Shape Memory Synthesis Research Articles

Synthesis and Characterization of the Temperature Controllable Shape Memory of Polycaprolactone/Poly(ethylene terephthalate) Copolyester

Synthesis and Characterization of the Temperature Controllable Shape Memory of Polycaprolactone/Poly(ethylene terephthalate) Copolyester

Synthesis, Structure and Optical Properties of NiTi Shape Memory Thin Films

NiTi Shape Memory Alloy (SMA) is now widely used in important applications due to its shape memory effect (SME) and biocompatibility. However, there is still a challenge to control the sizes and shapes of these nanoparticles. Here, we report on the use of pulsed laser deposition technique for the cultivation of NiTi nanoparticles on glass substrates. It discussed the implications of the case of the influence of depositing laser energy on the size of a grain of NiTi nanoparticle. The nominated effect on the optical properties of its thin-film was also discussed. X-ray diffraction (XRD) analysis revealed that the films prepared at 800[Formula: see text]mJ, 900[Formula: see text]mJ and 1000[Formula: see text]mJ were amorphous structures. The Atomic Force Microscopy (AFM) results confirmed that the thin films are made up of spherical particles that are evenly distributed (in terms of size). A blueshift in the bandgap was observed in the UV–Visible absorption spectra with increase in the depositing laser energy due to the quantum confinement effect of nanoparticle formation.

Ultra-low density three-dimensional nano-silicon carbide architecture with high temperature resistance and mechanical strength

Silicon carbide nanotube/nanowires (SiCNT/NWs) exhibit excellent mechanical properties in extreme thermal and oxidative environments. Here, we demonstrate an easily scalable process to synthesize millimeter-sized three-dimensional architectures using SiCNT/NW building blocks to create materials with excellent mechanical strength, stiffness, and resiliency with ultra-low density. The structure of these macro-materials is initially synthesized using carbon nanotubes, then utilizing the shape memory synthesis (SMS) method are converted to nano-silicon carbide. It is proposed that using this technique, any micro-structure can initially be created with nano-carbon building blocks, optimized for the necessary morphological features of a specific application. Here, the synthesis and subsequent SiCNT/NW conversion of carbon nanotube spheres and graphene foam, demonstrates the ability to use a simple, cost-effective conversion method to create a material that can mechanically perform in extreme environments.

Coating-free TiO2@β-SiC alveolar foams as a ready-to-use composite photocatalyst with tunable adsorption properties for water treatment.

Coating-free TiO2@β-SiC photocatalytic composite foams gathered within a ready-to-use shell/core alveolar medium the photocatalytically active TiO2 phase and the β-SiC foam structure were prepared via a multi-step shape memory synthesis (SMS) replica method. They were fabricated following a sequential two-step carburization approach, in which an external TiC skin was synthesized at the surface of a β-SiC skeleton foam obtained from a pre-shaped polyurethane foam during a first carburization step. The adsorption behaviour of the shell/core TiO2@β-SiC composite foams towards the Diuron pollutant in water was tuned by submitting the carbide foams to a final calcination treatment within the 550–700 °C temperature range. The controlled calcination step allowed (i) the selective oxidation of the TiC shell into a TiO2 crystallite shell owing to the β-SiC resistance to oxidation and (ii) the amount of residual unreacted carbon in the foams to be tuned. The lower the calcination temperature, the more pronounced the adsorption profiles of the composites and the higher the Diuron amount removed by adsorption on the residual unreacted carbon. The ready-to-use TiO2@β-SiC composite foams were active in the degradation of the Diuron pesticide, without any further post-synthesis immobilization or synthesis process at the foam surface. They displayed good reusability with test cycles and benefitted from an enhanced stability in terms of the titania release to water.

TiO2-coated alveolar clay foam as a photocatalyst for water detoxification

3D-clay foam support having alveolar open-cell structure of polyurethane sponge was produced by shape memory synthesis to enhance exposed surface area of TiO2 photocatalyst film for both light harvesting and liquid contact. The TiO2-coated alveolar clay foam photocatalysts were characterized in terms of compressive strength, mineral phase, light transmission ability and TiO2 film properties. The photocatalytic performances were evaluated as material and removal efficiencies of CHP solution under UV-A irradiation and TOC analysis. The material efficiency results of the photocatalysts coated with TiO2 films, synthesized by sol–gel method at various pHs, pointed out that the TiO2 film of pH 2 gave the highest CHP removal. It was also selected to repetitively operate in a recycle mode, and 94–96% of fresh CHP removal was retained in all the four runs.

Alveolar TiO2-β-SiC photocatalytic composite foams with tunable properties for water treatment

New alveolar TiO2-β-SiC photocatalytic composite foams gathering within a ready-to-use media, the TiO2 active phase and the β-SiC alveolar foam structure have been prepared through a Shape Memory Synthesis (SMS) replica method. They have been obtained by incorporating TiO2 powders inside the infiltration slurry used for transforming the pre-shaped polyurethane foam into its corresponding carbide. The photocatalytic composite foams contained 16 wt. % and 24 wt. % of TiO2, most of them being available for the reaction by being located in the external layer of the foam rather than dispersed within the foam matrix, so that no further post-synthesis immobilization process was needed for coating the foam with TiO2 active phase. The adsorption behaviour of the TiO2-β-SiC composite foams towards the Diuron pollutant in water was tuned by applying a final calcination treatment to the as-synthesized foams within the 400–700 °C range, that allowed to tune the amount of residual unreacted carbon within the foams, while allowing the formation of small TiO2 crystallites via the selective oxidation of TiC carbide, and thanks to the β-SiC resistance to oxidation. The TiO2-β-SiC composite foams calcined at 700 °C outperformed a reference β-SiC supported foam TiO2 catalyst in terms of diuron degradation, while the reference foam remained more efficient in terms of mineralization rate.

Polycyclic silicone polymer as novel single source precursor for the facile synthesis of nanostructured SiC

For the first time, SiC nanostructures have been synthesized from polycyclic silicones via a catalyst-free facile approach. These specialty precursor silicones were synthesized from 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (D4V) and 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) taken in three different molar ratios, through Pt complex catalyst assisted hydrosilylation reaction. The precursor polymers were self-crosslinked using the residual Pt catalyst present in the system. Thermogravimetric analysis under N2 environment proves that the formed polymers possess superior thermal stability, with an onset decomposition temperature of 600–630 °C and a very high ceramic yield of 82–85% at 900 °C, compared to conventional silicones. FT-IR and RAMAN spectroscopic analyses of the ceramic residues obtained by pyrolysis of the cured polymers at 1200 °C and 1500 °C prove the formation of Si-O-C and Si-C. FESEM analysis reveals that these polycyclic silicones function as promising precursors for nanostructured SiC ceramics, with varying morphologies, including wires and fibers. The in-situ derived free carbon, produced during pyrolysis, acts as the seed for the growth of nanostructures with well-defined morphologies through shape-memory synthesis.

Velcro-Inspired SiC Fuzzy Fibers for Aerospace Applications.

The most recent and innovative silicon carbide (SiC) fiber ceramic matrix composites, used for lightweight high-heat engine parts in aerospace applications, are woven, layered, and then surrounded by a SiC ceramic matrix composite (CMC). To further improve both the mechanical properties and thermal and oxidative resistance abilities of this material, SiC nanotubes and nanowires (SiCNT/NWs) are grown on the surface of the SiC fiber via carbon nanotube conversion. This conversion utilizes the shape memory synthesis (SMS) method, starting with carbon nanotube (CNT) growth on the SiC fiber surface, to capitalize on the ease of dense surface morphology optimization and the ability to effectively engineer the CNT-SiC fiber interface to create a secure nanotube-fiber attachment. Then, by converting the CNTs to SiCNT/NWs, the relative morphology, advantageous mechanical properties, and secure connection of the initial CNT-SiC fiber architecture are retained, with the addition of high temperature and oxidation resistance. The resultant SiCNT/NW-SiC fiber can be used inside the SiC ceramic matrix composite for a high-heat turbo engine part with longer fatigue life and higher temperature resistance. The differing sides of the woven SiCNT/NWs act as the "hook and loop" mechanism of Velcro but in much smaller scale.

Synthesis of shape memory polyurethane/clay nanocomposites and analysis of shape memory, thermal, and mechanical properties

AbstractIn this study, shape memory polyurethane/clay nanocomposites were synthesized by using two‐step in situ polymerization. The effects of nanoparticle content on mechanical, thermal, and shape memory properties were studied. Soft and hard segments of polyurethanes were based on polycaprolactone (PCL) diol and 4,4′‐diphenylmethane diisocyanate/1,4‐butanediol molar ratio with 70/30, respectively. The differential scanning calorimetry, tensile test, dynamic mechanical thermal analysis, parallel plate rheometer, and X‐ray diffraction were used to evaluate the properties of the nanocomposites. To evaluate shape memory properties, a tensile device equipped with a thermal chamber was used. Glass transition temperature of soft segments has been increased by nanoclay loading. Addition of nanoclay to polyurethane matrix caused to disrupt ordering in hard domains, decrease in elongation and tensile strength. The results show that crystallinity of soft segments and dispersion of nanoparticles affect on the mechanical properties and shape memory behavior of nanocomposites, distinctly. Nanocomposite containing 1 wt% shows the best shape memory properties. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Conversion of wooden structures into porous SiC with shape memory synthesis

Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood ( shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood.

Synthesis and Characterization of Shape Memory (Meth)Acrylate Co-Polymers and their Cytocompatibility In Vitro

A series of novel transparent shape memory co-polymers, made from (meth)acrylate monomers, intended to be used as intraocular lens, was synthesized. The thermo-mechanical properties, shape memory properties and optical properties of the co-polymers could be adjusted by using monomers with various alkyl chain lengths. The cytocompatibility of the prepared co-polymers to L929 mouse connective tissue fibroblasts was demonstrated in vitro, and the co-polymers exhibited favorable cytocompatibility, supporting cell viability and proliferation. This study showed that the prepared co-polymers, which exhibited good flexibility, adjustable shape memory properties, high transparency and favorable cytocompatibility, could find great promising applications as intraocular lens.

Stimulation of silicon carbide nanotubes formation using different ratios of carbon nanotubes to silicon dioxide nanopowders

In this article, fabrication of SiC nanotubes (SiCNTs) by using different ratios of single-walled carbon nanotubes to SiO 2 nanopowders (3:1, 2:1 and 1:1) is presented. In order to develop SiCNTs, shape memory synthesis (SMS) had been employed. Argon gas, the carrier gas was introduced into a furnace, heated to 1350 °C at a heating rate of 16 °C/min and the temperature was kept for 4 h. X-ray diffraction analysis verified that different polytypes of SiCNTs were formed through SMS method. The microscopy analysis revealed that the amount and morphology of SiCNTs synthesized was dissimilar when different ratios were used.

A new one-dimensional tungsten carbide nanostructured material

A new medium specific surface area one-dimensional tungsten carbide nanostructure was obtained by the Shape Memory Synthesis method, in which the macrostructural features of a carbonaceous 1D-preformed template were maintained during the carburization of tungsten oxide and determined the resulting carbide morphology.

High surface area submicrometer-sized β-SiC particles grown by shape memory synthesis method

A high surface area and non-microporous submicrometer-sized β-SiC material was successfully obtained according to the Shape Memory Synthesis (SMS) method. The attack by SiO vapors of a nanodiamond preform with sp 3-bound carbon, at 1200–1300 °C under dynamic vacuum, formed β-SiC nanoparticles by carboreduction of the SiO vapors. These β-SiC nanoparticles had a mean size distribution centered at 10 nm and a specific surface area of 140 m 2/g. The high carbon to carbide conversion obtained and the location of the remaining unreacted carbon in the core of the β-SiC nanoparticles allowed a direct use of the material as a catalyst support without any stabilizing post-synthesis oxidative treatment. The material showed dispersive properties and a good resistance towards oxidation, due to the presence of a thick and partially oxidized protecting amorphous coating, preventing from the extensive oxidation of SiC into silica.

Synthesis and characterization of a new medium surface area TiO2–β-SiC material for use as photocatalyst

A new medium surface area and non-microporous TiO2–β-SiC photocatalytic material was successfully obtained according to an extension of the Shape Memory Synthesis (SMS) method, and following a three step procedure. A high surface area TiO2 supported on an activated charcoal precursor was prepared in a first step by the sol–gel precipitation of titanium tetraisopropoxide in the presence of activated charcoal powder. The second step consisted of a gas–solid reaction between this precursor and SiO vapors at 1300 °C under dynamic vacuum which formed TiC–β-SiC, by carboreduction of SiO vapors and TiO2 into β-SiC and TiC respectively. The final step was oxidation in air at temperatures ranging from 420 °C to 600 °C which produced the TiO2–β-SiC material, using the high resistance of β-SiC towards oxidation to selectively form TiO2. The gross morphology of the activated charcoal precursor was maintained during the carburization and the subsequent oxidation processes according to the SMS concept. Both TiO2 and the β-SiC semiconductor phases were in intimate contact in the same grain of catalyst, without the usually problematic post-synthesis shaping of high mechanical strength SiC-based materials and using no binder. The TiO2-to-SiC ratio could be directly tuned by adjusting the TiO2 content of the precursor, whereas the anatase-to-rutile ratio could be modified by changing the post-synthesis calcination temperature, without altering the β-SiC properties or significantly increasing the average TiO2 particle size.

A new TiO 2–β-SiC material for use as photocatalyst

A new medium surface area TiO 2–β-silicon carbide (β-SiC) material was obtained by the Shape Memory Synthesis (SMS) method in which a pre-shaped high surface area activated charcoal (AC) supporting TiO 2, obtained by a sol–gel process starting from an alkoxide precursor, was attacked by SiO vapor at 1300 °C under dynamic vacuum. A post-synthesis oxidation using the inertness of β-SiC towards oxidation led to the TiO 2–β-SiC material.

Synthesis and characterisation of medium surface area silicon carbide nanotubes

Silicon carbide nanotubes with medium surface area (30–60 m 2/g) were successfully prepared by reaction between carbon nanotubes and SiO vapor according to the shape memory synthesis (SMS). The gross morphology of the carbon nanotubes was maintained during the carburization process. A calcination in air at 600 °C was performed to remove unreacted carbon domains in order to obtain pure carbon-free SiC nanotubes. The synthesized SiC nanotubes had a mean outer diameter of 100 nm and lengths up to several tens of micrometres.

Synthesis and catalytic uses of carbon and silicon carbide nanostructures

Carbon nanofibers and nanotubes with controlled diameters were synthesized by catalytic decomposition of an ethane/hydrogen mixture over nickel and iron supported catalysts. The synthesis of the first silicon carbide (SiC) nanotubes was performed according to the shape memory synthesis (SMS) method. The benefit of using carbon and SiC nanotubes as catalyst supports was evidenced, respectively in the case of the selective CC bond hydrogenation in the α,β-unsaturated cinnamaldehyde and the low temperature selective oxidation of H 2S into elemental sulfur (60 °C). Carbon nanotubes as support allowed to increase both cinnamaldehyde conversion and selectivity toward CC bond hydrogenation. Supporting a nickel-based catalyst on SiC nanotubes allowed to increase both desulfurization activity of the catalyst and its solid sulfur storage capacity. The inner partial pressure concept, or confinement effect, was developed to explain the high performances of this new SiC-based catalyst. The last section is devoted to further objectives for developing such highly performing new support materials.

The First Preparation of Silicon Carbide Nanotubes by Shape Memory Synthesis and Their Catalytic Potential

Two main innovations are presented in this article. (1) The first reproducible synthesis of silicon carbide nanotubes of different internal and external diameters. The method used, the shape memory synthesis, is based on the gas–solid reaction between a vapor of SiO and nanotubes of carbon for the high diameters, and nanofibers of carbon for the small diameters. (2) A significant increase in the rate of a catalytic reaction (oxidation of H2S in S) probably due to a microscopic increase of the partial pressure of H2S inside the nanotubes, produced by condensation and microcapillarity, while the macroscopic partial pressure outside the tubes remains unchanged. This phenomenon could be extended to many other reactions, with polar gaseous reactants which are prone to condensation by capillarity at the usual temperatures of catalytic reaction, or with liquid phase reaction by an overconcentration of one of the reactants inside the tubes.

Growth of SiC nanorods prepared by carbon nanotubes-confined reaction

SiC nanorods have been synthesized by means of the carbon nanotubes-confined reaction between SiO gas and carbon nanotubes. The diameters of SiC nanorods can be controlled by the local partial pressure of the CO gas produced during reaction. The morphology of SiC nanorods depends on the shape of the carbon nanotubes at high reaction temperatures. The growth mechanism of SiC nanorods is basically a shape memory synthesis.