Ultra-low Coefficient Of Thermal Expansion Research Articles

Polyimides with ultra-low coefficient of thermal expansion derived from diamine containing bisbenzimidazole and bisamide

To provide polyimide (PI) with high heat resistance and ultra-low coefficient of thermal expansion (CTE) for use in flexible display substrates, a novel diamine with bisbenzimidazole and bisamide groups, namely N,N'-(1H,1'H-[5,5'-bibenzo[d]imidazole]-2,2'-diyl)bis(4-aminobenzamide) (BZBA), was designed and successfully synthesized. Several poly(benzimidazole-amide-imide) (PBIAI) films were prepared by thermal imidization with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and 4,4'-(hexafluoroisopropylindene)-diphthalic anhydride (6FDA), respectively. Among them, BZBA-BPDA has a high glass transition temperatures ( Tg = 345 °C) while achieving an extremely low coefficients of thermal expansion (CTE = 1.9 ppm K−1), meeting the processing requirements of polymer flexible substrates in OLED devices. The effects of different dianhydrides on the performance of PBIAIs were compared, providing a meaningful reference for further adjusting the PI molecular structure to meet specific requirements for industrial polymer films.

Additive manufacturing of Invar 36 alloy

Invar 36 alloy, renowned for its ultra-low coefficient of thermal expansion (CTE), is a functional Fe–Ni alloy that finds wide applications in aerospace and precision instruments. Additive manufacturing (AM), as a rapid digital manufacturing process, can efficiently and flexibly fabricate Invar 36 alloy parts with complex geometric and exceptional properties. Considering the advantages of AM and the increasing interest and demand for Invar 36 alloy parts fabrication by AM in recent years, it is imperative to provide a comprehensive summary of the current research status and technological advancements pertaining to AM Invar 36 alloy. Firstly, an overview of the AM processes currently employed for fabricating Invar 36 alloy is provided, including laser powder bed fusion, selective laser sintering, directed energy deposition, cold spray additive manufacturing, wire arc additive manufacturing, and binder jetting. Additionally, the microstructure, mechanical properties, and CTE of Invar 36 alloy manufactured by AM are summarized. Even eliminating the post heat treatment, the as-printed Invar 36 alloy can achieve excellent low CTE and mechanical properties, comparable to or exceeding traditional manufacturing processes. Moreover, the advantages and research progress of AM Invar 36 alloy composites are introduced. Enhancing mechanical properties while reducing CTE is a common challenge for both AM Invar 36 alloy and Invar composites. Finally, the technical gaps, research trends, and potential applications of AM Invar 36 alloy are summarized and prospected.

High-Performance Bismaleimide Resin with an Ultralow Coefficient of Thermal Expansion and High Thermostability

High-Performance Bismaleimide Resin with an Ultralow Coefficient of Thermal Expansion and High Thermostability

Anisotropy of microstructure, mechanical properties and thermal expansion in Invar 36 alloy fabricated via laser powder bed fusion

Invar 36 is a renowned iron-nickel alloy with an ultra-low coefficient of thermal expansion (CTE), which is widely used in aerospace and precision instruments. Laser powder bed fusion (LPBF) as a prevalent metal additive manufacturing technique could break through the limitations of traditional processes, such as low material utilization and difficulties in forming complex structures. In this work, Invar 36 alloy specimens were fabricated via LPBF process in 0° (H0 specimen), 45° (D45 specimen), and 90° (V90 specimen) build orientations. The microstructure, tensile properties, thermal expansion, and magnetic properties of the three orientations specimens were comprehensively investigated, and the anisotropy of microstructure, yield strength and CTE were analyzed. The V90 specimen exhibited the highest elongation (62.70%), while the D45 specimen owned the highest yield strength (496 MPa). The anisotropic mechanical properties can be attributed to variations in dislocation density, grain size, and intrinsic yield strength. The CTE of LPBF-fabricated Invar 36 alloy specimens were all lower than that of traditional manufacturing process at all temperature ranges. Since CTE is more related to magnetic properties, not sensitive to microstructure, the anisotropy of CTE is not significant in three build orientations. This study has significant implications to produce Invar 36 alloy devices with exceptional properties and 3D dimensional stability via the LPBF process.

Ultralow Coefficient of Thermal Expansion and a High Colorless Transparent Polyimide Film Realized Through a Reinforced Hydrogen-Bond Network by In Situ Polymerization of Aromatic Polyamide in Colorless Polyimide.

Colorless polyimides (CPIs) are a key substrate material for flexible organic light-emitting diode (OLED) displays and have attracted worldwide attention. Here, in this paper, the dispersion and interfacial interaction of aromatic polyamide (PA) in CPI (synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB)) were significantly improved by in situ polymerization, and colorless transparent macromolecular polyimide composites (CPI-PAx) were successfully prepared by PA and CPI. By adjusting the ratio of PA to CPI, a high-performance engineering plastic with excellent film-forming properties was obtained. Molecular simulations confirmed the uniform distribution of PA in CPI and its interaction in polymers. In CPI-PAx, the CPI was locked by the PA chain, and numerous molecular chains were mutually entangled to form a hydrogen-bond network structure. Due to the strong interaction between the chains imparted by the hydrogen bonds of the PA, they do not slide under external forces and heating. In addition, the additive PA has excellent dimensional stability, thermal, and mechanical properties, and CPI has outstanding optical properties, so the synthesized CPI-PAx combines the comprehensive properties of PA and CPI. The CPI-PAx has excellent thermal and mechanical properties, with a thermal decomposition temperature of 499 °C, a glass transition temperature of 385 °C, a coefficient of thermal expansion of 0.8 ppm K-1, a tensile strength of 50.9 MPa, and an elastic modulus of 3.9 GPa. Particularly, CPI-PAx has a 90% transmittance in the visible region. These data prove that the strategy of combining PA and CPI by in situ polymerization is an effective method to circumvent the bottleneck of CPI in the current flexible window application, and this design strategy is universal.

Fabrication of High Thermal Conductivity Nanodiamond/Aramid Nanofiber Composite Films with Superior Multifunctional Properties.

Polymer-based thermally conductive materials are preferred for heat dissipation owing to their low density, flexibility, low cost, and easy processing. Researchers have been trying to develop a polymer-based composite film with excellent thermal conductivity (TC), mechanical strength, thermal stability, and electrical properties. However, synergistically achieving these properties in a single material is still a challenge. To address the above requirements, we prepared poly(diallyldimethylammonium chloride)-functionalized nanodiamond (ND@PDDA)/aramid nanofiber (ANF) composite films using a self-assembly strategy. Owing to a strong interfacial interaction arising from electrostatic attraction, ND particles attract strongly along the ANF axis to form ANF/ND "core-sheath" arrangements. These assemblies self-construct three-dimensional thermally conductive networks through ANF gelation precipitation, which was analyzed as the key parameter for the realization of high thermal performances. The as-prepared ND@PDDA/ANF composite films exhibited high in-plane and through-plane TCs up to 30.99 and 6.34 W/m·K, respectively, at a 50 wt % functionalized ND loading, representing the optimal values among all previously reported polymer-based electrical insulating composite films. Furthermore, the nanocomposites also achieved other properties necessary for realistic applications, such as outstanding mechanical properties, excellent thermal stability, ultra-low thermal expansion coefficient, excellent electrical insulation, low dielectric constant, low dielectric loss, and outstanding flame retardancy. Thus, this excellent comprehensive performance enables the ND@PDDA/ANF composite films to be used as advanced multifunctional nanocomposites in thermal management, flexible electronics, and intelligent wearable equipment.

Spectral properties of ultra-low thermal expansion Er3+/Yb3+ co-doped phosphate glasses

An Er3+/Yb3+ co-doped phosphate glass with an ultra-low thermal expansion coefficient (55 × 10−7 K−1) was developed. The EYAP5 glass (80Al(PO3)3–20AlF3-1.5Er2O3-7.5Yb2O3, mol%) exhibits excellent spectral properties, thermomechanical properties, and chemical durability. Compared with traditional high phosphorus-doped silica glasses, EYAP5 glass achieves a higher Er3+/Yb3+ doping concentration and energy transfer efficiency from Yb3+ to Er3+ ions. Meanwhile, the absorption spectra, emission spectra, and fluorescence decay were systematically measured and compared in the temperature range of 300–480 K. Unlike the cases at 915 and 974 nm, the absorption cross section at 940 nm (∼0.21 pm2) has the highest temperature stability, which facilitates the stable operation of the 1.5 μm high-average-power laser. Furthermore, the temperature rises increase the energy transfer efficiency from Yb3+ to Er3+ ions, effectively suppressing the amplified spontaneous emission (ASE) at ∼1 μm.

Cover Image, Volume 61, Issue 2

Journal of Polymer ScienceVolume 61, Issue 2 p. i-i COVER IMAGEFree Access Cover Image, Volume 61, Issue 2 First published: 15 January 2023 https://doi.org/10.1002/pol.20220761AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract In the work reported on page 174, Dandan Li and colleagues prepare new poly (benzimidazole imide)s derived from the N-substituted bisbenzimidazole diamines. The unique structures increase the interchain interaction and film-forming of PMDA-poly (benzimidazole imide)s. The obtained polyimide films provide super-high Tg up to 500°C and ultra-low coefficient of thermal expansion. (DOI: 10.1002/pol.20220623) Volume61, Issue215 January 2023Pages i-i RelatedInformation

Improving Tribological Behaviors of Invar 36 Alloy under Extremely Cryogenic and Dry Conditions Through Surface Micro-Texturing

Invar 36 alloy is an iron-nickel alloy with an ultra-low coefficient of thermal expansion, which is widely used in cryogenic fields of liquefied natural gas (LNG) and aerospace. However, the wear under extremely cryogenic and dry conditions is a key problem for Invar 36 alloy applied in the bearing of cryogenic submersible pump. In this work, we are mainly for improving the cryogenic tribological performance of Invar 36 alloy through laser surface texturing. Three different types of surface micro-textures were prepared on Invar 36 alloy specimens. And the effects of these micro-textures on the friction and wear properties of Invar 36 alloy were investigated. The results show that groove-channel micro-texture has the lowest coefficient of friction and wear rate under normal and -196 °C. Further research shows that this is because the channel structure of groove-channel micro-texture is more conducive to the transfer of most debris generated caused by wear, which successfully reduces the occurrence of abrasive wear. Scanning Electron Microscopy/Energy-dispersive X-ray spectroscopy was utilized to explain the cryogenic tribological performance of the micro-textures.

Polyimides with super‐highTgand ultra‐low coefficient of thermal expansion fromN‐substituted bibenzimidazole diamines

AbstractPolyimides (PIs) with super heat‐resistance and ultralow coefficient of thermal expansion (CTE) are required urgently to employ as plastic substrates in flexible‐display devices. To attain the target properties, we designed and synthesized a novel bibenzimidazole diamine characterized in having aN‐phenyl group, namely 1‐phenyl‐2,2′‐bibenzoimidazole‐5,5′‐diamine (PhDABZ), and focused on an aromatic poly(benzimidazole imide) series derived from 1,2,4,5‐benzenetetracarboxylic (PMDA). Incorporating bibenzimidazole andN‐substituent effectively increase the interchain interaction and chance for flexible film formation, which provides the PIs with high glass‐transition temperature (Tg > 480 °C) and dimensional stability (CTE < 10 ppm K−1). These data provide a feasible method to achieve higher thermal properties of PIs.

Vibration resistance FBG temperature sensor fabrication and its application in the motor for hydraulic pump

This paper fabricated a fiber Bragg grating (FBG) temperature sensor with rapid response and excellent anti-vibration performance. The lightweight and miniaturization of the sensor provided favorable conditions for its application in mechatronic components. Specifically, the Invar capillary with an ultra-low thermal expansion coefficient was selected to package the FBG, which avoided the separation possibility between capillary and FBG under sharp temperature differences. It implied a wide temperature measurement range of the sensor. Nanometer copper suspension filled the tiny gap between capillary and FBG. Its good thermal conductivity brought a fast response speed close to the bare FBG. In addition, the jitter of FBG in the capillary was significantly reduced thanks to the nanometer copper suspension occupying its motion space. This sensor realized the reliability, rapidity and stability together. The FBG temperature sensor was applied to the temperature monitoring of small-size motor for hydraulic pump and achieved ideal results.

Ultra-high Tg and ultra-low CTE polyimide films based on tunable interchain crosslinking

A novel interchain crosslinking system was designed to improve the thermal performance of PI films. A diamine containing Cl atom (Cl-DAXBA) was prepared and polycondensed with pyromellitic dianhydride and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, respectively. Two series of PI films (PM and BP) were prepared under different curing temperatures in the range of 320–380 °C. The crosslinking of free radicals produced by Cl-DAXBA decomposition occurred between the molecular chains, and the crosslinking degree increased with raising the curing temperature. The network structure formed by crosslinking effectively inhibited the movement of molecular chains and promoted their close packing. The glass transition temperature (Tg) of PM films increased from 378 °C to >450 °C, and the coefficient of thermal expansion (CTE) decreased from 66.3 ppm·K−1 to 4.9 ppm·K−1. The Tg of BP films increased from 349 °C to >450 °C, and the CTE decreased from 50.4 ppm·K−1 to 17.7 ppm·K−1. Definitely, the tunable interchain crosslinking provides an effective strategy to improve both Tg and CTE simultaneously.

Anomalous upconversion behavior and high-temperature spectral properties of Yb/Ho-SiAlON ceramics

Traditionally, NaYF4 and glass-based materials are considered the most efficient upconversion materials. However, those materials may show signs of thermal warping or risks of fracture during long-term service life in extreme environments. In contrast, SiAlON ceramics preserve their spectral and physical integrity during continuous use due to their ultra-low thermal expansion coefficient (∼3.0 × 10−6/K) even at extreme temperatures. Here, we investigate the upconversion photoluminescence properties of Ho and Yb co-doped SiAlON (Ho/Yb-SiAlON) ceramics, prepared by hot-press method, at room temperature and at high temperature (298–1023 K). At room temperature, Ho/Yb-SiAlON ceramics show intense red upconversion emission under 980 nm excitation. At the high-temperature range, the spectral shift is absent in Ho/Yb-SiAlON indicating that the SiAlON ceramics have high-temperature spectral stability, which may be attributed to the low thermal expansion coefficient of SiAlON ceramics. Ho and Yb concentration-dependent spectra show an anomalous upconversion emission behavior. It is found that a higher sensitizer and low activator concentration combination is not always an ideal choice for sensitized luminescence in SiAlON ceramics which is in stark contrast to the common understanding of sensitized luminescence. The mechanism involving the dominant cross-relaxation process has been proposed to explain the observed anomalous upconversion behavior.

High performance epoxy resin with ultralow coefficient of thermal expansion cured by conformation-switchable multi-functional agent

Epoxy resins with low or negative thermal expansion have been widely searched for a long time owing to their great potential application in aerospace and microelectronics field. For the filler/epoxy resin composites, one key parameter of epoxy resins is to have suitable low coefficient of thermal expansion (CTE) to match with the fillers, however, it still remains a big challenge. In this work, we design and synthesize a new kind of conformation-switchable curing agent that contains dibenzocyclooctadiene (DBCOD) unit, named as cis-diamine-DBCOD. The epoxy resins cured by cis-diamine-DBCOD possess controllable CTE from negative to positive due to the conformational switch of DBCOD units, and the CTE can be tuned by the DBCOD content. We demonstrate the DBCOD units can undergo conformational change from boat to chair conformer with the rise of temperature based on the theoretical calculation and experimental results. Several commercial epoxy resins cured by cis-diamine-DBCOD also exhibit low CTE (around 10 ppm/K), reflecting the universality of the conformation-switch curing agent. Compared with conventional arylamine curing agents, the epoxy resins cured by cis-diamine-DBCOD possess higher Tg (218 °C) from DMA, which has 49 °C increase comparing with the corresponding epoxy resin with similar elongation at break. Meanwhile, the cured epoxy resin has superior mechanical properties, the tensile strength has 46.3 % increase. Therefore, the cis-diamine-DBCOD as a multi-functional conformation-switchable curing agent endows the cured epoxy resin with high dimension stability, thermal and mechanical performances for the specific applications.

Transparent polyimide films with ultra-low coefficient of thermal expansion

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2′-bis (trifluoromethyl) −4.4′-diaminobiphenyl (TFMB) or trans-1.4′-cyclohexanediamine ( t-CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T550 nm> 88%), great heat stability (CTE <4.4 ppm/K; Tg >314°C; Td5% >478°C) and good mechanical strength (σ > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion.

Superstrong, Lightweight, and Exceptional Environmentally Stable SiO2@GO/Bamboo Composites.

Development of lightweight structural materials from fast-growing bamboos is of great significance to building a sustainable society. However, previously developed structural bamboos by delignification combined with densification would easily fail under large external loading after exposure to water due to structure collapse, severely limiting their practical applications. Here, we demonstrate an ultrastrong and exceptional environmentally stable bamboo composite consisting of a graphene oxide (GO)/bamboo core and hierarchical SiO2 protection layer. The GO/bamboo composite exhibits ultrahigh tensile strength (641.6 MPa), superb flexural strength (428.4 MPa), and excellent toughness (17.5 MJ/m3), which are increased by about 480, 250, and 360% compared with natural bamboo, respectively. As a result, the specific tensile strength of the GO/bamboo composite is up to 513.3 MPa·cm3/g due to its low density (1.25 g/cm3), outperforming engineering structural materials such as aluminum alloys, steels, and titanium alloys. These large improvements benefit from the well-preserved bamboo scaffold and the strong hydrogen bonds between bamboo fibers and GO nanosheets. On the other hand, the SiO2@GO/bamboo composite shows superhydrophobicity due to the construction of hierarchical SiO2 layers, which endows it with outstanding water resistance. Moreover, the bamboo composite shows an ultralow coefficient of thermal expansion (≈2.3 × 10-6 K-1), indicating its excellent dimensional stability. Considering the ultrahigh mechanical performance and outstanding environmental stability, the developed lightweight SiO2@GO/bamboo composite is hopeful to be a green and sustainable structural material for practical engineering applications.

High Performance Epoxy Resin with Ultralow Coefficient of Thermal Expansion Cured by Conformation-Switchable Multi-Functional Agent

High Performance Epoxy Resin with Ultralow Coefficient of Thermal Expansion Cured by Conformation-Switchable Multi-Functional Agent

Tailoring thermal expansion of shape memory alloys through designed reorientation deformation

Manipulating macroscopic linear thermal expansion (TE) through microstructure engineering is emerging as a new research topic of shape memory alloys (SMAs). Here, we perform a modelling-and-experiment combined study to design and tune the coefficient of TE (CTE) of polycrystalline martensitic SMAs based on reorientation deformation. Using Landau thermodynamic theory of first-order phase transition, we prove that the martensite lattices of most SMAs possess intrinsic negative (positive) TE along the directions of transformation elongation (contraction). As a combined result of such intrinsic lattice-level TE and the extrinsic reorientation-deformation texture, the overall linear CTEs of martensite polycrystals decrease (increase) with the amount of reorientation stretching (contraction). The deformation paths and strain magnitudes are designed to obtain zero linear TE in 17 types of bulk SMAs and are verified by the available experimental data. Furthermore, through designed cross-rolling on martensitic NiTi sheets, we obtain ultralow in-plane CTEs (+0.13 × 10−6 K−1 ∼ +1.4 × 10−6 K−1), which are smaller than the reported values of SMAs and are even smaller than the commercial FeNi Invar alloy (+2.0 × 10−6 K−1). Our work provides a theoretical base to design SMAs with desired linear CTEs for many applications.

Thermally Stable Colorless Copolyimides with a Low Dielectric Constant and Dissipation Factor and Their Organic Field-Effect Transistor Applications

We developed highly thermally resistant and colorless polyimides (CPIs) with an ultralow coefficient of thermal expansion (CTE) and sufficient mechanical durability as a flexible substrate for organic field-effect transistors (OFETs). The CPIs were synthesized from trans-1,4-cyclohexyl diamine (t-CHDA) with different ratios of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and pyromellitic dianhydride (PMDA). The effects of the composition of s-BPDA and PMDA on the thermal, mechanical, electrical, and optical properties of CPIs were investigated. The optimized CPI, PI-3 with 90 mol % s-BPDA and 10 mol % PMDA, showed a relatively high elongation at break (8%) with a low CTE of 14 ppm K–1, a high glass transition temperature (Tg) of 340 °C, and a large tensile modulus (E) of 4.1 GPa, respectively. Besides, PI-3 possessed a high transparency with a light transmittance at 400 nm (T400) of 81% and a low cutoff wavelength (λcutoff) of 349 nm. Next, the dimer diamine of DDA (Priamine 1074) was introduced into the PI-3 structure to reduce the dielectric constant and enhance the stretchability. For example, PI-6C, with 85 mol % t-CHDA and 15 mol % DDA, showed a low dielectric constant (Dk) of 2.8, a low dissipation factor (Df) of 0.004, and a high T400 of 86% with maintained thermal and mechanical properties. Finally, a flexible OFET device using PI-3 as the substrate and dielectric was fabricated and characterized and exhibited an outstanding performance preservation after 1000 bending cycles or the high-temperature heating test, suggesting its excellent durability. The experimental results indicate that the CPIs studied have potential applications for transparent organic electronic devices.

Improving dimensional stability at high temperature and toughness of polyimide films via adjustable entanglement density

Polyimide (PI) films with ultralow coefficient of thermal expansion (CTE) and high glass transition temperature (Tg) are in great demand for applications as substrates in flexible displays. Furthermore, trade-off between CTE and toughness is highly concerned due to strategies for reducing CTE always result in weakness of toughness. In this work, we developed a facile method to improve dimension stability and toughness of PI containing benzimidazole units via regulating entanglement density based on controlling molecular weight and solid content of precursor polyamic acid (PAA) solution. As a result, the Tg of PI films increased from 394.3 to 441.4 °C and the in-plane CTE (40–350 °C) decreased from 65.7 to 3.9 ppm/K with entanglement density increasing from 253.3 to 2868.6 mol/m3. Moreover, mechanical properties especially toughness of PI films were enhanced significantly (from 7% to 18%) as entanglement density increased. In short, we delineated the effects of entanglement on the properties of PI films and found that the decrease of CTE mainly arises from the increase of entanglement density. Our studies provide new insights into the future design of flexible PI substrates with low CTE.