Marcell Wolf

By means of Grazing Incidence Small Angle Neutron Scattering under hydrostatic pressure (HP - GISANS) and neutron reflectometry at the solid-liquid interface, we compare effects of pressure and temperature on two model homopolymer mixed brush systems in thin (< 100 nm) film geometry: a weakly incompatible (poly(methylmethacrylate) / poly(2-(dimethylamino)ethyl methacrylate)) (PMMA / PDMAEMA) and strongly incompatible ((poly((2,2,3,3,4,4,5,5-octafluoro)pentyl methacrylate))/ poly(2-(dimethylamino)ethyl methacrylate) ) (POFPMA/PDMAEMA) one. A dual responsive, temperature and pressure-sensitive, polymer (PDMAEMA) in both systems allows to explore the role of mixing incompatibilities between tethered macromolecules with solvent and also pressure on the morphological changes in the PDMAEMA-containing nanostructures. Our findings indicate distinct pressure-dependent response in both lateral (HP-GISANS) and transversal (specular NR) nanostructure depending on the chemical composition. Specular ToF-NR results suggest that temperature effects are found to be counteracted by pressure and also that presumably mixing non-idealities and residual unoccupied volume within the investigated mixed brushes are polymer-compatibility dependent as evidenced by enhanced D2O retention within the brush by the strongly incompatible POFPMA/PDMAEMA mixed brush. GISANS analysis indicates the presence of uncorrelated cylindrical hydrophobic nanostructures within a PDMAEMA-based swollen matrix. Moreover, off-specular scattering (OSS) analysis demonstrates that the spacing between hydrophobic domains and the associated surface coverage exhibits changes with pressure only for the strongly incompatible POFPMA/PDMAEMA mixed brush. Our HP - GISANS and off-specular scattering results suggest that the length scale of phase separation on the sample surface along the beam direction can strongly depend on the compositional variation in the mixed brushes.

Understanding the dynamic and structural properties of matter across different timescales and length scales is essential for elucidating their functionality. We focus here on soft-matter systems, which are typically particularly sensitive to relative humidity (RH) and temperature, necessitating well controlled experimental conditions. Quasi-elastic neutron scattering (QENS) and Raman spectroscopy offer complementary insights: QENS accesses diffusional dynamics, which are stochastic motions, while Raman spectroscopy provides information on periodic vibrational dynamics. To enable simultaneous QENS and Raman measurements on e.g. polymer films under controlled and variable RH and temperature, we have developed a dedicated sample environment (SE), which in the presented experiments covers an RH range of 5–85% and a temperature range of 20–50°C. This SE features a 3D-printed spherical chamber including a sample holder for films, a Raman spectrometer, a custom-built gas-flow system and a thermostat. The chamber can accommodate large samples (up to 5 × 5 cm) and provides space for additional measurement equipment. The 3D-printing technique allows the integration of channels into the chamber walls, which are used for cooling and heating, resulting in highly homogeneous temperature distributions. This is key to achieving a uniform humidity in the chamber. The chamber works with a variety of solvents and their mixtures, like heavy water or ethanol. We demonstrate the feasibility of this setup through simultaneous QENS and Raman measurements on poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) films on Si substrates, confirming that the chamber provides a stable and low scattering background environment.

Grazing-incidence small-angle neutron scattering (GISANS) under pressure (HP-GISANS) at the solid (Si)–liquid (D₂O) interface is demonstrated for the pressure-induced lateral morphological characterization of the nanostructure in thin (T = 45°C for two pressures, P = 1 bar and P = 800 bar. Our GISANS results reveal nanostructural rearrangements with increasing P, underlining P-induced effects in tethered polymer brush layers swollen with bulk solvent.

Ultralow thermal conductivity and fast ionic diffusion endow superionic materials with excellent performance both as thermoelectric converters and as solid-state electrolytes. Yet the correlation and interdependence between these two features remain unclear owing to a limited understanding of their complex atomic dynamics. Here we investigate ionic diffusion and lattice dynamics in argyrodite Ag₈SnSe₆ using synchrotron X-ray and neutron scattering techniques along with machine-learned molecular dynamics. We identify a critical interplay of the vibrational dynamics of mobile Ag and a host framework that controls the overdamping of low-energy Ag-dominated phonons into a quasi-elastic response, enabling superionicity. Concomitantly, the persistence of long-wavelength transverse acoustic phonons across the superionic transition challenges a proposed ‘liquid-like thermal conduction’ picture. Rather, a striking thermal broadening of low-energy phonons, starting even below 50 K, reveals extreme phonon anharmonicity and weak bonding as underlying features of the potential energy surface responsible for the ultralow thermal conductivity (−1 K⁻¹) and fast diffusion. Our results provide fundamental insights into the complex atomic dynamics in superionic materials for energy conversion and storage.

Inelastic incoherent neutron time-of-flight scattering was employed to measure the low frequency density of states for a series of addition polynorbornenes with bulky side groups.

In this work, the effects of the two anions Cl^- and NO₃^- on the phase behavior of bovine serum albumin (BSA) in solution with trivalent salts are compared systematically. In the presence of trivalent metal salts, negatively charged proteins such as BSA in solution undergo a reentrant condensation (RC) phase behavior, which has been established for several proteins with chlorides of trivalent salts. Here, we show that replacing Cl^- by NO₃^- leads to a marked change in the phase behavior. The effect is investigated for the two different cations Y³⁺ and La³⁺. The salts are thus YCl₃, Y(NO₃)₃, LaCl₃, and La(NO₃)₃. The experimental phase behavior shows that while the chloride salts induce both liquid-liquid phase separation (LLPS) and RC, the nitrate salts also induce LLPS but the RC becomes partial with La(NO₃)₃ and disappears with Y(NO₃)₃. The observed phase behavior is rationalized by the effective protein-protein interactions which are characterized using small angle X-ray scattering (SAXS). The results based on the reduced second virial coefficient B₂/B₂^HS and 1/I(q → 0) demonstrate that the NO₃^- salts induce a stronger attraction than the Cl^- salts. Overall, the effective attraction, the width of the condensed regime in the RC phase diagram and the nature of the LLPS follow the order LaCl₃ < YCl₃ < La(NO₃)₃ < Y(NO₃)₃. Despite the decisive role of cations in RC phase behavior, isothermal titration calorimetry (ITC) measurements indicate that replacing anions does not significantly influence the cation binding to proteins. The experimental results observed are discussed based on an “enhanced Hofmeister effect” including electrostatic and hydrophobic interactions between protein-cation complexes.

The inclusion of superparamagnetic iron oxide nanoparticles (SPIONs) in lipid mesophases is a promising strategy for drug-delivery applications, combining the innate biocompatibility of lipid architectures with SPIONs’ response to external magnetic fields.