This paper addresses the effect of polyelectrolyte stiffness on the surface structure of polyelectrolyte (P)/surfactant (S) mixtures. Therefore, two different anionic Ps with different intrinsic ...persistence length l P are studied while varying the salt concentration (0–10–2 M). Either monosulfonated polyphenylene sulfone (sPSO2-220, l P ∼20 nm) or sodium poly(styrenesulfonate) (PSS, l P ∼1 nm) is mixed with the cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) well below its critical micelle concentration and studied with tensiometry and neutron reflectivity experiments. We kept the S concentration (10–4 M) constant, while we varied the P concentration (10–5–10–3 M of the monomer, denoted as monoM). P and S adsorb at the air/water interface for all studied mixtures. Around the bulk stoichiometric mixing point (BSMP), PSS/C14TAB mixtures lose their surface activity, whereas sPSO2-220/C14TAB mixtures form extended structures perpendicular to the surface (meaning a layer of S with attached P and additional layers of P and S underneath instead of only a monolayer of S with P). Considering the different P monomer structures as well as the impact of salt, we identified the driving force for the formation of these extended structures: compensation of all interfacial charges (P/S ratio ∼1) to maximize the gain of entropy. By increasing the flexibility of P, we can tune the interfacial structures from extended structures to monolayers. These findings may help improve applications based on the adsorption of P/S mixtures in the fields of cosmetic or oil recovery.
The paper addresses the swelling of polyelectrolyte multilayers (PEMs) at varying humidity. In particular, a new model will be presented, which takes the gradual filling of voids into account. ...Absorption of water results in PEM swelling. This absorbed water can be distinguished into swelling and void water. Swelling water leads to an increase in thickness and a change of the optical properties of PEMs, while the void water results only in a change of the optical properties. In former studies, neutron reflectometry was used to distinguish between swelling and void water. However, as we show in this study, it is possible to resolve the two different kinds of water in PEMs by ellipsometry, a much simpler tool. The present study evaluates and interprets the refractive index of polystyrenesulfonate/polydiallyldimethylammonium chloride (PSS/PDADMAC) PEMs. Both the swelling behavior and the refractive index change as a function of relative humidity and were found to be independent of the layer number. The void model and the extended void model were used to describe the data. The void model allows fitting the experimentally determined refractive index at humidity beyond 20% RH but fails for humidity lower than 20% RH. Therefore, we modified the existing model in order to account for air–water exchange. The extended void model assumes a gradual air–water exchange at low h and describes the refractive index over the entire humidity range in a precise way. Up to 30% RH, air and water coexist. Above this threshold, the voids are completely filled with water and this threshold does not change either with layer number or with the outermost layer. Furthermore, this model allows the determination of the volume fraction of the voids (0.05 ± 0.01) and the refractive index of the pure polymer matter (1.592 ± 0.002).
The combination of polyelectrolyte multilayers (PEMs) and end-grafted brushes represents a valuable approach to the design of complex organic composite materials with tailored responsive properties. ...This article addresses the correlation between the swelling properties of composites and their internal structure. Here, we present composites of end-grafted 2-(methacryloyloxy)ethyl-trimethylammonium chloride (PMETAC) brushes covered with poly(sodium styrenesulfonate) (PSS) and poly(diallyldimethylammonium) chloride (PDADMAC) PEMs and characterize them under various relative humidities. Ellipsometry and neutron reflectometry are carried out to monitor the swelling behavior and the internal structure, respectively, of the composites, giving evidence of a significant mutual influence of the two components. The reflectivity data reveal a deep penetration of the PEMs’ polyelectrolyte chains into the underlying brush but also a significant humidity dependence of their spatial distribution, indicating considerable mobility within the brush. In contrast to a compact bare brush, for composites a pronounced stretching of the brush after PEM adsorption is observed. The water uptake of the brush is reduced. A PEM on top of a brush is less influenced by the latter one. Swelling gradually reduces the brush/PEM interpenetration, while water accumulates in the interfacial region between the brush and PEM so that these two compartments get increasingly separated with increasing humidity. The swelling process is largely reversible, which demonstrates the potential applicability of these composites as chemical gas or moisture sensors.
Reliable measurement of the size of polydisperse, complex-shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable ...methods exist for the accurate characterization of the size of non-aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano-powders tend to agglomerate and/or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer-Emmet-Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon-based hot-mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well-defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discussed.
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 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.
A novel method for the preparation of transparent Al2O3 coatings of polymers is presented. An environmental‐friendly sol–gel method is employed, which implies mild conditions and low costs. A ...thermoresponsive brush is chosen as a model surface. X‐ray photoelectron spectroscopy is used to characterize the samples during the conversion of the precursor Al(OH)3 into oxide and to prove the mildness of the protocol. The study evidences a relation between lateral homogeneity of alumina and the wettability of the polymer surface by the precursor solution, while morphology and elasticity are dominated by the polymer properties. The study of the swelling behavior of the underneath brush reveals the absence of water uptake, proving the impermeability of the alumina layer. The broad chemical and structural variety of polymers, combined with the robustness of transparent alumina films, makes these composites promising as biomedical implants, protective sheets and components for electric and optical devices.
Waterproof and transparent: A method for the preparation of transparent Al2O3 coatings of polymer brushes is presented. Layer composition, morphology, and mechanical properties were characterized by a combination of XPS, SEM, and AFM. The presence of the alumina layer preserved the underneath brush from swelling in water.
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