

The studies on the behavior of Auramine O (AuO) at the water-air interface and in the bulk phase of the aqueous solution of Kolliphor® ELP (ELP) and Kolliphor® RH 40 (RH40) and their mixture were based on the results obtained from the measurements of the contact angle of water, formamide and diiodomethane on the polytetrafluoroethylene covered by the AuO layer, the surface tension of the aqueous solution of AuO, AuO + ELP, AuO + RH40, AuO + ELP + RH40, density and fluorescence intensity. Based on the obtained results, it was possible to determine components and parameters of the AuO surface tension, concentration and composition of the mixed monolayer, including AuO, ELP and RH40, as well as that of the mixed micelles, and to determine the Gibbs standard free energy of adsorption, micellization and AuO solubilization. The obtained results also showed that surface tension isotherms of the studied solutions can be described by the Szyszkowski equation and the exponential function of the second order and predicted by the Fainerman and Miller equation. In addition, the mixed surface layer composition can be predicted based on the contribution of the components of this layer to the water surface tension reduction.

Influence of the Molecular Structure on the Electrocatalytic Hydrogenation of Carbonyl Groups and H2 Evolution on Pd

We investigated the electrocatalytic hydrogenation (ECH) of model aldehydes and ketones over carbon-supported Pd in the aqueous phase. We propose reaction mechanisms based on kinetic measurements and on spectroscopic and electrochemical characterization of the working catalyst. The reaction rates of ECH and of the H2 evolution reaction (HER) vary with the applied electric potential following trends that strongly depend on the organic substrate. The intrinsic rates of hydrogenation and H2 evolution are influenced, in opposing ways, by the sorption of the reacting organic substrate. Strong interactions, that is, higher standard free energies of adsorption of the organic compound, induce high hydrogenation rates. The fast hydrogenation kinetics produces a hydrogen-depleted environment that kinetically hinders the HER and the bulk phase transition of Pd to a H-rich bulk Pd hydride, which is triggered by the applied potential in the absence of reacting organic compounds. As a consequence of strong organic–metal interactions, hydrogenation dominates at low overpotential. However, the coverages of organic substrates on the metal surface decrease, and the rates of H2 evolution surpass those of hydrogenation with increasingly negative electric potential. We determined the range of electric potential favoring hydrogenation on Pd and quantitatively deconvoluted the effects of the sorption of the organic compound, and of the rates of proton-coupled electron transfers, on the kinetics of both ECH and HER. The results indicate that electrocatalysis offers hydrogenation pathways for polar molecules which are different and, in some cases, faster than those dominating in the absence of an external electric potential.

Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 103 M-1 and calculated standard free energy of adsorption was −33.03 kJ mol−1. The determined activation energy values were 55.58 kJ mol−1 and 96.86 kJ mol−1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.

Experimental studies on the corrosion inhibition performance of 2-(2-aminophenyl)benzimidazole for mild steel protection in HCl solution

BackgroundMild steel is one of the most widely used material in industry. However, this metal easily corrodes specifically in acidic solutions. Therefore, protection of this metal in this solutions is essential. There are many protection methods. The use of corrosion inhibitors is one of the widely them, which is a rapid, relatively easy and economical method. The choice of 2-(2-aminophenyl)benzimidazole (APBI) for this aim was based on its molecular structure, which bringing three N atoms and conjugated bonds as adsorption centers, and being a friendly compound. MethodsThe corrosion inhibition and adsorption properties of APBI on mild steel (MS) in 1 M HCI were studied by potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The MS surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The potential of zero charge (Epzc) of the steel in the presence of the inhibitor was determined by EIS method and an adsorption process was discussed. The effects of temperature and exposure time on the corrosion of MS were also reported. Significant findingsIt was found that the average inhibition efficiency of ABPI on the corrosion of MS determined from three electrochemical techniques is 98.8% in 1 M HCl solution. The high inhibition efficiency was assigned to its adsorption on the steel surface and forming a protective organic film. The PP studies showed that the corrosion current densitiy reduced almost 99% and open circuit potential moved from -0.48 V to -0.439 V in the presence of 10 mM inhibitor, which indicates a mixed type corrosion inhibition effect. SEM images showed good surface coverage of the inhibitor. The average percentage ratios of N and CI− on the metal which exposed to the inhibited solution were 0.97 % and 2.44 %, respectively. EDX mapping images indicated that the inhibitor distributed very homogenously. The adsorption of APBI on the mild steel surface in the corrosive solution was found to obey the Langmuir adsorption isotherm. The average value of equilibrium constant (Kads) and standard free energy of adsorption of the inhibitor (∆Goads) were found as 20.58 M−1 and -34.56 kJ mol−1, respectively. The activation energy (Ea) values are 77.28 kJ mol−1 and 78.00 kJ mol−1 for the corrosion process in the presence and absence of APBI, respectively. The CA and CV results clearly show that the inhibitor molecules are tightly adsorbed on the steel surface and form a very stable film.

Interaction of methylene blue with SDS in the premicellar solution of CPC in the aqueous and methanol-water system

Interactions between sodium dodecyl sulfate (SDS) and methylene blue (MB) have been studied in presence of cetylpyridinium chloride (CPC) in aqueous and methanol-water binary solvents via conductometric and tensiometric methods. The experiment was conducted to see the possibility of a synergistic effect of the SDS+CPC system and changes in the interactional behavior of SDS with MB in presence of CPC. The value of the molecular interaction parameter for micellization (βM) was found to be negative from the experimental results and the value of |βM| was found to be greater than ln(CMCSDS / CMCCPC), which didn’t describe synergism completely but indicated the strong striking interactions between the oppositely charged surfactants. However, the CMC of the SDS+CPC system was found to be very low as compared to the CMC of SDS alone. This result of CMC based on striking interactions between oppositely charged surfactants was used to calculate various parameters like Gibb’s free energy of micellization (∆Gmo), surface excess(Γmax), minimum surface area (Amin), surface pressure πCMC, standard free energy of adsorption (∆Gadso), pC20, minimum surface free energy (Gmins), packing parameter (P) and association equilibrium constant (K). The addition of methanol as a cosolvent enhances the CMC and α value of the SDS+CPC as well as the SDS+CPC-MB system. Correlation of ∆Gmo with different solvent parameters namely Gordon parameter (G), Reichardt's parameter (ET (30)), viscosity (ηo), and solvophobic parameter (SP) has also been evaluated.

Recycling Unused Midazolam Drug as Efficient Corrosion Inhibitor for Copper in Nitric Acid Solution.

The current work explores the potential for recycling unused or expired Midazolam (MID) drug, a benzodiazepine derivative, as an efficient corrosion inhibitor for copper in nitric acid solution. The technical advantage of recycling expired MID drug relates to the avoidance of organic inhibitor production costs and the reduction of disposal costs of the expired medication. A combination of electrochemical methods (potentiodynamic polarization and electrochemical impedance spectroscopy), weight loss, and quantum chemical calculation were used to assess the inhibition mechanism and efficiency of MID. It was found that inhibition efficiency increases with inhibitor concentration, reaching a highest value of 92.9% for a concentration of 10−4 M MID. MID was classified as a mixed-type inhibitor, showing a preferential cathodic suppression mechanism. The obtained values of −45.89 kJ mol−1 for the standard free energy of adsorption indicate that the inhibition mechanism is based on chemisorption of MID molecules on the copper surface, which obeys the Langmuir isotherm. Surface analysis using scanning electronic microscopy revealed that MID offers high protection against corrosion during both immersion and polarization tests. Molecular modelling and quantum chemical calculations indicated chemical interactions between MID molecules and the copper surface, as well as electrostatic interactions. The results obtained using the different techniques were in good agreement and highlight the effectiveness of MID in the corrosion inhibition of copper.

Experimental and theoretical studies of acridine orange as corrosion inhibitor for copper protection in acidic media

The corrosion process commonly limits the use of copper in practical applications. The use of corrosion inhibitors is one of the effective methods to reduce the corrosion rate of copper. In this research, the inhibition effect of acridine orange (3,6-bis(dimethylamine)acridine) (AcO) for the protection of copper in 0.5 ​M ​H2SO4 solution was studied. For this aim, the change of open circuit potential with exposure time (Eocp-t), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), anodic and cathodic potentiodynamic polarization measurements (PP) and chronoamperometry (CA) techniques were used. Some quantum chemical parameters (EHOMO, ELUMO and dipole moment) were calculated and discussed. The AcO film formed over the copper surface was examined by SEM, EDX, AFM and contact angle measurements. The electrochemical data showed that AcO is an effective corrosion inhibitor even at low concentrations (ranging between 99.1% and %99.4 ​at concentrations from 0.01 ​mM to 1 ​mM). The corrosion rate of copper decreases in the presence of the inhibitor by reducing both anodic and cathodic rates, which is depended on its concentration. This compound behaves as mixed-type corrosion inhibitors with predominantly cathodic type. Its adsorption on the copper surface obeys Langmuir adsorption isotherm. The value of adsorption equilibrium constant (Kads) and the standard free energy of adsorption were ΔGads 1.298 x 103 ​M−1 and -27.71 ​kJ/mol in the case of 0.5 ​M ​H2SO4 solution containing 1.0 ​mM AcO, which shows the adsorption is high and spontaneous. The adsorbed inhibitor film over the metal increase contact angle of the surface, which suggests the more hydrophobic properties of the surface are increasing coming from the orientation of hydrophobic sites to the electrolyte. The zero charge potential (Epzc) studies showed that the surface charge of the metal is positive in the corrosive media containing the inhibitor. Quantum chemical calculations showed that the binding of inhibitor molecules to the metal surface takes place through N atoms of the inhibitor.

Corrosion inhibitors: physisorbed or chemisorbed?

Adsorption mode of corrosion inhibitors is often determined by criteria based on the standard free energy of adsorption, with values greater than −20 kJ/mol attributed to physisorption and values smaller than −40 kJ/mol attributed to chemisorption. Several arguments are presented herein to show that these are not very reliable criteria to distinguish between physisorption and chemisorption. The most notable among them is that chemisorption may involve bond-breaking and bond-making that result in a rather “weak” standard adsorption free energy (or enthalpy). For this reason, more reliable criteria are recommended that are readily available in first-principle computational modeling studies. The strong molecule–surface interaction, involved in chemisorption, should also be detectable by spectroscopy.

Adsorption Properties of Hydrocarbon and Fluorocarbon Surfactants Ternary Mixture at the Water-Air Interface.

Measurements were made of the surface tension of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10 oxyethylene groups in the molecule (Triton X-100, TX100) and cetyltrimethylammonium bromide (CTAB) with Zonyl FSN-100 (FC6EO14, FC1) as well as with Zonyl FSO-100 (FC5EO10, FC2) ternary mixtures. The obtained results were compared to those provided by the Fainerman and Miller equation and to the values of the solution surface tension calculated, based on the contribution of a particular surfactant in the mixture to the reduction of water surface tension. The changes of the aqueous solution ternary surfactants mixture surface tension at the constant concentration of TX100 and CTAB mixture at which the water surface tension was reduced to 60 and 50 mN/m as a function of fluorocarbon surfactant concentration, were considered with regard to the composition of the mixed monolayer at the water-air interface. Next, this composition was applied for the calculation of the concentration of the particular surfactants in the monolayer using the Frumkin equation. On the other hand, the Gibbs surface excess concentration was determined only for the fluorocarbon surfactants. The tendency of the particular surfactants to adsorb at the water-air interface was discussed, based on the Gibbs standard free energy of adsorption which was determined using different methods. This energy was also deduced, based on the surfactant tail surface tension and tail-water interface tension.

Synthesis of cationic (CTAB-EDTA-CTAB/ CTAB-Glu-CTAB) and anionic (SDS-EDTA-SDS/ SDS-Glu-SDS) Gemini surfactants: Surface and anticorrosive properties

Gemini surfactants that served as environmentally friendly corrosion inhibitors, have been successfully synthesized by the reaction of SDS/ CTAB with glucose/ EDTA as spacer. Their molecular structure is confirmed by 1H-NMR and FTIR spectroscopy. By tensiometric method, the surface activity of the synthesized Gemini surfactants has been determined in terms of various parameters like the critical micelle concentration, surface excess at the air/water interface, minimum area per surfactant molecule, surface pressure at CMC, changes of standard free energies of adsorption, micellization and transfer. The obtained Gemini surfactants having EDTA as a spacer, exhibit a considerably higher effectiveness against corrosion as compare to Gemini surfactants having glucose as spacer.

Systematic Studies of Sodium γ-Octyl Aspartate to evaluate its Biodegradation, Surface Parameters, Micellization Aspects and Thermodynamic Properties of its Binary Mixture using Electrolytes

γ-octyl aspartate has been synthesized with 46.2% yield. The optimized conditions for esterification of aspartic acid and n-octanol are 24 hours duration and 1:1 molar ratio of reactants (aspartic acid: n-octanol). FT-IR, 1H NMR and CHNS element analysis techniques are used for structure elucidation of γ -octyl aspartate. Surface/ interfacial studies, micellization aspects, thermodynamic parameters, biodegradability and binary salt behaviour of sodium γ-octyl aspartate have been studied. The CMC of synthesized surfactants was 0.0078 mol/L, whereas minimum surface area per surfactant molecule was calculated as 29.49 Å2m2; calculated aggregation number was 34 and micelle radius (r) found to be 1.40 nm. The degree of counter-ion dissociation (α) was determined to be 0.86. Thermodynamic parameter - standard free energy of adsorption (ΔG0ads) was calculated as -18.70 kJ/mol. The shape of micelle of synthesized surfactant was noticed to be spherical but during binary studies in some cases, it was found to be cylindrical. OECD and Winkler’s method were used to determine biodegradation of sodium γ-octyl aspartate found to be 95.1 %.

Interfacial and micellization behavior of binary mixture of amino sulfonate amphoteric surfactant and octadecyltrimethyl ammonium bromide: Effect of short chain alcohol and its chain length

The interfacial and micellization behavior of binary mixture of an amino sulfonate amphoteric 3-(N-dodecyl ethylenediamino)-2-hydropropyl sulfonate (C12AS) and a cationic octadecyltrimethyl ammonium bromide (OTAB) were investigated in aqueous solution without or with a 70 g/L alcohol (including methanol, ethanol, 1-propanol and 1-butanol) at 313.15 K by both the tensiometry and the conductometry. The surface excess concentration, the minimum area per surfactant molecule at the saturated interface and the standard free energy of adsorption at the air-liquid interface were adopted to be characteristic of the interfacial adsorption monolayer. Based on the pseudophase separation model and the regular solution theory, the Clint’s model and the Rubingh’s model was used to obtain the related parameters including the interaction parameters between two surfactant molecules, the compositions and the activity coefficients in mixed micelle and thermodynamic parameters. The effect of the alcohol chain length on the interfacial adsorption and the mixed micellization was discussed. The addition of short chain alcohol influences the properties of mixed cosolvent, the conformation of C12AS molecule and the electrostatic interaction between two surfactant molecules. Thermodynamic data shows that the presence of alcohol with a longer chain is beneficial to form the adsorption monolayer and the mixed micelle, and also it depresses the contribution of entropy to the process of micellization. These findings help with understanding the mechanism on the effect of short chain alcohol on the interfacial and micellization behavior of binary surfactant mixtures and further designing the surfactant formulations.