Aqueous solutions of cationic surfactant systems with strongly binding counterions show the striking phenomenon of shear induced phase transitions. At low shear rates or angular frequencies, the solutions exhibit Newtonian flow. At high rates of shear, however, the rheological properties change dramatically. Above a well defined threshold value of the velocity gradient, a supermolecular structure can be formed from micellar aggregates. This shear induced structure (SIS) behaves like a gel and exhibits strong flow birefringence. The formation of the shear induced structure is very complicated and depends on the specific conditions of the surfactant system. In this paper we discuss new results which have been obtained from rheological measurements and from flow birefringence data. We examine the stability of the shear induced state as a function of temperature, surfactant concentration and salt concentration and we analyse the effect of solubilisation of alcohols and hydrocarbons. The results are interpreted in terms of a kinetic model which accounts for the observed behavior.
Three [2]catenanes and three [3]catenanes incorporating one or two pi-electron-rich macrocyclic polyethers and one pi-electron-deficient polycationic cyclophane have been synthesized in yields ranging from 4 to 38%. The pi-electron-rich macrocyclic components possess either two 1,4-dioxybenzene or two 1.5-dioxynaphthalene recognition sites. The pi-electron-deficient cyclophane components incorporate two bipyridinium and either one or two dialkylammonium recognition sites. The template-directed syntheses of these catenanes rely on i) pi...pi stacking interactions between the dioxyarene and bipyridinium recognition sites, ii) C-H...O hydrogen bonds between some of the bipyridinium hydrogen atoms and some of the polyether oxygen atoms, and iii) C-H...pi interactions between some of the dioxyarene hydrogen atoms and the aromatic spacers separating the bipyridinium units. The six catenanes were characterized by mass spectrometry and by both 1H and 13C NMR spectroscopy. The absorption spectra and the electrochemical properties of the catenanes have been investigated and compared with those exhibited by the component macrocycles and by related known catenanes. Broad and weak absorption bands in the visible region, originating from charge-transfer (CT) interactions between electron-donor and electron-acceptor units, have been observed. Such charge-transfer interactions are responsible for the quenching of the potentially fluorescent excited states of the aromatic units of the macrocyclic polyether components. The redox behavior of these novel compounds has been investigated and correlations among the observed redox potentials are illustrated and discussed. The catenanes undergo co-conformational switching upon one-electron reduction of the two bipyridinium units. One of them--in its reduced form--can be also switched by acid/base inputs and exhibits AND logic behavior. The co-conformational rearrangements induced by the redox and acid/base stimulations lend themselves to exploitation in the development of molecular-level machines and logic gates.
Phosphinoxyde (und Phosphonate) mit einer zur PO‐Gruppierung nachbarständigen CH‐Gruppe setzen sich mit Aldehyden und Ketonen unter Mitwirkung von Basen — vorteilhaft Kalium‐tert.‐butylat — zu Olefinen um. Die Reaktion verläuft über die Stufe der β‐Hydroxy‐alkylphosphinoxyde. Ein Vertreter dieser Verbindungsklasse, auf einem übersichtlichen Weg synthetisiert, zerfällt in Anwesenheit von Kalium‐tert.‐butylat in Phosphinsäure und Olefin. — Mit Phenyl‐lithium in α‐Stellung metallierte Phosphinoxyde reagieren mit Carbonylverbindungen zu β‐Hydroxy‐alkylphosphinoxyden. Durch Umsetzung von Phosphinoxyden mit Carbonsäureestern und Kalium‐tert.‐butylat als Kondensationsmittel entstehen β‐Keto‐alkylphosphinoxyde.
Phosphinoxyde mit einer zum Phosphor nachbarständigen Methylengruppe enthalten aktiven Wasserstoff und setzen sich in Gegenwart geeigneter Kondensationsmittel mit einigen Ketonen zu Olefinen und Phosphinsäuren um.
Publication costs assisted by Centre de Recherches sur les Macromolécules Ultrasonic absorption, pressure jump, temperature jump, and shock tube measurements have been performed to investigate the relaxation processes present in solutions of purified sodium lauryl sulfate and laurylpyridinium chloride, bromide, and iodide. The results show the presence of two relaxation processes characterized by the relaxation times and r2 with a ratio 2/ over a hundred. Both relaxation times depend on concentration (C) and ionic strength (µ). The slow process (t2) is more affected by µ than the fast one ( ). The various models presented to account for these two processes are discussed. It is shown that the available experimental data can be qualitatively explained by assigning to the exchange of detergent ions between the micellar phase and the bulk solvent and r2 to the micellization-dissolution equilibrium. The variation of with the chain length of the detergent ion can be quantitatively explained by assuming the exchange reaction to be diffusion controlled. The interpretation of the variation of 2 with C at various ionic strength leads to the conclusion that at concentration only slightly above the critical micelle concentration both the aggregation number and the rate constants for the exchange equilibrium depend on C.
We have studied the transformation of an LR phase composed of stacked bilayers to a vesicle phase under the influence of shear. The ionically charged stacked bilayer phase was prepared by protonation of an L3 phase from tetradecyldimethylamine oxide hexanol, and water. The protonation was accomplished by a hydrolysis reaction of an ester solubilized in this phase. By the protonation of the bilayers the L3 phase becomes unstable and, in the absence of shear, is transformed into a classical lamellar phase. This lowviscosity phase was then transformed into an onion phase by shear. The structural changes during this transformation process were monitored by means of scattering experiments and by rheological and conductivity measurements under shear. The following results were obtained when the shear rate was varied: (a) the transition from stacked lamellae to vesicles is irreversible and does not go back; (b) the formation of multilamellar vesicles requires a total strain of about 2000 (for a given surfactant concentration of 100 mM). In addition the influence of various parameters on the transformations of the LR phase was studied, such as chain length of the surfactant, chain length of the alcohol, and the total concentration of amphiphile.
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