Hard Domains Research Articles

Electromagnetic interference shielding composites and the foams with gradient structure obtained by selective distribution of MWCNTs into hard domains of thermoplastic polyurethane

In this paper, multilayer thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) electromagnetic interference shielding composite foams with gradient structure was prepared. The gradient distribution of effective concentration of filler and cell size were realized by selective distribution of MWCNTs into hard domains of TPU, which improved interlayer interface polarization of electromagnetic waves and impedance matching between the material and the air. The average electromagnetic interference shielding efficiency (EMI SE) of TPU/MWCNTs composites with gradient structure is 1.2 times larger than that of homogeneous composites. After foaming, the average EMI SE of the gradient foams was higher than that of the homogeneous foams, with maximum average EMI SE of 35.4 dB. This work is the first time to correlate the interaction of fillers with the soft domains and hard domains of TPU and EMI shielding performance, providing a feasible method for designing lightweight composites with low filler and better EMI shielding performance.

Dual-Functional Biopolyurethane Blends with Shape-Memory and Self-Healing Properties: Effects of Mixed Hard Domains on Structures and Properties

Dual-Functional Biopolyurethane Blends with Shape-Memory and Self-Healing Properties: Effects of Mixed Hard Domains on Structures and Properties

A low-cost strategy to enhance strength-ductility balance in AISI1045 steel

In the current research, the impact of cold single-roll drive rolling as a low-cost technique on the microstructural evolution and mechanical properties of the AISI1045 sheet was studied. The microstructure of the as-received sample was a lamellar structure consisting of soft domains (proeutectoid ferrite) and hard domains (pearlite). The average grain size of proeutectoid α decreased from 24.5 μm (for the initial steel) to 7.1 μm (for the 60 % rolled steel) due to the occurrence of continuous dynamic recrystallization (CDRX). With an increase in the rolling deformation, the homogeneity of the ferrite and pearlite distribution in the microstructure was improved. Fragmentation and bending of the θ lamellae and several shear bands were seen in the 60 % deformed steel. By increasing the strain, the rotation of ferrite grains towards the θ fiber (as shear texture) increased due to the introduction of severe shear plastic deformation caused by the single-roll drive rolling. By increasing the intensity of ⟨100⟩‖ND (caused by the rolling deformation increasing), the amount of hardness enhanced less in the RD-TD section compared to the RD-ND section. As the rolling reduction increased to 60 %, the yield and tensile strength significantly enhanced and reached a maximum of 993.1 MPa and 1017.8 MPa, respectively. This was due to work hardening, grain refinement strengthening of α, and fragmentation of θ. The decreasing trend of the work hardening of the 60 % rolled steel was not similar to the strain hardening behavior of homogeneous materials, indicating that the number of geometrically necessary dislocations accumulated at the hard domain/soft domain interfaces was large, which was beneficial to the increment of work hardening in the second stage. After the rolling reduction increased, the proportion of dimples reduced, the depth and number of dimples decreased, and the plasticity reduced, which had a large effect on the secondary cracks.

Mechanical Robust, Self-Healable Polyurethane Elastomer Enabled by Hierarchical Hydrogen Bonds and Disulfide Bonds.

The fabrication of mechanically robust and self-healing polymeric materials remains a formidable challenge. To address the drawbacks, a core strategy is proposed based on the dynamic hard domains formed by hierarchical hydrogen bonds and disulfide bonds. The dynamic hard domains dissipate considerable stress energy during stretching. Meanwhile, the synergistic effect of hierarchical hydrogen bonds and disulfide bonds greatly enhances the relaxation dynamics of the PU network chains, thus accelerating network reorganization. Therefore, this designed strategy effectively solves the inherent drawback between cohesive energy and relaxation dynamics of the PU network. As a result, the PU elastomer has excellent mechanical properties (9.9 MPa and 44.87 MJ/m3) and high self-healing efficiency (96.2%). This approach provides a universal but valid strategy to fabricate high-performance self-healing polymeric materials. Meanwhile, such materials can be extended to emerging fields such as flexible robotics and wearable electronics.

Building Ion-Conductive Supramolecular Elastomeric Protective Layer via Dynamic Hard Domain Design for Stable Zinc Metal Anodes.

The instability of zinc metal anode caused by zinc dendrite growth and severe parasitic reactions has significantly restricted the extensive application of rechargeable aqueous zinc-ion batteries (RAZBs). Herein, based on the strategy of dynamic hard domains, we develop an ion-conductive supramolecular elastomer consisting of Zn salts and the polyurethane-urea-polypropylene glycol polymer skeleton. This elastomer combines high mechanical strength, high ionic conductivity, decent hydrophobicity, and high adhesion to stabilize the electrode-electrolyte interface. In the elastomer system, this elastomer can dynamically adapt to the volume changes of Zn anodes during repeated zinc plating/stripping processes through the reversible dissociation/reassociation of hierarchical hydrogen bonds (H-bonds) formed by the polar groups of urea and urethane moieties. Meanwhile, the coordination of Zn2+ with soft polypropylene glycol (PPG) segments contributes to fast ion transport. This hydrophobic elastomer can also effectively inhibit water-induced corrosion by shielding the active Zn metal from the aqueous electrolyte. Based on the above synergies, the surface-modified anode shows excellent cycling stability above 550 h at a high current density of 5 mA cm-2 and a capacity of 2.5 mAh cm-2. Moreover, the assembled Zn//MnO2 full cell also displayed an enhanced electrochemical performance. This work provides inspiration for the design of solid electrolyte interphase (SEI) layers in aqueous battery chemistry to accelerate the application of RAZBs.

Influence of annealing‐induced phase separation on the shape memory effect of graphene‐based thermoplastic polyurethane nanocomposites

AbstractThermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long‐chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase‐separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene‐based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene‐based nanoparticles on the shape memory effect.

Healable, luminescent, notch-insensitive waterborne polyurethane via noncovalent crosslinking with hydrogen bonds and ionic interactions

Luminescent materials display their fascinating performance in wearable electronics, optoelectronics, and information interactions. Enhancing reliability and longevity is particularly attractive for next-generation luminescent polymeric materials. Here we fabricate a supramolecular healable, luminescent waterborne polyurethane (Supra-LWPU) by incorporating reversible hydrogen bonds and ionic interactions into the noncovalent crosslinking network. The Supra-LWPU polymer exhibits excellent mechanical performance with robust tensile strength (6.8 MPa), superior stretchability (1755.4 %), high toughness (70.9 MJ m−3), and damage tolerance (44.7 KJ m−2). Owing to the sacrificial and reversible hard domains, the damaged network demonstrates a dynamic rearrangement with efficient healing efficiency (92.1 %), accompanying the restored toughness (65.3 MJ m−3) at 60 °C after 24 h. Multiple H-bonds induce aggregation domain formation of tertiary amine groups, rendering a luminous polyurethane network. An aggregate luminescence behavior can effectively assist in observing the healing process of Supra-LWPU networks. The mechanically responsive luminescent (MRL) device with well-organized microcracks exhibits strain-dependent luminescence for fluorescent patterns, demonstrating promise in next-generation stimuli responsive light-emitting materials.

SDA-CLIP: surgical visual domain adaptation using video and text labels.

Surgical action recognition is an essential technology in context-aware-based autonomous surgery, whereas the accuracy is limited by clinical dataset scale. Leveraging surgical videos from virtual reality (VR) simulations to research algorithms for the clinical domain application, also known as domain adaptation, can effectively reduce the cost of data acquisition and annotation, and protect patient privacy. We introduced a surgical domain adaptation method based on the contrastive language-image pretraining model (SDA-CLIP) to recognize cross-domain surgical action. Specifically, we utilized the Vision Transformer (ViT) and Transformer to extract video and text embeddings, respectively. Text embedding was developed as a bridge between VR and clinical domains. Inter- and intra-modality loss functions were employed to enhance the consistency of embeddings of the same class. Further, we evaluated our method on the MICCAI 2020 EndoVis Challenge SurgVisDom dataset. Our SDA-CLIP achieved a weighted F1-score of 65.9% (+18.9%) on the hard domain adaptation task (trained only with VR data) and 84.4% (+4.4%) on the soft domain adaptation task (trained with VR and clinical-like data), which outperformed the first place team of the challenge by a significant margin. The proposed SDA-CLIP model can effectively extract video scene information and textual semantic information, which greatly improves the performance of cross-domain surgical action recognition. The code is available at https://github.com/Lycus99/SDA-CLIP.

High strength, high stiffness and toughness, defect‐tolerant waterborne polyurethane with healing and antibacterial abilities

AbstractThe nature creates many biomaterials such as spider silk which exhibits a combination of stiffness, strength and toughness. However, most of synthetic unfilled materials suffer from a trade‐off between toughness and stiffness. Inspired by the structure of spider silk but beyond it, we proposed a novel molecular design to achieve transparent unfilled waterborne polyurethane (WPU) with simultaneously enhanced stiffness (280.9 MPa), tensile strength (25.1 MPa) and toughness (140.0 MJ/m3) as well as good elasticity (710%). The designed WPU comprised homogeneous continuous phase (soft segments) and diverse H‐bonds (hard segments) dispersed in it. The increase of rigid molecular chain content and H‐bonds contributed to the high stiffness of WPU. Furthermore, the mismatch of stiffness between hard domains and soft segments might promote crack deflection and branching, which endowed the robust WPU with fracture energy of 81.16 kJ/m2. The robust WPU film could be healed to recover most of its original mechanical properties (strength for 24.4 MPa and elongation for 610%) under heating. In addition, the WPU films demonstrated good antibacterial performance against Staphylococcus aureus and Escherichia coli after chlorination.

High Performance Star Block Aliphatic Polyester Thermoplastic Elastomers Using PDLA-b-PLLA Stereoblock Hard Domains.

Star block (ABC)4 terpolymers consisting of a rubbery poly(γ-methyl-ε-caprolactone) (PγMCL) (C) core and hard poly(l-lactide) (PLLA) (B) and poly(d-lactide) (PDLA) (A) end-blocks with varying PDLA to PLLA block ratios were explored as high-performance, sustainable, aliphatic polyester thermoplastic elastomers (APTPEs). The stereocomplexation of the PDLA/PLLA blocks within the hard domains provided the APTPEs with enhanced thermal stability and an increased resistance to permanent deformation compared to nonstereocomplex analogs. Variations in the PDLA:PLLA block ratio yielded tunable mechanical properties likely due to differences in the extent and location of stereocomplex crystallite formation as a result of architectural constraints. This work highlights the improvements in mechanical performance due to stereocomplexation within the hard domains of these APTPEs and the tunable nature of the hard domains to significantly impact material properties, furthering the development of sustainable materials that are competitive with current industry standard materials.

Partial crystalline organosilicon-based polysiloxane-polyurethane copolymers

Partial crystalline polysiloxane-based polyurethane copolymers were prepared by using hydroxyethoxypropyl capped polydimethylsiloxane (PDMS) as soft segment and α,ω-(bis (hydroxyethylthioether) ethyl)-disiloxane as chain extender. Due to this partial crystalline structure, the copolymer shows fairly good tensile properties and multiple shape deformation property. Repeated tensile tests revealed that stretch led to crystal destruction, and the microstructure of samples became stable after twice stretches. The lost crystallinity got 85.1% recovered upon treated at 60 °C for 1 h. It was proved that partial crystallization properties of the polysiloxane-polyurethane copolymer were from combined effects of polysiloxane soft segment and disiloxane chain extender. This unique crystallization kinetics of -(Si-O-Si)x- structure coexisting in soft and hard segments is regarded as one main reason to form crystalline hard segment domains in a common two-step synthesis.

Coarse-grained molecular simulation of the role of curing rates on the structure and strength of polyurea

We present a reactive coarse-grained model that can more accurately simulate the interplay between step-growth polymerization and phase segregation in elastomeric copolymers such as polyurea. The coarse-grained force fields were calibrated by the iterative Boltzmann inversion method to reproduce the target structural distributions sampled from atomistic simulations of partially-cured, oligomeric prepolymers. Using this coarse-grained model, polymerization simulations were performed at simulated curing rate spanning five decades to draw connections between the rate of polymerization, the microstructure, and the high-strain rate mechanical properties of the cured elastomer. Analysis of the simulated polyurea systems suggests that curing at faster reaction rates leads to hard domains with smaller diameter ligaments that are more strongly interconnected with bridging soft segments than those formed at slow curing rates. Simulated uniaxial compression of the cured systems indicates that the key process-induced microstructural variation influencing the hardening behavior of the elastomer is the fraction of soft segments that bridge across hard domain ligaments, which can lead to a substantial increase in the flow stress at large compressive strains.

Development of robust and rapid self-healing polymers for the repair of microcracks in energetic composite materials

Adhesives with exceptional toughness and self-healing properties are vital for the practical application of energetic composite materials (ECMs). However, the majority of self-healing polymers used in ECMs lack sufficient toughness. In this study, we address this challenge by incorporating asymmetric alicyclic and bent biphenyl ring structures into the hard domain units of polymers. The synthesized PUDS-3 films exhibit a remarkable toughness of up to 20.93 MJ·m−3, recovering over 90% of this toughness within just 20 min after a complete fracture. This behavior results from the synergistic interaction between dynamic disulfide and hydrogen-bonding mechanisms during the restructuring process. Furthermore, elevated temperatures led to a rapid decrease in the relaxation modulus and characteristic relaxation time of the PUDS samples, effectively accelerating crack healing. Both experimental measurements and molecular dynamics simulations demonstrated that a higher hard segment content in the adhesive corresponded to increased strength in the interfacial interaction with 1,3,5-trinitro-2,4,6-triaminobenzene (TATB). Upon accidental mechanical damage, the cracked ECMs displayed significant and efficient self-healing capabilities within 24 h at 60 °C. The utilization of these self-healing and highly toughness adhesives hold promising prospects for enhancing the safety and longevity of ECMs.

Fast Li+ Transport Polyurethane-Based Single-Ion Conducting Polymer Electrolyte with Sulfonamide Side chains in the Hard Segment for Lithium Metal Batteries.

Single-ion conducting polymer electrolytes (SICPEs) are considered as one of the most promising candidates for achieving lithium metal batteries (LMBs). However, the application of traditional SICPEs is hindered by their low ionic conductivity and poor mechanical stability. Herein, a self-standing and flexible polyurethane-based single-ion conductor membrane was prepared via covalent tethering of the trifluoromethanesulfonamide anion to polyurethane, which was synthesized using a facile reaction of diisocyanates with poly(ethylene oxide) and 3,5-diaminobenzoic acid (or 3,5-dihydroxybenzoic acid). The polymer electrolyte exhibited excellent ionic conductivity, mechanical properties, lithium-ion transference number, thermal stability, and a broad electrochemical window because of the bulky anions and unique two-phase structures with lithium-ion nanochannels in the hard domains. Consequently, the plasticized electrolyte membrane showed exceptional stability and reliability in a Li||Li symmetric battery. The assembled LiFePO4||Li battery exhibited an outstanding capacity (∼180 mA h g-1), Coulombic efficiency (>96%), and capacity retention. This research provides a promising polymer electrolyte for high-performance LMBs.

Thermo‐mechanical property enhancement of rigid polyurethane foam composite using low cost, environment friendly fly ash over silica particles

AbstractLow cost and environment friendly fly ash particles and silica particles were used as additives in the rigid polyurethane foam composite. The usage of fly ash will decrease the need for its handling and exposure to environment. FTIR spectra show the absence of hydrogen bonded urea which indicates no aggregation of hard urea domains in the soft polyurethane matrix after the addition of silica/fly ash. The composite loaded with 20 weight percentage fly ash had the highest glass transition temperature. At 10 weight percentage of the additive, the gross calorific value in the fly ash loaded composite decreased by 12% when compared with the composite loaded with silica. Introduction of fly ash into the foam composite up to a certain weight percentage (10 wt%) enhanced the compressive strength of the rigid polyurethane foam composite. The percolate particle concentration was at 10 weight percentage of the additive. The addition of fly ash increased the compressive strength up to 21% compared to the foam composite loaded with silica. Addition of fly ash in the foam composite resulted in a decrease of water absorption up to 23% in comparison to the composite loaded with silica. Hence, low cost and environment friendly fly ash is suitable additive which can be loaded into rigid polyurethane foams for superior enhancement in mechanical and thermal properties.Highlights The addition of fly ash to the foam decreased the gross calorific value up to 12% compared to that of the silica loaded foam composite. The composite loaded with fly ash had highest normalized compressive strength and highest glass transition temperature than that of the unloaded foam. This can potentially replace conventional rigid polyurethane foam in timber constructions because of its higher compressive strength. We propose the addition of fly ash as a low cost, environment friendly additive as it improved the various properties of the polyurethane foam composite to a greater extent than silica particles. The greater usage of fly ash will help in the formation of a closed loop supply chain and alleviate the need for disposal of fly ash.

Facile approach for imparting shape memory behavior to traditional thermoplastic polyurethane via interaction between different hard segments

AbstractThe stability of hard domain is a key factor affecting the shape memory properties of thermoplastic polyurethane (TPU). However, the physical interaction in hard domains is weak for most kinds of TPU, leading to a plastic deformation and thus significantly decreasing the shape recovery ratio of TPU. In this work, a new strategy for constructing shape memory TPU was proposed, and the blends was prepared by simple solution mixing based on IPDI‐PU and HDI‐PU, in which isophorone diisocyanate (IPDI) with alicyclic structure was introduced in hard segments of IPDI‐PU, and hexamethylene diisocyanate (HDI) with linear structure was introduced in hard segments of HDI‐PU. With the introduction of HDI‐PU into IPDI‐PU, hydrogen bonds between mixed hard domains were formed more easily, which made it possible to tailor the stability of hard domains in PU blends by changing the composition of IPDI‐PU and HDI‐PU. Shape memory behavior of IPDI‐PU was difficult to be observed, while the shape fixity ratio and recovery ratio of the blends containing 30% HDI‐PU were respectively 94% and 72%. This simple and facile strategy can be used to develop the recyclable shape memory TPU, which will have a wider range of potential applications in smart devices.

Improved Elastic Recovery from ABC Triblock Terpolymers.

The promise of ABC triblock terpolymers for improving the mechanical properties of thermoplastic elastomers is demonstrated by comparison with symmetric ABA/CBC analogs having similar molecular weights and volume fraction of B and A/C domains. The ABC architecture enhances elasticity (up to 98% recovery over 10 cycles) in part through essentially full chain bridging between discrete hard domains leading to the minimization of mechanically unproductive loops. In addition, the unique phase space of ABC triblocks also enables the fraction of hard-block domains to be higher (fhard ≈ 0.4) while maintaining elasticity, which is traditionally only possible with non-linear architectures or highly asymmetric ABA triblock copolymers. These advantages of ABC triblock terpolymers provide a tunable platform to create materials with practical applications while improving our fundamental understanding of chain conformation and structure-property relationships in block copolymers.

Thermo‐mechanical property enhancement of rigid polyurethane foam using silica and alumina as hybrid fillers over single filler

AbstractSilica and alumina particles were loaded in the rigid polyurethane foam composite as hybrid fillers. After the successful addition of silica and alumina as fillers, various properties of the foam composite were enhanced up to a particular weight percentage (7.5 wt% of silica and alumina each) with respect to alumina loaded foams. Hard urea domains are well distributed in the urethane matrix which indicates the absence of the peak representing H‐bonded urea in the Fourier‐transform infrared spectroscopy results. The addition of hybrid fillers into the rigid polyurethane foam matrix improved the compressive strength of the foam composite by 14% in comparison to alumina loaded foams due to the synergistic effect of the hybrid fillers. The foam composite at 7.5 wt% loading of hybrid fillers was successful in decreasing the thermal conductivity by 9% with respect to the thermal conductivity of the unloaded foam. There was a reduction in the gross calorific value up to 7% in the hybrid filler loaded foam composite when compared with that of the alumina loaded composite. Hence, hybrid fillers should be added to enhance the composite's properties by a greater extent.Highlights From the compressive test results, an increase in the compressive strength up to 14% was observed in the samples loaded with hybrid fillers with respect to the samples loaded with alumina due to the synergistic effects of the two fillers. For the foam composite loaded with alumina, the gross calorific value decreased up to 6% when compared to the unloaded foam. The gross calorific value decreased by a further 7% when hybrid fillers were added to the polyurethane foam composite with respect to the alumina loaded foam composite. The foam composite loaded with 7.5 weight % of hybrid fillers had lower values of thermal conductivity when compared with that of the unloaded polyurethane foam. We propose the addition of both alumina and silica as hybrid filler particles as they enhanced the various properties of the polyurethane foam composite to a greater extent than the addition of alumina particles as a single filler and have potential to replace unloaded polyurethane foams in different applications.

Asymmetric Hard Domain-Induced Robust Resilient Biocompatible Self-Healable Waterborne Polyurethane for Biomedical Applications.

The synthesis of eco-friendly and biocompatible waterborne polyurethanes (WPUs) through judicious molecular engineering with supreme mechanical strength, good shape recoverability, and high self-healing efficiency is still a formidable challenge because of some mutually exclusive conflicts among these properties. Herein, we report a facile method to develop a transparent (80.57-91.48%), self-healable (efficiency 67-76%) WPU elastomer (strain 3297-6356%) with the highest reported mechanical toughness (436.1 MJ m-3), ultrahigh fracture energy (126.54 kJ m-2), and good shape recovery (95% within 40 s at 70 °C in water). These results were accomplished by introducing high-density hindered urea-based hydrogen bonds, an asymmetric alicyclic architecture (isophorone diisocyanate-isophorone diamine), and the glycerol ester of citric acid (a bio-based internal emulsifier) into the hard domains of the WPU. Most importantly, platelet adhesion activity, lactate dehydrogenase activity, and erythrocyte or red blood corpuscle lysis demonstrated the hemocompatibility of the developed elastomer. Simultaneously, the cellular viability (live/dead) assay and the cell proliferation (Alamar blue) assay of human dermal fibroblasts corroborated the biocompatibility under in vitro conditions. Furthermore, the synthesized WPUs showed melt re-processability with retention of mechanical strength (86.94%) and microbe-assisted biodegradation. The overall results, therefore, indicate that the developed WPU elastomer might be used as a potential smart biomaterial and coating for biomedical devices.

Block length distribution, morphology, and property of thermoplastic polyurethanes affected by production method: A polymer‐by‐process investigation

AbstractTwo thermoplastic polyurethanes (TPUs) based on the same monomers and composition were produced by two different production methods – hand mix batch process and continuous band casting. The soft segment was poly(hydrofuran) (PTHF) with a molar mass of 1000 and the hard segment was made of 1,4‐butanediol (BD) and 4,4′‐methylene diphenyl diisocyanate (MDI). The hard segment content amounted to 42%. The distinctions in crystallization and thermal behavior and mechanical properties of the two TPUs were ascribed to differences in the hard and soft block length distribution caused by the different production methods. Using thermal fractionation – a series of successive self‐nucleation and annealing steps – the minor differences in hard block length distribution could be shown and quantified. The length distribution of the hard and soft blocks of the machine‐produced sample was narrower than that of the hand‐cast sample. The former with the narrow block distribution showed thicker and mechanically and thermally more stable hard domains. The more uniform block length distribution facilitated crystallization and resulted in improved tensile recovery behavior and elasticity. The second with the broader distribution, however, showed the highest tensile strength at break, which was ascribed to an improved strain‐induced hardening of the soft phase.