The modelling of scattering data from foams is very challenging due to the complex structure of foams and is therefore often reduced to the fitting of single peak positions or feature mimicking. This ...article presents a more elaborate model to describe the small‐angle neutron scattering (SANS) data from foams. The model takes into account the geometry of the foam bubbles and is based on an incoherent superposition of the reflectivity curves arising from the foam films and the small‐angle scattering (SAS) contribution from the plateau borders. The model is capable of describing the complete scattering curve of a foam stabilized by the standard cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) with different water contents, i.e. different drainage states, and provides information on the thickness distribution of liquid films inside the foam. The mean film thickness decreases with decreasing water content because of drainage, from 28 to 22 nm, while the polydispersity increases. These results are in good agreement with the film thicknesses of individual horizontal foam films studied with a thin‐film pressure balance.
A new model for the interpretation of small‐angle neutron scattering data from aqueous foams is presented and validated using experimental data from a model foam system.
The investigation of the response kinetics of smart colloidal microgel films is crucial for their optimization to enable advanced applications. We study the classical thermoresponsive microgel model ...system N-isopropylacrylamide cross-linked with N,N′-methylenebisacrylamide. Without the typically used polyelectrolyte coating of the substrate, thin microgel films are prepared in a single spin-coating step. Atomic force microscopy 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 are investigated with in situ time-of-flight neutron reflectometry (TOF-NR) and in situ Fourier-transform infrared (FTIR) spectroscopy. With accounting for a nonconstant 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 atmospheres, TOF-NR and FTIR spectroscopy results show an increased affinity of the microgel films toward 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 continuous improvement of synthesis leads to a great variety in the internal architecture and functionality of colloidal hydrogels. A majority of envisioned applications use microgels as ...colloidal building blocks for layer formation at solid substrates. In this context, a fundamental understanding of the influence of these substrates on the internal structure and physical properties is essential. Especially, the nanomechanical properties of adsorbed poly(N-isopropylacrylamide) microgel particles are important for their application in cell cultivation, functional surface coatings, and others. Furthermore, these properties are closely related to the swelling behavior and the internal structure and dynamics of these microgels. However, the number of methods that are able to probe the viscoelasticity of adsorbed microgels over the entire vertical particle profile is limited. Grazing incidence neutron scattering techniques are suited to probe soft-matter samples with limited sample volumes at planar solid substrates and allow a resolution in the z-direction. We used neutron spin echo spectroscopy under grazing incidence to access fast thermal fluctuations (10–9 s) over the entire vertical particle profile. Atomic force microscopy nanoindentation was used to characterize the nanomechanical properties of adsorbed microgel particles prepared by batch and continuous monomer feeding methods. The resulting force maps revealed that batch microgels were “hard” and heterogeneous in their Young’s moduli, while the microgels from the continuous method were “soft” and homogeneous. Finally, neutron spin echo spectroscopy under grazing incidence revealed major differences in the vertical dynamic profile of both types of microgels.
The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the ...small-K advanced diffractometer (SKADI) beamline development group of the Jülich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ). Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.
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.
Polymer-stabilized foams and foam films have received considerable attention during the past years. This review paper gives an overview of recent studies dealing with polyelectrolyte/surfactant ...mixtures, proteins, and microgels adsorbed at single air/water interfaces, in foam films and in macroscopic foams. These polymeric systems have in common that their structure or shape changes when adsorbing at an air/water interface. These structural changes in comparison to their bulk behavior greatly influence the properties of foam films and foams. Regarding the foam stability, formation of adsorbed layers or aggregates plays an important role. The discrepancy between stabilization of macroscopic foams and destabilization of single foam films might be attributed to the blockage of Plateau borders and, therefore, slowed down drainage. Another important parameter is the interfacial viscoelasticity.
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•Foams are complex, hierarchical materials with various structures on different length scales.•For P/S mixtures, crucial factors for stability are structures of adsorbed layers and interaction strength between P and S.•Protein aggregates lead to stable foam due to either stabilization of single foam films or blocking of Plateau borders.•Microgels are a model system for soft deformable colloids.•Equilibrium and non-equilibrium structure formation have a strong impact on foamability and foam stability.
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