R. Strey

University of Cologne, Köln, North Rhine-Westphalia, Germany

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Publications (269)681.62 Total impact

  • Anna Klemmer · Helge Klemmer · Reinhard Strey · Peter Schmiedel
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    ABSTRACT: Nanoemulsions were observed in simple dilution experiments, mimicking the flushing step in washing. The used low-energy method takes advantage of the ultra-low interfacial tension of the three-phase region of the underlying microemulsion systems similar to the well-known PIC method but boosted by a simultaneous temperature jump. Following the aging of the nanoemulsions with time-resolved dynamic light scattering, a slow radial growth of order 10-5 nm/s and, more interestingly, a monomodal and quite narrow distribution of the formed oil droplets was observed, which was also confirmed with SANS measurements. The most astonishing observation was, however, that the aging kinetics of the droplet radius is linear in time (i.e. r ~ t). This is in contrast to the typical aging mechanisms, Ostwald ripening or coagulation, where the volume is linear with time (i.e. r 3 ~ t). Preliminary ideas regarding this unexpected and unconventional mechanism are discussed. Graphical abstract Nanoemulsion droplets formed by simultaneous dilution and temperature jump of a microemulsion including ionic and nonionic surfactants during washing. Surprisingly, they show linear radial growth as a function of time in contrast to all known aging mechanisms
    No preview · Article · Oct 2015 · Colloid and Polymer Science
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    ABSTRACT: Recently, it turned out that nano-structured reaction media containing highly inert solvents as tetrahydrothiophen-1,1-dioxid (sulfolane) are needed in strongly oxidizing or reductive reactions. Due to their ability of solubilizing polar and nonpolar solvents with a large nano-structured interface in particular microemulsions provide such interesting reaction media. Starting from the pseudo-ternary microemulsion H2O - n-octane - C12E4/C12E5 (polyoxyethylene n-alkylether) water was successively replaced by the highly inert tetrahydrothiophen-1,1-dioxid (sulfolane). We found that an increasing sulfolane content drives the system beyond the tricritical point. Replacing the already long chain surfactants C12E4 and C12E5 by a mixture of the even longer chain surfactants C18E6 and C18E8 we were able to prepare non-aqueous sulfolane-microemulsions for the very first time. We also teach how in a second step the phase behavior of the hydrophilic sulfolane - n-octane - C18E8 system can be tuned at constant temperature (as required by the reaction conditions) by addition of the hydrophobic cosurfactant 1-octanol (C8E0). The change in curvature by adding 1-octanol is demonstrated measuring the size of reverse micelles by DLS exhibiting radii which vary from at least 8 nm to 16 nm suitable sizes for inverse nano-reaction vessels.
    No preview · Article · Sep 2015 · Langmuir
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    ABSTRACT: Microemulsions with supercritical CO2 are promising alternatives for organic solvents, especially if both polar and non-polar components need to be dissolved. However, only fluorinated surfactants, which are known to be environmentally unfriendly, are appropriate to formulate well-structured microemulsions. While most approaches to increase the environmental performance of CO2-microemulsions deal with the design of new surfactants with a reduced degree of fluorination, we discovered that the partial substitution of CO2 by cyclohexane enables a considerable reduction of fluorinated surfactants. Thereby the most efficient solubilization of the CO2/cyclohexane mixture, which turned out to be pressure-dependent, was found at a cyclohexane-to-CO2 mass ratio between 1:6 and 1:4. In order to elucidate this unexpected effect a systematic small angle neutron scattering contrast variation study was performed. The analysis of the recorded scattering curves by the Generalized Indirect Fourier Transformation clearly shows that the scattering length density profiles differ considerably from scCO2-microemulsions without cyclohexane. Instead of a nearly constant scattering length density, a density profile that varies systematically over half of the droplet radius was detected. These results clearly indicate that the observed efficiency boosting is caused by the formation of a depletion zone of cyclohexane close to the fluorinated amphiphilic film.
    Preview · Article · Jan 2015 · Physical Chemistry Chemical Physics
  • Regina Schwering · David Ghosh · Reinhard Strey · Thomas Sottmann
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    ABSTRACT: Dynamic self-assembled structures found in complex fluids containing surfactant, water, and oil range from spherical and cylindrical aggregates to bicontinuous microemulsions and ordered liquid crystalline phases. These structures are extensively used as templates for the synthesis of nanomaterials. However, the topology of the initial structures and in particular their characteristic length scales often undergo significant changes during polymerization. Increasing the microemulsion viscosity should slow down its reorganization kinetics and, therewith, help to maintain the microemulsion nanostructure during the polymerization process. In this work, we report on systematic phase behavior studies of a new class of highly viscous microemulsions that comprise of surfactant, polymerizable oil, and concentrated water/(sucrose/trehalose) solutions. It is found that the substitution of H2O by sucrose/trehalose shifts the phase boundaries of nonionic microemulsions to lower temperatures, while the opposite trend holds for ionic microemulsions. Our systematic studies revealed that hydrophilic nonionic alkyl glycosides are the most suitable candidates for the preparation of highly viscous and polymerizable microemulsions.
    No preview · Article · Jan 2015 · Journal of Chemical & Engineering Data
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    ABSTRACT: We follow the nucleation of n-alcohols, n-propanol through n-pentanol, in two sets of supersonic nozzles having differing linear expansion rates. Combining the data from static pressure trace measurements with small angle X-ray scattering we report the experimental nucleation rates and critical cluster sizes. For n-propanol, position resolved measurements clearly confirm that coagulation of the 2 - 10 nm size (radius) droplets occurs on the timescale of the experiment but that the effect of coagulation on the results is minimal. Under the conditions of the current experiments, our results suggest that alcohols have critical clusters that range from the dimer (n-pentanol) to the hexamer (n-propanol). We then compare the experimental results with classical nucleation theory (CNT), the Girshick-Chiu variant of CNT (GC) and the mean field kinetic nucleation theory (MKNT). Both CNT and MKNT underestimate the nucleation rates by up to 5 and 7 orders of magnitude, respectively, while GC theory predicts rates within 2 orders of magnitude. Correspondingly, the critical cluster size for all alcohols is over-predicted by factors of 2 - 9 with agreement improving with increasing chain length. An interesting byproduct of our experiments is that we find that the coagulation rate is enhanced by a factor of 3 over the value one would calculate for the free molecule regime.
    No preview · Article · Oct 2014 · The Journal of Physical Chemistry B
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    ABSTRACT: The incorporation of surface-functionalized spindle-like hematite nanoparticles as particulate cross-linkers in poly(acrylamide) hydrogel matrices delivers ferrogels with a covalent type of particlematrix interaction. By systematic investigation of the stability and the internal architecture of the resulting gels, the regime of resilient gels is identified. The swelling properties and the rheological behavior are in accordance with a network structure based on particle nodes interlinked by long polymer segments and a significant fraction of loops.
    No preview · Article · Oct 2014 · Macromolecules
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    ABSTRACT: No abstract is available for this article.
    Full-text · Article · Sep 2014 · Chemie Ingenieur Technik
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    ABSTRACT: Control over the self-assembly of magnetic nanoparticles (MNP) into superstructures due to different types of coupling is of interest in the development of "bottom-up" fabrication schemes. Here we realize a simple strategy for the systematic variation of particle interaction potential in magnetic nanoparticles. This is achieved by varying the effective surface potential by means of a co-surfactant introduced in the course of the synthesis process. As a consequence, the ability to form chain-like assemblies is affected by the resulting balance of attractive and repulsive forces. We use electron microscopy, electron diffraction, and light scattering methods to study a series of cobalt nanoparticles as a characteristic example of ferromagnetic MNP. We demonstrate experimentally and substantiate theoretically that the observed behavior results from a balance between magnetic dipole-dipole, steric, and electrostatic interactions.
    No preview · Article · Aug 2014 · Journal of Colloid and Interface Science
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    ABSTRACT: CO2-microemulsions show strong pressure dependent properties. Using time-resolved SANS to investigate the kinetics of structural changes upon periodic pressure jumps of adjustable amplitude, we found that the compression-induced formation of cylinders occurs on a timescale of one second, whereas the expansion-induced disintegration into CO2 swollen spherical micelles is much faster.
    Preview · Article · Jul 2014 · Physical Chemistry Chemical Physics
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    S Quester · Mohsen Dahesh · R Strey
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    ABSTRACT: We have generated closed-cell microcellular foams from gliadin, an abundantly available wheat storage protein. The extraction procedure of gliadin from wheat gluten, which involves only the natural solvents water and ethanol, respec-tively, is described with emphasis on the precipitation step of gliadin which results in a fine dispersion of mostly spherical, submicron gliadin particles composed of myriad of protein molecules. A dense packing of these particles was hydrated and subjected to an atmosphere of carbon dioxide or nitrogen in a high-pressure cell at 250 bar. Subsequent heating to temperatures close to but still below 100 °C followed by sudden expansion and simultaneous cooling resulted in closed-cell microcellular foam. The spherical gliadin tem-plates along with the resulting foam have been analyzed by scanning electron microscope (SEM) pictures. The size distri-bution of the primary particles shows diameters peaked around 0.54 μm, and the final foam cell size peaks around 1.2 μm, at a porosity of about 80 %. These are the smallest foam cell sizes ever reported for gliadin. Interestingly, the cell walls of these microcellular foams are remarkably thin with thicknesses in the lower nanometer range, thus nourishing the hope to be able to reach gliadin nanofoam.
    Full-text · Article · Jun 2014 · Colloid and Polymer Science
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    ABSTRACT: Nucleation rates of n-propanol were investigated in the Laminar Flow Diffusion Chamber. Nucleation temperatures between 270 and 300 K and rates between 10(0) and 10(6) cm(-3) s(-1) were achieved. Since earlier measurements of n-butanol and n‑pentanol suggest a dependence of nucleation rates on carrier gas pressure, similar conditions were adjusted for these measurements. The obtained data fit well to results available from literature. A small positive pressure effect was found which strengthen the assumption that this effect is attributed to the carbon chain length of the n-alcohol [D. Brus, A. P. Hyvärinen, J. Wedekind, Y. Viisanen, M. Kulmala, V. Ždímal, J. Smolík, and H. Lihavainen, J. Chem. Phys. 128, 134312 (2008)] and might be less intensive for substances in the homologous series with higher equilibrium vapor pressure. A comparison with the theoretical approach by Wedekind et al. [Phys. Rev. Lett. 101, 12 (2008)] shows that the effect goes in the same direction but that the intensity is much stronger in experiments than in theory.
    No preview · Article · May 2014 · The Journal of Chemical Physics
  • J. Wölk · B. E. Wyslouzil · R. Strey
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    ABSTRACT: We provide a brief overview of the extensive scientific research that has been conducted to determine the degree to which pure water can be supercooled and the rates at which the relevant phase transitions occur. Beginning with condensation, we present the homogeneous vapor - liquid nucleation rates measured over 20 orders of magnitude with a variety of experimental devices. Some of the experimental methods used to examine nucleation from the vapor phase can also be used to study freezing. In particular, using a supersonic nozzle (SSN) apparatus we have followed the condensation and subsequent freezing of pure water droplets by combining our normal pressure trace measurements (PTM) with both small angle Xray scattering (SAXS) and Fourier transform infrared (FTIR) spectroscopy. The time dependence of the fraction of frozen droplets yields the volume based nucleation rates for the freezing transition, 7.66.1023 < Jice/cm-3s-1 < 4.23.1024, confirming and extending those reported in the literature.
    No preview · Article · May 2013
  • Laura Maria Feldmar · Judith Wölk · Reinhard Strey
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    ABSTRACT: New measurements of homogeneous nucleation onset data for argon and nitrogen from the cryogenic nucleation pulse chamber have been performed. By reducing the amount of carrier gas in the gas mixture, higher onset pressures and temperatures could be reached. The new results are consistent with older data from the same apparatus and literature data. Carrier gas-free experiments with nitrogen show no associative effects. Interestingly, the classical nucleation theory predicts the onset results of nitrogen more accurately than those of argon, despite argon being the more ideal substance of the two.
    No preview · Article · May 2013
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    ABSTRACT: We study the unary and binary nucleation and growth of nonane–D2O nanodroplets in a supersonic nozzle. Fourier Transform Infrared spectroscopy measurements provide the overall composition of the droplets and Small Angle X-ray Scattering experiments measure the size and number density of the droplets. The unary nucleation rates J max of nonane, 9.4 × 1015 < J max /cm−3 s−1 < 2.0 × 1016, and those of D2O, 2.4 × 1017 < J max /cm−3 s−1 < 4.1 × 1017, measured here agree well with previous results. In most of the binary condensation experiments new particle formation is dominated by D2O, but the observed nucleation rates are decreased by up to a factor of 6 relative to the rates measured for pure D2O, an effect that can be partly explained by non-isothermal nucleation theory. The subsequent condensation of D2O is inhibited both by the increased temperature of the binary droplets relative to the pure D2O droplets, and because the binary droplet surface is expected to be comprised largely of nonane. For the one case where nonane appears to initiate condensation, we find that the nucleation rate is about 50% higher than that observed for pure nonane at comparable p v0, consistent with significant particle formation driven by D2O.
    No preview · Article · May 2013
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    ABSTRACT: Pluronic F-127 hydrogels are highly efficient microenvironments for photochemical reactions, as demonstrated for singlet oxygen reactions of monoalkenes. Nonpolar substrates are localized in the nanosized polymer compartment, which can be visualized by neutron scattering. The efficiency of (1) O(2) reactions is strongly increased for tiglate derivatives and the regioselectivity of the ene reaction of trisubstituted alkenes is completely switched in comparison with solution phase and inverted in comparison with intrazeolite photo-oxygenations.
    No preview · Article · Dec 2012 · Chemistry - A European Journal
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    ABSTRACT: We present homogeneous vapor-liquid nucleation rates of the 1-alcohols (C(n)H(2n+1)OH, n = 2-4) measured in the well-established two-valve nucleation pulse chamber as well as in a novel one-piston nucleation pulse chamber at temperatures between 235 and 265 K. The nucleation rates and critical cluster sizes show a very systematic behavior with respect to the hydrocarbon chain length of the alcohol, just as their thermo-physical parameters such as surface tension, vapor pressure, and density would suggest. For all alcohols, except ethanol, predictions of classical nucleation theory lie several orders of magnitude below the experimental results and show a strong temperature-dependence typically found in nucleation experiments. The more recent Reguera-Reiss theory [J. Phys. Chem. B 108(51), 19831 (2004)] achieves reasonably good predictions for 1-propanol, 1-butanol, and 1-pentanol, and independent of the temperature. Ethanol, however, clearly shows the influence of strong association between molecules even in the vapor phase. We also scaled all experimental results with classic nucleation theory to compare our data with other data from the literature. We find the same overall temperature trend for all measurement series together but inverted and inconsistent temperature trends for individual 1-propanol and 1-butanol measurements in other devices. Overall, our data establishe a comprehensive and reliable data set that forms an ideal basis for comparison with nucleation theory.
    No preview · Article · Aug 2012 · The Journal of Chemical Physics
  • Article: Surfactants

    No preview · Article · Aug 2012 · Current Opinion in Colloid & Interface Science
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    ABSTRACT: We present a study of the structure and local dynamics of dispersed silica nanoparticles in the liquid crystal 4′-pentyl-4-biphenylcarbonitrile (5CB). Electron microscopy and X-ray scattering data demonstrate that the nanoparticles form agglomerates with a fractal structure. Investigation of the local dynamics of the particle agglomerates using X-ray photon correlation spectroscopy reveals pronounced anisotropy in the relaxation rate and aging behaviour. We suggest that the unusual relaxation behaviour is a consequence of the anisotropy of the host solvent.
    No preview · Article · Mar 2012 · Soft Matter
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    ABSTRACT: We report homogeneous ice nucleation rates between 202 K and 215 K, thereby reducing the measurement gap that previously existed between 203 K and 228 K. These temperatures are significantly below the homogenous freezing limit, T(H)≈ 235 K for bulk water, and well within no-man's land. The ice nucleation rates are determined by characterizing nanodroplets with radii between 3.2 and 5.8 nm produced in a supersonic nozzle using three techniques: (1) pressure trace measurements to determine the properties of the flow as well as the temperature and velocity of the droplets, (2) small angle X-ray scattering (SAXS) to measure the size and number density of the droplets, and (3) Fourier Transform Infrared (FTIR) spectroscopy to follow the liquid to solid phase transition. Assuming that nucleation occurs throughout the droplet volume, the measured ice nucleation rates J(ice,V) are on the order of 10(23) cm(-3) s(-1), and agree well with published values near 203 K.
    No preview · Article · Mar 2012 · Physical Chemistry Chemical Physics
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    ABSTRACT: The partial ternary phase diagram of anionic extended surfactant of alkyl polypropylene oxide sulfate C12(PO)4SO4 alone and combined with the cationic hydrotrope, tetrabutyl ammonium bromide with water and decane were determined under ambient conditions. Middle phase microemulsion was formulated using salinity scans in the dilute region of surfactant/brine/decane. Visual inspection as well as cross polarizer and optical microscopy were used to detect anisotropy. Spinning drop tensiometer was used to measure interfacial tension (IFT). The first ternary phase diagram using the extended surfactant alone showed three one phase regions, the anisotropic lamellar liquid crystalline phase, Lα and the isotropic L1 micellar liquid and L3 sponge phase. In the second ternary phase diagram using the extended surfactant combined with tetra butyl ammonium bromide, an isotropic micellar region, L1, appeared in the diluted area of the phase diagram. Meanwhile the Lα phase disappeared completely and the three phase region has a bluish transparent middle phase. Interfacial tension measurements between middle phase and brine, and between decane and brine yielded ultra low values. Calculated IFT values using the characteristic length obtained using De Gennes approximation gave almost half the measured values. The interfacial rigidity was also calculated and compared to values obtained from the literature.
    Full-text · Article · Mar 2012 · Journal of Dispersion Science and Technology

Publication Stats

10k Citations
681.62 Total Impact Points


  • 1997-2015
    • University of Cologne
      • • Department of Chemistry
      • • Institute of Physical Chemistry
      Köln, North Rhine-Westphalia, Germany
  • 2012
    • Institute for Pathology, Cologne
      Köln, North Rhine-Westphalia, Germany
  • 1979-2007
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
  • 2005
    • University of Hull
      Kingston upon Hull, England, United Kingdom
  • 1996
    • Universität Basel
      • Department of Physical Chemistry
      Bâle, Basel-City, Switzerland
  • 1995
    • Lund University
      • Department of Physical Chemistry
      Lund, Skåne, Sweden
  • 1991
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1988
    • University of Tennessee
      • Department of Chemistry
      Knoxville, Tennessee, United States