Superior Dimensional Stability Research Articles

Viscoelastic stability of pre-cured resin-composite CAD/CAM structures

ObjectivesTo study the effect of water storage (3 months) on the creep deformation and recovery of CAD/CAM composite materials to determine their viscoelastic stability. Materials and methodsFive CAD/CAM composite blocks, with increasing filler loading, and one polymer-infiltrated ceramic network (PICN) were studied. Six specimens of each material were separated into two groups (n=3) according to their storage conditions (24 h dry storage at 23°C versus 3 months storage in 37°C distilled water). A constant static compressive stress of 20 MPa was applied on each specimen via a loading pin for 2 h followed by unloading and monitoring strain recovery for a further period of 2 h. The maximum creep-strain (%) and permanent set (%) were recorded. Data were analysed via two-way ANOVA followed by one-way ANOVA and Bonferroni post hoc tests (<0.05) for comparisons between the materials. Homogeneity of variance was calculated via Levene’s statistics. ResultsThe maximum creep strain after 24 h dry ranged from 0.45% to 1.09% and increased after 3-month storage in distilled water to between 0.71% and 1.85%. The permanent set after 24 h dry storage ranged from 0.033% to 0.15% and increased after 3-month water storage to between 0.087% and 0.18%. The maximum creep strain also reduced with increasing filler loading. SignificanceThe PICN material exhibited superior dimensional stability to all of the pre-cured resin composite blocks in both storage conditions with deformation being predominantly elastic rather than viscoelastic. Notwithstanding, two of the resin-matrix composite blocks approached the PICN performance, when dry, but less so after water storage.

Highly transparent, stretchable, and rapid self-healing polyvinyl alcohol/cellulose nanofibril hydrogel sensors for sensitive pressure sensing and human motion detection

Wearable sensors have emerged as favored novel devices for human healthcare. Current sensors, however, suffer from low sensitivity, non-transparency, and lack of self-healing ability. In this study, we synthesized a polyvinyl alcohol/cellulose nanofibril (PVA/CNF) hydrogel with dual-crosslinked networks for highly transparent, stretchable, and self-healing pressure and strain sensors. The hydrogel contains dynamic borate bonds, metal–carboxylate coordination bonds, and hydrogen bonds, all of which contribute to the hydrogel’s superior dimensional stability, mechanical strength and flexibility, and spontaneous self-healing ability as compared to traditional PVA hydrogels. The developed hydrogel has a moderate modulus of 11.2 kPa, and a high elongation rate of 1900%. It spontaneously self-heals within 15 s upon contact without any external stimuli, has a high transmittance of over 90%, and has excellent compatibility with human fibroblasts. The capacitive sensor developed based on the PVA/CNF hydrogel has high sensitivity to very subtle pressure changes, such as small water droplets. When used as a strain sensor, it was capable of detecting and monitoring various human motions such as finger, knee, elbow, and head movements, breathing, and gentle tapping. The developed hydrogel and sensors not only show great potential in electronic skin, personal healthcare, and wearable devices, but may also inspire the development of transparent, intelligent skin-like sensors.

Constructing an internally cross-linked structure for polysulfone to improve dimensional stability and alkaline stability of high performance anion exchange membranes

The preparation of quaternary ammonium polysulfone anion exchange membranes (AEMs) with good dimensional stability and alkaline stability is an urgent problem to solve. In response, a series of cross-linked based on polysulfone and 4, 4′-trimethylenedipiperidine (TMDP) as crosslinkers with different degrees AEMs were developed in this work through a simple process. Among the fabricated AEMs, CAPSF-5 exhibits superb alkaline stability in a 1 M KOH aqueous solution at 60 °C for 15 days, whereas the non-crosslinked APSF membrane became tremendously brittle within 24 h and could not be further studied under the same conditions. In addition, even at 60 °C, CAPSF-5 demonstrates a superior dimensional stability compared to the non-crosslinked APSF membrane due to the formation of a dense internal network structure. These observations demonstrate that crosslinked CAPSF membranes can be a viable strategy to improve the deficiency of the polysulfone backbone, especially in terms of alkaline stability.

Development and Mechanical Characterization of Al6061-Zircon Composites

Composite materials are widely used in variety of applications such as aerospace, automotive and structural components resulting in savings of material and energy. Particulate reinforced Aluminium metal matrix composite materials which are having desirable properties such as high specific stiffness, high specific strength, high coefficient of thermal expansion, increased fatigue resistance and superior dimensional stability compared to unreinforced alloys. In the present work an attempt has been made to develop composites using Al 6061 as a matrix material reinforced with Zircon particulates using stir casting technique. The Zircon particulates were varied in steps of 0 %, 3%, 6%, 9% and 12%. The Specimens were prepared as per the ASTM standards. The prepared composites were characterized by microstructural studies using optical microscope and tensile strength and hardness properties were evaluated. Zircon particles were observed to refine the grains and were distributed homogeneously in the aluminium matrix at 9% of Zircon. The tensile and hardness properties were higher in case of composites when compared to unreinforced Al 6061 matrix. Also increasing addition level of Zircon has resulted in further increase in both tensile strength and hardness values and optimum value was obtained at 9% of Zircon.

A gel polymer electrolyte based on Polyacrylonitrile/organic montmorillonite membrane exhibiting dense structure for lithium ion battery

Polyacrylonitrile (PAN)/organic montmorillonite (OMMT) membranes served as a host which is swelled using a liquid electrolyte of 1.0M LiPF6 in carbonate solvent for gel polymer electrolyte have been fabricated by non-solvent induced phase separation (NIPS) method. The OMMT fillers have affected the morphology, thermal stability, electrolyte uptake, ionic conductivity and electrochemical properties of PAN/OMMT membranes in different ways. The PAN/OMMT membrane exhibits high liquid uptake (375.5%), superior dimensional stability under 150°C for 15min and superior electrochemical stability up to 4.62V. Moreover, the gel polymer electrolyte based on PAN/OMMT membrane not only possesses lower polarization and interfacial resistance, but also effectively suppresses the formation of Li dendrites as reflected in the surface morphology of lithium anode after cycling test. The application of natural montmorillonite has been demonstrated by a coin cell using Li metal as counter electrode at 1C, resulting in the high capacity of 141mAhg−1 after 100cycles and high capacity retention of 95.9%. The possibility of PAN/OMMT membrane applied for the sustainable safety lithium ion battery can be realized.

Clustered multi-imidazolium side chains functionalized alkaline anion exchange membranes for fuel cells

Clustered alkyl side chains bearing a string of three imidazolium cations with hexyl spacers are grafted to fluorene-based poly (arylene ether sulfone) successfully. Nanostructure is directly configured within the anion exchange membranes (AEMs) via the novel multi-cation side chains. As confirmed by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), percolating OH– conducting channels with the size of ionic clusters nearly 20nm endow the trimPES-0.4 membrane with an excellent ion conductivity in excess of 120mScm–1 at 80°C. Because of the self-assembly of ionic groups, water molecules are compartmentalized into the hydrophilic side chain regions instead of backbones, resulting in advantageous over water management. Together with the lengthened hydrophobic segments, TrimPES-0.2 exhibits superior dimensional stability (12.0%, 30°C) to conventional mono-cation type AEMs. Furthermore, the novel multi-cation TrimPES-0.4 displays a peak power density of 134.4mWcm–2 at a current density of 280mAcm–2. Therefore, these findings suggest that by tuning the distribution of cations, AEMs with well-balanced performance can be made for fuel cell applications.

Fabrication of ultrafiltration membranes with enhanced antifouling capability and stable mechanical properties via the strategies of blending and crosslinking

In this study, a novel polysulfone (PSf) with pendant tertiary amine groups was synthesized and this functionalized PSf could be further crosslinked based on a facile reaction between tertiary amine and 1,3-dibromopropane (DBP). The synthesis of this new polymer and the occurrence of the crosslinking reaction were evidenced by FTIR, 1H NMR and solid state 13C NMR spectroscopy. The crosslinked PSf and sulfonated poly(ether ether ketone) (SPEEK) were mixed together to fabricate ultrafiltration membranes by the phase inversion method. All the composite membranes exhibited improved hydrophilicity over the pristine PSf membrane, attributed to the presence of sulfonic acid groups and / or quaternary ammonium groups. The crosslinked membrane demonstrated superior permeability and antifouling properties than the uncrosslinked membrane due to the conversion of tertiary amine groups to more hydrophilic quaternary ammonium groups. In particular, the membrane with crosslinked PSf∶SPEEK ratio of 1∶1 showed the most favorable performance, including almost 3.5 times of pure water flux of the pristine PSf membrane and 97% of flux recovery ratio. Meanwhile, the crosslinked membrane maintained superior dimensional stability and mechanical properties compared to the uncrosslinked membrane, which is a major challenge faced by highly hydrophilic polymers, because of the restricted molecular chain movement caused by the crosslinking network and electrostatic interaction. All the resultant membranes were fully characterized, including surface properties, morphologies, mechanical strength, thermal stability, permeability, and antifouling properties.

Self-photodegradation of formaldehyde under visible-light by solid wood modified via nanostructured Fe-doped WO3 accompanied with superior dimensional stability

In this paper, solid wood with superior self-photodegradation of formaldehyde (HCHO) under visible-light was realized through a facile method at room temperature. Spherical Fe-doped WO3 nanostructured materials deposited on the wood substrate with diameters ranging from 100 to 150nm were mainly responsible for the self-photodegradation of formaldehyde. Fe-doped WO3 nanostructured materials were strongly adhered to wood surface through electrostatic and hydrogen bonding interactions. Additionally, the dimensional stability and the inherent anisotropic thickness swelling of wood were greatly improved and eliminated, respectively. Interestingly, a wood rabbit craft was also designed and showed a good visible-light-driven photocatalytic performance in a relatively larger area for different concentrations of HCHO. The research result would both fabricate a novel catalyst for the degradation of the hazardously gaseous pollutants and basically improve the wood intrinsic performance.

Investigation of Penetration Rate and Surface Topography in Ultrasonic Drilling of WC-Co Composite

WC-Co composite materials possess a vast range of industrial applications owing to their excellent properties such as superior hardness, toughness and dimensional stability. Present article has been targeted at investigating the impact of different experimental conditions (power rating, cobalt content, tool material, thickness of work piece, tool geometry, and abrasive grit size) on penetration rate in ultrasonic drilling of WC-Co composite material. Taguchi’s L-36 orthogonal array has been employed for conducting the experiments. Significant factors have been identified using analysis of variance (ANOVA) test. The experimental results revealed that power rating, abrasive grit size, and tool profile is most significant factor for penetration rate. From the microstructure analysis, the modes of material deformation have been observed and the parameters (i.e. work material properties, grit size, and power rating) were observed as the most crucial for the deformation mode.

Impact of bending on flexible metal oxide TFTs and oscillator circuits

Thin‐film circuits on plastic capable of high‐frequency signal generation have important applications in large‐area, flexible hybrid systems, enabling efficient wireless transmission of power and information. We explore oscillator circuits using zinc‐oxide thin‐film transistors (ZnO TFTs) deposited by the conformal, layer‐by‐layer growth technique of plasma‐enhanced atomic layer deposition. TFTs on three substrates—glass, 50‐µm‐thick freestanding polyimide, and 3.5‐µm‐thick spin‐cast polyimide—are evaluated to identify the best candidate for high‐frequency flexible oscillators. We find that TFTs on ultrathin plastic can endure bending to smaller radii than TFTs on commercial 50‐µm‐thick freestanding polyimide, and their superior dimensional stability furthermore allows for smaller gate resistances and device capacitances. Oscillators on ultrathin plastic with minimized parasitics achieve oscillation frequencies as high as 17 MHz, well above the cutoff frequency fT. Lastly, we observe a bending radius dependence of oscillation frequency for flexible TFT oscillators and examine how mitigating device parasitics benefits the oscillator frequency versus power consumption tradeoff.

A facile approach to make high performance nano-fiber reinforced composite separator for lithium ion batteries

The separator is a porous membrane located between the negative and the positive electrodes. In this work, a nano-fiber reinforced composite separator was developed. Compared with the commercial polyolefin separator, the composite separator showed superior (a) dimensional stability at elevated temperatures relative to conventional separators and (b) wettability by the liquid electrolyte. After being saturated with a commercial LiPF6-ethylene carbonate-dimethyl carbonate electrolyte, the composite separator enabled a high effective ionic conductivity (σeff) of 1.25 mS/cm. A stable cycle performance and an improved rate capability have been observed in the coin cells with the composite separator. This initial study shows that this type of composite membranes can be a promising alternative separator for lithium ion batteries.

Novel cellulose aerogel coated on polypropylene separators as gel polymer electrolyte with high ionic conductivity for lithium-ion batteries

The low ionic conductivity of polypropylene (PP) separators has stymied their use as polymer electrolytes in high-power lithium-ion batteries. To improve the ionic conductivity, we coated PP separators with cellulose aerogel based on hydroxyethyl cellulose (HEC), via ice segregation induced self-assembly (ISISA). The coating was characterized via scanning electron microscopy (SEM), attenuated total reflection–infrared spectra (ATR-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). In addition, the electrochemical performances of the separator were evaluated by using a cell consisting of the coated separator, lithium foil as the counter and reference electrodes, and LiFePO4 as the cathode. The porous cellulose aerogel-coated separator exhibited superior dimensional stability, electrolyte uptake, and hence a higher ionic conductivity and better cycling performance, than its non-coated counterpart. Furthermore, the separator was coated without the use of toxic solvents, thereby rendering the preparation process cost effective and highly efficient.

A new strategy for preparing oligomeric ionic liquid gel polymer electrolytes for high-performance and nonflammable lithium ion batteries

In the present work, a new strategy is used to economically synthesize an oligomeric ionic liquid from conventional phenolic epoxy resin. This oligomeric ionic liquid is further blended with PVdF-co-HFP and organic liquid electrolyte to prepare a high performance, nonflammable gel polymer membrane. Although the liquid electrolyte uptake is low (< 50%) for this novel gel polymer electrolyte, it possesses high ionic conductivities of 2.0mScm−1 at 30°C and 6.6mScm−1 at 80°C, respectively. The AC impedance results show that the interfacial compatibility between this gel polymer electrolyte and the electrodes is good. These two factors result in high cell capacity under different charge/discharge rates. Further, excellent cell-cycle stability after being charged and discharged 100 cycles is also demonstrated with the columbic efficiency to be up to 99. Due to the existence of the oligomeric ionic liquid, this novel gel polymer electrolyte exhibits superior dimensional stability; that is, at high temperature (150°C) the dimensional change is less than 1%. Notably, the electrolyte’s limiting oxygen index can be as high as 29, meaning that it achieves the flame-retardant requirement under a normal atmosphere, which is essential to the safety of lithium ion batteries. These features allow this novel gel polymer electrolyte to function as a high performance and high safety lithium ionic conductor as well as a separator for lithium-ion batteries.

A cellulose nanocrystal-based composite electrolyte with superior dimensional stability for alkaline fuel cell membranes

A cellulose nanocrystal-based composite electrolyte exhibited superior dimensional stability, handleability, and hydroxide conductivity.

Polyimide–Organosilicate Hybrids with Improved Thermal and Optical Properties

Through hydrolysis and polycondensation of amino-silane with alkyl bridged silane, a new type of polysilsesquioxane (PSSQ) was obtained. Here we use amine functionalized silane and bis(silyl)ethane to synthesize alkyl chain linked PSSQ. Compared to conventional polyhedral oligomeric silsesquioxane (POSS), this new silane compound has both enhanced thermal stability and improved compatibility with poly(amic acid). Gelation of this silane compound with poly(amic acid) provides polyimide-organosilicate composite materials. We show that films made from solutions of the composites exhibit higher optical transparency and superior dimensional stability during thermal treatment than films of pure polyimide or of polyimide composites with conventional POSS. Bridging of POSS and chemical bonding between POSS and polyimide chains significantly enhance the physical properties. These results provide useful information for designing molecular architecture for the fabrication of high-performance plastic substrates in the future display devices.

Mejoras en la construcción de camisas de cilindro de motores de combustión interna ciclo diesel

This study deals with the different types of wear as well as other parameters present in the tribological system pistonsegment- cylinder in a combustion engine. By means of engineering methods were defined the wear rates in the three components of the system. The biggest wear in the analysis resulted in the cylinder shirt. Specialized methods applied were used to analyze the prevailing metallographic characteristics in its original construction, obtaining a gray melted iron with perlitic matrix. A new material with bainitic matrix has been proposed for increasing wear resistance. To demonstrate the efficiency of this new product, the experimental techniques carried out, were based on a dynamometric testing in a internal combustion engine diesel cycle Scania of 150 kW. It was exposed to a full charge during 500 h with 30 % of potency rising. Compared with the perlitic one, it has been proved that the bainitic matrix allows a better result. Besides, a superior dimensional stability was obtained. The piston segments had a similar wear rate in both materials in reference to the original tribological pair of the project.

Influence of mesophase–crystal transition on thermal and mechanical properties of stretched poly(L‐lactide)

The mesophase in the as‐stretched poly(L‐lactide) (PLLA) exhibits low thermal stability and undergoes melting around Tg. As a consequence, without constraints as‐stretched PLLA can recover to its original (unstretched) length while being held above Tg. Upon constrained annealing at 70°C mesophase is transformed into highly oriented crystals, responsible for little free shrinkage and superior dimensional stability. At the same time, molecular orientation in the amorphous phase first decreases significantly due to thermodynamic relaxation, and then increases moderately with the advent of cold crystallization. It correlates well with the change of yield strength with respect to annealing time. POLYM. ENG. SCI., 53:2568–2572, 2013. © 2013 Society of Plastics Engineers

Perfluorinated Polymer Electrolytes Hybridized with In situ Grown Titania Quasi-Networks

Perfluorinated Nafion membranes, neutralized to various extents, were hybridized with titania quasi-networks that were grown in situ via catalyzed sol-gel reactions of an titanium isopropoxide precursor. The formation of Ti-O-Ti groups within the ionomer was verified by FTIR-ATR spectroscopy. EDAX studies confirmed that the extent of propagation of titania quasi-networks into the bulk of the ionomer film increased with ionomer neutralization. Compared to the unmodified control membrane, the hybrid membranes exhibited superior dimensional stability, modulus, stress, and strain at break and gas barrier properties. All hybrid membranes exhibited superior resistance to degradation when subjected to an accelerated stress test in an operating fuel cell environment, as a resultant of the better dimensional stability and gas barrier properties induced through addition of the inorganic titania phase.

Effect of Aging on Microstructure and Shape Memory Properties of a Ni-48Ti-25Pd (At. Pct) Alloy

The microstructure and properties of a precipitation-hardenable Ni-48Ti-25Pd (at. pct) shape memory alloy have been investigated as a function of various aging conditions. Both the hardness and martensitic transformation temperatures increased with increasing aging time up to 100 hours at 673 K (400 °C), while no discernable differences were observed after heat treatment at 823 K (550 °C), except for a slight decrease in hardness. For aging at 673 K (400 °C), these effects were attributed to the formation of nano-scale precipitates, while precipitation was absent in the 823 K (550 °C) heat-treated specimens. The precipitation-strengthened alloy exhibited stable pseudoelastic behavior and load-biased-shape memory response with little or no residual strains. The precipitates had a monoclinic base-centered structure, which is the same structure as the P-phase recently reported in Ni(Pt)-rich NiTiPt alloys. 3D atom probe analysis revealed that the precipitates were slightly enriched in Ni and deficient in Pd and Ti as compared with the bulk alloy. The increase in martensitic transformation temperatures and the superior dimensional stability during shape memory and pseudoelastic testing are attributed to the fine precipitate phase and its effect on matrix chemistry, local stress state because of the coherent interface, and the ability to effectively strengthen the alloy against slip.

Thermal Stability and Fracture Toughness of Epoxy Resins Modified with Epoxidized Castor Oil and Al2O3Nanoparticles

nanoparticles, Epoxidized castor oil, Thermal stabilities, Fracture toughness IntroductionEpoxy resins are used widely in non-structural (coatings,flooring, and painting) and structural (casting, tooling, andmatrices for advanced composites) applications owing totheir outstanding mechanical performance, good chemicaland electrical resistance, and superior dimensional stability.