Gerhard Platz

Investigations on a detergent system with rodlike micelles

Conductivity, kinetic, static and dynamic light scattering, electric birefringence and rheological measurements were carried out on aqueous solutions of Tetradecylpyridinium-n-Heptanesulfonate (C14PyC7SO3) up to high concentrations. In dilute solutions between the critical micelle concentration (cmc) and another characteristic concentration (ct) spherical micelles were detected whose radii were independent of detergent concentration and equal to the length of a detergent molecule; the aggregation numbern of these micelles of about 100 monomers per micelle was also in agreement with the existence of normal spherical micelles of aC14-detergent.Above the concentrationct, the spherical micelles were found to grow to rodlike aggregates whose short axis was still independent of concentration and equal to the length of a monomer, while the lengthsL of the rods increased with increasing detergent concentration. When the lengthsL of the rods became comparable with the mean distancea between them, the starting interaction between the rods slowed down their growth. In this concentration range of overlapping rods, the data could be evaluated with a recently developed theory by Doi and Edwards for stiff rods. The rods reached finally a maximum length of about 500 å and decreased again in size upon further increase of concentration when the overlap ratioL/a reached a value of about 1,5.

Zur Kinetik der Mizellbildung von Alkylpyridiniumhalogeniden

ZusammenfassungIn der vorliegenden Arbeit werden Ergebnisse von kinetischen Messungen an Alkylpyridiniumhalogeniden geschildert und diskutiert. Oberhalb der kritischen Mizellbildungskonzentration (cmc) konnten dabei an den meisten Systemen zwei Relaxationszeiten beobachtet werden, deren Konzentrations-, Temperaturund Gegenionenkonzentrationsabhängigkeit untersucht wurden.Nach einer vor kurzem entwickelten Theorie vonG. Aniansson et al. ist dabei die schnelle Relaxationszeit τ1 charakteristisch für die Verschiebung der Verteilungskurve im Aggregationsraum, wobei die Gesamtkonzentration der Mizellen konstant bleibt. Aus dieser Relaxationszeit kann die Lebensdauer eines Monomeren in der Mizelle sowie seine Einbau geschwindigkeit erhalten werden. Aus der Temperaturabhängigkeit von τ1 läßt sich die Reaktionsenthalpie für den Einbau eines Monomeren in die Mizelle gewinnen. Darüber hinaus kann bei bekannter Aggregationszahl die Verteilungsbreite erhalten werden. Im theoretischen Teil wird ein einfacher, aber vorher nicht bekannter Weg für die Herleitung der Relaxationsgleichung vorgestellt. Die langsame Relaxationszeit τ2 ist wesentlich bedingt durch die Konzentration der Oligomeren im Verteilungsminimum, die als Mizellkeime angesehen werden können. Die Konzentration dieser Keime läßt sich aus den Messungen gewinnen, und aus der Temperaturabhängigkeit von τ2 erhält man die Reaktionsenthalpie für die Keimbildung. Die relativ komplizierte Abhängigkeit der beiden Relaxationszeiten von den Parametern Totalkonzentration, Temperatur und Gegenionenkonzentration läßt sich quantitativ mit den beiden Relaxationsgleichungen beschreiben und verstehen. Die Untersuchungen führen zu dem überraschenden Ergebnis, daß die Reaktionsenthalpie für die Anlagerung eines MonomerenδH1 an ein bereits vorhandenes Aggregat von der Größe dieses Aggregats abhängt. Mit wachsender Assoziationszahl variiertΔH1 von positiven zu negativen Werten.SummaryKinetic measurements on alkylpyridiniumhalides are presented and the data are interpreted on the basis of the theory recently developed byG. Aniansson et äl.For most of the studied systems two relaxation times have been observed. Their dependence on surfactant concentration, temperature and concentration of counterions have been investigated.The fast relaxation time τ is characteristic for the shift of the distribution curve in the aggregation space. The total concentration of micelles remains constant during this process. The lifetime of a monomer in the micelle and its rate of insertion can be obtained from this relaxation time. The temperature dependence of τ1 gives the heat of reaction for the insertion of a monomer into the micelle. Furthermore, if the aggregation number of the micelle is known, the distribution width can be calculated too.In the theoretical section, a simple, but previously unknown method for the derivation of the relaxation equation is given.The slow relaxation time τ2 is essentially influenced by the concentration of oligomers at the distribution minimum, which can be regarded as nuclei for micelles. The concentration of these nuclei can be obtained from the measurements, and from the temperature dependence of τ2 the heat of reaction for the formation of the nuclei can be calculated. The relatively complicated dependence of the two relaxation times on the parameters total concentration, temperature and concentration of counterions can be quantitatively described and understood with the two relaxation equations. The investigations led to the surprising result, that the heat of reaction for the association of a monomer to an already existing aggregate depends on the size of this aggregate. With increasing aggregation numberΔH1 varies from positive to negative values.

Phase and aggregation behaviour of alkylglycosides

Abstract Alkylmonoglucopyranosides are the main compounds of technical alkylpoyglucosides. New contributions to crystallisation and thermotropic properties, phase and aggregation behaviour are presented because of their central interest for understanding the technical products. Synchrotron and neutron scattering give a detailed insight into the micelle formation of pure compounds and to the sphere–rod transition as a function of added long chain alcohols. The phase behaviour of the surfactant systems and microemulsions is heavily influenced by traces of ionic surfactants.

The influence of the salt concentration on the aggregation behavior of viscoelastic detergents

Abstract The influence of excess NaCl on the properties of viscoelastic detergent solutions of Cetypyridiniumsalicylate (CPySal) has been studied by static and dynamic light scattering, electric birefringence and rheological measurements. It is obeserved that the rodlike micelles of length L which are present in these solutions and which are responsible for their elastic properties grow in length with the increase of the NaCl concentration. As long as the rods are shorter than their mean distance, their length can be determined from the rheological and electric birefringence measurements. For very small shear fields these solutions behave as Newtonian fluids. The viscosity of the solution increases strongly when the rods begin to overlap. Solutions with overlapping rods are elastic. It is postulated from the results that the cmc II (the critical concentration above which rods are present) and the length L of the rods are partially determined by the intermicellar interaction energy. It is furthermore postulated that this intermicellar interaction energy has an influence on the polydispersity of the rods and seems to make the rods relatively monodisperse.

Kinetic investigations at the cloud point of nonionic surfactants

Abstract Kinetic relaxation measurements using the T-jump technique, electric birefringence, and light-scattering measurements were carried out with aqueous solutions of the neutral detergents C10H21-(OC2H4)4OH, C12H25(OC2H4)4OH, C8H17(OC2H4)4OH, C9H19Ph(OC2H4)5OH, C9H19Ph(OC2H4)8OH, and Triton X-100 (Ph stands for the phenylen group) above and below the cloud point Tc. Two relaxation processes could be detected in the clear solutions below Tc. These processes could be associated with the change of the aggregation number and concentration of micelles according to the theory of Aniansson and Wall. The C12E4 system shows electric birefringence below Tc from which it can be concluded that the micelles are nonspherical. In the turbid solutions above Tc up to six relaxation times could be observed by recording the turbidity as a function of time. These processes could be associated with the normal micellar effects in clear solutions, with the transport of matter to the droplets of the dispersed new phase that is formed above Tc and with the equilibration of the droplets, respectively. The aggregation number of the micelles and the dimensions of the droplets are calculated from the relaxation times. These values agree fairly well with the values obtained from light-scattering measurements.

Preparation of alkyl α- and β-d-glucopyranosides, thermotropic properties and X-ray analysis ☆

Abstract Monohydrates of heptyl to decyl α- d -glucopyranosides as obtained from product mixtures of the Fischer glucosylation were crystallized from water at the Krafft point. The results of the single-crystal X-ray analysis of anhydrous α anomers and their monohydrates provide for a better understanding of crystal formation and stability of their hydrates. The preparation of alkyl β- d -glucopyranosides—without concomitant formation of α anomers as by-products—has been described. The thermotropic properties have been investigated for the α compounds and their monohydrates, and for the β- d -glucopyranosides.

Crystal structures and thermotropic properties of alkyl α-d-glucopyranosides and their hydrates

Thermotropic properties and crystal structures of alkyl alpha-D-glucopyranosides and their hydrates were estimated by X-ray, DSC and thermogravimetric measurements (TGA). Monohydrates rapidly lose their crystal water several degrees below the melting point of the anhydrous glucopyranosides. The melting points of the monohydrates measured in DSC pressure cells (chain length longer than seven) are lower, and the clearing points higher than those of the anhydrous glucosides. Layer distances of smectic and crystalline phases of anhydrous compounds were established. Melting points, densities and layer distances of the crystalline anhydrous glucopyranosides display strong even-odd effects. The strong decrease of these effects in the case of the monohydrates can be elucidated by the results of X-ray crystal structure analysis.

Electron microscopic and light scattering observation on a system with two iridescent phases

Electron microscopic observations and classical light-scattering measurements have been carried out for dodecyldimethylaminoxide/hexanol/water mixtures in the concentration range where iridescent colors occur. This system has two different iridescent phases. The iridescent phase with more hexanol forms quickly, and the phase with less hexanol forms very slowly. Three different isotropic phases which show strong flow birefringence are found near both iridescent phases. The electron microscopic pictures show clearly that only one of these isotropic phases with strong flow birefringence is a bicontinuous sponge phase (L3h-phase). This is the phase which comes out by adding some alkanol to the upper lamellar phase. The flow birefringent phase below the lower lamellar phase forms unilamellar vesicles. The flow birefringent phase which occurs between both iridescent phases contains multilamellar vesicles and is shown to be a precursor of a lamellar phase.

Gel-like rheological behavior of mesophases in photoreactive azodye/water/KCl systems

Publisher Summary Chapter describes dyes, which are useful as dyestuffs, paints, and coloring materials on various industrial applications. Especially, azo-dyes are photoreactive compounds which induce photochromic cis-trans isomerization. Amphiphiles including azo-dye as a rigid spacer form bilayers in aqueous dispersions and supramolecular assemblies in aqueous methanol solutions. The amphiphilic azo-dye in aqueous methanol solutions forms rodlike swarms at low amphiphilic azo-dye concentrations and liquid crystals at high amphiphilic azo-dye concentrations. This chapter illustrates a phase diagram for ternary systems of azo-dye Levafix Goldgelb E-G (F9)/water/KCl. The ternary systems of dilute F9 concentrations display three isotropic (Li, sb, and L3mBl) phases, an anisotropic (L α) phase, and an inhomogeneous (L α+ qlc) phase. The chapter also describes the investigation of the rheological behavior by oscillatory measurements and shear stress–strain examinations. In addition of viscoelastic behavior, apparent yield stress is observed for L3mBl and L α phases. While the rheological behavior is independent of KCl concentration, it strongly depends on the F9 concentration. The storage modulus, loss modulus, and apparent yield stress are scaled against F9 concentration over L3mBl and L α phases, indicating the existence of gel-like structure.