Polymerisation of liquid crystalline phases in binary surfactant/water systems

The binary phase behaviour of two potentially polymerisable quaternary ammonium surfactants in water has been investigated. Allyldodecyldimethylammonium bromide (ADAB) a single-chain surfactant displays a conventional phase progression upon increasing concentration. Whereas the doublechain analogue allyldidodecylmethylammonium bromide (ADDAB) forms two lamellar liquid crystalline phases built from surfactant bilayers, which transform via a first order phase transition. The formation of two distinct lamellar phases and their coexistence has been evidenced by optical microscopy, small-angle x-ray scattering and D₂O deuterium quadrupolar nuclear magnetic resonance spectroscopy. The lamellar phase formed at higher surfactant compositions is a normal lamellar phase (typeL ) consisting of bilayers which are on average parallel and flat. The lower compositional lamellar phase (typeL ) in contrast may not be comprised of planar bilayers but rather aggregates having a high degree of curvature in comparison to those of theL phase. The presence of the allyl polymerisable moiety in the head group position of these surfactants has the effect of reducing the rigidity of the surfactant and increasing its solubility in comparison to nonpolymerisable analogues. Polymerisation of the surfactants was attempted by using thermal and photochemical initiation in isotropic and self-assembled systems. Polymerisation occurred to approximately 30% for DADB but did not occur for ADDAB. Where polymerisation did occur the polymer was incorporated into the monomer matrix by interweaving between the surfactant aggregates. The polymers had a molecular wieght not greater than 8000 Daltons, independent of the monomer concentration of the original solution and type of polymerisation.     

Polymorphic transitions mediated by surfactants in liquid crystal nanodroplet

Recently, various techniques have been developed using photonic crystals. Liquid crystals (LC) confined in a nanodroplet mimicked photonic crystals, such as those of opal. Therefore, investigating the phase behaviour of LC molecules in nanodroplets is very important in the next-generation optical field. In this study, the chemical interaction between surfactants and LCs in nanodroplets is reproduced using a dissipative particle dynamics method. We identify the phase behaviour of LCs and investigate how the chemical interaction affect on the orientation of LCs. In particular, by adding surfactant molecules, various morphological behaviours were observed in the LC nanodroplet. The phase transition temperature varied depending on R_ND (amount of surfactant molecules). Furthermore, difference of the self-assembly structure also appeared inside the droplet depending on R_ND. Our simulation offers a theoretical guide to control morphologies of self-assembled LCs inside a nanodroplet, a novel system that may find applications in nanofluidic devices or in photonic crystal technology.     

Thermodynamics of aqueous carbohydrate surfactant solutions

The paper deals with the application of the micelle formation theory, developed by Nagarajan and Ruckenstein [R. Nagarajan, E. Ruckenstein, Langmuir 7 (1991) 2934–2969] and Nagarajan [R. Nagarajan, in: K. Esumi (Ed.), Structure–Performance Relationships in Surfactants, Dekker, New York, 1997, pp. 1–81; R. Nagarajan, Adv. Colloid Interface Sci. 26 (1986) 205-264] to various n-alkyl-β-d-glucopyranoside surfactants, differing in the surfactant tail length (n-octyl-β-d-glucopyranoside C₈G₁, n-decyl-β-d-glucopyranoside C₁₀G₁ and dodecyl-β-d-glucopyranoside C₁₂G₁). The model predicts that the carbohydrate surfactant molecules assemble for energetic reasons in spherical bilayer vesicles. The critical micellar concentration as function of the temperature shows a minimum value. The formed micellar aggregates exhibit a broad distribution of sizes. It is demonstrated in this study that the thermodynamic theory in combination with phase separation thermodynamics can be used successfully to described the phase separation, which occurs for the system C₁₀G₁+water and C₁₂G₁+water at low surfactant concentrations.     

Aqueous Phase Behavior of Diglycerol Fatty Acid Esters

We have studied the phase behavior of homologous series of diglycerol fatty acid esters (Qn‐D, for n=10, 12, 14, and 16, where n represents the carbon number in the alkyl chain length of amphiphile) in aqueous solution as a function of temperature and surfactant concentration. The different equilibrium phases present over a wide range of composition and temperature studied were characterized by means of visual observation under normal and polarized light, and x‐ray scattering techniques at small (SAXS) and wide angle (WAXS) regions. In diglycerol monocaprate (Q10‐D) and diglycerol monolaurate (Q12‐D)/H₂O systems, lamellar liquid crystal (L_α) phase is present in the surfactant rich region and it swallows an appreciable amount of water. The amount of water swallowed by the L_α phase was determined by plotting the interlayer spacing, d, as a function of reciprocal of the surfactant weight fraction W_s . In the dilute regions, dispersion of L_α phase in water is observed over a wide range of temperature. At higher temperatures, the L_α phase melts to isotropic two‐liquid phases in water rich region whereas to isotropic reverse micellar solution (O_m) in surfactant rich region. The L_α‐O_m transition temperature is increased on increasing the hydrocarbon chain length of the surfactant from Q10‐D to Q12‐D. There is surfactant solid phase in equilibrium with water up to 25°C in diglycerol monomyristate (Q14‐D)/H₂O system and the solid phase could solubilize 25 wt% water. The melting temperature of solid phase is practically constant in a wide range of compositions. Both the solid present region and the extent of water solubilization are increased in diglycerol monopalmitate (Q16‐D)/H₂O system. At lower surfactant concentrations, excess water appears and dispersion of solid in water is formed. The structure of the solid is identified by WAXS measurement and it is confirmed to α‐solid. Normal vesicular aggregates are formed in L_α+W regions in the Q14‐D/H₂O system at 25°C.     

Review of: “Physico-Chemical Properties of Selected Anionic Cationic and Nonionic Surfactants”. N.M van Os,J.R. Haak and L.M. Rupert (Eds.). Elsevier,Amsterdam, 1993, pp. viii + 608 pages. $245.75.(ISBN 0-444-89691-0)

The phase behavior in water of pentaglycerol monostearate (C₁₈G₅) and pentaglycerol monooleate (C_18:1G₅) surfactants has been studied as a function of temperature and surfactant weight fraction, W _s . The equilibrium phases present at each composition and temperature studied were characterized by means of visual observation under normal and polarized light, differential scanning calorimetry (DSC), and X‐ray scattering, both at small (SAXS) and at wide angle (WAXS). In the temperature range 0–46°C, C₁₈G₅ presents a thermotropic α‐gel structure. However, at higher temperatures, the α‐gel phase melts and a lamellar liquid crystalline (L_α) phase is formed. The amount of water that can be solubilized by α‐gel and L_α was determined by plotting the interlayer distance, d, as a function of the reciprocal of W _s . Water is soluble in the α‐gel phase up to 21 w/w% water concentration and in the L_α phase up to 30 w/w% water concentration. At higher water concentrations, excess water appears and a dispersion of α‐gel (α‐gel+W) and lamellar liquid crystal (L_α+W) in water is formed, respectively. In contrast, C_18:1G₅ is liquid in the whole range of temperatures studied (0–100°C). While at low temperatures, C_18:1G₅ presents a L_α structure, at about 63°C L_α melts and an isotropic liquid reverse micellar solution (O_m) phase is formed. The amount of water that can be solubilized by both O_m and L_α increases with temperature.     

Nonlinear viscoelasticity of polystyrene solutions. I. Strain-dependent relaxation modulus

Strain-dependent relaxation moduli G(t,s) were measured for polystyrene solutions in diethyl phthalate with a relaxometer of the cone-and-plate type. Ranges of molecular weight M and concentration c were from 1.23 × 10⁶ to 7.62 × 10⁶ and 0.112 to 0.329 g/cm³. Measurements were performed at various magnitudes of shear s ranging from 0.055 to 27.2. The relaxation modulus G(t,s) always decreased with increasing s and the relative amount of decrease (i.e.,–log[G(t,s)/G(t,0)]) increased as t increased. However, the detailed strain dependences of G(t,s) could be classified into two types according to the M and c of the solution. When cM < 10⁶, the plot of log G(t,s) versus log t varied from a convex curve to an S-shaped curve with increasing s. For solutions of cM > 10⁶, the curves were still convex and S-shaped at very small and large s, respectively, but in a certain range of s (approximately 3 < s < 7) log G(t,s) decreased rapidly at short times and then very slowly; a peculiar inflection and a plateau appeared on the plot of log G(t,s) versus log t. The strain-dependent relaxation spectrum exhibited a trough at times corresponding to the plateau of log G(t,s). The longest relaxation time τ₁(s) and the corresponding relaxation strength G₁(s) were evaluated through the “Procedure X” of Tobolsky and Murakami. The relaxation time τ₁(s) was independent of s for all the solutions studied while G₁(s) decreased with s. The reduced relaxation strength G₁(s)/G₁(0) was a simple function of s (The plot of log G₁(s)/G₁(0) against log s was a convex curve) and was approximately independent of M and c in the range of cM <10⁶. This behavior of G₁(s)/G₁(0) was in agreement with that observed for a polyisobutylene solution and seems to have wide applicability to many polymeric systems. On the other hand, log G₁(s)/G₁(0) as a function of log s decreased in two steps and decreased more rapidly when M or c was higher. It was suggested that in the range of cM < 10⁶, a kind of geometrical factor might be responsible for a large part of the nonlinear behavior, while in the range of cM > 10⁶, some “intrinsic” nonlinearity of the entanglement network system might be important.     

Assembly properties of Triton X-100/phosphatidylcholine aggregates during liposome solubilization

The assembly properties of the nonionic surfactant Triton X-100 and phosphatidylcholine (PC) aggregates during the overall solubilization process of PC liposome were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light scattered by liposome suspensions. A direct dependence was established between the bilayer/aqueous phase surfactant partition coefficients (K), the growth of vesicles and the leakage of entrapped CF in the initial interaction steps (surfactant to phospholipid molar ratioRe up to 0.2). These changes may be related to the increasing presence of surfactant molecules in the outer monolayer of vesicles. In theRe range 0.2–0.35 the coexistence of a low vesicle growth with a constant increase of CF release may be correlated with the decrease inK (increased rate of flip-flop of surfactant molecules). Furthermore, in theRe range between 0.64 and 2.0 (lytic levels) almost a linear dependence was detected between the composition of these aggregates (Re) and the decrease in both the surfactant-PC aggregate size and the static light scattered by the system. This dependence was not observed in the last solubilization steps (Re range 2.0–2.60) possibly due to the increased formation of mixed micelles in this interval. The fact that the free Triton X-100 concentration at sublytic and lytic levels showed respectively lower and similar values than its critical micelle concentration confirms that permeability alterations and solubilization were determined respectively by the action of surfactant monomer and by the formation of mixed micelles.Abbreviations PC phosphatidylcholine - PIPES piperazine-1,4 bis(2-ethanesulphonic acid) - T_X-100 Triton X-100 - CF 5(6)-carboxyflucrescein - Re enective surfactant/lipid molar ratio - Re _SAT effective surfactant/lipid molar ratio for bilayer saturation - Re _SOL enective surfactant/lipid molar ratio for bilayer solubilization - S _W surfanctant concentration in the aqueous medium - S _B surfactant concentration in the bilayers - S _T total surfactant concentration - K bilayer/aqueous phase surfactant partition coefficient - K _SAT bilayer/aqneous phase surfactant partition coefficient for bilayer saturation - K _SOL bilayer/aqueous phase surfactant partition coefficient for bilayer solubilization - PL phospholipid - TLC-FID thinlayer chromatography/flame ionization detection system - PI polydispersity index - CMC critical micellar concentration - r ² regression coefficient     

Solubility effects of multicomponent liquid crystal blends towards poly (n-butyl-acrylate)

Blends composed of isotropic linear poly (n-butylacrylate) of molecular weight M _w?=?112,000 g mol^?1 and the commercial four-component nematic low molecular weight liquid crystal (LC) mixture E7 exhibit a strong shift of the single nematic–isotropic transition temperature T _NI compared to that of the pure LCs, which was evidenced by using two complementary experimental techniques: differential scanning calorimetry (DSC) and high-performance liquid chromatography. The first one provides direct information about phase behaviour and variation of T _NI of the polymer/LC blends, whereas the second one consists of analysing qualitatively and quantitatively the composition of millimetre-sized segregated LC domains in the two-phase region of the phase diagram.

In order to understand the origin of the unusual phase behaviour, several LC blends were prepared by modifying the concentration of the four single LC components that are present in the eutectic E7 mixture, following the results from the previous chromatographic analysis. These model blends were investigated by DSC measurements, showing that the variation, particularly of the terphenyl LC compound concentration, plays a determining role for the phase behaviour of the LC mixture and the shift of T _NI.     

Phase behaviour of lyotropic liquid crystalline side chain polymers in aqueous solutions

Amphiphilic lyotropic liquid crystalline surfactants are synthesized displaying 10-undecenoic acid as hydrophobic and ethyleneglycol units as hydrophilic parts of the molecules. By addition reaction of the monomeric surfactants with poly [oxy(methylsilylene)], the surfactants are attached as side chains to the siloxane main chain. The phase behaviour of a polymer-water system and the corresponding monomer-water system is investigated by polarizing microscopy. The monomeric surfactant exhibits a liquid crystallineM ₁-phase of hexagonally packed, rod-like micelles in a concentration range of 49 to 70% surfactant. The liquid crystalline state of the polymeric surfactant is more stable, which is indicated by a broader temperature- and concentration range (35%–90% polymer surfactant). At lower concentration aM ₁-phase exists, which is separated by a cubic phase from a lamellarG-phase at higher concentration of the polymer surfactant. Compared to the monomeric system, the increased stability of the polymeric mesophase can be understood by the restriction of motions of the amphiphiles due to the linkage to the polymer main chain.Dedicated to Prof. Dr. F. H. Müller.The authors are greatly indebted to Wacker Chemie, D-Burghausen, FRG for kindly delivering the poly(hydrogensiloxane).     

Aggregate morphology and flow behaviour of micellar alkylglycoside solutions

Solutions of n-nonyl-β-D-glucoside (C₉G₁), n-decyl-β-D-glucoside (C₁₀G₁), n-dodecyl-β-D-maltoside (C₁₂G₂), n-tetradecyl-β-D-maltoside (C₁₄G₂) and C₉G₁/C₁₀G₁ mixtures have been characterised by capillary viscometry and rheology in H₂O and D₂O, in order to map the influence of surfactant characteristics on micellisation over a wide concentration range. For the maltosides, the micellar solutions are shear thinning with a zero-shear viscosity that scales with concentration according to a power law with an exponent of about 5.8. In contrast, solutions of the glucosides C₉G₁, C₁₀G₁ and their mixtures show Newtonian flow behaviour and a much lower scaling exponent (<2.4). In C₉G₁/C₁₀G₁ mixtures, the scaling exponent decreases monotonously with increasing C₁₀G₁ content. The flow behaviour correlates with the packing requirements of the various surfactants, and are compatible with the idea that the maltosides form worm-like micelles, whereas the glucosides form branched, interconnected micelles (C₉G₁) and space-filling micellar networks (C₁₀G₁).     

Rheological studies of aqueous alkylpolyglucoside surfactant solutions

Alkylpolyglucosides (C _Y G _X ) are industrial products of mixtures consisting of a hydrocarbon chain with Y carbon atoms linked to X sugar residues. Based on detailed analytical investigation of technical grade alkylpolyglucosides (C_8–10G _X , C_12–14G _X and C_8–16G _X )/water systems using high-performance liquid chromatography in combination with a special kind of mass spectroscopy their rheological behaviour is discussed and compared to the rheological behaviour of pure alkyl monoglycosides (C₈G₁ and C₁₀G₁) in water. The rheological properties that exhibit a dependence on the alkyl chain length, Y, and the degree of polymerisation, X, are investigated by rotation and oscillation experiments over an extended concentration range. The Maxwell model fits the frequency dependence of the dynamic functions fairly well. The viscosity shows an Arrhenius-like dependence on temperature. A comparison is drawn between the monoglucosides and the polyglucosides, which shows that the rheological properties are more sensitive to the a change in chain length than in the degree of polymerisation. Phase transitions, especially liquid-crystalline to isotropic solutions, phase split into two coexisting liquid phases, and could be followed using visual observation and rheology. Depending on the difference in the rheological properties of the corresponding phases, viscoelastic measurements showed these transitions clearly. Additionally, the changes in viscosities were measured after addition of a second surfactant. Received: 4 January 1999 Accepted in revised form: 12 April 1999     

Dielectric and electro-optical properties of a photosensitive liquid crystal

The temperature dependencies of the dielectric and electro-optical properties of a pure photo-ferroelectric liquid crystal have been investigated, in the chiral smectic C (SmC*) phase, with and without ultraviolet (UV) illumination. The SmC* dielectric Goldstone mode characteristics, the spontaneous polarization, the tilt angle and the rotational viscosity are affected by UV irradiation. Under increasing UV light intensities the dielectric strength Δ?_G increases whereas the relaxation frequency f_G , the spontaneous polarization P _s, the electro-optical rotational viscosity γ_eo and the tilt angle θ decrease. The twist elastic constant K ₃ and the Goldstone mode rotational viscosity γ_G of the studied compound are deduced from dielectric experimental results. Good agreement was found between both viscosities. The observed dielectric behaviours are controlled by the elastic constant and the rotational viscosity variations.     

Synergism in cationic gemini – additive systems

A series of dicationic gemini surfactants with the general formula C₁₆H₃₃(CH₃)₂N⁺?(CH₂)_s?N⁺(CH₃)₂C₁₆H₃₃, 2Br^? (where s?=?4–6), designated as 16-s-16, were synthesised. Their interaction with organic additives: n-alcohols (C₃H₇OH, C₇H₁₅OH, C₈H₁₇OH) and the corresponding amines (C₃H₇NH₂, C₇H₁₅NH₂, C₈H₁₇NH₂) in the absence and presence of KNO₃ at 30°C was studied viscometrically to observe their effect on assembly formation and micellar transition. The simultaneous presence of KNO₃ and organics induced rich aggregates morphologies in the gemini micellar systems by giving high viscosity values. On comparing the behaviour of the gemini surfactant series for a given alkyl chain length of the organic additive, the spacer is found to markedly influence the behaviour; shorter the spacer, earlier the sphere-to-rod transition. In the case of the conventional surfactant, CTAB, the concentration of KNO₃ used with the geminis was insufficient to induce any transition.     

The Effect of Anomeric Head Groups, Surfactant Hydrophilicity, and Electrolytes onn-Alkyl Monoglucoside Microemulsions

The effects of the variables of head group structure and salt concentration on microemulsions formed in mixtures of water, alkyl ethylene glycol ethers (C_kOC₂OC_k), andn-alkyl β- -glucopyranosides (C_mβG₁) are explored. Phase behavior of mixtures containing an anomer of the surfactant (n-alkyl α- -glucopyranoside, C_mαG₁), or surfactants with long head groups (n-alkyl maltopyranosides, C_mG₂), or NaCl or NaClO₄as electrolyte are systematically reported as a function of temperature and composition. The substitution ofn-alkyl α- -glucopyranosides forn-alkyl β- -glucopyranosides causes precipitation under some conditions in all mixtures studied. These solubility boundaries begin in the water–surfactant binary mixture at the Krafft boundary, then extend to high concentrations of both surfactant and oil. Increasing the effective length of the surfactant head group by adding C_mG₂to water–C_kOC₂OC_k–C_mβG₁mixtures moves the phase behavior dramatically up in temperature when even small amounts of C_mG₂are used. Adding a lyotropic electrolyte, NaCl, to water–C_kOC₂OC_k–C_mβG₁mixtures moves the phase behavior down in temperature, while the hydrotropic electrolyte NaClO₄moves the phase behavior up in temperature.     

Radiolysis of resist polymers. III. Copolymers of methyl-α-chloroacrylate and trihaloethylmethacrylates

Homopolymers of 2,2,2-trifluoroethyl(methacrylate) (TFEMA) and 2,2,2-trichloroethyl-(methacrylate) (TCEMA) and copolymers with methyl-α-chloroacrylate (MCA) in a range of compositions were synthesized. The reactivity ratios were obtained; the two copolymerizations were close to ideal. Poly(MCA) showed G_s = 7.4 and G_s = 0.9 by γ-radiolysis. On the other hand, poly(TFEMA) and poly(TCEMA) and G_s values of 2.0 and 2.4, respectively, and G_x = 0. Radiolysis of copolymers was initiated to a large degree by dissociative electron capture by the halogen atoms in both comonomers, as revealed by the ESR spectra of radicals derived from them. Germinal recombinations in irradiated poly(TFEMA) suggested the presence of radicals in proximity. This process was absent in the copolymers. GC-MS analysis of volatile products and other supporting evidence showed that TFEMA monomers tended to depolymerize; the TCEMA monomers did not. The radiolysis yields varied monotonically with the comonomer composition for the MCA–TFEMA system but the yield–composition relationship was irregular in MCA–TCEMA copolymers. Four noncrosslinking systems are potential radiation resists arranged in increasing order of promise: poly(TFEMA) (G_s = 2.0, T_g = 70°); poly(TCEMA) (G_s = 2.7, T_g = 142°); poly(94MCA-co-6TCEMA) (G_s = 2.7, T_g = 142°); and poly(68MCA-co-32TFEMA) (G_s = 3.0, T_g = 112°). These materials merit further investigation for E-beam or x-ray lithographic applications. Mechanisms of radiolysis for these materials, based on ESR, GC-MS, and radiolysis yield data, were discussed.     

Solubilization of oil in a mixed cationic liquid crystal

The mixing fraction of didodecyldimethylammonium bromide (DDAB) in dodecyltrimethylammonium bromide + DDAB to produce a lamellar liquid crystal (L _α) abruptly decreases upon addition of a small amount of m-xylene, whereas the mixing fraction becomes constant at high m-xylene content. Similar results were obtained in saturated hydrocarbon systems. It is considered that oil molecules in the surfactant palisade layer increases the effective cross-sectional area per surfactant head group, a_s, whereas a_s is constant if the oil molecules are solubilized in the core of the liquid crystal. The volume fraction of penetrating oil in the total solubilized oil is defined as a penetration parameter, Pe, which is calculated from small-angle X-ray scattering data. Pe is high in the m-xylene system, whereas it is low in the n-decane system. Even in the same oil system, Pe decreases dramatically with increasing solubilization. Hence, most of the oil added penetrates into a palisade layer at an early stage of oil addition. This causes a change in the mixing fraction of surfactant in the L _α phase. Thereafter the oil is solubilized in the core of the bilayer with further addition of oil. Received: 20 April 1998 Accepted: 16 July 1998     

Enantioseparation of Some New 1-(2-Naphthyl)-1-ethanol Ester Derivatives by HPLC on Chiralcel OD

The direct enantiomeric resolution of racemic 2-(1H-imidazole-1-yl)-1-naphthalene-2-yl)ethanol esters, 1-(naphthalene-2-yl)ethanol esters, and 1-(1-hydroxynaphthalene-2-yl)-2-(1H-imidazole-1-yl)ethanol on silica-based cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) column is described. The separations were performed using mobile phases which consist of alcohol (methanol, ethanol or 2-propanol)/n-hexane in various proportions. The effect of structural features of the solutes along with the nature and concentration of alcohol in the mobile phase on the discrimination between the enantiomers was examined for different mobile phase compositions. The results suggest that not only the structure and concentration of alcohol in the mobile phase, but also the subtle structural differences in racemates can have a pronounced effect on enantiomeric separation and retention. Baseline separations were obtained for 2-(1H-imidazole-1-yl)-1-naphthalene-2-yl)ethanol esters carrying imidazole ring in addition to ester functional group in their structures. The α values of the resolved enantiomers of 2-(1H-imidazole-1-yl)-1-naphthalene-2-yl)ethanol esters were in the range of 1.49–1.62 while the R _s values varied from 4.20 to 6.75 when methanol/n-hexane (70:30 v/v) was used as mobile phase.

     

Prediction of LC retention of steroids using solvatochromic parameters

Summary The proportion of organic modifier and pH of the hydroorganic mobile phase were optimized to separate a series of nine important steroids by LC. It has been shown that linear plots of logk′ against Reichardt’sE _T ^N parameter for the mobile phase is observed over the whole range of compositions of practical importance. Data from these plots summarize an approach for optimization of resolution from only two retention measurements for each compound. pH is shown to be irrelevant. This behaviour could be extrapolated to other steroids and drastically reduce the number of retention values needed for mobile phase optimization for screening analysis of steroids in doping investigations.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

Energetics of anionic surfactant-additive systems at the cloud point

The energetics of clouding in anionic surfactant (SDBS) and tetrabutylammonium bromide system in the presence of additives, such as ureas, amino acids and sugars is reported. The change of standard Gibbs energy of solubilization (ΔG _s ^o) for all of the additives was found to be negative. The values of change of standard enthalpy (ΔH _s ^o) and that of standard entropy (TΔS _s ^o) values were found to depend on the type and chemistry of the additive. The results were explained on the basis including chemistry of additives, their effect on water structure, and solubilization of additives either in the micellar or in aqueous phases.