Lamellar Network Research Articles

Anisotropic and self-healing hydrogels with multi-responsive actuating capability

Inspired by smart biological tissues, artificial muscle-like actuators offer fascinating prospects due to their distinctive shape transformation and self-healing function under external stimuli. However, further practical application is hindered by the lack of simple and general routes to fabricate ingenious soft materials with anisotropic responsiveness. Here, we describe a general in situ polymerization strategy for the fabrication of anisotropic hydrogels composed of highly-ordered lamellar network crosslinked by the metal nanostructure assemblies, accompanied with remarkably anisotropic performances on mechanical, optical, de-swelling and swelling behaviors. Owing to the dynamic thiolate-metal coordination as healing motifs, the composites exhibit rapid and efficient multi-responsive self-healing performance under NIR irradiation and low pH condition. Dependent on well-defined anisotropic structures, the hydrogel presents controllable solvent-responsive mechanical actuating performance. Impressively, the integrated device through a healing-induced assembly way can deliver more complicated, elaborate forms of actuation, demonstrating its great potentials as superior soft actuators like smart robots.

Study of microstructure and thermal properties of as-cast high carbon and high chromium tool steel

This work aims to investigate the microstructural and thermal properties of as-cast high carbon and high chromium cold work tool steel. The microstructure was investigated by using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) method. It was determined that at room temperature the microstructure of the investigated tool steel includes a lamellar network of M7C3 carbide precipitates along grain boundaries of ferrite grains in the base. Thermal diffusivity, specific heat capacity and thermal conductivity of the investigated steel alloy were determined in the temperature interval from 25 to 400 °C by using the laser-flash method. Thermal conductivity increases from 24.9 at 25 °C to 26.9 W/m·K at 400 °C. Phase transition temperatures in the temperature region from room temperature to 1250 °C were experimentally determined using differential scanning calorimetry (DSC). One endothermic effect in the temperature interval from 803 to 820 °C, corresponding to the ferrite/austenite phase transformation, was detected during sample heating. Experimental results were compared with the results of phase equilibria calculations obtained from the ThermoCalc software and TCFE6 database.

Effect of laser scanning speed on surface properties of Ti-Si laser clad intermetallic coatings fabricated on Ti-6Al-4V alloy

A binary Ti-Si (1 : 1) alloy coating was fabricated on Ti-6Al-4V alloy using laser cladding technique where Neodymium yttrium aluminium garnet laser was utilised. Micro-atomised powders of Ti and Si were used for deposition of multi-track clad coatings utilising power of 1.5 kW and a varied speed of 1.2 m/min, 1.6 m/min and 2.0 m/min. Scanning electron microscope coupled with energy dispersive spectrometer was used for microstructural characterisation and elemental analysis while a digital light microscope was used for optical imaging and coating thickness measurements. Phase identification was conducted using X-ray diffraction analyser and transverse microhardness evaluated at 100 gf for 10 s dwell time was achieved with the use of a Vickers hardness machine. The laser fabricated coatings were found to exhibit a decrease in grain size with an increase in the laser scanning speed. The microstructure of the coatings ranged from irregular refined grains, faceted grains and lamellar eutectic network of TiSS + Ti5Si3. The hardness of the coatings exhibited Ti, Si, TiS2 and Ti5Si3 phases averaged a 247.4% increase with maximum hardness recorded at 1.2 m/min scanning speed.

Extension decelerated crystallization in γ-irradiated isotactic polypropylene: The role of asymmetric chain relaxation

Extension induced crystallization of γ-irradiated isotactic polypropylene (γ-iPP) was studied with the combination of extensional rheology and in-situ wide-angle X-ray scattering (WAXS). The high gel content and markedly frequency-dependent storage modulus of γ-iPP indicates the occurrence of slight crosslinking accompanied by formation of free branching/dangling chains during irradiation. With WAXS, it is found that an abnormal slowing down of crystallization occurs when engineering stress passes its maximum. Lamellar network built of parent and daughter crystal also appears in this region, where daughter crystallization is commonly frustrated under such strong flow. Further increasing strain, crystallization is accelerated gradually and the acceleration becomes more significant after occurrence of strain-hardening. Interestingly, the orientation of crystal increases monotonically during this process. It is supposed that the difference in relaxation rate of cross-linked network and free branching/dangling chains is the origin of the abnormal deceleration and unique structure morphology.

Influence of the emollient structure on the properties of cosmetic emulsion containing lamellar liquid crystals

In the present study the effect of cosmetic emollients (oils and esters) varying from their chemical structure on the lamellar liquid crystals organization has been investigated. The cetearyl alcohol/cetearyl glucoside emulsifier, known for its ability to form lamellar phases was used at a level of 10% in emulsions. At this high concentration a strong lamellar network is formed. Also, each of the seven selected emollients was incorporated at level of 20%, as for a classical cosmetic emulsion. These quantities were necessary in order to assure the presence of lamellar phases in all the samples and to amplify the impact of the emollient on the structural organization of the surfactant. Additionally, a control sample was formulated, containing only emulsifier and water. Emollients were divided as a function of their chemical structure in group A (without heteroatom) and B (with heteroatom). They were first described as a function of the interfacial tension against water, in order to classify them according to their hydrophobicity.The presence of the lamellar phases in all samples was confirmed by means of optical microscopy under polarized light, and then the differences between emulsions physical properties were evidenced by static light scattering and rheological measurements. It was shown that use of A group emollients induces larger droplets size and, respectively, more elastic behavior to the emulsions. This phenomenon is related to the lamellar organization, which is dominated by α-gel for A group oils and by lamellar liquid crystals combined to α-gel for B group emollients, as showed through wide angle X-ray diffraction technique. Moreover, the influence of such structures on usage properties of emulsions was characterized via thermal analyses and spreadability tests.

"Electron/Ion Sponge"-Like V-Based Polyoxometalate: Toward High-Performance Cathode for Rechargeable Sodium Ion Batteries.

One key challenge facing room temperature Na-ion batteries lies in identifying earth-abundant, environmentally friendly and safe materials that can provide efficient Na+ storage sites in Na-ion batteries. Herein, we report such a material, polyoxometalate Na2H8[MnV13O38] (NMV), with entirely different composition and structure from those cathode compounds reported before. Ex-situ XPS and FTIR analyses reveal that NMV cathode behaves like an "electron/Na-ion sponge", with 11 electrons/Na+ acceptability per mole, which has a decisive contribution to the high capacity. The extraordinary structural features, evidenced by X-ray crystallographic analysis, of Na2H8[MnV13O38] with a flexible 2D lamellar network and 1D open channels provide diverse Na ion migration pathways, yielding good rate capability. First-principle calculations demonstrate that a super-reduced state, [MnV13O38]20-, is formed with slightly expanded size (ca. 7.5%) upon Na+ insertion compared to the original [MnV13O38]9-. This "ion sponge" feature ensures the good cycling stability. Consequently, benefiting from the combinations of "electron/ion sponge" with diverse Na+ diffusion channels, when revealed as the cathode materials for Na-ion batteries, Na2H8[MnV13O38]/G exhibits a high specific capacity (ca. 190 mA h/g at 0.1 C), associates with a good rate capability (130 mA h/g at 1 C), and a good capacity retention (81% at 0.2 C). Our results promote better understanding of the storage mechanism in polyoxometalate host, enrich the existing rechargeable SIBs cathode chemistry, and enlighten an exciting direction for exploring promising cathode materials for Na-ion batteries.

Decanol effect on viscoelasticity and rheology in lamellar mesophases

ABSTRACTThe lyotropic lamellar mesophase consists of amphiphilic molecules arranged in bilayer sheets separated by layers of water . Among its various rheological properties, two are worth mentioning: yield-point and viscoelasticity. In this work, we studied lamellar samples of lauryl sulfate /Decanol /water system, as described in the phase diagram proposed by Quist and colleagues. (molar ratio fixed in ). We have investigated the changes in and viscoelasticity properties as a function of the molar ratio . The lamellar mesophases are characterized by using polarized light microscopy and conoscopy. All the rheological measurements were performed using rotational and oscillatory rheometry. The results show that the lamellar phase exhibits gel-like behavior. The increase of molar ratio weakens the microstructure of the lamellar network, affecting the elastic properties and the yield stress values.

Two unique hydroxyl bridged lanthanide polymers incorporating mixed carboxylate ligands: Syntheses, structures, luminescence and magnetic property

Two lanthanide–organic coordination polymers incorporating both substituted imdazole dicarboxylate and benzene monocarboxylate auxiliary ligand, namely, {[Gd2(μ3-OH)(pimda)(imba) (H2pimda) H2O]·2H2O}n (1) and {[Tb2((μ3-OH)(pimda)(imba) (H2pimda) H2O]·2H2O}n (2) (H3pimda=2-propyl-1H-imidazole-4,5-dicarboxylic acid and H2imba=4-(1H-imidazole-1-ly) benzoic acid) have been obtained under the hydrothermal conditions, and have been structurally characterized by elemental analysis, IR spectrum and single X-ray diffraction. The polymers are isostructural, both crystallizing in the triclinic system, with space group of p-1. They display one dimensional (1-D) double-stranded ribbon chains based on hydroxyl-bridged [Ln4pimda2] tetranuclear unit as second building block, which are interlinked forming 2-D corrugated layer. The extensive hydrogen bondings further extend these 2-D lamellar networks into 3-D supramolecular architecture. The emission spectrum of polymer 1 exhibits ligand-to-ligand charge-transfer (LLCT) transition luminescence; polymer 2 shows characteristic f-f transition luminescence, which can be considered as a fluorescent molecular sensor for zinc(II) ions in environment. Variable-temperature magnetic susceptibility measurement reveals that multi-bridging fashion of carboxylic group in 1 results in depopulation of the stark levels for a single Gd(III) ion and/or possible antiferromagntic interactions between adjacent Gd(III) cations within the carboxylato bridged binuclear unit.

Semi-solid processing of high-chromium tool steel to obtain microstructures without carbide network

Treatment of high-alloy tool steels that involves transition to the semi-solid state can transform the sharp-edged primary carbides which usually form during solidification. These carbides severely impair toughness and are virtually impossible to eliminate by conventional treatment routes. Upon classical semi-solid processing which dissolves these carbides, the resulting microstructure consists of polyhedral and super-saturated austenite embedded in lamellar austenite-carbide network. This type of microstructure reflects in the mechanical properties, predominantly in material behaviour under tensile loading. Such a network, however, can be removed by appropriate thermomechanical treatment.In the present experiment, various procedures involving heating to the semi-solid state were tested on X210Cr12 tool steel. The feedstock was heated to the temperature range of 1220 – 1280 °C. The heating was followed by procedures involving either water quenching to the forming temperature, room temperature or temperature from the range from 500 °C to 1000 °C followed by reheating to the forming temperature. It was found that the development of the lamellar network strongly depends on the temperature of heating to semi-solid state. Thermomechanical treatment produced microstructures in which the matrix consisted of a mixture of polyhedral austenite grains and the M-A constituent. In addition, the initial lamellar eutectic network was partially or even completely melted and substituted with a mixture of very fine recrystallized austenite grains and precipitates of chromium carbides. Some fine M7C3 carbides were present in the austenitic-martensitic matrix as well. When appropriate processing parameters were chosen, very good mechanical properties were obtained, among them a hardness of 860 HV10.

Effect of nanoparticle dispersion on enhancing the specific heat capacity of quaternary nitrate for solar thermal energy storage application

Molten salt is considered to be part of the main direction for studying high temperature heat transfer and storage medium in concentrated solar power due to its good thermo physical properties. Specific heat capacity performs a significant role in increasing the overall cycle efficiency and reducing the cost of heat transfer and storage. In this paper, in order to enhance the specific heat capacity, 1wt% SiO2 nanoparticles are added into a quaternary nitrate (Ca(NO3)2-KNO3-NaNO3-LiNO3 with a low melting point called the low melting point salt (LMPS), which are mixed through ultra-sonication. Experimental results show that the specific heat capacity can be enhanced when nanoparticles are evenly distributed in the quaternary nitrate. The optimal ultra-sonication time with a frequency of 45kHz is researched. The average specific heat capacity of nano-LMPS can reach up to 1.87J/(gK) and the average enhancement reaches 19.4%. There is a good linear relationship between the specific heat capacity of nano-LMPS and ultra-sonication time. Scanning electron microgram images reveal that lamellar networks with higher density phase on the solid nano-LMPS surface exist and may cause the specific heat capacity enhancement of nano-LMPS.

Synthesizing 2D MoS2 Nanofins on carbon nanospheres as catalyst support for Proton Exchange Membrane Fuel Cells.

Highly dense 2D MoS2 fin-like nanostructures on carbon nanospheres were fabricated and formed the main catalyst support structure in the oxygen reduction reaction (ORR) for polymer electrolyte membrane (PEM) fuel cells. These nanofins were observed growing perpendicular to the carbon nanosphere surface in random orientations and high resolution transmission electron microscope confirmed 2D layers. The PEM fuel cell test showed enhanced electrochemical activity with good stability, generating over 8.5 W.mgPt−1 as compared to standard carbon black of 7.4 W.mgPt−1 under normal operating conditions. Electrochemical Impedance Spectroscopy confirmed that the performance improvement is highly due to the excellent water management of the MoS2 lamellar network, which facilitates water retention at low current density and flood prevention at high current density. Reliability test further demonstrated that these nanofins are highly stable in the electrochemical reaction and is an excellent ORR catalyst support.

Advanced Anticorrosion Coating Materials Derived from Sunflower Oil with Bifunctional Properties.

High-performance barrier films preventing permeation of moisture, aggressive chloride ions, and corrosive acids are important for many industries ranging from food to aviation. In the current study, pristine sunflower oil was used to form uniform adherent films on iron (Fe) via a simple single-step thermal treatment (without involving any initiator/mediator/catalyst). Oxidation of oil on heating results in a highly conjugated (oxidized) crystalline lamellar network with interlayer separation of 0.445 nm on Fe. The electrochemical corrosion tests proved that the coating exhibits superior anticorrosion performance with high coating resistance (>10(9) ohm cm2) and low capacitance values (<10(-10) F cm(-2)) as compared to bare Fe, graphene, and conducting polymer based coatings in 1 M hydrochloric acid solutions. The electrochemical analyses reveal that the oil coatings developed in this study provided a two-fold protection of passivation from the oxide layer and barrier from polymeric films. It is clearly observed that there is no change in structure, morphology, or electrochemical properties even after a prolonged exposure time of 80 days. This work indicates the prospect of developing highly inert, environmentally green, nontoxic, and micrometer level passivating barrier coatings from more sustainable and renewable sources, which can be of interest for numerous applications.

Coordination Polymers of Increasing Complexity Derived from Alkali Metal Cations and (4-Amino-1-hydroxybutylidine)-1,1-bisphosphonic Acid (Alendronic Acid): The Competitive Influences of Coordination and Supramolecular Interactions

Reactions of (4-amino-1-hydroxybutylidine)-1,1-bisphosphonic acid (alendronic acid = LH5) with 1 equiv of the group 1 metal bases KOH, KHCO3, Rb2CO3, RbOH, or Cs2CO3 in aqueous solution at pH 4–5 gave the corresponding complexes [M(LH4)(H2O)n]·m(H2O), M = K (1), Rb (2), or Cs (3). Crystallization of the products under varying conditions yielded differing hydrates and/or polymorphic phases. Rapid crystallization of the potassium complex 1 from water/EtOH or water/DMSO gave 2[K(LH4)]·3(H2O) (1a), whereas slow crystallization from water or water/DMSO gave [K2(LH4)2(H2O)2]·2H2O (1b phase I). For the rubidium complex 2, rapid crystallization from water/EtOH gave the analogous [Rb2(LH4)2(H2O)2]·2H2O (2b phase I), whereas slow crystallization from water/DMSO also gave 2b, but as a mixture of phase I and the structural polymorph [Rb(LH4)(H2O)]·H2O (2b phase II). In contrast, only [Cs(LH4)(H2O)]·H2O (3b phase II) was obtained for the cesium complex 3 under all crystallization conditions. A second complex type [M(LH4)(LH5)]·2H2O (M = Rb 4, Cs 5), incorporating an additional coordinated alendronic acid molecule, was also observed for the larger metals Rb and Cs as a minor product in some syntheses and isolated by fractional crystallization for 4, but as the sole product from Cs(O2CH) and LH5 for 5. The crystal structures of the complexes [M(LH4)(H2O)n]·m(H2O) 1a, 2b (phase II), and 3b (phase II) comprise edge-shared or corner-shared polyhedral chains that are linked by bridging bisphosphonate ligands into two-dimensional (2-D) sheets. The 4-ammoniobutylidene chains protrude above and below the coordination layers and interact with neighboring layers through hydrogen bonding of the terminal ammonium group forming distinctive supramolecular three-dimensional (3-D) arrays. The phase I structure of 1b and 2b comprises ribbons of parallel M4(LH4)4(H2O)4 subunits arranged in a more close packed 3-D supramolecular network. For [M(LH4)(LH5)]·2H2O (M = Rb 4, Cs 5), isolated M+ cations, bridged by bisphosphonate ligands, are arranged into 2-D sheets, with the pendant 4-ammoniumbutylidene chains resulting in a 3-D lamellar network similar to those of 1a and 2b/3b (phase II). All of the [M(LH4)(H2O)n]·m(H2O) and [M(LH4)(LH5)]·2H2O structures display strong PO–H···O(phosphonate) and N–H···O(phosphonate/water) hydrogen bond motifs which significantly impact the observed structures. Reactions of LH5 with 2 equiv of the group 1 metal bases MOH (M = Na, K, Rb, Cs) at pH 9–10 gave the dimetalated complexes [M2(LH3)(H2O)n]·m(H2O) (M = Na 6, K 7, Rb 8, Cs 9). Crystallization of 6 from water/MeOH gave [Na2(LH3)(H2O)4]·H2O (6a) as a single phase. For 7, crystallization from water/MeOH gave K2(LH3)·3(H2O) (7a) as the bulk product, whereas crystals of [K2(LH3)(H2O)6] (7b) were grown from water/DMSO solutions. On standing, the crystals of 7b were converted into the bulk product 7a. The structures of 6a and 7b are chain rather than sheet bisphosphonate coordination polymers, with a high number of coordinated water molecules. Moreover, their 3-D supramolecular structures are distinguishable, viz. a pillared array for 6a and a more compact bilayer structure for 7b. The [M2(LH3)(H2O)n]·m(H2O) complexes of the larger group 1 metal cations 8 and 9 each crystallized as a mixture of phases. Crystals of [Rb2(LH3)(H2O)5]·(H2O) (8a) and [Cs4(LH3)2(H2O)9]·2(H2O) (9a), respectively, were identified as the major component after crystallization from DMSO/H2O. The lesser hydrates [Rb4(LH3)2(H2O)8]·(H2O) (8b) and [Cs2(LH3)(H2O)4] (9b) were also identified, but were not isolated as bulk materials. The structures of 8a, 8b, 9a, and 9b each were complex 2-D sheets of bisphosphonate metal coordination polymers, which assembled through supramolecular interactions into compact 3-D arrays.

Reorganization of actin and microtubule systems in human vein endothelial cells during intercellular contact formation

Endothelial cells tightly joined to each other line the interior surface of all vessels in living organisms and ensure the regulation of vascular permeability and exchange between the blood circulating in vessels and tissue fluids of those organs in which these vessels are located. In vitro, the endothelial cell monolayer retains the basic barrier function of the native endothelium. We use endothelial cells growing in vitro as a model system to study the interaction between cytoskeleton and adhesion structures in endotheliocytes. In the present paper, cultured human vein endothelial cells were used to quantify cytoskeleton alterations from cell spreading and formation of the first cell–cell contacts to confluent monolayer formation. The actin filament system in vein endothelial cells consists of a cortical network and stress fibers arranged parallel to the substrate. This cells express two isoforms of nonmuscle actin: β- and γ-cytoplasmic actins. Antibodies to β-actin stain actin filament bundles, whereas antibodies to γ-actin visualize cortical and lamellar networks. To evaluate the state of actin structures we analyzed their fluorescence intensity near the free edge and zone of cell–cell contacts. Fluorescence intensity of β-actin structures was higher in the areas of cell–cell contacts. Fluorescence of γ-actin was the highest at the leading edges of lamellae and the weakest in the stable edges of the cells with formed cell–cell contacts. The endothelial monolayer formation was accompanied by microtubule system alteration: the number of microtubules increased at the cell edge, and what was more, the quantity of microtubules in the area of the already-formed cell–cell contact always being higher than in the leading edge region.

Percolating transport and the conductive scaling relationship in lamellar block copolymers under confinement.

The topology and transport behavior of the lamellar morphology self-assembled by block copolymers in thin films are shown to depend on the length scale over which they are characterized and can be described by percolation in a network under confinement. Gold nanowires replicating the lamellar morphology were fabricated via self-assembled poly(styrene-block-methyl methacrylate) thin films and a lift-off pattern transfer process. The lamellar morphology exhibits long-range connectivity (macroscopic scale); however, characterization of electrical conduction over confined areas (5-500 μm) demonstrates a discrete probability of disconnection that arises due to the underlying network structure and a lack of self-similarity at these microscale dimensions. In particular, it is proved that the lamellar network morphology under confinement has a conductance that is nonlinear with channel length or width. The experimental results are discussed in terms of percolation theory, and a simple, two-dimensional Monte Carlo model is shown to predict the key trends in the network topology and conductance in lamellar block copolymers, including the dependencies on composition, extent of spatial confinement, and confinement geometry. These results highlight the need to exquisitely control or engineer the self-assembled nanostructured pathways formed by block copolymers to ensure consistent device performance for any application that depends upon percolating material, ionic, or electrical transport, especially when confined in any dimension. It is also concluded that the two most promising approaches for enhancing conductivity in block copolymer materials may be achieved either at the limits of (1) perfectly oriented, single-crystalline or (2) high defect density, polycrystalline microphase separated morphologies and that nanostructured systems with intermediate defect densities would be detrimental to transport in confined systems.

Evolution of Globular Microstructures during Direct Partial Re-Melting Experiment of AISI D2 Tool Steel

Steel is a mostly challenging metal to semisolid process because of the high temperatures implicated and the prospective for surface oxidation. Slurry processing experiment was performed with AISI D2 cold work tool steel to identify the evolution of globular microstructures via Direct Partial Re-Melting Method (DPRM). Samples were heated in an argon atmosphere up to 1330°C which corresponded to about 38% of liquid fraction and held for 5 minutes. The typical microstructure after DPRM consists of globular grains (average grain size about 50μm) while the remaining interspaces were filled by precipitated eutectic carbides on the grain boundaries and lamellar network. Based on the requirements of thixoformability, the current work confirms the suitability of the AISI D2 cold work tool steel as a candidate material for semi-solid forming.

Natural Brazilian Raw Material to Develop O/W Emulsions Containing Lamellar Gel Phase (Development and Analysis of Emulsion with Vegetable Oils)

Oil-in-water emulsions were developed employing the HLB system and emulsion phase inversion (EPI) method. X-ray diffraction revealed that the anisotropic structures around the inner phase globules were lamellar gel network phases. The calculated distances between the lamellae made after preparation and 3 month latter showed that there was no swelling of the lamellar gel network indicating good stability and few changes during storage. The developed emulsions were stable and have potential to be employed for cosmetic and pharmaceutical purposes. The gel phase network and vegetal components seemed to be contributing factors.

A ytterbium polymer incorporating ethyl-4,5-imidazole-dicarboxylate and formate coligand: Structure, luminescent, and magnetic properties

A new lanthanide-organic coordination polymer incorporating both substituted imdazole dicarboxylate and formate auxiliary ligand, namely {[Yb3(HEimda)4(μ2-HCOO) · 4H2O] · 2H2O}n (I) (H3Eimda = 1H-2-ethyl-4,5-imidazole-dicarboxylic acid), has been prepared and was structurally characterized by elemental analysis, IR and X-ray diffraction. It crystallizes in the monoclinic system, space group of C2/c. The polymer I is built from two dimensional (2D) double decker networks based on the Ln4HEimda4 tetranuclear basic carboxylate as secondary building unit. The extensive hydrogen bonds extend the 2D lamellar network into a 3D supramolecular aggregate. The emission spectrum of polymer I exhibits ligand-to-metal charge-transfer luminescence. Variable-temperature magnetic susceptibility measurement reveals that the end to end bridging fashion of formate group results in the depopulation of the stark levels for a single Yb3+ ion and/or possible antiferromagntic interactions between Yb3+ ions within the carboxylato bridged dinuclear unit.

Microstructural Evolution during DPRM Process of Semisolid Ledeburitic D2 Tool Steel

Semisolid metal processing is a relatively new technology that offers several advantages over liquid processing and solid processing because of the unique behaviour and characteristic microstructure of metals in this state. With the aim of finding a minimum process chain for the manufacture of high-quality production at minimal cost for forming, the microstructural evolution of the ledeburitic AISI D2 tool steel in the semisolid state was studied experimentally. The potential of the direct partial remelting (DPRM) process for the production of AISI D2 with a uniform globular microstructure was revealed. The liquid fraction was determined using differential scanning calorimetry. The microstructures of the samples were investigated using an optical microscope and a scanning electron microscope equipped with an energy dispersive spectroscopy analyser, while X-ray phase analysis was performed to identify the phase evolution and the type of carbides. Mechanical characterisation was completed by hardness measurements. The typical microstructure after DPRM consists of metastable austenite which was located particularly in the globular grains (average grain size about 50 μm), while the remaining interspaces were filled by precipitated eutectic carbides on the grain boundaries and lamellar network.

Lamellar Structures of MUC2-Rich Mucin: A Potential Role in Governing the Barrier and Lubricating Functions of Intestinal Mucus

Mucus is a ubiquitous feature of mammalian wet epithelial surfaces, where it lubricates and forms a selective barrier that excludes a range of particulates, including pathogens, while hosting a diverse commensal microflora. The major polymeric component of mucus is mucin, a large glycoprotein formed by several MUC gene products, with MUC2 expression dominating intestinal mucus. A satisfactory answer to the question of how these molecules build a dynamic structure capable of playing such a complex role has yet to be found, as recent reports of distinct layers of chemically identical mucin in the colon and anomalously rapid transport of nanoparticles through mucus have emphasized. Here we use atomic force microscopy (AFM) to image a MUC2-rich mucus fraction isolated from pig jejunum. In the freshly isolated mucin fraction, we find direct evidence for trigonally linked structures, and their assembly into lamellar networks with a distribution of pore sizes from 20 to 200 nm. The networks are two-dimensional, with little interaction between lamellae. The existence of persistent cross-links between individual mucin polypeptides is consistent with a non-self-interacting lamellar model for intestinal mucus structure, rather than a physically entangled polymer network. We only observe collapsed entangled structures in purified mucin that has been stored in nonphysiological conditions.