Partition of <Emphasis Type="Italic">n</Emphasis>-Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

The partition of n-butanol in Winsor type III (W-III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n-butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W-III microemulsions obtained by salinity scanning, relatively constant n-butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n-butanol content in each phase is important for those systems having low solubilization ability. For the W-III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n-butanol distributed into the interfacial layer decreased while the fraction of n-butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n-butanol. For the different optimum W-III microemulsion systems tested, most of the surfactant-to-alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n-butanol content in the EO and EW phases, the standard free energy, ΔG _o→in ^* (T = 298.15 K) of n-butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔG _o→in ^* values. For microemulsions with the same components, n-butanol content is an important factor influencing the ΔG _o→in ^* value, and a high absolute value of ΔG _o→in ^* leads to high solubilization ability.     

Zinc Corrosion in Acidic Solutions Containing Single and Mixed Surfactants

The influence of surfactant synergism on Zn corrosion inhibition in 0.1-M HCl aqueous solutions has been determined at room temperature. Solutions of single and mixed surfactants consisting of sodium dodecylsulfate (SDS) and N,N-dimethyldodecan-1-amine oxide (DDAO) in water and in 0.1-M HCl were also prepared at room temperature. Critical micelle concentration (CMC) data were obtained through surface tension measurements as a function of mixing composition. A regular solution model was considered to analyze CMC values. The interaction parameter (β), the composition of mixed micelles (x) and the activity coefficients (f) were estimated by a regular solution model for all amphoteric–anionic mixed systems. β Vvalues showed synergism for the binary mixtures of these solutions in the absence and presence of 0.1-M HCl at all investigated compositions. Zinc corrosion in single and binary SDS/DDAO mixed solutions at 5-mM total surfactant concentrations in the presence of 0.1-M HCl was also investigated at static and dynamic conditions. The weight loss data revealed corrosion inhibition activity obeyed the following order: binary (0.75 DDAO + 0.25 SDS) > binary (0.50 DDAO + 0.50 SDS) > single DDAO > single SDS, suggesting an enhancement in the corrosion inhibition activity of DDAO in the presence of a proper amount of SDS. Conductivity time measurements show a similar trend as that obtained by a weight loss method at (0.50 DDAO + 0.50 SDS). The results were illustrated on the basis of synergistic interaction between the mixed surfactants.     

The cyclization index and toughness of gel spun polyacrylonitrile (PAN) proportionality with its heat of stabilization

The spun tapes of synthesized PAN, its copolymer with 1 wt% itaconic acid, and doped version with 1 wt% sodium dodecyl sulfate (SDS) all showed stripy, even, and compact cross-sections as the hallmark of gel forming products. PAN doping with SDS and acrylonitrile copolymerization with itaconic acid reduced its dimethylformamide (DMF) solution structural viscosity index (Δη) by 50% and 30%, respectively, at 675 s^??1. In addition, the modification of synthesized PAN through doping and acrylonitrile copolymerization with itaconic acid led to severe and mild gelation temperature decrease, respectively. The stabilization peak of the synthesized PAN tape was enhanced as much as 25 °C by 900% hot drawing, decreased by about 10 °C through copolymerization, while experienced small temperature changes through doping. The second derivative of Fourier transform infrared and Gaussian fitting was used to analyze the tapes cyclization due to stabilization treatment through introducing I_sd index. 10 min I_sd index was raised as much as 430% and 800% in comparison with the synthesized PAN through its doping or acrylonitrile copolymerization with itaconic acid, respectively. Further 180 min of I_sd index, however, showed the same proportional increase as toughness of the drawn tapes versus their heat of stabilization through their physical and chemical modifications.     

Biolytic Effect of Rhamnolipid Biosurfactant and Dodecyl Sulfate Against Phagotrophic Alga <Emphasis Type="Italic">Ochromonas danica</Emphasis>

Surfactants can affect biological activities and pose serious threats to the aquatic ecosystem if discharged without proper treatment. Rhamnolipid is a biosurfactant with promising agricultural, industrial and biomedical applications. It is important to assess the risks posed by rhamnolipid before it is adopted for large scale use. In this study, toxicity of rhamnolipid was estimated with the effects of motility loss, membrane permeability, and cell lysis using a phagotrophic alga Ochromonas danica. O. danica is a sensitive algal species without a protective cell wall and it represents a group of phagotrophic flagellates ecologically important in the aquatic ecosystem. A common synthetic surfactant, sodium dodecyl sulfate (SDS), was used for comparison. Results suggested that rhamnolipid is significantly less biolytic than SDS and the effects required longer exposure. Lysis of O. danica cells by rhamnolipid was serious only at concentrations over its critical micelle concentration. Motility loss was, however, significantly more sensitive; about 75% loss after 20 min exposure to 50 mg/L rhamnolipid.     

Synergistic Behavior and Microstructure Transition in Mixture of Zwitterionic Surfactant,Anionic Surfactant,and Salts in Sorbitol/H<Subscript>2</Subscript>O Solvent: 1. Effect of Surfactant Compositions

The phase behavior and rheological properties of a multi-component system, made of a zwitterionic surfactant cocoamidopropyl betaine (CAPB), an anionic surfactant sodium lauryl sulfate (SLSS), and mixed salts (tetrasodium pyrophosphate, sodium acid pyrophosphate, sacharrin, and sodium fluoride) in sorbitol/H₂O mixed solvent at different mass fraction of SLSS (X _SLSS) were systematically investigated by steady and dynamic rheology, dynamic light scattering, and diffusion ordered spectroscopy (DOSY). When fixing the salt concentration and the mass ratio of sorbitol in mixed solvent (R), the zero-shear viscosity increases first and then decreases showing a maximum with increasing X _SLSS, resulting from the formation and entanglement of wormlike micelles. Especially when X _SLSS is between 0.33 and 0.80, the mixture is dominated by entangled wormlike micelles coexisting with small micelles and separated wormlike micelles, and shows high viscoelasticity. The maximum of the zero-shear viscosity is ca. 5 orders of magnitude larger than that of sorbitol/H₂O mixed solvent or the CAPB/SLSS aqueous solution. The characteristic structural parameters for the micellar solutions at different X _SLSS are also estimated from further analysis of the rheological results, and indicate the stronger network structures of the wormlike micelles are formed in our systems compared with the wormlike micelles formed by a traditional zwitterionic/anionic surfactant aqueous solutions. The great improvements of rheological properties are attributed to the strong screening effects of the mixed salts and the strong solvophobic effect of sorbitol on the electrostatic and hydrophobic interaction between the CAPB and SLSS molecules. The present work has improved our understanding about the aggregation behavior of zwitterionic/anionic mixed surfactants with salts in less polar solvent/H₂O mixture, which would be of widely practical importance to optimize the formulation of products for personal care and household cleaning.     

Synthesis and Evaluation of Bis-quaternary-Based Surfactants as Additives for Water-Based Mud

Two series of cationic gemini surfactants, alkanediyl-α,ω-bis[N,N-dimethyl alkyl (octyl or dodecyl)ammonium] dibromide (R-s-R; s = 6, 10, 12 and R = 8 and 12) were prepared and evaluated as additives for water-based mud. The chemical structures of the prepared surfactants were confirmed using FTIR and mass spectroscopy. Surface activity of these compounds has been studied and their surface properties including surface tension, emulsification power, critical micelle concentration, effectiveness, maximum surface excess and minimum surface area were determined. The results showed that the prepared compounds have significant surface activity, especially those of longer hydrophobic chain length. The prepared cationic gemini surfactants were evaluated as viscosifiers and filter loss additives for water-based mud formulated from local Na-montmorillonite clay. XRD analysis was carried out to the Na-montmorillonite clay to determine the interaction of the surfactants with inter layers of the clay structure. Rheological properties, gel strength, thixotropy, filtration properties and the effect of temperature on rheological properties of the water-based mud were studied. The results indicated that the gemini surfactants have a positive effect on the rheological and filtration properties of the Na-montmorillonite clay according to American Petroleum Institute specifications.     

A Novel Study on the Gel Phase Formed in a Catanionic Surfactant System

A novel gel phase was constructed in a catanionic surfactant system with the compositions of 1-tetradecyl-3-methylimidazolium chloride (C₁₄mimCl) and sodium dodecyl sulfate (SDS). The gel phases were studied through visual observations, differential scanning calorimetry (DSC), rheological measurements, and scanning electron microscopy (SEM). The visual observation and DSC confirmed the formation of gels and phase transitions from gel to sol. The dynamic rheological results showed the viscoelastic properties of gels. The SEM technique was used to further indicate the microstructure of gels. Finally, the formation mechanisms of gels are proposed based on the critical packing parameter. We expect to develop a new route to construct the gels.     

Synergetic association of grafted PLA and functionalized graphene on the properties of the designed nanocomposites

The synergetic association of poly(lactic acid) grafted with maleic anhydride (MA-g-PLA) containing 0.44 wt% of maleic anhydride and epoxy-functionalized graphene (GFe) on the properties of the designed nanocomposites was studied. Rheological, mechanical and barrier properties of PLA nanocomposites were studied using different content of epoxy-functionalized graphene and MA-g-PLA compatibilizer. The PLA/MA-g-PLA/GFe nanocomposites prepared by melt blending, containing 5 wt% of MA-g-PLA, yield a maximum in storage modulus G′ and a rheological plateau at low frequencies, with a content of epoxy-functionalized graphene comprised between 4 and 7 wt%. This phenomenon was ascribed to a pseudo-solid behavior resulting from the high degree of epoxy-functionalized graphene exfoliation due to strong interfacial interactions with PLA and epoxy-functionalized graphene. The better mechanical and barrier performances were obtained with PLA/GFe containing 10 wt% of epoxy-functionalized graphene and 5 wt% of MA-g-PLA compatibilizer. The variation of the percentage of compatibilizer showed that 5 wt% of maleated PLA was sufficient to improve the thermal, rheological, mechanical and barrier properties of the PLA nanocomposite containing 7 wt% of epoxy-functionalized graphene.     

Selective Enrichment of Conjugated Linoleic Acid Isomers in Their Mixtures Using Combined Chemical and Enzymatic Methods

The aim of this study was to selectively enrich t10,c12-conjugated linoleic acid (t10,c12-CLA) and c9,t11-CLA in commercial CLA mixtures using a combination of urea crystallization and lipase-catalyzed esterification. The objective of the urea fractionation is to remove saturated and monounsaturated fatty acids (FA) from the CLA mixtures. CLA-enriched free FA (FFA) mixtures containing 53.8 wt% t10,c12-CLA and 39.1 wt% c9,t11-CLA were produced from the CLA mixtures containing ~34 wt% each of the two CLA isomers by a urea crystallization using methanol and the urea-to-FA weight ratio of 2.5:1. The CLA-enriched FFA mixtures were partially esterified with dodecan-1-ol in a recirculating packed-bed reactor using an immobilized lipase from Candida rugosa to further enrich the t10,c12-CLA and c9,t11-CLA in an FFA fraction and an FA dodecyl ester fraction, respectively, under the optimal conditions, i.e., temperature, 20 °C; FA-to-dodecan-1-ol molar ratio, 1:1; water content, 2 wt% of total substrates; residence time, 5 min; and reaction time, 24 h (for t10,c12-CLA enrichment) and 12 h (for c9,t11-CLA enrichment). After the reaction, an FFA fraction with 72.6 wt% t10,c12-CLA was obtained. Another FFA fraction with 62.0 wt% c9,t11-CLA was recovered after the saponification of the FA dodecyl ester fraction. The yields of t10,c12-CLA and c9,t11-CLA in the FFA fractions were 43.6 and 21.5 wt%, respectively, based on their initial weights in the CLA mixtures.     

Sonocrystallization of Interesterified Fats with 20 and 30% of Stearic Acid at the sn-2 Position and Their Physical Blends

Physical blends (PB) of high oleic sunflower oil and tristearin with 20 and 30% stearic acid and their interesterified (IE) products where 20 and 30% of the fatty acids are stearic acid at the sn-2 position crystallized without and with application of high intensity ultrasound (HIU). IE samples were crystallized at supercooling temperatures (ΔT) of 12, 9, 6, and 3 °C while PB were crystallized at ΔT = 12 °C. HIU induced crystallization in PB samples, but not in the IE ones. Induction in crystallization with HIU was also observed at ΔT = 6 and 3 °C for IE C18:0 20 and 30% and at ΔT = 9 °C only for the 30% samples. Smaller crystals were obtained in all sonicated samples. Melting profiles showed that HIU induced crystallization of low melting triacylglycerols (TAGs) and promoted co-crystallization of low and high melting TAGs. In general, HIU significantly changed the viscosity, G′, and G″ of the IE 20% samples except at ΔT = 12 °C. While G′ and G″ of IE 30% did not increase significantly, the viscosity increased significantly at ΔT = 9, 6, and 3 °C from 1526 ± 880 to 6818 ± 901 Pa.s at ΔT = 3 °C. The improved physical properties of the sonicated IE can make them good contenders for trans-fatty acids replacers.     

Atmospheric nitrogen loss factor (<Emphasis Type="Italic">f</Emphasis>) used in determining nitrogen-based municipal wastewater effluent irrigation rates: design and nitrogen-balance estimated <Emphasis Type="Italic">f</Emphasis> values

Design irrigation rates for treated municipal wastewater effluent (MWE) are usually determined from nitrogen (N) mass-balances, in which the fraction (f) of the total N in the MWE that is lost to the atmosphere is commonly obtained from US Environmental Protection Agency (USEPA) tabulated (design) values: 0.15–0.25 for secondary-treated effluents and 0.1 for tertiary-treated effluents. In 2011 and 2012, f values from an N balance in a tall fescue (Festuca arundinacea Schreb.) hay field in Central Pennsylvania were quantified and compared to the USEPA design f values. The grass field was spray-irrigated with MWE (C:N ratio = 0.04–0.2; near neutral pH, and 70–87% of the MWE-TN was NO₃–N) at a rate of ≤5-cm wk^?1. Monthly N balances were calculated from April to September in the surface horizon of a Hagerstown soil. The f values of 0.05, 0.1, and 0.2 seemed appropriate for the months of May and June, August and September, and July, respectively. Positive fnb estimates and the logarithm of measured monthly N removal in the aboveground biomass (kg ha^?1) were negatively correlated (R² = 0.99 for monthly mean air temperatures ≥20 °C and R² = 0.2 for monthly mean air temperatures <20 °C). The study’s results suggest that existing design f values are likely less applicable especially due to the biological N-removal processes currently present in many wastewater treatment plants needing to meet effluent N limits. Thus, more studies to determine empirical f values in effluent irrigation are needed to refine design f values.     

Development of natural and synthetic polymer-based semi-interpenetrating polymer network for controlled drug delivery: optimization and in vitro evaluation studies

This research paper describes the development, optimization and in vitro characterization of chemically cross-linked pectin–polyvinyl alcohol-co-poly(2-Acrylamido-2-methylpropane sulfonic acid) semi-interpenetrating polymer network hydrogel [pectin–PVA-co-poly(AMPS) semi-IPN hydrogel] for controlled delivery of model drug tramadol HCl. Response surface methodology based on 3² factorial design was used for optimization and investigating the effect of independent factors: polymer-blend ratio (pectin:PVA = X ₁) and monomer (AMPS = X ₂) concentration on the dependent variables, swelling ratio (q _18th), percent drug release (R _18th, %), time required for 80 % drug release (t _{80 %}, h), drug encapsulation efficiency (DEE, %) and drug loaded contents (DLC, mg/g) in pectin-PVA-co-poly(AMPS) gels prepared by free radical polymerization. The optimized semi-IPN gel (FPP-10) showed controlled in vitro drug release (R _18th) of 56.34 % in 18 h, t _{80 %} of 30 h, and DEE of 23.40 %. These semi-IPN hydrogels were also characterized through SEM, FTIR, sol–gel analysis, swelling studies and drug release characteristics. Therefore, this newly synthesized polymeric network could be a potential polymeric system for controlled drug delivery of tramadol HCl for prolonged drug release.     

A coarse-grained model for polylactide: glass transition temperature and conformational properties

In this article, we present a coarse-grained (CG) model of poly(lactic acid) (PLA) developed by the iterative Boltzmann inversion (IBI) method. The coarse-grained potential was derived by matching the structural probability distribution functions to those of reference atomistic simulation. The resulting coarse-grained potential was found to be temperature-dependent when trying to reproduce the thermal expansion behavior of PLA. To satisfactory reproduce this behavior, the potential needs to be modified by a temperature factor of (T/T ₀)^0.3; T ₀ = 327 K is the temperature at which the potential has been derived. The glass transition temperature (T _g) as predicted by the modified CG potential compared favorably with those from experiment and atomistic simulation. Chain conformational properties were also evaluated in terms of a chain length (N)-radius of gyration (R _g) relation and the persistence length. The model we develop was also noted to provide a considerable speed-up of computer time compared to its atomistic counterpart.     

The Origin and Ecological Function of an Ion Inducing Anti-Predator Behavior in <Emphasis Type="Italic">Lithobates</Emphasis> Tadpoles

In aquatic environments, chemical cues are believed to be associated with prey response to predation risk, yet few basic cue compositions are known despite the pronounced ecological and evolutionary significance of such cues. Previous work indicated that negatively-charged ions of m/z 501 are possibly a kairomone that induces anti-predator responses in amphibian tadpoles. However, work described here confirms that this specific ion species m/z 501.2886 is produced by injured tadpoles, exhibits increased spectral intensity with higher tadpole biomass, and is not produced by starved predators. These results indicate the anion is an alarm cue released from tadpoles. High resolution mass spectrometry (HR-MS) revealed a unique elemental composition for [M-H]^?, m/z 501.2886, of C₂₆H₄₅O₇S^? which could not be determined in previous studies using low resolution instruments. Collision induced dissociation of m/z 501 ions formed product ions of m/z 97 and m/z 80, HSO₄^? and SO₃^?, respectively, showing the presence of sulfate. Green frog tadpoles, Lithobates clamitans, exposed to the m/z 501 anion or sodium dodecyl sulfate exhibited similar anti-predator responses, suggesting organic sulfate is a tadpole behavior modifier.     

Synthesis and properties of amphiphilic thermo-sensitive block copolymers

Octadecyl acrylate (ODA) as hydrophobic monomer and N-isopropylacryamide (NIPAAm) as hydrophilic monomer were chosen to synthetize the thermo-sensitive block copolymers PODA_x-PNIPAAm_y-PODA_x (BAB-type) via reversible-addition-fragmentation chain transfer (RAFT) polymerization, the block copolymers could self-assemble to flower-like micelles in aqueous solution with hydrophobic PODA as the inner core and stabilized by hydrophilic PNIPAAm as the outer shell. The characterizations of the micelles such as surfactivity, thermo-sensitivity, micelle hydrodynamic radius (R _h ) and polydispersity index (PdI) were demonstrated by surface tension technique, UV-Vis, and dynamic light scattering (DLS) measurements, respectively. The longer the hydrophilic chain was, the higher the critical micellization concentration (CMC) would be, and the higher content of the PODA was, the lower the lower critical solution temperature (LCST) would be. The average R _h remained at about 100 nm below LCST, but decreased sharply to about 42 nm and kept constant when reaching and above LCST, which meant the non-aggregation of BAB type block copolymers. The micelle was homogeneous with the small PdI within the range of research. B_0.5mA_24mB_0.5m had the largest capacity to encapsulate lipophilic Sudan Red IV model drugs and the drug loading efficiency was 9.76%.     

Synthesis of polyamine-grafted chitosan and its adsorption behavior

The development of new environment-friendly and efficient adsorbents has attracted a great interest in recent years. In this study, ethylene diamine-grafted chitosan copolymer (CS–MAA–EN) and triethylene tetramine-grafted chitosan copolymer (CS–MAA–TN) were synthesized to remove heavy metal ions from water. The influence of pH, adsorbents dosage and initial metal concentration were investigated to study the adsorbing effect of CS–MAA–EN and CS–MAA–TN for the removal of Cu²⁺ from aqueous solutions. The equilibrium adsorption capacities of CS–MAA–EN and CS–MAA–TN were 85.91 and 102.67 mg/g, respectively. The adsorption process was fitted better by the Langmuir isotherm model (R ² = 0.9993, 0.9991) than the Freundlich isotherm model (R ² = 0.8781, 0.8775). The adsorption kinetics confirmed that the adsorption mechanism could be better described by the pseudo-second-order equation. Two adsorbents showed excellent desorption efficiency (D _e) and reuse ratio (R _u). D _e and R _u of CS–MAA–EN were evaluated as 95.2 and 89.35 %, respectively, and those values of CS–MAA–TN were 92.73 and 83.25 %. The competitive adsorption results of the two adsorbents indicated that the rate sequence was Fe³⁺ > Cu²⁺ > Cr⁶⁺ > Ni²⁺ > Zn²⁺.     

Crystallinity of large single crystals of FAU-type zeolites with a wide range of Si/Al ratios

Large colorless single crystals of FAU-type zeolites were synthesized from gels with the composition xSiO₂ : 2.0NaAlO₂ : 7.5NaOH : 454H₂O : 5.0TEA, where x = 2.0–6.0. FAU-type zeolite with Si/Al = 1.26(4) was nearly pure and the maximum size of the single crystals was ca. 150 μm. In case of FAU-type zeolites with Si/Al = 1.54(5), the maximum size of single crystals was ca. 200 μm and the ratio of FAU/impurity was 0.07. The framework Si/Al ratio of the as-synthesized FAU-type zeolite tended to increase with the Si/Al ratio of gel composition. All of the large single crystals had good crystallinities for single-crystal X-ray diffraction, leading to enough numbers of significant reflections which have strong intensity. The structure of a single crystal of dehydrated zeolite Na-X (Si/Al = 1.41(4)) with composition |Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU per unit cell was determined by X-ray diffraction methods in the cubic space group \( Fd \bar{3} m; \) a = 24.9434(6) Å at 294 K. The structure was refined by using all intensities to the final error indices (using only the 771 reflections for which F _o > 4σ(F _o)), R ₁ = 0.048 (based on F) and R ₂ = 0.188 (based on F ²). In the crystallographic studies, the Si/Al ratio of the synthetic FAU-type zeolite is 1.41(4) which is quite consistent with the SEM–EDS analysis.     

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu⁰ but with surface oxidation, and show a faceted morphology, which is more textured (R _q = 460 ± 90 nm) compared to the SAM (R _q = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl₂/PdCl₂ catalyzed electroless deposition, using formaldehyde (CH₂O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu²⁺ to the iNA is proposed to facilitate reduction to Cu⁰ and create the seed for subsequent growth. The films show good adhesion to the functionalized surface.     

A Comprehensive Study on the Synthesis and Micellization of Disymmetric Gemini Imidazolium Surfactants

Two groups of disymmetric Gemini imidazolium surfactants, [C₁₄C₄C _m im]Br₂ (m = 10, 12, 14) and [C _m C₄C _n im]Br₂ (m + n = 24, m = 12, 14, 16, 18) surfactants, were synthesized and their structures were confirmed by ¹H NMR and ESI–MS spectroscopy. Their adsorption at the air/water interface, thermodynamic parameters and aggregation behavior were explored by means of surface tension, electrical conductivity and steady-state fluorescence. A series of surface activity parameters, including cmc, γ _cmc, π _cmc, pC ₂₀, cmc/C ₂₀, Γ _max and A _min, were obtained from surface tension measurements. The results revealed that the overall hydrophobic chain length (N _c) for [C₁₄C₄C _m im]Br₂ and the disymmetry (m/n) for [C _m C₄C _n im]Br₂ had a significant effect on the surface activity. The cmc values decreased with an increase of N _c or m/n. The thermodynamic parameters of micellization (ΔG _m ^θ , ΔH _m ^θ , ΔS _m ^θ ) derived from the electrical conductivity indicated that the micellization process of [C₁₄C₄C _m im]Br₂ and [C _m C₄C _n im]Br₂ was entropy-driven at different temperatures, but the contribution of ΔH _m ^θ to ΔG _m ^θ was enhanced by increasing N _c or m/n. The micropolarity and micellar aggregation number (N _agg) were estimated by steady-state fluorescence measurements. The results showed that the surfactant with higher N _c or m/n can form larger micelles, due to a tighter micellar structure.     

Gas Chromatographic Separation and Identification of Jacaric and Punicic 2-Ethyl-1-Hexyl Esters

The present study demonstrates the separation of a critical pair of conjugated linolenic acid (CLN) isomers—jacaric acid (JA; c8, t10, c12-18:3) and punicic acid (PA; c9, t11, c13-18:3)—on a 60-m conventional Supelcowax 10 column. The alkyl esters of different alcohols (C₁–C₈) of JA and PA were prepared and analyzed isothermally at 220, 230 and 240 °C. The adequacy of their separation was determined from the separation factors (α) and peak resolutions (R _s). Acceptable resolution (R _s = 1.01) of JA and PA was obtained with their 2-ethyl-1-hexyl ester derivatives at a column temperature of 230 °C. In addition, the Gibbs energy of transfer from solution to gas of the three double bonds \((\Delta_{\text{sln}}^{\text{g}} G_{\text{u}}\)) could be used to describe the interactions of the double bond with the stationary phase. Characterization of 2-ethyl-1-hexyl esters of Jacaranda mimosifolia seed oil at 230 °C demonstrates that the oil contains JA and α- and β-calendic acid as a CLN without the presence of PA. The results suggested that JA could be resolved from PA on a 60-m Supelcowax 10 column as the ethyl hexyl ester.