Gibbs Energy Of Adsorption Research Articles

Stability Evaluation of Cation Bridging on Muscovite Surface for Improved Description of Ion-Specific Wettability Alteration

By using molecular dynamics (MD) simulations and potential of mean force (PMF) calculations, we studied the stability of model acidic oil molecules (C9H19COOH or C9H19COO–) adsorbed on muscovite surfaces in aqueous solution. The muscovite surfaces are covered by different cations (Na+, K+, Mg2+, and Ca2+). It was found that Ca2+-covered muscovite surface significantly enhances the adsorption of C9H19COO– with adsorption Gibbs energy 1 order of magnitude higher than that of Na+-covered surface and 3 times higher than that of K+-covered surface. Furthermore, we found clear evidence that Ca2+ and K+ cause cation bridging, whereas Mg2+ and Na+ cause water bridging. The adsorption Gibbs energy is much higher for cation bridging than that of water bridging. The ion specific effect is not observed when the carboxyl group is protonated (i.e., C9H19COOH). These results well explain the results of previous wettability and core flooding experiments and support their key findings that adsorption of Ca2+ cations induc...

Electrocatalytic application for gold nanoparticles decorated sulfur-nitrogen co-doped graphene oxide nanosheets and nanosized cobalt tetra aminophenoxy phthalocyanine conjugates

Sulfur and nitrogen affinity for gold is utilized to self-assemble gold nanorods (AuNRs) on S, N doped or S/N co-doped graphene oxide nanosheets (SGONS/AuNRs, NGONS/AuNRs or SNGONS/AuNRs) for enhancement of the electrocatalytic activity of nanosized cobalt tetra aminophenoxy phthalocyanine (complex 1) towards hydrogen peroxide detection. Of the electrodes containing AuNRs, 1-SNGONS/AuNRs-GCE gave the lowest limits of detection (LOD) of 0.012μM followed by 1-SGONS/AuNRs-GCE and 1-AuNRs-SNGONS(seq)-GCE both with LOD of 0.016μM. This work shows that in the absence of GONS (when AuNRs are alone and in the presence of 1 in 1/AuNRs-GCE), unfavorable detection limits are obtained and that doping of GONS is important in improving LOD. 1-SNGONS/AuNRs-GCE showed concentration dependent mechanisms resulting in two adsorption Gibbs energies (ΔGo) of −18.55kJmol−1 and −17.35kJmol−1 at high and low concentrations, respectively.

Spontaneous Interfacial Tension Changes at the Interface of Metal Chloride Nitrobenzene Solution and Aqueous Stearyltrimethylammonium Chloride Solution: the Role of Metal Ions

Abstract The authors examine the roles of chemical compounds that can generate spontaneous interface motion, especially in the Nakache and Dupeyrat system, which normally uses a stearyltrimethylammonium chloride (STA-Cl) aqueous solution and a KI + I2 nitrobenzene solution. The authors observed spontaneous behavior at the interface of a system comprising the STA-Cl aqueous solution and a nitrobenzene solution of ZnCl2 or FeCl3. To investigate the role of metal ions, in-situ electrochemical measurements of systems of various metal halides, such as KCl, CaCl2, AlCl3, ZnCl2, and FeCl3, were conducted and discussed regarding the relationship of the spontaneous interface motion with the consideration of standard Gibbs energy of surfactant adsorption, solubility into the oil phase, and hydration enthalpy. The importance of electric potential dependence of surfactant adsorption–desorption at the oil/water interface is suggested and supported using an FeCl3 chlorobenzene solution. A material design with the consideration of a potential barrier of surfactant desorption would enable us to obtain a spontaneous motion system not utilizing toxic substances.

Site-Specific Reactivity of Ethylene at Distorted Dangling-Bond Configurations on Si(001).

Differences in adsorption and reaction energetics for ethylene on Si(001) are reported with respect to distorted dangling-bond configurations induced by hydrogen precoverage, as obtained by DFT calculations. This can help to understand the influence of surface defects and precoverage on the reactivity of organic molecules on semiconductor surfaces in general. The results show that the reactivity of surface dimers fully enclosed by hydrogen-covered atoms is essentially unchanged compared to the clean surface. This is confirmed by scanning tunneling microscopy measurements. On the contrary, adsorption sites with partially covered surface dimers show a drastic increase in reactivity. This is due to a lowering of the reaction barrier by more than 50 % relative to the clean surface, which is in line with previous experiments. Adsorption on dimers enclosed by molecule (ethylene)-covered surface atoms is reported to have a strongly decreased reactivity, as a result of destabilization of the intermediate state due to steric repulsion; this is quantified through periodic energy decomposition analysis. Furthermore, an approach for the calculation of Gibbs energies of adsorption based on statistical thermodynamics considerations is applied to the system. The results show that the loss in molecular entropy leads to a significant destabilization of adsorption states.

Review on the Determination of Frumkin, Langmuir, and Temkin Adsorption Isotherms at Electrode/Solution Interfaces Using the Phase-Shift Method and Correlation Constants

This review article described the electrochemical Frumkin, Langmuir, and Temkin adsorption isotherms of over-potentially deposited hydrogen (OPD H) and deuterium (OPD D) for the cathodic H2 and D2 evolution reactions (HER, DER) at Pt, Ir, Pt-Ir alloy, Pd, Au, and Re/normal (H2O) and heavy water (D2O) solution interfaces. The Frum-kin, Langmuir, and Temkin adsorption isotherms of intermediates (OPD H, OPD D, etc.) for sequential reactions (HER, DER, etc.) at electrode/solution interfaces are determined using the phase-shift method and correlation constants, which have been suggested and developed by Chun et al. The basic procedure of the phase-shift method, the Frumkin, Lang-muir, and Temkin adsorption isotherms of OPD H and OPD D and related electrode kinetic and thermodynamic param-eters, i.e., the fractional surface coverage (0 ≤ θ ≤ 1) vs. potential (E) behavior (θ vs. E), equilibrium constant (K), interaction parameter (g), standard Gibbs energy (ΔGθ˚) of adsorption, and rate (r) of change of ΔGθ˚ with θ (0 ≤ θ ≤ 1), at the interfaces are briefly interpreted and summarized. The phase-shift method and correlation constants are useful and effective techniques to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters (θ vs. E, K, g, ΔGθ˚, r) at electrode/solution interfaces.

Surface tension and density of mixtures of m-xylene + n-alkane at 293.15 K: Analysis under the extended Langmuir and Shereshefsky models

Surface tension (σ) and density (ρ) for {m-xylene+n-pentane, hexane, heptane and octane} at the temperature 293.15K and pressure 1.013bar have been determined as a function of mole fraction. In order to analyze the surface tension behavior, the extended Langmuir (EL) and Shereshefsky models were used and parameters of the models were obtained for these mixtures. The standard Gibbs energy of adsorption (-ΔG∘) was calculated using both models. The free energy change of replacing one mole of solute with one mole of solvent in surface region (ΔGS) and the excess number of molecular layers of solute in the surface region were calculated using Shereshefsky model. The magnitude of ΔGS and (-ΔG∘) was discussed in terms of nature and type of intermolecular interactions in binary mixtures. The Redlich-Kister polynomial equation was fitted to each of the experimental surface tension deviation (δσ) and excess molar volume (vE) results. Using the resulting polynomial equations, the surface tension deviations and the excess molar volumes (δσ, vE) were calculated over the entire composition range.

Synthesis, Surface and Antimicrobial Activity of Piperidine-Based Sulfobetaines

A new method for the preparation of new heterocyclic amine surfactants based on sulfobetaines is proposed. Interfacial activities of the surfactants obtained in aqueous solution were studied by surface tension measurements. The critical micelle concentration, surface excess concentration, minimum area per surfactant molecule, and standard Gibbs energy of adsorption were determined. The adsorption properties of these compounds depend significantly on the alkyl chain length. Alkyl chain length also affects biological properties of the new surfactants, determining the minimum inhibitory concentration and size of inhibited growth zone. The compounds have high antimicrobial activity.

Self-association behavior of an amphiphilic drug nortriptyline hydrochloride under the influence of inorganic salts

Herein, the micellization phenomena of an amphiphilic antidepressant drug nortriptyline hydrochloride (NOT) have been studied using tensiometric technique in the absence and presence of different concentration of inorganic salts (NaCl, NaBr and KCl) at 298.15 K. NOT is employed for the relief of symptoms of depression. In presence of inorganic salt the CMC value decreases which is explained on the basis of nature and ion size. Various parameters, i.e., the maximum surface excess concentration at the air/solution interface (Γmax), minimum area per head group at the air/solution interface (Amin), free energy of micellization (ΔG m o), minimum energy of surface (G min) and standard Gibbs energy of adsorption (ΔG ads o) were evaluated and discussed in detail.

Thermodynamic study of seven micropollutants adsorption onto an activated carbon cloth: Van't Hoff method, calorimetry, and COSMO-RS simulations.

The thermodynamic of the adsorption of seven organic pollutants, namely benzotriazol, bisphenol A, caffeine, carbamazepine, diclofenac, ofloxacin, and pentachlorophenol, was studied on a microporous-activated carbon fabric. The isosteric adsorption quantities (Gibbs energy, enthalpy, and entropy variations) at high coverage ratio (around 1mmol/g) have been determined from the adsorption isotherms at three temperatures (13, 25, and 40°C). The adsorption heats at very low coverage (about 10-5mmol/g) have been measured by flow micro calorimetry. The experimental adsorption energies were correlated to the adsorbate-adsorbent and the adsorbate-solvent interaction energies calculated by simulations using the COSMO-RS model. The main role of the van der Waals forces in the adsorption of the studied molecules was established. The bulkier the adsorbate is, the lower the adsorption Gibbs energy variation at high coverage deduced from the isotherms. The heterogeneity of the adsorption sites was brought out by calorimetric measurements. At high coverage, a physisorption phenomenon was observed. At very low coverage, high values of the adsorption heats were found (ranging from -58 to -110kJ/mol), except for pentachlorophenol characterized by an athermal adsorption controlled by Pi-anions interactions.

Effect of tartrazine dye on micellisation of cationic surfactants: conductometric, spectrophotometric, and tensiometric studies

The interactions between anionic dye (tartrazine) and cationic surfactants (dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide) have been studied by conductometric, spectrophotometric, and tensiometric techniques. The conductance and surface tension of dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide in pure water as well as in aqueous tartrazine when plotted with surfactant concentration gave values of the critical micelle concentration at different temperatures. As well as increasing the length of the carbon chain of surfactants, the presence of tartrazine reduces the critical micelle concentration. From specific conductivity data, the counterion dissociation constant, standard free energy, enthalpy, entropy of micellisation, surface excess concentration, surface tension at critical micelle concentration, minimum area per molecule, surface pressure at critical micelle concentration, and Gibbs energy of adsorption were evaluated. Spectroscopic studies reveal that the binding of dye to micelles brings a bathochromic shift in dye absorption spectra that indicates dye–surfactant interaction.

Transfer of non-ionic surfactants across the water-oil interface: A molecular dynamics study

Compounds able to adsorb at the interface of two immiscible liquids are of high importance for numerous chemical, physical and biological processes. Deeper understanding of the interfacial phenomena in such systems can contribute significantly to the rational practical application of small amphiphiles in electrochemistry, extraction, stabilization of emulsions, and drug design. Particularly interesting are the oil-water formulations, where the aqueous and the hydrophobic phases tend to express different molecular structure and characteristics under identical conditions. Surfactant behaviour in such environments is known to differ distinctly from the one observed in bulk water or oil or at the gas-liquid interface. It has been demonstrated that the free energy of adsorption and transfer of amphiphiles across water-oil interfaces can be decomposed into specific contributions of molecular fragments. The models developed so far do not provide information about the specifics of the functional groups contributions. To elaborate further on this topic, classical molecular dynamics simulations, combined with umbrella sampling calculations and weighted histograms method analysis are applied to reconstruct the free energy profile for several water-oil-amphiphile models along a relocation coordinate normal to the interface. Normal pentane, hexane, and heptane are chosen as models of the hydrophobic liquids and three short-chained normal alcohols⿿as low-molecular-weight amphiphiles. Gibbs energies of transfer and adsorption, as well as the average contributions per unit of elongation of the alkyl chain, are estimated and compared to experimental data and empirical results. The experimental trends of all quantities are reproduced correctly. Some quantitative differences are discussed. A detailed analysis of the free energy change vs. position of alcohol molecules shows that the transfer process can be decomposed into several stages. Such more precise stratification of the interfacial region is employed to determine and rationalize the free energy contributions of the separate alkanol functional groups.

Effect of 1-ethyl-3-methylimidazolium bromide on interfacial and aggregation behavior of mixed cationic and anionic surfactants

Aggregation behavior and interaction of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB) and their mixtures with an excess of anionic surfactant in the presence of imidazolium-based ionic liquid, 1-ethyl-3-methylimidazolium bromide (EMIm Br) were investigated using surface tension, electrical conductivity, dynamic light scattering (DLS), transmission electron microscopy (TEM) and cyclic voltammetry measurements. Different physicochemical properties such as critical micelle concentration (CMC), degree of counterion dissociation (αdiss), interfacial properties, the standard Gibbs energy of adsorption and the size of aggregates were determined. The effects of ionic liquid (IL) as additive on the interactions between the surfactants; TTAB, SDS and their mixtures were analyzed on the basis of regular solution theory, both for mixed monolayers at the air/liquid interface (βδ) and for mixed micelles (βM). Interaction parameter values suggested that the formation of aggregates is due to the synergistic interactions in the case of SDS/TTAB systems and becomes more affected by adding IL. It was shown that an excess of cationic surfactant and IL resulted in an increase in the nano-aggregate sizes. The synergism observed for three component systems (surfactant–water–IL) revealed the effect of attractive electrostatic interaction, formation of a three-dimensional hydrogen bond network and hydrophobic forces on mixed micelle formation.

First-Principle Theory to Understand Autocatalysis in Electroless Cu Deposition

Electroless deposition of a metal takes place without any external applied current. Electroless Cu deposition is used for protective coatings, surface finishing, and advanced nano-scale interconnect fabrication in microprocessors. The commonly used Cu electroless deposition precursor is [Cu(II)EDTA]2- which is reduced to Cu(0) by formaldehyde or glyoxylic acid in basic medium. The measured mixed potential and the deposition rate during electroless deposition are substantially different compared to the theoretical mixed potential and rate (predicted using the mixed potential theory). This indicates the interdependent relationship between the anodic and cathodic half-reactions.1 To understand the catalytic mechanisms involved in [Cu(II)EDTA]2- reduction with formaldehyde or glyoxylic acid, a comprehensive first principle approach was used. Different Cu cluster models were simulated and used in the Gaussian 09 code to calculate the activation energies for carbon-hydrogen bond breaking in hydrolyzed formaldehyde, yielding H(ads) and a formic acid anion, the proposed reducing agent. Low-coordinated surface Cu atoms were found to facilitate H abstraction. Also, we have hypothesized possible steps for anodic and cathodic half-reactions during electroless Cu deposition in base: the Cu(II) complex is reduced Cu(I) and then to Cu(0). The adsorbed H gives rise to evolution of H2(g), as observed. The reversible potentials for electron-transfer steps for reduction were calculated using Interface 1.0, a code that applies density functional theory with dielectric continuum and modified Poisson-Boltzmann theory.2 We chose three-layer thick Cu slab models for the reversible potential calculations, optimizing the structure for the layer on which the adsorption was studied. For electron-transfer steps taking place on the surface, the reversible potentials were assumed to be well-approximated as the standard reversible potentials (U 0) perturbed by adsorption Gibbs energies at the potential of zero charge (pzc). The standard reversible potentials (U 0) are for the corresponding reactions with all species in bulk solution.In summary, we propose the following mechanism for the [Cu(II)EDTA]2- reduction to Cu(0,ads) using formaldehyde as a model: the formaldehyde reacts with H2O and OH- to give H2C(OH)O-(aq) (methanediol anion) which undergoes C-H bond breaking over low-coordinated Cu atoms to give [HCOOH]-(aq) (formic acid anion). These anions lose their hot electrons3 through space or through the Cu surface to become HCOOH (formic acid) molecules and reduce nearby Cu(II) complexes stepwise to Cu(0,ads). Due to the fact that one H atom is deposited on the surface by every C-H bond broken, and because of the weakness of Cu-H bonds, H2 can form, as is observed during the electroless deposition process. This hypothesized mechanism should also hold when glyoxylic acid is used since both reducing agents contain the aldehyde group, HRC=O , which is the key to the process since it involves breaking C-H bond and putting H on the surface, generating the active anion intermediates.

Repulsive interactions induced by specific adsorption: Anomalous step diffusivity and inadequacy of nearest-neighbor Ising model: (part I experimental)

This is Part I of two closely related papers, where we show that the specific adsorption of anions leads to a failure of the nearest-neighbor Ising model to describe island perimeter curvatures on Au(100) electrodes in dilute KBr, HCl and H2SO4 electrolytes and the therewith derived step diffusivity vs. step orientation. This result has major consequences for theoretical studies aiming at the understanding of growth, diffusion and degradation phenomena. Part I focuses on the experimental data.As shown theoretically in detail in Part II (doi:10.1016/j.susc.2016.03.022), a set of nearest-neighbor and next-nearest-neighbor interaction energies (ϵNN, ϵNNN) can uniquely be derived from the diffusivity of steps along 〈100〉 and 〈110〉. We find strong repulsive next-nearest neighbor (NNN) interaction in KBr and HCl, whereas NNN interaction is negligibly for H2SO4. The NNN repulsive interaction energy ϵNNN therefore correlates positively with the Gibbs adsorption energy of the anions. We find furthermore that ϵNNN increases with increasing Br− and Cl− coverage.The results for ϵNNand ϵNNN are quantitatively consistent with the coverage dependence of the step line tension. We thereby establish a sound experimental base for theoretical studies on the energetics of steps in the presence of specific adsorption.

Interaction of cationic amphiphilic drug nortriptyline hydrochloride with TX-100 in aqueous and urea solutions and the studies of physicochemical parameters of the mixed micelles

The interaction of amphiphilic antidepressant drug nortriptyline hydrochloride (NOT) with nonionic surfactant Triton X-100 (TX-100) was studied in this work using tensiometry in aqueous and in urea (500mmol∙kg−1 and 1000mmol∙kg−1) solutions at 303.15K. Various models such as Clint, Rubingh, and Rosen etc. were employed to get the information regarding the nature of interaction between the compounds in bulk and at the interface. The CMC values of the mixed systems of NOT and TX-100 were found to be in between the CMC value of pure components, which suggest nonideal mixed system having attractive interactions in the absence and presence of urea. Enhancement in the surface charge of the micelles was obtained in the company of urea followed by halt of the micelles formation. Various physicochemical parameters, such as, micellar mole fraction (X1Rub) of TX-100, interaction parameters (βσ, βm) at monolayer air–water interface as well as in bulk solutions, thermodynamic parameters, activity coefficients (f1m, f2m), surface pressure at the CMC (πCMC), for the TX-100 and NOT in the mixed micelles were determined as discussed in detail. Thermodynamic parameters (minimum energy of surface (Gmin), standard Gibbs energy of adsorption (ΔGads∘), free energy of micellization (ΔG°m), excess Gibbs energy of the mixed monolayer (ΔGexσ), excess Gibbs energy of the micelle formation (ΔGexm) and free energy of micellization (ΔGMaeda0) (calculated by Maeda model)) and surface properties exposed that the addition of urea changes the relevant physicochemical properties which influence the process of micellization.

Competitive adsorption of nitrogen and sulphur compounds on a multisite model of NiMoS catalyst: A theoretical study

Using density functional theory including dispersion corrections, we establish a scale of enthalpies and Gibbs energies of adsorption of various organo-nitrogen molecules on a multisite model of the NiMoS active phase, which includes coordinatively unsaturated Lewis sites (Mo or Ni) and Brønsted –SH sites located on the M-edge and S-edge. Dispersion corrections and entropic effects are shown to impact significantly Gibbs energies of adsorption. In particular, protonation of pyridine derivatives is enhanced at high temperature on the Brønsted –SH sites of the M-edge and S-edge. For pyridine, a vibrational frequency analysis of the adsorption modes is undertaken. Stable adsorption configurations are identified for thiophene and 4,6-DMDBT on Lewis and Brønsted sites, and compared to N-containing molecules. While pyrrole derivatives are weak poisons of adsorption sites, pyridine derivatives are the stronger inhibitors. Furthermore, ammonia exhibits a non-negligible inhibitor character. We finally discuss the impact of inhibitors on 4,6-DMDBT hydrodesulphurization pathways.

The effect of salts on micellization in C12mimBr/Triton X-100 aqueous mixtures and on the surface properties of the solutions

Herein, we report our studies on the mixed aqueous solutions of 1-dodecyl-3-methylimidazolium bromide (C12mimBr) and Triton X-100 in the presence of sodium bromide and sodium chloride by surface tension and conductivity measurement methods. The critical micelle concentration and several other parameters such as maximum surface excess, minimum area per molecule and surface pressure at the CMC were calculated from the data of surface tension investigation. The critical micelle concentration values decreased with the increase of salt concentration. Rubingh’s theory was applied to calculate the mole fraction (X 1) of C12mimBr in the mixed systems. The results showed that X 1 increased most significantly with the concentration of the salt in the presence of NaBr. The values of standard Gibbs energies of micellization and interfacial adsorption have also been calculated; both were found to be negative for all systems, indicating the spontaneity of micellization and adsorption of the surfactants.

Mixed Micellization and Interfacial Properties of Ionic Liquid‐Type Imidazolium Gemini Surfactant with Amphiphilic Drug Amitriptyline Hydrochloride and its Thermodynamics

AbstractThe thermodynamics of mixed micellization of amitriptyline hydrochloride (AMT) with ionic liquid‐type imidazolium gemini surfactant ([C10‐4‐C10im] Br2), was investigated at different mole fractions and temperatures by surface tension measurements. The deviation of the critical micelle concentration (CMC) from the ideal critical micelle concentration (CMC*), micellar mole fraction () from ideal micellar mole fraction (), the values of interaction parameter () and activity coefficients () (for both mixed micelles and mixed monolayer) explained the non‐ideal behavior (i.e., synergistic behavior) of binary mixtures. The excess free energy (∆Gex) for the AMT‐[C10‐4‐C10im] Br2 binary mixtures explained the mixed micelles stability in comparison to micelles of [C10‐4‐C10im] Br2 and pure AMT. Interfacial parameters, i.e., Gibbs surface excess (), minimum head group area at air/water interface (), free energy of micellization (), and standard Gibbs energy of adsorption (∆Gadso) were also evaluated for the systems. The standard entropy of adsorption (∆Sadso) was found higher than the standard entropy of micellization (∆Smo) at all mole fractions of AMT (α1).

Effect of Polar Organic Solvents on Self‐Aggregation of Some Cationic Monomeric and Dimeric Surfactants

AbstractSurface and micellization behavior of some cationic monomeric surfactants, viz., cetyldiethylethanolammonium bromide (CDEEAB), cetyldimethylethanolammonium bromide (CDMEAB), tetradecyldiethylethanolammonium bromide (TDEEAB) and dimeric surfactants, i.e., alkanediyl‐α, ω‐bis(dimethylhexadecylammonium bromide) (C16‐s‐C16, 2Br− where s = 4, 12), butanediyl‐1,4‐bis(dimethyldodecylammonium bromide (C12‐4‐C12, 2Br−) and 2‐butanol‐1,4‐bis(dimethyldodecylammonium bromide) (C12‐4(OH)‐C12, 2Br−), was studied in water‐organic solvents [10 and 20 % v/v ethylene glycol (EG) and diethylene glycol (DEG)] by conductivity, surface tension and steady‐state fluorescence methods at 300 K. The main focus of the present work is on the study of the effect of organic solvents on the critical micelle concentration (CMC), Gibbs free energy of micellization (ΔG°m), Gibbs free energy of transfer (ΔG°trans), Gibbs adsorption energy (ΔG°ads) and some interfacial parameters such as the surface excess concentration (Γmax), minimum area per surfactant molecule (Amin) and surface pressure (πCMC). The aggregation number (Nagg) and Stern‐Volmer quenching constant (KSV) were also determined by the steady‐state fluorescence method. It was observed that Nagg decreased with increasing volume percent of organic solvent. The results exhibited an increase in CMC in water‐organic solvents as compared to the respective surfactants in pure water. The negative values of ΔG°m and ΔG°ads indicate a spontaneous micellization process. The thermodynamics of micellization revealed that the micellization‐reducing efficiency of glycols increases with the concentration and the number of ethereal oxygens in the glycol.

Effect of surfactant structure on the mixed micelle formation of cationic gemini–zwitterionic phospholipid systems

The micellization behavior of mixed zwitterionic/cationic solutions, that is, of zwitterionic phospholipid, 1, 2-dioctanoyl-sn-glycero-3-[phospho-L-serine] (sodium salt) (PL) and cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium bromide (alkyl: 14 or 16 and alkane: butane, pentane or hexane) (m-s-m), have been studied by surface tension measurements. Various physicochemical properties, viz., critical micelle concentration (cmc), surface excess concentration (Γmax), minimum area per molecule (Amin), interaction parameters (βm, βσ), and thermodynamic parameters such as standard Gibbs energy of micellization (ΔGmic°), standard Gibbs energy of adsorption (ΔGads°), and excess free energy of mixing (ΔGexm,ΔGex°), have been evaluated. The obtained results indicate that the mole fraction of PL in the mixed micelles, calculated on the basis of Rubingh's model, is different from stoichiometric mole fraction of PL (α1). The negative values of ΔGmic° and ΔGads° show that the micelle formation and adsorption of surfactants at the air/solution interface is energetically favorable with the magnitude of ΔGads° greater than that of ΔGmic°. The negative values of ΔGexm and ΔGexσ indicate better stability of the mixed systems. The insights presented herein on the gemini-phospholipid mixed micelle properties may find use towards their applications in the relevant areas of solubilization/drug delivery/etc.