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1.
The segmental dynamics of functional graphene (fGR)/poly(ether sulfone ether ketone ketone) (PESEKK) nanocomposites were investigated via differential scanning calorimetry and dynamic mechanical analysis (DMA) measurements. First, fGR was prepared using graphene oxide and sodium dodecylbenzene sulfonate. Subsequently, a series of fGR/PESEKK nanocomposites were prepared through solution blend. When the sulfone groups were introduced into the segments of PESEKK polymers, the glass transition temperature (Tg) of PESEKK was higher than that of free sulfone functionalized poly(ether ketone ketone). The fGR/PESEKK nanocomposites displayed a uniform nanostructure because of the strong interfacial interaction between fGR and PESEKK. With the increase in the fGR contents, the Tg values of fGR/PESEKK nanocomposites decreased. Two loss factor peaks were noted in the fGR/PESEKK nanocomposites, which were characterized via DMA. The α′‐relaxation of the nanocomposites at low temperature was assigned to polymer chains close to the polymer/filler interface with mobility higher than that in the bulk unfilled PESEKK (α‐relaxation). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44391.  相似文献   

2.
Effects of in situ synthesized silica and titania nanoparticles, 5 and 20-40 nm in diameter, respectively, on glass transition and segmental dynamics of poly(dimethylsiloxane) networks were studied by employing differential scanning calorimetry, thermally stimulated depolarization currents and broadband dielectric relaxation spectroscopy techniques. Strong interactions between the well dispersed fillers and the polymer suppress crystallinity and affect significantly the evolution of the glass transition in the nanocomposites. Next to the α relaxation associated with the glass transition of the bulk amorphous polymer fraction, two more segmental relaxations were recorded, originating from polymer chains restricted between condensed crystal regions (αc-relaxation) and the semi-bound polymer in an interfacial layer with strongly reduced mobility due to interactions with hydroxyls on the nanoparticle surface (α′ relaxation), respectively. Interactions with the polymer were found to be stronger in the case of titania than silica, leading to an estimated interaction length of around 2 nm for silica and at least double for titania nanocomposites.  相似文献   

3.
The glass‐transition and gas‐transport properties of rubbery polymer nanocomposites based on crosslinked poly(ethylene oxide) and metal oxide nanoparticles were studied. Nanocomposite samples were prepared by the UV photopolymerization of poly(ethylene glycol) diacrylate (n ~ 14) in the presence of magnesium oxide or silica nanoparticles. The thermomechanical properties of the composites were investigated with dynamic mechanical and dielectric spectroscopy methods. The inclusion of nanoparticles in the crosslinked poly(ethylene glycol) diacrylate network led to a systematic increase in rubbery modulus and a modest positive offset (~6°C) in the measured glass‐transition temperature for both systems. Bulk density measurements indicated only minimal void volume fraction in the composites, and CO2 and light gas permeability decreased with particle loading; for example, the CO2 infinite dilution permeability at 35°C decreased from 106 barrer in the unfilled polymer to 55 barrer in a nanocomposite containing 30 wt % magnesium oxide nanoparticles. The inclusion of toluene diluent in the prepolymerization mixtures produced a limited enhancement in sample permeability, but the sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in the crosslinked poly(ethylene glycol) diacrylate composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

4.
The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-Tg relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.  相似文献   

5.
The viscoelasticity of poly(trimethylene terephthalate)/maleinized poly(octene‐ethylene) copolymer/organomontmorillonite (OMMT) nanocomposites were investigated at both liquid and glassy states by using the rotational rheometer and dynamic mechanical analysis, respectively. The viscoelasticity results suggest that OMMT has many important influences on the structure, modulus, toughness, and cold‐crystallization of the nanocomposites. The OMMT has a strip‐like sheet morphology in the polymer matrix and when OMMT content increases to 4 wt%, the physical network‐like structure begins to form in the nanocomposites. The pseudoplasticity of the melts is increased by OMMT. In addition, the complex viscosity, storage modulus, and viscous behavior of the melts are increased with increasing OMMT content. The creep resistance of the nanocomposites is improved by OMMT, and it plays an important role on reinforcing the melts. The stress relaxation of the melts suggests that the nanofillers can not only enhance the interfacial interactions of the nanocomposites but also inhibit the recovery of the polymer chain segments. At glassy state, the nanocomposites' storage modulus increases with increasing OMMT content. As glass transition occurs, the loss factor and loss modulus suggest that OMMT toughens the polymer matrix. At rubber‐elastic state, OMMT depresses the cold‐crystallization of the polymer matrix due to its limitation effect on the motion of molecular chains. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers  相似文献   

6.
Yonghui Li  Jun Li 《Polymer》2011,52(11):2367-6055
Bionanocomposites from biopolymers and inorganic nanoparticles are of great interest for packaging materials due to their enhanced physical, thermal, mechanical, and processing characteristics. In this study, poly(lactic acid) (PLA) nanocomposites with covalent bonding between TiO2 nanowire surface and PLA chains were synthesized through in situ melt polycondensation. Molecular weight, structure, morphology, and thermal properties were characterized. Fourier transform infrared spectroscopy confirmed that PLA chains were covalently grafted onto TiO2 nanowire surface. Transmission electron microscopy images also revealed clearly a third phase presence on the nanowires after the grafting process. Those grafted PLA chains exhibited significantly increased glass transition temperature and thermal stability, compared with pure PLA. The weight-average molecular weight of PLA/2% TiO2 nanowire bulk nanocomposites increased by 66% compared with that of pure PLA. The electron microscopy results showed that strong interfacial interaction and homogeneous distribution were achieved between inorganic nanowires and organic PLA matrix in the bulk nanocomposites. The PLA matrix in bulk nanocomposites exhibited elevated glass transition temperature and decreased crystallization ability as the TiO2 nanowire concentrations were increased from 0 to 2%.  相似文献   

7.
DSC, dielectric relaxation and dynamic mechanical thermal analysis (DMTA) were carried out on two multi‐component poly(ether‐co‐amide) samples having different weight ratios of polyamide prepared by condensation polymerization with 12‐aminododecanoic acid, adipic acid and polyetherdiamine consisting of poly(tetramethylene oxide) and poly(propylene oxide). The melting temperature was lowered by an increase in the weight ratio of the polyamide segment. Three relaxation modes, α′, αs and β, were found from dielectric relaxation measurements in different temperature ranges. The high temperature relaxation mode, α′, has a large dielectric constant, which disappears at the melting temperature of the polyamide crystal in the sample. The relaxation times for the segmental motion, αs, were different for the samples, which is attributed to the difference in the composition of the uncrystallized polyamide segments in the amorphous domain. The glass transition temperature estimated from DMTA is located between those of constituting polymers. On the other hand, the activation energy of β‐mode observed at low temperatures is the same for samples with different polyamide ratios, which is attributed to the local motion of the polyether segments. The uncrystallized polyamide segments are miscible with the polyether segments, which results in a lowering of the glass transition temperature of the amorphous domain and enlarges the temperature range of the rubber state of the copolymer due to the high melting temperature of the polyamide segments. © 2016 Society of Chemical Industry  相似文献   

8.
A poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) (80/20 w/w) polymer blend was studied by mechanical spectroscopy. Two relaxations can be distinguished: in the glassy state, a very large secondary relaxation in the range of 100 K to 325 K which results from the combination of secondary relaxations of PVC and PMMA; and only one main relaxation at 364 K associated to the glass rubber transition. The relaxation spectrum in the range of the β relaxation has been described by a relaxation time distribution function based upon a Gaussian function and a series-parallel model. The α relaxation was studied by means of a theoretical approach for the nonelastic deformation of polymers. We found that the miscibility of this blend appears to be a function of the observation scale: the PVC/PMMA blend is heterogeneous at the scale of molecular movements involved for the β relaxation process but homogeneous at the scale of the chain segments responsible for the α relaxation dynamics. © 1996 John Wiley & Sons, Inc.  相似文献   

9.
The mechanical behaviour of plasticized poly(vinyl chloride) in the glassy state was revisited in order to provide some understanding of the properties observed on the molecular scale. Nine samples were investigated, consisting either of pure poly(vinyl chloride) or of plasticized formulations including different amounts of di‐octyl phthalate or benzyl butyl phthalate in the range 5–20 wt%. Presence of the additives resulted in the depression of the glass transition temperature, Tg, and the main mechanical relaxation temperature, Tα, as determined by differential scanning calorimetry and dynamic mechanical analysis, respectively. These expected results were related to the plasticizing character of the additives on the long‐range cooperative polymer motions. In addition, a marked reduction of the secondary mechanical relaxation β was observed for additive concentrations equal to or larger than 10 wt%. This antiplasticizing effect was interpreted as the hindrance of main‐chain local polymer motions, due to poly(vinyl chloride)–additive interactions. Occurrence of such interactions was confirmed by mid‐ and near‐infrared measurements. The plastic behaviour of the materials in the glassy state was also examined. Particular attention was paid to the strain‐softening amplitude (difference between yield stress and plastic flow stress), to the percentage of non‐elastic deformation and to the mechanical energy to yield. All these quantities are strongly affected by the chain‐mobility characteristics. Copyright © 2003 Society of Chemical Industry  相似文献   

10.
Benjamin D Fitz  Saša Andjeli? 《Polymer》2003,44(10):3031-3036
A novel experimental set up consisting of dielectric spectroscopy and small angle light scattering (or potentially any other optical technique used in combination) is introduced. The sample is enclosed in a Dielectric-Optical-Shear (DOS) cell capable of precisely controlling temperature and thickness. This method allows for simultaneous in situ, real-time monitoring of the changes in the molecular dynamics and corresponding development of supramolecular structure of a given polymer system during various time-sensitive processes. The DOS cell is utilized to investigate relaxation phenomena related to the glass transition, Tg, of poly(l(−)-lactide) during isothermal crystallization under quiescent, partially constrained conditions. A decrease in Tg was observed in situ via a shift in dipolar relaxation to higher frequency (confirmed calorimetrically, ex situ). The shift was most rapid in the spherulitic impingement stage of crystallization, at approximately 30% overall crystallinity.  相似文献   

11.
The influence of nanoconfinement on segmental relaxation behavior of poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile) miscible blend and its nanocomposites with spherical and layered nanoparticles have been investigated. Dynamic mechanical analysis was employed to examine the effect of geometry of nanoparticles on the temperature dependence and relaxation function breadth of segmental dynamics (α-relaxation) in the glass transition region. The maxima of the loss modulus curves were used to fit to the Vogel–Fulcher–Tamman equation to describe the temperature dependence of the characteristic relaxation times. Furthermore, the T g-normalized semi-logarithmic Arrhenius plots (fragility plots) were exploited to indicate the changes in cooperative segmental motions across the glass transition. The master curves for relaxation modulus were also constructed for each sample as a function of time using the time–temperature superposition principle. The investigated nanocomposites showed a narrower segmental dispersion in the glass transition region compared to the neat systems. The relaxation modulus master curves were fitted by the Kohlrausch–Williams–Watts (KWW) function. It was observed that the distribution parameter of segmental relaxation time increased with addition of nanoparticles which was correlated with a decrease in fragility index. In addition, the increase of the KWW distribution parameter (β KWW) for spherical silica nanocomposites was less than that for nanocomposites prepared with layered silicates (organoclay).  相似文献   

12.
Blends of poly(acrylic acid) (PAA) and poly(sodium styrene sulfonate) (PSSNa) were prepared from polymer solutions by solvent evaporation. The observed decrease in PAA-solution pH upon addition of PSSNa suggests an inter-penetration of the two polymer chains, thus the polymer compatibility, in solution. The blend compatibility was studied with the attenuated total reflection-Fourier transform infrared (atr-FTIR) and the differential scanning calorimetry (DSC) techniques. The unique and composition-dependent glass transition temperature indicates that the two polymers are compatible, but the ΔTg broadening suggests a certain degree of nano-heterogeneity. The Tg of pure PSSNa which was non-detectable in DSC, was calculated from the Fox equation. From FTIR data, the polymer compatibility could be attributed to the establishment of hydrogen bonds, and dipole-ion interactions between carboxylic groups, sulfonate groups, and sodium ion on the polymer segments.  相似文献   

13.
Sumod Kalakkunnath 《Polymer》2006,47(20):7085-7094
The dynamic mechanical and dielectric relaxation properties of a commercial poly(trimethylene terephthalate) [PTT] have been investigated for both quenched and isothermally melt-crystallized specimen films. The relaxation characteristics of PTT were consistent with those of other low-crystallinity semiflexible polymers, e.g. PET and PEEK. While the sub-glass relaxation was largely unperturbed by the presence of the crystalline phase, both calorimetric and broadband dielectric measurements across the glass transition indicated the existence of a sizeable rigid amorphous phase (RAP) fraction in melt-crystallized PTT owing to the constraining influence of the crystal surfaces over the crystal-amorphous interphase region. A strong increase in measured dielectric relaxation intensity (Δ?) with temperature above Tg indicated the progressive mobilization of the RAP material, as well as an overall loss of correlation amongst the responding dipoles.  相似文献   

14.
The dynamic behaviour of a set of copolyesters made of 1,4-butanediol, terephthalic acid and 5-tert-butyl isophthalic acid, as well as the two parent homopolymers was studied. Although the insertion of the tert-butyl isophthalate units in the main chain of poly(butylene terephthalate) modified the glass transition, the β relaxation did not change dramatically. By using broadband dielectric spectroscopy we have obtained a detailed picture of the dynamic behaviour of these systems. In all cases, a strong correlation between the α relaxation and the β relaxation above Tg was observed in accordance with recent proposals based on the coupling model.  相似文献   

15.
Mian Wang  Suat Hong Goh 《Carbon》2006,44(4):613-617
We have studied the dynamic mechanical behavior of poly(methyl methacrylate) (PMMA)/acidified multiwalled carbon nanotube (MWNT) composites compatibilized with amine-terminated poly(ethylene oxide) (PEO-NH2). PEO-NH2 is ionically associated with acidified MWNTs via ionic interaction as shown by XPS and FTIR. The miscibility between PEO and PMMA improves the interfacial adhesion between polymer matrix and MWNTs, leading to an increase in the storage modulus values of the composites. The effects of PEO-NH2 on storage modulus and glass transition temperature are discussed.  相似文献   

16.
Various bionanocomposites were prepared by dispersing fumed silica (SiO2) nanoparticles in biocompatible polymers like poly(vinyl pyrrolidone) (PVP), chitosan (Chi), or poly(vinyl alcohol) (PVA). For the bionanocomposites preparation, a solvent evaporation method was followed. SEM micrographs verified fine dispersion of silica nanoparticles in all used polymer matrices of composites with low silica content. Sufficient interactions between the functional groups of the polymers and the surface hydroxyl groups of SiO2 were revealed by FTIR measurements. These interactions favored fine dispersion of silica. Mechanical properties such as tensile strength and Young's modulus substantially increased with increasing the silica content in the bionanocomposites. Thermogravimetric analysis (TGA) showed that the polymer matrices were stabilized against thermal decomposition with the addition of fumed silica due to shielding effect, because for all bionanocomposites the temperature, corresponding to the maximum decomposition rate, progressively shifted to higher values with increasing the silica content. Finally, dynamic thermomechanical analysis (DMA) tests showed that for Chi/SiO2 and PVA/SiO2 nanocomposites the temperature of β‐relaxation observed in tanδ curves, corresponding to the glass transition temperature Tg, shifted to higher values with increasing the SiO2 content. This fact indicates that because of the reported interactions, a nanoparticle/matrix interphase was formed in the surroundings of the filler, where the macromolecules showed limited segmental mobility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

17.
In this study, waterborne graphene oxide/poly(siloxane-urethane)s (GO/SWPUs) nanocomposites were in situ synthesised. Therein, siloxane units facilitated the crosslinking of polyurethanes, and GO imparted the nanocomposites with special functions. With increasing GO content, the average particle size, viscosity, and ionic conductivity of the GO/SWPU dispersion increased, but the absolute value of the zeta potential decreased; this was due to ionic interactions between the COO?NH+(C2H5)3 ions of the SWPU and COO?H+ ions of the GO. The surface roughness of the GO/SWPU film was larger as GO content was higher, which was due to a strong interaction between the GO and SWPU phases. Increasing the GO content improved the thermal resistance, dynamic glass transition temperature, and tensile strength of the GO/SWPU film, but adding more than 0.1 wt% GO yielded unfavourable results. Thus, adding GO improved the thermal and mechanical properties of the GO/SWPU nanocomposites, but this improvement was observed only up to a certain GO concentration, possibly because of the agglutination of GO in SWPU. In addition, the surface and volumetric electrical resistivities of the GO/SWPU nanocomposites decreased when the GO content were increased.  相似文献   

18.
In this article, we report the influence of organic modifier structure (alkyl chain length C8-C20, single vs ditallow) and thereby, the effect of hydrophobicity on the structure, thermal and mechanical properties of poly(methyl methacrylate) (PMMA)-clay hybrids. Melt processed PMMA-clay hybrids were characterized using wide-angle X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The organoclays having an alkyl chain length of more than 12 CH2 groups resulted in the formation of nanocomposites. The glass transition temperature (Tg) of PMMA increased in the presence of clay. The mean-field lattice model was used to predict the free energy for nanocomposite formation, which showed a reasonable match with the experimental results and provided a general guideline for the proper selection of polymer and organoclay (ie, organic modifier) to obtain nanocomposite. Tensile modulus showed maximum improvement of 58% for the nanocomposites compared to 9% improvement for the composites. Tensile modulus increased with increases in the alkyl chain length of the organic modifier and clay loading. The level of improvement for the tensile properties of nanocomposites prepared from primary and secondary ammonium-modified clay is the same as that obtained with the commercial organoclays.  相似文献   

19.
Miscibility studies on blends of polycarbonate (PC) and poly(phenyl methacrylate) (PPMA) were undertaken by means of differential scanning calorimetry (DSC), dynamic mechanical, and dielectric relaxation methods. PC and PPMA were mixed by dissolving in tetrahydrofuran (THE) and subsequently coprecipitated in methanol. DSC studies showed a single glass transition (Tg) that shifts systematically with composition. These Tgs are reproducible in repeated DSC heating cycles, suggesting true miscibility of the pair. The dry PC and PPMA pellets were melt mixed in a Mini-Mixer/Molder. The extrudates were compression molded. These melt-mixed PC/PPMA blends exhibited glass like transparency and also showed a single Tg in the DSC scans. The true miscibility of PC and PPMA was further confirmed by dynamic mechnaical and dielectric relaxation methods. The net birefringence has been reduced substantially because of the opposite sign of the itrinsic birefringence of PC and PPMA molecules. At the 12/88 PC/PPMA, the birefringence remains zero at all draw ratios, indicating the achievement of birefringence free polymer alloys.  相似文献   

20.
We have synthesized a series of block copolymers of poly(2,6-dimethyl-1,4-phenylene oxide) and polystyrene (PPO-b-PS copolymer) by atom transfer radical polymerization. The PS content in these copolymer systems was determined by using infrared spectroscopy, thermal gravimetric analysis, and solution and solid-state NMR spectroscopy; good correlations exist between these characterization methods. DSC analyses indicated that the PPO-b-PS copolymers have higher glass transition temperatures than do their corresponding PPO/PS blends. Our FTIR and solid-state NMR spectroscopic analyses suggest that the PPO-b-PS copolymers possess stronger specific interactions that are responsible for the observed relatively higher values of Tg. We found one single dynamic relaxation from the dynamic mechanical analysis, which implies dynamic homogeneity exists in the PPO-b-PS copolymer; this result is consistent with the one single proton spin-lattice relaxation time observed in the rotating frame [T1ρ(H)] during solid state NMR spectroscopic analysis. In addition, the 2D FTIR spectroscopy reveals evidence for the stronger interactions between segments of PPO and PS through the formation of π-cation complexes.  相似文献   

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