Incidence X-ray Diffraction Method Research Articles

Morphology-Dependent Photocatalytic Activity of Nanostructured Titanium Dioxide Coatings with Silver Nanoparticles.

This study aims to improve the photocatalytic properties of titanium dioxide nanorods (TNRs) and other related nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) by modifying them with silver nanoparticles (AgNPs). This preparation is carried out using a two-step method: sol-gel dip-coating deposition combined with hydrothermal crystal growth. Further modification with AgNPs was achieved through the photoreduction of Ag+ ions under UV illumination. The investigation explores the impact of different growth factors on the morphological development of TiO2 nanostructures by modulating (i) the chemical composition, the water:acid ratio, (ii) the precursor concentration involved in the hydrothermal process, and (iii) the duration of the hydrothermal reaction. Morphological characteristics, including the length, diameter, and nanorod density of the nanostructures, were analyzed using scanning electron microscope (SEM). The chemical states were determined through use of the X-ray photoelectron spectroscopy (XPS) technique, while phase composition and crystalline structure analysis was performed using the Grazing Incidence X-ray Diffraction (GIXRD) method. The results indicate that various nanostructures (dense nanorods, needle-like nanorods, nanoballs, and nanoflowers) can be obtained by modifying these parameters. The photocatalytic efficiency of these nanostructures and Ag-coated nanostructures was assessed by measuring the degradation of the organic dye rhodamine B (RhB) under both ultraviolet (UV) irradiation and visible light. The results clearly show that UV light causes the RhB solution to lose its color, whereas under visible light RhB changes into rhodamine 110, indicating a successful photocatalytic transformation. The nanoball-like structures' modification with the active metal silver (TNRs 4 Ag) exhibited high photocatalytic efficiency under both ultraviolet (UV) and visible light for different chemical composition parameters. The nanorod structure (TNRs 2 Ag) is more efficient under UV, but under visible-light photocatalyst, the TNRs 6 Ag (dense nanorods) sample is more effective.

Strain-drived giant flexoelectric field and its efficient modulation in (111) BiFeO3 films

Flexoelectric effect in ferroelectric epitaxy films has attracted significant attention due to its theoretical and application potentials. However, the origin and control of flexoelectric field is not yet fully understood. In this study, we investigated the surface structure of single-domain epitaxial BiFeO3 films with a (111) orientation using grazing incidence X-ray diffraction and X-ray reflection methods. We observed large strain gradient on the surface of the BiFeO3 films, which produces a giant flexoelectric field up to 82.55 MV/m at the surface of 15 nm thick BiFeO3 film. Additionally, we discovered the presence of a surface layer with lower electron density than that of the underlying BiFeO3 layer, which is related to the flexoelectric field. Moreover, with increased film thickness, we found the strain distribution along growth direction of the film is changed, thereby leads to the decreased flexoelectric field and increasing thickness of the surface layer respectively. These findings convinced the coupling between the strain state and surface structure, changing the thickness of the ferroelectric film and consequently the strain state is an efficient way to adjust the flexoelectric field and the surface structure.

Growth, structural and vibrational properties of hydrogenated nanocrystalline silicon thin films prepared by radiofrequency magnetron sputtering technique at room temperature

The main objective of this paper is to produce the hydrogen-free and hydrogenated nanocrystalline silicon (nc-Si:H(x)) thin films deposited onto the single-crystalline Si(100) wafer by radio-frequency magnetron sputtering (RF-MS) at a substrate temperature of ∼ 300 K. Sputtering was effectuated by a microwave plasma in a mixture of argon and hydrogen (Ar + (H2(x)) gasses taken at different proportions of hydrogen dilution: x = 0, 2.5, and 5 sccm (standard cubic centimeter per minute). The deposition rates of the nc-Si:H were fully controlled, and the thickness of these films was ∼ 200 and 300 Å. Pt-capping layer was deposited in order to protect the nc-Si:H layer from oxidation. The thickness of the capping layer was fixed at ∼ 5 Å.The effects of the hydrogen flow rate and post-growth thermal treatment on the crystalline structure and morphology of as-grown nanocrystalline silicon thin films were systematically investigated by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS), atomic force microscopy (AFM), grazing incidence x-ray diffraction (GI-XRD) and micro-Raman spectroscopy methods. From the measured data, the average nanocrystallite sizes, surface morphology and other important characteristics of these thin films were analyzed. The grown nc-Si:H thin films may be used as a semiconducting electrode material for electrochemical proton production, which is of great technological importance, especially for solid-state electrochromic device applications.

Increase in the density of Sr2Fe1.5Mo0.5O6-δ membranes through an excess of iron oxide: The effect of iron oxide on transport and kinetic parameters

Due to its widespread application in modern industry, the ongoing development of all the most important technological directions in the field of sensors, oxygen membranes, and reforming is undoubtedly a promising trend in world research and development (R&D). The search for modern highly oxygen-conducting materials used as oxygen separation membranes continues today. In this work, we investigated the following well-proven oxygen-conducting material, such as strontium ferrite-molybdate Sr2Fe1.5Mo0.5O6-δ. As an alternative for obtaining high-density ceramics, we used a co-synthesis method with a sintering additive (Fe2O3). We investigated the influence of sintering additive on the structural characteristics by certifying the phase composition by X-ray phase analysis; matrix continuity and volume distribution of Fe2O3 by secondary electron microscopy using energy dispersive X-Ray analysis; and elemental analysis of ceramic surface by X-ray photoelectron spectroscopy. The influence of Fe2O3 on the electrical conductivity was investigated using the four-probe DC method in the temperature range 100–800 °C in air. The kinetic dependences of 18O isotope-labeled oxygen on time were also obtained in the temperature range 600–800 °C and absolute oxygen pressure of 10−2 atm. The rate of heterogeneous oxygen exchange, the oxygen diffusion coefficient, and the corresponding rates of elementary processes of dissociative adsorption and incorporation of oxygen are calculated. Furthermore, it was revealed that the diffusion coefficient in the near-surface area significantly differs from the bulk one. As a consequence, this paper evaluates the observed effect and carefully analyzes the results obtained. All considered material parameters were analyzed and the regularities of the influence of surface composition on the rate-determining step of oxygen exchange were revealed. This research has made it possible to obtain dense ceramics at low temperatures and to identify a step that determines the rate of the oxygen exchange process. Finally, how strontium molybdate based thin layer on the surface and between the grains of the polycrystalline strontium ferrite-molybdates influence on the oxygen surface exchange and diffusivity is considered. The presence of such a phase in the form of a nanosized layer on the surface was convincingly proven by X-ray photoelectron spectroscopy and a grazing incidence X-Ray Diffraction method. Furthermore, the corresponding layer thickness, as well as the oxygen diffusion coefficients of the near-surface layer and the interface layer, were estimated experimentally and by modeling.

Nanostructured Ga doped ZnO thin films prepared by Sol-Gel spin-Coating / Filmes finos de ZnO NanoestruturadoS Ga doped preparados por sol-Gel spin-Coating

ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission devices, UV-photosensors and many others in Optoelectronics.In the present work we studied nanocrystalline ZnO:Ga thin films prepared by the sol–gel dip-coating technique. Samples were characterized by Grazing Incidence X-ray Diffraction(GIXD), X-ray Reflectivity (XR) and Grazing Incidence Small-Angle X-ray Scattering(GISAXS) methods and Field Effect Scanning Electronic Microscopy (FESEM). Characterization of the samples shows that the obtained films were uniform, continuous, with a crystallite size around 12 nm, an average pores size of around 3.5nm, and a volume fraction of nanoporosity between 0.18 and 0.3. Comparison of densities between doped and undoped films is discussed.

Theoretical and experimental assessment of a green corrosion inhibitor extracted from Malva sylvestris

A novel green corrosion protective film was generated on the mild steel utilizing Malva sylvestris (MS) extract and characterized by Ultraviolet–visible (UV–Vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), and grazing incidence X-Ray diffraction (GIXRD) methods. The generation film provided an inhibition efficiency of 91% in the saline media. The formation of the protective film with the total resistance of 12, 14, and 16KΩcm2 was attained at the concentrations of 1000, 1500, and 2000 ppm, respectively. In addition, the potentiodynamic polarization analysis demonstrated that the anodic reaction is greatly suppressed in the presence of MS. The outstanding corrosion resistance of the separate application of MS, along with excellent protection stability (120 h), can be a new horizon in the organic inhibitors as a practical environmental substitution for the synergistic organic/inorganic inhibitors. Theoretical studies based on quantum chemistry/molecular modelings were performed to confirm the Malva sylvestris molecules adsorption on the metal surface through their reactive sites.

Gradient of Residual Stress and Lattice Parameter in Mechanically Polished Tungsten Measured Using Classical X-rays and Synchrotron Radiation

In this work, the stress gradient in mechanically polished tungsten sample was studied using X-ray diffraction methods. To determine in-depth stress evolution in the very shallow subsurface region (up to 10 μm), special methods based on reflection geometry were applied. The subsurface stresses (depth up to 1 μm) were measured using the multiple-reflection grazing incidence X-ray diffraction method with classical characteristic X-rays, while the deeper volumes (depth up to 10 μm) were investigated using energy-dispersive diffraction with white high energy synchrotron beam. Both complementary methods allowed for determining in-depth stress profile and the evolution of stress-free lattice parameter. It was confirmed that the crystals of tungsten are elastically isotropic, which simplifies the stress analysis and makes tungsten a suitable material for testing stress measurement methods. Furthermore, it was found that an important compressive stress of about − 1000 MPa was generated on the surface of the mechanically polished sample, and this stress decreases to zero value at the depth of about 9 μm. On the other hand, the strain-free lattice parameter does not change significantly in the examined subsurface region.

Precise structural analysis of polymer materials using synchrotron X-ray scattering and spectroscopic methods

Polymers can exist in many different conformations and exhibit a variety of unique and complicated hierarchical structures, which are dominated mainly by entropy and sometimes by kinetics rather than thermodynamics due to the intrinsic high viscosity, polydispersity, and so on. The physical properties of polymeric materials are determined not only by their primary structures but also by their higher order (hierarchical) structures. Hence, precise determination of the structures at all spatial scales is essential to control the physical properties of polymeric materials. This focus review details the use of various characterization techniques, including variable-temperature (VT) synchrotron (SR) X-ray scattering, VT SR X-ray diffraction, and infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS), to determine the structure of fully liquid-crystalline ABA-type triblock copolymers, highly crystalline aromatic polyimides, and thin-film polyimides, respectively. The advantages of these methods are briefly reviewed, and the relationship between the macroscopic physical properties and the inherent microstructure is discussed. Physical properties of polymer materials are deeply related to not only the primary structure but also the higher ordered structure such as periodic structures and molecular orientation. If the target material consists of ordered and non-ordered region, the former structure can be selectively detected by X-ray scattering method, whereas structural information of both the regions is obtained by infrared absorption spectroscopy. Particularly for thin film materials, infrared pMAIRS (p-polarized multiple-angle incidence resolution spectroscopy) and GI-XRD (grazing incidence X-ray diffraction methods are very useful for precise structural analyses.

Direct observation of amorphous to crystalline phase transitions in Ge–Sb–Te thin films by grazing incidence X-ray diffraction method

Ge–Sb–Te (GST)-based PCM alloys are currently used in optical data storage. The crystallization of GST materials is the rate-limiting step for these devices, hence a deeper knowledge of the crystallization mechanism is crucial for insightful development of faster devices. In the present work, the diffraction patterns for GST-225 thin films are studied using the in situ Grazing Incidence X-ray Diffraction method upon heating. It is shown that initial amorphous film in the temperature range from 120 to 140 °C is crystallized into two phases-cubic GST-225 (Fm$${\bar{3}}$$m), and trigonal GST-147 (P$${\bar{3}}$$m1). The crystallized film is stressed and highly textured, and should be characterized by the value of the lattice parameters averaged over all crystallographic planes. The structural transition of GST-225 from cubic to trigonal phase begins at T > 180 °C. The appearance of large-scale inhomogeneities in GST-225 film at T ≥ 100 °C indicates that the process of rearrangement of atoms Ge, Sb, and Te in the as-deposited amorphous film begins long before the onset of crystallization.

Non-destructive Surface Residual Stress Profiling by Multireflection Grazing Incidence X-Ray Diffraction: a 7050 Al Alloy Study

The multireflection grazing incidence X-ray diffraction method (MGIXD) was used to analyze the surface residual stresses in 7050 Al alloy samples. This technique can provide a non-destructive stress profile in function of sample depth, avoiding the relaxation effects intrinsic to destructive methods. The state of residual stress in aeronautical aluminium samples was modulated by milling and shot peening processes. After structural characterization, the residual stress states of the samples were analyzed by multireflection and conventional stress measurement methods. The milled samples presented tensile surface residual stress relaxation attributed to thermal effects and the shot peened samples showed strong compressive stress at sub-surface, which intensity was reduced near the surface. The residual stress profiles of the Al samples were obtained by MGIXD method that evidenced properties commonly undetected in conventional residual stress studies.

Depth profile crystal orientation determination of Cu(In1−xGax)Se2 thin films by GIXRD method applying skin depth theory

In this study, Cu(In1−xGax)Se2 (CIGS) thin film was deposited on molybdenum (Mo) coated glass substrate by thermal co-evaporation technique and depth profile crystal orientation of the this film was examined by grazing incidence X-ray diffraction (GIXRD) method. The crystal structure of the CIGS thin film was determined within 20° to 80° (2θ) scanning range at 0.5° to 15° incidence angle of X-ray. Cross section images were investigated by scanning electron microscope measurements and these measurements showed that bilayer Mo thickness and CIGS thickness are approximately 480 nm and 2 µm, respectively. The surface roughness of films investigated by atomic force microscopy (AFM) and average roughness Ra was found 11.07 nm. According to GIXRD measurements; the interdiffusion of the constituent elements and their effect on the crystal structure were defined both electromagnetic field penetration (skin depth) and mass attenuation viewpoints, and also these results were supported by energy dispersive spectroscopy measurements. As a result, it was seen that the GIXRD method can be used with ease to define the crystal phase homogeneity and depth profile characterization of thin film volume applying skin depth theory.

Residual stress depth profiling of a coated WC-Co hardmetal - Part I of II: Equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method

The damage behavior of hard coated structures such as used for metalworking tools is influenced by residual stresses since they are superimposed with the load stresses that arise in application. Information on the depth gradient of these residual stresses in a coating's substrate is crucial to understand the evolution of damage in the substrate-coating composite. In the current work, the equi-penetration grazing incidence X-ray diffraction (EP-GIXD) method was adapted for the determination of the residual stress depth profile in the WC-Co hardmetal substrate below an AlCrN-based hard coating. The limits of this method in terms of coating thickness, up to which the EP-GIXD method is applicable to determine the residual stress state in the substrate, were investigated by recording the X-ray absorption in the hard coating in rocking curves. To this end, the diffraction intensity was recorded as a function of the path length in the coating that depends on the incident angle of the X-rays. Subsequently, the obtained residual stress profile was determined as a function of various mean penetration depths selected via the variation of the angle of incidence. The EP-GIXD method facilitates a significant reduction of experimental effort compared to e.g. synchrotron-based approaches for the future study of the residual stress state of substrates in substrate-coating composite structures.

Mechanical and structural properties of ODS RAF steels submitted to low-energy ions irradiation

The effect of ion implantation on mechanical and structural properties of 12%Cr ODS steel have been investigated. Specimens were submitted to single (He+ or Fe+) and dual ion beam (He+ and Fe+) implantation campaigns. Modification of three mechanical parameters: hardness, Young modulus and yield strength were characterized by means of nanoindentation technique. Structural properties were measured by using Grazing Incidence X-ray Diffraction (GIXRD) method. Correlation between obtained mechanical and structural results have been found. Recorded results show that ion-irradiation causes hardening effect which may be associated with creation of radiation defects and dislocation loops. The weakest effects have been observed for single He-ion implantation, whereas the dual beam irradiation led to significant change of all mechanical parameters. During structural analysis, small shifts of α-Fe peaks have been observed. Reported structural changes can be attributed to the effect of local stress introduced during ion irradiation.

Polycyclic aromatic hydrocarbons in model bacterial membranes – Langmuir monolayer studies

High molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) are persistent organic pollutants which due to their limited biodegradability accumulate in soils where their increased presence can lead to the impoverishment of the decomposer organisms. As very hydrophobic PAHs easily penetrate cellular membranes of soil bacteria and can be incorporated therein, changing the membrane fluidity and other functions which in consequence can lead to the death of the organism. The structure and size of PAH molecule can be crucial for its membrane activity; however the correlation between PAH structure and its interaction with phospholipids have not been investigated so far. In our studies we applied phospholipid Langmuir monolayers as model bacterial membranes and investigated how the incorporation of six structurally different PAH molecules change the membrane texture and physical properties. In our studies we registered surface pressure and surface potential isotherms upon the monolayer compression, visualized the monolayer texture with the application of Brewster angle microscopy and searched the ordering of the film-forming molecules with molecular resolution with the application of grazing incidence X-ray diffraction (GIXD) method. It turned out that the phospholipid-PAH interactions are strictly structure dependent. Four and five-ring PAHs of the angular or cluster geometry can be incorporated into the model membranes changing profoundly their textures and fluidity; whereas linear or large cluster PAHs cannot be incorporated and separate from the lipid matrix. The observed phenomena were explained based on structural similarities of the applied PAHs with membrane steroids and hopanoids.

Nanomechanical Imaging of the Diffusion of Fullerene into Conjugated Polymer.

The large Young's modulus difference between chemically modified fullerene (PCBM) and a conjugated polymer was used to nanomechanically map the diffusion of PCBM into PTB7, a high-efficiency low-band-gap conjugated polymer. The sharp tip in nanomechanical atomic force microscopy ensures a high-resolution nanomechanical characterization of the diffusion front, with the intrinsic benefits of revealing the mechanical properties of the mixtures. Localized structure changes induced by diffusion were investigated by grazing incidence X-ray diffraction methods. We found a most unusual diffusion behavior that shows Case II characteristics, where a front of PTB7 saturated with PCBM moves into the pure PTB7 with a linear time dependence. This diffusion is due mainly to a majority fraction of the disordered PTB7 that has continuous paths for PCBM diffusion without obvious energetic barriers, and as diffusion proceeds, the paths for diffusion gets larger, leading to a step in the concentration profile. The donor/acceptor-dependent diffusion constants may also contribute to the observed Case-II-like diffusion front.

Fabrication of disordered porous structures by solvent-assisted reorganisation of liquid crystal materials

ABSTRACTShaping of self-assembled soft materials is of interest for material science and nanotechnology applications because it can provide a flexible and easy method to obtain a single domain in a large area, which is used in opto-electronic and patterning applications. Here, we fabricated disordered porous structures of liquid crystals (LCs) by using a solvent-assisted treatment. Initially, the LC-based layered structures had either toric focal conic domains (TFCDs) or planar aligned samples. After treatment, disordered porous structures with randomly oriented layers were obtained although both initial and final states exhibited short-range ordering of the LC molecules. This behaviour was precisely analysed by polarised optical microscopy (POM), field-emission scanning electron microscopy (FESEM) and grazing incidence X-ray diffraction (GIXD) methods. Our resultant platform showed that disordered porous structures formed by LC materials can be used for tuneable and reversible multiple scattering applications.

Surface properties and mechanism of corrosion resistance enhancement in a high temperature nitrogen ion implanted medical grade Ti

Abstract The surface characteristics and mechanism of corrosion resistance enhancement in a high temperature nitrogen ion implanted medical grade Ti was investigated. The implantations were carried out in a constant energy (80 keV) and dose (2.1 × 10+ 18 Ion cm− 2) at room temperature (~ 300 K, without heating the substrate) and at different elevated temperatures (473 K, 673 K and 873 K by external heating of the substrate). For implantation temperature optimization, the nitride phase formation on the implanted samples was characterized using grazing incidence X-ray diffraction (GI-XRD) method and also the electrochemical polarization tests in the Ringer's solution as a simulated body fluid were carried out. A significantly enhanced corrosion resistance was achieved for the titanium sample implanted at 473 K between different implantation temperatures, which was attributed to the higher protective performance of the nitride layer over this sample, resulted from the accelerated formation of uniform and dense nitride phases on its surface. The corroded surface of the samples was observed by a field emission scanning electron microscope (FE-SEM). Several delaminations and detachments in the nitride layer were observed over the room temperature implanted sample, however the 473 K implanted sample was relatively intact. The deteriorated corrosion resistance of the 673 K and 873 K samples was attributed to the non-uniformity of the surface and phase transition from α to β-Ti, respectively. For the 473 K implanted sample as a selected implantation temperature, the enhanced corrosion resistance mechanism was investigated more accurately. The surface layer of 473 K implanted sample was studied by a Multi-Beam Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) and was compared with an unimplanted and a 300 K implanted sample. The cross section of samples was channeled using FIB method to study the distribution of nitrogen atoms by EDS mapping technique. The depth profiles of the nitrogen atoms in the implanted samples were also obtained from EDS analysis. Surface feature and roughness of samples were studied by atomic force microscopy (AFM). According to the AFM results, the surface of 473 K implanted sample with uniformly distributed nano-scaled islands, showed a higher roughness value compared to the 300 K implanted one and was predicted to have more compatibility with body tissues. Electrochemical behavior of unimplanted, 300 K and 473 K implanted samples was studied using impedance spectroscopy methods in the Ringer's solution as a simulated body fluid. The mechanism of the corrosion resistance improvement at high temperature implanted sample was developed according to the impedance spectroscopy results.

Equi-penetration grazing incidence X-ray diffraction method: Stress depth profiling of ground silicon nitride

In this work a new modification of the grazing incidence X-ray diffraction method for residual stress determination is presented. This equi-penetration grazing incidence X-ray diffraction method is especially suitable for the precise determination of the residual stress depth profile in materials. It originates from a sin2ψ approach based on the determination of the lattice spacing of various selected diffraction planes. Additionally, for each measurement the condition ∂τ/∂ψ=0 is here fulfilled and one dataset corresponds strictly to a specific mean penetration depth τ independent of the tilt angle ψ. This can be achieved by the individual adjustment of the incidence angle for each measured diffraction maximum. In the actual work, the influence of different surface finishes on the stress depth profile of commercial silicon nitride ceramic samples is investigated. The ground specimen displays an almost biaxial compressive stress parallel and near to the specimen surface of 3GPa, which decreases almost up to zero in a depth of 5μm. After the polishing process, the specimens show a strongly reduced compressive stress maximum at the surface of 1GPa, which diminishes similarly with increasing depth. The orientation between the stress component and the grinding direction is of minor influence. Furthermore, the influence of a possible residual stress component perpendicular to the sample surface is discussed.

High resolution X-ray and electron microscopy characterization of PZT thin films prepared by RF magnetron sputtering

Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt/TiO2/SiO2/Si(1 0 0) substrates in the thickness range of ∼30–550 nm by radio frequency (RF) magnetron sputtering method under different sputtering pressures were studied in the present work. High resolution grazing incidence X-ray diffraction method for residual stress and electron microscopy, particularly cross sectional transmission electron microscopy (XTEM), were used to identify the crystalline phases, and structure of the thin films at the nano-scale. Microstructure of the ultrathin films in <50 nm thickness range, consists predominantly of para-electric, oxygen deficient pyrochlore phase of Pb2Ti2O6 structure co-existing with ferroelectric perovskite PZT phase in tetragonal form. In films with thickness around 500 nm, sputtering pressure shows a strong influence on the purity of PZT phase grown. High resolution X-ray diffraction method for wafer curvature measurement and Stoney's equation were used to evaluate the biaxial stress in the films. It is found that the ultrathin films are compressively stressed with high magnitude of the order of 2 GPa which gets reduced with increasing film thickness. In the thickness range of ∼500 nm, at an optimum sputtering pressure of 4.5 Pa, the stress becomes tensile in nature with a small magnitude of 2.3 MPa. At this pressure, the film consists of almost pure perovskite phase and comparatively better electrical characteristics. X-ray reflectometry study indicates very low density of PZT films with an interlayer formed at the interface with Pt. XTEM study throws valuable insight into the nano-scale structure and reveals the presence of nano-porosity along the interface as well as within the film microstructure. This has been attributed to the observed interface roughness, reduced density, tensile residual stress as well as the poor ferroelectric properties encountered.

Does cholesterol preferentially pack in lipid domains with saturated sphingomyelin over phosphatidylcholine? A comprehensive monolayer study combined with grazing incidence X-ray diffraction and Brewster angle microscopy experiments

In this work, the Langmuir monolayers were used as a model for the analysis of the influence of cholesterol on 1,2-distearoyl-sn-glycero-3-phosphocholine – DSPC and stearoyl sphingomyelin – SSM, as well as their equimolar mixture. The aim of these studies was to compare the affinity of cholesterol to sphingomyelin and phosphatidylcholine and discuss the effectiveness of cholesterol packing with these phospholipids. The experiments involved the registration of the surface pressure–area isotherms combined with the application of Brewster angle microscopy (BAM) images and grazing incidence X-ray diffraction methods. We have performed a thorough analysis of the properties of both one-component DSPC and SSM films as well as their 1:1 mixture. Next, the effect of cholesterol on these systems was verified based on the results for 2:1 SSM/Chol, 2:1 DSPC/Chol, and 1:1:1 DSPC/SSM/Chol mixtures. It was found that both phospholipids form highly condensed monolayers, however, they differ in the orientation of acyl chains, namely the acyl chains are more tilted in DSPC film as compared to SSM monolayer as well as DSPC/SSM mixture. Furthermore, the area contraction provoked by the addition of cholesterol was found to be more pronounced for DSPC monolayer than in DSPC/SSM and SSM films. However, all the collected results allow one to postulate that the ability of cholesterol to form ordered domains with DSPC and SSM is similar and is predominantly driven by hydrophobic forces between molecules. The differences in the area condensation induced by cholesterol on the studied phospholipids films results from differences in molecular organization of pure phospholipids films rather than specific cholesterol–phospholipid interactions.