Complex formation in mixtures of 4,4'-disubstituted diphenyldiacetylenes with cyanobiphenyls

We investigated 1:1 mixtures of a variety of 4,4'-disubstituted diphenyldiacetylenes (PTTP series) and cyano-containing mesogens for possible complex formation. Complexes were formed when alkyl/alkoxy cyanobiphenyls (CB series) were mixed with alkyl/alkoxy PTTP homologues. We found complexes having a melting temperature higher than that for either component, and complexes with lower melting temperatures. A fluoro substituent on the PTTP gave an enhanced nematic phase and a cyclohexane ring in place of a benzene ring yielded an enhanced smectic A phase, but a cyano on the PTTP gave poor liquid crystalline properties. Phase diagrams were constructed for PTTP-24/5-CB and PTTP-24/80-CB mixtures. Both complexes formed had melting temperatures higher than those for either component. These complexes were recrystallized and shown by X-ray studies to be 1:1 complexes. The PTTP-24/5-CB complex showed only a monotropic nematic phase, but the PTTP-24/80-CB complex showed induced smectic A and hexatic B phases in addition to an enantiotropic nematic phase.     

Complex formation in alkyldimethylamine oxide/sodium palmitate/water mixtures

The complex formation between nonionic alkyldimethylamine oxide (CnDMAO, n=14, 16, and 18) and sodium palmitate (NaPa) in the solid phase of CnDMAO/NaPa mixtures and the dependence of the interaction parameter beta of the regular solution theory (RST) on the mixed micelle composition of C16DMAO/NaPa mixtures were investigated. The dissolution temperature showed a maximum at a NaPa mole fraction X(Pa)(*) of 0.3-0.4 for C16DMAO/NaPa and 0.2 for C18DMAO/NaPa. The compositions of the complexes suggested by X(Pa)(*) are C16DMAO: NaPa=3:2 or 2:1 and C18DMAO:NaPa=4:1. The composition X(Pa)(*) depended on the chain length of the amine oxides. The maximum was not observed in the case of the C14DMAO/NaPa/water system. In the range 0.7< or =X(Pa)< or =1.0, dissolution temperature depression was observed with decreasing X(Pa). The dissolution temperature depression was analyzed by taking into account the nonideal behavior in the mixed micelles and the counterion binding on the mixed micelle surface. The negative beta values were obtained for all three mixed systems. It was shown that the counterion activity remained practically constant in the range of 0.7< or =X(Pa)< or =1.0. The cmc values of C16DMAO/NaPa mixtures were determined by pyrene fluorescence measurement. For C16DMAO/NaPa mixtures, the dependence of the RST interaction parameter beta on the mixed micelle composition X(Pa) was determined for a wide range (0.2< or =X(Pa) < or =0.9). In the range 0.2< or =X(Pa)< or =0.5, the beta values were obtained from an analysis of cmc based on the RST. In the range 0.7< or=X(Pa)< or=0.9, the beta values were obtained from an analysis of the dissolution temperature depression. From the analysis of the micelle composition dependence of the beta values, a short-range attractive interaction between the headgroup of C16DMAO and palmitate anion is suggested.     

Complex formation of Al2(SO4)3 in water-formamide mixtures

The kinetics of formation of AlSO ₄ ⁺ has been investigated in mixtures of water and formamide. In contrast to similar measurements with BeSO₄, the substitution of solvating formamide molecules by the sulfate ion cannot be observed on the aluminum cation. On the other hand, with Al³⁺ cations three well separated water substitution processes are observed, as compared to a single one only with Be²⁺. An explanation for this behavior and for the different pH dependence of the sulfate complex formation for Al³⁺ and Be²⁺ cations is suggested.     

One-step formation of multiple emulsions in microfluidics

We present a robust way to create multiple emulsions with controllable shell thicknesses that can vary over a wide range. We use a microfluidic device to create a coaxial jet of immiscible fluids; using a dripping instability, we break the jet into multiple emulsions. By controlling the thickness of each layer of the jet, we adjust the thicknesses of the shells of the multiple emulsions. The same method is also effective in creating monodisperse emulsions from fluids that cannot otherwise be controllably emulsified, such as, for example, viscoelastic fluids.     

Complex formation of silver(I) with 18-crown-6 in methanol-DMF binary mixtures

Dependence of the stability of the silver(I)-18-crown-6 complex on the composition of the binary methanol-DMF solvent was studied potentiometrically. It was found that the increase in DMF content in the binary mixture decreased the stability of the coordination compound. New approach to analysis of the solvation contributions of reagents in the variation of Gibbs energy while substitution of solvent with another one was suggested. It was shown that the shift in the complex formation equilibrium is determined by variation in the solvate state of the central ion.     

Physico-chemical characteristics of oil-in-water emulsions based on whey protein-phospholipid mixtures

Emulsions prepared with whey proteins, phospholipids and 10% of vegetable oil were used for a model typifying dressings, coffee whitener and balanced diets. For the present study, two whey proteins (partial heat-denatured whey protein concentrate (WPC) and undenatured whey protein isolate (WPI)) in combination with different phospholipids (hydrolysed and unmodified deoiled lecithin) were chosen to investigate the interactions between proteins, phospholipids and salt (sodium chloride) in such emulsion systems. Oil-in-water (o/w) emulsions (10 wt.% sunflower oil) containing various concentrations of commercial whey proteins (1-2%), phospholipids (0.39-0.78%) and salt (0.5-1.5%) were prepared using a laboratory high pressure homogeniser under various preparation conditions. Each emulsion was characterised by droplet size, creaming rate, flow behaviour and protein load. The dynamic surface activity of the whey proteins and lecithins at the oil-water interface was determined using the drop volume method. The properties of emulsions were significantly influenced by the content of whey protein. Higher protein levels improved the emulsion behaviour (smaller oil droplets and increased stability) independent of the protein or lecithin samples used. An increase of the protein content resulted in a lower tendency for oil droplet aggregation of emulsions with WPC to occur and emulsions tending towards a Newtonian flow behaviour. The emulsification temperature was especially important using the partial heat-denatured WPC in combination with the deoiled lecithin. A higher emulsification temperature (60 degrees C) promoted oil droplet aggregation, as well as an increased emulsion consistency. Emulsions with the WPC were significantly influenced by the NaCl content, as well as the protein-salt ratio. Increasing the NaCl content led to an increase of the droplet size, higher oil droplet aggregation, as well as to a higher creaming rate of the emulsions. An increase of the lecithin content from 0.39 to 0.78% in the emulsion system resulted in a small reduction of the single droplet size. This effect was more pronounced when using the hydrolysed lecithins.     

Physicochemical behavior of oil-in-water emulsions: influence of milk protein mixtures, glycerol ester mixtures and fat characteristics

Different emulsions based on two protein mixtures (skim milk powder (SMP) and functional dairy proteins (FDP)), two mono-di-glyceride mixtures (MDG) (saturated and partially unsaturated), three fats (hydrogenated and refined coconut oils and refined palm oil) were studied to investigate the interactions occurring between the oil phase, low molecular weight emulsifiers and proteins. Immediately following the emulsification process, high diameters of fat globules were obtained in FDP-based systems, relevant of an aggregation phenomenon. At this stage, the fat globule size characteristics were dependent on the emulsifier and fat types present in the formulation. In contrast, SMP-based emulsions were characterized by low proportions of aggregated particles regardless the formulations. Ageing (24 h at 4 °C) promoted disaggregation in FDP formulations, while SMP emulsions were well stabilized. Just after the homogenization step, less proteins were required to stabilize the globule interface in FDP systems as compared to SMP ones. Only with SMP, the amount of protein load at the fat globule surface was influenced by the oil nature and/or by the emulsifier type. A competitive adsorption of caseins, over whey proteins, was demonstrated in the case of FDP. The ageing period promoted a displacement of the proteins adsorbed at the oil droplet interface, suggesting a disruption of the interfacial protein interactions. This disruption was more marked with SMP than with FDP and, in both cases, was more or less influenced by the emulsifier and oil phase natures. The variations of the viscosity and rheological parameters (elastic and viscous moduli) were not dependent on one specific component of the formulation.     

Alloy formation in mechanically activated mixtures

The physical mixtures of hydroxocarbonates of Cu and Ni with aluminium were activated using a laboratory planetary mill. The chemical reactions and alloy formations as the effects of grinding were followed by the phase analysis of solid products based on the thermogravimetry and X-ray diffractometry. Experimental evidence indicates that the nature of reactions and products of mechanical activation was dependent on the amount of aluminium and time of grinding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Direct radioimmunoassay of testosterone in human saliva

A simple direct radioimmunoassay for testosterone in 400 μl of whole human saliva is reported. Neither extraction nor chromatography is needed. The direct assay involves a commercially available, highly selective antiserum raised against testosterone-19-(O-carboxymethyl)-ether-BSA, an iodinated tracer, a serum added to give parallel inhibition of analyte and tracer binding to serum proteins and a double antibody/polyethylene glycol separation technique. The lower limit of determination is about 3 pM salivary testosterone and the calibration curve covers the range of clinical interest both for males and females (0–868 pM). The assay is specific as judged from recovery and dilution tests, from the cross-reactivity of the antiserum used and from comparisons with an extraction procedure. Within-assay and between-assay relative standard deviations are 4.1, 1.9, 10.5% and 6.3, 2.8, 15.3% for saliva samples with testosterone concentrations of 310, 117 and 52.7 pM, respectively.     

Liquid clathrate formation in ionic liquid-aromatic mixtures

1-Alkyl-3-methylimidazolium containing ionic liquids with hexafluorophosphate, bis(trifyl)imide, tetrafluoroborate, and chloride anions form liquid clathrates when mixed with aromatic hydrocarbons; in the system 1,3-dimethylimidazolium hexafluorophosphate-benzene, the aromatic solute could be trapped in the solid state forming a crystalline 2:1 inclusion compound.     

Pattern formation in phase separating binary mixtures

We experimentally investigate the interplay of thermodynamics with hydrodynamics during phase separation of (quasi-) binary mixtures. Well defined patterns emerge while slowly crossing the cloud point curve. Depending on the material parameters of the experimental system, two distinct scenarios are observed. In quasi-binary mixtures of methanol-hexane patterns appear before macroscopic phase separation sets in. In course of time the patterns turn faint while the overall turbidity of the sample increases until the mixtures become completely turbid. We attribute this pattern formation to a latent heat induced instability resembling a Rayleigh-Bénard instability. This is confirmed by calorimetric data and an estimate of its Rayleigh number. Mixtures of C(4)E(1)-water doped with decane phase separate under heating. After passing the cloud point curve these mixtures first become homogenously turbid. While clearing up, pattern formation is observed. We attribute this type of pattern formation to an interfacial tension induced Bénard-Marangoni instability. The occurrence of the two scenarios is supported by the relevant dimensionless numbers.     

Complex formation and dynamics in polymer melts

The viscoelastic properties of polymer chains with a few number of pairwise associating functional groups are studied as a function of polymer molecular weight, degree of substitution and polymer concentration. As a model system, polybutadienes of narrow molecular weight distribution are used as starting materials. These polymer chains are modified by introducing few 1,2,4-triazolidine-3,5-dione (urazole) groups U. These form defined dimeric hydrogen bond complexes U + U → U₂.     

Thermodynamics of complex formation in chloroform-oxygenated solvent mixtures

Complex formation equilibria in binary mixtures of chloroform with dipropyl ether (PE), diisopropyl ether (IPE), methyl tert-butyl ether (MBE), tetrahydrofuran (THF). 1,4-dioxane (DOX), acetone (AC), and methyl acetate (MA) have been analyzed in detail using several association models. Vapor-liquid equilibria, excess enthalpy and excess heat capacity data for these mixtures have been correlated using a multiproperty global fitting procedure. The thermodynamic properties for chloroform +PE, +IPE, +MBE, +AC, and +MA are best correlated using the ideal association model while for chloroform +THF and +DOX the best model is an athermal solvation model where the Flory-Huggins expression for the species activity coefficients is considered. The model parameters, i.e., the equilibrium constant, enthalpies and heat capacities of complexation, were found to be reliable, well representing the chloroform-oxygenated solvent H-bonded complexes. A detailed discussion is given on the test proposed by McGlashan and Rastogi to decide whether the solution contains only 11 complexes or 21 complexes as well. The complex formation equilibria in chloroform mixtures is compared to those previously examined for halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) mixed with the same oxygenated solvents. It was found that the H-bonds formed by halothane are stronger than those formed by chloroform.     

The stereochemistry of enolate formation in THF-hexane mixtures

The effect of solvent on the stereochemistry of deprotonation of 4-heptanone in THF-hexane mixtures is plotted in the figure on the following page. The E/Z ratio varies from 1.5 in pure THF to 0.7 in 90% hexane.     

Mechanism of HTO formation in gaseous tritium mixtures

The mechanisms for the conversion of molecular tritium gas to tritiated water are examined for tritium mixtures with (1) oxygen and nitrogen, (2) oxygen and argon, and (3) water and helium, for which previous experimental data exist. By analyzing results of these experiments in light of the radiation chemistry involved in a mixture of tritium and other gases, an understanding of the conversion mechanisms is reached. The formation of H and/or OH free radicals as intermediate species is of particular significance in the formation of HTO in that these radicals initiate a number of reactions which lead to the formation of water. These reactions are analyzed in terms of steady-state kinetics to obtain predictive models which can be judged against the experimental observations. For the three experimentally observed mixtures, model agreement is found to be within a factor of 2–3.     

Stability of xylene-in-water emulsions in the presence of cetyltrimethyl ammonium bromide/cetyl alcohol mixtures

Interfacial tension (γ) measurements at the xylene/aqueous cetylrimethylammonium bromide (CTABr) solutions in the presence and absence of cetyl alcohol have shown that addition of cetyl alcohol reduces γ and increases the adsorption of CTA⁺ ions at the O/W interface. The same increase was observed in the presence of 0.5 and 1 mole l⁻¹ NaCl in the aqueous phase. Microelectrophoresis measurements at various CTABr concentrations in the presence and absence of cetyl alcohol showed a gradual increase of zeta potential (ξ) with increase of CTABr concentration, followed by a rapid increase in zeta potential and eventually ξ reached a limiting value which increased progressively with increase of the alcohol content in the mixture. These results confirm the increased adsorption of the cationic surfactant on addition of alcohol. This increase may be due to the more dense packing of the CTA⁺ ions as a result of the reduction of the repulsion between the head groups when the alcohol adsorbs between the surfactant ions.The rate of coalescence of xylene/water emulsions was measured by droplet counting (using optical microscopy) as a function of time. The rate constant K of coalescence was calculated from the slope of the tangent of the log N_t versus t curves. The results showed that addition of cetyl alcohol (10, 20, and 30 mole %) reduces the rate of coalescence significantly and, at 30 mole % cetyl alcohol, very stable emulsions were produced. Similar results were obtained in the presence of 1 mole l⁻¹ NaCl and 0.5 mole l⁻¹ CaCl₂. The enhanced stability is probably due to the formation of a coherent strong interfacial film which acts as a “barrier” preventing coalescence, possibly by virtue of its rheological properties, e.g. dilational viscoelasticity.     

String formation and demixing in monolayers of dipolar colloidal mixtures

Employing hypernetted chain (HNC) integral equations and a stability analysis we investigate the structure and phase behavior of bidisperse mixtures of dipolar hard spheres with different size ratios s=σ(S)/σ(L) confined to a plane. The dipole moments of the particles are perfectly ordered along an in-plane direction, yielding anisotropic interactions favoring chain formation. Exploring a range of size ratios and compositions, our study predicts a complex interplay between aggregation phenomena, on the one hand, and volume phase transitions, on the other hand. In dilute, strongly asymmetric systems (s = 0.5), our HNC analysis indicates chain formation of the large particles, while the small particles act as a weakly correlated background. According to our fluctuation analysis, this aggregation behavior results in combined condensation-demixing transitions, with a trend towards pure demixing when the concentration of the large particles, c(L), becomes small. In dense systems, the most interesting results are found for intermediate size ratios, s ~ 0.7-0.8. Here we find signatures of a concentration-driven transition from pure chains of large particles (large c(L)) to mixed chains with alternating order of large and small particles (small c(L)). The two regimes are separated by a characteristic "jump" in the HNC non-solution line.     

Two-phase formation of nitrophenols at the radiolysis of nitrobenzene-water emulsions

Two-phase additivity rule for radiation yields of p-nitrophenol, m-nitrophenol and p-nitrosophenol has been demonstrated. The data of partial radiation yields indicated that the nitrobenzene phase is by several times more reactive than a water phase /H₂O, 3M HNO₃ or 1.5M H₂SO₄/ in respect of nitrophenols formation.