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2016 Volume 34 Issue 12
2016, 34(12): 1411-1422
doi: 10.1007/s10118-016-1850-0
Abstract:
The microlayer or nanolayer coextrusion of hundreds or thousands of alternating low density polyethylene (LDPE)/polystyrene (PS) microlayers or nanolayers were used to study the orientation of LDPE crystals in the confined quasi-two-dimensional or two-dimensional space. The clear and continuous layer structures from microscale to nanoscale can be found in SEM images. The morphology evolution of LDPE crystals in the confined microlayer or nanolayer can be varied from 3D spherulites, 2D spherulites, stacked edge-on lamellar, to single edge-on lamellar. Due to the orientation of the LDPE crystals, the tensile strength of the films increases obviously when the layer thickness reduces to nanoscale. The 2D small angle X-ray scattering (SAXS) patterns can reflect the average degree of orientation of LDPE in the confined layers. The stacking of LDPE lamellae is suppressed in interlamination and oppositely in parallel to the extrusion direction. The specific orientation function f can be calculated from the patterns. The infrared dichroism further confirms the mutation of the orientation of LDPE crystals from microscale to nanoscale in the confined space.
The microlayer or nanolayer coextrusion of hundreds or thousands of alternating low density polyethylene (LDPE)/polystyrene (PS) microlayers or nanolayers were used to study the orientation of LDPE crystals in the confined quasi-two-dimensional or two-dimensional space. The clear and continuous layer structures from microscale to nanoscale can be found in SEM images. The morphology evolution of LDPE crystals in the confined microlayer or nanolayer can be varied from 3D spherulites, 2D spherulites, stacked edge-on lamellar, to single edge-on lamellar. Due to the orientation of the LDPE crystals, the tensile strength of the films increases obviously when the layer thickness reduces to nanoscale. The 2D small angle X-ray scattering (SAXS) patterns can reflect the average degree of orientation of LDPE in the confined layers. The stacking of LDPE lamellae is suppressed in interlamination and oppositely in parallel to the extrusion direction. The specific orientation function f can be calculated from the patterns. The infrared dichroism further confirms the mutation of the orientation of LDPE crystals from microscale to nanoscale in the confined space.
2016, 34(12): 1423-1435
doi: 10.1007/s10118-016-1860-y
Abstract:
Dual-asymmetric poly (vinylidene fluoride) (PVDF) separators have been fabricated by thermally induced phase separation with dimethyl sulfone (DMSO2) and glycerol as mixed diluents. The separators have a porous bulk with large interconnected pores (~1.0 μm) and two surfaces with small pores (~30 nm). This dual-asymmetric porous structure endows the separators with higher electrolyte uptake amount and rapider uptake rate, as well as better electrolyte retention ability than the commercialized Celgard 2400. The separators even maintain their dimensional stability up to 160℃, at which temperature the surface pores close up, leading to a dramatic decrease of air permeability. The electrolyte filled separators also show high ion conductivity (1.72 mS·cm-1) at room temperature. Lithium iron phosphate (LiFePO4)/lithium (Li) cells using these separators display superior discharge capacity and better rate performance as compared with those from the commercialized ones. The results provide new insight into the design and development of separators for high-performance lithium ion batteries with enhanced safety.
Dual-asymmetric poly (vinylidene fluoride) (PVDF) separators have been fabricated by thermally induced phase separation with dimethyl sulfone (DMSO2) and glycerol as mixed diluents. The separators have a porous bulk with large interconnected pores (~1.0 μm) and two surfaces with small pores (~30 nm). This dual-asymmetric porous structure endows the separators with higher electrolyte uptake amount and rapider uptake rate, as well as better electrolyte retention ability than the commercialized Celgard 2400. The separators even maintain their dimensional stability up to 160℃, at which temperature the surface pores close up, leading to a dramatic decrease of air permeability. The electrolyte filled separators also show high ion conductivity (1.72 mS·cm-1) at room temperature. Lithium iron phosphate (LiFePO4)/lithium (Li) cells using these separators display superior discharge capacity and better rate performance as compared with those from the commercialized ones. The results provide new insight into the design and development of separators for high-performance lithium ion batteries with enhanced safety.
2016, 34(12): 1436-1447
doi: 10.1007/s10118-016-1861-x
Abstract:
A series of poly (L-glutamate) s grafted with oligo (ethylene glycol) (OEG) side-chains through the thioether linkages (PALGn-g-EGx, x=2, 3 and 4) were prepared by ring-opening polymerization (ROP) of γ-allyl-L-glutamate N-carboxyanhydride (ALG-NCA) and thiol-ene photoaddition. The chemical structures and physical properties were characterized by 1H-NMR, Fourier transform infrared (FTIR), circular dichroism (CD), etc. The PALGn-g-EGx samples with x=3 and 4 displayed lower critical solution temperature (LCST) in water due to the presence of OEG units. The clouding point (CP) of polypeptides can be finely tuned by changing the side chain structures, molecular weights and sample concentrations. In addition, the thioether linkages in the side chains offer additional redox-responsive properties. The influence of both OEG units and thioether linkages on the LCST behavior was systematically investigated. This work provides an efficient way to prepare multi-stimuli responsive materials with highly tunable properties.
A series of poly (L-glutamate) s grafted with oligo (ethylene glycol) (OEG) side-chains through the thioether linkages (PALGn-g-EGx, x=2, 3 and 4) were prepared by ring-opening polymerization (ROP) of γ-allyl-L-glutamate N-carboxyanhydride (ALG-NCA) and thiol-ene photoaddition. The chemical structures and physical properties were characterized by 1H-NMR, Fourier transform infrared (FTIR), circular dichroism (CD), etc. The PALGn-g-EGx samples with x=3 and 4 displayed lower critical solution temperature (LCST) in water due to the presence of OEG units. The clouding point (CP) of polypeptides can be finely tuned by changing the side chain structures, molecular weights and sample concentrations. In addition, the thioether linkages in the side chains offer additional redox-responsive properties. The influence of both OEG units and thioether linkages on the LCST behavior was systematically investigated. This work provides an efficient way to prepare multi-stimuli responsive materials with highly tunable properties.
2016, 34(12): 1448-1455
doi: 10.1007/s10118-016-1862-9
Abstract:
Polytetrafluoroethylene (PTFE) was irradiated with protons in a ground-based simulation facility to study the effects of proton irradiation on the structural and tribological properties of PTFE. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (ATR-FTIR), while the tribological properties were evaluated by friction and wear tests. It was found that proton irradiation induced the degradation of PTFE molecular chains, resulting in the increase of C concentration and the decrease in F concentration on the sample surfaces, and the surface chemical structure and morphology of the samples changed, which affected the friction coefficient and decreased the wear rate of the specimens as the friction and wear tests revealed.
Polytetrafluoroethylene (PTFE) was irradiated with protons in a ground-based simulation facility to study the effects of proton irradiation on the structural and tribological properties of PTFE. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (ATR-FTIR), while the tribological properties were evaluated by friction and wear tests. It was found that proton irradiation induced the degradation of PTFE molecular chains, resulting in the increase of C concentration and the decrease in F concentration on the sample surfaces, and the surface chemical structure and morphology of the samples changed, which affected the friction coefficient and decreased the wear rate of the specimens as the friction and wear tests revealed.
2016, 34(12): 1456-1468
doi: 10.1007/s10118-016-1863-8
Abstract:
A series of D-π-A type sulfonium salt photoacid generators with different π-conjugated structures, such as triphenyl, phenylstilbene, styryl-biphenyl, and stilbene, were designed to determine the effect of molecular structures on the photochemical and photophysical properties. The mechanisms of photochemical generation of H+ were studied by UV-Vis spectroscopy, theoretical calculations, and fluorescence spectroscopy. It is found that the frontier orbits determine the absorption, the molar extinction coefficients, and the quantum yields of photoacid generation. Triphenyl systems connected with sulfonium are beneficial to increase the quantum yields of acid generation. The photoreactivity of four sulfonium salts was further evaluated through the polymerizations of various epoxide monomers at different irradiation wavelengths (365-425 nm) by using the real-time infrared spectroscopy with light-emitting diodes. The high quantum yields for acid generation (ΦH+=~0.32 to 0.58) and the high molar extinction coefficients (ε=~23500 L·mol-1·cm-1 to 31000 L·mol-1·cm-1) of the sulfonium salts lead to high conversion rates (over 50%-80%). Hence, these photoinitiators exhibit potential for the photocuring applications.
A series of D-π-A type sulfonium salt photoacid generators with different π-conjugated structures, such as triphenyl, phenylstilbene, styryl-biphenyl, and stilbene, were designed to determine the effect of molecular structures on the photochemical and photophysical properties. The mechanisms of photochemical generation of H+ were studied by UV-Vis spectroscopy, theoretical calculations, and fluorescence spectroscopy. It is found that the frontier orbits determine the absorption, the molar extinction coefficients, and the quantum yields of photoacid generation. Triphenyl systems connected with sulfonium are beneficial to increase the quantum yields of acid generation. The photoreactivity of four sulfonium salts was further evaluated through the polymerizations of various epoxide monomers at different irradiation wavelengths (365-425 nm) by using the real-time infrared spectroscopy with light-emitting diodes. The high quantum yields for acid generation (ΦH+=~0.32 to 0.58) and the high molar extinction coefficients (ε=~23500 L·mol-1·cm-1 to 31000 L·mol-1·cm-1) of the sulfonium salts lead to high conversion rates (over 50%-80%). Hence, these photoinitiators exhibit potential for the photocuring applications.
2016, 34(12): 1469-1478
doi: 10.1007/s10118-016-1864-7
Abstract:
A series of polyimide fibers containing phosphorus element derived from (3-aminophenyl) methyl phosphine oxide (DAMPO) diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit (LEO). The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen (AO) exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine (DAMPO) into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.
A series of polyimide fibers containing phosphorus element derived from (3-aminophenyl) methyl phosphine oxide (DAMPO) diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit (LEO). The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen (AO) exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine (DAMPO) into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.
2016, 34(12): 1479-1489
doi: 10.1007/s10118-016-1865-6
Abstract:
High density polyethylene (HDPE) with moderate content of crosslink network (CPE) was successfully prepared through chemical method. Specimens for structural characterization have been molded by conventional injection molding (CIM) and pressure vibration injection molding (PVIM). Influence of crosslink network on hierarchical morphology distribution and mechanical properties was systematically studied. Polarized light microscopy (PLM) revealed that both CIM and PVIM PE samples have a typical "skin-core" structure and the thickness of shear layer of CIM PE and PVIM CPE samples obviously increase. Scanning electron microscopy (SEM) showed that shish-kebab structures are clearly observed in shear layer of CIM CPE sample, indicating that the crosslink network can surely improve the formation of shish-kebab structures. Moreover, we suppose that shish-kebab structures emerged in shear and core layer of PVIM CPE sample. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) confirmed that more orientation and shish-kebab structures form even in core layer of PVIM CPE sample, which demonstrated that the hierarchical morphology was apparently altered by periodical shear and crosslink network. Finally, the mechanical properties revealed that this oriented structure increase the tensile strength from 31 MPa of CIM PE sample to 46 MPa of PVIM CPE sample. However, the tensile behavior tended to change from ductile fracture to brittle fracture.
High density polyethylene (HDPE) with moderate content of crosslink network (CPE) was successfully prepared through chemical method. Specimens for structural characterization have been molded by conventional injection molding (CIM) and pressure vibration injection molding (PVIM). Influence of crosslink network on hierarchical morphology distribution and mechanical properties was systematically studied. Polarized light microscopy (PLM) revealed that both CIM and PVIM PE samples have a typical "skin-core" structure and the thickness of shear layer of CIM PE and PVIM CPE samples obviously increase. Scanning electron microscopy (SEM) showed that shish-kebab structures are clearly observed in shear layer of CIM CPE sample, indicating that the crosslink network can surely improve the formation of shish-kebab structures. Moreover, we suppose that shish-kebab structures emerged in shear and core layer of PVIM CPE sample. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) confirmed that more orientation and shish-kebab structures form even in core layer of PVIM CPE sample, which demonstrated that the hierarchical morphology was apparently altered by periodical shear and crosslink network. Finally, the mechanical properties revealed that this oriented structure increase the tensile strength from 31 MPa of CIM PE sample to 46 MPa of PVIM CPE sample. However, the tensile behavior tended to change from ductile fracture to brittle fracture.
2016, 34(12): 1490-1499
doi: 10.1007/s10118-016-1849-6
Abstract:
An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.
An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.
2016, 34(12): 1500-1509
doi: 10.1007/s10118-016-1867-4
Abstract:
The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline (PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6×10-10 to 2.0×10-5 S·cm-1 in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/PCNTs become stiffer, stronger and tougher as compared to the neat systems.
The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline (PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6×10-10 to 2.0×10-5 S·cm-1 in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/PCNTs become stiffer, stronger and tougher as compared to the neat systems.
2016, 34(12): 1510-1522
doi: 10.1007/s10118-016-1866-5
Abstract:
The multiple endothermic peaks of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (P (HB-co-HV)) in differential scanning calorimetry (DSC) results, as one representative phenomenon of polymer with unique cocrystallization behavior, were generally considered as the results of melting/recrystallization. In this study, wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) experiments were conducted to analyze the phenomena of multiple endothermic peaks in DSC results. The results of these analyses indicated that the multiple endotherms were mainly caused by different lamellae structures. For P (HB-co-HV) with lower HV content, it was comprised of two structures of HV total exclusion and HV partial inclusion in the crystal lamellae. For P (HB-co-HV) with higher HV content, it was also comprised of two structures of HV total inclusion and HV partial inclusion in the crystal lamellae. However, only structure with HV partial inclusion in the crystal lamellae remained existing after first melting peak for all samples.
The multiple endothermic peaks of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (P (HB-co-HV)) in differential scanning calorimetry (DSC) results, as one representative phenomenon of polymer with unique cocrystallization behavior, were generally considered as the results of melting/recrystallization. In this study, wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) experiments were conducted to analyze the phenomena of multiple endothermic peaks in DSC results. The results of these analyses indicated that the multiple endotherms were mainly caused by different lamellae structures. For P (HB-co-HV) with lower HV content, it was comprised of two structures of HV total exclusion and HV partial inclusion in the crystal lamellae. For P (HB-co-HV) with higher HV content, it was also comprised of two structures of HV total inclusion and HV partial inclusion in the crystal lamellae. However, only structure with HV partial inclusion in the crystal lamellae remained existing after first melting peak for all samples.
