Transition from a Sponge-Like to an Onion-Like Nanostructure in the L Phase - Part I.

Hypothesis: In the phase diagram of the system HO/NaCl - AOT (sodium bis(2-ethylhexyl) sulfosuccinate) a homogeneous L channel can be detected at T = 25 °C as a function of the surfactant and the NaCl mass fraction. Our hypothesis is that a structural transition from a sponge-like to an onion-like structure occurs in this channel.

Experiments: We (a) determined the relevant part of the phase diagram, (b) carried out electrical conductivity and viscosity measurements, (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM) and freeze fracture direct imaging (FFDI), (d) determined the characteristic length scales from Small Angle Neutron Scattering (SANS) curves.

Experimental evidence of a transition from a sponge-like to a foam-like nanostructure in water-rich L phases.

Hypothesis: The micrometer-sized gas bubbles of a liquid foam with a dispersed gas phase of > 74 vol% are polyhedral and surrounded by a continuous aqueous phase. The structure of a water-rich microemulsion with a water phase of > 74 vol% normally consists of oil droplets in water or is bicontinuous. We hypothesize that at these high water contents polyhedral water droplets in oil can also exist.

Formation Kinetics of Oil-Rich, Nonionic Microemulsions.

The formation kinetics of oil-rich, nonionic microemulsions were investigated along different mixing pathways using a fast stopped-flow device in combination with the new high-flux small-angle neutron spectrometer D33 (ILL, Grenoble, France). While the kinetics along most pathways were too fast to be resolved, two processes could be detected mixing brine and the binary cyclohexane/C10E5 solution. Here, too, the formation of large water-in-oil droplets was found to be faster than 20 ms and therewith faster than the accessible dead time.

A Journey toward Sulfolane Microemulsions Suggested as Inert, Nonaqueous Reaction Media.

Recently, it turned out that nanostructured reaction media containing highly inert solvents as tetrahydrothiophen-1,1-dioxide (sulfolane) are beneficial for strongly oxidizing or reductive reactions. Because of their ability of solubilizing polar and nonpolar solvents with a large nanostructured interface in particular microemulsions provide such interesting reaction media. Starting from the pseudoternary microemulsion H2O-n-octane-C12E4/C12E5 (polyoxyethylene n-alkyl ether), water was successively replaced by the highly inert tetrahydrothiophen-1,1-dioxide (sulfolane).

Co-condensation of nonane and D2O in a supersonic nozzle.

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 Jmax of nonane, 9.

Controlling the self-assembly of magnetic nanoparticles by competing dipolar and isotropic particle interactions.

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.

Kinetics of pressure induced structural changes in super- or near-critical CO2-microemulsions.

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.

Homogenous nucleation rates of n-propanol measured in the Laminar Flow Diffusion Chamber at different total pressures.

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.

Singlet oxygen photo-oxygenation in water/pluronic F-127 hydrogels: increased reaction efficiency coupled with a switch in regioselectivity.

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.

Nucleation of ethanol, propanol, butanol, and pentanol: a systematic experimental study along the homologous series.

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.

Freezing water in no-man's land.

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.

Microstructure of supercritical CO2-in-water microemulsions: a systematic contrast variation study.

Microemulsions of the type H(2)O-scCO(2)-surfactant are potential candidates for novel solvent mixtures in the field of green chemistry. Furthermore, scCO(2)-microemulsions are highly interesting from a fundamental point of view since their properties such as the bending elastic constants can be strongly influenced solely by varying the pressure without changing the components. With this motivation we studied the phase behavior and the microstructure of water-rich scCO(2)-microemulsions.

Soft fluctuating surfactant membranes in supercritical CO2-microemulsions.

The bending rigidity of surfactant membranes in novel bicontinuous CO(2)-microemulsions of the type H(2)O/NaCl-scCO(2)-Zonyl FSH/Zonyl FSN 100 was determined using both high pressure small angle neutron scattering and neutron-spin echo spectroscopy. As an important result it was found, that the stiffness of the membrane increases solely by an increase of the pressure.

Homogeneous water nucleation in a laminar flow diffusion chamber.

Homogeneous nucleation rates of water at temperatures between 240 and 270 K were measured in a laminar flow diffusion chamber at ambient pressure and helium as carrier gas. Being in the range of 10(2)-10(6) cm(-3) s(-1), the experimental results extend the nucleation rate data from literature consistently and fill a pre-existing gap. Using the macroscopic vapor pressure, density, and surface tension for water we calculate the nucleation rates predicted by classic nucleation theory (CNT) and by the empirical correction function of CNT by Wolk and Strey [J.

Phase behaviour of propane- and scCO(2)-microemulsions and their prominent role for the recently proposed foaming procedure POSME (Principle of Supercritical Microemulsion Expansion).

In this study we present a systematic investigation of the phase behaviour of microemulsions containing near- or supercritical solvents. The starting point of this study are microemulsions of the type water/NaCl-propane-polyethyleneglycol mono-n-alkyl ether at a pressure of p = 220 bar. Replacing propane stepwise by supercritical carbon dioxide the typical phase behavior of microemulsions systems can still be observed using scCO(2) as the only nonpolar solvent.

Argon nucleation in a cryogenic supersonic nozzle.

We have measured pressures p and temperatures T corresponding to the maximum nucleation rate of argon in a cryogenic supersonic nozzle apparatus where the estimated nucleation rates are J=10(17+/-1) cm(-3) s(-1). As T increases from 34 to 53 K, p increases from 0.47 to 8 kPa.

Homogeneous nucleation of a homologous series of n-alkanes (C(i)H(2i+2), i=7-10) in a supersonic nozzle.

Homogeneous nucleation rates of the n-alkanes (C(i)H(2i+2); i=7-10) were determined by combining information from pressure trace measurements and small angle x-ray scattering (SAXS) experiments in a supersonic Laval nozzle. The condensible vapor pressure p(J max), the temperature T(J max), the characteristic time Deltat(J max), and supersaturation S(J max) corresponding to the peak nucleation rate J(max) were determined during the pressure trace measurements. These measurements also served as the basis for the subsequent SAXS experiments.

Crossover from nucleation to spinodal decomposition in a condensing vapor.

The mechanism controlling the initial step of a phase transition has a tremendous influence on the emerging phase. We study the crossover from a purely nucleation-controlled transition toward spinodal decomposition in a condensing Lennard-Jones vapor using molecular dynamics simulations. We analyze both the kinetics and at the same time the thermodynamics by directly reconstructing the free energy of cluster formation.

Homogeneous nucleation of nitrogen.

We investigated the homogeneous nucleation of nitrogen in a cryogenic expansion chamber [A. Fladerer and R. Strey, J.

Evaluating nucleation rates in direct simulations.

We compare different methods for obtaining nucleation rates from molecular dynamics simulations of nucleation, using the condensation of Lennard-Jones argon as an example. All methods yield the same nucleation rate at the conditions where they can be applied correctly, with discrepancies smaller than a factor of 2. We critically examine the different approaches and highlight their respective strengths and possible limitations.

Using small angle x-ray scattering to measure the homogeneous nucleation rates of n-propanol, n-butanol, and n-pentanol in supersonic nozzle expansions.

In our earlier publication [M. Gharibeh et al., J.

Microemulsions with alkyldimethyl phosphine oxides and alkyldiethyl phosphine oxides.

Alkyldimethyl phosphine oxides (C n DMPO) as well as alkyldiethyl phosphine oxides (C n DEPO) with chain lengths of n = 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) were synthesized and purified to study how the formation of microemulsions depends on the size of the headgroup and on the length of the alkyl chain. For that purpose, equal amounts of water and n-octane were taken and surfactant was added to solubilize the two solvents. The resulting fish-shaped phase diagrams for C 10DEPO, C 12DEPO, and C 14DEPO show that the longer the hydrophobic chain the more efficient the surfactant.

Gelled polymerizable microemulsions. 2. Microstructure.

Using bicontinuous microemulsions as templates opens a new field for the design of novel structures and thus novel materials, but has significant challenges due to the very small composition and temperature windows in which microemulsions are bicontinuous. In previous work we had shown that we can take a ternary base system (water-n-dodecane--C 13/15E 5), add monomer and cross-linker ( N-isopropylacrylamide and N, N'-methylenebisacrylamide) to the water phase, and add a gelator (12-hydroxyoctadecanoic acid) to the oil phase while remaining in the one-phase region of the phase diagram. It was also possible to allow the gelator to form an organogel by changing the temperature such that we crossed the sol--gel line, which fell within the one-phase region.