Lamellar Layers Research Articles

Structure and Properties of Graphene Oxide Aerogels by Freeze-Drying Process

The structure and properties of graphene oxide aerogels (GOA), prepared by a modified Hummer’s method followed by a freezing-drying process in addition to a pre-oxidized procedure, were studied through FTIR, Raman, SEM and XDR techniques. FTIR results indicated the existence of -C-O, -C-OH and -C=O function groups on the GOA surface. Therefore, the D band intensity of GOA sample exhibited remarkable increasing in the Raman spectra compared with of graphite; it may be due to change the order-structure of graphite to disorder-structure of GOA. The diffractive peak for the graphite at 2θ of 26.5° vanishes instead the one around 10.0° occurred in the XRD pattern for the GOA supported that the structure and d-spacing changed seriously from graphite to GOA. The SEM images revealed that the micro-structure of graphene layer of GOA was wrinkler and softer than that of graphite, however, the former involved fewer lamellar layer appearance with wrinkles on the edges of the graphene. All the characterized evaluation confirmed that the graphite powder has been transformed into a GOA structure through the modified Hummers’ method.

Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly)n model peptides

Solid-state NMR is a powerful analytical technique to determine the composite structure of Bombyx mori silk fibroin (SF). In our previous paper, we proposed a lamellar structure for Ala-Gly copolypeptides as a model of the crystalline fraction in Silk II. In this paper, the structure and dynamics of the crystalline fraction and of a better mimic of the crystalline fraction, (Ala-Gly-Ser-Gly-Ala-Gly)n (n = 2–5, 8), and 13C selectively labeled [3-13C]Ala-(AGSGAG)5 in Silk II forms, were studied using structural and dynamical analyses of the Ala Cβ peaks in 13C cross polarization/ magic angle spinning NMR and 13C solid-state spin-lattice relaxation time (T1) measurements, respectively. Like Ala-Gly copolypeptides, these materials have lamellar structures with two kinds of Ala residues in β-sheet, A and B, plus one distorted β-turn, t, formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement. However, because of the presence of Ser residues at every sixth residue in (AGSGAG)n, the T1 values and mobilities of B decreased significantly. We conclude that the Ser hydroxyls hydrogen bond to adjacent lamellar layers and fix them together in a similar way to Velcro®.

Influence of Tool Offset on Performance of Thin Al–Cu Dissimilar Metal Friction Stir Butt Welded Joint

The 1-mm-thick Al to Cu friction stir welding is successfully performed at the tool offsets toward Al side ranging from 0 to 2 mm. With increasing tool offset, the phenomenon of material sticking to tool shoulder surface is restricted and the area of Al–Cu mixing zone is reduced progressively. As the tool offset is increased from 0 to 1 mm, the weld shows a variation of intermetallic phases from CuAl2 + Cu9Al4 to CuAl2 and exhibits a lowering in hardness and tensile properties. The 2-mm-offset weld without intermetallic phases discernible exhibits the highest hardness due to the thinness of Cu lamellar and Al-rich compound layers, and the joint featured by a failure at the relatively soft region adjacent to harder Al–Cu mixing zone in a ductile pattern shows the best tensile strength equivalent to 80% of that of the base material.

Formation mechanism of surface oxide layer of grain-oriented silicon steel

The surface oxide layer of grain-oriented electrical steels was investigated by scanning electron microscopy. The formation mechanism and the influence on the glass film of the surface oxide layer were analyzed by the calculation of thermodynamics and kinetics. The surface oxide layer with 2.3 μm in thickness is mainly composed of SiO2, a small amount of FeO and Fe2SiO4. During the formation of surface oxide layer, the restriction factor was the diffusion of O in the oxide layer. At the initial stage of the decarburization annealing, FeO would be formed on the surface layer. SiO2 and silicate particles rapidly nucleated, grew and formed a granular oxide layer in the subsurface. As the oxidation layer thickens, the nucleation of new particles decreases, and the growth of oxide particles would be dominant. A lamellar oxide layer was formed between the surface oxide layer and the steel matrix, and eventually formed a typical three-layer structure. During the high temperature annealing, MgO mainly reacted with SiO2 and Fe2SiO4 in the surface oxide layer to form Mg2SiO4 and Fe2SiO4 would respond first, thus forming the glass film with average thickness of 4.87 μm.

Biobased Cycloolefin Polymers: Carvone-Derived Cyclic Conjugated Diene with Reactive exo-Methylene Group for Regioselective and Stereospecific Living Cationic Polymerization.

Carvone, a naturally abundant chiral cyclic α,β-unsaturated carbonyl compound, was chemically transformed into cyclic exo-methylene conjugated dienes. The exo-methylene group had high reactivity in cationic polymerization and was efficiently polymerized in a controlled manner via regioselective 1,4-conjugated additions using initiating systems effective for living cationic polymerization of vinyl ethers. The obtained polymers with 1,3-cyclohexenyl units and tetra-substituted olefins in the main chain showed high glass transition temperatures over 110 °C. The chiral monomer underwent stereospecific polymerization to result in polymers with low solubility and weak packing of the rigid main chain in the lamellar layers. The racemic mixture resulted in soluble amorphous polymers, which were subsequently hydrogenated into cycloolefin polymers with enhanced thermal properties.

Synthesis, crystal structure of a iron-manganese bimetal MOF and its graphene composites with enhanced microwave absorption properties

FeMn-MOF (namely 35pFeMn) and FeMn-MOF/G composites (G: graphene; namely 35pFeMn/G-5 and 35pFeMn/G-10) were synthesized by facile one-pot solvothermal reactions. The structures and morphologies of the as-prepared samples were characterized by scanning electronic microscope (SEM), X-ray diffractometry (XRD),X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The structure of 35pFeMn was determined via the single crystal diffraction data and the XRD data indicate that the other composites have the identical structure to 35pFeMn. The experimental results show that graphene adhere entirely to the surface of the FeMn-MOF consisting of lamellar layer, moreover, the unique structure effectively decreases the density of the composites. Microwave absorption (MWA) properties of paraffin containing 40 wt% samples were investigated at room temperature in the frequency region of 1–18 GHz. The results indicated 35pFeMn/G-10 shows the most excellent MWA properties as its reflection loss is below −10 dB (90% absorption) at 12.59–16.17 GHz, and the minimal RL is almost −34.47 dB at 14.1 GHz with a sample thickness of only 1.5 mm. The intrinsic physical and chemical properties of the materials, the synergy of 35pFeMn and graphene, and particularly the interfacial polarization between 35pFeMn and graphene are fundamental to the enhancement of MWA properties. The as-prepared 35pFeMn/G-10 exhibits a promising designable approach to lightweight, strong-absorbed MWA materials.

A new genus Turneroconcha (Bivalvia: Vesicomyidae: Pliocardiinae) for the giant hydrothermal vent clam 'Calyptogena' magnifica.

A new monotypic genus, Turneroconcha, is established for T. magnifica (Boss Turner) which was originally assigned to the genus Calyptogena Dall. The distinguishing morphological characters of the new genus are the combination of both conchological and anatomical features including: the presence of only two tooth elements in the right valve; submerged location of the posterior part of the posterior lamellar ligament layer; the absence of a subumbonal pit, lunular incision, escutcheon and pallial sinus; the presence of both pairs of demibranchs; the tubular structure of marginal parts of the interlamellar septa in gills; an inner valve of the inhalant siphon without processes; tentaculate inner mantle fold 3 and a Z-shaped digestive tract. Analysis of morphological data on Recent and fossil pliocardiines shows that Turneroconcha gen. nov. can be presently considered as a monotypic genus. The comparative morphological analysis of the new genus with described pliocardiine genera is consistent with available molecular results. Turneroconcha gen. nov. is endemic to the East-Pacific Rise and Galapagos Rift and occurs at water depths of 2251 to 2791 m. It is the only pliocardiine genus known so far with a mainly epifaunal life habit. No fossils of Turneroconcha gen. nov. are known.

Atomic-scale insights into interface thermal resistance between epoxy and boron nitride in nanocomposites

The out-plane thermal conductivity of hexagonal boron nitride nanosheet (hBNNS)/epoxy resin (EP) composites in the perpendicular to the lamellar layers direction as well as the interface thermal resistance (ITR) between EP and hBNNS in nanocomposites are investigated via molecular dynamics (MD) simulations, and compared with those of the graphene nanosheet (GNS)/epoxy nanocomposites and experimental results. Results show that the out-plane thermal conductivity of the hBNNS/EP is higher than that of GNS/EP at the same volume fraction of the fillers. The obtained ITR between EP and GNS is (4.48-8.43)×10−9 m2KW−1, consistent with the previous reported experimental and simulation results. Interestingly, the calculated ITR between EP and hBNNS is (2.42–3.62)×10−9 m2KW−1, smaller than that between EP and GNS. The ITRs exponentially decay with the number of layers of hBNNS (or GNS). This work provides insights into predicting and understanding the thermal conductivity of hBN and graphene-based nanocomposites using computational approaches.

Thermal-oxidative aging mechanism of asphalt binder based on isothermal thermal analysis at the SARA level

To better understand the thermal-oxidative aging mechanism of asphalt binder at the component level, a new isothermal agingmethod was developed to discuss thermal behaviors of saturates, aromatics, resins and asphaltenes (SARA) fractions. Volatile constituents released from SARA fractions were identified and the changes in chemical compositions, morphology and elements of SARA fractions were characterized before and after the thermal-oxidative aging. Results indicate that the mass losses of saturates and resins are 2.1% and 0.7%, respectively. However, the aromatics and asphaltenes masses are increased by 2.0% and 5.2%, respectively. Also, endothermic reactions occur in saturates and aromatics, and endothermic and exothermic reactions are basically equivalent in resins, and exothermic reactions occur in asphaltenes. Further, CO, CO2, CH4 and light oxygen-containingcompounds are released during the aging of SARA fractions, and short-chain alkanes are generated in saturates. Low molecular hydrocarbons, CO2, and SO2 are emitted, and more aromatic ring products are generated in aromatics. Carboxylic acids, small molecular unsaturated hydrocarbons and SO2 are volatilized, and fused aromatic rings, alcohols and ethers are produced in resins. Unsaturated hydrocarbons are released, and the molecular polymerization becomes obvious in asphaltenes. Additionally, after the isothermal aging, pores or bulges are left in saturates, and obvious folds and pores appear on aromatics. Cluster whiskers, lumps and disordered lamellar layers are observed on resins, and resins and asphaltenes become loose, dry and rough. C element content is increased, but O element content is decreased. Finally, various volatiles are released from SARA fractions at different aging stages. The thermal-oxidative aging of asphalt binder consists of the volatilization of light components and the oxidation of side chains in benzene methyls and aliphatic hydrocarbons, leading to the content changes of SARA fractions in asphalt binder.

Molecular Simulations of Laser Spike Annealing of Block Copolymer Lamellar Thin-Films.

We use molecular dynamics simulations to study the phase behavior of a coarse-grained lamella-forming A-b-B diblock copolymer under thin-film soft confinement for different heating cycle lengths, film thicknesses, and substrate-polymer affinities. This model describes the effect on thin-film morphology with a free surface (air-polymer interface) and a solid substrate. Our simulation results were first validated by showing that they capture changes for the order-disorder transition temperature with annealing conditions consistent with those found in laser spike annealing experiments, when the vertical lamella phase formed on neutral substrates. In addition, simulations with a substrate selective for a particular block revealed the formation of other phases, including a mixed vertical-horizontal lamella and a metastable island phase having horizontal but incomplete lamella layers. The nanoscale roughness features of this island phase, and hence its surface wettability, can be tuned with suitable choices of chemistry and annealing conditions.

Phase Behavior and Phase Diagram of Polystyrene-b-Poly(Perfluorooctylethyl Acrylates).

Fluorocontaining polymers bearing special properties are unique and important materials in modern society. In this work, we focused on the phase behavior and phase diagram of poly(styrene-block-perfluorooctylethyl acrylate) with a volume fraction varying from 0.2 to 0.8. Small-angle X-ray scattering and transmission electron microscopy showed the phase formation in the sequence of hexagonally packed cylinders (HEX) to lamellar layers (LAM) to inverse hexagonally packed cylinders (iHEX) in this series of block polymers. Wide-angle X-ray diffraction experiments proved that the fluorodomains of the LAM phases and the matrix of iHEX phases contained layered structures formed by the crystallization of fluorosegments. During heating, the self-assembled lattice remained intact even after the melting of fluorodomain, with barely changed lattice parameters. Such hierarchical structural formation was understood by chain conformation and domain interaction, which may provide new insight into the molecular design of advanced materials.

Two-Dimensional Ultrathin Multilayers ZIF-8 Nanosheets with Sustained Antibacterial Efficacy for Aeromonas Hydrophila

In this study, a simple and efficient strategy with bola-form template to construct the two-dimensional ultrathin multilayers ZIF-8 nanosheets was developed, the nanosheet was used as antibacterial for Aeromonas hydrophila (A. hydrophila) for the first time. It shows the obviously lamellar structure with eleven ZIF-8 lamellar crystal layers uniformly distributed in each nanosheet, the thickness of the whole nanosheet is approximately 36 nm, and the distance between the two adjacent layers is approximately 3.6 nm. It has the high antibacterial efficacy for A. hydrophila, which can be killed within 8 h.

Role of Defects in Achieving Highly Asymmetric Lamellar Self-Assembly in Block Copolymer/Homopolymer Blends.

Lamellar structure is a prominent state in soft condensed matter. Swelling lamellar layers to highly asymmetric structures by a second component is a facile, cost-effective strategy to impart materials with adaptive size and tunable properties. One key question that remains unsolved is how defects form and affect the asymmetric lamellar order. This study unravels the role of defects by swelling a miktoarm block copolymer with a homopolymer. Ordered lamellae first lose translational order by a significant increase in the number of dislocations and then lose orientational order by the generation of disclinations. The homopolymers are not uniformly distributed in defective lamellae and primarily segregate in the vicinity of disclination cores. The free energy of defects is mainly contributed by molecular splay and significantly alleviated by an increased radius of local curvature. This study provides direct evidence to reveal the role of defects and lamellar order in block copolymer/homopolymer blends and also sheds light on understanding analogous structural transitions in other soft systems, including lyotropic liquid crystals, phospholipid membranes, and polymer nanocomposites.

Exosomes from Human Adipose Tissue-Derived Mesenchymal Stem Cells Promote Epidermal Barrier Repair by Inducing de Novo Synthesis of Ceramides in Atopic Dermatitis.

Atopic dermatitis (AD) is a multifactorial, heterogeneous disease associated with epidermal barrier disruption and intense systemic inflammation. Previously, we showed that exosomes derived from human adipose tissue-derived mesenchymal stem cells (ASC-exosomes) attenuate AD-like symptoms by reducing multiple inflammatory cytokine levels. Here, we investigated ASC-exosomes’ effects on skin barrier restoration by analyzing protein and lipid contents. We found that subcutaneous injection of ASC-exosomes in an oxazolone-induced dermatitis model remarkably reduced trans-epidermal water loss, while enhancing stratum corneum (SC) hydration and markedly decreasing the levels of inflammatory cytokines such as IL-4, IL-5, IL-13, TNF-α, IFN-γ, IL-17, and TSLP, all in a dose-dependent manner. Interestingly, ASC-exosomes induced the production of ceramides and dihydroceramides. Electron microscopic analysis revealed enhanced epidermal lamellar bodies and formation of lamellar layer at the interface of the SC and stratum granulosum with ASC-exosomes treatment. Deep RNA sequencing analysis of skin lesions demonstrated that ASC-exosomes restores the expression of genes involved in skin barrier, lipid metabolism, cell cycle, and inflammatory response in the diseased area. Collectively, our results suggest that ASC-exosomes effectively restore epidermal barrier functions in AD by facilitating the de novo synthesis of ceramides, resulting in a promising cell-free therapeutic option for treating AD.

High-amylose wheat and maize starches have distinctly different granule organization and annealing behaviour: A key role for chain mobility

For regular starches, gelatinization occurs over a relatively narrow temperature range in excess water; however, high-amylose starches typically gelatinise over an extended temperature range by a process that is less understood. The present study compared granule organisation of high-amylose starches from wheat (HAWS) and maize (HAMS), and investigated the role of granule organization in determining the gelatinization heterogeneity and different responses to annealing. During gelatinization (starch/water = 1:2), the melting peaks of double helices and amylose-lipid complexes are merged in HAMS, whereas the peaks are separated for HAWS. It is hypothesized that the glucan chains in HAWS are relatively more mobile (i.e., fewer inter-chain interactions), compared to HAMS. Due to this mobility, hot water leaches amylose more readily from HAWS than from HAMS at similar levels of apparent amylose content. After two-step annealing, To (gelatinization onset temperature) of HAWS increased from 58 to 84 °C, while To of HAMS only increased from 70 to 82 °C. For HAWS, annealing apparently extended double helical lengths and made semi-crystalline lamellae more heterogeneous, but reduced double helix content. For HAMS with more organised granular structure, annealing has a relatively limited effect on lamellar layers and chain conformation. The study demonstrates that HAMS and HAWS have distinctly different granule organisation and behaviours during hydrothermal processing and that HAWS, with more mobile chains, has the potential to form thermostable molecular order. The molecular basis for these differences is proposed to be the greater proportion of very long chains/branches in HAWS than HAMS.

Differences in mechanical behaviors and characteristics between natural graphite/copper composites and carbon-coated graphite/copper composites

Natural graphite/copper (NG/Cu) composites and carbon-coated graphite/copper (CCG/Cu) composites were prepared via powder metallurgy by using electrolytic copper powder, natural graphite and phenolic resin as raw materials. The mechanical deformation behaviors and characteristics and the structure evolution of the two composites under the actual force form during friction (bending and compression) were investigated in detail. The results show that CCG/Cu composites exhibit ductile fracture and can withstand higher loads in the bending test, which is due to a high compactness and continuity matrix and a uniform distribution of intact CCG, while NG/Cu composites show brittle fracture. Owing to the low compactness and continuity matrix and the incomplete NG structure of NG/Cu composites themselves, the deflection and tear of matrix, the deflection and lamellar layers slide of NG and some NG connection occur from deformation to failure in the compression test, and these structural defects are exacerbated until the main crack penetrates through the sample, leading to failure. Although CCG/Cu composites eventually fail in the compression test, carbon coating with phenolic resin on natural graphite effectively delays the deformation and failure and improves the compression strength of CCG/Cu composites. This work provides a reliable mechanical analysis for the failure mechanism of graphite/copper composites during friction.

Comparison of embryonic and adult shells of Sepia officinalis (Cephalopoda, Mollusca)

Development and evolution of the shell in cephalopods is difficult to establish as there is few species with a calcified shell that could be fossilized (stable in geological time). Internal cuttlebone of sepiids is so particular that homologies are difficult to find. The developmental sequence in embryos give some response elements by comparison with adult cuttlebone. The macro and microstructure of adult shell is well known but an approach at nanostructural level allows to determine structure and composition of the two main parts, the dorsal shield and chambered part. We evidence in the embryonic shell, mainly organic, a light calcification of the shell, which occurs directly as aragonite, as it is all along the formation of the shell and whatever the parts. In embryonic shell, the prismatic and/or lamellar layers, present in adult, are not differentiated and the dorsal shield grows progressively, from posterior to anterior. Despite microstructural differences, all layers of both chambered part and dorsal shield are composed of rounded nanogranules (between 50 and 100 nm), similar to what is found in other mollusc shells. Finally, the presence of pillars evidenced in embryo suggests either that their absence in extinct lineages of sepiids is the result of a diagenetic process or that they are a novelty in present sepiid species.

Tissue Engineering the Annulus Fibrosus Using 3D Rings of Electrospun PCL:PLLA Angle-Ply Nanofiber Sheets

Treatments to alleviate chronic lower back pain, caused by intervertebral disc herniation as a consequence of degenerate annulus fibrosus (AF) tissue, fail to provide long-term relief and do not restore tissue structure or function. The future of AF tissue engineering relies on the production of its complex structure assisted by the many cells that are resident in the tissue. As such, this study aims to mimic the architecture and mechanical environment of outer AF tissue using electrospun fiber scaffolds made from a synthetic biopolymer blend of poly(ε-caprolactone) (PCL) and poly(L-lactic) acid (PLLA). Initially, an aligned bilayer PCL:PLLA scaffold was manually assembled at ±30° fibers direction to resemble the native AF lamellar layers; and bovine AF cells were used to investigate the effect of construct architecture on cell alignment and orientation. Bilayer scaffolds supported cell adhesion and influenced their orientation. Furthermore, significant improvements in tensile stiffness and strength were achieved, which were within the reported range for human AF tissue. Electrospun bilayer scaffolds are, however, essentially two-dimensional and fabrication of a complete three-dimensional (3D) circular construct to better replicate the AF's anatomical structure is yet to be achieved. For the first time, a custom-built Cell Sheet Rolling System (CSRS) was utilized to create a 3D circular lamellae construct that mimics the complex AF tissue and which overcomes this translational limitation. The CSRS equipment is a quick, automated process that allows the creation of multilayered, tube-like structures (with or without cells), which is ideal for mimicking human cervical AF tissue in term of tissue architecture and geometry. Tube-like structures (6 layers) were successfully created by rolling ±30° bilayer PCL:PLLA scaffolds seeded with bovine AF cells and subsequently cultured for 3 weeks. Cells remained viable, purposefully oriented with evidence of collagen type I deposition, which is the main structural component of AF tissue. This is the first study focused on applying CSRS technology for the fabrication of a more clinically-relevant, 3D tissue engineered scaffold for AF tissue regeneration.

Theoretical prediction for mechanical properties in nanotwinned and hierarchically nanotwinned metals with different twin orders

The mechanism-based plasticity model on the mechanical properties in nanotwinned and hierarchically nanotwinned metals is further developed, in which the analytical formulae of flow stress and failure strain with respect to various factors are provided. The strength, ductility and fracture toughness in metals with different twin orders are analyzed systemically based on the theoretical model, and the effects of grain size and twin spacing are emphasized. It shows that the effect of twin spacing is significant, and high strength combined with good ductility can be achieved by optimizing the combination of twin spacing in different layers of twin lamellae. Regarding to metals with different twin orders, the variation of mechanical properties with the twin spacing is different, and relatively good mechanical performance can also be achieved in materials with low twin order by adjusting the twin spacing, and it could even be better than that in metals with higher twin orders. Besides, grain size also contributes to the mechanical properties, there may be a critical grain size at which the ductility in the hierarchically nanotwinned metal reaches the peak value, and the relationship between the mechanical property and the twin spacing would change in the case of extremely small grain size. Related analysis is of great importance for the material design in which the optimization of mechanical properties is achieved and the manufacture difficulty can be reduced.

The difference of creep compliance for wood cell wall CML and secondary S2 layer by nanoindentation

Wood is generally considered a linear orthotropic viscoelastic. The creep of cell wall under long-term load is important for the deformation and destruction of wood. The aim of this study was to investigate the difference of creep compliance between compound middle lamella (CML) and secondary S2 layers by nanoindentation creep testing. The results indicated that the creep compliance of cell wall under compression along grain increased with the maximum load and loading rate increasing. Furthermore, the creep compliances and creep compliance percentages of the CML layer were more than that of the secondary S2 layer, and the viscoelastic behavior of the CML layer also was more sensitive to MC compared with the S2 layer. Finally, the Burgers’ model was appropriate for predicting the viscoelastic behavior of wood cell walls. The parameters of Burgers’ model dropped markedly with increased MC. These parameters in the CML layer also were lower than those of S2 layer. The differences of creep properties between the CML and S2 layers can prove that the slippage failure of cell wall under compression along grain occurs in the S2 layer.