Thermal Dimensional Stability Research Articles

Easy manufacturing constraint based topology optimization of dual-scale and dual-constituent lattice metastructure with thermal dimensional stability

Thermal dimensional stability (TDS) is a crucial issue in the development of high-end industry equipment and precision instruments that work in fluctuating thermal environments. To endow meta-structures with high load-carrying capacity and TDS functionality simultaneously, this paper proposes a topology optimization framework to optimize the topologies of lattice meta-structures at macroscopic structural and microscopic material scales concurrently. An important feature of the current optimization model is the introduction of a material concentration distribution (MCD) constraint to reduce the number of dual-constituent interfaces (DIs), which enables the easy manufacturing of the optimized structures because an additional fabrication process is required for the connection of heterogeneous lattice members. Designs for two dual-scale TDS structures, potentially employed for satellite payload platforms and the supporting structure of space telescopes, are completed. Compared with mono-scale TDS structures, the dual-scale schemes exhibit superior structural performances due to the opening of the dual-scale design space. Numerical experiments are performed to validate the ultra-low structural thermal deformations of the optimized TDS structures with values of 0.0743 μm/℃ and 0.153 μm/℃. Furthermore, the imposition of the MCD constraint significantly reduces the number of DIs from 38 to 10 within a lattice cell, enabling the easy assembly of the demonstrative 3D printing dual-constituent samples.

Highly Stretchable Polyurethane Porous Membranes with Adjustable Morphology for Advanced Lithium Metal Batteries.

A highly flexible, tunable morphology membrane with excellent thermal stability and ionic conductivity can endow lithium metal batteries with high power density and reduced dendrite growth. Herein, a porous Polyurethane (PU) membrane with an adjustable morphology was prepared by a simple nonsolvent-induced phase separation technique. The precise control of the final morphology of PU membranes can be achieved through appropriate selection of a nonsolvent, resulting a range of pore structures that vary from finger-like voids to sponge-like pores. The implementation of combinatorial DFT and experimental analysis has revealed that spongy PU porous membranes, especially PU-EtOH, show superior electrolyte wettability (472%), high porosity (75%), good mechanical flexibility, robust thermal dimensional stability (above 170 °C), and elevated ionic conductivity (1.38 mS cm-1) in comparison to the polypropylene (PP) separator. The use of PU-EtOH in Li//Li symmetric cell results in a prolonged lifespan of 800 h, surpasing the longevity of PU or PP cells. Moreover, when subjected to a high rate of 5 C, the LiFePO4/Li half-cell with a PU-EtOH porous membrane displayed better cycling performance (115.4 mAh g-1) compared to the PP separator (104.4 mAh g-1). Finally, the prepared PU porous membrane exhibits significant potential for improving the efficiency and safety of LMBs.

3D Printed P(VdF‐HFP)/SBA‐15 composite‐based gel polymer electrolyte versus commercial celgard: A comparative investigation on thermal stability and electrochemical performance for lithium‐ion battery application

AbstractThe current work reports on tailoring of 3D printed gel polymer electrolyte (GPE) employing poly(vinylidene fluoride‐co‐hexafluoropropylene) P(VdF‐HFP) as the host matrix and mesoporous Santa Barbara Amorphous‐15 (SBA‐15) mesoporous sieve as ceramic filler. Further, this work envisages an investigation on its physicochemical properties, thermal shrinkage behavior, and electrochemical performance. An effort has been undertaken to formulate 3D printable P(VdF‐HFP)/SBA‐15 composite‐based GPE ink with suitable rheological properties. The breath figure method is followed to investigate the influence of 1‐methyl‐2‐pyrrolidinone (NMP)/tetrahydrofuran (THF) mixture as a solvent on the porosity of 3D printed GPE, through which enhanced porosity is evident from scanning electron microscopy (SEM) analysis. The morphological analysis further confirms the hybrid porous structure facilitated by the addition of SBA‐15 into the P(VdF‐HFP) matrix. The 3D printed P(VdF‐HFP)/SBA‐15 (10%) composite‐based GPE shows promising ionic conductivity in the order of 0.2 × 10−4 S/cm at room temperature and demonstrates excellent dimensional thermal stability up to 175°C. The electrochemical measurement of 3D printed GPE is tested separately using 3D printed cathode half‐cell (3D printed LFP vs. Li+) and 3D printed anode half cell (3D printed LTO vs. Li+) with GPE as separator. Further, also tested with conventionally prepared electrode and the coin cell studies show discharge capacity of 3D printed P(VdF‐HFP)/SBA‐15 (10%) composite‐based GPE is comparable to commercial celgard separator. All these features speculate that the 3D printed fabricated in the current work may find potential application in lithium‐ion battery.

The metamaterial with high thermal-mechanical stability and the practical application as the microwave antenna: Mechanical designs, theoretical predictions, and experimental demonstrations

To address the demand of maintaining the structural configuration upon extreme temperature changes, metamaterials with high thermal-mechanical stability have attracted wide attention recently. However, there are still some challenges for previous studies regarding mechanical design and practical application exploration. This manuscript proposes the design strategy for the lattice sandwich metamaterial with excellent zero thermal-induced warping, along with the metamaterial-based antenna with a high stability of electromagnetic signal transmission. Through the design strategy of discrete lattice units of the metamaterial, the ultra-low thermal warping of the metamaterial is realized upon the non-uniform temperature field. Here, the theoretical model is established to predict both heat transfer and thermal-induced deformation behavior upon complex mechanical-thermal loading conditions. The combination of theoretical predictions, finite element analysis, and experiments verifies the thermal dimensional stability of the metamaterial proposed here. Compared with the heterogeneous bilayer plate, experimental thermal warping of the metamaterial specimen is reduced by 99.7%. Additionally, compared with the bilayer-based specimen, gain attenuation, the main lobe's offset angle, and the voltage standing wave ratio offset of the metamaterial-based antenna specimen are experimentally reduced by 99.5%, 99.9% and 74.2%, revealing the huge application potential of this metamaterial in the field of spacecraft communication.

Revealing packing structure in benzimidazole-containing polyimides: Anti-parallel offset π-π stacking

Aromatic polyimides (PIs) exhibit excellent mechanical and thermal properties due to the charge transfer (CT) interactions. The introduction of benzimidazole with hydrogen interactions is a notably effective strategy for yielding exceptional superheat resistance and high thermal dimensional stability of PIs. Decoupling the stacking behavior under CT interactions and hydrogen interactions is crucial for elucidating the behavior of PIs macromolecules. Herein, the packing structure of PIs guided by hydrogen interactions was visualized using three plausible model compounds and theoretical simulations. The phthalimide fragment exhibited a preference for anti-parallel offset stack π-π stacking, while the phenylbenzimidazole fragment formed a shoulder-to-shoulder arrangement, resulting in the adoption of a Mixed Layer Packing (MPL) conformation, which is not the common Preferred Layer Packing (PLP) conformation. The CT interactions of phthalimide served as the primary stacking driving force, rather than the hydrogen interaction of benzimidazole. The intrinsic nature of packing behavior was that the minima and maxima parts of the electron density deviated from the midperpendicular of benzene and succinimide, where the LOL-π map, ESP map and SAPT calculations provided insights into the microscopic electronic structure. Finally, experimental PI fibers was prepared and their XRD pattern further confirmed the presence of an anti-parallel offset π-π stack conformation.

Preparation and properties of cationic waterborne polyurethane/acrylate for fluorine‐free water repellents

AbstractIn this work, cationic waterborne polyurethane/acrylate (WPUA) was synthesized for water repellent in cotton fabrics to replace fluorine‐containing finishing agents with the concerns of ecosystems and human health. First, the tertiary amines monomers, N‐methyl diethanolamine, 3‐dimethylamine‐1, 2‐propylene glycol, N,N′‐bis (2‐hydroxyethyl)piperazine, were used as chain extenders to prepare waterborne polyurethane, respectively. Long‐chain octadecyl acrylate monomers were then grafted to the waterborne polyurethane by a self‐emulsifying method. The stable WPUA suspensions of positively charged latexes were obtained and could be finished on cotton fabrics via a simple pad‐curing process. The coated cotton fabrics were capable of repelling common liquids without any penetration, and the contact angles of the treated cotton fabrics could reach 150°. The WPUA latex films also exhibited good tensile mechanical properties and thermal dimensional stability. The cotton fabric coated with the WPUA showed good laundering durability, and its static water contact angle was still maintained at 142° even after 50 times washing. This work not only highlights the structural design and preparation but also provides a feasible strategy for fluorine‐free water repellency in cotton fabrics, which has great potential application prospects for a variety of fields.

Synthesis and comparative study of high Tg and colorless polyamide‐imides with different amide‐to‐imide ratio

AbstractColorless polyimide (CPI), a heat‐resistant polymer being widely used in optoelectrical devices, has attracted worldwide attention. Polyamide‐imides due to the incorporation of amide groups into the CPI chains enhance the polymer performance by improving the thermal dimensional stability and excellent mechanical properties without sacrificing the optical transparency. In this article, CPI films PI‐(1‐3) are synthesized from one‐step polymerization of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and cyclopentanone bis‐spironorbornane tetracarboxylic dianhydride (CpODA) with amide‐containing diamine N,N′‐(2,2′‐bis(trifluoromethyl)‐[1,1′‐biphenyl]‐4,4′‐diyl)bis(4‐aminobenzamide) (AB‐TFDB) and bis(trifluoromethyl)benzidine (TFDB). In comparison, by adjusting the ratio of imide and amide groups in the repeating unit, PI‐(4‐5) are prepared from copolymerization of terephthaloyl chloride (TPC), 6FDA, and CpODA with TFDB diamine. PI‐(1‐5) with 90% transmittance in the visible region tailored the excellent thermal and mechanical properties. Particularly, PI‐3 exhibited a high glass transition temperature of 412°C, a coefficient of thermal expansion of 20.8 ppm/K, a tensile strength of 128 MPa, and an elastic modulus of 5.4 GPa. The results also concluded that irrespective of the polyamide‐imide synthesis strategy, CPI films with similar amide‐to‐imide ratio in polymer chain demonstrated comparable optical, thermal, and mechanical properties.

Study on the orientation structure and thermal dimensional stability of polyimide films based on infrared dichroism method

Study on the orientation structure and thermal dimensional stability of polyimide films based on infrared dichroism method

Preparation and characterization of fluorine-containing benzimidazole polyimide films with a micro-branched crosslink structure

In order to solve the problem of high-water absorption and low transparency of benzimidazole polyimide (PBII) films, this study introduced fluorine-containing groups into the benzimidazole polyimide molecule chains, and a series of benzimidazole polyimide films with different fluorine-containing ratios were prepared. In addition, a micro-branched crosslinking structure was established by adding triamino compounds to the system, and the effect of the micro-branched crosslinking structure on the film properties was investigated. The research showed that adding a certain amount of fluorine-containing groups could effectively improve the optical properties and decrease water absorption of polyimide films while having a small effect on the heat resistance and thermal dimensional stability. The incorporation of a small amount of triamino compounds effectively compensated for the adverse effects on the mechanical properties, heat resistance, and thermal dimensional stability caused by the addition of fluorine-containing groups and lowering the imidization temperature. In addition, the water absorption could be further reduced by establishing a cross-linked structure. In this study, a new design idea was provided to achieve the balance of heat resistance, thermal dimensional stability, water absorption, transparency, and mechanical properties of benzimidazole polyimide films.

Dual-Modified Electrospun Fiber Membrane as Separator with Excellent Safety Performance and High Operating Temperature for Lithium-Ion Batteries.

Polyacrylonitrile/Boric acid/Melamine/the delaminated BN nanosheets electrospun fiber membrane (PB3N1BN) with excellent mechanical property, high thermal stability, superior flame-retardant performance, and good wettability are fabricated by electrospinning PAN/DMF/H3BO3/C3H6N6/ the delaminated BN nanosheets (BNNSs) homogeneous viscous suspension and followed by a heating treatment. BNNSs are obtained by delaminating the bulk h-BN in isopropyl alcohol (IPA) with an assistance of Polyvinylpyrrolidone (PVP). Benefiting from the cross-linked pore structure and high-temperature stability of BNNSs, PB3N1BN electrospun fiber membrane delivers high thermal dimensional stability (almost no size contraction at 200°C), excellent mechanical property (19.1MPa), good electrolyte wettability (contact angle about 0°), and excellent flame retardancy (minimum total heat release of 3.2MJm-2). Moreover, the assembled LiFePO4/PB3N1BN/Li asymmetrical battery using LiFePO4 as the cathode and Li as the anode has a high capacity (169mAhg-1 at 0.5C), exceptional rate capability (129mAh g-1 at 5C), the prominent cycling stability without obvious decay after 400 cycles, and a good discharge capacity of 152mAh g-1 at a high temperature of 80°C. This work offers a new structural design strategy toward separators with excellent mechanical performance, good wettability, and high thermal stability for lithium-ion batteries.

Crosslinked PVA/Citric Acid Nanofibrous Separators with Enhanced Mechanical and Thermal Properties for Lithium-Ion Batteries

Electrospinning polyvinyl alcohol (PVA) nanofibrous membranes have gained increased attention for their uses as separators for lithium-ion batteries (LIBs) due to their high porosity and excellent electrolyte wettability, but their poor mechanical and thermal properties have limited their further development. In this work, a crosslinked PVA composite separator (PVA/CA-H) was first prepared via the electrospinning of the PVA and citric acid (CA) mixed solution and then the heating of the nanofibrous membrane, and the effects of the amount of CA on the structure and performance of the PVA/CA-H separator were investigated. The hydroxyl group of PVA and the carboxyl group of CA were crosslinked under the heat treatment, resulting in a slight reduction in the porosity and pore size of the composite separator compared to pure PVA, and to compensate for this issue, the mechanical strengths, as well as the thermal dimensional stability of the PVA/CA-H separator, were significantly improved. Meanwhile, the PVA/CA-H separator exhibited good electrolyte uptake (158.1%) and high ionic conductivity (1.63 mS cm−1), and, thus, the battery assembled with the PVA/CA-H separator exhibited a capacity retention of 96.3% after 150 cycles at 1 C. These features mean that the crosslinked PVA composite separator can be considered as a prospective high-safety and high-performance separator for LIBs.

Fabrication of high‐performance poly(vinyl alcohol) tubes via stable melt extrusion by reversible crosslinking of boric acid

AbstractThe unique intermolecular interactions of poly(vinyl alcohol) (PVA) endow it with excellent barrier properties to oxygen and nonpolar hydrocarbon organic solvents, thus having potential applications in the fields of oil and gas transmission. In view of the difficulties in thermal processing of PVA and based on the molecular complexation technology established by our research group, the melt extrusion of PVA tubes was achieved. To improve the extrusion stability of PVA tubes, boric acid (BA), which could form reversible crosslinking with PVA, was further introduced, and the influences of BA content on the interactions between BA and PVA, the thermal processability of PVA, as well as the mechanical properties and gasoline barrier properties of PVA tubes were systematically studied. The results showed that BA could form both chemical and physical crosslinking with PVA, so controlled the violent evaporation of water, one of plasticizers with low boiling point, and at the same time ensured the good thermal processing of PVA, lastly realizing the stable melt extrusion of PVA tubes. With the increase of BA content, the crystallinity of PVA decreased, but the glass transition temperature, mechanical properties, thermal dimensional stability, as well as water resistance of PVA tubes increased. The gasoline barrier of PVA tubes reached the best at the BA content of 0.10 wt%, that is, 0.97 g mm/m2 day.

Chitosan nanofiber paper used as separator for high performance and sustainable lithium-ion batteries

Separators are indispensable components in lithium-ion batteries (LIBs), providing efficient pathways for lithium ions to travel and isolating the positive and negative electrodes to avoid short circuits. However, traditional polyolefin-based separators exhibit inferior electrolyte affinities, limited porosities, and low thermal stabilities. In this study, a novel method was developed to prepare chitosan micro/nanofiber membranes as LIB separators using natural materials. The pore sizes of the chitosan micro/nanofibers separators were modulated by changing the diameters of the chitosan fibers. The results demonstrated that the chitosan nanofiber separators (CSNFs) had superior electrolyte uptake (281 %), excellent thermal dimensional stability, and electrochemical performance in LiFePO4/Li half-cell, as indicated by the higher discharge capacity after 100 cycles, and higher rate capacity than commercial Celgard2325 separator. This study paves the way for the fabrication of eco-efficient and environment-friendly separators for high-performance LIBs.

Optimizing the thermal properties of fiber reinforced phthalonitrile composites

AbstractThe development of lightweight composites with desirable thermo‐mechanical properties is progressively increasing. Phthalonitrile (PN) based composites have shown great potential in this regard. However, the basic thermal properties of PN composites required for engineering design are not yet fully understood. In this work, we investigated the thermal stability, thermal expansion behavior and thermal conductivity of PN composites reinforced with carbon fiber (CF) and high silicon fiberglass (HSF) via combined experimental studies and numerical simulations. The results indicated that CF/PN performs better in thermostability than HSF/PN at temperatures below 500°C. Moreover, the incorporation of CF and HSF lowered the coefficient of thermal expansion (CTE) and thermal insulation of PN. At room temperature, the in‐plane CTE of CF/PN and HSF/PN were 1.97E‐6 and 9.24E‐6°C−1, respectively, while the out‐plane thermal conductivities of CF/PN and HSF/PN were 0.65 and 0.34 W/(m K). It is worth noting that an excessively high fiber volume fraction would lead to poor thermal insulation and lightweight properties of the PN composites, while a low fiber volume fraction would result in poor stiffness and thermal dimensional stability. Determined via TOPSIS model, a fiber volume fraction range of 50%–60% was ideal for both composites with comprehensive optimal properties, respectively.

A Light-Thin Chitosan Nanofiber Separator for High-Performance Lithium-Ion Batteries.

With the development of portable devices and wearable devices, there is a higher demand for high-energy density and light lithium-ion batteries (LIBs). The separator is a significant component directly affecting the performance of LIBs. In this paper, a thin and porous chitosan nanofiber separator was successfully fabricated using the simple ethanol displacement method. The thickness of the CME15 separator was about half that of mainstream commercial Celgard2325 separators. Owing to its inherent polarity and high porosity, the obtained CME15 separator achieved a small contact angle (18°) and excellent electrolyte wettability (324% uptake). The CME15 separator could maintain excellent thermal dimensional stability at 160 °C. Furthermore, the CME15 separator-based LIBs exhibited excellent cycling performance after 100 cycles (117 mAh g-1 at 1 C). The present work offers a perspective on applying a chitosan nanofiber separator in light and high-performance lithium-ion batteries (LIBs).

Improving the lightfastness and thermal stability of black urushi (oriental lacquer) by kraft lignin oleate

Urushi, an oriental lacquer, is sensitive to light and easily deteriorates upon light exposure, leading to the fading and loss of gloss of its coatings. In this study, we attempted to improve the lightfastness of black urushi by utilizing the UV-absorbing properties of kraft lignin. Oleic acid-esterified kraft lignin was prepared and added to the black urushi to improve the compatibility. No aggregation of oleic acid-esterified lignin occurred in the black urushi, and the physical properties of the films were maintained to a large extent. A possible chemical interaction between lignin and black urushi was suggested upon thermal analysis. It was also found that the addition of lignin improved the thermal dimensional stability of black urushi. Finally, the high gloss factor of the black urushi film was maintained by adding oleic acid-esterified lignin after 168 h of light irradiation. Oleic acid-esterified lignin therefore appears as a promising functional additive to improve photostability of urushi coatings.

Click-chemistry and ionic cross-linking induced double cross-linking ionogel electrolyte for flexible lithium-ion batteries

With the expansion of portable devices, high-security and flexible energy storage technologies are gaining popularity. However, because of the use of poisonous, flammable, and unstable organic liquid electrolytes in commercial lithium-ion batteries, they cannot provide sufficient protection for the safety and long-term life of portable devices. A thiolate click reaction and ion interaction are used to successfully create a double cross-linking ionogel electrolyte (DC-Ionogel) by sealing 1-ethyl-3methyimidazolium bis (trifluoromethyl) imide (EMIm(TFSI)) in a double cross-linked network. An ion cross-linking network and a covalent cross-linking network are interlaced in the double cross-linked network, which considerably increased the flexibility and stability of the ionogel electrolyte. As a result, DC-Ionogel outperformed in terms of flame retardancy and thermal dimensional stability and outperformed in terms of electrochemical performance, with higher room ionic conductivity (1.79 × 10−3S cm−1) and a broader electrochemical window (5 V). Due to its excellent performance, it is more likely to be used in flexible energy-storage devices.

Poly(ether ether ketone) Conferred Polyolefin Separators with High Dimensional Thermal Stability for Lithium-Ion Batteries.

The traditional polyolefin separators used in lithium-ion batteries (LIBs) are plagued by limitations such as poor wetting of electrolytes and insufficient thermal stability, hindering the progress of LIBs. To overcome these limitations, we have developed a modified phase inversion technique to efficiently and durably coat polyolefin separators with poly(ether ether ketone) (PEEK). The resulting PEEK-coated polyolefin separators exhibit mechanical properties similar to those of unmodified polyolefin separators, with comparable tensile strength and modulus. Furthermore, the PEEK coating provides outstanding thermal stability, as the modified separators maintain their stability even at temperatures up to 200 °C, which is among the best results reported for polyolefin-based separators. In addition, the PEEK coating enhances ionic conductivity by more than 100% compared to polyolefin counterparts, leading to significant improvement in the electrochemical performance of prototype half cells. The modified phase inversion technique presented here offers a practical solution for coating polyolefin separators with functional polymers, paving the way for next-generation separator materials.

Properties of transparent bamboo based on different positions of bamboo

Based on the preparation of transparent bamboo, this study optimized the preparation process by selecting different position of bamboo and adjusting the delignification time. It is concluded that the transparent bamboo prepared from middle layer bamboo after 5 h delignification treatment has the best comprehensive performance, with light transmittance of 89.6% and haze of 43.3%. It has excellent tensile strength (89.7 MPa), good thermal insulation performance (0.187Wm−1K−1), certain UV aging resistance, thermal dimensional stability and waterproof properties for outdoor conditions. It can not only select transparent bamboo with the best performance, but also save raw materials as much as possible, so that its application range is wider.

Preparation and characterization of low CTE thermoplastic copolyimide resins based on the structural design of block sequence

In order to solve the challenge of balancing the thermoplastic processing properties and thermal dimensional stability of polyimide (PI) resin, in this research, 3,3′,4,4′-biphenyl tetracarboxylic diandhydride (BPDA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB) were used as rigid components, 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-diaminodiphenyl sulfone (DDS) as flexible components. A series of random copolyimide resins was prepared by adjusting the molar ratio of rigid and flexible monomers. Determining the molar ratio which could balance the thermoplastic processing properties and thermal dimensional stability, block copolyimide resins with different rigid and flexible block lengths were then prepared in this ratio. The research showed that the molar ratio of monomers and the sequence structure of molecular chains had a strong influence on the performance of PI resins. When the content or block length of rigid component increased, the coefficient of thermal expansion (CTE) decreased but the glass transition temperatures (Tg) and melt viscosity increased. The PI-B343 resin had a CTE value of 40.63 ppm/K and the lowest melt viscosity reached 675 Pa·s, achieved the simultaneous regulation of the thermoplastic processing properties and thermal dimensional stability for PI resin.