Memory Materials Research Articles

Dope-dyed polyurethane electrospun nanofibers

Electrospun polyurethane nanofibrous mats are used in stretchable, flexible, memory and other technical materials. Lately, their potential for aesthetic purposes has been explored, and various dyeing techniques, as an additional process, and the environmental impact have been reported. Herein, the dope dyeing technique of polyurethane electrospun nanofibers with disperse dyes is reported as a part of the electrospinning process. Dope dyeing when compared to other techniques consumes lesser time, reduced cost and environmental impact, and produces better color and uniformity. The preparation of dope solution, electrospinning and post dye curing processes was optimized for producing the colored polyurethane nanofibrous mat. Dope-dyed polyurethane nanofibrous mats produced good colored yield and colorfastness results. Moreover, the morphology of undyed and dyed polyurethane nanofibers was similar as observed in the SEM analysis and presence of the dye molecules were evident in the FTIR analysis.

Colorless, transparent, and shape memory polyurethane networks with high strength and recyclability

AbstractThe traditional thermoset polyurethanes (PUs) can be recycled through the dynamic carbamate bonds under specific conditions. However, there is limited research on the structural evolution and property changes of these PUs before and after recycling. Herein, we designed and fabricated a thermoset polyurethane network (PCU) using polyhexamethylene carbonate diol (PHMC‐diol) as soft segments, and isophorone diisocyanate (IPDI) and glycerol (GLY) as hard segments. Through careful formulation design, the PCU demonstrated colorless transparency (with up to 86% transmission), shape memory properties, and reprocessing capabilities, all achieved without introducing other dynamic covalent bonds. Furthermore, the PCU exhibited excellent mechanical properties, boasting a tensile strength of 59.2 ± 3.7 MPa and the elongation at break of 674.8 ± 37.3%. Of particular interest, the PCU samples displayed solid‐state plasticity and impressive shape memory performance, with shape fixity and recovery ratios exceeding 90%. Leveraging the combination of solid‐state plasticity and shape memory, the PCU samples demonstrated the ability to achieve arbitrary shape manipulations. Upon recycling, it was observed that the cross‐linking density of the PCU samples decreased, resulting in the formation of byproducts and subsequently leading to a reduction in tensile strength. Nonetheless, the PCU samples prepared in this study exhibit potential as thermadapt shape memory and recyclable materials.

Repeat testing enhances long-term verbal memory in children with epilepsy

ABSTRACT To (i) determine whether accelerated long-term forgetting (ALF) can be found using standardized verbal memory test materials in children with genetic generalized epilepsy (GGE) and temporal lobe epilepsy (TLE), and (ii) to establish whether ALF is impacted by executive skills and repeat testing over long delays. One hundred and twenty-three children aged 8 to 16, (28 with GGE, 23 with TLE, and 72 typically developing; TD) completed a battery of standardized tests assessing executive functioning and memory for two stories. Stories were recalled immediately and after a 30-min delay. To examine whether repeat testing impacts long-term forgetting, one story was tested via free recall at 1-day and 2-weeks, and the other at 2-weeks only. Recognition was then tested for both stories at 2-weeks. Children with epilepsy recalled fewer story details, both immediately and after 30-min relative to TD children. Compared to TD children, the GGE group, but not the TLE group, showed ALF, having significantly poorer recall of the story tested only at the longest delay. Poor executive skills were significantly correlated with ALF for children with epilepsy. Standard story memory materials can detect ALF in children with epilepsy when administered over long delays. Our findings suggest that (i) ALF is related to poor executive skills in children with epilepsy, and (ii) repeated testing may ameliorate ALF in some children.

Reversible Amorphous-Crystalline Phase Transformation in an Ultrathin van der Waals FeTe System.

Searching for new phase-change materials for memory and neuromorphic device applications and further understanding the phase transformation mechanism are attracting wide attention. Phase transformation from the amorphous phase to the crystal phase has been unraveled in iron telluride (FeTe) bulk film deposited by pulsed laser deposition, recently. However, the van der Waals-layered feature of FeTe in the crystal form was not noted, which will benefit the scaling of the memory devices and shine light on phase-change heterostructures or interfacial phase-change materials. Moreover, the demonstration of advanced memory or neuromorphic device applications is lacking. Here, we investigate the phase transformation of FeTe starting from mechanically exfoliated van der Waals layers from a bulk single crystal. Surficial amorphization is revealed at the surface layers of FeTe flakes after exfoliation under ambient conditions, which could be transformed back to the crystalline phase with laser irradiation or heating. The conductance drop of the flake devices near 400 K verifies the phase transformation electrically. Memristor behavior of the amorphous surface in FeTe has been further demonstrated, proving the reversibility of the phase transformation and shining light on the possible applications of neuromorphic devices.

Highly Inductive Coil Spring Strain/Compress Sensors Integrated with Shape Memory Alloy and Shape Memory Polymers-CNTs.

Future wearable electronic gadgets offer greatpotential for using stretchable, strain-sensitive materials to instantly detect human motion and record physiological information. This paper presens a strain/compress sensor made from a Shape memory alloy (SMA) coil spring covered with silver pastes and the composite of carbon nanotubes and Shape memory polymer (SMP). The combination of the shape memory materials that expand or contract automatically by temperature improved the mechanics of the sensor. First, the proposed sensors showed an excellent ability to broad-range strain of 250% and compress of 50% with a relative inductance (∆L/L0 ) range from -35% to 50%, respectively. Durability during 1000 loading and unloading cycles at 200% strain is included. Secondly, by monitoring changes in resistance, inductance, and time, it is determined how many silver layers appropriate for transformation should be in order to improve the recovery time of the SMA coil spring. Moreover, the presence of CNTs in the composite-covered outer of sensors helps to reduce the influence of the relation between resistance and temperature in the range from 30 °C to 110 °C. Finally, a device is suggested for monitoring arm and triceps brachii muscle movements based on the stretchable area as a key parameter.

A Need for New Standards: Communicating Shape Transformations in the Technical Documentation of Products

Abstract Advances in additive manufacturing have enabled functional grading and multi-material deposition to produce “4D printed” parts that are net or near net shape; creating highly complex features that are difficult to produce with conventional manufacturing processes. This article addresses the fundamental challenge of how to ensure that the design, manufacturing, and functional intent for 4D printed parts can be accurately and unambiguously communicated across the design, manufacturing, inspection, and supply value chain. The use case of a generic mini-gripper sheds light on the benefits that a new standard could bring to the engineering and design of shape memory materials.

Smart materials: The next generation in science and engineering

In recent years, fascinating developments in various areas of materials science have happened. Smart materials, also known as intelligent or stimuli-responsive materials, have attracted attention in science and engineering. Smart materials are divided into six different groups: shape memory materials, piezoelectric materials, magnetostrictive materials, electro-rheological and magneto-rheological fluids, and self-healing materials. Shape-memory and self-healing materials are the most popular and important kinds of smart materials. Shape-memory materials have the ability to react to certain stimuli, such as temperature, pH, light, magnetic fields, and electric fields, and transform from a temporary shape to their original shape after exposure to these stimuli. Shape-memory alloys and shape-memory polymers have attracted the most attention and are widely used among all kinds of shape-memory materials developed. The two most important properties of shape-memory alloys are shape memory and superelasticity. Shape-memory polymers are gaining popularity because of specific benefits such as their high shape recovery rate, light weight, low density, high strength-to-weight ratio, high shape deformability, and readily tailorable glass transition temperature. Self-healing materials have the ability to fully or partially repair their features and functionality after repeated damage. Self-healing materials are divided into two categories: intrinsic and extrinsic, as well as autonomous and non-autonomous. These materials have the potential to increase their lifetime while reducing maintenance costs. Smart materials have a wide range of applications, including aerospace, automotive, biomedicine, and construction. The goal of this paper is to provide an overview of smart materials.

Three-Dimensional Printing of Shape Memory Liquid Crystalline Thermoplastic Elastomeric Composites Using Fused Filament Fabrication.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials utilised in shape memory applications. The processability of these materials via advanced manufacturing is being paid increasing attention to advance their volume production on an industrial scale. Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technique that offers the potential to address this. The critical challenge, however, is the rheological characteristics of LCEs that need to be tuned to achieve a facile processability through the extrusion-based method. In this work, new filaments of liquid crystalline thermoplastic elastomer (LCTPE) and its composites with lignin were made by the ternary system of LCE, thermoplastic polyurethane (TPU), and lignin. The results showed that TPU improves the melt flow index of the LCTPE system to approximately 10.01 g/10 min, while adding lignin further enhances the value of this index for the composites up to 21.82 g/10 min. The microstructural analysis indicated that the effective distribution of lignin and reduced domain size of the LCEs in the ternary blend contribute to the enhanced flowability of this filament through 3D printing. Samples of 3D-printed LCTPE and LCTPE/lignin composites maintained their shape memory characteristics via thermomechanical activation. Full shape recovery of the new LCTPE matrix and its composites with lignin was achieved in 39 s and 32 s at 130 °C, followed by 28 s and 24 s at 160 °C, respectively. The successful fabrication of LCTPE and LCTPE/lignin composite samples through 3D printing demonstrates a potential procedure for processing these shape memory materials using the FFF technique, and lignin offers a sustainable and cost-effective material solution that enhances the properties of this composite material.

Design and Test of Embedded Reconfigurable Mode Converter Based on Spontaneous Deformable Materials.

The mode converter, as a passive mode conversion device in transmission lines, is well-investigated and widely implemented in various electromagnetic systems. However, most traditional mode converters can only realize a single conversion mode. Thus, a mode converter achieving multiple controllable output modes is urgently needed. In this paper, a reconfigurable mode converter operating in the microwave range is achieved by embedding a deformable all-dielectric material with quadrilateral shape into a rectangular waveguide based on coupled-mode theory. It can achieve different target modes with controllable output for the same input by exciting the deformable all-dielectric material. The design principle of the mode converter is expounded concretely and simulation is carried out using HFSS software 2022 R2. Experimental results, consisting of the simulation results, demonstrate that the proposed mode converter can achieve various mode conversions with mode purity higher than 95%. This article innovatively applies deformable materials to waveguide mode conversion, expanding the application of deformable memory materials in electromagnetic devices.

Structural, morphological, and magneto-dielectric features of Ni-Co-Pr ferrites for high density memory and high frequency devices

Praseodymium (Pr3+) substituted Nickel-Cobalt ferrites with composition Ni0.3Co0.7PrxFe2-xO4 and concentration (x = 0.00, 0.05, 0.10, 0.15, 0.20) were synthesized via sol–gel approach. The crystallite size was lying in 10.94–25.44 nm range having decreasing tendency and lattice constant was varying between 8.30 and 8.39 Å. Two absorption bands were seen in infrared spectroscopy around 550 cm−1 and 430 cm−1, representing spinel structure. Morphological analysis revealed particle size of ≈ 26.87 nm. Magnetic investigations disclosed decreasing trend in saturation magnetization (Ms), retentivity (Mr) and coercivity (Hc) and were determined in 19.77–50.75 emu/g, 0.77–19.48 emu/g, and 87.23–943.27 Oe range, respectively. Dielectric parameters showed decreasing trend with increase in frequency. Dielectric constant and loss were decreased from 3.64 to 2.59 and 0.502–0.420 for Pr3+ concentration × = 0.00–0.20 at 0.5 GHz, respectively. AC conductivity showed elevation with increasing applied frequency. These reported magneto-dielectric features suggest possible use of material in high density memory and high frequency devices.

Design of Superhydrophobic Shape Memory Composites with Kirigami Structures and Uniform Wetting Property.

With the continuous increase in human demand to improve aircraft performance, intelligent aircraft technologies have become a popular research field in recent years. Among them, the deformable skin structure has become one of the key technologies to achieve excellent and reliable performance. However, during the service, deformable skin structures may encounter problems such as surface impact and adhesion of droplets in rainy weather or surface icing in low-temperature environments, which can seriously affect the flight safety of the aircraft. One way to overcome these issues is to use superhydrophobic shape memory materials in the structure. In this regard, first, shape memory composites were prepared with shape memory epoxy resin as the matrix and carbon fiber orthogonal woven fabric as the reinforcement material. Superhydrophobic shape memory composites (SSMCs) were then obtained by casting the kirigami composite with superhydrophobic carbon nanotube-polydimethylsiloxane (CNT@PDMS) mixture, and the surface was processed by laser micromachining. Shape memory performance and surface wetting performance were determined by material testing methods. The results showed that the shape memory recovery rate can reach 85.11%, the surface is superhydrophobic, the average water contact angle is 156.9 ± 4.4°, and the average rolling angle is 3 ± 0.5°. The three-point bending test of the specimens with different kirigami cell configurations showed that the shape memory composite based on the rectangular structure has the best deformability with an aspect ratio of 0.4. From the droplet impact test, it was found that the impact speed of water droplets and the curvature of the surface can greatly affect the dynamic performance of water. This work is expected to be of significant research value and importance for developing functional deformable skin materials.

A type of shape memory material based on ethylene-propylene-diene rubber (EPDM)/ polypropylene (PP) thermoplastic vulcanizates compatibilized by magnesium maleate

The effects of magnesium maleate (MgMA) and maleic anhydride (MAH) on the interfacial interaction and the shape memory properties of ethylene propylene diene monomer (EPDM) and polypropylene (PP) thermoplastic vulcanizate (TPV) with sea island structure prepared by dynamic vulcanization were investigated in this study. PP matrix could maintain the temporary shape of TPVs and the crosslinked EPDM phase supplied stress to drive the deformed shape recovery during the shape memory process. MgMA and MAH grafted on PP and EPDM chains verified by FTIR, DMA and SEM, which improved the interfacial compatibility of EPDM and PP and enhanced the efficiency of stress transfer in the shape memory process. The shape fixity ratio (Rf) and shape recovery ratio (Rr) of TPVs compatibilized by MgMA and MAH were almost above 80%. The shape memory property and the mechanical performance of TPVs were all improved compared to that of the sample without compatibilization.

Preliminary experimental study on simultaneous polishing and shape setting of Nitinol wire

Separate processes for shape setting and polishing of Nitinol workpieces are well investigated in scientific literature and adopted industrially. However, a simultaneous process for shape setting and polishing of Nitinol has not yet been reported. In this study, preliminary results of such process are presented, providing insights and directions for further research on post-processing shape memory materials. For this purpose, Nitinol wire samples with phase transformation temperatures Af = 4.5 °C, Af = 31 °C and Af = 61 °C were plasma electrolytic polished (PEP) while fitted in a specially designed sample holder at three electrolyte temperatures te = 50 °C, te = 65 °C and te = 80 °C. The PEP process duration was τPEP = 60 s, τPEP = 180 s and τPEP = 300 s. After the PEP processes, the samples were investigated for the shape memory effect (SME). The training effect, known to be present in shape memory alloys (SMA), was taken into account. The surface roughness of the investigated wires was measured before and after the PEP process. The obtained results demonstrate that both a phase transformation temperature and an electrolyte temperature have a strong effect on polishing and shape setting results.

Crystallization behavior of MnTe/GeTe stacked thin films for multi-level phase change memory

With substantial data storage requirements, enhancing the storage density of emerging non-volatile memories is a common challenge for achieving commercial applications. Phase change memory is capable of multi-level data storage in a storage cell, which can be applied in neural-inspired and all-photonic memory computing. In this study, we propose a MnTe/GeTe stacked thin film structure suitable for multi-level phase change memories and systematically study on the correlation between structure and performance. As the temperature rises, the stacked thin film sequentially crystallizes into form MnTe2, GeTe and Te phases, resulting in three changes in resistance. By utilizing different resistance states, the phase change memory cell based on the MnTe (15 nm)/GeTe (35 nm) stacked thin film can achieve multi-level storage with a 50 ns electrical pulse. The results show that the amorphous thermal stability of the stacked thin films is improved and that the minimal thickness variation before and after crystallization enhances its reliability. Therefore, the MnTe/GeTe stacked thin film is a phase change memory material with favorable structural properties and potential for multi-level storage applications.

Special Isssue on Advances in Memory Materials

Special Isssue on Advances in Memory Materials

Introduction to Shape Memory Material: Biomedical, Prosthetic and Orthotic Application

The need for prosthetic and orthotic devices is increasing significantly all over the world. Due to the increasing incidenceof sports injuries and road accidents, the rising number of diabetes-related amputations, and the growing prevalence ofosteosarcoma around the world are poised to drive the global market. Sports-induced injury is anticipated to drive demand,aiding market growth during the forecast period. The global prosthetics and orthotics market was valued at USD 6.39 billionin 2021 and is expected to expand at a compound annual growth rate (CAGR) of 4.3% from 2022 to 2030. Materials likepolymers (Polypropylene, Silicon, etc.), metals (Aluminium, Iron, etc.), alloys (stainless steel, bronze etc.), and carbon fibersare now used for making prosthetic and orthotic devices. Shape memory polymers (SMP) and shape memory alloys (SMA) arehaving ability to change and regain their original shape after changes in external stimuli like temperature, PH, heat, etc. Thisreview has discussed shape memory materials’ mechanical, chemical, and general properties, including their classification,advantages, disadvantages, FDA regulations, and applications in prosthetics and orthotics. This review will help prosthetists,orthotist, and biomedical engineers better understand these materials and how they increase the medical devices’ quality,durability and functionality.

Environment-Induced Degradation of Shape Memory Alloys: Role of Alloying and Nature of Environment.

Shape memory effects coupled with superelasticity are the distinctive characteristics of shape memory alloys (SMAs), a type of metal. When these alloys are subject to thermomechanical processing, they have the inherent ability to react to stimuli, such as heat. As a result, these alloys have established their usefulness in a variety of fields and have in recent years been chosen for use in stents, sensors, actuators, and several other forms of life-saving medical equipment. When it comes to the shape memory materials, nickel-titanium (Ni-Ti) alloys are in the forefront and have been chosen for use in a spectrum of demanding applications. As shape memory alloys (SMAs) are chosen for use in critical environments, such as blood streams (arteries and veins), orthodontic applications, orthopedic implants, and high temperature surroundings, such as actuators in aircraft engines, the phenomenon of environment-induced degradation is of both interest and concern. Hence, the environment-induced degradation behavior of the shape memory alloys (SMAs) needs to be studied to find viable ways to improve their resistance to an aggressive environment. The degradation that occurs upon exposure to an aggressive environment is often referred to as corrosion. Environment-induced degradation, or corrosion, being an unavoidable factor, certain techniques can be used for the purpose of enhancing the degradation resistance of shape memory alloys (SMAs). In this paper, we present and discuss the specific role of microstructure and contribution of environment to the degradation behavior of shape memory alloys (SMAs) while concurrently providing methods to resist both the development and growth of the degradation caused by the environment.

Tailoring Mid‐Gap States of Chalcogenide Glass by Pressure‐Induced Hypervalent Bonding Towards the Design of Electrical Switching Materials

AbstractPhase change memory (PCM) and ovonic threshold switching (OTS) materials using chalcogenide glass are essential elements in advanced 3D memory chips. The mid‐gap states, induced by the disorder and defects in the glass, are the physical mechanisms of the electrical switching behavior, while the origin of these trap states is still under debate and the medium‐range clusters that break the global octet rule, such as over‐coordinated atoms, are known to be responsible in various glass. Here, it is discovered that a large fraction of over‐coordinated clusters fails to generate mid‐gap states, which are probably caused by hypervalent bonding, a multi‐centered covalent bond participated by delocalized lone‐pair electrons. This is confirmed by the pressure‐driven simulations of amorphous GeSe models, in which it is found that octahedral motifs and hypervalent bonds prevent the over‐coordinated medium‐range clusters from providing excessive electrons. In practical applications, compatible dopants can be used to change the number of hypervalent bonds, thus controlling the number of mid‐gap states and consequently the performance of PCM and OTS materials. These results reveal the origin of mid‐gap states in chalcogenide glasses, enabling extensive control in the development of pioneering electrical switching materials.

지역아동센터 프로그램 운영 경험에 관한 자문화기술지

This study aimed to identify the fundamental factors and core values necessary to develop and implement a program for children at local child centers, considering their needs and characteristics. To achieve this, the research questions were set as follows: “What do researchers experience in operating programs at local child centers?” and “What does the experience of operating programs at local child centers mean to researchers?” The research employed the autoethnographic research method, and data were collected through memory materials, cultural artifacts, and self-reflection materials spanning from 2011 to 2022. The collected data were analyzed using the end-point coding method. The research findings revealed four types of programs: “Program of Living as I Am,” “Replica Program of Becoming an Expert,” “Superficial Program of Wanting to Become an Expert,” and “Subtle Program of Becoming an Expert.” These research results are significant as they provide direction and important guidelines for program development and operation. Additionally, they offer insights into the role of operators when utilizing the programs.

Shape Memory Materials Analysis and Research Tool (SM2ART): Finding Data Anomalies and Trends

Shape Memory Materials Analysis and Research Tool (SM2ART): Finding Data Anomalies and Trends