Pseudophase Micellar Model Research Articles

Role of ionic surfactants on the activation of K2S2O8 for the advanced oxidation processes

Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate were studied to elucidate the persulfate based in-situ chemical oxidation of subsurface contamination. Advanced oxidation processes (AOP) utilizing Fenton’s like reagent was investigated for the degradation of acid orange 7 (AO7) with and without ionic surfactants. The new findings are that the CTAB and SDS retarding the S2O82− activation to some extent. The kinetics of S2O82− assisted decomposition of AO7 were performed under different reaction parameters such as [S2O82−], [Fe2+], [AO7], pH, and temperature. The rate constants (kψ) were decreased markedly in presence of both surfactants. CTAB showed the most potential deactivation than that of SDS. The stability of both surfactants were determined in presence of S2O82−, and no drastic changes was observed in the critical micellar concentration (CMC). The columbic attraction and repulsion between the reactants (S2O82−, and AO7) with ionic head groups of CTAB and SDS are responsible to deactivating the S2O82− decomposition. AO7 and S2O82−, respectively, solubilized and transferred from bulk phase to micellar surface through electrostatic interactions, which may contribute to the inhibitory role of CTAB micelles in the AOP of AO7. Finally the role of surfactants in the Fenton’s like oxidation of AO7 based on the micellar-pseudo phase model was proposed and discussed.

Significance of dimeric surfactant on kinetic study of organophosphorus compounds

AbstractDimeric surfactants have shown significant role on hydrolysis of organo‐phosphorus compounds. In this study, we have studied the kinetic hydrolysis of p‐nitrophenyl acetate (PNPA), p‐nitrophenyl benzoate (PNPB), and p‐dinitrophenyl diphenyl phosphate (PNPDPP) in presence of novel dimeric surfactants 12‐4‐12, 2Br– (butanediyl‐1,4‐bis(dimethyldodecylammonium bromide), 12–4(OH)‐12, 2Br– (2‐butanol‐1,4‐bis(dimethyldodecylammonium bromide) with conventional nucleophiles, benzohydroxamic acid (BHA), and salicylhydroxamic acid (SHA) by spectrophotometry at 27°C. Kinetic study on effect of micelles on reaction rates have been investigated and rationalization effects of micelles determination using kinetic model. The experimental kinetic data were fitted with micellar pseudophase model for determination micellar substrate binding and parameters. The second order rate constant is processed for comparing the reactivities in aqueous and micellar pseudophase.

Humic Acids Aggregates as Microheterogeneous Reaction Media: Alkaline Hydrolysis Reactions

The influence of humic aggregates in a water solution upon the chemical stability under basic conditions of different substrates was reviewed. The kinetic behavior of each substrate was modeled in terms of a micellar pseudophase model.

Role of ionic surfactants on the plasmonic oxidative dissolution of silver nanoparticles by ferric ions

Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the optical sensing of AgNPs toward ferric ions were investigated spectrophotometrically in an aqueous media. Surface Plasmon resonance (SPR) intensity of AgNPs was decreases after addition of ferric ions at room temperature. CTAB and SDS, respectively, catalyzed and inhibited the oxidative dissolution rates of AgNPs. The redox reaction between AgNPs and Fe3+ ions proceeds through the complex formation. The reaction follows first-, and fractional-order kinetics with AgNPs and Fe3+ ions, respectively. CTAB catalytic role was explained with micellar pseudo-phase model, and associated parameters were estimated. The activation parameters (Ea, ΔH#, and ΔS#) were found to be 23.7 kJ/mol, 16.6 kJ/mol, −226 J/K/mol, and 16.5 kJ/mol, 13.5 kJ/mol, −238 J/K/mol for aqueous and CTAB assisted dissolution of AgNPs. SDS coordinated with Fe3+ through electrostatic interactions in pre-, and post-micellar region, which in turn reduces the electron gaining tendency of Fe3+, and overall rates of sensing reaction decreases.

The effect of sonication on the ion exchange constant, [formula omitted] of CTABr/chlorobenzoates micellar systems

The ion exchange constant, KXBr (for the case of cetyltrimethylammonium bromide, CTABr, in this study) is a method dependant characterization of ion exchange process by counterions, X and Br with different relative binding ratios. In this report, the ion exchange constant, KXBr values for micelle systems irradiated under 2 min of sonication at 120 W power using a probe sonicator with 1 cm tip were determined to be 85.2, 125.6 and 122.4 when X = o-, m- and p-chlorobenzoates, respectively. The values were quantified using a semiempirical kinetic method coupled with Pseudophase Micellar model, and later compared to the same system in the absence of sonication. The sonication was found to amplify the KXBr values by ~ 13-fold for X = o-chlorobenzoate and ~ 2.5-fold for X = m- and p-chlorobenzoates. This is due to the improvement of ion exchange process by the oscillation of bubbles generated by acoustic cavitation. An active ion exchange process indicates better stabilization of the micelle aggregational structure by the penetration of the introduced counterions, X into the micelle Stern layer leading to the growth of the micelle. This is supported by the remarkable increase in the viscosity of the micelle system by > 7-fold for X = o-chlorobenzoate and by > 2-folds for X = m- and p-chlorobenzoates. Sonication was also found to induce maximum viscoelasticity at lower concentration ratio of [CTABr]:[X]. The ability of ultrasound to induce micelle growth and exhibiting viscoelasticity at lower concentration of counterionic additive will be very useful in technologies where viscoelastic solution is desired such as in oil drilling and centralized heating and cooling system.

Micellar and Mixed-Micellar Effects on Alkaline Hydrolysis of tris(1,10–phenanthroline)iron(II): Kinetic Exploration

The kinetics of alkaline hydrolysis of tris(1,10–phenanthroline)iron(II) has been studied in the presence of nonionic and mixed nonionic–ionic micellar media at 308 K. The effects of mixed-micellar environments of nonionic with ionic surfactants (C12E23/ATABs and C12E23/SDS) on the hydrolytic rate have been studied. The rate decreases monotonically with an increment of [C12E23]T (total Brij 35 concentration) at constant [−OH]0 and has been discussed with the pseudo-phase micellar model. The rate also decreases with [C12E23]T at a continuous addition of ionic surfactants (ATABs and SDS). The observed rate constant kobs follows the empirical relation: kobs = (k0 + θK [C12E23]T)/(1 + K [C12E23]T) (where θ and K are empirical constants). The values of θ remain unaffected, whereas K decreases nonlinearly with [ATABs]T in a mixed C12E23−ATAB micellar system. But the kobs in a mixed C12E23–SDS micellar system is much lower than that of the C12E23–ATAB system and do not comply with any micellar kinetic models.

Alkaline hydrolysis of vinclozolin: Effect of humic acids aggregates in water

The influence of natural organic substances as humate colloidal aggregates in water solutions upon the chemical stability of vinclozolin has been investigated in basic media. A large inhibition (9 times-fold) has been observed and it has been rationalized in terms of a micellar pseudophase model. The observed behaviour could increase significantly the half-life of this fungicide. Moreover, these experimental results have been compared with the corresponding ones of other substances in these natural colloidal aggregates.

Stability study of Iprodione in alkaline media in the presence of humic acids

The influence of humic aggregates in water solution upon the chemical stability of Iprodione has been investigated under basic conditions. Taking into account that an important part of soils are colloids, the possibility of its presence implies that soil composition and its structure will play an important role in the stability of this pesticide. A kinetic model was applied to this system and the kinetic coefficients were obtained. An inhibition upon the alkaline hydrolysis of Iprodione (2-fold) was observed and it was rationalized in terms of the micellar pseudophase model. These results have been compared with the corresponding ones in the same natural colloidal aggregates in the presence of other pesticides.

Degradation of carbofuran and carbofuran-derivatives in presence of humic substances under basic conditions

The influence of humic aggregates in water solution upon the chemical stability of carbofuran (CF) and the carbofuran-derivatives, 3-hydroxy-carbofuran (HCF) and 3-keto-carbofuran (KCF), has been investigated in basic media. An inhibition upon the basic hydrolysis of 3-hydroxy-carbofuran and 3-keto-carbofuran (∼1.7 and ∼1.5-fold, respectively) was observed and it was rationalized in terms of the micellar pseudophase model. Nevertheless, non-significant effect upon the carbofuran stability was found in the presence of humic substances. These behaviors have been compared with the corresponding ones in other synthetic colloidal aggregates.

Influence of anionic and nonionic micelles upon hydrolysis of 3-hydroxy-carbofuran

The effect of nonionic and anionic micelles upon the stability of 3-hydroxy-carbofuran in basic media has been studied. The presence of micelles in the reaction medium implies a large inhibition of the basic hydrolysis of 3-hydroxy-carbofuran, due to the association of 3-hydroxy-carbofuran with the micellar core. The kinetic constants for the basic hydrolysis in these microheterogeneous media have been obtained on the basis of a micellar pseudophase model. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 402–408, 2011

Effects of nonionic micelles on the rate of alkaline hydrolysis of N-(2′-methoxyphenyl)phthalimide (1): Kinetic and rheometric evidence for a transition from spherical to rodlike micelles under the typical reaction conditions

Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of N-(2′-methoxyphenyl)phthalimide (1) decrease nonlinearly with increasing total concentration of nonionic surfactant CmEn (i.e. [CmEn]T where m and n represent the respective number of methyl/methylene units in the tail and polyoxyethylene units in the headgroup of a surfactant molecule and m/n=16/20, 12/23 and 18/20) at constant 2% v/v CH3CN and 1.0mM NaOH. The kobsvs. [CmEn]T data follow the pseudophase micellar (PM) model at ⩽50mM C16E20, ⩽1.4mM C12E23 and ⩽2.0mM C18E20 where rate of hydrolysis of 1 in micellar pseudophase could not be detected. The values of kobs fail to follow the PM model at > ∼50mM C16E20, > ∼1.4mM C12E23 and > ∼2.0mM C18E20 which has been attributed to a micellar structural transition from spherical to rodlike which in turn increases CmEn micellar binding constant (KS) of 1 with increasing values of [CmEn]T. Rheological measurements show the presence of spherical micelles at ⩽50mM C16E20, ⩽1.4mM C12E23 and ⩽3.0mM C18E20. The presence of rodlike micelles is evident from rheological measurements at > ∼50mM C16E20, > ∼1.4mM C12E23 and > ∼3.0mM C18E20.

Kinetic and rheological measurements of the effects of inert 2-, 3- and 4-bromobenzoate ions on the cationic micellar-mediated rate of piperidinolysis of ionized phenyl salicylate

The effects of the concentration of inert organic salts, [MX], (MX = 2-, 3- and 4-BrBzNa with BrBzNa = BrC 6H 4CO 2Na) on the rate of piperidinolysis of ionized phenyl salicylate (PS −) have been rationalized in terms of pseudophase micellar (PM) coupled with an empirical equation. The appearance of induction concentration in the plots of k obs versus [MX] (where k obs is pseudo-first-order rate constants for the reaction of piperidine (Pip) with PS −) is attributed to the occurrence of two or more than two independent ion exchange processes between different counterions at the cationic micellar surface. The derived kinetic equation, in terms of PM model coupled with an empirical equation, gives empirical parameters F X/S and K X/S whose magnitudes lead to the calculation of usual ion exchange constant K X Br (= K X/ K Br with K X and K Br representing cationic micellar binding constants of counterions X − and Br −, respectively). The value of F X/S measures the fraction of S − (=PS −) ions transferred from the cationic micellar pseudophase to the aqueous phase by the optimum value of [MX] due to ion exchange X −/S −. Similarly, the value of K X/S measures the ability of X − ions to expel S − ions from cationic micellar pseudophase to aqueous phase through ion exchange X −/S −. This rather new technique gives the respective values of K X Br as 8.8 ± 0.3, 71 ± 6 and 62 ± 5 for X − = 2-, 3- and 4-BrBz −. Rheological measurements reveal the shear thinning behavior of all the surfactant solutions at 15 mM CTABr (cetyltrimethylammonium bromide) indicating indirectly the presence of rodlike micelles. The plots of shear viscosity ( η) at a constant shear rate ( γ), i.e. η γ , versus [MX] at 15 mM CTABr exhibit maxima for MX = 3-BrBzNa and 4-BrBzNa while for MX = 2-BrBzNa, the viscosity maximum appears to be missing. Such viscosity maxima are generally formed in surfactant solutions containing long stiff and flexible rodlike micelles with entangled and branched/multiconnected networks. Thus, 15 mM CTABr solutions at different [MX] contain long stiff and flexible rodlike micelles for MX = 3- and 4-BrBzNa and short rodlike micelles for MX = 2-BrBzNa.

Influence of colloid suspensions of humic acids on the alkaline hydrolysis of N‐methyl‐N‐nitroso‐p‐toluene sulfonamide

AbstractThe influence of humic substances (HSs) upon the alkaline hydrolysis of N‐methyl‐N‐nitroso‐p‐toluene sulfonamide has been studied. Important inhibition of hydrolysis reaction has been reported. This inhibition has been explained in terms of association of reactants to the humic substances. Kinetic results have been modeled using the micellar pseudophase model. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 316–322, 2010

Effects of Cationic Micelles on the Rate of Alkaline Hydrolysis of N-(2-methoxyphenyl)phthalimide

Pseudo-first-order rate constants (kobs), obtained for the reaction of N-(2-methoxyphenyl)phthalimide (1) with HO− at a constant [NaOH] and varying concentrations of cetyltrimethylammonium bromide ([CTABr]T = 0.0–0.20 M), have been analyzed in terms of both pseudophase ion-exchange (PIE) model and Berezin's pseudophase (BPP) model. Although both models give the best observed data fit with least-squares values not significantly different from each other, the calculated values of KS from BPP model appear to be more reliable compared to those from PIE model. The nonlinear decrease of kobs with the increase of [NaBr] at the constant [NaOH] and [CTABr]T is explained in terms of pseudophase micellar model coupled with an empirical equation which could indirectly give the measure of the ion-exchange Br−/HO−.

Effects of long-chains of zwitterionic micelles on binding constants of triflusal and acetylsalicylic acid

A spectrophotometric study of the reaction of the alkaline hydrolysis of triflusal (TFL) and acetylsalicylic acid (ASA) in the presence of zwitterionic micelles was carried out, with the objective of determining the effects of the hydrophobic and electrostatic interactions on the micellar union of both drugs. A series of zwitterionic surfactants of alkyldimethylammonio propanesulfonate (SB3- n) were used: decyldimethylammonio propanesulfonate (SB3-10), tetradecyldimethylammonio propanesulfonate (SB3-14), hexadecyldimethylammonio propanesulfonate (SB3-16). This reaction is inhibited at higher surfactant concentrations. The experimental data has been processed according to the micellar pseudophase model. The values of the binding constants of both drugs in the micelle ( K S ) determine the importance of the hydrophobic and electrostatic interactions in the micelle solubilization of both drugs.

Influence of colloid suspensions of humic acids upon the alkaline fading of carbocations

AbstractThe influence of humic substances (HSs) upon the alkaline hydrolysis of crystal violet (CV) and malachite green (MG) has been studied. Important inhibition of hydrolysis reaction has been reported. This inhibition has been explained in terms of association of reactants to the humic substances. Kinetic results have been modelized using the micellar pseudophase model. Copyright © 2008 John Wiley & Sons, Ltd.

Kinetic Coupled with UV Spectral Evidence for Near-Irreversible Nonionic Micellar Binding of N-Benzylphthalimide under the Typical Reaction Conditions: An Observation Against a Major Assumption of the Pseudophase Micellar Model

Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-benzylphthalimide (1) show a nonlinear decrease with the increase in [C(m)E(n)]T (total concentration of Brij 58, m = 16, n = 20 and Brij 56, m = 16, n = 10) at constant [CH(3)CN] and [NaOH]. These nonionic micellar effects, within the certain typical reaction conditions, have been explained in terms of the pseudophase micellar (PM) model. The values of micellar binding constants (KS) of 1 are 1.04 x 10(3) M(-1) (at 1.0 x 10(-3) M NaOH) and 1.08 x 10(3) M(-1) (at 2.0 x 10(-3) M NaOH) for C(16)E(20) as well as 600 M(-1) (at 7.6 x 10(-4) M NaOH) and 670 M(-1) (at 1.0 x 10(-3) M NaOH) for C(16)E(10) micelles. The pseudo-first-order rate constants (kM) for hydrolysis of 1 in C(16)E(20) micellar pseudophase are approximately 90-fold smaller than those (kW) in water phase. The values of kM for hydrolysis of 1 in C(16)E(10) micelles are almost zero. Kinetic coupled with UV spectral data reveals significant irreversible nonionic micellar binding of 1 molecules in the micellar environment of nearly zero hydroxide ion concentration at >or=0.14 M C(16)E(20) and 1.0 x 10(-3) M NaOH while such observations could not be detected at <or=0.17 M C(16)E(20) and 2.0 x 10(-3) M NaOH. Significantly, such irreversible C(16)E(10) micellar binding of 1 molecules could be detected at 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH as well as at >or=3 x 10(-3) M C(16)E(10) and 7.6 x 10(-4) M NaOH, while the rate of hydrolysis of 1 is completely ceased at >or=0.05 M C(16)E(10) and 7.6 x 10(-4) M NaOH. The rate of hydrolysis of 1 at 5.0 x 10(-2) and 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH reveals the formation of presumably phthalic anhydride, whereas such observation was not observed in the C(16)E(20) micellar system under similar experimental conditions.

Influence of Micelles on the Basic Degradation of Carbofuran

The effect of micellar aggregates upon the stability of carbofuran in basic media has been studied. The effect of the presence of micelles upon the basic hydrolysis of carbofuran is a function of the nature of the surfactant monomer. Important catalysis of basic hydrolysis of carbofuran in the presence of colloid aggregates with positive surface charge has been reported. On the other hand, the presence of anionic and nonionic surfactants implies a large inhibition of the basic hydrolysis of carbofuran. Both catalysis and inhibition are due to the association of carbofuran with the micellar core. The kinetic constants for the basic hydrolysis of carbofuran in these microheterogeneous media have been obtained on the basis of a micellar pseudophase model. No significant changes in the intrinsic reactivity of HO- against carbofuran have been observed.

Reactive micelles: nitroso group transfer from N‐methyl‐N‐nitroso‐p‐toluenesulfonamide to amphiphilic amines

AbstractThe reactivity of N‐methyl‐N‐nitroso‐p‐toluene sulfonamide (MNTS) towards n‐alkylamines in water and in micellar aggregates was studied. Kinetic constants in both media were obtained. The pseudophase micellar model allows a satisfactory prediction of the experimental behaviour in all cases. The value obtained for the micellar pseudophase rate constant, k, is lower than that in bulk water. The increase in the observed rate constant, ko, with n‐alkylamine concentration is due to an increase in the local concentration of reactants in the micellar surface. The differences between kw and k values is due to the polarity of micellar pseudophase being lower than that in bulk water. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Micellization and catalytic activity of the cetyltrimethylammonium bromide–Brij 97–water mixed micellar system

Surface tension measurements and the kinetic study of the basic hydrolysis of ethyl p-nitrophenyl chloromethyl phosphonate were used to examine the structural behavior and catalytic activity of the cethyltrimethylammonium bromide (CTAB)–polyoxyethylene (10) oleyl ether, C 18H 35(OCH 2CH 2) 10OH (Brij 97)–water mixed micellar system. Application of the regular solution model to the experimental data yields the value of the interaction parameter β as −4.6, which indicates an attractive interaction of the surfactants in the mixed micelle and reflects synergistic solution behavior of the mixture. The mixed micellar composition is found to be enriched in the surfactant with the lower critical micelle concentration (cmc). In the kinetic study a nonmonotonic change in the pseudo-first-order rate constant of basic hydrolysis of the substrate is observed with increasing mole fraction of nonionic surfactant. The pseudophase micellar model reveals that the concentration factor mainly contributes to the catalytic effect, while the microenvironmental factor plays a negative role.