Selective laser sintering of barium titanate–polymer composite films

A selective laser sintering process has been used to consolidate electro-ceramic thin films on silicon substrates. Methods of forming pre-positioned layers of barium titanate were investigated by spin-coating the feedstock powder mixed with a commercial polymer photo-resist. The ceramic–polymer composite was deposited directly onto a nickel film which was evaporated onto a silicon substrate, pre-oxidised to form an electrically insulating layer. A range of laser processing parameters was identified in which consolidated barium titanate layers could be formed. The laser power was found to be more influential in forming sintered microstructures than laser exposure time. The microstructure of barium titanate films is sensitive to the SLS laser-processing conditions, with the optimum laser powers for the processing of the BaTiO₃–polymer found to be in the range 17–20 W. This article highlights the possibility of using ‘direct write’ techniques to produce piezoelectric materials upon silicon substrates.     

Influence of the structure of a modifier layer on the compatibility of polymers with a modified montmorillonite

The dependence of the compatibility of a modified montmorillonite with different-polarity polymers on the structure of a modifier layer formed on the montmorillonite surface has been investigated. It is shown that the layers forming an ordered structure in the interplane spaces of the clay do not provide an exfoliation of the silicate plates of the clay or a significant intercalation of polymer chains into the interlayer space of the montmorillonite. An optimum structure of a modifier layer, providing a significant intercalation of polymer chains into the interlayer spaces of the montmorillonite and an exfoliation of the clay in its compounds with a maleinized polypropylene, obtained by mixing in a melt, has been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 35–40, September–October, 2005.     

Structure and properties of nylon 6–clay nanocomposites: effect of temperature and reprocessing

Melt-compounding is a technique which has been commonly used for producing polymer–clay nanocomposites with enhanced mechanical, thermal, and physical properties. Twin-screw extruders have been found to effectively exfoliate the clay platelets due to their high shear intensity. However, concerns about polymer and organoclay degradation have been raised in some studies. In this investigation, a composite of nylon 6–Cloisite 30B with fully exfoliated and well-dispersed clay particles was produced using a single-screw extruder and hence with limited polymer degradation. We show that processing temperature plays an important role in enhancing dispersion and that reprocessing at a higher temperature can enhance both dispersion and exfoliation and thus can result in composites with superior properties. We attempt to elucidate how the change in melt viscosity—coupled with the change in processing temperature—affects clay exfoliation and dispersion.     

Multi-scale modeling in damage mechanics of composite materials

This paper addresses the multi-scale modeling aspects of damage in composite materials. The multiplicity of the scales of the operating mechanisms is discussed and clarified by taking examples of damage in a unidirectional ceramic matrix composite and in a cross ply polymer matrix composite laminate. Two multi-scale modeling strategies––the hierarchical and the synergistic––are reviewed in the context of deformational response. Finally, the “big picture” as it relates to the cost-effective manufacturing of composite structures intended for long-term performance is outlined and desired future direction in multi-scale modeling is discussed.     

Creep of electrical resistance under uniaxial pressures for carbon black–silicone rubber composite

A composite comprised of dispersed conductive particles in an insulating polymer matrix is an excellent sensing material and could be used in flexible pressure sensors and tactile sensors. In this study, we investigated the variation of electrical resistance as a function of pressure for carbon black–silicone rubber composite. Samples were fabricated with different carbon black volume fractions. From experimental results, it was found that the composite has not only piezoresistivity but also electrical resistance creep behavior, which illustrates the relationship between electrical resistance and time. To describe and predict the above two phenomena, a mathematical model was established for particles filled polymer composites. When the piezoresistive composite was applied as a pressure-sensing unit, errors were seen due to “resistance creep” behavior. Based on this study, a method to inhibit such errors were investigated, developed, and realized.     

Organic solvent treatment and physicochemical properties of nanoporous polymer–SBA-15 composite materials

Mesoporous polymer–silica composites are attractive new materials because these systems can combine the advantages of highly porous silica and the vast functional diversity of organic polymers in a single robust structure. This contribution deals with the effects of organic solvent treatment on the physicochemical properties of mesostructured polymer–SBA-15 silica nanocomposites. For this study, two distinct reference mesoporous nanocomposites were prepared using a previously reported surface-confined polymerization technique, e.g., poly(styrene)(PS)–SBA-15 composite and poly(2-hydroxyethyl methacrylate)(PHEMA)–SBA-15 composite. The resulting materials are treated either with chloroform or toluene under heating for a prolonged period of time (24 h). Both materials are characterized prior and after solvent treatment by nitrogen physisorption at −196 °C, thermogravimetry and Attenuated Total Reflection Infra-Red (ATR-IR) spectroscopy. In general, solvent stability is excellent for both types of composite, even for low cross-linking degree of the polymer. Our data reveal that a treatment of mesoporous PHEMA–SBA-15 with chloroform or toluene has a minor, but reproducible, effect on the composite material in terms of porosity. Here, a reorganization of the polymer layer–silica interface seems to occur to some extent, which is leading to slight variation of the intrawall porosity. As a consequence, an increase of the thermal stability is clearly observed, with, however, no marked difference in the mean mesopore diameter. On the other hand, the PS–SBA-15 composite treated with the same solvents shows higher specific surface area values and an improved homogeneity in terms of polymer coating compared to untreated materials, especially for composites synthesized using benzoyle peroxide as the polymerization initiator. However, no increase in thermal stability is observed in this case.     

Phenomenon of specific fiber formation in polypropylene/copolyamide mixtures containing polyethyleneglycol

We have investigated the influence of a polyethyleneglycol additive and a binary mixture of compatibilizers ethylene copolymer with vinylacetate/polyethyleneglycol on the flow behavior and the processes of structure formation in 30/70 polypropylene/copolyamide mixtures. It has been shown that polyethyleneglycol decreases the viscosity and increases the elasticity of the polymer mixture melt. From the point of view of fiber formation, polyethyleneglycol is an effective compatibilizer for the polypropylene/copolyamide mixture. The introduction of binary mixtures of compatibilizers is more effective than the introduction of individual substances. It has been established that individual compatibilizers and their mixtures stabilize liquid polypropylene jets in the copolyamide matrix, which permits obtaining microfibers of smaller diameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 114–117, September–October, 2005.     

Nucleation and growth mechanism of apatite on a bioactive and degradable ceramic/polymer composite with a thick polymer layer

Nucleation and growth mechanism of apatite on a bioactive and degradable PLLA/SiO₂–CaO composite with a thick PLLA surface layer were investigated compared to that on a bioactive but non-degradable polyurethane (PU)/SiO₂–CaO composite with a thick PU surface layer. The bioactive SiO₂–CaO particles were made by a sol–gel method from tetraethyl orthosilicate and calcium nitrate tetrahydrate under acidic condition followed by heat treatment at 600 °C for 2 h. The PLLA/SiO₂–CaO and PU/SiO₂–CaO composites were then prepared by a solvent casting method which resulted in thick PLLA and PU surface layers, respectively, due to precipitation of SiO₂–CaO particles during the casting process. Two composites were exposed to SBF for 1 week and this exposure led to form uniform and complete apatite coating layer on the PLLA/SiO₂–CaO composite but not on the PU/SiO₂-CaO composite. These results were interpreted in terms of the degradability of the polymers. A practical implication of the results is that a post-surface grinding or cutting processes to expose bioactive ceramics to the surface of a composite with a thick biodegradable polymer layer is not required for providing apatite forming ability, which has been considered as one of the pragmatic obstacles for the application as a bone grafting material.     

Generalized fragility of eutectic Al–Si alloys modified with phosphorus

A new concept of fragility of superheated melt is used to analyze the viscosity of eutectic Al–12 wt%Si melts modified with phosphorus (P). The influence of P on the melt is investigated on the basis of Arrhenius law and fragility concept. The value of generalized fragility M named here is determined and available for evaluating the stability of modified eutectic Al–12 wt%Si melts and predicting the modifying effect of P.     

Synthesis of multilayered composite nanotube heterostructure; SiC–SiO2, C–SiO2, and C–SiC–SiO2 nanotubes

Three types of composite nanotube heterostructures (two double-layered and one triple-layered structure) are synthesized by simple heat treatment, forming SiC–SiO₂, C–SiO₂, and C–SiC–SiO₂ composite coaxial nanotubes. These multilayered composite nanotubes consist of several components with different electrical properties, for example, metal, semiconductor, and insulator components. In particular, C–SiC–SiO₂ triple-layered nanotubes with metallic, semiconducting, and insulating layers are synthesized for the first time. These multilayered nanotubes can be expected to find applications in nanoscale heterostructure electronic and optical devices.     

Non-equilibrium Thermodynamic Model for the Estimation of the Soret Coefficient in Dilute Polymer Solutions

In the present work a theoretical model based on linear non-equilibrium thermodynamics and the concept of Eyring’s activation energy of viscous flow is developed to estimate the Soret coefficient in dilute polymer solutions. The model is capable of predicting a sign change in the Soret coefficient, when the polymer molecular weight changes. The key part of the model is the way that the net heat of transport of the polymer molecules is simulated. Employing the Mark–Houwink equation, which correlates the polymer solution intrinsic viscosity with its molecular weight, the net heat of transport of the polymer is correlated with the activation energy of viscous flow of the polymer’s monomer in the liquid state, the Mark–Houwink solution parameter, and the polymer molecular weight. The model is evaluated against the experimental data, where qualitative and in some cases quantitative agreement is found.     

In situ synthesized ceramic–polymer composites for bone tissue engineering: bioactivity and degradation studies

As an alternative to current bone grafting strategies, a poly-lactide-co-glycolide/calcium phosphate composite microsphere-based scaffold has been synthesized by the direct formation of calcium phosphate within forming microspheres. It was hypothesized that the synthesis of low crystalline calcium phosphate within forming microspheres would provide a site-specific delivery of calcium ions to enhance calcium phosphate reprecipitation onto the scaffold. Both polymeric and composite scaffolds were incubated in simulated body fluid (SBF) for 8 weeks, during which time polymer molecular weight, scaffold mass, calcium ion concentration of SBF, pH of SBF, and calcium phosphate reprecipitation was monitored. Results showed a 20% decrease in polymeric scaffold molecular weight compared to 11–14% decrease for composite scaffolds over 8 weeks. Composite scaffold mass and SBF pH decreased for the first 2 weeks but began increasing after 2 weeks and continued to do so up to 8 weeks, suggesting interplay between pH changes and calcium phosphate dissolution/reprecipitation. Free calcium ion concentration of SBF containing composite scaffolds increased 20–40% over control values within 4 h of incubation but then dropped as low as 40% below control values, suggesting an initial burst release of calcium ions followed by a reprecipitation onto the scaffold surface. Scanning electron micrographs confirm calcium phosphate reprecipitation on the scaffold surface after only 3 days of incubation. Results suggest the composite scaffold is capable of initiating calcium phosphate reprecipitation which may aid in bone/implant integration.     

Liquid-crystal state in the system polysaccharide-mesophasogenic solvent

Data on the influence of vapors of nitromethane — a mesophasogenic solvent, i.e., a solvent forming with a polymer a lyotropic liquid-crystal phase — on the structure of acetate fibers are presented. It has been established that nitromethane in the vaporous state initiates in the polymer matrix orientation processes: induced anisotropy, spontaneous elongation of the fiber (which, in terms of Flory, is considered to be the transition to the nematic phase), as well as the process inverse to the self-elongation discovered for the first time, etc. It has been shown that the realization of both the direct and inverse processes of spontaneous deformation of cellulose acetate in mesophasogenic solvent vapors is associated with the optical asymmetry, i.e., the optical activity of the polysaccharide. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 1, pp. 139–147, January–February, 2006.     

Physical,optical, and electrical properties of a new conducting polymer

This work studies the electrical and optical properties of the conducting polymer composite films of polypyrrole–chitosan (PPy–CHI). The surface plasmon resonance (SPR) technique was used to study the optical properties of PPy and PPy–CHI composite films. Then, the values of the real and imaginary parts of the refractive indexes of PPy and PPy–CHI films were obtained by nonlinear least square fitting using Fresnel equations for a three-layer system of SPR system. The electrical conductivity measurements showed that the conductivity of the electrochemical prepared films improved in the presence of CHI and can be controlled by varying the CHI amount in the composite. The thermal diffusivity of the PPy–CHI composite films was measured by open photoacoustic spectroscopy and it has been shown that the thermal diffusivity is related to the electron migration in the conjugation chain length. The increase in electromagnetic interference shielding effectiveness (EMI SE) with the increase in electrical conductivity of the films is mostly from shielding by reflection rather than absorption.     

Work of adhesion influence on the rheological properties of silica filled polymer composites

As the work of adhesion, W _a, increases between a silica filler surface and a polymer matrix, the dynamic viscosity and the shear modulus of the composite material increase. The logarithms of these properties decrease linearly as W _a decreases. At lower dynamic test frequencies, a change in W _a has a more dramatic impact on these properties than at higher frequencies. An “effective silica particle size” model can be used to explain why W _a affects the viscosity and the shear modulus of a composite. According to that model, the thickness of the interphase layer increases as the W _a increases. An increase in effective particle size decreases the “free” polymer volume, and the decrease free volume polymer causes both the viscosity and the shear modulus to increase. Increasing the dynamic test frequency releases some of the immobilized polymer from the filler surface which causes the effective particle size to decrease. As the effective particle size decreases because of the increased testing frequency and approaches the mean size of the original filler, the impact of the W _a value on viscosity and shear modulus should decrease. However, the friction experienced between the filler interphase and the polymer, the so called “skin friction”, depends on the magnitude of W _a and the more general term, bond energy density (BED). The skin friction determines the viscosity of the composite, particularly at lower frequencies. Higher W _a values induce higher skin friction and thereby higher flow resistance (viscosity) as polymer chains move along the filler surface.     

Hydroxyapatite nanorod-reinforced biodegradable poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) composites for bone plate applications

Novel PLLA composite fibers containing hydroxyapatite (HAp) nanorods with or without surface lactic acid grafting were produced by extrusion for use as reinforcements in PLLA-based bone plates. Fibers containing 0–50% (w/w) HAp nanorods, aligned parallel to fiber axis, were extruded. Lactic acid surface grafting of HAp nanorods (lacHAp) improved the tensile properties of composites fibers better than the non-grafted ones (nHAp). Best tensile modulus values of 2.59, 2.49, and 4.12 GPa were obtained for loadings (w/w) with 30% lacHAp, 10% nHAp, and 50% amorphous HAp nanoparticles, respectively. Bone plates reinforced with parallel rows of these composite fibers were molded by melt pressing. The best compressive properties for plates were obtained with nHAp reinforcement (1.31 GPa Young’s Modulus, 110.3 MPa compressive strength). In vitro testing with osteoblasts showed good cellular attachment and spreading on composite fibers. In situ degradation tests revealed faster degradation rates with increasing HAp content. To our knowledge, this is the first study containing calcium phosphate–polymer nanocomposite fibers for reinforcement of a biodegradable bone plate or other such implants and this biomimetic design was concluded to have potential for production of polymer-based biodegradable bone plates even for load bearing applications.     

Comparation about efficiency of Al–10Sr and Mg–10Sr master alloys to grain refinement of AZ31 magnesium alloy

In the article, the effects of Al–10Sr and Mg–10Sr master alloys on the grain refinement of AZ31 magnesium alloy, are compared and analyzed. The results indicate that adding Al–10Sr or Mg–10Sr master alloys to AZ31 magnesium alloy could effectively reduce its grain size, but the refinement efficiency of Mg–10Sr master alloys is higher than that of the Al–10Sr master alloys. In addition, for a given melt holding time, the refinement efficiency of the two master alloys respectively increase with Sr adding amount increasing from 0 to 0.1 wt%, and the increasing laws are similar. For a given Sr adding amount, the refinement efficiency of Al–10Sr mater alloy gradually increases with the melt holding time increasing from 20 to 80 min, but its changing is not obvious for the Mg–10Sr mater alloy. The difference of refinement efficiency for the Al–10Sr and Mg–10Sr master alloys might be related to the dissolution modes and rates of Al₄Sr and Mg₁₇Sr₂ phases in the melt of AZ31 magnesium alloy.     

An investigation into the capability of unconventional amount of aluminum and nano-alumina to alter the mechanical response of magnesium

In the present study, magnesium aluminum alloys with aluminum content exceeding conventional alloying limit (Mg–10Al, Mg–15Al, and Mg–20Al) and the composite of Mg–10Al alloy with 1.5 volume percentage of nano-alumina particulates are created using the technique of disintegrated melt deposition. Significant improvements in microstructure and mechanical properties compared with pure magnesium are obtained. Intermetallic phase Mg₁₇Al₁₂ was detected in all the materials. The increase in amount of aluminum in magnesium led to a reduction in coefficient of thermal expansion and a marginal increase in porosity. Yield strength, ultimate tensile strength, and hardness increased significantly with an increasing amount of aluminum. The 0.2% yield strength increased from 140 to 394 MPa (181%) in the case of Mg–20Al. Ductility reduced with progressive addition of aluminum. However, the addition of both Al and nano-alumina particulates significantly increased not only strengths, but also ductility of pure Mg. The overall tensile properties assessed in terms of work of fracture increased by almost 143% in the case of composite sample. An attempt is made in this study to correlate the tensile response of alloys and composite with their microstructural characteristics.     

A gel-forming poly-l-guluronic acid produced from no guluronate-rich marine algae using new hydrolysis method: test for endovascular embolization

To prepare a gel-forming poly-l-guluronic acid (Poly-G) from no guluronate-rich Laminaria japonica, a new hydrolysis method was employed with a lower HCl concentration (0.025–0.15 M) and a shorter treatment time (5 min). The Poly-Gs were set to measure purity, presence of poly-l-guluronic block, molecular weight distribution, polymer yield, viscosity, and compressive gel strength. Finally, the Poly-G was tested to embolize the renal vascular system by using a rabbit model and angiography. Optimized Poly-G could be selected with respect to wt% concentration, polymer yield, gel-forming stability, viscosity, and gel strength as an endovascular embolizing agent. Overall, 0.4–0.6% of 0.03 M-Poly-G obtained from acid treatment with 0.03 M of HCl had molecular weights greater than 80 kDa, and the best gelling capacity with an injectable viscosity (30–120 cP). It was successfully delivered into the vascular bed of a rabbit kidney and was shown angiographically to embolize the renal vascular system.     

Behavior of magnesium and silicon in the formation of MgO/AlN composite

MgO/AlN composites have been fabricated by directed metal nitridation of Al–Si alloy in flowing N₂ at 1473 K. A mixture of magnesia particles and chemically pure magnesium powder was placed on the surface of Al–Si alloy block as reinforcement materials. Mg powder initiates the infiltration and nitridation of Al alloy melt by eliminating protective Al₂O₃ film at the reaction frontier. New Mg vapor from the interface reaction between Al and MgO particles, keeps as continuous deoxidization agent as the added Mg powder. The spinel layer thickness due to the reaction of Al melt with MgO particles is controlled by Mg content. Si not only reduces the surface tension and viscosity of Al alloy melt, but also leads to increase in N₂ content.