3D Printed Architectured Silicones with Autonomic Self-healing and Creep-resistant Behavior

Self-healing silicones that are able to restore the functionalities and extend the lifetime of soft devices hold great potential in many applications. However, currently available silicones need to be triggered to self-heal or suffer from creep-induced irreversible deformation during use. Here, we design and print silicone objects that are programmed at the molecular and architecture levels to achieve self-healing at room temperature while simultaneously resisting creep. At the molecular scale, dioxaborolanes moieties are incorporated into silicones to synthesize self-healing vitrimers, whereas conventional covalent bonds are exploited to make creep-resistant elastomers. When combined into architectured printed parts at a coarser length scale, layered materials exhibit fast healing at room temperature without compromising the elastic recovery obtained from covalent polymer networks. A patient-specific vascular phantom is printed to demonstrate the potential of architectured silicones in creating damage-resilient functional devices using molecularly designed elastomer materials

Powder-based processing of highly-loaded platelet-reinforced composites

Conventional processes commonly used for the fabrication of composites with high volume fraction of reinforcing elements usually require the infiltration of monomers that are subsequently consolidated into a continuous polymer matrix. Such infiltration step often leads to long processing times and limits the choices of materials that can be used as soft polymer matrices. In this work, we present a new infiltration-less route in which a co-suspension of organic/inorganic powders is assembled through vacuum-assisted magnetic alignment and the resulting composite consolidated by uniaxial hot pressing at temperatures close to the melting point of the polymer phase. [1] We demonstrate that the fabrication process of thermoset- and thermoplastic-reinforced composites containing up to 50% in volume of aligned reinforcing platelets can be significantly simplified using this infiltration-less method (Figure 1a). Consolidation of thermosets matrices through hot pressing of assembled powder mixtures is achieved by employing polymers containing dynamic covalent bonds as crosslinking points in their molecular structure. As illustrated in Figure 1b, incorporation of 50% in volume of reinforcing platelets within dynamic polymer matrices enhances the flexural modulus and flexural strength by 14-fold and 3-fold as compared to the pure polymer, reaching values as high as 13 GPa and 90 MPa, respectively. As expected, the strain at rupture decreases from 3.0% to 0.8% upon addition of brittle ceramic platelets. These results demonstrate the potential of using infiltration-less routes to enable the fabrication of high-performance platelet-reinforced composites with high volume fraction of reinforcing ceramic particles and polymer matrices that are difficult to be infiltrated using conventional methods. Please click Additional Files below to see the full abstract

Strategies for synthesis of polyurethane-based molecular composites

In this work, we investigated strategies to obtain polyurethanebased molecular composites containing metal oxide nanoparticles chemically attached to polyurethane polymeric chain. In Strategy 1, nanoparticles functionalized with OH organic groups were added in a typical reaction to obtain thermoplastic polyurethane. The obtained materials were transparent, presented brown-color and typical characteristics of thermoplastic polymers. The results revealed that the addition of functionalized nanoparticles plays an important role in the chain growth process, suggesting that nanoparticles OH organic groups are consumed during the polymerization process, forming a primary bond between the material components. However, it was not possible to identify that primary bond by the characterization methods used in this work. On the other hand, in the Strategy 2, efforts were spent on the development of methods to obtain functional organic molecules constituted by linear chains with silane groups in both ends (called here as connecting agents). The connecting agents were used as nanobuilding blocks in a condensation reaction with metal oxide nanoparticles in order to obtain a linear hybrid chain with alternated organic and inorganic blocks. Despite it was not possible obtain linear hybrid chain molecular composite, the results contributed to a better comprehension of the mechanism involved in that method, suggesting that the use small nanoparticles (< 10 nm) and large organic molecules (molar mass between 10.000 e 50.000 g/mol) is necessary to synthesize the linear hybrid chain. Furthermore, bifunctional nanoparticles must be used to avoid the formation of a tridimensional network by cross-linking processes.Universidade Federal de Minas GeraisNeste trabalho, investigaram-se estratégias para a obtenção de compósitos moleculares derivados de poliuretanas contendo nanopartículas de óxidos metálicos ligadas quimicamente às cadeias poliméricas. Na Estratégia 1, nanopartículas funcionalizadas com grupos orgânicos OH foram adicionadas em uma reação de obtenção de uma poliuretana termoplástica (método da polimerização in situ ). Obtiveram-se materiais transparentes, de cor marrom e com características de polímeros termoplásticos. Os resultados mostraram que a adição das nanopartículas funcionalizadas desempenha um papel importante no processo de crescimento da cadeia polimérica, sugerindo que os grupos OH das nanopartículas sejam consumidos durante a reação, formando uma ligação primária entre os componentes do material. Entretanto, não foi possível identificar a formação desta ligação através dos métodos analíticos utilizados. Já na Estratégia 2, esforços foram realizados no desenvolvimento de métodos para a obtenção de moléculas orgânicas funcionais constituída por cadeias lineares com grupos silano em ambas extremidades (chamadas aqui de agentes de conexão). Os agentes de conexão foram utilizados com nanoblocos de construção numa reação de condensação com nanopartículas de óxido metálico para a obtenção de cadeias híbridas lineares com blocos orgânicos e inorgânicos alternados. Apesar de não ter sido possível a obtenção do compósito molecular com cadeia híbrida linear, os resultados contribuíram para uma melhor compreensão do mecanismo envolvido nesta reação, sugerindo que a utilização de nanopartículas pequenas (< 10 nm) e moléculas orgânicas grandes (com massa molar entre 10.000 50.000 g/mol) são necessárias para obtenção da cadeia híbrida linear. Além disso, nanopartículas bifuncionais devem ser usadas para evitar a formação de uma rede tridimensional através da formação de ligações inter-cruzadas

Architectured Silicone Vitrimers with Light-Tunable Mechanical and Self-Healing Behavior

Architectured materials synergistically harness chemical and microstructural features to create monoliths with antagonistic properties. Although it is a hallmark of biological composites, this material design concept has only recently been applied to synthetic elastomers and vitrimers. Here, we propose a light-based platform to manufacture architectured silicone vitrimers with locally tunable mechanical properties. Vitrimers are created through photocuring of polymer mixtures containing silica particles, silicone prepolymers and thiol crosslinkers. Dioxaborolane groups are incorporated in the silicone prepolymers to form dynamic bonds in the covalent adaptive network. Experiments showed that the mechanical properties and self-healing behavior of the silicone vitrimers are strongly influenced by the illumination conditions used during photo-curing. This dependence is exploited to manufacture architectured silicone vitrimers combining high stretchability and locally programmable mechanical stiffness. The high stretchability, tunable local properties and adaptive nature of these polymers makes them attractive for applications in soft robots, biomedical implants, and wearable devices

3D-Printed Architectured Silicones with Autonomic Self-Healing and Creep-Resistant Behavior

Self-healing silicones that are able to restore functionalities and extend the lifetime of soft devices hold great potential in many applications. However, currently available silicones need to be triggered to self-heal or suffer from creep-induced irreversible deformation during use. Here, a platform is proposed to design and print silicone objects that are programmed at the molecular and architecture levels to achieve self-healing at room temperature while simultaneously resisting creep. At the molecular scale, dioxaborolanes moieties are incorporated into silicones to synthesize self-healing vitrimers, whereas conventional covalent bonds are exploited to make creep-resistant elastomers. When combined into architectured printed parts at a coarser length scale, the layered materials exhibit fast healing at room temperature without compromising the elastic recovery obtained from covalent polymer networks. A patient-specific vascular phantom and fluidic chambers are printed to demonstrate the potential of architectured silicones in creating damage-resilient functional devices using molecularly designed elastomer materials.ISSN:0935-9648ISSN:1521-409

High-efficient microwave synthesis and characterisation of SrSnO3

Strontium stannate (SrSnO3) nanostructures were obtained by microwave- assisted calcination of a SrSn(OH)(6) precursor powder. Compared to other conventional calcination methods mentioned in the literature, this procedure led to a remarkable decrease of the reaction time and the synthesis temperature owing to direct interaction of radiation with the material. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and photoluminescence measurements were performed. A comparison of the characterisation results obtained by microwave and conventional methods was conducted, and differences concerning the properties of conventionally high-temperature calcined SrSnO3 from that obtained by microwave-assisted calcination were observed. Furthermore, two different morphologies (nanosticks and nanobrushes) were obtained by a variation of the concentration of the reactants. (C) 2009 Elsevier B.V. All rights reserved.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Synthesis, characterization and catalytic properties of nanocrystaline Y2O3-coated TiO2 in the ethanol dehydration reaction.

In the present study, TiO2 nanopowder was partially coated with Y2O3 precursors generated by a sol-gel modified route. The system of nanocoated particles formed an ultra thin structure on the TiO2 surfaces. The modified nanoparticles were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) analysis, Zeta potential and surface area through N2 fisisorption measurements. Bioethanol dehydration was used as a probe reaction to investigate the modifications on the nanoparticles surface. The process led to the obtainment of nanoparticles with important surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. The ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased over modified nanoparticles

Bio-inspired self-shaping ceramics

Shaping ceramics into complex and intricate geometries using cost-effective processes is desirable in many applications but still remains an open challenge. Inspired by plant seed dispersal units that self-fold on differential swelling, we demonstrate that self-shaping can be implemented in ceramics by programming the material’s microstructure to undergo local anisotropic shrinkage during heat treatment. Such microstructural design is achieved by magnetically aligning functionalized ceramic platelets in a liquid ceramic suspension, subsequently consolidated through an established enzyme-catalysed reaction. By fabricating alumina compacts exhibiting bio-inspired bilayer architectures, we achieve deliberate control over shape change during the sintering step. Bending, twisting or combinations of these two basic movements can be successfully programmed to obtain a myriad of complex shapes. The simplicity and the universality of such a bottom-up shaping method makes it attractive for applications that would benefit from low-waste ceramic fabrication, temperature-resistant interlocking structures or unusual geometries not accessible using conventional top–down manufacturing.ISSN:2041-172