Microstructure and structural transition in microemulsions stabilized by aldonamide-type surfactants

Significant efforts were undertaken to characterize the microstructure and structural properties of water-in-oil (w/o), oil-in-water (o/w), and bicontinuous (bc) microemulsions composed of N-alkyl-N-methylgluconamides (n-alkyl = n-C(12)H(25), n-C(14)H(29), n-C(16)H(33)) and n-alcohols (ethanol, n-propanol, n-butanol) or iso-alcohols (iso-propanol, iso-butanol) as cosurfactants, as well as iso-octane and water. The internal structure of so created four-component system was elucidated by means of an analysis of isotropic area magnitudes in phase diagrams and conductivity measurements. Dynamic light scattering (DLS) measurements provided the microemulsion size and polydispersity. Polarity and viscosity of microemulsion microenvironment were acquired by means of electron paramagnetic resonance (EPR), UV-vis absorption spectroscopy (in the case of w/o droplets), and steady-state fluorescence (SSF) (in the case of o/w droplets). The results show that both the surfactant and the cosurfactant types affect the shape and extent of microemulsions. The size of droplets depends strongly on the type of examined microemulsion and the type of cosurfactant (linear or brunched) but is almost independent of the length of the surfactant alkyl chain. The size of microemulsion droplets ranges from 8.1 to 22.6 nm and from 3.7 to 14.3 nm respectively, for o/w and o/w microemulsions, making them good candidates for both template-based reactions and household components solubilizing media.     

Synthesis and Surface Properties of N-Alkyl-N-methylgluconamides and N-Alkyl-N-methyllactobionamides

Three series of nonionic N-alkylaldonamides, N-alkyl-N-methylgluconamides (Cn-MGA, Cn: n-C(10)H(21), n-C(12)H(25), n-C(14)H(29), n-C(16)H(33), and n-C(18)H(37)), N-alkyl-N-methyllactobionamides (Cn-MLA, alkyl as above-mentioned), and N-oleyl-N-methylglucon/lactobionamide, were synthesized in the reaction of an appropriate N-alkyl-N-methylamine with delta-D-glucolactone and lactobionic acid, respectively. Krafft temperatures of aqueous solutions and surface properties of these surfactants at 20 degrees C, i.e., surface excess concentration, Gamma(cmc), surface area demand per molecule, A(min), efficiency in surface tension reduction, pC(20), effectiveness in surface tension reduction, Pi(cmc), critical micelle concentration, CMC, and CMC/C(20) parameter as well as standard free energies of adsorption, DeltaG degrees (ads), and of micellization, DeltaG degrees (mic), were determined. It was shown that introduction of the methyl group to the amide nitrogen increased the solubility of the surfactants, which was confirmed by their Krafft temperatures. Lactobionamides are more water soluble than gluconamides. On the other hand, the Cn-MGA surfactants are more surface active than the respective Cn-MLA ones. This observation is based on the determined adsorption and micellization parameters. The presence of one double bond in a hydrocarbon chain as in oleyl-amides increases their hydrophilic character compared with that of saturated C18 derivatives. No distinct differences were observed between the A(min) values obtained for both series studied, although they differ markedly in the size of the hydrophilic groups. Copyright 2001 Academic Press.     

Surface properties of ionomers based on styrene-b-acrylic acid copolymers obtained by copolymerization in emulsion

Surface properties of styrene-b-acrylic acid copolymers obtained in emulsion and suitable ionomers before and after UV-irradiation were studied by measurements of contact angles and FTIR-ATR spectroscopy.The research focused on the influence of different content of carboxylic acid groups in copolymers, of various types and contents of alkali metal salts in ionomers and of cesium acrylate or methacrylate in ionomers on hydrophilicity of the surfaces of these samples and the course of photodegradation in them.Hydrophilicity of initial copolymer surfaces was higher than this of polystyrene as a result of presence of carboxylic acid groups, which also made the surfaces of these copolymers more sensitive to UV-irradiation.Hydrophilicity of the surfaces of ionomers containing cesium acrylates depended on the content of cesium salt in the samples. The course of ionomer photooxidation was also dependent on the content of this salt.The surface of ionomer containing cesium methacrylate was more polar than this of ionomer containing cesium acrylate.Styrene-based ionomers containing 3.7 mol% of various alkali metal acrylates had less polar surfaces than initial copolymer and they were also more resistant to UV-irradiation in comparison to the initial copolymer.Copolymers obtained in emulsion and suitable ionomers had more polar surfaces and they were more sensitive to UV-light compared to copolymers obtained in bulk and their ionomers.     

Modeling the TDFD dissolution of Al–Fe–Mn–Si particles in an Al–4.5Zn–1Mg alloy

Dissolution of large particles in DC-cast 7xxx aluminum alloys is one of the primary objectives of the homogenization process. A mathematical model to describe and predict this complex thermodynamical and kinetical process is of great significance. In this paper, the details of a diffusion-limited dissolution model, based on the thinning, discontinuation and full dissolution (TDFD) mechanism, to predict the dissolution of the Al₁₇(Fe_3.2, Mn_0.8)Si₂ particles is described. The model is capable of predicting the volume fraction and thickness of the particles during homogenization at different temperatures and time intervals. The predicted results are in good agreement with measurements using quantitative X-ray diffraction (QXRD) and quantitative field emission gun-scanning electron microscopy (QSEM). The model predictions of the supersaturation parameter, interface position, interface movement rate of the planar surfaces and the cylindrical edges, and the effect of the occurrence of discontinuities on the dissolution extent are presented.     

Time-resolved mass spectrometric study of the reaction H + Trans-2-Butene

The title reaction was studied in a discharge flow system using mass flow and modulated molecular beam sampling with phase-sensitive detection in order to obtain time-resolved mass spectrometric analysis. At total conversion exceeding 30%, the major products are methane and ethane when initially hydrogen atoms are in excess; when butene is in excess, the major products are ethane and propylene. No hydrocarbons with more than 4 carbon atoms were detected in the products. The reaction is a complicated one since the simplest reaction scheme that successfully simulates the experimental results comprises 20 elementary reactions. The simulation, coupled with sensitivity analysis, shows that with hydrogen atoms in excess, significant amounts of propylene formed in the initial decomposition of the butyl radical react further with hydrogen atoms to form methane and ethane. When butene is in excess, approximately [C₃H₆] ≈ [CH₄] + ½[C₂H₆] which means that this propylene does not react further and almost all methyl radicals end up as CH₄ or C₂H₆. At small conversion, simulation shows that the major product by far is propylene regardless of the [H]/[butene] ratio. The absence of higher hydrocarbons in the products is at variance with earlier results of Rabinovitch and coworkers; however the present work leads to a comparable value for the average rate constant ??_a = ωD/S where D and S is the amount of products arising from the decomposition and stabilization, respectively, of the butyl radical and ω is the collision frequency.     

Comparative study on the enantiomer separation of 1,1'-binaphthyl-2,2'diyl hydrogenphosphate and 1,1'-bi-2-naphthol by liquid chromatography and capillary electrophoresis using single and combined chiral selector systems

The chiral recognition ability of single and dual selectors, that were used as additives, have been investigated by HPLC and CE. Native beta- and gamma-cyclodextrins, permethylated beta-cyclodextrin, hydroxypropyl-beta-cyclodextrin, cholic acid and taurodeoxycholic acid sodium salts were applied as chiral selectors, whereas the atropisomers of 1,1'-binaphthyl-2,2'-diyl hydrogenphosphate, and 1,1'-bi-2-naphthol served as model compounds. It was found that all investigated selectors, except for gamma-cyclodextrin, display the same affinity pattern for binaphthyl enantiomers, i.e., binding the S more strongly than the R enantiomer. However, the differences in the phase distribution of chiral selectors led to the opposit elution order of enantiomers: with cyclodextrins, the first eluted is S enantiomer, while R is the first eluted for bile salts. Under the conditions studied, cyclodextrins (except gamma-cyclodextrin), as well as cholic acid sodium salts acting singly, enable the separation of 1,1'-binaphthyl-2,2'-diyl hydrogenphosphate enantiomers both by HPLC and CE methods, while 1,1'-bi-2-naphthol enantiomers were resolved only under CE conditions with permethylated cyclodextrin or bile salts. In both techniques the application of dual systems could improve resolution or make it worse (oreven cancel), depending on the sign of enantioselectivity of particular selectors, their concentrations and localization: mobile or stationary phase. It has been found that the mechanism of separation as well as interactions occurring between two selectors may be followed by using combined HPLC and CE methods. The obtained results proved that, as well as beta-CD, TM-beta-D and gamma-CD also form inclusion complexes with cholic acid sodium salts. The reversal of elution order may be realized by two procedures: changing a single selector, i.e., cyclodextrin on cholic acid sodium salt or vice versa, and by changing the proportion of selectors in the combined bile salt-cyclodextrin system.     

Multilayered Curcumin-Loaded Hydrogel Microcarriers with Antimicrobial Function

The design of multifunctional microcarriers has attracted significant attention because they combine various functions within a single system. In this study, we developed a set of multilayered hydrogel microcarriers, which were first loaded with chemotherapeutic curcumin (CUR), then, using the layer-by-layer (LbL) technique, coated through a polyelectrolyte shell consisting of chitosan (CHIT) or poly(allylamine hydrochloride) (PAH). As an outer layer with antimicrobial function, newly synthesised alkylene quaternary ammonium salt functionalised polyelectrolytes (A-QAS-PEs) were applied. For this purpose, poly(acrylic acid) (PAA) was decorated with different hydrophobic side chains (n-hexane and n-dodecane side entities) and different degrees of substitution (m) of quaternary ammonium groups (abbreviated as PAA-C(O)O-(CH₂)_n-N⁺(CH₃)₃(m); n = 6, 12; m = 8–14%). The grafting approach of PAA with the alkylene quaternary ammonium salt moiety was performed under mild reaction conditions using Steglich esterification followed by quaternisation. The structure of antimicrobial decorated PAA was confirmed by ¹H NMR and FTIR, and the mean diameter of all multifunctional microparticles was characterised by SEM. The viscoelastic properties of the functional layers were studied using quartz crystal microbalance with a dissipation (QCM-D). The release of CUR from the microcarriers was described using a hybrid model, i.e., a combination of first-order kinetics and the Korsmeyer-Peppas model. The antimicrobial activity of functionalised PAA and multilayered CUR-loaded hydrogel microcarriers with quaternary ammonium function was assessed against Staphylococcus aureus and Serratia marcescens by the agar diffusion assay method. Only a limited inhibition zone of PAA was observed, but in the case of both antimicrobial decorated PAA and the corresponding multilayered nanocarriers, the inhibitory activity increase was achieved against both strains of bacteria.     

Mass spectra of some perfluoroalkyl and perfluoroalkylether substituted 1,2,4-oxadiazoles

Electron impact fragmentation patterns were obtained for 1,4-bis[(5-perfluoro-n-heptyl)-1,2,4-oxadiazolyl]-benzene, its perfluoroalkylether substituted analogue, 3,5-bis(perfluoroalkyl)-, 3,5-bis(perfluoroalkylether)- and 3-perfluoroalkylether-5-perfluoroalkyl-1,2,4-oxadiazoles. In the compounds containing the phenylene group the molecular ion constituted the base peak; the main process was the breakdown of the oxadiazole ring with concurrent liberation of the perfluoroalkyl or perfluoroalkylether nitrile molecule; cleavage of the fluorinated chain α to the oxadiazole ring was found to take place to a considerable degree. In the perfluorinated 1,2,4-oxadiazoles cleavage β to the oxadiazole ring occurred preferentially; fragmentation of the ring itself took place to a limited degree only. The 3-perfluoroalkylether-5-perfluoroalkyl-1,2,4-oxadiazole appeared to undergo the primary β-cleavage exclusively at the perfluoroalkylether sidechain.