Andreas Josef Schmid

The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading and most brilliant neutron source and aims at starting user operation at the end of 2023. Among others, two small angle neutron scattering (SANS) machines will be operated. Due to the high brilliance of the source, it is important to minimize the downtime of the instruments. For this, a collaboration between three German universities and the ESS was initialized to develop and construct a unified sample environment (SE) system. The main focus was set on the use of a robust carrier system for the different SEs, which allows setting up experiments and first prealignment outside the SANS instruments. This article covers the development and construction of a SE for SANS experiments with foams, which allows measuring foams at different drainage states and the control of the rate of foam formation, temperature, and measurement position. The functionality under ESS conditions was tested and neutron test measurement were carried out.

As part of the development of the new European Spallation Source (ESS) in Lund (Sweden), which will provide the most brilliant neutron beams worldwide, it is necessary to provide different sample environments with which the potential of the new source can be exploited as soon as possible from the start of operation. The overarching goal of the project is to reduce the downtimes of the instruments related to changing the sample environment by developing plug and play sample environments for different soft matter samples using the same general carrier platform and also providing full software integration and control by just using unified connectors. In the present article, as a part of this endeavor, the sample environment for in situ SANS and dynamic light scattering measurements is introduced.

The investigation of the response kinetics of smart colloidal microgel films is crucial for their optimization to enable advanced applications. We study the classical thermo-responsive microgel model system N-isopropylacrylamide (NIPAM) cross-linked with N,N’-methylenebisacrylamide (BIS). Without the typically used polyelectrolyte coating of the substrate, thin microgel films are prepared in a single spin-coating step. Atomic force microscopy (AFM) measurements reveal an extremely dense packing, resulting in a homogeneous compact thin film of microgel particles. The hydration kinetics of these films in H2O and D2O atmospheres as well as the kinetics of the solvent exchange between both water species is investigated with in situ time-of-flight neutron reflectometry (TOF-NR) and in situ Fourier-transform infrared spectroscopy (FTIR). With accounting for a non-constant humid atmosphere, the intrinsic diffusion dynamics of water molecules into the thin microgel film are modeled and the specific time constant τ and the effective Flory-Huggins interaction parameter χeff are determined. Comparing the results in H2O and D2O atmosphere, TOF-NR and FTIR spectroscopy results show an increased affinity of the microgel films towards H2O as compared to D2O. From the FTIR spectroscopy data we further identify different kinetics of intermolecular processes and order them according to their temporal evolution.

The use of smart colloidal microgels for advanced applications critically depends on their response kinetics. We use pressure jump small angle neutron scattering with supreme time resolution to study the rapid volume phase transition kinetics of such microgels. Utilizing the pressure induced microphase separation inside the microgels we were able to resolve their collapse and swelling kinetics. While the collapse occurs on a time scale of 10 ms, the particle swelling turned out to be much faster. Photon correlation spectroscopy and static small angle neutron scattering unambiguously show, that the much slower collapse can be associated with the complex particle architecture exhibiting a loosely-crosslinked outer region and a denser inner core region. These insights into the kinetics of stimuli-responsive materials are of high relevance for their applications as nano-actuators, sensors or drug carriers. Moreover, the used refined pressure jump small angle neutron scattering technique is of broad interest for soft matter studies.

We report on hollow shell-shell nanogels with two polymer shells that have different volume phase transition temperatures. By means of small angle neutron scattering (SANS) employing contrast variation and molecular dynamics (MD) simulations we show that hollow shell-shell nanocontainers are ideal systems for controlled drug delivery: The temperature responsive swelling of the inner shell controls the uptake and release, while the thermoresponsive swelling of the outer shell controls the size of the void and the colloidal stability. At temperatures between 32 °C < T < 42 °C, the hollow nanocontainers provide a significant void, which is even larger than the initial core size of the template, and they possess a high colloidal stability due to the steric stabilization of the swollen outer shell. Computer simulations showed, that temperature induced switching of the permeability of the inner shell allows for the encapsulation in and release of molecules from the cavity.

In this study, we compare the experimental static structure factors of concentrated solutions of amphoteric poly(N-isopropylacrylamide) (PNIPAM) microgels with those of the polydisperse hard-sphere model. We use zwitterionic microgels as model systems for amphoteric microgels with an equal amount of positive and negative charges located in a defined distance. Using small angle neutron scattering (SANS), we measure the static structure factors, S _M(q), of a series of zwitterionic microgels with increasing amount of zwitterion, including a reference sample of pure PNIPAM. The experimental S _M(q) is compared with predictions based on the Percus-Yevick approximation for hard spheres. We also compare with the PNIPAM reference sample measured for zwitterionic microgels. We find no significant influence of the zwitterionic comonomer on the effective pair potential. The PNIPAM and the zwitterionic microgels can be described by the hard-sphere model for smaller volume fractions ϕ T ≲ 0.4 only.