Corrosion Inhibition Efficiency of Polytriethanolamine Surfactants for Pipe-Lines Carbon Steel in 1M HCl

Fifteen organic compounds were prepared from triethanolamine and its derivative. The triethanolamine was polymerized by condensation to get P₄, P₆, and P₈ at different molecular weight. The P8 was ethoxylated at different ethylene oxide units (en) (40, 100, and 120) to obtain three compounds (E(en)P₈). Every degree of ethoxylate was esterified with 1, 4, and 8 moles of oleic acid to get on 9 ethoxylated polytriethanolamine esters (E(en)P₈Om). The effect of adding these organic compounds on the electrochemical behavior of carbon steel in 1 M HCl was investigated by using the weight loss technique. The reported results in this study show that the addition of these surfactants inhibits the corrosion of carbon steel. The inhibition efficiency (I%) for each inhibitor increases with increasing the concentration. The maximum inhibition efficiency (95%) was obtained by (E(40)P₈O₁) at 600 ppm. The inhibitive efficiency was discussed on the light of chemical structure of the used inhibitors.     

EVALUATION OF MODEL FOR STRATUM CORNEUM LIPID BARRIER AGAINST STEROID DIFFUSION

The ability of three matrices to model the barrier properties of the lipid domain of stratum corneum (SC) against permeation of seven steroids was studied. Model matrices were water and oleic acid/oleate; a mixture of unsaturated and saturated fatty acids/soap; or a more complex matrix also containing phospholipids, sphingolipids, cholesterol and ceramides.

Permeability coefficients (K.) were similar in the three models, supporting the hypothesis that the barrier to steroid permeation is determined by the structural organization of the lipids, not by the chemical structure of individual substances. Parabolic relationships were found between K values and octanol/water partition coefficients (P_oct) of the steroids, with an optimum permeability at log P_oct, of 3·0. All three models showed good resistance to permeability by steroids. The effects of cationic, anionic and non-ionic surfactants on the permeability of hydrocortisone within the water oleic acid/oleate matrix were also investigated. Permeability increased with anionic surfactants, decreased with cationic surfactants and varied little with non-ionic surfactants. The matrices tested appeared able to model the effect of surfactants on the permeability of hydrocortisone through the SC     

Synthesis and Evaluation of Anionic Copolymeric Surfactant as Dispersing Agent for Some Heterocyclic Azo-Dyes

Series of polymeric surfactants based on decylacrylate (M ₁ ) as hydrophobe and oxypropylated maleate (Mm _{2,4,6 and 8} with different molar ratios of propylene oxide) as hydrophiles were prepared by copolymerization in presence of 1mole% azobiisobutyronitrile (AIBN) as free radical initiator to afford [PMm₂, PMm₄, PMm₆, and PMm₈] _a–i . The reaction mixtures were followed by sulfation and neutralization to attain [PMmS₂, PMmS₄ PMmS₆, and PMmS₈]_a–i as anionic copolymeric surfactants, in good yield. These derivatives were purified and characterized by microanalysis, infrared, and ¹H-NMR spectra studies. Also, surface activity, dispersing properties, and biodegradability were evaluated. The prepared anionic copolymeric surface active agents revealed good surface activities and high dispersing properties above 70% special for PMms8_d with 8 mole propylene oxide and equal molar ratio from hydrophilic and hydrophobic monomers. Also, they are more biodegradable than traditional surfactants.     

Synthesis of Some Novel Nonionic Ethoxylated Surfactants Based on α-Amino Acids and Investigation of Their Surface Active Properties

Eight novel ethoxylated nonionic surfactants were prepared based on oil soluble α-amino acids. The L-phenylalanine and L-leucine were esterified and amidated with cetyl alcohol and palamitic acid, respectively; two amides and two esters of α-amino acids were obtained. The ethylene oxide was condensed with the prepared amides and esters to get three different polyethylene oxide units (40, 60, and 100) as phenylalanine derivatives. The amide and ester of α-L-leucine were ethoxylated at (60 ethylene oxides units). The analytical micro analysise, FTIR, ¹H NMR, ¹³C NMR, mass spectra were carried out to confirm the chemical structures. The surface tension of the water soluble prepared compounds was measured at 25°C, further the surface active properties were determined and calculated. Such that critical micelle concentration (CMC), surface excess (Γ_max); area per molecule (A_min), effectiveness (γ_CMC) free energy of micellization and adsorption (ΔG_mic, ΔG_ad). From the data obtained it was found that the CMC of phenylalanine esters is greater than that obtained for the amide derivatives. The Γ_max decreased as the ethylene oxide units (EO) increased. It was found also that the ΔG_ad was greater than the ΔG_mic. The obtained data and discrepancy were discussed on the light of surfactant chemical structure.     

Demulsification Efficiency of Some New Demulsifiers Based on 1,3,5-Triethanolhexahydro-1,3,5-triazine

This study mainly concentrates on the synthesis of three novel demulsifiers and the investigation of their demulsification efficiency. The demulsifiers were derived from 1,3,5-triethanolhexahydro-1,3,5-triazine, which was prepared by the reaction of monoethanol amine with formaldehyde. The 1,3,5-triethanolhexahydro-1,3,5-triazine was ethoxylated by introducing 20 units of ethylene oxide and then esterified at different molar ratios with oleic acid (1, 2, and 3) to give three demulsifiers, namely, E₂₀TO, E₂₀TO₂, and E₂₀TO₃. The chemical structures of the prepared demulsifiers were confirmed by ¹H NMR and FTIR spectrum. The demulsification efficiency of these demulsifiers was tested on the natural water-in-oil (w/o) emulsions (50% water content). From the obtained results, it has been found that the investigated demulsifiers have a great potential to break the w/o emulsions. The trioleat ester (E₂₀TO₃) exhibited the maximum demulsification efficiency (96%) after 120 minutes at 55°C.     

Effect of Polymer on Dynamic Interfacial Tensions of Anionic–nonionic Surfactant Solutions

The dynamic interfacial tensions (IFTs) of enhanced oil recovery (EOR) surfactant/polymer systems against n-decane have been investigated using a spinning drop interfacial tensiometer in this paper. Two anionic–nonionic surfactants with different hydrophilic groups, C₈PO₆EO₃S (6-3) and C₈PO₆EO₆S (6-6), were selected as model surfactants. Partially hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM) were employed. The influences of surfactant concentration, temperature, polymer concentration, and oleic acid in the oil on IFTs have been studied. The experimental results show that anionic–nonionic surfactants can form compact adsorption films and reach ultralow IFT (10^?3 mN/m) under optimum conditions. The addition of polymer has great influence on dynamic IFTs between surfactant solutions and n-decane mainly by the formation of looser mixed films resulting from the penetration of polymer chains into the interface. The compact surfactant film will also be weakened by the competitive adsorption of oleic acid, which results in the increase of IFT. Moreover, the penetration of polymer chains will be further destroyed surfactant/polymer mixed layer and lead to the obvious increase of IFT. On the other hand, polymers show little effect on the IFTs of 6-6 systems than those of 6-3 because of the hindrance of longer EO chain of 6-6 at the interface.     

Syntheses and properties of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer

A new type of ethoxylated double‐tail trisiloxane surfactants containing a propanetrioxy spacer of the general formula ROCH₂CH(OR)CH₂O(CH₂CH₂O)_xCH₃ [R = Me₃SiOSiMe(CH₂)₃OSiMe₃, x = 8.4, 12.9, 22] has been synthesized. Their structures were characterized by ¹H‐NMR, ¹³C‐NMR and ²⁹Si‐NMR spectroscopy. The critical micelle concentration (CMC) values of these double‐tail trisiloxane surfactants were at the level of 10⁻⁵ mol l⁻¹, and the surface tension values of their aqueous solutions at CMC were in the range of 21‐24.9 mN m⁻¹. Only the double‐tail trisiloxane surfactant with average ethoxy units of 8.4 ( 1P ) possesseda good spreading ability (SA) value. Its SA values of aqueous solutions (5.0 × 10⁻³ mol l⁻¹) on parafilm and Ficus microcarpa leaf surfaces were more than 15 (within 10 min) and 13 (within 3 min), respectively. The trisiloxane surfactant 1P was also found to have the strongest hydrolysis resistant ability among all of the double‐tail trisiloxane surfactants prepared. Its aqueous solutions were stable for 130 days in an acidic environment (pH 4.0) and 59 days in an alkaline environment (pH 10.0) with surface tension values less than 23 mN m⁻¹. It is suggested that this surfactant can be used as a wetting agent or spreading agent in certain extreme pH environments. Copyright © 2011 John Wiley & Sons, Ltd.     

Systems Tl2MoO4-E(MoO4)2, where E = Zr or Hf, and the crystal structure of Tl8Hf(MoO4)6

Systems Tl₂MoO₄-E(MoO₄)₂ (E = Zr, Hf) are studied using X-ray powder diffraction, DTA, and IR spectroscopy. Compounds Tl₈E(MoO₄)₆ and Tl₂E(MoO₄)₂ are found in these systems. T-x diagrams for the Tl₂MoO₄-Zr(MoO₄)₂ system are designed. Single crystals are grown and structure is solved for Tl₈Hf(MoO₄)₆. The compound crystallizes in a monoclinic structure with the unit cell parameters a = 9.9688(6) Å, b = 18.830(1) Å, c = 7.8488(5) Å, β = 108.538(1)°, Z = 2, space group C2/m. The main structural fragment is a [HfMo₆O₂₄]^8? isle group. Three crystallographically independent types of Tl polyhedra uniformly fill spaces between [HfMo₆O₂₄]^8? fragments to form a three-dimensional framework.     

The Surface and Thermodynamic Properties of Ethoxylated Sodium Monoalkyl Sulfosuccinate Surfactants

A series of ethoxylated sodium monooctyl sulfosuccinates [E(n)SMOSS] and ethoxylated sodium monolauryl sulfosuccinates [E(n)SMLSS] have different units of ethylene oxide (n = 9, 14, 23) were synthesized. The surface and thermodynamic properties of these surfactants have been compared with sodium dioctyl sulfosuccinate surfactant (SDOSS) as a commonly used surfactant. The surface tension measurements at 25, 35, 45, and 55°C were used to determine of the critical micelle concentration (CMC) and surface active properties of these surfactants. The effect of the ethylene oxide (EO) unit and the alkyl chain length on the surface properties for the prepared surfactants was studied. The results show that the ethoxylated sodium monoalkyl sulfosuccinates generally have lower values of CMC than that of sodium dioctyl sulfosuccinate. The values of surface active parameters indicate that the ethoxylated sodium monooctyl sulfosuccinates and ethoxylated sodium monolauryl sulfosuccinates surfactants have adsorption properties better than the sodium dioctyl sulfosuccinate surfactant as a resulted presence of ethylene oxide in molecules of the prepared surfactants. The thermodynamic parameters show that the (EO) unites in the chemical structure of ethoxylated sodium monoalkyl sulfosuccinate surfactants improve their micellization and adsorption properties.     

Crystal structure and spectroscopic characterization of a coordination polymer of Copper(II) chloride with ethylenediamine and the 2-hydroxybenzoate ion

A new mixed-ligand one-dimensional copper(II) coordination polymer [Cu(en)(sal)Cl] _n where en = ethylenediamine(C₂H₈N₂) and Hsal = 2-hydroxybenzoic acid (salicylic acid; C₇H₆O₃) is synthesized and characterized by FTIR spectroscopy and single crystal X-ray diffraction. The structure contains Cu²⁺ ions in two different distorted octahedral coordination environments: an axially extended CuN₄Cl₂ moiety arising from a pair of bidentate en ligands and a CuO₄Cl₂ moiety arising from a pair of asymmetrically coordinated sal^– anions. The chloride ions bridge the copper ions into a zigzag chain propagating in [001]. The structure is consolidated by N–H???O and N–H???Cl hydrogen bonds which generate a layered network. Crystal data: C₉H₁₃ClCuN₂O₃, M _r = 296.20, monoclinic, P2₁/c, a = 13.9179(10) Å, b = 10.4900(8) Å, c = 8.5181(6) Å, β = 105.518(4)°, V = 1198.30(15) ų, Z = 4, R(F) = 0.026, w R(F ²) = 0.068.     

Benzophenone‐(phenylthio)acetic acid phosphonium salts as initiators of free‐radical photopolymerization of vinyl monomers: Mechanistic studies

The mechanism of the benzophenone‐sensitized photooxidation of phosphonium salts of (phenylthio)acetic acid was studied as a means for understanding how these salts function as coinitiators in the free‐radical photopolymerization of vinyl monomers. Both steady‐state and nanosecond flash photolytic methods were used to determine, in a quantitative manner, the mechanism of primary and secondary photoreactions for three quaternary phosphonium salts containing butyl and/or phenyl groups, i.e., P⁺(C₄H₉)₄, P⁺(C₄H₉)(C₆H₅)₃, and P⁺(C₆H₅)₄. It was found that the initial polymerization rates were the same for all three phoshonium salts of (phenylthio)acetic acid and were equal to those found previously for tetralkyl ammonium salts. The polymerization rates were more than twice the rates found for direct initiation by benzophenone and by the benzophenone‐(phenylthio)acetic acid initiating system. These results correlate well with the large quantum yields of ^?CH₂SC₆H₅ radicals (the main initiating radicals) found in the complementary photochemical investigation. It was found that a detailed knowledge of the photochemical reactions in the photoinitiating systems was critical to understand the kinetics of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8013–8022, 2008     

Synthesis and Crystal Structure of meso-Δ,Λ-μ-Peroxo-μ-hydroxobis[bis(ethylenediamine)rhodium(III)]trifluoromethane Sulfonate

The reaction of the meso-diol, Δ,Λ-[(en)₂Rh(OH)₂Rh(en)₂]⁴⁺, with aqueous H₂O₂ and 1 equiv. of NaOH at 90° forms the μ-peroxo-μ-hydroxo-bridged species Δ,Λ-[(en)₂Rh(O₂,OH)Rh(en)₂]³⁺ in a yield of ca. 50%. The compound was crystallized as perchlorate and trifluoromethanesulfonate salts. The structure of the latter salt was determined by single-crystal X-ray diffraction. The crystals are triclinic with space group P1 and lattice constants a = 11.895(5), b = 12.491(4), c = 13.053(5) Å, α = 103.98(3), β = 92.59(3), γ = 119.52(6)°. The distances of the metal centres to the bridging peroxo ligand are 1.999(8) and 1.983(6) Å. The O? O distance in the peroxo group is 1.521(14) Å, and the dihedral angle of the Rh? O? O? Rh unit deviates 65° from planarity. The peroxo complex reacts reversibly with acid, and spectrophotometric studies suggest that the reaction involves protonation of the peroxo bridge, with pK_a = 2.70(2) at 25° in 1M NaClO₄.     

Application of CO2-Switchable Oleic-Acid-Based Surfactant for Reducing Viscosity of Heavy Oil

CO₂-switchable oligomeric surfactants have good viscosity-reducing properties; however, the complex synthesis of surfactants limits their application. In this study, a CO₂-switchable “pseudo”-tetrameric surfactant oleic acid (OA)/cyclic polyamine (cyclen) was prepared by simple mixing and subsequently used to reduce the viscosity of heavy oil. The surface activity of OA/cyclen was explored by a surface tensiometer and a potential for viscosity reduction was revealed. The CO₂ switchability of OA/cyclen was investigated by alternately introducing CO₂ and N₂, and OA/cyclen was confirmed to exhibit a reversible CO₂-switching performance. The emulsification and viscosity reduction analyses elucidated that a molar ratio of OA/cyclen of 4:1 formed the “pseudo”-tetrameric surfactants, and the emulsions of water and heavy oil with OA/cyclen have good stability and low viscosity and can be destabilized quickly by introducing CO₂. The findings reported in this study reveal that it is feasible to prepare CO₂-switchable pseudo-tetrameric surfactants with viscosity-reducing properties by simple mixing, thus providing a pathway for the emulsification and demulsification of heavy oil by using the CO₂-switchable “pseudo”-oligomeric surfactants.     

Acid soap formation of oleic acid and catanionic complex formation in the alkyldimethylamine oxide/sodium oleate equimolar mixtures

The influence of adding alkyldimethylamine oxide (CnDMAO) with varying alkyl chain lengths (n_c) on the acid soap formation of oleic acid was investigated. The solutions of equimolar mixtures of CnDMAO and sodium oleate (Na⁺Ol^–), each 25 mmol kg^–1, became turbid at a certain critical pH (pH_c) on decreasing pH. Values of the pH_c depended on n_c and showed the minimum at C10DMAO/NaOl mixture. The presence of the minimum was interpreted in terms of two different kinds of the complex formed in the micelles depending on n_c: the catanionic complex (CnDMAOH⁺/Ol^–) in the mixed micelles of n_c=16, 14, 12 and 10, and the acid soap of oleic acid for C6DMAO/NaOl and C8DMAO/NaOl mixtures. At pH_c where the amounts of these complexes of double-chain nature reached certain critical values in the mixed micelles, a phase separation (most probably lamella formation) took place. It was expected that the critical amount of the catanionic complex was smaller for the mixtures of higher n_c values and hence pH_c increased with n_c for the mixtures n_c10. For the mixtures of n_c<10, it was expected that the amount of the acid soap in the mixed micelles increased with decreasing n_c at a given pH and the pH_c increased with decreasing n_c. Micelle compositions at cmc were evaluated on the basis of the regular solution theory coupled with the pseudo phase approximation. The micelle compositions at 100 mmol kg^–1 were examined with ¹³C-NMR. The results showed the mixed micelle formation for n_c=16–10, while the micelles mostly consisting of oleic acid for the mixtures of n_c=8 and 6. The assumption of two different complexes for the two groups of the mixture was thus supported. The cmc range of mixed micelles was evaluated and it was well correlated with the observed concentration range of pyrene fluorescence change.     

Sterospecific Syntheses and Spectroscopic Properties of Isomeric 2,4,6,8-Undecatetraenes. New Hydrocarbons from the Marine Brown Alga Giffordia mitchellae. Part IV.

Giffordene (=(2Z,4Z,6E,8Z)-2,4,6,8-undecatetraene; 9f ) and five steroisomers are new C₁₁H₁₆ hydrocarbons from the marine brown alga Giffordia mitchellae. Their synthesis is based on non-stereoselective Wittig reactions of (E)-2-alkenals with appropriate acetylenic phosphoranes and subsequent chromatographic separation of the resulting (E/Z)-pairs. The uniform enynes (>98% purity) are then stereospecifically reduced to (Z)-alkenes with Zn(Cu/Ag) in aq. MeOH at r.t. ¹³C- and ¹ H-NMR data of the new tetraenes are presented. Biosynthetically, giffordene ( 9f ) originates from dodeca-3,6,9-trienoic acid via an unstable (3Z,5Z,8Z)-1,3,5,8,-undecatetraene followed by a thermally allowed antarafacial 1,7-sigmatropic hydrogen shift to the (2Z,4Z,6E,8Z)-isomer 9f .     

Surface Active and Thermodynamic Properties in Relation to the Demulsification Efficiency for Some Ethoxylated Derivatives of Alkyldiamines and Polyalkylenepolyamines

In this work, nine monostearic esters of ethoxylated dialkyle-amine (group I) and ethoxylated polyalkylenepolyamine (group II) nonionic surfactants were prepared and characterized by FTIR spectroscopy and nitrogen content. The 1,4-diaminobutane (DAB), 1,6 diamino hexane (DAH), 1,8-diamino-octane (DAO), diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) were ethoxylated at 50, 100, 150 ethylene oxide units individually. The ethoxylated products of (group I) reacted with stearic acid to give the monostearate products. The surface tension of the prepared compounds were measured at 25°C and 60°C. The thermodynamic parameters of micellization and adsorption were also calculated. The surface active properties, such as critical micelle concentration (CMC), maximum surface excess concentration (Γ_max), effectiveness of surface tension reduction (π_cmc), and minimum area per molecule at the aqueous solution-air interface (A_min), have been calculated. The surface active and thermodynamic properties of the prepared compounds were correlated to their chemical structure. It was found that CMC decreases when increasing the molecular weight of polyethylene oxide units. Furthermore, the data show that the synthesized surfactants favor adsorption than micellization, so that they can be used as demulsifiers for waxy crude oil emulsion (BSW 18%). In this respect, the demulsification test was carried out and the results of demulsification efficiency were correlated to the chemical composition of the investigated compounds. Some factors that affect the demulsification efficiency were also considered such HLB, concentration and time. The maximum demulsification efficiency (100%) was obtained by DAOE_150-M and TEPAE₁₅₀ at 60 and 45 minutes (300 ppm), respectively.     

Extraktiv-photometrische Bestimmung von Rhodium unter Verwendung von Diphenylselenoxid

Zusammenfassung Innerhalb der substituierten Selenoxide eignet sich Diphenylselenoxid, das in salzsaurer Lösung die Verbindung RhCl₃·OSe(C₆H₅) bildet, zur extraktiv-photometrischen Bestimmung des Rhodiums besonders neben Co²⁺, Ni²⁺ und Fe³⁺.

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Summary Among the substituted selenium oxides, diphenylselenium oxide, that in hydrochloric acid solution yields the compound RhCl₃·OSe(C₆H₅)₂, is especially suitable for the extractive-photometric determination of rhodium, particularly in the presence of Co²⁺, Ni²⁺ and Fe³⁺.

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Résumé Dans le cadre des oxydes de sélénium substitués, le diphényloxyde de sélénium qui forme le composé RhCl₃·OSe(C₆H₅) en solution chlorhydrique se prête au dosage photométrique par extraction du rhodium, en particulier en présence de Co²⁺, Ni²⁺ et Fe³⁺.

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Der Deutschen Forschungsgemeinsehaft und dem Fonds der chemischen Industrie danken wir für die Förderung unserer Arbeit durch Sachbeihilfen.     

Crystal structures, magnetic, dielectric and ferroelectric properties of two copper(II) complexes with m-nitrobenzoic acid

Reactions of CuCl₂, m-nitrobenzoic acid (HNBA) and NaOH with 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in aqueous ethanol afforded two Cu(II) complexes Cu(bpy)(NBA)₂, 1, and [Cu(phen)(H₂O)₂(NBA)](NBA), 2. The monomolecular Cu(bpy)(NBA)₂ moieties are both bridged by hydrogen bonding interactions and interlayer π ^*–π ^*stacking interactions to form a 3D (3,4,6)-connected supramolecular architecture with the Schäfli symbol of (4⁴·6²)(4⁴·6⁶·8⁵)(6³)₂. Complex 2 crystallizes in a noncentrosymmetric space group P2₁ where all molecules show the same orientation along the polar b axis. Preliminary investigations suggest that 2 exhibits ferroelectric hysteresis loops at room temperature with remanent polarization (P _r) of ca. 0.09 μC cm^?2 and coercive electric fields of 2.53 kV cm^?1, respectively. It may be a potential ferroelectric with a relatively large spontaneous polarization (P _s) of 0.22 μC cm^?2. Furthermore, permittivity property measurements reveal a dielectric constant (ε _r) of 6.36. Variable-temperature (2–300 K) magnetic susceptibility measurements showed the presence of weak ferromagnetic interactions between the Cu(II) ions for both 1 and 2.     

Twisted Baskets

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)‐ 1 _syn) or left ((M)‐ 1 _syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)‐ 1 _syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)‐ 1 _syn is accomplished by its transesterification with (1R,2S,5R)‐(?)‐menthol in the presence of a Ti^IV catalyst to give diastereomeric 8 ^P and 8 ^M . It was found that dendritic‐like cavitands 8 ^P and 8 ^M , in CD₂Cl₂, undergo self‐inclusion (¹H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was (¹H NMR spectroscopy) found to be greater in the case of 8 ^P than 8 ^M . Accordingly, it is suggested that different folding characteristic of 8 ^P and 8 ^M ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8 ^P/ 8 ^M , encompassing right‐ and left‐handed “cups”, was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8 ^P/ 8 ^M .     

Surface-active properties of new cationic gemini surfactants with cyclic spacer

Three cationic gemini surface active compounds of the type (1r,4r)-1,4-dialkyl-1,4-dimethy-l-piperazine-1,4-diium bromide (Ia, Ib, and Ic), were synthesized. They were characterized using elemental analysis and ¹H-NMR spectra. Their surface-active properties were measured in aqueous solutions with different concentrations at different temperatures (25, 40, and 55°C). Various surface measurements of these gemini surfactants, (compared to the conventional one, 1-Dodecyl-1-methylpiperidinium bromide (a)) were estimated, specifically critical micelle concentration (CMC), effectiveness (π_CMC), efficiency (P_C20) as well as maximum surface excess (Γ_max) and minimum surface area (A_min). The measurements of the gemini compounds gave low CMC, high efficiency in reducing the surface tension, and intense adsorption at air/water interface. These surfactants have lower Krafft points and thus better solubility. Thermodynamic data, free energy, entropy, and enthalpy changes (ΔG°, ΔS°, and ΔH°) for micellization at the air/water interface and also for adsorption in the bulk of surface-active solutions were calculated.