Spreading of trisiloxanes over thin aqueous layers

Surfactants are widely spread in nature and are increasingly used in industry as wetting, cleaning and disinfecting agents. Recently, there are newly discovered trisiloxanes and other silicone based surfactants which show very unusual spreading behaviour. Although a number of experimental and theoretical investigations have been carried out, the underlying spreading mechanism remains unclear. Experiments using trisiloxanes and comparison with 3 different poly(ethylene glycol) monododecyl ethers (C₁₂E₄, C₁₂E₅, and C₁₂E₆) surfactants were performed to understand the influence of Marangoni force as the driving force for the spreading. We then compared our experimental results to available theoretical predictions in the literature. The obtained experimental data showed the opposite trend as compared with the theoretical predictions developed for regular surfactants. The latter is assumed to be a special feature of “superspreaders”. The article is published in the original.     

Thermodynamics of aqueous mixtures of 2-(2-Hexyloxyethoxy)ethanol at 5°C

The densities and the ultrasonic speeds of the aqueous solutions of 2-(2-hexyloxyethoxy)ethanol (C₆E₂) were measured over the entire range of mole fractions at 5°C. Excess molar volumes V ^E were readily calculated from the densities. The densities, in combination with the ultrasonic speeds, furnish estimates of the molar (and excess molar) isentropic compressibilities K _S and the deviations u ^D of the ultrasonic speeds from the values calculated for ideal mixtures. Radical changes in the mole fraction derivatives of the excess molar properties of the (C₆E₂ + water) system, in the vicinity of an amphiphile mole fraction of 0.003, indicate that C₆E₂ like C₆E₃ is capable of micelle formation. Our data have been compared with those reported earlier for (C₄E₂ +, C₂E₂ +, and C₆E₃ + water). We have employed both mass action and pseudophase approaches to data analysis, together with the four-segment model approach.     

Analysis of volumes of mixing for propyl and butyl formate withn-alkanes in terms of the Nitta model

The excess molar volumes of eight binary systems formed of propyl or butyl formate with four n-alkanes (from C₆ to C₉) have been determined at 25°C and atmospheric pressure. The data were obtained indirectly from densities measured experimentally with a vibrating-tube densimeter and then compared with those estimated using the Nitta model. This method yields good predictions of the symmetry of the v ^E curves given an average overall error for all the systems analyzed here smaller than 6 percent.     

Density and viscosity studies of poly(ethylene-oxide) alkyl alcohols

Density and viscosity of binary systems water-nonionic surfactants poly(ethylen-oxide) alkyl alcohols type, [C_nH_2n+1(OCH₂CH₂)_mOH, C_nE_m], have been studied. The partial molar volumes in the dilute solution range and the viscosity B-coefficients were calculated. The nonionic surfactants partial molar volumes were compared with those of ethylene glycol and poly(ethylenglycol) (PEG). The comparison shows that the ethoxy unit volume, (OCH₂CH₂), seems to be independent of the particular system. The consequences of this are discussed. A model for interpreting the experimental B values has been proposed. The model treats the macroscopic viscosity as the superimposition of different local effects. The following surfactants have been considered: C₅E₁, C₅E₂, C₆E₁, C₆E₂, C₆E₃, C₆E₄.     

Spontaneous formation of monodisperse vesicles near the cloud point of an aqueous amphiphilic system

 Monodisperse vesicular structures have been produced spontaneously from an almost structure-less aqueous amphiphilic system: water/di(ethylene glycol) mono-hexyl ether (C₆E₂)/sodium cholate. Individually, neither C₆E₂ nor the bile acid produces noticeable aggregate structures in an aqueous solution. However, the presence of small amounts of bile acid in the C₆E₂/water binary system is found to produce large microstructures, besides pushing the miscibility gap to higher temperatures. Dynamic light scattering studies indicate the presence of very monodisperse structures of sizes ranging from 15 to 50 nm in radii. The radii of these structures show strong dependence on the concentrations of the components and on the distance in temperature from the cloud point. For a given set of conditions the sizes are very stable and reproducible. Electron microscopy and conductivity measurements confirm these structures as vesicles. These may be formed due to the association of bile acid with C₆E₂ producing the geometrical parameters necessary for the formation of vesicles. Received: 23 January 1998 Accepted: 11 June 1998     

2H NMR study on the lyomesophases of the system hexaethylene glycol dodecyl methyl ether/water Temperature dependence of quadrupole splittings

Abstract

The liquid-crystalline phases of the system hexaethylene glycol n-dodecyl methyl ether (C₁₂E₆C₁)/water are studied by deuteron NMR spectroscopy. Information about the molecular orientation is derived from the quadrupole splittings of two selectively deuteriated derivatives of C₁₂E₆C₁, one deuteriated at the α-position of the alkyl chain, the other at the methoxy group. The temperature dependence of the quadrupole splittings reveals a continuous decrease of orientational order on approach to the macroscopic phase transformations. This behaviour is explained by an increase of defects and fluctuations in the microstructure of the mesophases.     

High-temperature collisional energy transfer in highly vibrationally excited molecules II: Isotope effects in isopropyl bromide systems

Values for 〈ΔE_down〉, the average downward energy transferred from the reactant to the bath gas upon collision, have been obtained for highly vibrationally excited undeuterated and per-deuterated isopropyl bromide with the bath gases Ne, Xe, C₂H₄, and C₂D₄, at ca. 870 K. The technique of pressure-dependent very low-pressure pyrolysis (VLPP) was used to obtain the data. For C₃H₇Br, the 〈ΔE_down〉 values (cm^?1) are 490 (Ne), 540 (Xe), 820 (C₂H₄), and 740 (C₂D₄), and for C₃D₇Br, 440 (Ne), 570 (Xe), 730 (C₂H₄), and 810 (C₂D₄). The uncertainties in these values are ca. ±10%. The 〈ΔE_down〉 values for the inert bath gases Ne and Xe show excellent agreement with the theoretical predictions of the semi-empirical biased random walk model for monatomic/substrate collisional energy exchange [J. Chem. Phys., 80 , 5501 (1984)]. The relative effects of deuteration of the reactant molecule on 〈ΔE_down〉 also compare favorably with the predictions of this theoretical model. Extrapolated high-pressure rate coefficients (s^?1) for the thermal decomposition of reactant are 10^13.6±0.3 exp(?200 ± 8 kJ mol^?1/RT) for C₃H₇Br and 10^13.9±0.3 exp(?207 ± 8 kJ mol^±1/RT) for C₃D₇Br, which are consistent with previous studies and the expected isotope effect.     

Binary and Ternary Complexes Between Lauryl Hexaoxyethylene, Benzoate and Cyclodextrin. Part II. β-CD

The characterization of binary and ternary complexes of benzoate, lauryl hexaoxyethylene (C₁₂E₆) and -CD is presented. The complexation equilibrium was characterized by UV-Vis spectrophotometry, titration microcalorimetry, capillary electrophoresis, and 2D ROESY ¹H-NMR. Results suggested that -CD forms one complex with C₁₂E₆in the stoichiometric ratio of -CD : C₁₂E₆1.5 : 1, with a stability constant 1.3 × 10⁵ M^-1.5. The 2-D ROESY ¹H-NMR spectrum indicated that C₁₂E₆is included inside the -CD cavity. The primary binding site of C₁₂E₆ is on the lauryl subunit of this molecule. Analogous to a previously reported study of -CD, the combination of -CD and C₁₂E₆precipitated from the solution. Addition of benzoate seemed to dissolve the precipitate and nearly doubled the apparent stability constant of the complex. Results from the various techniques supported formation of ternary complexes between -CD, C₁₂E₆, and benzoate.     

Differential scanning calorimetric study of phase changes in poly(ethylene glycol) dodecyl ether-water systems

Phase changes in binary systems of poly(ethylene glycol) dodecyl ethers, C₁₂H₂₅(OC₂H₄)_xOH (x=5, 6 and 8) with water have been studied between –40 to 100 C by differential scanning calorimetry. A number of transitions, including the liquidliquid phase separation, were seen and the transition temperatures and enthalpy changes were determined. The observed temperatures were generally in good agreement with reported phase diagrams. In the C₁₂E₅ system, three of the four three-phase lines were seen and a more complete phase diagram is suggested for the water-rich part of the system. Most of the phase changes seen above 0 C are accompanied by small endothermic enthalpy changes of 0.7 to 0.9 kJ (mol C₁₂E_x)^–1, independent of system studied, type of transition and transition temperature. Water-rich solutions and liquid crystalline phases separate upon freezing into ice and crystals of hydrated amphiphile. Eutectics are developed at the following temperatures and compositions: C₁₂E₅ –3.0 C and 54 wt % C₁₂E₅; Q₂E₆ –4.5 C and 54 wt % C₁₂E₆, C₁₂E₈ –3.8 C and 49 wt % C₁₂E₈.     

The aggregation of nonionic surfactants in the presence of poly(methacrylic acid)

The solution properties of homogeneous hexaethylene and octaethylene glycol mono(n-dodecyl) ethers, C₁₂E₆ and C₁₂E₈, respectively, and octaethylene glycol mono(n-decyl) ether, C₁₀E₈, with poly(methacrylic acid) (PMA) were investigated by dye solubilization, surface tension, fluorescence, viscosity, and pH measurements. The data were discussed regarding non-cooperative and cooperative binding of surfactant to polymer. Whereas in the interaction with poly(acrylic acid) (PAA), the critical aggregation concentrations (cac or T ₁) of these surfactants were lower than the respective critical micelle concentration (cmc), in that with the more hydrophobic PMA, T ₁’s of C₁₂E₆ and C₁₂E₈ were higher than the respective cmc, but that of C₁₀E₈ was lower than its cmc. These may be ascribed to the hydrophobic microdomains (HMD) of the PMA coil in water, probably in its inside. It is considered that some surfactants are bound first to the HMD non-cooperatively and then they are abruptly bound cooperatively at T ₁. This raises T ₁ higher than cmc when the cmc is low, and the amount bound by the HMD is relatively large and vice versa. T ₁ of C₁₂E₆ or C₁₂E₈ is the former case, and that of C₁₀E₈ is the latter. Thus, different from PAA, T ₁ for PMA + nonionic surfactant system consists of the amount of non-cooperative binding and the cac of the cooperative binding in equilibrium. Therefore, this T ₁ has a different meaning from that for PAA and should be called apparent T ₁. As the binding to the HMD is dependent on PMA concentration and cac is not, which is like in the PAA system, separation of apparent T ₁ from the HMD binding was achieved by extrapolating T ₁’s to zero PMA concentration (denoted intrinsic T ₁). This value for C₁₂E₈ was found to be lower than the respective cmc and also lower than the respective T ₁ for PAA. With increase in surfactant concentration, the pH of PMA solution rose and demonstrated a peak. This pH rise and fall may be induced by loosening of the HMD coil due to binding increase and by rearrangement of PMA + surfactant complex in high surfactant concentrations region. By raising the initial pH, the HMD were loosened; consequently, T ₁ rose a little, and at higher pH, no surfactant binding took place.     

Inversion of the substituent effects on the rates of ArSC1 AdE-reactions with styrenes

The inversion of the reactivity order of R²C₆H₄SC1 in Ad_E-reactions with R¹C₆H₄CHCH₂ owing to the variations in R¹ and R² has been found and interpreted in terms of two kinetically distinguishable Ad_E-2 mechanisms.     

Distortion of the triplet state of benzene in a borazole host. A study by microwave induced delayed phosphorescence at 1.2 K

The zero-field splitting parameters of C₆H₆ and C₆D₆ in a borazole crystal host have been measured. The absolute value of the parameter E is three times as large as for C₆H₆ in C₆D₆. The relative rate constants for radiative decay in some vibronic bands have been obtained by MIDP methods. In the OO band of the phsophorescence spectrum the radiation stems from the upper zf level indicating a quinoid electronic structure for benzene in borazole, i.e. opposite to that for C₆H₆ in C₆D₆.     

Isomer effects in the excess enthalpies of mixtures of alkanes and cycloalkanes

Using the Picker flow calorimeter, excess molar enthalpies H ^E have been obtained at 25°C for mixtures of 1,2-, 1,3- and 1,4-cis- and trans-dimethylcyclohexane and cis- and trans-decalin with n-hexadecane and the highly branched C₁₆ isomer, 2,2,4,4,6,8,8-heptamethylnonane. Values of H ^E are also obtained for cis- and trans-decalin mixed with C₆, C₇, and C₉ isomers. Anomalously low values of H ^E occur for normal alkanes mixed with cycloalkanes in the di-equatorial configuration, suggesting the presence of a negative contribution in H ^E possibly due to a restriction of n-alkane molecular motion by the flat, plate-like cycloalkane.     

Excess molar heat capacities and excess molar volumes of some mixtures of propylene carbonate with aromatic hydrocarbons

Excess molar volumes V ^E and excess molar heat capacities C _P ^E at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C₄H₆O₃; PC) + benzene (C₆H₆;B), + toluene (C₆H₅CH₃;T), + ethylbenzene (C₆H₅C₂H₅;EB), and + p-xylene (p-C₆H₄(CH₃)₂;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: V ^E (cm³-mol^–1) at the minimum ranges from about –0.31 at x₁=0.43 for {x₁C₄H₆O₃+x₂p-C₆H₄(CH₃)₂}, to –0.45 at x₁=0.40 for {x₁C₄H₆O₃+x₂C₆H₅CH₃}. For the systems (PC+T), (PC+EB) and (PC+p-X) the C _P ^E s are all positive and even more skewed. For instance, for (PC+T) the maximum is at x _1,max =0.31 with C _P,max ^E =1.91 J-K^–1-mol^–1. Most interestingly, C _P ^E of {x₁C₄H₆O₃+x₂C₆H₆} exhibits two maxima near the ends of the composition range and a minimum at x _1,min =0.71 with C _P,min ^E =–0.23 J-K^–1-mol^–1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Quantum chemical metabolism‐based simulation of carcinogenic potency of benzene derivatives

Using an oxenoid model, we investigated dependences of carcinogenic potency of the benzenes C₆H₅‐X on a nature of substituents X. According to the model, a P450 enzyme breaks a dioxygen molecule and generates the oxens, which readily react with substrates. We suggest that a stability of the intermediate OC₆H₆‐X with tetrahedrally coordinated C atom relative to the molecule C₆H₅‐X determines a rate of substrate biotransformation. Using MO LCAO MNDO approach, we calculated the total energies of molecules C₆H₆‐X and arene oxides OC₆H₆‐X. A difference ΔE_min of these values determines activation energy of oxidation reaction. The compounds with the low ΔE_min values are noncarcinogenic. Benzene derivatives with high ΔE_min values belong to carcinogenic compounds series. The carcinogenicity of amino‐ and nitro‐substituted benzenes is also determined by N‐oxidation of amino and reduction of the nitro group. As the phenylhydroxylamines XC₆H₄NHOH and nitrenium ions XC₆OH₄NH⁺ are the common metabolites of the nitro‐ and amino‐substituted benzenes and nitrenium ions XC₆H₄NH⁺ are the ultimate carcinogens, we use the differences ΔE_N = E(XC₆H₄NH⁺) ? E(XC₆H₄NHOH) as the second parameter characterizing the carcinogenic activity of amino‐ and nitro‐substituted benzenes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Modeling of the three-phase equilibrium in systems of the type water + nonionic surfactant + alkane

Liquid–liquid equilibria of systems water (A) + C_iE_j surfactant (B) + n-alkane (C) have been modeled by a mass-action law model previously developed and so far successfully applied to a series of binary water + C_iE_j systems and to the ternary system water + C₄E₁ + n-dodecane. These calculations provide the basis for the presented modeling. The aqueous systems give information about the association constants and the χ_AB-parameter of the Flory–Huggins theory and the ternary C₄E₁-system provides universal temperature functions for the χ_AC- and the χ_BC-parameter. The three-phase equilibrium for seven ternary C_iE_j systems (i = 6–12, j = 3–6) has been calculated by fitting one additional parameter for each of both temperature functions to the characteristic “fish-tail” point. The agreement with the experimental data is reasonably well. For systems with very small three-phase areas the results can considerably be improved by individual temperature functions that incorporate the experimental temperature maximum of the “fish” into the parameter fit. Based on the parameters of the system water + C₈E₄ + n-C₈H₁₈ the “fish-shaped” phase diagram of the system water + C₈E₄ + n-C₁₄H₃₀ was predicted reasonably well.     

X-traps in isotopically mixed benzene crystals: phosphorescence spectrum and zero-field splitting of the lowest triplet state

We have observed temperature-dependent X-trap phosphorescence in C₆H₆ crystals doped with C₆D₆. The observed X-trap is identified as C₆H₆ which is perturbed by the presence of C₆D₆ in a nearest-neighbor crystal site. Zero-field optical-microwave double resonance measurements on the X-traps give for the zero-field anisotropy parameter |E| a value of 20 ± 5 MHz. This is an order of magnitude smaller than that observed for C₆H₆ in C₆D₆ and indicates for the X-traps a nearly hexagonal distribution of spin density in the ³B_1u state. This difference shows that the electronic structure of the ³B_1u state is sensitive to subtle changes in its environment.     

N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons

Stable N‐heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C₆H₄)(IPr)] and [(IPr)(C₆H₄)₂(IPr)] ( 4 and 5 , respectively; IPr=C{N(2,6‐iPr₂C₆H₃)}₂CHCH), are reported. In a nickel‐catalyzed double carbenylation of 1,4‐Br₂C₆H₄ and 4,4′‐Br₂(C₆H₄)₂ with IPr ( 1 ), [(IPr)(C₆H₄)(IPr)](Br)₂ ( 2 ) and [(IPr)(C₆H₄)₂(IPr)](Br)₂ ( 3 ) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC₈. Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet?triplet energy gap ΔE_S?T of 10.7 kcal mol^?1, whereas 4 features more quinoidal character with a rather large ΔE_S?T of 25.6 kcal mol^?1. In view of the low ΔE_S?T, 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character.     

Micellization of sodium dodecyl sulfate and polyoxyethylene dodecyl ethers in solution

The effect of polyoxyethylene type nonionic surfactants (C₁₂E _n n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of C₁₂E _n , micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence of NaCl. Micellar growth is most significant in presence of shorter moieties of C₁₂E _n (e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm this assumption are reported. The cloud point of C₁₂E _n has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were present.     

Prediction of the cloud point of polyethoxylated surfactants and their mixtures by the thermodynamic model of Flory-Huggins-Rupert

The cloud point curves of polyethoxylated surfactants are established experimentally. These experimental data are preliminary to the development of the cloud point extraction process, which appears as an interesting alternative to the usual solvent extraction unit operation. Starting from the thermodynamic model developed by Flory and Huggins for phase separation of polymer aqueous solutions, this paper aims at the prediction of cloud point curves. In this work, Rupert’s approach is extended to commercial nonionic surfactants, mixtures of homologous species, namely a few alkylphenol and alcohol ethoxylates. The limit of such an approach is clearly demonstrated, provided that a fitting parameter is finally required for a successful model application to pilot-plant manufactured surfactants, like C₈ΦE_n (n?=?7.5, 10, 12), C₉ΦE_n (n?=?8, 10, 12), C₁₂E₄, C₁₂E₆ and commercial Tergitol 15-S-7 (linear C₁₂-C₁₄ secondary alcohol with an average of 7 ethylene oxide units).GRAPHICAL ABSTRACT