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Effects of non-ionic surfactants and related compounds on the cooperative and molecular dynamics of their aqueous solutions

URN to cite this document: urn:nbn:de:bvb:355-opus-4614

Schrödle, Simon (2005) Effects of non-ionic surfactants and related compounds on the cooperative and molecular dynamics of their aqueous solutions. PhD, Universität Regensburg

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Abstract (English)

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.

Translation of the abstract (German)

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.

Item Type:	Thesis of the University of Regensburg (PhD)
Referee:	Richard (Apl. Prof. Dr.) Buchner
Date of exam:	02 February 2005
Institutions:	Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > PD Dr. Richard Buchner
Keywords:	Nichtionisches Tensid , Dynamik , Dielektrische Relaxation , Perkolation , , non-ionic surfactant , dynamics , dielectric relaxation , percolation , microemulsion
Subjects:	500 Science > 540 Chemistry & allied sciences
Status:	Published
Refereed:	Yes, this version has been refereed
Created at the University of Regensburg:	Yes
Owner:	Universitätsbibliothek Regensburg
Deposited On:	27 Oct 2009 07:58
Last Modified:	07 Nov 2012 10:33
Item ID:	10295

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