Konrad Quitzsch

Rate constants of the thermal cis-trans isomerization of azobenzene dyes in solvents, acetone/water mixtures, and in microheterogeneous surfactant solutions

Rate constants kiso of the thermal cis-trans isomerization of four 4,4’-nitro-aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to λmax from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on kiso- and λmax-values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted. In microheterogeneous water/surfactant solutions kiso-values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton®X-100, C12EO8 in water, and varied with the composition of bicontinuous microemulsions of Igepal® CA-520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity. Replacement of H2O by D2O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects.

Phase equilibria of microemulsion forming system n-decyl-β-d-glucopyranoside/water/n-octane/1-butanol

A systematic investigation of the phase behaviour involving microemulsions is presented with respect to experimental and calculated data for the four-component system n-decyl-β- d -glucopyranoside/water/n-contane/1-butanol and its corresponding ternaries at 25°C. The main feature of this kind of multicomponent system is the coexistence of a highly structural liquid phase enriched with amphilic compounds and an excess water or an excess oil phase or both of them. The phase behaviour was studied experimentally by use of turbidity titration and HPLC measurements and theoretically by application of the UNIQUAC-equation and the UNIFAC-method. The UNIFAC-method is able to describe the phase behaviour in the quaternary system qualitatively, without fitting parameters. However, by applying the UNIQUAC-method, with adjustable parameters, it was only possible to model the ternary subsystems. The modelling of the quaternary system is not satisfactory.

Heats of immersion of ZSM—5 zeolite in n-alkanes, 1-alkenes and 1-alcohols at 30°C

Abstract Integral immersional effects in ZSM—5/n-alkane, -/1-alkene, -/n-alcohol and in silicalite/n-alkane, -/n-alcohol systems have been measured calorimetrically at 303 K using an isothermal LKB-microcalorimeter 2107 modified in the part containing the BATCH-vessel. The results are discussed in terms of a chain-length dependence of integral heats of immersion.

Experimental and theoretical studies of the system n-decyl-β-D-maltopyranoside+water

Abstract A class of non-ionic surfactants that is useful for formulating microemulsions, and that is becoming increasingly important for industrial purposes, is the series of alkyl polyglucosides (CXGY). These surfactants have x carbons in the hydrophobic alkyl chain and y glucose units in the hydrophilic headgroup, with commercial products typically containing noninteger values of both x and y. Commercial CXGY blends contain many other compounds besides alkyl-β-D-glucopyranosides, including n-alkyl-α-glucopyranosides, n-alkyl-β-D-maltopyranosides, and other isomers and materials that contain a larger number of glucose units. In this paper, we investigate the physical properties of the system n-decyl-β-D-maltopyranoside (C10G2)+water over a wide concentration range, using various experimental techniques (surface tension measurement, rotation rheometer, DSC, polarising microscopy) and a molecular aggregation formation model. The theory is based on calculating the size distribution of the aggregates, which in turn depends on the free energy of forming an aggregate. This free energy is modelled as the sum of several free-energy contributions and an ideal entropy of mixing. For each free-energy contribution, we have highlighted schematically only the relevant characteristics of the surfactant tails or the surfactant heads. The theoretical results are compared to those found in the literature for alkyl-β-D-glucopyranosides (CXG1) aqueous solutions. In surfactant solutions, rheological behaviour is intimately linked to internal microstructure and micellar architecture. The diluted surfactant system demonstrates Newtonian behaviour and complex non-Newtonian behaviour within the high shear stress regime. In the middle concentration range, the surfactant solutions exhibit an unexpected rheological behaviour, where the viscosities are not dependent on temperature. At high surfactant concentration phase transition, especially liquid-crystalline to isotropic solution, could be followed using rheological experiments. In performing DSC experiments, emphasis is put on the melting behaviour for the dry surfactant and C10G2+water systems at high surfactant concentrations. The melting behaviour can be characterised by transitions from a crystalline phase to a liquid crystalline phase and finally to an isotropic solution. The identification of the liquid-crystalline phase was carried out from textural observation, using polarising microscopy. The lyotropic behaviour follows the classical pattern established for the surfactants. Applying polarising microscopy, textures of the hexagonal and lamellar phases could be observed for the system C10G2+water.

Adsorption of C4 hydrocarbons on X-zeolites containing Li+, Na+, K+, Rb+ and Cs+ cations

Abstract The adsorption isotherms and integral heats of adsorption of the isomeric n-butenes and n-butane adsorbed on NaLi56-X, Na-X, NaK44-X, NaRb51-X and NaCs50-X were measured at 30°C over a wide range of loading. The weight of adsorbed C4 hydrocarbons was determined by a gravimetrical method with a vacuum microbalance. The virial equation of Bradley and Wilkins was used for a mathematical description of the experimentally determined course of the isotherms. Henrys constants, limiting amounts and entropies of the adsorbed molecules were calculated from adsorption equilibrium data. The heat of adsorption was measured calorimetrically by use of an LKB sorption microcalorimeter 2107. All of the results obtained were discussed in terms of the distribution of cations in the X zeolites.

Vapour-liquid equilibria and heats of mixing in alakane-1-alcohol systems. II. Heats of mixing in 1-alcohol-n-undecane systems

Abstract Excess enthalpies of seven binary systems in the 1-alcohol-n-undecane series and of the ternary system 1-dodecanol-1-propanol-n-undecane have been determined using an LKB 8700 titration calorimeter. The binary experimental data are correlated alone, or, whenever possible, in combination with phase equilibrium data, using the NRTL, Wilson and UNIQUAC equations with linearly temperature-dependent parameters only.

Simultaneous surfactant aggregation in aqueous solution and at the solid–liquid interface. Coadsorption of decanoyl-N-methylglucamide and phenol on silica gel☆

Abstract The adsorption isotherm of the nonionic surfactant decanoyl-N-methylglucamide (MEGA-10) on silica gel exhibits two steps, the latter of which arising from the formation of micelle-like surface aggregates, as is evident from coadsorption experiments with phenol. Deviating from general adsorption characteristics of surfactants on hydrophilic substrates, the onset of the second step coincides with the critical micelle concentration (CMC). Hence, the hemimicelle concept is extended to the limiting case of a simultaneous self-assembly of dissolved and adsorbed surfactant molecules, admitting a minor increase in the content of non-associated monomers in the micellar region. At a given phenol concentration, the composition of the surface aggregates is nearly independent of the adsorbed amount of surfactant and resembles the respective composition of the coexisting bulk micelles.

Micellar incorporation without solubilizing effect. A study on the system waterphenoldecanoyl-N-methylglucamide

Abstract The nonionic surfactant decanoyl-N-methylglucamide (MEGA-10) causes a pronounced decrease in the solubility of phenol in water. Despite the absence of the expected solubilizing effect, the micelles were shown to incorporate the additive as a cosurfactant. It could be located on the basis of shifts in the proton NMR spectrum of the micellized surfactant. Shape and size of the aggregates were investigated by means of dynamic light scattering in combination with rheological measurements. Phenol was found to induce a sphere-to-rod transition, which was attributed to the space requirement of the inserted phenyl groups. In order to estimate the quantitative composition of the mixed micelles, two thermodynamic approaches were compared.