title: Effects of non-ionic surfactants and related compounds on the cooperative and molecular dynamics of their aqueous solutions
Creators: name: Schrödle, Simon
Publisher: name: Universität Regensburg
Year: 2005
Subjects: subject: Nichtionisches Tensid , Dynamik , Dielektrische Relaxation , Perkolation , , non-ionic surfactant , dynamics , dielectric relaxation , percolation , microemulsion
subject: 540 Chemie

description: This study presents an investigation of the dynamics of aqueous non-ionic surfactant solutions and related systems. Various systems were studied, starting from water + 1,4-dioxane, which represents a simple binary mixture, up to non-ionic microemulsions featuring percolation transitions and a high degree of structuring. For a better understanding of surfactant + water binary systems the present study was based on a set of oligomeric model compounds which allow the investigation of increasing degrees of internal freedom on the dynamics of hydrogen-bond networks. A careful evaluation of existing literature data showed major discrepancies and a quite incomplete coverage. Therefore, thermodynamic properties, especially the densities and heat capacities were determined and analyzed. The dielectric investigations revealed that compounds without H-bond donor groups like 1,4-dioxane and oligo(ethylene glycol) dimethyl ethers cause a quite pronounced microheterogenous structure and show cooperative relaxation of water-rich domains even at high concentration of the organic solute. In contrast to this, compounds with groups acting as H-bond donors can be incorporated easily into the H-bond network and large effects on the relaxation times where found. The dielectric properties of pentaethylene glycol monododecyl ether (C12E5) + water binary mixtures in the isotropic-micellar, lamellar and hexagonal phase were studied. Two dielectric dispersion steps were resolved and assigned to intermolecular cooperative dynamics of water at the micellar interface and in remaining bulk water domains. From the quantitative analysis of the bulk water response, which was further investigated by heavy water as a substitute for H$_2$O, the ratio of slow water molecules per mole surfactant was calculated. Additionally, the effective dipole moment of water dipoles incorporated in the relaxation process of water at the interface was determined and found considerably lower than that of pure water. Further work was carried out on percolating KCl-'doted' water/n-octane/C12E5 W/O microemulsions, and critical exponents were obtained that agree well with the universal parameters predicted by dynamic percolation theory. Some properties do not follow a scaling law, a fact that points out the importance of specific interactions for non-ionic microemulsion.
description: Die vorliegende Arbeit behandelt die Dynamik wässriger Lösungen nichtionischer Tenside und verwandter Systeme. Zahlreiche binäre Mischungen wurden untersucht, ausgehend von 1,4-Dioxane+Wasser, bis zu nichtionischen Mikroemulsionen, die Perkolationsübergänge aufweisen. Für das bessere Verständnis der Tensidlösungen wurden Modellsysteme oligomerer Ethylenglykolmono- und dimethylether mit den Methoden der dielektrischen Spektroskopie und der Thermodynamik untersucht. Die dielektrischen Untersuchungen zeigten, dass Systeme, deren organische Komponente nur Wasserstoffbrückenakzeptoren besitzt, hochgradig mikroheterogene Strukturen aufweisen und der kooperative Wasser-Relaxationsprozess bis hin zu hohen Konzentrationen der organischen Komponente erhalten bleibt. Desweiteren wurden die dielektrischen Eigenschaften von Pentaethylenglykolmonododezylether (C12E5) in isotrop-micellärer, lamellarer und hexagonaler Phase untersucht. Es konnte zwei Relaxationsprozesse identifiziert werden. Aus der quantitativen Analyse der Prozesse wurden Hydratationszahlen und effektive Dipolmomente bestimmt. Ein weitere Schwerpunkt der Arbeit liegt auf dielektrischen Prozessen in perkolierenden Mikroemulsionen. Für das System Wasser/n-Oktan/C12E5 wurde kritische Exponenten bestimmt die mit theoretischen Voraussagen in Einklang stehen. Einige Eigenschaften folgen allerdings keinem Skalierungsgesetz, was auf spezifische Wechselwirkungen hindeutet.