Anja Hörmann

Technische Universität Berlin

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Michael Gradzielski

Technische Universität Berlin

Sylvain Prévost

European Synchrotron Radiation Facility

Ingo Hoffmann

Institut Laue-Langevin

Dominic W. Hayward

Forschungszentrum Jülich

Ralf Schweins

Institut Laue-Langevin

Albert Prause

Technische Universität Berlin

E. Lewitzki

Max Planck Institute of Biophysics

Peggy Heunemann

ETH Zurich

Andreas F. Thünemann

Federal Institute For Materials Research and Testing

Markus von Raumer

Idorsia (Switzerland)

Cooperative Institutions

Technische Universität Berlin

Institut Laue-Langevin

University of Bristol

Centre National de la Recherche Scientifique

Institut Langevin

European Synchrotron Radiation Facility

University of Potsdam

Freie Universität Berlin

CEA Paris-Saclay

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

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Incorporation and structural arrangement of microemulsion droplets in cylindrical pores of mesoporous silica

Molecular Physics (2021)

Albert Prause Anja Hörmann Viviana Cristiglio Glen J. Smales Andreas F. Thünemann

The behaviour of microemulsion (ME) droplets in mesoporous systems is highly important for understanding the immobilisation of drugs or chemical formulations, cleaning processes or enhanced oil recovery. The loading of pores as well as the structural organisation of MEs within the pores is a relevant parameter, especially for immobilisation applications. For this reason, the uptake of microemulsions in cylindrical pores of SBA-15 was investigated via adsorption and small-angle neutron scattering (SANS). Adsorption isotherms revealed an adsorption of the microemulsion droplets based on the adsorption of surfactant as a driving force. The adapted scattering model is based on the analysis of bare SBA-15 in full contrast conditions and employs microemulsions inside of SBA-15 measured at the silica contrast matching point. Accordingly, the structural arrangement of microemulsion droplets in the pores of SBA-15 was determined in good detail. Microemulsion droplets smaller than the pore size access the pores while retaining their spherical shape and become increasingly ordered for higher loading, where the droplets arrange in a dense packing of spherical droplets in a cylindrical pore. Interestingly, microemulsion droplets larger than the pore size can easily be incorporated, but become deformed upon entering and are present as elongated rod-like structures.

Microemulsion

10.1080/00268976.2021.1913255

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Citations (7)

A temperature-controlled electric field sample environment for small-angle neutron scattering experiments

Review of Scientific Instruments (2021)

Dominic W. Hayward Germinal Magro Anja Hörmann Sylvain Prévost Ralf Schweins

A new sample environment is introduced for the study of soft matter samples in electric fields using small-angle neutron scattering instruments. The sample environment is temperature controlled and features external electrodes, allowing standard quartz cuvettes to be used and conducting samples or samples containing ions to be investigated without the risk of electrochemical reactions occurring at the electrodes. For standard 12.5 mm quartz cuvettes, the maximum applied field is 8 kV/cm, and the applied field may be static or alternating (up to 10 kHz for 8 kV/cm and up to 60 kHz for 4 kV/cm). The electric fields within the sample are calculated and simulated under a number of different conditions, and the capabilities of the setup are demonstrated using a variety of liquid crystalline samples. Measurements were performed as a function of temperature and time spent in the electric field. Finally, the advantages, drawbacks, and potential optimization of the sample environment are discussed with reference to applications in the fields of complex soft matter, biology, and electrorheology.

Cuvette

Soft matter

Sample (material)

10.1063/5.0040675

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Citations (6)

Adsorption Kinetics of Oppositely Charged Hard and Soft Nanoparticles with Phospholipid Membranes

Langmuir (2021)

Marek Bekir Anja Hörmann Christoph Brückner Ingo Hoffmann Sylvain Prévost

Nanoparticles (NPs) have great potential for biological applications as typically they exhibit strongly size-dependent properties. Specifically, the interaction of NPs with phospholipid membranes is significantly relevant to nanomedicine and the related field of nanotoxicology. Therefore, the investigation of interactions of NPs with model membranes is not only fundamentally important but also practically valuable to understand interactions of NPs with more complex cell membranes. Here, we report on the interaction of anionic vesicles of different charge densities and cationic SiO2 NPs, either covered by a bare surface functionalized with amino moieties (-NH2) or covered by poly[2-(dimethylamino) ethyl methacrylate]. We studied the kinetics of binding of NPs to the vesicle surface by time-resolved scattering experiments. A key result of the study is that binding is favored in the presence of electrostatic attraction, but the polymer layer decreases the binding rate drastically.

Cationic polymerization

Surface charge

Receptor–ligand kinetics

POPC

10.1021/acs.langmuir.0c03553

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Citations (4)

Kinetics of Oil Exchange in Nanoemulsions Prepared with the Phase Inversion Concentration Method

Langmuir (2016)

Ingo Hoffmann Miriam Simon Anja Hörmann Thorsten Klaus Otto Gravert Peggy Heunemann

Nanoemulsions (NEs) are metastable emulsions with droplet sizes between 20 and 100 nm and with a wide range of applications, for example, in polymerization, in pharmaceutical and cosmetic formulations, and as drug delivery systems. Even though they are not in thermodynamic equilibrium, they can be metastable over relatively long times and have the advantage that they can be formed easily by low energy input methods. In particular, the phase inversion concentration (PIC) method allows the formation of NEs by the dilution of a suitable mixture of oil and surfactants with water. In this paper, we investigate the kinetics of the oil exchange process of NEs formed by the PIC method by looking at the exchange of different hydrophobic oils and by employing contrast variation stopped flow small-angle neutron scattering. These experiments demonstrate that this exchange becomes substantially slower by increasing the chain length of the alkane. This indicates a mechanism where monomer exchange is relevant, which would indicate also that for aging one would expect Ostwald ripening to be the determining factor. Such investigations can be carried out in a unique fashion by means of neutron scattering, and the results have important implications for the optimization of NE formulations.

Ostwald ripening

Metastability

Dilution

Phase inversion

10.1021/acs.langmuir.6b03009

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Citations (7)

Journal of Thermal Analysis and Calorimetry (1999)

E. Grell E. Lewitzki Markus von Raumer Anja Hörmann

Endothermic process

Amphiphilic molecule

10.1023/a:1010158312153

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Citations (9)

High unimer concentration and asymmetric bilayer observed in small unilamellar vesicles of mixed surfactants TDMAO/LiPFO

The Journal of Chemical Physics (2023)

Anja Hörmann Artem Feoktystov Theyencheri Narayanan Jérémie Gummel Michael Gradzielski

The mixed surfactant system of tetradecyldimethylamine oxide (TDMAO) and lithium perfluorooctanoate (LiPFO) is known to spontaneously self-assemble into well-defined small unilamellar vesicles. For a quantitative analysis of small-angle x-ray scattering on this model system, we complemented the measurements with densitometry, conductimetry, and contrast-variation small-angle neutron scattering. The analysis points to two main findings: first, the vesicles formed to contain a much higher mole fraction (0.61-0.64) of TDMAO than the bulk sample (0.43) and predicted by Regular Solution Theory (RST, 0.46). In consequence, the unimer concentration of LiPFO is more than 5 times higher than predicted by RST. Second, the vesicle bilayer is asymmetric with a higher fraction of LiPFO on the outside. These findings on a model system should be of broader relevance for the understanding of similar mixed surfactant vesicle systems and thereby also be of importance for their use in a number of applications.

Small-angle X-ray scattering

Mole fraction

Small-Angle Scattering

10.1063/5.0150223

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