Hubert Kuhn

Photoelectron spectra and electronic structures of some indigo dyes

Abstract The He(I) photoelectron spectra of thioindigo (3), selenoindigo (4), bi(4,4-dimethyltetrahydropyrrole-3-one-2-ylidene) (5), bi(4,4-dimethyltetrahydrothiophene-3-one-2-ylidene) (6), octahydroindigo (8), 4,4-dibutyl-5,5-dimethylpyrrolindigo (9), and thiophenindigo (10) have been obtained by evaporating the compounds at temperatures up to about 350°C. The ionization potentials (IPs) are compared with those of the parent compound indigo (1) and are related to orbital energies or electronic states of the respective radical cations with the aid of semi-empirical SCF MO calculations. A satisfactory interpretation of the spectra is achieved with the Outer Valence Greens function method OVGF in combination with PM3 results. The first three IPs of all indigoid molecules in this study have the same origin, i.e. they relate to similar molecular orbitals. Because of the close relationship of the electronic structures of indigoid molecules, the IPs of the unknown unsubstituted pyrrolindigo (7) could be estimated.

Molecular orientation of monododecyl pentaethylene glycol (C12E5) surfactants at infinite dilution at the air/water interface. A molecular dynamics computer simulation study

In n this publication we used a molecular dynamics computer simulation in order to get more detailed insights into the adsorption process of monododecyl pentaethylene glycol (C12E5) surfactants. We investigated the surface n between water and air at infinite small surfactant concentrations. Measured in respect to the surface normal vector the average tilt angle of the C12 chain was found to be of the order of 67.4°±18.3°. For the polar pentaethylene glycol chains we observed tilt angles of 78.0°±8.5°. These results indicate that the molecules n are lying nearly flat on the water surface. This observation is in fairly good agreement with neutron reflection experiments of C12E3 and also with a previously performed simulation of sodium dodecylsulfate. Additionally, it turned out that the conformations of C12E5 surfactant molecules adsorbed at the air/water interface n are similar to the molecular arrangements of C12E5 n in the n vacuum phase. n This holds, at least, n for the regime of infinitely small surfactant concentrations.

A new class of interfacial tension isotherms for nonionic surfactants based on local self-consistent mean field theory: classical isotherms revisited

In this paper we use purely local density functional theory for the conformation of surfactant tails to obtain analytical interfacial tension isotherms of liquid–fluid interfaces in the presence of nonionic surfactants. For illustration, we derive the interfacial tension isotherm for nonionic surfactants at the air–water or the oil–water interface based on the Self-Consistent Field (SCF) theory, originally developed to treat grafted polymer brushes. The obtained interfacial tension isotherm turns out to be universal for a broad range of surfactant concentrations. We provide a feasible route for derivation of a whole class of adsorption isotherms based on the SCF theory. Comparison is given between the derived SCF adsorption isotherm with the classical isotherms of Frumkin and van der Waals. It is shown that these classical isotherms can be obtained as particular cases of a general SCF local density functional, corresponding to rigid surfactant tails. The SCF theory is shown to account for the flexibility of the surfactant chains in the adsorbed monolayer which modifies the interaction term in the surface tension and the adsorption isotherms. We compare experimental data for the surface tension and the surfactant adsorption isotherms for a nonionic surfactant with the predictions of the new theoretical isotherm. Very good agreement between nonionic surfactant adsorption at the air–water interface, calculated from the surface tension isotherm and neutron reflectivity and ellipsometry data, is obtained.

Mesoscale Computer Simulations on the Phase Behavior of the Non-Ionic Surfactant C12E5

Abstract Dissipative Particle Dynamics is a mesoscopic simulation method which allows to predict the self-assembly of amphiphilic polymers and surfactants. It was possible to reproduce the phase behavior of the non-ionic surfactant C12E5 in water. The three different phases L1, La and L2 could be characterized with Dissipative Particle Dynamics.

The Self-Assembly of an Amphiphilic Block Copolymer: A Dissipative Particle Dynamics Study

Abstract The self-assembly of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) blockcopolymer (EO13PO30EO13) in the presence of water was investigated. The phases have been studied with the mesoscopic simulation technique Dissipative Particle Dynamics (DPD). The micellar, hexagonal, lamellar, bicontinuous and inverse micellar phase have been identified with this method and showed remarkable agreement with the experimental phase behavior. This work showed that the Dissipative Particle Dynamics simulations are also suitable for complicated polymer systems such as the EO13PO30EO13 triblock copolymer.