An investigation on shape memory behaviours of hydro-epoxy/glass fibre composites

Shape-memory polymers (SMPs) have the capacity to return large strains by external stimuli. Among various SMPs, shape-memory epoxy has received considerable attention because of its superior mechanical and thermal properties as well as excellent shape-memory performance. In this study, short glass fibre-reinforced shape-memory hydro-epoxy composites are developed to improve further the mechanical property of shape-memory epoxy resin. The thermomechanical and shape-memory properties of the developed composite materials are investigated by dynamic mechanical analysis, bend test and shape recovery test. The results indicate that the glass modulus and bend strength of the developed composite materials initially increase and then slightly decrease with increasing short glass fibre content. The glass transition temperature of the developed composite materials does not change with increasing short glass fibre. When the short glass fibre content is less than 4.5 wt.%, full recovery can be observed after only several minutes at different temperatures. The shape-memory property of the composite materials is not affected greatly. However, when the short glass fibre content is more than 4.5 wt.%, the material would be destroyed after deformation.     

Electromagnetic shielding effectiveness of copper/glass fiber knitted fabric reinforced polypropylene composites

The main objectives of this research work are to develop conductive knitted fabric composite materials and to determine their electromagnetic shielding effectiveness (EMSE). Polypropylene is the matrix phase and glass fibers are the reinforcement phase of the composite material. Copper wires are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of copper in the composite material is varied by changing the yarn composition, fabric knit structure and stitch density. The EMSE of various knitted fabric composites is measured in the frequency range of 300 kHz to 3 GHz. The variations of EMSE of knitted fabric composites with fabric structure, stitch density and yarn compositions are described. Suitability of conductive knitted fabric composites for electromagnetic shielding applications is also discussed.     

A reactive electrospinning approach for nanoporous PLA/monetite nanocomposite fibers

Nanoporous fibers of PLA/monetite nanocomposite were fabricated using a reactive electrospinning approach using appropriate precursors. Monetite is formed in-situ during the electrospinning of PLA matrix. The crystal phase and morphological structure of the monetite/PLA fibers were characterized using X-ray diffraction and Scanning Electron Microscope. The monetite particles were uniformly distributed through the electrospun fibers. Water and heat were produced during the formation of monetite as by-products. Both water and heat had the ability to modify the surface of the electrospun PLA/monetite fibers. Water induced pore formation (WIPF) was the most likely mechanism to explain the pore formation during the reactive electrospinning process. Electrospinning parameters such as feed rate, spinning voltage and monetite contents in the composite fibers were correlated to pore formation in the fibers. The feed rate had a significant effect on the pore formation. There was a little decrease in the value of the BET surface area for the fibers electrospun at high rate compared to that of the fibers electrospun at low rate. At low spinning voltage of 10 kV, most surfaces were nonporous. However, at a greater voltage (e.g. 26 kV) the number of pores increased on the surfaces. As the monetite contents increased, the pores were produced in a longitudinal shape and surface became rough. The final morphology of the pore formation implies a competition between the amounts of the generated by-product water and heat. By controlling the electrospinning parameter, it is possibly to manipulate fibers with the controlled pore area.     

智能变色材料在包装上的应用及设计形式研究

目的探索适用于智能变色材料在包装运用领域的理念和方法,结合智能材料从设计学层面探究智能变色包装的设计形式。方法以智能变色材料的物理属性为基础,对智能变色包装进行分类研究,并结合相关的设计实例,分析、归纳和总结智能变色包装的设计形式,为智能变色包装设计的发展和科学研究从设计学层面提供一种新的角度和研发依据。结果智能"光敏、温敏、电敏、气敏"变色材料在包装上的应用可通过颜色对比设计、颜色渐变设计、颜色变化融入图形创意这3种设计形式应用于包装安全、包装防伪、包装交互等领域。结论智能变色包装材料在实际应用过程中结合了包装设计学原理和包装的品牌诉求,采用了"科技与艺术"相结合的变色方案,设计出了符合消费审美的智能包装作品。     

Shape-memory surfaces for cell mechanobiology

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.     

Shape-memory surfaces for cell mechanobiology

Abstract

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.     

Softenable composite boom for reconfigurable and self-deployable structures

This article investigates (experimentally and numerically) the time and temperature-dependent folding and unfolding behavior, including the structural nonlinearity, of thin-walled softenable composite structures. The composites are fabricated with woven fabric fibers and a heat softenable material of the shape memory polymer (SMP) resin. A numerical model is developed. The model is based on the elastic properties of the woven fabric fibers, their fabric geometry, and the thermo-viscoelastic properties of the SMP resin. A thin-walled cylindrical boom, which can be flexibly folded into an arbitrary configuration and be self-deployed, is fabricated using the heat softenable composite. The viscoelasticity and the shape memory behaviors are investigated during the folding and unfolding of the boom at elevated temperatures.     

Textile-fiber-embedded multiluminescent devices: A new approach to soft display systems

In the recent remarkable advances in soft electronic systems, light-emitting functions play a prominent role. In particular, polymer composite systems with embedded luminescent particles have attracted considerable attention as a luminescent component owing to their flexibility and simple fabrication. However, most flexible composite-based electroluminescent (EL) devices have coplanar structures, requiring mechanically compliant electrodes with high transmittance, durability, and stable electrical conductivity. This is a limitation for systems designed for providing superior flexible characteristics without loss of luminescence. Here, we introduce a novel EL device architecture—a durable/flexible textile-fiber-embedded polydimethylsiloxane and zinc sulfide (PDMS + ZnS) composite, driven by an in-plane electric field, which eliminates the requirement for high transmittance. On applying an AC voltage, light is radially emitted from the ZnS particles surrounding the fibers, originating from the radially distributed electric/optical fields; the rolling and stretching flexibilities are maintained during this process. The device also exhibits strong EL intensities in a thick emitting layer—a parameter on which EL and mechanoluminescent (ML) intensities in coplanar structures are dependent. This is because the electric field is applied between in-plane fibers. Using this smart design, simultaneously high EL and ML intensities can be simply achieved by embedding fibers in strong ML-emitting PDMS + ZnS. We also present a patterned device controlled by different fiber embedding depths, utilizing the vertical and in-plane electric fields. This application may provide a basis for the development of emerging soft display systems that require high luminescence as well as flexibility in the light-emitting components.     

Optical properties (bidirectional reflectance distribution function) of shot fabric

To study the optical properties of materials, one needs a complete set of the angular distribution functions of surface scattering from the materials. Here we present a convenient method for collecting a large set of bidirectional reflectance distribution function (BRDF) samples in the hemispherical scattering space. Material samples are wrapped around a right-circular cylinder and irradiated by a parallel light source, and the scattered radiance is collected by a digital camera. We tilted the cylinder around its center to collect the BRDF samples outside the plane of incidence. This method can be used with materials that have isotropic and anisotropic scattering properties. We demonstrate this method in a detailed investigation of shot fabrics. The warps and the fillings of shot fabrics are dyed different colors so that the fabric appears to change color at different viewing angles. These color-changing characteristics are found to be related to the physical and geometrical structure of shot fabric. Our study reveals that the color-changing property of shot fabrics is due mainly to an occlusion effect.     

Werkstoffverhalten metallischer Faserverbunde unter Druckschwellbeanspruchung

Behaviour of metallic fiber composites under pulsating compression The behaviour of metallic fiber composite materials is investigated in stress controlled pulsating compression tests in the low cycle fatigue range. Two fiber composites are chosen as the test material which are used in electric industry as contact materials: copper matrix reinforced by continuous austenitic steel fibers as well as silver matrix reinforced by nickel fibers. Especially the successive buckling of the slim fibers arising during cyclic compression loading is studied by means of metallographic methods. Buckled fibers form a kinkband with localized fiber bending. The kinkband formation is found to be independent on fiber volume and stress amplitude.     

Preparation and characterization of ω-functionalized polystyrene–magnetite nanocomposites

Magnetite (Fe₃O₄) nanoparticles were prepared by in situ precipitation and oxidation of ferrous ions in the presence of ω-functionalized polystyrenes having carboxylate, sulfonate, thiol, and thiolated groups. Based on the results for the orthogonal experimental design, both the ratio of the concentration of iron precursor to polymer and the reaction temperature were the major factors controlling the particle size and its shape morphology. By adjusting the reaction conditions, the iron oxide particle size can be effectively controlled in the range between 2 and 20 nm. The magnetite-based polymer composite was characterized by UV–vis spectroscopy, thermogravimetric analysis, transmission electron microscopy, and X-ray diffraction. Magnetization measurements revealed that the nanocomposite materials exhibit superparamagnetic behavior at room temperature.     

Shape-memory materials and hybrid composites for smart systems: Part I Shape-memory materials

A review is presented of the current research and development of shape-memory materials, including shape-memory alloys, shape-memory ceramics and shape-memory polymers. The shape-memory materials exhibit some novel performances, such as sensoring (thermal, stress or field), large-stroke actuation, high damping, adaptive responses, shape memory and superelasticity capability, which can be utilized in various engineering approaches to smart systems. Based on an extensive literature survey, the various shape-memory materials are outlined, with special attention to the recently developed or emerged materials. The basic phenomena in the materials, that is, the stimulus-induced phase transformations which result in the unique performance and govern the remarkable changes in properties of the materials, are systematically lineated. The remaining technical barriers, and the challenges to improve the present materials system and develop a new shape memory materials are discussed.     

Shape control of NITINOL-reinforced composite beams

The shape of composite beams is controlled by sets of flat strips of a shape memory nickel–titanium alloy (NITINOL). The strips are embedded in the composite fabric of these beams inside sleeves, which are placed on the neutral axes. Prior to their insertion inside the beams, the NITINOL strips are thermally trained to provide and memorize controlled transverse deflections. Proper activation of the shape memory effect of the appropriate strips is utilized to produce controlled shapes of the NITINOL-reinforced beams.

A mathematical model is developed to describe the behavior of this class of SMART composites. The model describes the interaction between the elastic characteristics of the composite beams and the thermally induced shape memory effect of the NITINOL strips. The effect of various activation strategies of the NITINOL strips on the shape of the composite beams is determined.

The theoretical predictions of the model are validated experimentally using a fiberglass composite beam made of 8 plies of unidirectional BASF 5216 prepregs, which are 9.75 cm wide and 21.20 cm long. The beams are provided with four NITINOL-55 strips, which are 1.2 mm thick and 1.25 cm wide. The time response characteristics of the beam are monitored and compared with the corresponding theoretical characteristics. Close agreement is obtained between the theoretical predictions and the experimental results. The obtained results suggest the potential of the NITINOL strips in controlling the shape of composite beams without compromising their structural stiffness.     

无机颗粒形状对高储能密度有机复合材料介电性能的影响

通过在有机基体内添加无机陶瓷颗粒形成二相复合材料是当前研究高储能密度的热点和难点,材料的静电储能特性由其内部电场分布决定。对于纯高聚物材料在均匀外电场环境中其内部电场分布均匀,但当填充无机颗粒形成复合材料时,材料局部电场会发生畸变,进而影响复合材料的介电性能。本文通过有限元方法系统研究了不同形状颗粒,包括球型、纤维状和圆片状颗粒及其空间分布的电响应特性,进而分析其对复合材料储能特性的影响。结果表明,颗粒形状及空间分布的不同均会产生不同的局部电场分布,对于球型颗粒其顶端和低端会出现明显的电场集中现象;对于纤维状颗粒,当其长径比较小时,其端部束缚电荷产生的电场畸变不能被忽略。最后,本文建立了不同形状颗粒填充复合材料三维有限元模型,计算结果表明,在相同填充浓度下,一维纤维状颗粒填充复合材料的介电常数最大,二维圆片状颗粒填充复合材料介电常数最小,而球型颗粒填充复合材料介于二者之间。本文对理解复合材料储能特性的微观机制具有重要的意义。      

‘Two way’ shape memory composites based on electroactive polymer and thermoplastic membrane

A practical and facile strategy was proposed to fabricate composites that not only use the properties of individual components (commercial electroactive polymer and thermoplastic resin) to their advantage, but also produce synergy effect of ‘two way’ shape memory properties. In this design, electroactive polymer is treated as soft segment which provides actuation force via converting electrical energy to dynamic energy. Thermoplastic material serves as ‘hard segment’ to help with fixation of temporary shape thanks to its re-structuring and stiffness/modulus changing abilities through the reversible transitional temperature. Compared with traditional one way and two way shape memory materials, this composite material has the capability of changing shape without pre-programming. High shape recover property (99 ± 0.3%.) has been obtained due to the rubber elasticity of electroactive polymer matrix. Many features could be brought up based on this design, such as accurate control over deformation by changing strength of applied electric field as well as tailorable stimulus temperature and mechanical properties.     

Die elektrische Emission beim Versagen von Faserverbundwerkstoffen und ihren Komponenten

The electric emission during failure of fiber reinforced materials and their components Deformation and failure of fiber-reinforced materials (FRM) can cause electric charge displacements. This, consequently, leads to variations in the external electric field. These can be observed and recorded during the loading process without any contact to the sample. Analyzing these signals named electric emission (EE) can be done individually and also statistically when an acoustic emission equipment is used. Fracture of carbon and glass fibers yields EE signals of large amplitudes, whereas the polycarbonate matrix material exhibits smaller ones. The signals obtained in a tensile test with the composite materials exceed the ones of the matrix material but do not attain those of the fiber material. From the shape of the EE signals conclusions can be made on the elementary fracture process. From these experiments it can be concluded that the EE method is a valuable tool with respect to the detection of failure occurence of composite materials as is the acoustic emission technique. The EE technique is a field method and does, therefore, not require any sample preparation. This makes it a low cost technique which can be possibly applied in the field as well as in the laboratory.     

Distributed Electric Field Induces Orientations of Nanosheets to Prepare Hydrogels with Elaborate Ordered Structures and Programmed Deformations

Living organisms use musculatures with spatially distributed anisotropic structures to actuate deformations and locomotion with fascinating functions. Replicating such structural features in artificial materials is of great significance yet remains a big challenge. Here, a facile strategy is reported to fabricate hydrogels with elaborate ordered structures of nanosheets (NSs) oriented under a distributed electric field. Multiple electrodes are distributed with various arrangements in the precursor solution containing NSs and gold nanoparticles. A complex electric field induces sophisticated orientations of the NSs that are permanently inscribed by subsequent photo-polymerization. The resultant anisotropic nanocomposite poly(N-isopropylacrylamide) hydrogels exhibit rapid deformation upon heating or photoirradiation, owing to the fast switching of permittivity of the media and electric repulsion between the NSs. The complex alignments of NSs and anisotropic shape change of discrete regions result in programmed deformation of the hydrogels into various configurations. Furthermore, locomotion is realized by a spatiotemporal light stimulation that locally triggers time-variant shape change of the composite hydrogel with complex anisotropic structures. Such a strategy on the basis of the distributed electric-field-generated ordered structures should be applicable to gels, elastomers, and thermosets loaded with other anisotropic particles or liquid crystals, for the design of biomimetic/bioinspired materials with specific functionalities.     

Influence of properties at micro- and meso-scopic levels on macroscopic level for weft knitted fabrics

Knitted fabrics and particularly weft knitted fabrics are used as composite material reinforcements due to their ability to be draped and to give three-dimensional shape by molding or by knitting. This paper presents the strong connection of all the scales of the knitted fabric (fiber, yarn and fabric) on the final knitted fabrics and its mechanical and physical properties. For this purpose, only one polymer material is used, made of two different fibers in terms of length and fineness. These fibers are used to make different yarns with two structures then three plain-weft-knitted-fabrics are considered in terms of the loop length. The fibers have not the same bending rigidity because fiber cross-section areas are different. This has an influence on the three-dimensional loop shape and on the roughness, thickness and real area of contact of fabrics. This phenomenon is the same with the two yarn structures. The results presented here bring into light that the loop length does not influence the fabric thickness.     

Piezoelectricity of chiral polymeric fiber and its application in biomedical engineering

Poly-L-lactic acid (PLLA), which is a type of chiral polymer, exhibits a high shear piezoelectric constant. To realize a higher shear piezoelectric constant, we spun PLLA resin into fibers. We succeeded in controlling the piezoelectric motion of a PLLA fiber by applying a dc voltage and ac voltage, similar to the control of a piezoelectric actuator. On the basis of this experimental result, we designed a catheter using a PLLA fiber (PLLA fiber catheter) and tweezers using a pair of PLLA fibers (PLLA fiber tweezers), controlled by adjusting the applied voltage. Then, using the PLLA fiber tweezers or catheter, we successfully picked up and removed small samples, such as a thrombosis in a blood vessel.     

Conductive,self-cleaning,and short-circuit proof multi-functional graphene aerogel composite fibers

This work reports the superior properties of flexible multi-functional composite fibers based on graphene aerogel fibers. With the addition of phase change materials, the graphene aerogel fibers were synthesized by wet spinning and supercritical drying. The phase change materials can improve the structural uniformity and thermal stability of the composite fibers. The fibers coated with polydimethylsiloxane and fluorocarbon can respond to various external stimuli (e.g., electrons, photons, and heat), as well as have excellent properties of shape compliance, self-cleaning, and insulated surfaces. After coating fluorocarbon, the maximum water contact angle of graphene aerogel fibers increases from 132.18° to 151.77°. It is worth mentioning that adding an insulation layer of polydimethylsiloxane avoids the high-temperature problem caused by the short circuit of graphene aerogel fibers. The short-circuit temperature of graphene aerogel fibers is as high as 65 °C, while that of the composite fiber is only 41.5 °C after coating with polydimethylsiloxane. The temperature of graphene aerogel fibers with polyethylene glycol can increase to 39.3 °C under simulated sunlight. In addition, graphene aerogel fibers have excellent electrical conductivity (4.85?×?10³ S m^?1) at 300 K. After coating with polyethylene glycol, its electrical conductivity is still as high as 2.95?×?10³ S m^?1. The good electrical conductivity makes the aerogel fibers have promising application in advanced wearable systems.