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Siegel der Universität
Department für Chemie - Arbeitsgruppe Prof. Strey

Dr. Helge Klemmer

Physical Chemistry
University of Cologne
Luxemburger Str. 116
D-50939 Cologne

Tel.:  +49-(0)-221-470-6308
Fax:  +49-(0)-221-470-5104

email: helge.klemmer(at)uni-koeln.de

field of activity: complex fluids

 

 

Research topics

  • Formation kinetics of self-aggregation

In contrast to their equilibrium properties, hardly anything is known about the formation kinetics of self-aggregating systems like microemulsions. The equilibration is nevertheless a key parameter for processes like template strategies to produce nanoparticles and nanofoams or for the load-dependent introduction of water into Diesel fuel. Hence, the the results of the analysis of the formation kinetics can be utilized to counter aging phenomena like Ostwald ripening during foaming processes or to optimize the combustion of microemulsion fuels.

 

 

Fig. 1: Time-resolved neutron scattering data of the mixing of two unstructured precursor solution (D<sub>2</sub>O und C<sub>10</sub>E<sub>5</sub>/cyclohexane) to form the oil-rich nonionic microemulsion D<sub>2</sub>O - cyclohexane - C<sub>10</sub>E<sub>5</sub> (pentaethylenglycolmonodecylether) measured at D33, ILL Grenoble using a BioLogic SFM 300 stopped-flow in bulk- (left) und flmcontrast (right). During the course of the formation the internal interface forms spontaneously below the intstrumental dead time. Then a transition from a highly polydisperse, bimodale droplet mixture to a normal droplet microemulsion takes place, that can be associated with the water-uptake of the system.
  • Time-resolved scattering techniques in combination with stopped-flow (experiments and method development)

 

To analyse the formation kinetics of self-aggregating systems a number of different techniques can be used, like periodically oscillating pressure jumps, temperature jumpfs or stopped-flow. In case of microemulsions their high temperature sensitivity has to be accounted for. Furthermore the instrumental dead time has to be as low as possible. Hence, for an optimal analysis  continiously improved detection head pieces with a high degree of temperature stability are essential. As a result it is an important aim to develope the optimal head piece in cooperation with the precision machine workshop of this Institute.

 

 

 

 

Current stopped-flow detection head piece on top of a BioLogic SFM300 at the D33, ILL, Grenoble.
Various stopped-fow detection head pieces: original temperature unstable head piece (left), highly temperature stable SANS head piece (middle) and highly temperature stable light scattering head piece including an index match bath and simultaneous multiangle detection (right).
  • Amphiphilic, high molecular weight polymers and macromolecules and their influence on self-aggregated nanostructures and their formation kinetics

 

Amphiphilic high molecular weight polymers and related macromolecules like proteins are known for their membrane activity. Here, just as it is the case for simple microemulsions, the equilibrium properties are extensively studied. However, the integration kinetics of such molecules into surfactant or lipid membranes and other interfaces as well as their influence on self-aggregation processes have been subject to hardly any study. Based on the enormous technological and biological relevance of these processes, it is a major aim to resolve the processes with time-resolved scattering techniques.

 

 

 

Research interest

Our everyday life is shaped by self-aggregation and related processes. Starting from such obvious situations as washing and cleaning, via food applications or pharmaceutics up to high impact research such as the production of nanostructured isolation materials or complex medical questions such as membrane protein transport disorders a deep knowledge of the basic physical chemistry behind it is the key strategy to tackle the corresponding challenges. Throughout the last 150 years researcher like Lord Rayleigh, Pockels, Langmuir, Winsor, Hoar, Schulman and finally Kahlweit and Strey, to name a few, created a vast collection of fundamental knowledge regarding amphiphilic self-aggregation. Here equilibrium properties such as phase behavior, nanostructure or interfacial tension were analyzed experimentally while precise theories were developed to describe all occurring phenomena. However, the non-equilibrium properties, such as the formation kinetics of self-aggregating systems and processes, are hardly studied so far, except for processes like the formation of vesicles starting from micellar aggregates.

By combination of time-resolved light, neutron and x-ray scattering techniques and a modified ultra-fast and highly temperature stable stopped-flow setup, we were for the first time able to resolve the formation of microemulsion systems with different nanostructures by mixing completely unstructured precursor solution. Although even the fastest neutron scattering setup available at the ILL, Grenoble still has a too long dead-time to completely resolve the formation process, several key features of the formation process of oil-rich nonionic microemulsion could be resolved: While the interface forms in less a few milliseconds, structural reorganisation takes place afterwards and is, just like the corresponding water-uptake, a strong function of the interfacial tension between the precursor solutions as well as the other membrane properties. By addition of amphiphilic high molecular weight polymers, it could furthermore be shown, that an increased membrane stiffness results in a deceleration of the still complex formation kinetics. Currently, these finding are transferred to water-rich nonionic systems in new systematic experiments, while simultaneously changing the systems to more and more life-like membranes, with the final goal, to resolve the integration of proteins into a membrane in situ and maybe even in vivo. Here, as in all other experimental series, systematic contrast variation are key to gaining as much detail about the kinetics as possible. By understanding the integration mechanism of proteins into membranes, it might even be possible, to counter the effect of membrane protein transport disorders or prevent these diseases at all.

 

 

PhD thesis

Amphiphilic Polymers in Microemulsions:

The Influence on Structure and Formation Kinetics

 

Microemulsions are thermodynamically stable, macroscopically isotropic, nano?structured mixtures of at least three components. They excel due to their multifarious nanostructure and ultra?low interfacial tension which goes hand in hand with a high solubilisation capacity. Despite their obviously high application potential, they are not appealing for industry, as their formation requires ? compared to marco?emulsions ? high surfactant loads. About 15 years ago it was found that the solubilization capacity can be strongly increased by the addition of amphiphilic block copolymers. In this thesis the effect of polymers of the structure motive poly(ethylenebutylene) ? poly(ethyleneoxide) (PEBx ? PEOy) on oil?rich microemulsions and in particular the closed loop was studied. Surprisingly, it was found that the closed loop diminishes through the addition of polymers. Thus, although the polymer increases the solubilization capacity of surfactants strongly, the phase behaviour in the oil?rich part of the phase diagram resembles that of microemulsions containing inefficient short-chain surfactants like C6E2. An essential drawback of the polymer addition is the stabilization of various mesophases that cover large parts of the phase space. In this thesis prove was given that newly derived so called tapered diblock copolymers increase the efficiency significantly, while simultaneously suppressing the formation of lamellar phases. Parallel to the elucidation of the influence of amphiphilic polymers on the equilibrium properties of microemulsions, the structural formation kinetics of oil-rich non-ionic microemulsions and the influence of amphiphilic polymers thereupon were studied. Therefore an ultra-fast stopped?flow setup was upgraded with the possibility to monitor the formation of microemulsions by transmitted light, scattered light and small angle scattering. Utilizing time?resolved small angle neutron scattering measurements it was found that after already 20 ms the microstructure (water?in?oil micelles) exists and undergoes and aspect ratio change to more elongated micelles resulting in the final microstructure. Detailed analysis of the scattering data revealed that the addition of amphiphilic polymers increases the nevertheless still very fast formation times. Though not all trends observed in neutron scattering could be detected by transmitted and scattered light, in general they confirmed the observed phenomena and formation rates.

 

 

Diploma thesis

Wetting microemulsions from sugar?water, triglycerides and lecithin

 

Most people became aware of the healthiness of their food. Thus, it is a primary wish in nutrition industry to include more valuable ingredients into food. Microemulsions are a powerful tool to introduce these components in nutrition, e.g. water in order to reduce the fat content. However, edible microemulsions can be formulated at high surfactant mass fractions only. Therefore, Strey, Schetzberg and Klemmer found a way to reduce the amount of surfactant needed by applying a three-phase or lamellar phase region of food?grade microemulsions (so called X?mas principle). It is a mighty tool to make otherwise immiscible components miscible, by shielding them from each other. Suitable food?grade microemulsions based on phospholipids and triglycerides inspired by Schetzberg are formulated by starting with a well known model system and changing it stepwise to an edible system based on triolein and finally, cocoa butter. Thus, this work presents the formulation of a phospholipid based long?chain triglyceride microemulsion appropriate to use the X?mas principle in chocolate. A wetting microemulsion is necessary to achieve a complete shielding. Astonishingly, it was shown that the middle-phase of these systems wets. This property is temperature invariant as well as not affected by changing the composition of the surfactant mixture or the water content of these microemulsions. In addition a variety of multiphase regions has been observed (different three?, a four? and a five?phase region) in the systems. Performed SANS measurements proved that a L3?phase coexistence with a bicontinuous phase. All observed phases within the developed three-phase microemulsions can be used as an expandible reservoir to be swollen with water.

 

 

Publications

Patents:

  • WO/2012/082866,

    U. Loeser, G. Fischer, K. Paggios, H. Klemmer, S. Schetzberg, R. Strey, M. Seyller, F. Ullrich


    "Process for making low-calorie confectionery product and confectionery product"

 Presentations:

  • H. Klemmer, T. Sottmann, R. Strey, I. Grillo

    Formation kinetics of oil-rich, non-ionic microemulsions and the influence of additives

    Surfactants in Solution 2014, Coimbra, Portugal, 2014

  • H. Klemmer, T. Sottmann, R. Strey, I. Grillo

    Formation kinetics of oil-rich microemulsions: Rapid mixing study by time-resolved SANS

    86th ACS Colloid & Surface Science Symposium, Baltimore, USA, 2012