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We investigated the impact of irreversible adsorption on the mechanisms of thermal expansion of 1D confined polymer layers. For spincoated films (polystyrene on aluminum) of constant thickness, the thermal expansion coefficient of the melt drops upon annealing following the kinetics of irreversible adsorption of the chains onto the supporting substrate, while the thermal expansion of the glass is annealing invariant. These perturbations are explained in terms of the reduction in free volume content, upon immobilization of monomers onto the substrate. To shed more light on this phenomenon, we performed an extensive investigation of the thermal expansion of irreversibly adsorbed layers of polystyrene on silicon oxide. We verified that, contrarily to recent speculations, these films cannot be modeled as dead layers -- immobilized slabs lacking of segmental relaxation. On the contrary, thin adsorbed layers show an increase in thermal expansion with respect to the bulk, due to packing frustration. Immobilization plays a role only when the thickness of the adsorbed layers overcomes ~10 nm. Finally, we showthat for adsorbed layers the difference in thermal expansion between the melt and the glass is sufficiently high to investigate the glass transition down to 3 nm. Owing to this unique feature, not shared by spincoated films, adsorbed layers are the perfect candidate to study the properties of extremely thin polymer films. [ABSTRACT FROM AUTHOR]

Neutron specular reflectometry (SR) and off‐specular scattering (OSS) are nondestructive techniques which, through deuteration, give a high contrast even among chemically identical species and are therefore highly suitable for investigations of soft‐matter thin films. Through a combination of these two techniques, the former yielding a density profile in the direction normal to the sample surface and the latter yielding a depth‐resolved in‐plane lateral structure, one can obtain quite detailed information on buried morphology on length scales ranging from the order of ångströms to ∼10 µm. This is illustrated via quantitative evaluation of data on SR and OSS collected in time‐of‐flight (ToF) measurements of a set of films composed of immiscible polymer layers, protonated poly(methyl methacrylate) and deuterated polystyrene, undergoing a decomposition process upon annealing. Joint SR and OSS data analysis was performed by the use of a quick and robust originally developed algorithm including a common absolute‐scale normalization of both types of scattering, which are intricately linked, constraining the model to a high degree. This, particularly, makes it possible to distinguish readily between different dewetting scenarios driven either by the nucleation and growth of defects (holes, protrusions etc.) or by thermal fluctuations in the buried interface between layers. Finally, the 2D OSS maps of particular cases are presented in different spaces and qualitative differences are explained, allowing also the qualitative differentiation of the in‐plane structure of long‐range order, the correlated roughness and bulk defects by a simple inspection of the scattering maps prior to quantitative fits. [ABSTRACT FROM AUTHOR]

The surface pressure of monolayers of insoluble diblock copolymers has been measured. One of the blocks is made of poly(t-butyl acrylate) (PtBA), and the other one by polystyrene (PS). The interface is a good solvent for PtBA, while it is a poor solvent for PS. For the sake of comparison, monolayers of a PtBA homopolymer (good solvent conditions) and of poly(4-hydroxy styrene) (P4HS) (poor solvent conditions) have been also measured. It has been found that the relative length of the blocks plays an important role on the shape of the surface pressure Π versus surface concentration Γ curves and also on the shape of the equilibrium compressibility versus Γ curves. However, it does not affect the maximum value of Π reached at high Γ’s. Surprisingly, the ellipsometric thickness of the copolymer monolayers is almost independent of the relative length of the blocks. The dynamics of the monolayers has been studied by step compression and by surface-light scattering techniques. When Mw,PtBA>Mw,PS single exponential relaxations are observed. However, stretched exponentials are obtained for Mw,PS>=Mw,PtBA. The relaxation times decrease with increasing Γ for all the copolymers studied. This is the behavior usually found for poor solvent conditions (P4HS) and opposite to that found for homopolymers under good solvent conditions [PtBA, poly(vinylacetate)]. This means that the solvent quality of the interface does not determine the pressure dependence of τ. The elasticity modulus of the monolayers in the kilohertz range takes values that are similar to those of the high-frequency limit of the relaxation experiments. This means that the relaxation processes have characteristic frequencies below 1 Hz. [ABSTRACT FROM AUTHOR]

Probing molecules using perdeuteration (i.e deuteration in which all hydrogen atoms are replaced by deuterium) is extremely useful in a wide range of biophysical techniques. In the case of lipids, the synthesis of the biologically relevant unsaturated perdeuterated lipids is challenging and not usually pursued. In this work, perdeuterated phospholipids and sterols from the yeast Pichia pastoris grown in deuterated medium are extracted and analyzed as derivatives by gas chromatography and mass spectrometry respectively. When yeast cells are grown in a deuterated environment, the phospholipid homeostasis is maintained but the fatty acid unsaturation level is modified while the ergosterol synthesis is not affected by the deuterated culture medium. Our results confirm that the production of well defined natural unsaturated perdeuterated lipids is possible and gives also new insights about the process of desaturase enzymes. [ABSTRACT FROM AUTHOR]

We have investigated the dewetting behaviour of a thin polystyrene film on top of cross-linked network of the same polymer. By changing the cross-linking density, the dynamic of the dewetting is modified. The behaviour of the contact angle and dewetting velocity can be related to the interfacial width between the polymers. We observe moreover that while the lost of entropy of the network connected to the penetration of the free chains will favour the dewetting; the possible presence of 'connectors' between the layers will tend to stabilize the wetting. By modifying the entropy of the mesh by swelling the cross-linked system with a reservoir of the same polymer, the mesh is saturated and a stable interface without interdiffusion between the layers is obtained: in this case a constant contact angle and slippage length are obtained. Networks with higher cross-linking density are more difficult in general to swell - the mesh size is smaller - and the complete saturation is not reached. [ABSTRACT FROM AUTHOR]

In this paper, the deposition and characterization of plasma-polymerized polystyrene (pp-PS) using PECVD under atmospheric pressure on a variety of substrates was investigated. An atmospheric RF plasma torch and an HF dielectric-barrier- discharge (DBD) system were used to deposit thin pp-PS coatings on PTFE, HDPE, stainless steel, glass, and silicon wafer. The styrene vapor was carried by Ar or He. The pp-PS films were characterized by Fourier transform infrared spectroscopy (FTIR) (infrared reflection absorption spectroscopy), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), static secondary ion mass spectroscopy (SSIMS), and optical microscopy, and the plasma phase was studied by optical-emission spectroscopy. The major features that characterize PS are present in the FTIR, SSIMS, and XPS spectra of our films, although some differences are observed between pp-PS and their conventionally polymerized counterparts: oxygenation, branching, degree of cross-linking, and unsaturation. According to the WCA and XPS results, the films deposited by the RF plasma torch (placed in a Plexiglass chamber) are more oxygenated than those deposited by DBD, which is operated under a much more controlled atmosphere. A comparison of the chemical structure of the deposited coatings (branching, cross-linking) as a function of the nature of the earner gas was established by FTIR: pp-PS synthesized in the presence of Ar (for both processes) exhibit more branching and a higher degree of cross-linking than pp-PS synthesized with He as the main plasma gas. The optical microscopy points out a diversity of structures that depend on the nature of the substrate and the plasma parameters. [ABSTRACT FROM AUTHOR]

The kinetics of the formation of the interfacial width between immiscible polymer pairs are studied using neutron reflectivity. Bilayers of deuterated polystyrene (d-PS) and poly(methyl methacrylate) of high molecular weight are used. The time dependence of the formation of the interface in both cases where the thickness of the top d-PS layer is thin (less than 200 Å) and thick (greater than 1000 Å) is investigated. Following an initial rapid increase, a logarithmic dependence of the interfacial width on time is observed. We interpret this result as arising from the slow equilibration of long-wavelength capillary-wave fluctuations; comparison of our results with theory yields a value of the interfacial tension in good agreement with the self-consistent field theory prediction. [ABSTRACT FROM AUTHOR]