Ping Lin Kuo

Function and performance of silicone copolymer. Part IV. Curing behavior and characterization of epoxy–siloxane copolymers blended with diglycidyl ether of bisphenol-A

Abstract In this research, a siloxane-type epoxy resin (SG copolymer), which has pendant epoxide rings on the side chain of the polysiloxane polymer backbone, was synthesized by the hydrosilylation reaction of poly(methylhydrosiloxane) with allyl glycidyl ether. The polymer structures were characterized by 1H NMR. The SG resin was then blended with a commercial epoxy resin (diglycidyl ether of bisphenol-A, DGEBA) at various ratios, using dicyandiamide (DICY) as a curing agent. The curing behaviors were studied by DSC. It was found that the initial curing temperature (Ti) and peak curing temperature (Tp) were increased by the addition of SG copolymer to the epoxy resin. Their morphology, mechanical properties and the stability of the cured piece were investigated using SEM, DMA and TGA, respectively. The results show that the addition of SG copolymer increases the mobility of the crosslinked network, and increases the thermal stability.

Poly(ethylene oxide)-co-poly(propylene oxide)-based gel electrolyte with high ionic conductivity and mechanical integrity for lithium-ion batteries

Using gel polymer electrolytes (GPEs) for lithium-ion batteries usually encounters the drawback of poor mechanical integrity of the GPEs. This study demonstrates the outstanding performance of a GPE consisting of a commercial membrane (Celgard) incorporated with a poly(ethylene oxide)-co-poly(propylene oxide) copolymer (P(EO-co-PO)) swelled by a liquid electrolyte (LE) of 1 M LiPF6 in carbonate solvents. The proposed GPE stably holds LE with an amount that is three times that of the Celgard-P(EO-co-PO) composite. This GPE has a higher ionic conductivity (2.8×10(-3) and 5.1×10(-4) S cm(-1) at 30 and -20 °C, respectively) and a wider electrochemical voltage range (5.1 V) than the LE-swelled Celgard because of the strong ion-solvation power of P(EO-co-PO). The active ion-solvation role of P(EO-co-PO) also suppresses the formation of the solid-electrolyte interphase layer. When assembling the GPE in a Li/LiFePO4 battery, the P(EO-co-PO) network hinders anionic transport, producing a high Li+ transference number of 0.5 and decreased the polarization overpotential. The Li/GPE/LiFePO4 battery delivers a discharge capacity of 156-135 mAh g(-1) between 0.1 and 1 C-rates, which is approximately 5% higher than that of the Li/LE/LiFePO4 battery. The IR drop of the Li/GPE/LiFePO4 battery was 44% smaller than that of the Li/LE/LiFePO4. The Li/GPE/LiFePO4 battery is more stable, with only a 1.2% capacity decay for 150 galvanostatic charge-discharge cycles. The advantages of the proposed GPE are its high stability, conductivity, Li+ transference number, and mechanical integrity, which allow for the assembly of GPE-based batteries readily scalable to industrial levels.

Formation of silver nanoparticles under structured amino groups in pseudo-dendritic poly(allylamine) derivatives

The syntheses of silver nanoparticles stabilized by poly(allylamine) (PAA) and by polyethyleneiminated poly(allylamine) (PAA(EI)n (n = 2, 5.8)) are reported. The architectural effects in particle on the nanoparticle size, size distribution, and agglomeration behavior are determined from the UV−vis plasmon absorption band and transmission electron microscopic (TEM) analyses. The data show that PAA(EI)n display better stabilizing effects than PAA to prevent silver particles from agglomeration. Different phenomena of the polymer-protected nanoparticles at various silver ion concentrations are observed and are explained in terms of a mechanism of structure-dependent stabilization.

High performance of transferring lithium ion for polyacrylonitrile- interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte

A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.

Design of poly(acrylonitrile)-based gel electrolytes for high-performance lithium ion batteries.

The use of polyacrylonitrile (PAN) as a host for gel polymer electrolytes (GPEs) commonly produces a strong dipole-dipole interaction with the polymer. This study presents a strategy for the application of PAN in GPEs for the production of high performance lithium ion batteries. The resulting gel electrolyte GPE-AVM comprises a poly(acrylonitrile-co-vinyl acetate) copolymer blending poly(methyl methacrylate) as a host, which is swelled using a liquid electrolyte (LE) of 1 M LiPF6 in carbonate solvent. Vinyl acetate and methacrylate groups segregate the PAN chains in the GPE, which produces high ionic conductivity (3.5 × 10 (-3) S cm(-1) at 30 °C) and a wide electrochemical voltage range (>6.5 V) as well as an excellent Li(+) transference number of 0.6. This study includes GPE-AVM in a full-cell battery comprising a LiFePO4 cathode and graphite anode to promote ion motion, which reduced resistance in the battery by 39% and increased the specific power by 110%, relative to the performance of batteries based on LE. The proposed GPE-based battery has a capacity of 140 mAh g(-1) at a discharge rate of 0.1 C and is able to deliver 67 mAh g(-1) of electricity at 17 C. The proposed GPE-AVM provides a robust interface with the electrodes in full-cell batteries, resulting in 93% capacity retention after 100 charge-discharge cycles at 17 C and 63% retention after 1000 cycles.

Solid polymer electrolytes V: microstructure and ionic conductivity of epoxide-crosslinked polyether networks doped with LiClO4

Abstract A crosslinked polyether network was prepared from poly(ethylene glycol) diglycidyl ether (PEGDE) cured with poly(propylene oxide) polyamine. Significant interactions between ions and polymer host have been observed for the crosslinked polyether network in the presence of LiClO4 by means of FT-IR, DSC, TGA, and 7Li MAS solid-state NMR. Thermal stability and ionic conductivity of these complexes were also investigated by TGA and AC impedance measurements. The results of FT-IR, DSC, TGA and 7Li MAS solid-state NMR measurements indicate the formation of different types of complexes through the interaction of ions with different coordination sites of polymer electrolyte networks. The dependence of ionic conductivity was investigated as a function of temperature, LiClO4 concentration and the molecular weight of polyether curing agents. It is observed that the behavior of ion transport follows the empirical Vogel–Tamman–Fulcher (VTF) type relationship for all the samples, implying the diffusion of charge carrier is assisted by the segmental motions of polymer chains. Moreover, the conductivity is also correlated with the interactions between ions and polymer host, and the maximum ionic conductivity occurs at the LiClO4 concentration of [O]/[Li+]=15.

Synthesis and characterization of amphiphilic graft copolymers based on poly(styrene-co-maleic anhydride) with oligo(oxyethylene) side chains and their GPC behavior

Abstract A series of amphiphilic graft copolymers were synthesized based on poly(styrene-co-maleic anhydride) (SMAs) (backbone copolymers) and methoxypolyethylene glycols (MPEGs) (grafts) in this study. Selection of proper reaction conditions using p-toluenesulfonic acid (PTSA) as catalyst and toluene as solvent in the present research can prevent crosslinking reactions which may occur due to the presence of di-functional polyethylene glycol in the commercial MPEGs. The structures and compositions of the graft copolymers were determined by gel permeation chromatography (GPC) and 1H NMR analysis. It is noteworthy that the GPC behavior of these graft copolymers follows the rule of thumb for GPC, i.e. the higher molecular weight copolymers have lower retention volumes. This is very different from the GPC behavior of similar graft copolymers reported previously in the literature. Also, differential scanning calorimetry (DSC) characterization shows that there are two transition temperatures for some of these amphiphilic copolymers owing to the existence of another aggregation phase of MPEG grafts.

Stabilization of Embedded Pt Nanoparticles in the Novel Nanostructure Carbon Materials

An extremely durable and highly active Pt catalyst has been successfully prepared by embedding Pt(0) nanoparticles inside the pores of the nitrogen-dotted porous carbon layer surrounding carbon nanotubes (Pt@NC-CNT). The Pt@NC-CNT catalyst has a high BET surface area of 271 m(2) g(-1) (62 m(2) g(-1) for Pt/XC-72) and comparably high electrochemically active surface area of 64.3 m(2) g(-1) (68.2 m(2) g(-1) for Pt/XC-72). The prepared Pt nanoparticles are small in size (2.8 ± 1.3 nm) and have a strong interaction of nitrogen to platinum, as evidenced by the binding energy observed at 399.5 eV. The maximum current densities (I(f)) during methanol oxidation observed for Pt@NC-CNT (13.2 mA cm(-1)) is 1.2 times higher than that of Pt/XC-72 (10.8 mA cm(-1)) catalysts. Remarkably, in the long term durability test, the I(f) after 1000 cycles for Pt@NC-CNT decreased to 10.6 mA cm(-1) compared with Pt/XC-72, which decreased to 2.6 mA cm(-2). This means that the Pt@NC-CNT catalyst has a tremendously stable electrocatalytic activity for MOR because of the unique structure of Pt@NC-CNT formed in this novel synthesis technique.

Morphological, thermal and solid-state NMR study on a novel PMMA/crosslinked silicone semi-IPN

Abstract A novel PMMA/silicone semi-IPN, in which linear PMMA and silicone network were the guest and host polymers, respectively, was synthesized in this study. The silicone network formed by the self-condensation reaction among the pendent reactive methoxysilane groups on the polymethylphenylsiloxane (DC3074). Before curing, PMMA and DC3074 were miscible at any blended ratio, but phase separation occurred when the silicone network formed. The morphology of this semi-IPN was investigated by SEM and DSC, an inward-shift Tg for the pure components in the blends and a particular broad Tg were observed in the 50/50 blend. The phase structure for the blends was further investigated by the dynamic relaxation experiments of 13C-CP/MAS NMR spectroscopy. A multi-exponential relaxation rate of T1(H) at 50/50 ratio shows that this semi-IPN is not homogeneous at the interfacial on the length scale of 21xa0nm. The decrease of TCH and the change of T1ρ(H) for this semi-IPN, comparing to the pure materials, imply that intermolecular polarization transfer between PMMA molecules and silicone network is possible.

Benzylamine-assisted noncovalent exfoliation of graphite-protecting Pt nanoparticles applied as catalyst for methanol oxidation.

A novel method has been developed to physically exfoliate graphite and uniformly disperse Pt nanoparticles on graphite nanoplates without damaging the graphene structures. A stable aqueous suspension of graphite nanoplates was achieved by benzylamine-assisted noncovalent fuctionalization to graphite and characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. A uniform dispersion of Pt nanoparticles was then prepared on the graphite nanoplates, where the benzylamine acts as a stabilizer. These Pt loaded graphite nanoplates were then prepared as an electrode, which significantly increased catalytic activity toward the methanol oxidation reaction, resulting in a 60% increment in mass activity compared to that of E-TEK.