Structural and Mechanical Properties of the Organic Matrix Layers of Nacre

The type of nanostructure referred to in biomineralization as a mineral bridge has been directly observed and measured in the organic matrix layers of nacre by transmission electron microscopy and scanning electron microscopy. Statistical analysis provides the geometric characteristics and a distribution law of the mineral bridges in the organic matrix layers. Experiments reveal that the nanostructures significantly influences the mechanical properties of the organic matrix layers. In addition, the mechanical analysis illustrates the effects of the nanostructures on the behaviors of the organic matrix layers, and the analytical results explain the corresponding experimental phenomena fairly well. The present study shows that the mineral bridges play a key role in the mechanical performances of the organic matrix layers of nacre. The results obtained provide a guide to the interfacial design of synthetic materials.

Microstructure and characteristics in the organic matrix layers of nacre

The direct observation of a type of microstructure in the organic matrix layers of nacre was obtained with a transmission electron microscope. The microstructure, which is referred to as mineral bridge in the biomineralization, is nanoscale and randomly distributed in the layers. Statistical analysis gives the distribution laws and characteristics of mineral bridges in the organic matrix layers. The existence of mineral bridges in nacre was confirmed, and it was shown that the microarchitecture of nacre should be described as a "brick-bridge-mortar" arrangement rather than traditional "brick and mortar" one.

Effects of Nanostructures on the Fracture Strength of the Interfaces in Nacre

A strengthening mechanism arising from a type of inorganic nanostructure in the organic matrix layers is presented by studying the structural and mechanical properties of the interfaces in nacre. This nanostructural mechanism not only averagely increases the fracture strength of the organic matrix interfaces by about 5 times, but also effectively arrests the cracks in the organic matrix layers and causes the crack deflection in this biomaterial. The present investigation shows that the main mechanism governing the strength of the organic matrix interfaces relies on the inorganic nanostructures rather than the organic matrix. This study provides a guide to the interfacial design of synthetic materials.

Mineral Bridges of Nacre and Its Effects

Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the micro architecture that is traditionally described as a "brick and mortar" arrangement. In this paper, a new microstructure, referred to as mineral bridge in the biomineralization, is directly observed in the organic matrix layers (mortar) of nacre. This is an indication that the organic matrix layer of nacre should be treated as a three-dimensional interface and the micro architecture of nacre ought to be considered as a "brick-bridge-mortar" structure rather than the traditional one. Experiments and analyses show that the mineral bridges not only improve the mechanical properties of the organic matrix layers but also play an important role in the pattern of the crack extension in nacre.

Effect Of A Negative Poisson Ratio In The Tension Of Ceramics

The effect of a negative Poisson ratio is experimentally revealed in the tension deformation of a natural layered ceramic. This effect can increase the volume strain energy per unit volume by 1100% and, simultaneously, decrease the deformation strain energy per unit volume by about 44%, so that it effectively enhances the deformation capacity by about 1 order of magnitude in the tension of the material. The present study also shows that the physical mechanisms producing the effect are attributed to the climbing on one another of the nanostructures in the natural material, which provides a guide to the design of synthetic toughening composites.

Bioorganic/inorganic hybrid composition of sponge spicules: Matrix of the giant spicules and of the comitalia of the deep sea hexactinellid Monorhaphis

The giant basal spicules of the siliceous sponges Monorhaphis chuni and Monorhaphis intermedia (Hexactinellida) represent the largest biosilica structures on earth (up to 3 m long). Here we describe the construction (lamellar organization) of these spicules and of the comitalia and highlight their organic matrix in order to understand their mechanical properties. The spicules display three distinct regions built of biosilica: (i) the outer lamellar zone (radius: >300 mu m), (ii) the bulky axial cylinder (radius: <75 mu m), and (iii) the central axial canal (diameter: <2 mu m) with its organic axial filament. The spicules are loosely covered with a collagen net which is regularly perforated by 7-10 mu m large holes; the net can be silicified. The silica layers forming the lamellar zone are approximate to 5 mu m thick; the central axial cylinder appears to be composed of almost solid silica which becomes porous after etching with hydrofluoric acid (HF). Dissolution of a complete spicule discloses its complex structure with distinct lamellae in the outer zone (lamellar coating) and a more resistant central part (axial barrel). Rapidly after the release of the organic coating from the lamellar zone the protein layers disintegrate to form irregular clumps/aggregates. In contrast, the proteinaceous axial barrel, hidden in the siliceous axial cylinder, is set up by rope-like filaments. Biochemical analysis revealed that the (dominant) molecule of the lamellar coating is a 27-kDa protein which displays catalytic, proteolytic activity. High resolution electron microscopic analysis showed that this protein is arranged within the lamellae and stabilizes these surfaces by palisade-like pillars. The mechanical behavior of the spicules was analyzed by a 3-point bending assay, coupled with scanning electron microscopy. The load-extension curve of the spicule shows a biphasic breakage/cracking pattern. The outer lamellar zone cracks in several distinct steps showing high resistance in concert with comparably low elasticity, while the axial cylinder breaks with high elasticity and lower stiffness. The complex bioorganic/inorganic hybrid composition and structure of the Monorhaphis spicules might provide the blueprint for the synthesis of bio-inspired material, with unusual mechanical properties (strength, stiffness) without losing the exceptional properties of optical transmission. (C) 2007 Elsevier Inc. All rights reserved.

Fabrication of self-assembled palladium nanosheets using layered organic/inorganic hybrid as the template

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl2) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl4}(2-) network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

Analysis of the strengthening and toughening of a biomaterial interface

Based on the transmission electron micrographs of nacre, the existence of mineral bridges in the organic matrix interface is confirmed. It is proposed that the microarchitecture of nacre should be considered as a "brick-bridge-mortar" (BBM) arrangement rather than traditional "brick and mortar" (BM) one. Experiments and analyses indicate that the mineral bridges effectively affect the strength and toughness of the interfaces in nacre. Comparison with a laminated composite with BM structure, SiC/BN, shows that the pattern of the crack extension and the toughening mechanism of the two materials are different. This reveals that the mineral bridges play a key role in the toughening mechanisms of nacre, which gives a conceptual guidance in material synthesis.

Nanostructure of nacre and its mechanical effects

A type of nanostructure in the organic matrix interfaces of nacre, which is referred to as mineral bridge in the biomineralization, is directly observed with a transmission electron microscope. It is showed that the existence of mineral bridges in nacre i

High-performance 980-nm quantum-well lasers using a hybrid material system of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm(2) (at a cavity length of 1500 mu m), internal quantum efficiency of similar to 95%, and low internal loss of 1.8 cm(-1). Both broad-area and ridge-waveguide laser devices are fabricated. For 100-mu m-wide stripe lasers with a cavity length of 800 Irm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T-0) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-mu m-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A.

The investigation of exfoliation process of organic modified montmorillonite in thermoplastic polyurethane with different molecular weights

Cloisite 30B (30B) was melt-mixed with two kinds of thermoplastic polyurethane (TPU) with different molecular weights to discern the roles of molecular diffusion and shear in the exfoliation process. The higher level of exfoliation was achieved in TPU matrix with higher molecular weight due to the appropriate viscosity. In order to have an insight into the mechanism of exfoliation, the degree of dispersion and exfoliation of 30B was characterized by wide angle X-ray diffraction and transmission electron microscopy. The layers of 30B were exfoliated via a slippage process, which was also observed in polyamide 12 nanocomposites recently.

Charge transport in accumulation layers of organic heterojunctions

We studied the charge transport in organic heterojunction films consisting of copper phthalocyanine (CuPc) and copper hexadecafluorophthalocyanine (F16CuPc). The heterojunction effect between CuPc and F16CuPc induced high-density carriers at both sides of heterojunction. The Hall effect was observed at room temperature, which demonstrated the existence of free carriers and their delocalized transport under heterojunction effect. The Hall mobility of 1.2 cm(2)/V s for holes and 2.4 cm(2)/V s for electrons indicated that the transport capability of the heterojunction films is comparable to single crystals. The transport process was further explained by the multiple trap-and-release model according to the temperature dependence of conduction.

Undercut structure fabricated by complementary-structure micropatterning technique for the passive-matrix display of organic light-emitting diodes

This paper reports a new patterning method, the complementary-structure micropatterning (CSMP) technique, to fabricate the undercut structures for the passive-matrix display of organic light-emitting diodes (OLEDs). First, the polyvinylpyrrolidone (PVP) stripe patterns with a trapeziform cross-section were formed by micromolding in capillaries. Then the photoresist was spin coated on the substrate with the patterned PVP stripes and developed in water.

Very low hysteresis organic thin-film transistors

Very low hysteresis vanadyl-phthalocyanine/para-sexiphenyl thin-film transistors (TFTs) have been fabricated using benzocyclobutenone (BCBO) derivatives/tantalum pentoxide (Ta2O5)/BCBO triple gate dielectrics. The field effect mobility, on/off current ratio and threshold voltage of organic TFTs are 0.45 cm(2) V-1 s(-1), 3.5 x 10(4) and -6.8 V, respectively. To clarify the mechanism of hysteresis, devices with different dielectrics have been studied. It is found that the bottom BCBO derivatives (contact with a gate electrode) block the electron injection from a gate electrode to dielectrics.