Synthesis and Characterization of a Novel Short Fluorocarbon Chain Cationic Surfactant

A novel short fluorocarbon chain cationic surfactant has been synthesized to reduce the bioaccumulation of traditional fluorocarbon surfactants and maintain excellent surface properties simultaneously. The structure, surface activity, and micelle formation of surfactants have been investigated by surface tension, conductivity, dynamic light scattering, steady-state fluorescence, Fourier transform infrared spectroscopy, and Nuclear magnetic resonance. The novel surfactant (yield more than 81%) exhibited good surface activity, the critical micelle concentration and surface tension were below 2.35 mmol L⁻¹ and 20.54 mN m⁻¹ in the range of temperature from 288 to 303 K, respectively. The surface tension decreased to 17.45 mN m⁻¹ with an increase in temperature. The thermodynamic parameters (, and ) of micellization for surfactants were evaluated, which implying the micellization process was contributed primarily by the entropy driving. In addition, the aggregation behavior of surfactants was also studied in detail, which demonstrated a small micelle aggregation number of 9.40 and large size distribution of 164–342 nm.     

Elucidation of Interactions between l-Ascorbic Acid and Mixed Micellar Aggregates of Catanionic {Sodium Dodecylsulfate + Cetyltrimethylammonium Bromide} Surfactants via Physicochemical and Spectroscopic Studies

Surfactant micelles mimic the microenvironment present in biological systems and can act as a medium for antioxidant studies. Moreover, the thermodynamic profile of micellization and spectroscopic studies provides very good information about interactions in these systems. Thus, the mixed micellar behavior of sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) at varying mole fractions of SDS was studied in (0.01, 0.02, and 0.03) mol kg⁻¹ ʟ-ascorbic acid_(aq) solutions with the aid of various techniques viz., conductivity, density and sound velocity, and spectroscopy. From the CMC values of the mixed surfactants, the degree of ionization (β) and thermodynamic parameters (, , and ) were evaluated at 298.15, 308.15, and 318.15 K. The UV absorption spectra were recorded in (1–3) × 10⁻⁴ mol kg⁻¹ ʟ-ascorbic acid_(aq) solutions at various mole fractions of SDS. The proton (¹H) NMR spectra of mixed (SDS + CTAB) surfactants were studied in (0.01–0.03) mol kg⁻¹ ʟ-ascorbic acid solutions. Hydrodynamic diameters (D_h) of mixed micellar aggregates were obtained from the dynamic light scattering (DLS) studies. The present studies suggest the predominance of ionic-hydrophilic interactions between the ionic head groups {O-SO₃⁻ or N⁺ (CH₃)₃} of surfactants and the polar (–OH, –C=O and –O–) sites of ʟ-ascorbic acid.     

Influence of Different Additives on the Interaction of Quinolone Antibiotic Drug with Surfactant: Conductivity and Cloud Point Measurement Study

Conductometric and cloud point (CP) measurement studies have been performed to investigate the interaction of tetradecyltrimethylammonium bromide (TTAB) and Triton® X-100 (TX-100) with ciprofloxacin hydrochloride (CFH) in different solvents over the temperature range of 295.15–315.15 K. CFH is used for the treatment of various bacterial infections. The observed critical micelle concentration (CMC) values of TTAB were found to be reduced in the presence of electrolytes (Na₂SO₄/Na₃PO₄), and this reduction proceeds with the elevation of salt concentration. The order of the CMC of TTAB follows the trend: > >. The observed CMC values of TTAB were found to increase with increasing temperature and decrease with increasing concentration of CFH in aqueous medium. The values of Gibbs free energy of micellization () for the TTAB/TTAB + CFH mixture were found to be negative, implying spontaneous micellization. The estimated CP of TX-100 decreases with increasing concentration of TX-100 in aqueous medium. The CP values first decrease with increasing concentration of CFH and then increase at higher concentration of CFH almost in all cases investigated. The values of free energy of clouding were found to be positive in all cases studied implying that phase separation of TX-100 was nonspontaneous. The other thermodynamic parameters associated with the micellization of TTAB and the phase separation of TX-100 were estimated and explained.     

Effect of Sodium Halide on Micellar and Surface Properties of Cationic Silicone Surfactants

The effect of sodium halide on aggregation behavior of four cationic silicone surfactants, Si₃mamCl, Si₄mamCl, Si₄PyCl, and Si₄minCl, in solution was investigated using surface tension and conductivity measurements. The ability of sodium halide (NaCl, NaBr, and NaI) to reduce critical micelle concentration (CMC) values was in the order NaI > NaBr > NaCl. However, the γ_CMC values of the cationic silicone surfactants, Si₄mamCl, Si₄PyCl and Si₄minCl, in sodium halide solution are almost the same as those of the salt-free system. The values of and are negative, indicating that the micellization process and adsorption of the four cationic silicone surfactants at the air-solution interface are spontaneous.     

Insight of molecular interactions between short-chain tetraalkylammonium bromides and cetyltrimethylammonium bromide: A spectroscopic and thermodynamic approach

The influence of tetraalkylammonium salts, viz., tetraethylammonium, tetrapropylammonium, and tetrabutylammonium bromides (0.005, 0.010, 0.015 mol kg⁻¹) on the micellar behavior of aqueous solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB, 0.2–2 mmol kg⁻¹) over the 298.15–313.15 K temperature range has been studied by conductometric method. From conductivity versus surfactant concentration plots, the critical micelle concentration (CMC) of CTAB has been determined, which shows that the tetraalkylammonium bromides promote the formation of CTAB aggregates. Further, from the temperature dependence of CMC values, the degree of ionization, the counterion binding constant along with some thermodynamic parameters of micellization, such as standard free energy change ($\mathrm{\Delta }{G}_m^o$), standard enthalpy change ($\mathrm{\Delta }{H}_m^o$), standard entropy change ($\mathrm{\Delta }{S}_m^o$) have been calculated. From the values of $\mathrm{\Delta }{G}_m^o$, $\mathrm{\Delta }{H}_m^o$ and $\mathrm{\Delta }{S}_m^o$, it has been concluded that our ternary system is both enthalpy as well as entropy controlled. Similar CMC values were obtained from UV–Visible spectrometry measurements, using pyrene as a probe at ambient temperature. Also ¹H-NMR and FTIR methods give a greater understanding of the molecular scale interactions between the tetraalkylammonium bromides and the cationic surfactant.     

Effect of Benzheterazoles on the Micellar Behavior of Sodium Dodecylsulfate in Dimethylsulfoxide: A Conductometric and Spectroscopic Approach

In this article, we report intermolecular interactions in terms of the effect of benzfused heterocyclic compounds, i.e., 2-thioureidobenzimidazole and 2-thioureidobenzoxazole (0.00, 0.01, and 0.05 mol kg⁻¹), on the micellization behavior of sodium dodecylsulphate (SDS) (1–52 mmol kg⁻¹) in dimethylsulphoxide (DMSO) at different temperatures (293.15–313.15 K) through conductometric and spectroscopic investigations. The variation of specific conductance with SDS concentration has been utilized to estimate the critical micelle concentration ( CMC). The above-performed techniques infer that the presence of additives results in a decrease in the CMC values. Various standard thermodynamic parameters such as free energy change (), enthalpy change (), and entropy change () of micellization have been determined using the temperature dependence of CMC. The above calculated parameters and also UV–visible and fluorescence spectroscopy have been used to obtain information regarding the various interactions between the compounds and surfactant aggregates. In addition, an attempt has also been made to examine the minimum inhibitory concentration (MIC) of the heterocompounds, which indicates the effectiveness of these compounds against fungus growth at a particular concentration. These synthetic heterocyclic compounds find increasing applications in material science, medicinal chemistry, and biochemistry due to their antifungal and antioxidant properties.     

Surface,Micellar, and Aggregation Behavior of Non-cytotoxic Imidazolium Gemini Surfactants

The micellar, surface, and aggregation properties of biocompatible, imidazolium-based hydroxyl group-containing gemini surfactants, 1,1′-(propane-1,3-diyl-2-ol) bis(3-alkyl-1H-imidazol-3-ium)bromide, [C_nIm-3OH-ImC_n]Br₂, were studied. The surface parameters like maximum surface excess concentration at air/water interface (Γ_max), the minimum surface area occupied by surfactant molecules (A_min) and the related thermodynamic parameters such as, standard Gibbs free energy of micellization (), standard free energy of adsorption (), and free energy of surface at equilibrium ) were also determined from the surface parameters. The aggregation behavior has been elucidated from transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques which showed that these gemini surfactants have potential self-aggregation efficiency. Besides, some other physicochemical properties like foam stability, emulsifying power, and viscosity have been determined. The structural features of [C_nIm-3OH-ImC_n]Br₂ enhance their surface-active properties. These features of gemini surfactants are of primary significance from pharmaceutical and biomedical viewpoints. The gemini surfactants may have great implications in drug formulations and delivery owing to their prominent aggregation and non-cytotoxic nature.     

The Effect of Polar Head and Chain Length on the Physicochemical Properties of Micellization and Adsorption of Amino Alcohol-Based Surfactants

In this work, we have synthesized a series of quaternary ammonium from amino alcohols and n-bromoalkanes. The compounds are referred to as C_nEtOH, C_nPrOH, and C_niPrOH (where n = 12 and 14 carbons, EtOH = ethanol, PrOH = propanol, iPrOH = iso-propanol). Their structures were checked using the usual spectroscopic methods [¹H, ¹³C nuclear magnetic resonance (NMR) and infrared (IR)]. Their physicochemical properties in aqueous solution were studied using conductivity, surface tension, and ultra violet (UV)–visible absorption spectroscopy measurements. This study was conducted to show the effect of the linear hydrophobic chain and the location of the OH polar group with respect to the N⁺ quaternary ammonium on the physicochemical properties of the surfactants. The comparison between the physicochemical properties of the surfactants studied shows a distinct effect of the position of the OH group on the critical micelle concentration (CMC), the ionization degree (α), the area occupied at the interface (A_min), the free energy of adsorption (), and the free energy of micellization (). The intermolecular interaction between the synthetic surfactants and the methyl orange (OM) dye is related to the degree of hydration of the micelle, proven by the hypsochromic displacement of OM wavelength (λ_max) and ionization (α) of the micelles. The CMC, the degree of ionization, and the degree of hydration of the micelle follow the same trend.     

The Influence of an Organic Salt on Micellization Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Solutions of Trisubstituted Ionic Liquid [Odmim][Cl]

The influence of sodium benzoate (Na-Bz) on micellization behavior of the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) in aqueous media of trisubstituted imidazolium-based ionic liquid (IL), 1,2-dimethyl-3-octylimidazolium chloride [odmim][Cl], was investigated using conductometry, tensiometry, fluorescence,¹H NMR, Dynamic Light Scattering (DLS), and Rheology techniques. It was observed that with an increase in salt concentration, the critical micelle concentration (CMC) values of the system decrease. The CMC and various thermodynamic parameters like standard Gibbs free energy of micellization (), standard enthalpy change (), and standard entropy change () were calculated using conductometry and surface parameters such as surface pressure at the interface (П_cac), maximum surface excess concentration (Г_max), minimum surface area per molecule (A_min), and pC₂₀ (adsorption efficiency) were calculated using the tensiometry technique. The aggregation number (N_agg) was calculated using fluorescence measurements. ¹H NMR spectra shed light on interactions between the salt and the cationic surfactant in 0.1 wt% IL. DLS gives information about the size distribution of micelles in solution at different concentrations of salt.     

Aggregation Behavior of Sodium Dodecyl Sulfate and Cetyltrimethylammonium Bromide Mixtures in Aqueous/Chitosan Solution at Various Temperatures: An Experimental and Theoretical Approach

A conductometric study of the mixed micellization behavior between cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic surfactant) was carried out in the absence/presence of various percentages of chitosan in the temperature range of 298.15–318.15 K. The deviations of critical micelle concentration (cmc) from the ideal values indicate the interaction between CTAB and SDS. The micellar mole fraction values according to different proposed models X₁^Rub (Rubingh), X₁^M (Motomura), X₁^Rod (Rodenas), and X₁^id (ideal mole fraction) were estimated and the results obtained reveal the high contribution of CTAB in the mixed micellization, which enhances with the increase of the mole fraction of CTAB. The negative magnitudes of indicate the spontaneous formation of mixed micelles between CTAB and SDS. The values of activity coefficients (f₁ and f₂) were less than unity and the values of the interaction parameter (β) are negative in all cases, which indicate the attractive interaction between CTAB and SDS. The negative values of excess free energy of micellization (ΔG_ex) signify the stability of the mixed micelles. The negative values of in the chitosan systems indicate that micellization is exothermic. The values of were found to be positive in all cases.     

Thermal Degradation of p-Hydroxybenzoic Acid in Macadamia Nut Oil,Olive Oil,and Corn Oil

p-Hydroxybenzoic acid (PHBA) plays a significant role in sustaining the oxidative stability of macadamia nut oil (MNO). However, PHBA undergoes thermal decarboxylation and loses its bioactive antioxidant properties. In this study, we determine PHBA degradation kinetics in oils at various heating temperatures, which provides fundamental understanding of PHBA thermal degradation in oils and oil quality changes during high-temperature processing. PHBA degradation kinetics in MNO, olive oil, and corn oil were evaluated at temperatures typical for cooking and frying. PBHA headspace concentration was measured using selected ion flow tube mass spectrometry. PHBA decarboxylation followed a zero-order reaction, where degradation could be affected by factors such as the type of oil matrix having different FA compositions, antioxidants, and component interactions. PHBA degradation activation energies (E _a) showed that PHBA was more stable against thermal decarboxylation in MNO (85 kJ mol^–1) than in olive oil (40 kJ mol⁻¹) or corn oil (22 kJ mol⁻¹). The higher enthalpy () of decarboxylation in MNO (82 kJ mol⁻¹) indicates that PHBA is more inhibited from decomposition than olive oil (37 kJ mol⁻¹) or corn oil (19 kJ mol⁻¹). Moreover, the negative entropy values () of PHBA degradation from MNO (−192 J mol⁻¹ K⁻¹), olive oil (−277 J mol⁻¹ K⁻¹), and corn oil (−325 J mol⁻¹ K⁻¹) indicates that these oils impart some inhibitory properties against PHBA thermal decarboxylation.     

Theoretical Approaches on the Synergistic Interaction between Double-Headed Anionic Amino Acid-Based Surfactants and Hexadecyltrimethylammonium Bromide

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, −aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X^σ), interaction parameters at the bulk/interface (β^R/β^σ), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (α_AAS), the magnitude of the (β^R/β^σ) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing α_AAS, the micellar mole fraction of HTAB (X₂) decreased insignificantly and X₂ values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS () differed from micellar mole fraction of AAS (X₁), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( ∆G_m ) values are more negative than the free energy of micellization for ideal mixing (), indicating the micellization process is spontaneous. With increasing α_AAS, the enthalpy of micellization (ΔH_m) and entropy of micellization (ΔS_m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.     

Influence of Additives and Temperature on the Interaction of Acid Red 151 Dye with Cetyltrimethylammonium Bromide: A Conductometric Study

The interaction of an anionic textile dye, acid red 151 (AR), with a cationic surfactant, cetyltrimethylammonium bromide (CTAB), in aqueous electrolyte medium (e.g., KCl, NaCl) and in H₂O + ethanol medium was observed using the conductometric method. Two critical micelle concentrations (CMC) were found for the AR + CTAB system in water and H₂O + ethanol medium, but only one CMC was detected for AR + CTAB in salt+H₂O media and for pure CTAB in all solutions. The change in CMC behavior of CTAB in the presence of AR indicates the occurrence of strong interaction between AR and CTAB. The extent of solubility increases with an increase of temperature, which disfavors micellization. The CMC values in NaCl solution are comparatively lower than those found in KCl solution, which signifies that the micelle formation is more favorable in attendance of NaCl. In aqueous ethanol solution, two CMC values were also observed for AR + CTAB that are higher than those obtained in water. The free energy of micellization () was negative, which illustrates a thermodynamically spontaneous micellization process. The values of enthalpy () and entropy () of micellization show that the process was entirely entropically driven at a lower temperature; but, enthalpic events are favored at elevated temperature in electrolyte medium, whereas both enthalpy and entropy are reduced in attendance of ethanol. In aqueous medium, the thermodynamic parameters signify the presence of electrostatic interaction between AR and CTAB at higher temperatures, while the hydrophobic interaction is the main driving force at a lower temperature. A linear expression of as a function of demonstrates enthalpy-entropy compensation over the experimental conditions employed in this study.     

Experimental study and molecular simulation on aggregation behavior of surface-active ionic liquids containing saturated nitrogen heterocycles in aqueous solution

The aggregation behavior of N-decyl-N-methylmorpholinium bromide (DMMB) in aqueous solutions was systematically investigated by experimental measurements and molecular simulation, including surface tension, electrical conductivity, fluorescence measurement, ¹H NMR and dissipative particle dynamic (DPD) simulation. The critical micelle concentration (cmc) of DMMB which was obtained by different techniques showed a pretty good agreement. From the surface tension measurements, a series of surface adsorption properties such as surface tension at the cmc (γ_cmc), effectiveness of surface tension reduction (∏_cmc), maximum surface excess concentration (Γ_max), minimum surface area per molecule (A_min), were determined. The cmc values and a variety of thermodynamic parameters (, and ) of micellization in the temperature range of 25–45°C were obtained via electrical conductivity experiments. In the investigated temperature range, the thermodynamic parameters reveal that micelle formation is entropy-driven. Furthermore, micelle aggregation number (N_agg) of DMMB was calculated through the fluorescence measurement. Analysis of the ¹H NMR spectrum indicates the micelle formation mechanism. The DPD simulation reflects the process of micro-phase separation. From the simulation results, at concentrations higher than cmc, spherical micelles can be formed. The investigation of DMMB micelles may help us gain a better understanding about surfactant micellization process and expand the range of potential application in materials science.     

Synthesis and Surface Properties of Polyether-Based Silicone Surfactants with Different Siloxane Groups

A series of polyether-based silicone surfactants with different hydrophobic chains (trimethylsiloxy, triethylsiloxy, and triisopropylsiloxy) were synthesized. The molecular structures were confirmed using ¹H nuclear magnetic resonance (NMR), ¹³C NMR, ²⁹Si NMR, and fourier transform infrared spectroscopy (FT-IR). The effect of the siloxane groups on the physicochemical properties, surface tension (γ), critical micelle concentration (CMC), surface tension at the CMC (γ_CMC ), adsorption efficiency (pC₂₀), surface pressure at the CMC (π_CMC ), maximum surface excess (Γ_max ), single silicone surfactant molecule at the air/water interface (A_min ), and the standard free energy of adsorption (), of the polyether-based silicone surfactants was investigated. Results indicate that the polyether-based silicone surfactants can reduce the surface tension of water to approximately 25–31 mN m⁻¹ and the surface activity of silicone surfactants is enhanced with increasing branched trimethylsiloxyl and sterically hindered siloxane groups.     

Investigation of Mixing Behavior of both a Conventional Surfactant and Different Inorganic Salts with a Cationic Gemini Surfactant in Aqueous Solution

N,N′-bis [3-(dodecanoylamino)propyl]-N,N,N′,N′-tetramethylhexane-1,6-diaminium dibromide is a cationic Gemini surfactant including quaternary ammonium salt with amide groups. Critical micelle concentration (CMC) and some thermodynamic parameters of the cationic Gemini surfactant were investigated using surface tension and conductivity methods. Mixed micellization of binary mixtures of the cationic Gemini surfactant with a conventional surfactant cetyl trimethylammonium bromide (CTAB) was investigated using the conductometric method at five different temperatures ranging from 303.15 to 323.15 K. CMC, micellar ionization degree (α_m), counterion binding constant (g₁), interaction parameter (β), and activity coefficients ( and ) of mixed systems were found out from data of conductivity at different mole fractions for all studied temperatures. Additionally, the effects of some inorganic salts with different concentrations on the surface properties of cationic Gemini surfactant were examined by surface tension measurements. Some surface properties of the pure cationic Gemini surfactant and mixed salts systems were calculated using the data of surface tension.     

Imidazolium‐Based Ionic Liquid as Modulator of Physicochemical Properties of Cationic,Anionic, Nonionic,and Gemini Surfactants

The aggregation morphology of 2 cationic surfactants (cetyldimethylethanolammonium bromide and cetyldiethylethanolammonium bromide), an anionic surfactant (sodium dodecylbenzenesulfonate), a nonionic surfactant (Triton X‐100), and 2 gemini surfactants (16‐4‐16,2Br^?[butanediyi‐1,4‐bis(dimethyldohexylammonium bromide)] and 16‐6‐16,2Br^?[hexanediyi‐1,6‐bis(dimethyldohexylammonium bromide)]) in the presence of the ionic liquid (IL) 1‐ethyl‐3‐methylimidazoliumbromide [Emim][Br] is studied using various techniques such as surface tension, conductivity, and UV–visible and fluorescence spectroscopy. Increasing the concentration of [Emim][Br] results in a decrease in the critical micelle concentration (CMC) value of the surfactants. Various interfacial properties, namely the surface excess concentration (Г_max), minimum area per molecule at the air–water interface (A_min)_, and surface pressure at the CMC (π_cmc), as well as the thermodynamic parameters such as free energy of the given air/water interface (), Gibbs free energy of micelle formation (), Gibbs free energy of micellization per alkyl tail (), Gibbs energy of transfer (), and standard free energy of adsorption () were also investigated. The aggregation number (N_agg) was determined by the fluorescence method. It was observed that N_agg decreased with increasing weight‐percent of the IL.     

Synthesis and Investigation of Surface Active Properties of Counterion Coupled Gemini Surfactants

Three counterion coupled gemini (cocogem) surfactants in the series 1,6‐bis(N,N‐alkyldimethylammonium) adipate, referred as n‐6‐n (n = 12, 14, 16), were synthesized, purified and characterized by ¹H NMR and ¹³C NMR. Their physicochemical properties were investigated by electrical conductivity and surface tension measurements. The degree of ionization, critical micelle concentration (CMC), surface excess at the air/solution interface (Γ_max), minimum area per surfactant molecule at the air/solution interface (A_min), surface tension at the CMC (γ_CMC), and pC₂₀ (negative log of the surfactant molar concentration, required to reduce the surface tension of water by 20 mN m^?1) were calculated. Increase in tail length of the surfactants increases the efficiency of surfactants to decrease the surface tension of water. Thermodynamic parameters, viz. molar free energy at the maximum adsorption attained at CMC (G_min), standard Gibb's energy of micellization (), and standard Gibbs energy of adsorption (), were also calculated. The and values show that the monomers were preferred to be adsorbed at the air/water interface and then in the micellar formation in the bulk. Additionally, fluorescence measurements were used to find the aggregation number. Other relevant surface properties (Krafft point, emulsion stability, foaming ability, micellar stability and dye solubilization ability) were also evaluated. These results suggest that with respect to emulsion formation, micellar stability and dye solubilization, the cocogem with a 16‐carbon chain gives better results, producing 89 % more stable foams and shows better aggregational behavior.     

The Effect of Methanol on the Micellar Properties of Dodecyltrimethylammonium Bromide (DTAB) in Aqueous Medium at Different Temperatures

The micellar properties of dodecyltrimethylammonium bromide (DTAB) in water and methanol water mixtures at different temperatures have been studied by conductivity and surface tension measurements. The critical micelle concentrations (CMC), degree of ionization (α), standard Gibbs free energy of micellization (), standard enthalpy of micellization (), standard entropy of micellization () and free energy of transfer () were evaluated from conductivity data. The CMC, maximum excess surface concentration ( ), area occupied per surfactant molecule ( ), surface pressure at the CMC ( ), packing parameter (P) and standard free energy interfacial adsorption ) were estimated from surface tension measurements. The CMC of DTAB was found to increase with increasing volume fraction of methanol and increasing temperature. Thermodynamic parameters and surface properties revealed that the addition of methanol changes the relevant physicochemical properties which affect the process of micellization.     

The Aggregation Behavior and Antioxidative Activity of Amphiphilic Surfactants Based on Quinuclidin-3-ol

The self-aggregation and thermodynamic properties of three cationic quaternary ammonium surfactants were investigated. The physicochemical properties of compounds containing quinuclidin-3-ol with even number of carbon atoms (10, 12, and 14) in the hydrophobic tail were measured by conductivity, dynamic light scattering (DLS), and Zeta-potential measurements. DLS and Zeta-potential measurements show a similar size distribution for all surfactants with excellent uniformity, and Zeta-potential increases significantly with increase in the size of hydrocarbon tail. The critical micelle concentration (CMC) and the degree of micelle ionization (β) were determined using conductivity measurements. The CMC values of surfactants were found to be between 3.4 and 23.8 × 10⁻³ M. The standard Gibbs free energy () was derived from conductivity measurements and suggests that surfactants containing longer chains spontaneously form micelles. The antioxidative properties of these cationic surfactants were evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays. Among the tested samples, N-tetradecyl-3-hydroxyquinuclidinium bromide (QOH-C14) exhibited the highest antioxidative potential (388.30 nmol (TE) equivalents mL⁻¹), which was further investigated by the DNA nicking assay.