Xianghai Ran

The induction of poly(vinylidene fluoride) electroactive phase by modified anodic aluminum oxide template nanopore surface

The desired electroactive β and γ phases of poly(vinylidene fluoride) (PVDF) nanostructures are rarely obtained through wetting methods using anodic aluminum oxide (AAO) as a template. Further and systematic studies on the corresponding induction mechanism are also lacking. Herein, we designed and fabricated PVDF nanowires using a solution wetting method with pristine and modified AAO templates. The morphology and crystalline structure of the PVDF nanowires were characterized by SEM and micro-FTIR respectively. Then, the induction mechanism was investigated by AFM, FTIR, TGA and contact angle measurements. It is found that the polarity of the solvent and the surface hydroxyl groups on the template nanopores both have an inductive effect on the polar phase. After the oxygen plasma treatment, the proportion of β phase of the PVDF nanowires becomes higher although the total polar phase content remains the same. This is attributed to the high polarity of the nanopore surface and regular arrangement among the hydroxyl groups. The polar phase content of the PVDF nanowires increases from 40% when prepared by the pristine template to 71% when prepared by a 3-aminopropyltrimethoxysilane (APMS) modified template. It can be explained that more interaction points and stronger interactions result in the formation of more of the electroactive phase.

Crystalline phase of inorganic montmorillonite/poly(vinylidene fluoride) nanocomposites: influence of dispersion of nanolayers

Abstract Inorganic montmorillonite (MMT)/poly(vinylidene fluoride) nanocomposites were prepared by two methods: co-precipitation and solution casting. The effect of preparation methods and thermal treatment on crystalline phase was investigated by Fourier transform infrared spectroscopy and differential scanning calorimetry tests. The isothermal crystallization process was observed with polarized optical microscopy. It was found that the solution-casting method was more effective than the co-precipitation method in inducing the polar phase in the melt-isothermal crystallization process. The addition of inorganic MMT by the solution-casting method without further thermal treatment promoted the β-phase crystallization. The inorganic MMT significantly improved the γ phase of the solution-cast samples in the melt-recrystallization process. The degree of dispersion of inorganic MMT influenced the relative content of the polar phase and the crystallinity of the samples in the same crystallization conditions, i.e. the preparation method and the thermal treatment. The effect of dispersion on crystallization kinetics was also studied to verify the enhancement of finely dispersed nanolayer clusters on the γ phase.

Dual-shape memory effect in radiation crosslinked thermoplastic blends: fabrication, optimization and mechanisms

Recently, as an important class of mechanically active smart materials, thermoplastic dual-shape memory polymers (SMPs) have attracted notable attention and can be fabricated in many different manufacturing techniques. Here in this paper, we present experimental results, demonstrating a cost-effective manufacturing technique to enable thermoplastic SMPs with enhanced properties for a wide variety of applications. Thermoplastic SMPs based on low density polyethylene (LDPE) and polypropylene (PP) with various compositions were prepared by melt compounding, followed by a post-processing of e-beam irradiation at 5, 10, 15, 25, 50 and 100 kGy. SEM, DSC, tensile test, rheological properties measurement, sol/gel analysis and shape memory test were performed sequentially to investigate the relationship between the phase morphologies, the content fluctuations, the e-beam irradiation and the shape memory performances. In addition, we also optimized the fabrication process and studied mechanisms of shape memory performances. It was found that the melting point associated to the LDPE soft phase Tm,LDPE is almost independent of the content fluctuations. At the same time the mechanical properties (determined at 25 °C) and rheological properties (measured at 180 °C) can be varied systematically by controlling the structure and radiation dose. More importantly, the results also revealed that (1) irradiated LDPE-rich blends were more suitable and effective than both irradiated PP-rich and non-irradiated blends to be dual-SMPs with advantageous shape memory properties, and (2) increased radiation dose could give rise to enhanced shape recovery capacity without significantly weakening the shape fixity.

Promotion of poly(vinylidene fluoride) on thermal stability and rheological property of ethylene-tetrafluoroethylene copolymer

Abstract In this work, the thermal stability, rheological properties and mechanical properties of ethylene-tetrafluoroethylene copolymer (ETFE)/poly(vinylidene fluoride) (PVDF) blends were investigated by thermogravimetric analysis, rheometer and the tensile test. Thermal results indicated that blends had better thermal oxidation resistance than pure ETFE. Particularly, the initial thermal decomposition temperature (Td0) and the temperature at maximum decomposition rate (Tdmax) of PVDF/ETFE (10/90 wt%) blends were at 374.49°C and 480°C, which were 52.6°C and 34°C higher than pure ETFE. The activation energy of thermal degradation (Ed) of ETFE was 66 kJ/mol, while the PVDF/ETFE (10/90 wt%) blends presented a higher Ed, near 187 kJ/mol. Furthermore, rheological measurements demonstrated that the shear-thinning tendency of blends became stronger with increasing PVDF content. PVDF/ETFE (10/90 wt%) blends had somewhat lower mechanical properties than ETFE, which was still high enough for various applications. Blends with PVDF provided an efficient method to extend the application area of ETFE.