Lamellar Size Research Articles

Crystallization Behavior and Mechanical Properties of Microinjection Molded High Density Polyethylene Parts

Ultra-thin high density polyethylene (HDPE) parts with two different molecular weights were prepared by microinjection molding (MIM). The dependence of crystalline morphology and orientation, as well as the resulting mechanical properties of the samples, on molecular weight is described. The toughness of the high-molecular-weight (HMW) sample was over 2 times that of the low-molecular-weight (LMW) one, in parallel with a significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), were performed to investigate the variations of the microstructure. It is suggested that the increased crystallinity and higher degree of both molecular and lamellar orientation were beneficial to the enhancement of strength of the HMW sample. SAXS results showed that a highly oriented crystalline structure, i.e. shish-kebabs, were formed in parts of both of the two HDPE. Furthermore, a larger number of shish and kebab structure or lamellae was formed in the HMW sample due to the fact that the crystallinity was increased and the lamellar thickness and lateral crystallite size was reduced. Therefore, a stronger physical cross-linking network was formed in the HMW sample because of the increased connection points, which was in favor of the notable improvement of toughness. We suggest this issue is of great significance for achieving materials with high performance by tailoring the microstructure.

Effects of microstructure on fatigue crack propagation behavior in a bi-modal TC11 titanium alloy fabricated via laser additive manufacturing

In this study, the crack propagation behaviors in the equiaxed and equiaxed-columnar grain regions of a heat-treated laser additive manufacturing (LAM) TC11 alloy with a special bi-modal microstructure are investigated. The results indicate that the alloy presents a special bi-modal microstructure that comprises a fork-like primary α (αp) phase surrounded by a secondary α colony (αs) in the β phase matrix after the heat treatment is completed. The samples demonstrate a fast crack growth rate with larger da/dN values through the equiaxed grain sample versus across the equiaxed-columnar grain sample at low ΔK values (<13.8). The differences that are observed between the crack propagation behaviors (in the crack initiation stage) of the samples can be mostly attributed to the different size and morphology of the αp lamellae and αs colony within the grains in the equiaxed and columnar grain regions rather than the grain boundaries. The cracks prefer to grow along the α/β boundary with a smooth propagation route and a fast propagation rate in the equiaxed grain region, where the αp and α clusters have a large size. However, in the columnar grain region, small and randomly distributed αp lamellae generate a zigzag-shaped propagation path with a reduction in the da/dN value. Additionally, the change in the size of the αp lamellae in the equiaxed grains (heat affected bands, HAB) is also observed to influence the propagation behavior of the crack during the crack initiation stage.

Macro- and Micromechanics of Pearlitic-Steel Deformation in Multistage Wire Production

Ninefold drawing of pearlitic steel wire is investigated. On the basis of multiscale computer models, the behavior of pearlite colonies at the surface of the wire and in its central layer is analyzed. The key factors are the orientation of the cementite lamellae relative to the drawing axis, the interlamellae distance, and the shape of the cementite inclusions. On the basis of finite-element models, the laws governing the reorientation of the pearlite colonies, change in shape and size of the cementite lamellae, and localization of the deformation in the ferrite are determined. The model results are verified by means of metallographic results and industrial experiments.

Nanostructured Oil in Cosmetic Paraffin Waxes

This work examines the oil-binding behavior of cosmetic paraffin wax–mineral oil systems using powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and pulsed nuclear magnetic resonance (pNMR). Neat paraffin wax crystals and paraffin wax oleogels crystallized into the same polymorphic forms; however, the oleogels had a larger lamellar thickness and crystal domain size. This increase in lamellar size could indicate that the oil was structured in between individual wax crystalline lamellae (i.e., nanostructured oil). The amount of crystalline material determined by pNMR of wax oleogels increased with temperature below their melting point, because interlamellar nanostructured oil lost some mobility and displayed solid-like behavior. These results provide experimental evidence for the existence of nanostructured oil, in support of simulation studies in the literature, and shed light into the oil-binding mechanism of some materials.

Structure of tetragonal martensite in the In95.42Cd4.58 cast alloy

The structure of martensite in the In95.42Cd4.58 alloy has been studied by metallography, X-ray diffraction, dilatometry, and transmission electron microscopy. It has been shown that a massive structure built of colonies of tetragonal lamellar plates divided by a twin boundary {101}FCT is formed in the alloy under cooling below the martensite FCC → FCT transition temperature. The alloy recrystallizes after a cycle of FCT → FCC → FCT transitions with a decrease in the grain size by several times compared with the initial structure such fashion that the size of massifs and individual martensite lamella in the massif correlates with the change in the size of the alloy grain. Using thermal cycling, it has been revealed that the alloy tends to stabilize the high-temperature phase.

Fabrication of porous ceramics with double-pore structure by stepwise freeze casting using water/diphenyl methane emulsion

Porous alumina with double-pore structure was fabricated by stepwise freeze casting using water/diphenyl methane (DPM) emulsion as freezing medium. The effects of DPM content in the alumina slurry on the pore structure, mechanical properties, and specific surface area of porous ceramics were investigated. The porosity of porous ceramics was not significantly affected by DPM content in the alumina slurry due to their same solid contents. The lamellar pore size decreased, and the spherical pore size increased in porous alumina with increasing DPM content in the slurry. Closed spherical pores were formed in lamellar pore walls when the DPM content was 10vol%. The compressive strength slightly increased, and the specific surface area decreased in the samples with DPM compared with those in porous ceramics with pure water as freezing medium. The specific surface area of porous alumina was 0.566m2/g, and the interception rate for titan yellow was 44.16% when the DPM content reached 25vol% because the large spherical pore was connected to the outside. Hence, the fabricated porous alumina with DPM exhibited potential as adsorption and filtration materials.

Effects of lamella size and connectivity on fatigue crack resistance of TRIP-maraging steel

The effect of austenitization time on the fatigue crack resistance of transformation-induced plasticity (TRIP)-maraging steel was investigated by observing the crack initiation site, propagation path and fracture surface. Our analyses show that austenitization for a longer time increases austenite/martensite lamella size and connectivity of austenite. Simultaneously, increasing lamella size leads to a reduction in austenite hardness; higher austenite connectivity accelerates crack propagation. In addition, remarkable roughness on the crack surface associated with the laminated structure was observed in both steels, which caused roughness-induced crack closure.

Influence of crystallinity on the dielectric relaxations of poly(butylene succinate) and poly[(butylene succinate)-co-(butylene adipate)

Amorphous and semi-crystalline poly(butylene succinate) (PBS) and poly[(butylene succinate)-co-(butylene adipate)] (PBSA) are studied with Differential Scanning Calorimetry and Broadband Dielectric Spectroscopy (BDS). It was shown that 21mol% of butylene adipate group decreases drastically the degree of crystallinity and the size of the crystal lamellae of the PBSA. For the two semi-crystalline polymers, the microstructure is well described by a three-phase model including a small degree of rigid amorphous fraction. Fragility indexes of the main dielectric relaxation are identical for each sample which shows similar segmental dynamics of their amorphous phase. BDS allows detecting complex secondary relaxations in semi-crystalline PBS and PBSA. Local motions are impacted by the microstructure and a new relaxation occurs in more constrained amorphous environments. Correlations between molecular mobility and barrier properties are proposed.

Understanding how the aggregation structure of starch affects its gastrointestinal digestion rate and extent

Regulating the starch gastrointestinal digestion rate by control of its aggregation structure is an effective way, but the mechanism is still not clear. Multi-scale structure of waxy and normal wheat starches were studied by confocal laser scanning and scanning electron microscopes, as well as wide-angle and small-angle X-ray techniques in this study. In vitro digestion kinetics of those two starches and structure–digestion relationship were also discussed. Both waxy and normal starches show A-type diffraction pattern, but waxy variety shows a slightly higher crystallinity. Small-angle X-ray scattering results show that waxy wheat starch has higher scattering peak intensity (Imax) and a larger crystallinity lamellar repeat distance (Lp) compared with the normal wheat starch. We suggested that the higher digestion rate of waxy starch at initial stage is mainly due to more small-size particles, but the higher crystallinity and the larger crystalline lamellar size limit the digestion extent.

Morphological characteristics of solution spun nanocomposite fibers synthesized from ultra high molecular weight polyethylene, nylon-6 and carbon nanotubes, compatibilized with polyethylene-graft-maleic anhydride

Hybrid nanocomposite fibers from a blend of Ultrahigh molecular weight polyethylene (UHM-WPE)+Nylon-6+single-walled carbon nanotubes (SWCNT) were produced using a solution spinning process, both with and without a compatibilizer, Polyethylene-graft-Maleic Anhydride (PEG-g-MAH). The loading of Nylon-6, PE-g-MAH and SWCNTs was 20, 3, and 2 wt% of UHMWPE. A comparative morphological study of the fibers was performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) analysis. SEM images of hybrid fiber cross-sections have shown polymer-coated SWCNTs aligned along the direction of extrusion inside the polymer. The blends with compatibilizer have shown rough and indistinct interfacial separation of the constituent phases, as seen in both cross-sectional and longitudinal views of fibers in SEM micrographs. Whereas, the samples without compatibilizer showed distinct minor polymer phase as droplets. DSC results indicate reduction of crystallinity, crystallization rate and lamellar size in the compatibilized blends. Comparative FTIR analysis of the fiber blends showed the presence of new absorbance peaks (at 1753.62 and 1210–990 cm–1) suggesting formation of imide linkages between the UHMWPE backbone and Nylon-6 chains in the blends with compatibilizer via reactive functional groups present in the PE-g-MAH. The appearance of these peaks were more prominent when nanotubes were present in the blend.

Ultrasound-assisted reconstruction and delamination studies on CaAl layered double hydroxides

Two kinds of CaAl layered double hydroxides (CaAl-LDHs) were synthesized with chloride and nitrate anions by co-precipitation method. The samples were calcined and finally reconstructed by rehydration using ultrasounds, in the presence of NaCl or NaNO3. Reconstructed samples presented smaller lamella size than the parent ones. All samples were characterized by X-ray powder diffraction, FT-IR spectroscopy, thermogravimetric analysis and TEM microscopy. Delamination was not achieved by mechanical stirring for 2days, whereas most samples underwent delamination by the use of ultrasounds. Additionally, a hybrid CaAl-LDHs with CdTe quantum dots was synthesized by reconstruction of a calcined CaAl-LDHs in the presence of the quantum dots.

Pediatric genetic disease of the cornea.

Our objective is to evaluate the literature regarding selected genetic diseases of the cornea, including megalocornea, keratoglobus, keratoconus, cystinosis, the mucopolysaccharidoses, sclerocornea, Peters' anomaly, familial dysautonomia, and various corneal dystrophies. The transparency of the cornea is a consequence of uniformity in both size and spacing of the collagen lamellae. The cornea's clarity depends on a delicate biochemical and structural balance; consequently, genetic disorders that disrupt either its metabolic or anatomic function can cause opacity and vision loss. Many childhood corneal diseases have a genetic etiology and are associated with known syndromes. Each disorder has unique associated set of possible complications. Prognosis often depends on the extent of opacity and disorganization of the anterior segment. Corneal transplantation has been performed for these disorders with variable success.

Structure effect of thin film polypropylene view by dielectric spectroscopy and X‐ray diffraction: Application to dry type power capacitors

ABSTRACTThis work reports on the relationship between structure and dielectric properties of biaxially oriented polypropylene. The morphology of semicrystalline bioriented isotactic polypropylene films is investigated using wide angle X‐ray diffraction and Polarized Optical Microscopy. A β‐orthorhombic structure, with a crystallinity ratio of about 46%, and “Crater” morphology of the β‐form is identified. Dielectric properties are measured by Broadband Dielectric Spectroscopy over a wide temperature range (−150 to 125°C). Since the dissipation factor of the PP is very low, special care was taken to obtain valid data. Two main relaxation processes are observed: a α‐relaxation peak associated to the glass transition temperature (Tg) at temperature about −7°C, and a broad β*‐relaxation at about −60°C, partly attributed to CH orientation. The variation of the dissipation factor versus sample thickness (from 3.8 to 11.8 µm) is correlated and partly explained by the increase of crystallinity ratio and lamella size at larger thicknesses. It comes out that the thinnest film seems perfectly meet the application requesting, namely lowest dissipation factor and highest permittivity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42602.

Sized WS2 Lamellae and their Texture Orientations Growth

The tungsten disulfide (WS2) thin films, considered as inert, non-toxic, non-corrosive lubrication that is resistant to most fuel solvents, is the best solid lubricant for general industry. In this paper, WS2 thin films were deposited on steel and silicon &lt;110&gt; type substrates by DC sputtering methods with optimized experimental conditions and parameters. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were employed to characterize the surface morphology and determine the geometrical size of WS2 lamellae or microtubes. The investigation showed that both SEM and AFM analysis revealed oriented WS2 crystalline lamellae on silicon substrate while they are entangled on the steel substrate. This result leads to say precociously that the WS2 thin films deposition depend on the substrate type. Moreover, using the AFM results, we could determine the average lamella (or microtube) size which has from 200 nm to 500 nm in width and from 1mm to 1.5mm in length. The EDS tool allows attaining the composition of deposited WS2 where the tungsten and the disulfide represent about 40 and 55%, respectively.

Chemical and ultrastructural changes of ash wood thermally modified using the thermo-vacuum process: I. Histo/cytochemical studies on changes in the structure and lignin chemistry

AbstractChanges in structure and lignin chemistry were investigated in ash wood thermally modified (TMW) by the thermo-vacuum (Termovuoto) process for 3 h at 190–220°C by means of light, fluorescence, and transmission electron (TEM) microscopy combined with histo/cytochemistry. Variation in changes in native cell color in TMWs was positively correlated with differences in lignin content between cell types and cell wall regions in the reference wood. Histochemical staining showed increasing amounts of acidic groups in TMWs with different response to ethanol extraction between secondary cell walls and CMLcc(compound middle lamella/middle lamella cell corner) regions. Fluorescence microscopy of TMWs and references showed a difference in intensity and color emission of lignin autofluorescence, reflecting modification of lignin in TMWs. Changes in histochemistry and fluorescence were prominent at and above 200°C. With TEM, increased intensity of lignin staining and distortion of fiber S1layers were detected in TMW treated for 3 h at 220°C (TMW3 h, 220°C). TMW3 h, 220°Cdiffered significantly in molecular ultrastructure of fiber cell walls compared to references, such as loss of the lamellar structure and size and distribution of lignin aggregates. The modification in CMLccstructure in ash TMW3 h, 220°Cis different from that of softwoods.

Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules.

Melting of native tapioca starch granules in aqueous pastes upon heating is observed in situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) and solution viscometry. Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure. Before melting, WAXS results reveal mixed crystals of A- and B-types (∼4:1 by weight), whereas SAXS results indicate that the semicrystalline layers are composed of lamellar blocklets of ca 43 nm domain size, with polydisperse crystalline (≃7.5 nm) and amorphous (≃1.1 nm) layers alternatively assembled into a lamellar spacing of ≃8.6 nm with 20% polydispersity. Upon melting, the semicrystalline lamellae disintegrate into disperse and molten amylopectin nanoclusters with dissolved and partially untangled amylose chains in the aqueous matrix which leads to increased solution viscosity. During subsequent cooling, gelation starts at around 347 K; successively increased solution viscosity coincides with the development of nanocluster aggregation to a fractal dimension ≃2.3 at 303 K, signifying increasing intercluster association through collapsed amylose chains owing to decreased solvency of the aqueous medium with decreasing temperature.

Foam stability: The importance of film size and the micellar structuring phenomenon

AbstractThe kinetic stability of SDS foam was probed using Bartsch method at concentrations above CMC (0.03 M and 0.06 M) and below CMC (0.006 M). The foam created from the higher concentration (0.06 M) of micellar solution was more kinetically stable than that produced from the 0.03 M SDS solution and showed a stepwise decrease. On the other hand, the foam produced from SDS surfactant concentration below CMC (0.006 M) did not show such a behaviour and the height remained more or less constant. The effect of the foam lamella size on the bulk foam stability was also investigated. It was found that the critical lamella area is independent of the hydrostatic pressure. And, it took longer to reach the critical lamella area in the 0.06 M SDS system than to reach the critical lamella area in the 0.03 M SDS system. We probed the foam stability by studying the stability of a single foam lamella and observed the micellar layering phenomenon. We found 5 film thickness transitions in the case of 0.06 M SDS system and 3 thickness transitions for 0.03 M SDS system. Therefore, the foam lamella formed from the 0.06 M SDS solution is kinetically more stable than that formed from the 0.03 M SDS solution because the better layering structure in the former case slows down the liquid film drainage. Therefore, this study clearly demonstrates that both the size of the foam lamella and the micellar concentration are important factors in controlling the bulk foam stability.

Designed bimodal size lamellar O microstructures in Ti 2 AlNb based alloy: Microstructural evolution, tensile and creep properties

Abstract Microstructure evolution, tensile and creep properties of designing bimodal size lamellar O phases by thermo-mechanical processing including conventional forging, isothermal forging process and heat treatment for Ti–22Al–25Nb (at%) orthorhombic alloy were investigated. The microstructures were obtained by different solution- and age-treatment temperatures, and analyzed by the BSE technique. The creep behavior of the alloy was studied at 650 °C/150 MPa for 100 h in air. The tensile strength of the alloy at room temperature and 650 °C was also investigated. The experimental results showed that the microstructure of the isothermally forged alloys at 1080 °C contained the non-uniform distribution of lamellar O phases and B2 matrix. The advantage of the bimodal lamellar size distributed alloy can be concluded that firstly, the coarse lamellar O formed during solution process makes the alloy owns good elongation and secondly, the fine lamellar O precipitate during the aging process strengthens the alloy. The volume fraction and mean thickness of the lamellar O could be well controlled by the heat treatment. The yield strength was sensitive to the thickness of lamellar O, increase in the aging temperature leads to a decrease in strength and an increase in ductility. The relationship between creep resistance of alloys and microstructural features, such as the volume fraction of each phases, the morphology of lamellar O phases was also discussed.

A study on graphite extrusion phenomenon under the sliding wear response of cast iron using microindentation and microscratch techniques

This study focuses on the graphite flakes extrusion mechanism during microindenting and microscratching of cast iron. Observations on the graphite response under abrasive conditions revealed that the matrix deformation which is occurred during a sliding wear condition could have a significant influence on its lubricating performance. Simple microindentation and microscratch tests were conducted to explore the lamellar graphite contribution to tribofilm formation under abrasive wear conditions. The results obtained showed that induced plastic deformation which developed adjacent to the graphite compressed the lamellas and in turn resulting in extrusion of the graphite from its natural position. Further investigations on both indentation and scratch tests indicated that, surprisingly, the graphite began to be fractured and extruded from the centre of graphite lamellas, irrespective of the lamella size. Additionally, a mechanism was proposed to explain the self-lubricating and the extrusion behaviour of the lamellar graphite as a result of indentation.

Glia ECM interactions are required to shape the Drosophila nervous system

Organs are characterized by a specific shape that is often remodeled during development. The dynamics of organ shape is in particular evident during the formation of the Drosophila nervous system. During embryonic stages the central nervous system compacts, whereas selective growth occurs during larval stages. The nervous system is covered by a layer of surface glial cells that form the blood brain barrier and a thick extracellular matrix called neural lamella. The size of the neural lamella is dynamically adjusted to the growing nervous system and we show here that perineurial glial cells secrete proteases to remodel this matrix. Moreover, an imbalance in proteolytic activity results in an abnormal shape of the nervous system. To identify further components controlling nervous system shape we performed an RNAi based screen and identified the gene nolo, which encodes an ADAMTS-like protein. We generated loss of function alleles and demonstrate a requirement in glial cells. Mutant nolo larvae, however, do not show an abnormal nervous system shape. The only predicted off-target of the nolodsRNA is Oatp30B, which encodes an organic anion transporting protein characterized by an extracellular protease inhibitor domain. Loss of function mutants were generated and double mutant analyses demonstrate a genetic interaction between nolo and Oatp30B which prevented the generation of maternal zygotic mutant larvae.