We use neutron reflectometry to study how the polymeric binder, poly(acrylic acid) (PAA), affects the in situ formation and chemical composition of the solid–electrolyte interphase (SEI) formation ...on a silicon anode at various states of charge. The reflectivity is correlated with electrochemical quartz crystal microbalance to better understand the viscoelastic effects of the polymer during cycling. The use of model thin films allows for a well-controlled interface between the amorphous Si surface and the PAA layer. If the PAA perfectly coats the Si surface and standard processing conditions are used, the binder will prevent the lithiation of the anode. The PAA suppresses the growth of a new layer formed at early states of discharge (open circuit voltage to 0.8 V vs Li/Li+), protecting the surface of the anode. At 0.15 V, the SEI layer underneath the PAA changes in chemical composition as indicated by an increase in the scattering length density and thickness as the layer incorporates components from the electrolyte, most likely the salt. At lithiated and delithiated states, the SEI layer changes in chemical composition and grows in thickness with delithiation and shrinks during lithiation.
Neutron reflectometry has emerged as a powerful method for studying the structure of thin films in contact with solution at sub-molecular spatial resolution (Penfold and Thomas, J Phys Condens Matter ...2:1369-1412, 1990). This type of experiment is undertaken at large international central facilities and experience in data analysis and interpretation is not always available "locally". Here, we describe the application of the refnx software suite (Nelson and Prescott, J Appl Crystallogr 52:193-200, 2019) to the analysis of a single phospholipid bilayer deposited at a silicon/buffer interface. The data is modeled such that the fitted parameters are readily interpretable by researchers working with lipid bilayers.
Cartoons of the mixed monolayers of GO and DPPC and evolution of the volume fraction of each component with the surface pressure.
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Graphene oxide-based nanotechnology has aroused a ...great interest due to its applications in the biomedical and optoelectronic fields. The wide use of these materials makes it necessary to study its potential toxicity associated with the inhalation of Graphene Oxide (GO) nanoparticles and its interaction with the lung surfactant. Langmuir monolayers have proven to be an excellent tool for studying the properties of the lung surfactant and the effect of intercalation of nanoparticles on its structure and properties. Therefore, to know the origin of the phospholipids/GO interaction and the structure of the lipid layer with GO, in this work we study the effect of the insertion of GO sheets on a Langmuir film of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC).
Surface pressure-area isotherms, Neutron (NR) and X-ray Reflectivity (XRR) and Grazing Incidence X-ray Diffraction (GIXD) measurements of hydrogenated and deuterated DPPC monolayers with and without GO have been carried out.
The results outline a strong interaction between the GO and the zwitterionic form of DPPC and prove that GO is in three regions of the DPPC monolayer, the aliphatic chains of DPPC, the head groups and water in the subphase. Comparison between results obtained with hydrogenated and deuterated DPPC allows concluding that both, electrostatic attractions, and dispersion forces are responsible of the interaction GO/DPPC. Results also demonstrated that the insertion of GO into the DPPC aliphatic chains does not induce significant changes on unit cell of DPPC.
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Supported lipid bilayers (SLBs) are commonly used to investigate the structure and dynamics of biological membranes. Vesicle fusion is a widely exploited method to produce SLBs. ...However, this process becomes less favoured when the vesicles contain complex lipid mixtures, e.g. natural lipid extracts. In these cases, it is often necessary to change experimental parameters, such as temperature, to unphysiological values to trigger the SLB formation. This may induce lipid degradation and is also not compatible with including membrane proteins or other biomolecules into the bilayers. Here, we show that the peptide discs, ~10 nm discoidal lipid bilayers stabilized in solution by a self-assembled 18A peptide belt, can be used as precursors for SLBs. The characterizations by means of neutron reflectometry and attenuated total reflectance-FTIR spectroscopy show that SLBs were successfully formed both from synthetic lipid mixtures (surface coverage 90–95%) and from natural lipid mixtures (surface coverage ~85%). Traces of 18A peptide (below 0.02 M ratio) left at the support surface after the bilayer formation do not affect the SLB structure. Altogether, we demonstrate that peptide disc formation of SLBs is much faster than the SLB formation by vesicle fusion and without the need of altering any experimental variable from physiologically relevant values.
Little is known experimentally about the detailed orientation of membrane-bound maculatin 1.1 (Mac1), an antimicrobial peptide from the skin secretions of Australian tree frogs. In this work multiple ...15N-labelled or 2H-labelled Mac1 with dodecylphosphocholine (DPC) micelles and isotropic DMPC/DHPC (q = 0.5) bicelles were investigated by solution NMR, circular dichroism (CD) spectroscopy, neutron reflectometry and molecular dynamics (MD) simulations in explicit solvent. In buffer, the 15N-1H HSQC and CD spectra were indicative of the peptide being random coiled. In the presence of micelles or isotropic bicelles, a unique and helical peptide structure that was confirmed by CD was found. The titration of the soluble paramagnetic agent gadolinium (Gd-DTPA) into the Mac1-DPC solution led to enhanced relaxation of all 15N labelled residues. The peptide N-terminus was more exposed to Gd-DTPA than the C-terminus in micelles, while only the Gly-4 and Ala-18 resonances were significantly reduced in the presence of isotropic bicelles. MD simulations of Mac1 fully inserted into a DPC micelle converged towards a solvent exposed orientation and a topology where Mac1 was wrapped around the DPC micelle with the more hydrophobic side facing inward. MD simulations of Mac1 fully inserted into a phosphatidylcholine (PC) bilayer converged towards a kinked transmembrane orientation with water molecules penetrating around Lys-8. A deuterium labelled Mac1 used in neutron reflectometry experiments suggested a preferred orientation in zwitterionic PC bilayers. These results give insight into the membrane disrupting activity of Mac1 against cell membranes.
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•Conformation of the antimicrobial peptide maculatin 1.1 was studied in planar bilayers and in micelles.•Isotopically labelled maculatin 1.1 was used to determine orientation in lipid bilayers.•Maculatin 1.1 adopts a preferred orientation in zwitterionic lipid bilayers.•In planar bilayers both the N-terminus and C-terminus are solvent exposed indicating pore-formation.
The online data reduction service reductus transforms measurements in experimental science from laboratory coordinates into physically meaningful quantities with accurate estimation of uncertainties ...from instrumental settings and properties. This reduction process is based on a few well known transformations, but flexibility in the application of the transforms and algorithms supports flexibility in experiment design, enabling a broader range of measurements than a rigid reduction scheme for data. The user interface allows easy construction of arbitrary pipelines from well known data transforms using a visual data flow diagram. Source data are drawn from a networked, open data repository. The Python back end uses intelligent caching to store intermediate results of calculations for a highly responsive user experience. The reference implementation allows immediate reduction of measurements as they are recorded for the three neutron reflectometry instruments at the NIST Center for Neutron Research, without the need for visiting scientists to install additional software on their own computers.
A web‐based flexible scientific data reduction system is presented, which accesses published data stores and transforms raw measurements into interpretable data through data flow diagrams that are converted to advanced calculations on a Python 3 back end; the results are returned in real time through the web interface. The application was developed for handling neutron and X‐ray reflectometry results at a user facility.
Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic ...motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures.
The vertical composition distribution of a bulk heterojunction (BHJ) photoactive layer is known to have dramatic effects on photovoltaic performance in polymer solar cells. However, the vertical ...composition distribution evolution rules of BHJ films are still elusive. In this contribution, three BHJ film systems, composed of polymer donor PBDB-T, and three different classes of acceptor (fullerene acceptor PCBM, small-molecule acceptor ITIC, and polymer acceptor N2200) are systematically investigated using neutron reflectometry to examine how donor–acceptor interaction and solvent additive impact the vertical composition distribution. Our results show that those three BHJ films possess homogeneous vertical composition distributions across the bulk of the film, while very different composition accumulations near the top and bottom surface were observed, which could be attributed to different repulsion, miscibility, and phase separation between the donor and acceptor components as approved by the measurement of the donor–acceptor Flory–Huggins interaction parameter χ. Moreover, the solvent additive 1,8-diiodooctane (DIO) can induce more distinct vertical composition distribution especially in nonfullerene acceptor-based BHJ films. Thus, higher power conversion efficiencies were achieved in inverted solar cells because of facilitated charge transport in the active layer, improved carrier collection at electrodes, and suppressed charge recombination in BHJ solar cells.
The effect of electrolyte identity on the conformation of homopolymer brushes of poly(2-(2-methoxyethoxy) ethyl methacrylate) (PMEO2MA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA), as well as ...a P(MEO2MA-co-DEA) copolymer brush of 90:10 mol% composition has been examined. PMEO2MA is a thermoresponsive polymer with a lower critical solution temperature of ~28 °C, PDEA a weak polybase with an apparent pKa of ~7.5, while the copolymer brush exhibits both pH and temperature responsive behaviour. Brushes were synthesised using surface initiated ARGET ATRP. The effect of temperature at low and high pH in the presence of different electrolytes on the thickness of the P(MEO2MA-co-DEA) 90:10 mol% brush was tracked with ellipsometry and the polymer volume fraction profile was elucidated with neutron reflectometry. The effect of each electrolyte on the copolymer brush conformation as the temperature changes could be switched by changing the pH from low (charged DEA segments) to high (uncharged DEA segments). The overall behaviour of the copolymer in each salt was PDEA-like at low pH, and MEO2MA-like at high pH. At low pH a reverse Hofmeister effect was observed, while at high pH a direct Hofmeister effect was observed.
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•Copolymer brushes of P(MEO2MA-co-DEA) were synthesised via ARGET ATRP.•Brush thickness was measured with ellipsometry and neutron reflectometry.•The brush responds to temperature, pH and electrolyte identity.•Temperature-dependent Hofmeister effects could be changed by altering pH.•Overall brush behaviour was PDEA-like at low pH and PMEO2MA-like at high pH.
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