Shicheng Zhao

The disordered distribution of ionic groups in sulfonated polyimide (SPI) proton exchange membranes (PEMs) hinders the construction of efficient proton transport pathways and aggravates membrane swelling and methanol crossover, thereby limiting their practical application in direct methanol fuel cells (DMFCs). Herein, a protonated porphyrin-induced ionic aggregation regulation strategy is proposed to regulate ionic aggregation behavior and optimize the ionic microphase-separated morphology, enabling simultaneous enhancement of proton conductivity, dimensional stability, and methanol resistance. A series of SPI PEMs with different porphyrin contents was initially fabricated by incorporating porphyrin branching units into the copolymer backbone. In particular, the SPI-TAPP-2.0 membrane containing 2.0% porphyrin exhibited a high proton conductivity of 156.7 mS cm–1 at 80 °C, while maintaining a low swelling ratio of 42.7%. Consequently, the SPI-TAPP-2.0 membrane achieved a peak power density of 84.3 mW cm–2 and demonstrated long-term durability over 200 h with a low voltage decay rate of 0.85 mV h–1. The characterization results from small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), atomic force microscopy (AFM), and other techniques revealed that the enhanced performance was mainly attributed to the π–π stacking interactions among porphyrin units, which established ionic assembly centers, together with acid–base interactions between pyridinic nitrogen sites and sulfonic acid groups that regulated ionic aggregation and optimized the microphase-separated structure, ultimately constructing appropriately sized, highly interconnected, and selective hydrophilic proton transport networks. This work provides a strategy for optimizing microphase-separated morphology in SPI PEMs toward high-performance DMFC applications.

Conventional hindered amine light stabilizers (HALS) often fail to meet the antiphotoaging requirements for Polyolefin Elastomer (POE) photovoltaic encapsulation films under harsh environmental conditions due to migration and leaching. In this research, a novel reactive hindered amine light stabilizer (rHALS) for in situ grafting during cross-linking of POE photovoltaic encapsulation films was synthesized and its performance in enhancing the photoaging resistance of POE encapsulation films was investigated. First, the successful synthesis of rHALS was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and H Nuclear Magnetic Resonance spectroscopy (1H NMR). Subsequently, rHALS was employed to enhance the photoaging resistance of POE encapsulation films. FTIR analysis after photoaging revealed that rHALS effectively reduced the formation of carbonyl species (with a 42% reduction in carbonyl peak area), indicating significant inhibition of photoaging. Rheological studies further demonstrated that rHALS more effectively mitigated the decline in the storage modulus induced by photoaging compared to conventional HALS with similar structures, indicating enhanced resistance to cross-linked network degradation and thus enhanced antiphotoaging performance. Finally, the mechanism responsible for the enhanced antiphotoaging property of rHALS was investigated. Both FTIR and X-ray photoelectron spectroscopy (XPS) results confirmed that rHALS was grafted onto the POE backbone during cross-linking. This chemical bonding rendered rHALS more resistant to migration and leaching. XPS analysis revealed that after prolonged thermal treatment, the surface nitrogen content (indicative of HALS leaching) increased by 33% in POE films using conventional HALS, whereas those with rHALS showed only a 4% increase. These results demonstrate that rHALS possesses a stronger antiphotoaging performance due to its significantly reduced migration and leaching. This study offers a new technical strategy for designing POE encapsulation films with enhanced antiphotoaging properties, thereby broadening their potential applications under severe service conditions.

The occurrence of shear creep in polyethylene under applied stress results in deformation, which restricts the service life of the final product. However, the factors influencing shear creep and its underlying mechanisms remain unclear. This article investigates the effects of average molecular weight and comonomer on the shear creep behavior and underlying mechanisms of high-density polyethylene (HDPE). The materials chosen were HDPE with weight-average molecular weights (Mw) of 148,100, 191,800, 226,500, 252,700 and 325,100 g/mol, as well as copolymers incorporating propylene or octene as comonomers. The results indicate that creep deformation decreases with increasing Mw, and that polyethylene copolymers incorporating propylene and octene cause increased creep deformation compared to homopolymers. Dynamic mechanical analysis (DMA) and rheological testing were used to investigate the influence of Mw and comonomer on shear creep behavior. The experimental results demonstrate that increasing the weight-average molecular weight enhances molecular chain entanglement, thereby improving creep resistance. The incorporation of comonomers introduces branches into the polyethylene structure, reducing entanglement density and leading to diminished creep resistance. This study provides valuable insights and references for the development of polyethylene materials that resist shear creep.