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Electrochromic (EC)/electrofluorochromic (EFC) bifunctional materials are receiving great attention because of their promising applications in optoelectronic devices. However, the development of ideal EC/EFC bifunctional materials is still a great challenge because of the poor integration of EC/EFC performances (optical contrast, response speed, and switching stability). Herein, we reported two novel diphenylamine-based mixed valence (MV) polyamides (S-HPA and P-HPA) with spirobifluorene (2,7-positions) and pyrene (1,6-positions) as bridged fluorescence units, respectively, showing impressive cyclability and fluorescence contrast with rapid switching. Through the formation of an effective electronic coupling between the two nitrogen centers using spirobifluorene/pyrene bridges, we demonstrated that different bridges have significant effects on the thermal and electrooptical characteristics of polyamides. In addition to lower fluorescence quantum yield and glass transition temperature, the S-HPA exhibited superior cyclability (contrast change

Laser joining technology with the advantages of high efficiency and good processing flexibility has the good application prospects in the connection of the Carbon Fibre Reinforced Thermoplastics Plastics (CFRTP) and aluminum alloy. Laser joining of CFRTP and 6061 aluminum alloy is investigated with various laser processing parameters. The microstructure characteristics and energy dispersive spectroscopy (EDS) results are analyzed. Besides, the fracture morphologies of the laser connection joints are studied. The results indicate that there is a partial unconnected area between the resin and the 6061 aluminum alloy due to the existence of the air bubbles, while most of the interface area is tightly connected where the mechanical anchoring effect exists.

Spray flash evaporation is a method for the new desalination technology driven by renewable energy. This paper studies the flash evaporation phenomenon of the seawater jet sprayed into a low-pressure chamber. A droplet flash evaporation model has been developed to enable an in-depth understanding of the flash evaporation. This model is capable of predicting the spray flash speed, the evaporated mass rate and the flashing efficiency under different working conditions. Applying this model, the effects of different operating variables on the flash evaporation process are investigated. Results from the developed model reveal a larger Jakob number, Reynolds number and Weber number all lead to the increase of the production rate. The flashing efficiency can attain values larger than 0.9 with the nozzle diameter ranging 5–14 mm when the flash chamber is 150 mm height. The flashing efficiency with nozzle diameter of 5 mm is larger than 0.9 when the flash chamber is 25 mm height. The flow velocity of 10 m/s is recommended for the current case to obtain a large production rate. A flash chamber larger than 500 mm height is needed for complete evaporation considering the presence of dissolved salt in sea water.

To develop colorless and soluble polyimide films, a novel dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And two series of polyimides were prepared via a two-step thermal imidization, PI−(1–4) were obtained from IMDA and four kinds of aromatic diamines while PI−(5–7) from IMDA and three kinds of semiaromatic diamines. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough and colorless films with transparency up to 89% at 450 nm. Especially, polyimides simultaneously containing 1,4:3,6-dianhydrohexitol units in diamine and dianhydride exhibited comparable optical and soluble performance with the alicyclic fluorinated ones. Meanwhile, it was certified that 1,4:3,6-dianhydrohexitol fragment in dianhydride was more determinant in solubility and transmittance of polyimides than that in diamine. An overall investigation of these polyimides on thermal, mechanical, morphological, soluble, optical and dielectric properties was presented, and their structure-property relationships were discussed in detail.

In order to prepare novel polyimides (PI) with high transparency and solubility in common solvents, three diamine monomers containing pyridine or methyl-substituted pyridine and cyclohexane, 1,1′-bis[4-(5-amino-2-pyridinoxy)phenyl]cyclohexane (IIIa), 1,1′-bis[4-(5-amino-3-methyl-2-pyridinoxy)phenyl]cyclohexane (IIIb), and 1,1′-bis[4-(5-amino-2-methyl-6-pyridinoxy)phenyl]cyclohexane (IIIc), were synthesized and characterized. The diamine monomer (IIIa) was subsequently polymerized with 3,3′,4,4′-oxydiphthalic anhydride, 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) to obtain PIs, PI-1 and PI-2. Furthermore, PI-3 (IIIb/6FDA) and PI-4 (IIIc/6FDA) were prepared for structure–property comparison studies. The structures of the resulting PIs were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, and elemental analysis. The physical properties of the PI films were investigated by thermogravimetric analysis, differential scanning calorimetric analysis, dynamic mechanical analysis, and ultraviolet–visible spectroscopy. In general, the PIs showed excellent thermal properties and good mechanical properties. Most had good solubility in polar organic solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, N-methylpyrrolidone (NMP), m-cresol, and even soluble in low boiling solvents such as tetrahydrofuran (THF) and CHCl3. The PI films also exhibited high optical transmittance of 94–97% at 500 nm and cut-off wavelength at 345–359 nm. In summary, the introduction of methyl, cyclohexane, and pyridine groups into the backbone was shown to improve the solubility and transparency of PI films.

Polyimides (PIs) with single phenyl pendant substitution were prepared based on three diamines containing phenyl pendant group, namely, 2,5-bis(4-aminophenoxy) biphenyl, 2-phenyl-4,4′-diaminodiphenyl ether, and 2,5-diaminobiphenyl (p-PDA), with the dianhydride component of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride, respectively. The physical properties of the membranes were examined, including thermal properties, fractional free volume ( FFV), solubility, and morphological structures, and were compared with the analogues without phenyl pendant. Gas transport properties of the membranes were investigated and discussed from the viewpoint of structure–property relationship. For 6FDA-derived PI membranes, gas permeability increased as the degree of PI backbone rigidity leveled up. Gas transport properties were not improved by the incorporation of phenyl pendant group for 6FDA type containing ether linkage and marginally improved as compared between PI (6FDA/p-PDA) and PI (6FDA/p-phenylenediamine (PDA)). To increase the phenyl substitution density of 6FDA/PDA-type backbone, a novel diamine bearing two phenyl pendant groups, that is, 2,6-diphenyl-1,4-diaminobenzene (p, p′-PDA) was synthesized, and PI derived from 6FDA and p, p′-PDA was prepared. The gas permeability coefficients of PI (6FDA/p, p′-PDA) were remarkably larger than those of PI (6FDA/p-PDA) and PI (6FDA/PDA).

A simple strategy is provided to construct novel shape memory polyimides with both physical and chemical crosslinks. The resulting materials exhibited an ultrahigh strain and a multiple shape memory effect without sacrificing the shape fixity and recovery, thereby presenting its potential application in the aerospace industry.

In order to obtain highly optical transparency polyimides, two novel aromatic diamine monomers containing pyridine and kinky structures, 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]diphenylmethane (BAPDBP) and 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]-1-phenylethane (BAPDAP), were designed and synthesized. Polyimides based on BAPDBP, BAPDAP, 2,2-bis[4-(5-amino-2-pyridinoxy)phenyl]propane (BAPDP) with various commercial dianhydrides were prepared for comparison and structure-property relationships study. The structures of the polyimides were characterized by Fourier transform infrared (FT-IR) spectrometer, wide-angle X-ray diffractograms (XRD) and elemental analysis. Film properties including solubility, optical transparency, water uptake, thermal and mechanical properties were also evaluated. The introduction of pyridine and kinky structure into the backbones that polyimides presented good optical properties with 91–97% transparent at 500 nm and a low cut-off wavelength at 353–398 nm. Moreover, phenyl pendant groups of the polyimides showed high glass transition temperatures (T g) in the range of 257–281 °C. These results suggest that the incorporating pyridine, kinky and bulky substituents to polymer backbone can improve the optical transparency effectively without sacrificing the thermal properties.

A series of polyimide (PI) membranes were prepared based on three triphenylamine-based diamines, namely 4,4′-diaminotriphenylamine, 4,4′-diamino-3′′,5′′-dimethyltriphenylamine, and 4,4′-diamino-3′′,5′′-ditrifluoromethyltriphenylamine, via thermal imidization procedure. The PI membranes displayed good thermal properties, with glass transition temperatures of 279–341°C and 5% weight loss temperatures above 515°C under a nitrogen atmosphere. The gas permeation properties of the membranes were investigated and interpreted from the viewpoint of the PI backbone structure. The gas permeation coefficients increased as the substituent pendant groups at the 3′′,5′′ positions of the triphenylamine varied from –H to –CH3 and –CF3, and the permselectivity of gas pairs (including hydrogen/nitrogen (N2), oxygen/N2, carbon dioxide (CO2)/N2, and CO2/methane) decreased in this order. The diffusion coefficients and solubility coefficients were calculated, and the results revealed the variation of the substituted triphenylamine units principally influenced the diffusion coefficients, indicating that the substituted triphenylamine affected the gas transport properties by “diffusivity-controlled” modification.

Two kinds of electrochromic and photoluminescence-active semi-aromatic polyamide and polyimide were prepared via condensation polymerization from a novel diamine, N,N-di-(4-aminophenyl)-2-amino-9,9-diphenylfluorene, with cycloaliphatic dicarboxylic acid and dianhydride, respectively. These polymers showed excellent solubility and increased thermal stability with 10% weight loss in excess of 450 °C in a N2 atmosphere. Due to the stable electrochemistry and improved solid-state fluorescence properties, the polymer films exhibited repeatable and high-contrast electroswitching in both coloration and emission (ΔT% = 80–85%, Ioff/Ion = 152.1–177.9). Especially, the polyamide still showed excellent electroswitching stability even after hundreds of cycles.

To achieve the superheat-resistant polymers for flexible display substrates, two new diamines, namely 6-amine-2-(4-aminobenzene)-1-methyl-benzimidazole (m-MePABZ), 5-amine-2-(4-amino-benzene)-1-methyl-benzimidazole (p-MePABZ) containing N-methyl benzimidazole (BI) were synthesized and a serials of poly(benzimidazole imide) (PBII) films were prepared through thermal imidization. Among them, the flexible polyimide (PI) film derived from m-MePABZ and pyromellitic dianhydride (PMDA) has an ultra-low coefficient of thermal expansion (CTE) down to 2.5 ppm K−1 and an outstanding high glass-transition temperature (Tg) up to 431 °C. Furthermore, the employment of N-methyl overcame an issue of the high H2O-absorption of traditional PBIIs, and the effect of “para-” and “meta-connecting” methyl on molecular packing and properties of these PIs was investigated. These data provided a useful guide to develop high performance PBIIs by incorporating N-methyl.

To investigate the effect of introducing 2,2′-dichloro substituted biphenyl linkage into the polymer backbones on the properties of polyimides (PI), 2,2′-dichloro-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DCBPDA) was polymerized with aromatic diamines, including 2,2′-bis(trifluoromethyl)benzidine (TFMB) in m-cresol to obtain a series of soluble polyimides. For comparison, PI without 2,2′-dichloro substitution was prepared derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The inherent viscosities of the DCBPDA derived polyimides were tested in the range of 0.88–2.14 dL g−1. Thermal analysis revealed DCBPDA type polyimides had coefficients of thermal expansion in the range of 15.1–29.5 ppm.K−1. Their glass transition temperatures were in the range of 355 °C–437 °C, and were higher than the BPDA derived counterpart. Additionally, the employment of DCBPDA resulted in better organo solubility and optical transparency. For example, PI(DCBPDA/TFMB) could be dissolved in acetone and ethyl acetate at room temperature, the film showed a transparent and colorless feature. The results were analyzed from the perspective of structure-property relationship, and may provide helpful knowledge for the topic of polyimide chemistry.