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In a two–neutron transfer experiment, performed in Bucharest in July 2016 at sub–Coulomb barrier energy,a photon decay hindered – solely – by a nuclear shape change was identified in the 66Ni nucleus. Such a rare process, at spin zero, was clearly observed before only in actinide nuclei in the 1970’s,where fission isomers were found. The experimental findings on 66Ni have been well reproduced by the Monte Carlo Shell Model Calculations of the Tokyo group, which predict a multifaceted scenario of coexistence of spherical, oblate and prolate shapes in neutron–rich Ni isotopes. The results on 66Ni encouraged a comprehensive gamma–spectroscopy investigation of neutron–rich Ni isotopes, in particular 62Ni and 64–Ni, at IFIN–HH (Bucharest), IPN Orsay and ILL (Grenoble), employing different reaction mechanisms to pin down the wave function composition of selected excited states. The aim is to shed light on the microscopic origin of deformation in neutron–rich Ni nuclei, possibly locating other examples of “shape–isomer–like” structures inthis region.

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 carrier 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. Index Terms--Plasma CVD, plasma materials-processing applications, plasmas, plastics.

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]

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]

The activity of the potent but highly toxic antifungal drug Amphotericin B (AmB), used intravenously to treat systemic fungal and parasitic infections, is widely accepted to result from its specific interaction with the fungal sterol ergosterol. While the effect of sterols on AmB activity has been intensely investigated, the role of membrane phospholipid composition has largely been ignored, and structural studies of native membranes have been hampered by their complex and disordered nature. We show for the first time that the structure of fungal membranes derived from Pichia pastoris yeast depends on the degree of lipid polyunsaturation, which has an impact on the structural consequences of AmB activity. AmB inserts in yeast membranes even in the absence of ergosterol, and forms an extra-membraneous layer whose thickness is resolved to be 4–5 nm. In ergosterol-containing membranes, AmB insertion is accompanied by ergosterol extraction into this layer. The AmB-sponge mediated depletion of ergosterol from P. pastoris membranes gives rise to a significant membrane thinning effect that depends on the degree of lipid polyunsaturation. The resulting hydrophobic mismatch is likely to interfere with a much broader range of membrane protein functions than those directly involving ergosterol, and suggests that polyunsaturated lipids could boost the efficiency of AmB. Furthermore, a low degree of lipid polyunsaturation leads to least AmB insertion and may protect host cells against the toxic effects of AmB. These results provide a new framework based on lipid composition and membrane structure through which we can understand its antifungal action and develop better treatments. [ABSTRACT FROM AUTHOR]

Abstract: Polymorphism of α,ω-dioctylterthiophene (DOTT) thin films (less than 100nm-thick) deposited onto standard silicon substrates is investigated by combining specular and in-plane grazing incidence X-ray diffraction measurements. Two crystal phases are revealed: the bulk phase (b) and the surface-induced phase (s). Previous results showed that s-phase was the most favored close to the substrate surface while b-phase is predominant at the DOTT-air interface. We show here that the relative proportion of these polymorphs is related to sample preparation. Indeed, the preferential crystallization of one phase or the other can be tuned as a function of substrate temperature during film deposition, s-phase being mainly present at high substrate temperature while b-phase is most observed at low substrate temperature. Particularly noteworthy is that thin films exhibiting only b-phase or only s-phase can be obtained according to sample preparation. Furthermore, when samples are annealed above the melting temperature (smectic G phase), the polymorph observed after cooling back to room temperature depends upon the cooling rate, s-phase being predominant at high cooling rate while it is rather b-phase for slow cooling. This behavior is independent of the crystalline phase that was present at room temperature before annealing. [Copyright &y& Elsevier]

The interaction between two immiscible materials is related to the number of contacts per unit area formed by the two materials. For practical reasons, this information is often parametrized by the interfacial free energy, which is commonly derived via rather cumbersome approaches, where properties of the interface are described by combining surface parameters of the single materials. These combining rules , however, neglect any effect that geometry might have on the strength of the interfacial interaction. In this Article, we demonstrate that the number of contacts at the interface between a thin polymer coating and its supporting substrate is altered upon confinement at the nanoscale level. We show that explicitly considering the effect of nanoconfinement on the interfacial potential allows a quantitative prediction of how sample geometry affects the number of contacts formed at the interface between two materials., Competing Interests: The authors declare no competing financial interest.

The discussions on the nanoconfinement effect on the glass transition and glassy dynamics phenomena have yielded many open questions. Here, the thickness dependence of the thermal glass transition temperature T g therm of thin films of a PVME/PS blend is investigated by ellipsometry. Its thickness dependence was compared to that of the dynamic glass transition (measured by specific heat spectroscopy) and the deduced Vogel temperature ( T 0 ). While T g therm and T 0 showed a monotonous increase, with decreasing film thickness, the dynamic glass transition temperature ( T g dyn ) measured at a finite frequency showed a nonmonotonous dependence that peaks at 30 nm. This was discussed by assuming different cooperativity length scales at these temperatures, which have different sensitivities to composition and thickness. This nonmonotonous thickness dependence of T g dyn disappears for frequencies characteristic for T 0 . Further analysis of the fragility parameter showed a change in the glassy dynamics from strong to fragile, with decreasing film thickness.

Controlling polymer/substrate interfaces without modifying chemistry is nowadays possible by finely tuning the formation of adsorbed layers. The complex processes leading to irreversible attachment of chains onto solid substrates are governed by two mechanisms: molecular rearrangement and potential-driven adsorption. Here we introduce an analytical method to differentiate these two mechanisms. By analyzing experiments and simulations, we investigate how changes in thermal energy and interaction potential affect equilibrium and nonequilibrium components of the adsorption kinetics. We find that the adsorption process is thermally activated, with activation energy comparable to that of local noncooperative processes. On the other hand, the final adsorbed amount depends on the interface interaction only (i.e., it is temperature independent in experiments). We identify a universal linear relation between the growth rates at short and long adsorption times, suggesting that the monomer pinning mechanism is independent of surface coverage, while the progressive limitation of free sites significantly limits the adsorption rate.

When cooled at constant rate, a 25 nm thin film of poly(4- tert -butylstyrene) vitrifies 50 K lower than in bulk. This record sets the largest depression in thermal glass transition temperature ( T g ) ever observed upon confinement at the nanoscale level. Same as for other supported polymer layers, this reduction in T g has been attributed to the presence of a free surface, the ensemble of molecules at the interface with air remaining in the liquid state also at temperatures well below bulk T g . Here, we verify that such tremendous shifts can be erased upon prolonged annealing in the liquid state, hinting at a metastable nature of confinement effects. We demonstrate that the recovery of bulk behavior and the manifestation of the free surface are enslaved to the kinetics of irreversible adsorption of chains on the supporting substrate.

The effects of interface roughness between donor and acceptor in a bilayer heterojunction solar cell were investigated on a polymer-polymer system based on poly(3-hexylthiophene) (P3HT) and poly(dioctylfluorene-alt-benzothiadiazole) (F8BT). Both polymers are known to reorganize into semicrystalline structures when heated above their glass-transition temperature. Here, the bilayers were thermally annealed below glass transition of the bulk polymers (≈140 °C) at temperatures of 90, 100, and 110 °C for time periods from 2 min up to 250 min. No change of crystallinity could be observed at those temperatures. However, X-ray reflectivity and device characteristics reveal a coherent trend upon heat treatment. In X-ray reflectivity investigations, an increasing interface roughness between the two polymers is observed as a function of temperature and annealing time, up to a value of 1 nm. Simultaneously, according bilayer devices show an up to 80% increase of power conversion efficiency (PCE) for short annealing periods at any of the mentioned temperatures. Together, this is in agreement with the expectations for enlargement of the interfacial area. However, for longer annealing times, a decrease of PCE is observed, despite the ongoing increase of interface roughness. The onset of decreasing PCE shifts to shorter durations the higher the annealing temperature. Both, X-ray reflectivity and device characteristics display a significant change at temperatures below the glass transition temperatures of P3HT and F8BT.

The origins of specific polymorphic phases within thin films are still not well understood. The polymorphism of the molecule dioctyl-terthiophene is investigated during the presence of a silicon-oxide surface during the crystallisation process. It is found that a monolayer of molecules forms two-dimensional crystals on the surface. In the case of thicker films crystalline islands are formed, a comparison of the three polymorphic phases observed within thin films and the thermodynamically more stable single crystal phases reveals distinct differences which can be related to an adaption of the molecular packing with the flat surface of the substrate.

Substrate-induced phases (SIPs) are polymorphic phases that are found in thin films of a material and are different from the single crystal or "bulk" structure of a material. In this work, we investigate the presence of a SIP in the family of [1]benzothieno[3,2-b]benzothiophene (BTBT) organic semiconductors and the effect of aging and solvent vapor annealing on the film structure. Through extensive X-ray structural investigations of spin coated films, we find a SIP with a significantly different structure to that found in single crystals of the same material forms; the SIP has a herringbone motif while single crystals display layered π-π stacking. Over time, the structure of the film is found to slowly convert to the single crystal structure. Solvent vapor annealing initiates the same structural evolution process but at a greatly increased rate, and near complete conversion can be achieved in a short period of time. As properties such as charge transport capability are determined by the molecular structure, this work highlights the importance of understanding and controlling the structure of organic semiconductor films and presents a simple method to control the film structure by solvent vapor annealing.

A detailed structural study of the bulk and thin film phases observed for two potential high-performance organic semiconductors has been carried out. The molecules are based on [1]benzothieno[3,2-b]benzothiophene (BTBT) as conjugated core and octyl side groups, which are anchored either symmetrically at both sides of the BTBT core (C8-BTBT-C8) or nonsymmetrically at one side only (C8-BTBT). Thin films of different thickness (8-85 nm) have been prepared by spin-coating for both systems and analyzed by combining specular and grazing incidence X-ray diffraction. In the case of C8-BTBT-C8, the known crystal structure obtained from single-crystal investigations is observed within all thin films, down to a film thickness of 9 nm. In the case of C8-BTBT, the crystal structure of the bulk phase has been determined from X-ray powder diffraction data with a consistent matching of experimental and calculated X-ray diffraction patterns (Rwp = 5.8%). The packing arrangement of C8-BTBT is similar to that of C8-BTBT-C8, that is, consisting of a lamellar structure with molecules arranged in a "herringbone" fashion, yet with lamellae composed of two head-to-head (or tail-to-tail as the structure is periodic) superimposed molecules instead of only one molecule for C8-BTBT-C8. As for C8-BTBT-C8, we demonstrate that the same phase is observed in bulk and thin films for C8-BTBT whatever the film thickness investigated.

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.