Showing papers in "Journal of Polymer Science Part B in 2007"
TL;DR: In this paper, the mechanical, thermal, and electrical properties of graphite/PMMA compo- sites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphite nanofillers: ''as received graphite'' (ARG), ''expanded graphite,'' (EG) and ''graphite nanoplatelets'' (GNPs).
Abstract: Mechanical, thermal, and electrical properties of graphite/PMMA compo- sites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: ''as received graphite'' (ARG), ''expanded graphite,'' (EG) and ''graphite nanoplatelets'' (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of � 10 nm. Solution-based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical imped- ance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can signifi- cantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. V
256 citations
TL;DR: In this article, the authors investigate how particle shape influences the melt shear viscosity and tensile strength of polymer nanocomposites, which they determine via molecular dynamics simula- tions.
Abstract: Nanoparticles can influence the properties of polymer materials by a variety of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet nanocom- posites in mind, we investigate how particle shape influences the melt shear viscosity ! and the tensile strength " , which we determine via molecular dynamics simula- tions. Our simulations of compact (icosahedral), tube or rod-like, and sheet-like model nanoparticles, all at a volume fraction # ! 0.05, indicate an order of magnitude increase in the viscosity ! relative to the pure melt. This finding evidently can not be explained by continuum hydrodynamics and we provide evidence that the ! increase in our model nanocomposites has its origin in chain bridging between the nanopar- ticles. We find that this increase is the largest for the rod-like nanoparticles and least for the sheet-like nanoparticles. Curiously, the enhancements of ! and " exhibit opposite trends with increasing chain length N and with particle shape anisotropy. Evidently, the concept of bridging chains alone cannot account for the increase in " and we suggest that the deformability or flexibility of the sheet nanoparticles con- tributes to nanocomposite strength and toughness by reducing the relative value of the Poisson ratio of the composite. The molecular dynamics simulations in the present work focus on the reference case where the modification of the melt structure associ- ated with glass-formation and entanglement interactions should not be an issue. Since many applications require good particle dispersion, we also focus on the case where the polymer-particle interactions favor nanoparticle dispersion. Our simulations point to a substantial contribution of nanoparticle shape to both mechanical and processing prop- erties of polymer nanocomposites. © 2007 Wiley Periodicals, Inc." J Polym Sci Part B: Polym
201 citations
TL;DR: In this paper, the nonisothermal cold crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) was studied using differential scanning calorimetry, polarized optical microscope, X-ray diffractometer, dynamic mechanical thermal analysis, and Fourier transform infrared spectrometer.
Abstract: The nonisothermal cold crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) was studied using differential scanning calorimetry, polarized optical microscope, X-ray diffractometer, dynamic mechanical thermal analysis, and Fourier transform infrared spectrometer. The results show that both the cold crystallization temperature (Tcc) and melting point (Tm) of PLA matrix decreases monotonously with increasing of clay loadings, accompanied by the decreasing degree of crystallinity (Xc%) at the low heating rates (≤5 °C/min). However, the Xc% of PLACNs presents a remarkable increase at the high heating rate of 10 °C/min in contrast to that of neat PLA. The crystallization kinetics was then analyzed by the Avrami, Jezioney, Ozawa, Mo, Kissinger and Lauritzen–Hoffman kinetic models. It can be concluded that at the low heating rate, the cold crystallization of both the neat PLA and nanocomposites proceeds by regime III kinetics. The nucleation effect of clay promote the crystallization to some extent, while the impeding effect of clay results in the decrease of crystallization rate with increasing of clay loadings. At the high heating rate of 10 °C/min, crystallization proceeds mainly by regime II kinetics. Thus, the formation of much more incomplete crystals in the PLACNs with high clay loadings due to the dominant multiple nucleations mechanism in regime II, may have primary contribution to the lower crystallization kinetics, also as a result to the higher degree of crystallinity and lower melting point in contrast to that of neat PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1100–1113, 2007
185 citations
TL;DR: In this paper, the authors investigated the nonlinear effect at small strains (Payne effect) in the case of silica-filled styrene-butadiene rubber and found that the increasing amount of covering agents was found to reduce the amplitude of the Payne effect.
Abstract: The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-filled styrene-butadiene rubber. The originality of this study lies in the careful preparation of samples in order to fix all parameters except one, that is, the modification of the silica surface by grafting silane (introduced at different concentrations) via reactive mixing. The organosilane can be either a coupling or a covering surface treatment with an octyl alkyl chain. A careful morphological investigation has been performed prior to mechanical characterization and silica dispersion was found to be the same whatever the type and the amount of silane. The increasing amount of covering agents was found to reduce the amplitude of the Payne effect. A similar decrease is observed for low coupling agent concentration. At higher concentrations, the evolution turns through an increase due to the contribution of the covalent bonds between the matrix and the silica acting as additional crosslinking. The discussion of the initial modulus was done in the frame of both the filler-filler and filler-polymer models. It is unfortunately not possible to distinguish both scenarios, because filler-filler and filler-matrix interactions are modified in the same manner by the grafting covering agent. On the other hand, the reversible decrease of the modulus versus strain (Payne effect) is interpreted in terms of debonding of the polymeric chains from the filler surface.
179 citations
166 citations
TL;DR: In this article, the percolation threshold of poly(e-caprolactone) composites was investigated by using the parallel-plate rheometer, differential scanning calorimeter, and TGA.
Abstract: Multi-walled carbon nanotube/poly(e-caprolactone) composites (PCLCNs) were prepared by melt compounding. The rheology, nonisothermal crystallization behavior, and thermal stability of PCLCNs were, respectively, investigated by the parallel-plate rheometer, differential scanning calorimeter, and TGA. Cole–Cole plots were employed successfully to detect the rheological percolation of PCLCNs under small amplitude oscillatory shear. PCLCNs present a low percolation threshold of about 2–3 wt % in contrast to that of clay-based nanocomposites. The percolated nanotube network is very sensitive to the steady shear deformation, and is also to the temperature, which makes the principle of time-temperature superposition be invalid on those percolated PCLCNs. Small addition of nanotube cannot improve the thermal stability of PCL but can increase crystallization temperature remarkably due to the nucleating effect. As the nanotube is much enough to be percolated, however, the impeding effect becomes the dominant role on the crystallization, and the thermal stability increases to some extent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3137–3147, 2007
155 citations
TL;DR: In this paper, three polystyrene (PS)/clay hybrid systems have been prepared via in situ polymerization of styrene in the presence of unmodified sodium montmorillonite (Na-MMT) clay, MMT modified with zwitterionic cationic surfactant octadecyldimethyl betaine (C18DMB) and MMT with polymerizable cationi-clay modified with vinylbenzyldime-thyldodecylammonium chloride (VDAC).
Abstract: Three polystyrene (PS)/clay hybrid systems have been prepared via in situ polymerization of styrene in the presence of unmodified sodium montmorillonite (Na-MMT) clay, MMT modified with zwitterionic cationic surfactant octadecyldimethyl betaine (C18DMB) and MMT modified with polymerizable cationic surfactant vinylbenzyldime-thyldodecylammonium chloride (VDAC). X-ray diffraction and TEM were used to probe mineral layer organization and to expose the morphology of these systems. The PS/Na-MMT composite was found to exhibit a conventional composite structure consisting of unintercalated micro and nanoclay particles homogeneously dispersed in the PS matrix. The PS/C18DMB-MMT system exhibited an intercalated layered silicate nanocomposite structure consisting of intercalated tactoids dispersed in the PS matrix. Finally, the PS/ VDAC-MMT system exhibited features of both intercalated and exfoliated nanocomposites. Systematic statistical analysis of aggregate orientation, characteristic width, length, aspect ratio, and number of layers using multiple TEM micrographs enabled the development of representative morphological models for each of the nanocomposite structures. Oxygen barrier properties of all three PS/clay hybrid systems were measured as a function of mineral composition and analyzed in terms of traditional Nielsen and Cussler approaches. A modification of the Nielsen model has been proposed, which considers the effect of layer aggregation (layer stacking) on gas barrier.
144 citations
TL;DR: In this article, high energy ball milling (HEBM) was used to incorporate carbon nanotubes (CNTs) into a polyethylene (PE) matrix avoiding: high temperatures, solvents, ultrasonication, chemical modification of carbon Nanotubes.
Abstract: High energy ball milling (HEBM) was utilized, as an innovative process, to incorporate carbon nanotubes (CNTs) into a polyethylene (PE) matrix avoiding: high temperatures, solvents, ultrasonication, chemical modification of carbon nanotubes. Composites with 1, 2, 3, 5, and 10 wt % of carbon nanotubes were prepared. Films were obtained melting the powders in a hot press. Morphology and physical properties (thermal, mechanical, electrical properties) were evaluated. The used processing conditions allowed to obtain a satisfactory level of dispersion of CNTs into the PE matrix with a consequent improvement of the physical properties of the samples. The thermal degradation was significantly delayed already with 1–2% wt of CNTs. The mechanical properties resulted greatly improved for low filler content (up to 3% wt). The electrical measurements showed a percolation threshold in the range 1–3 wt % of CNTs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 597–606, 2007
137 citations
TL;DR: Buffa, Fabian Alejandro, et al. as mentioned in this paper presented a paper on the work of Buffa and Alejandro at the Centro Cientifico Tecnologico Conicet -Mar del Plata.
Abstract: Fil: Buffa, Fabian Alejandro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina
125 citations
TL;DR: In this paper, a magnetic suspension balance was employed in experiments to measure gas solubility in the polymer melts, and the effects of the branched structure on the swollen volume of polypropylene (PP) were discussed.
Abstract: A magnetic suspension balance was employed in experiments to measure gas solubility in the polymer melts. The gas solubilities of CO2 and N2 in both linear and branched Polypropylene (PP) were investigated. The swollen volumes predicted by the Sanchez–Lacombe equation of state (EOS) and Simha–Somcynsky EOS were applied to incorporate the buoyancy effect, which is essential for the accurate measurement of solubility data. The effects of the branched structure on the swollen volume and gas solubility were discussed. It was observed that the long chain branched PP exhibited less expandability than the linear PP, due to the entangled molecular chain structure. Therefore, the total amount of gas that was able to dissolve into the long chain branched PP turned out to be less. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2497–2508, 2007
111 citations
TL;DR: In this article, the interplay of POSS molecular geometry, composition, and concentration in relation to the tribological, nanomechanical, surface energy, and bulk properties of the nanocomposites were investigated.
Abstract: Hybrid organic–inorganic polymer nanocomposites incorporating polyhedral oligomeric silsesquioxane (POSS) nanoparticles are of increasing interest for high performance materials applications. Octaisobutyl POSS/polypropylene nanocomposites were prepared at varying POSS concentrations via melt blending. The interplay of POSS molecular geometry, composition, and concentration in relation to the tribological, nanomechanical, surface energy, and bulk properties of the nanocomposites were investigated. Ultra-low friction and enhanced hardness, modulus, and hydrophobicity were observed for the nanocomposite surfaces, with minimal changes in the bulk thermomechanical properties. Parallel AFM, SEM, TEM, and spectroscopic analyses demonstrated significant differences in POSS distribution and aggregation in the surface and the bulk, with preferential segregation of POSS to the surface. Additionally, contact angle studies reveal significant reduction in surface energy and increase in hysteresis with incorporation of POSS nanoparticles. The differences in bulk and surface properties are largely explained by the gradient concentration of POSS in the polymer matrix, driven by POSS/POSS and POSS/polymer interactions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2441–2455, 2007
TL;DR: In this article, the effects of polymer molecular weight and temperature on the physical aging of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is examined Gas permeability and refractive index were monitored during the aging process for PPO film samples at three aging temperatures below the glass transition temperature.
Abstract: The effects of polymer molecular weight and temperature on the physical aging of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is examined Gas permeability and refractive index were monitored during the aging process for PPO film samples at three aging temperatures below the glass transition temperature Comparisons between the two samples of PPO that differ widely in molecular weight reveal an insignificant difference, which support the notion that above a critical molecular weight range there is little influence on aging rate Increased temperature, over the limited range of 35–55 °C, results in higher aging rates for films made from both PPO materials The rate of aging decreases strongly with increasing film thickness over the range examined, ∼04–25 μm © 2007 Wiley Periodicals, Inc J Polym Sci Part B: Polym Phys 45: 1390–1398, 2007
TL;DR: In this article, three levels of exfoliation of synthetic α-zirconium phosphate (α-ZrP) nanoplatelets in epoxy matrices have been achieved.
Abstract: By manipulating processing conditions, three levels of exfoliation of synthetic α-zirconium phosphate (α-ZrP) nanoplatelets in epoxy matrices have been achieved. Transmission electron microscopy and wide angle X-ray diffraction were utilized to confirm the three different levels of exfoliation of nanoplatelets in epoxy/α-ZrP nanocomposites. As expected, it was found that modulus and strength of the nanocomposite are affected by how well the nanoplatelets disperse. It was also found that the operative fracture mechanisms depend strongly on the state of the nanoplatelets dispersion. The crack deflection mechanism, which leads to a tortuous path crack growth, was only observed for poorly dispersed nanocomposites. Delamination of intercalated nanoplatelets and crack deflection were observed in a moderately dispersed system. In the case of fully exfoliated system, the crack only propagated in a straight fashion, which indicates that the fully exfoliated individual nanoplatelet can not affect the propagation of crack at all. The implication of the present findings for structural applications of polymer nanocomposites is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1459–1469, 2007
TL;DR: In this article, a multilwalled carbon nanotube/poly(butylene terephthalate) nanocomposites (PCTs) were investigated using transmission electron micrographs and Fourier transform infra red spectrometer.
Abstract: Multi-walled carbon nanotube/Poly(butylene terephthalate) nanocomposites (PCTs) were prepared by melt compounding. The microstructure of PCTs was investigated using transmission electron micrographs and Fourier transform infra-red spectrometer. The linear and nonlinear as well as transient rheological properties of PCTs were characterized by the parallel plate rheometer. The results reveal that the surface modification can improve the dispersion state of nanotube in matrix. PCTs present a low percolation threshold of about 1–2 wt % in contrast to that of Poly-(butylene terephthalate)/clay nanocomposites. The network structure is very sensitive to both the quiescent and large amplitude oscillatory shear deformation, and is also to the temperature, which makes the principle of time-temperature superposition (TTS) be valid on PCTs only in a very restricted temperature range. The stress overshoots to the reverse flow are strongly dependent on both the rest time and shear rate but show a strain-scaling response to the startup of steady shear, indicating that the broken network can reorganize even under quiescent condition. The nanotube may experience the long-range, more or less order during annealing process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2239–2251, 2007
TL;DR: Amorphous polymers exhibit a primary (glass, or α-) relaxation process and a low-temperature relaxation process associated with polymer backbone motion usually referred to as the β-relaxation process as mentioned in this paper.
Abstract: Amorphous polymers exhibit a primary (glass, or α-) relaxation process and a low-temperature relaxation process associated with polymer backbone motion usually referred to as the β-relaxation process. The latter process can be observed below the glass transition temperature of the polymer and usually merges with the α-relaxation process at temperatures somewhat above the glass transition temperature. While it is widely held that both the α-relaxation and β-relaxation processes are engendered by localized (segmental) motions of the polymer backbone, and that there is a strong mechanistic connection between them, the molecular mechanisms of the α-relaxation and β-relaxation processes in amorphous polymers are not well understood. Recently, atomistic molecular dynamics simulations of melts and blends of 1,4-polybutadiene have provided insight into the relationship between the α- and β-relaxation processes in glass-forming polymers and an improved understanding of their molecular origins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 627–643, 2007
TL;DR: In this article, the authors re-examined the crystal density and determined the heat of fusion for the stereo-complex (sc) crystals of poly(l-lactic acid) (PLLA) and poly(d-Lactic acid), and the results were significantly higher than those previously reported (1.21-1.27 g/cm3).
Abstract: Measured densities of films, consisting of only stereo-complex (sc) crystals of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA), are sometimes significantly higher than the density of the sc-crystal calculated on the basis of the previously proposed triclinic and trigonal unit cells. In this work, we reexamined the crystal density and determined the heat of fusion for the sc-crystal. Twenty wide-angle X-ray reflections from a highly oriented sc-film could be well indexed on the basis of a trigonal unit cell previously proposed by Cartier et al. The refined parameters of the trigonal cell are a = b = 1.50 nm, c = 0.823 nm, α = β = 90°, and γ = 120°. The c-axis determined from the WAXD fiber pattern was significantly shorter than those (0.87–0.93 nm) previously reported. The crystal density of the modified cell was 1.342 ± 0.002 g/cm3, which was significantly higher than those previously reported (1.21–1.27 g/cm3). The heat of fusion for the sc-crystal, extrapolated from the linear increase in the observed heat of fusion with decreasing the specific volume for the samples consisting of only sc-crystals, was 155 ± 5 J/g. This value was significantly higher than those of α-form and β-form homo-crystals of PLLA suggesting stronger interactions between the 32 helices of PLLA and 31 helices of PDLA in the sc-crystal. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2632–2639, 2007
TL;DR: In this article, multwalled carbon nanotubes (MWNTs) were surface modified and grafted with poly(L-lactide) to obtain poly-L-latide-grafted MWNTs (i.e., MWNT-g-PLLA).
Abstract: In this work, multiwalled carbon nanotubes (MWNTs) were surface-modified and grafted with poly(L-lactide) to obtain poly(L-lactide)-grafted MWNTs (i.e. MWNTs-g-PLLA). Films of the PLLA/MWNTs-g-PLLA nanocomposites were then prepared by a solution casting method to investigate the effects of the MWNTs-g-PLLA on nonisothermal and isothermal melt-crystallizations of the PLLA matrix using DSC and TMDSC. DSC data found that MWNTs significantly enhanced the nonisothermal melt-crystallization from the melt and the cold-crystallization rates of PLLA on the subsequent heating. Temperature-modulated differential scanning calorimetry (TMDSC) analysis on the quenched PLLA nanocomposites found that, in addition to an exothermic cold-crystallization peak in the range of 80–120 °C, an exothermic peak in the range of 150–165 °C, attributed to recrystallization, appeared before the main melting peak in the total and nonreversing heat flow curves. The presence of the recrystallization peak signified the ongoing process of crystal perfection and, if any, the formation of secondary crystals during the heating scan. Double melting endotherms appeared for the isothermally melt-crystallized PLLA samples at 110 °C. TMDSC analysis found that the double lamellar thickness model, other than the melting-recrystallization model, was responsible for the double melting peaks in PLLA nanocomposites. Polarized optical microscopy images found that the nucleation rate of PLLA was enhanced by MWNTs. TMDSC analysis found that the incorporation of MWNTs caused PLLA to decrease the heat-capacity increase (namely, ΔCp) and the Cp at glass transition temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1870–1881, 2007
TL;DR: In this paper, a drawing at 80 °C of α-phase films was shown to contain about 20% of phase α, a crystallinity degree of 40% and a β-phase crystallographic c-axis orientation factor of 0655.
Abstract: Oriented β-phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 °C of predominantly α-phase films, and by drawing almost exclusively β-phase films obtained by crystallization at 60 °C from dimethylformamide (DMF) solution with subsequent pressing Wide angle X-ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase α, a crystallinity degree of 40% and β-phase crystallographic c-axis orientation factor of 0655 Drawing at 90 °C and with R = 4 of originally β-phase films results in exclusively β-phase films with crystallinity degree of 45% and orientation factor of 0885 Crystalline phase, crystallinity degree, and crystallographic c-axis orientation factor of both phases were also determined for α-phase oriented films obtained by drawing α-phase films at 140 °C For films drawn at 140 °C the α to β phase transition drops to about 22% Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 °C compared with 80 °C Moreover, for both phases the c-axis orientation parallel to the draw direction is higher at draw temperature of 140 °C than at 80 °C © 2007 Wiley Periodicals, Inc J Polym Sci Part B: Polym Phys 45: 2793–2801, 2007
TL;DR: In this article, the authors studied the changes in the electrical resistance of carbon black filled silicone rubber composite, which is the sensitive element of the flexible force sensor, as a function of time during compression.
Abstract: We studied the changes in the electrical resistance of carbon black filled silicone rubber composite, which is the sensitive element of the flexible force sensor, as a function of time during compression. The experimental results show that there is a sudden increase of the electrical resistance along with the sudden increase of the stress immediately after the compression. When the sample strain is kept constant, the electrical resistance and the stress both decay with time. The data of the stress relaxation and the resistance relaxation both can be fitted by the linear combination of two exponential functions. Based on the shell structure theory, the experimental phenomena are explained from the view that the uniaxial pressure induces the changes in the effective conductive paths. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2700–2706, 2007
TL;DR: In this article, the two-phase structures of poly(epsilon-caprolactone)-based segmented polyurethanes (PCLUs) were analyzed using differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis.
Abstract: Poly(epsilon-caprolactone)-based segmented polyurethanes (PCLUs) were prepared from poly(epsilon-caprolactone) diol, diisocyanates (DI), and 1,4-butanediol. The DIs used were 4,4'-diphenylmethane diisocyanate (MDI), 2,4-toluenediisocyanate (TDI), iso-phorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis were employed to characterize the two-phase structures of all PCLUs. It was found that HDI- and MDI-based PCLUs had higher degree of microphase separation than did IPDI- and TDI-based PCLUs, which was primarily due to the crystallization of HDI- and MDI-based hard-segments. As a result, the HDI-based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard-segment domains during the sample deformation was responsible for the incomplete shape-recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation.
TL;DR: In this article, the authors used atom transfer radical polymerization (ATRP) to graft polystyrene chains to the surfaces using silica nanoparticles, which ranged from 8 to 48 kDa.
Abstract: Silica nanoparticles (17 ± 4 nm in diameter) were modified by grafting polystyrene chains to the surfaces using atom transfer radical polymerization (ATRP). The molecular weight of the grafted chains ranged from 8 to 48 kDa. These modified nanoparticles were mixed in solution with poly(styrene) homopolymer (18–120 kDa) and symmetric poly(styrene-b-butadiene) (PS-PB) diblock copolymer (34–465 kDa) and the states of dispersion in the dried composites were characterized by transmission electron microscopy (TEM). In the so-called wet brush limit, when the graft molecular weight equals or exceeds the matrix value, the silica particles form a uniform random dispersion in poly(styrene). Increasing the homopolymer matrix, molecular weight above the graft value results in particle clustering and macroscopic-phase separation. Mixtures of the lamellar forming block copolymer and nanoparticles exhibit a very different trend, with particle clustering at the lower PS-PB molecular weights and dispersion at the highest value. This latter finding is rationalized on the basis of packing constraints associated with lamellar order and the effective particle dimensions, and the degree of solvation at ordering, both of which favor higher molecular weight block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2284–2299, 2007
TL;DR: In this article, three commercial triblock copolymers from Arkema were evaluated as potential toughening agents for two different lightly crosslinked epoxies, and the results showed that the plane strain fracture toughness was on the order of 3.0 MPa√m for 10 parts per hundred resin (phr) of NanoStrength™ E20 resin.
Abstract: Three different commercial triblock copolymers from Arkema were evaluated as potential toughening agents for two different lightly crosslinked epoxies. It was found that the plane strain fracture toughness, K IC , was on the order of 3.0 MPa√m for 10 parts per hundred resin (phr) of NanoStrength™ E20 resin (a styrene-butadiene-methylacrylate, SBM, type triblock copolymer) in epoxies cured with either aminoethylpiperazine or piperidine. In contrast, 10 phr NanoStrength E40 resin (also an SBM type triblock copolymer) was ineffective in toughening such epoxies. The difference in toughening effectiveness was attributed to the smaller amount of polybutadiene present in the E40 resin. The third toughening agent from Arkema was NanoStrength M22 resin, which is a symmetric triblock copolymer consisting of side blocks of PMMA surrounding a center block of poly(butyl acrylate) and is designated as MAM. At 10 phr MAM both lightly crosslinked epoxies exhibited improvements in toughness. Morphologies were characterized using TEM and toughening mechanisms revealed using SEM and TOM.
TL;DR: In this paper, a parametric study of scratch performance on polypropylene (PP) substrate with a spherical-tipped indenter was performed using finite element analysis (FEA) to learn how material and surface properties of PP affect scratch behavior.
Abstract: Parametric studies were performed using finite element analysis (FEA) to learn how material and surface properties of polypropylene (PP) affect scratch behavior. Three-dimensional FEA modeling of scratching on a PP substrate with a spherical-tipped indenter is presented. Three different loading conditions, that is constant scratch depth, constant normal load, and linearly increasing normal load, are adopted for this parametric study. From the FEA findings, it is learned that Poisson's ratio has a negligible effect on scratch performance, whereas raising the coefficient of adhesive friction induces a significantly larger residual scratch depth and tangential force on the scratch tip. Increasing the Young's modulus of a material does not necessarily improve its overall scratch performance. On the other hand, modifying the yield stress of a material has a major impact on scratch resistance as a higher yield stress reduces the residual scratch depth. From this numerical effort, it is concluded that the yield stress and coefficient of adhesive friction are the most critical parameters to influence the scratch performance of a material. Analyses also suggest that the general trend in the parametric effect of the above four parameters on scratch behavior is independent of the applied normal load level.
TL;DR: In this article, a constitutive phenomenological model completing the Gent-Thomas concept is carried out to formulate laws governing the hyperelastic behavior of incompressible rubber materials, and comparisons of the outcome of the proposed model with that of the molecular model from the combined concepts of Flory-Erman and Boyce-Arruda (2000), and with those of the phenomenological models of Ogden (1982), Yeoh-Fleming (1997), Pucci-Saccomandi (2002) and Beda (2005) are made.
Abstract: A constitutive phenomenological model completing the Gent-Thomas concept is carried out to formulate laws governing the hyperelastic behavior of incompressible rubber materials. It is shown that the phenomenological Gent-Thomas model (1958) and the constrained chain model (1992) give similar precise results at small to moderate deformation. On the other hand, comparisons of the outcome of the proposed model with that of the molecular model from the combined concepts of Flory-Erman and Boyce-Arruda (2000), and with those of the phenomenological models of Ogden (1982), Yeoh-Fleming (1997), Pucci-Saccomandi (2002) and Beda (2005) are made. Residual inconveniences raised by attractive continuum models in rubber elasticity literature have been successfully overcome. Results from both the statistical and phenomenological mechanics concepts are compared with the data of some useful classical materials (rubbers of Treloar, Rivlin-Saunders, Pak-Flory and Yeoh-Fleming). The results permit one to see salient equivalence of the two theories for a more reliable prediction of stress-stretch response for all states of any mode of deformation. A complete and exhaustive analysis of the Mooney plot that combines small and very large extension-compression has been quite essential in assessing the validity of models. A method of identification of material parameters is presented and data of the simple tension suffice for the determination of the parameter values. It is shown that the ordinary identification procedures, such as the usual least squares, a very much used numerical method in materials investigation, can be unsuitable in some cases of hyperelastic modeling. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1713–1732, 2007
TL;DR: In this paper, a new family of thermoplastic nanocomposites based on isotactic polypropylene (iPP) and inorganic fullerene-like tungsten disulfide (IF-WS2) has been successfully prepared.
Abstract: A new family of thermoplastic nanocomposites based on isotactic polypropylene (iPP) and inorganic fullerene-like tungsten disulfide (IF-WS2) has been successfully prepared. A very efficient dispersion of IF-WS2 material was obtained by mixing in the melted polymer without using modifiers or surfactants. The addition of IF-WS2 nanoparticles induces a remarkable enhancement of the thermal stability of iPP, as well as an increase in the crystallization rate of the matrix when compared with pure iPP. The nucleating efficiency of IF-WS2 solid lubricant nanoparticles on the α-phase of iPP reaches very high values (60–70%), the highest values observed hitherto for polypropylene nanocomposites. The incorporation of IF-WS2 has also been observed to increase the size and stability of the crystals formed. The melting behavior of the nanocomposites indicates the formation of more perfect crystals as determined by differential scanning calorimetry and time-resolved synchrotron X-ray scattering experiments. The new nanocomposites show an increase in the storage modulus with respect to pure iPP measured by dynamic mechanical analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2309–2321, 2007
TL;DR: In this paper, a polyaniline (PAni) is prepared electrochemically from an aqueous solution of aniline and HCl in a single compartment electrochemical cell and different PAni samples obtained by varying monomer concentration, acid concentration, applied potential, reaction time and reaction temperature are subjected to conductivity and dielectric tests.
Abstract: The polyaniline (PAni) is prepared electrochemically from an aqueous solution of aniline and HCl in a single compartment electrochemical cell. Different PAni samples obtained by varying monomer concentration, acid concentration, applied potential, reaction time, and reaction temperature are subjected to conductivity and dielectric tests. The degree of crystallinity, d-spacing, interchain separation, and crystallite size are determined form X-ray analysis, the oxidation state is determined from infrared spectroscopy (FTIR) analysis, and the doping level is estimated from TGA analysis for all the PAni samples synthesized under different conditions. All these structural properties are correlated with electrical properties. The whole result reveals that all the aforementioned reaction parameters affect the structural properties, which in turn affect the electrical properties of PAni. The mathematical model correlations between conductivity and reaction parameters are established from the regression analysis for individual variables as well as for all the variables together. These relationships give the conductivity as an output when we input the value of reaction variables. The output obtained from the model relations found in well agreement with the experimental results under identical conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2046–2059, 2007
TL;DR: In this paper, a combination of the UPE and EMS resulted in an excellent combination for a new biobased thermoset material with a relatively high elastic modulus and a constant glass transition temperature with up to 25% replacement with EMS.
Abstract: Biobased unsaturated polyester (UPE) materials containing epoxidized methyl soyate (EMS) were processed with cobalt naphthenate as a promoter and 2-butanone peroxide as an initiator. A certain amount of the UPE resin was replaced by EMS. The combination of the UPE and EMS resulted in an excellent combination for a new biobased thermoset material with a relatively high elastic modulus and a constant glass transition temperature with up to 25 wt % replacement with EMS. The Izod impact strength was almost constant while the amount of EMS was changed.
TL;DR: In this article, the effects of solution processing and thermal annealing on thin film morphology and crystalline structures of regioregular poly(3-hexyl thiophene) (RR P3HT) are studied in terms of molecular weight (M{sub w}).
Abstract: The effects of solution processing and thermal annealing on thin film morphology and crystalline structures of regioregular poly(3-hexyl thiophene) (RR P3HT) are studied in terms of molecular weight (M{sub w}). Using grazing-incidence X-ray diffraction, {pi}-conjugated planes in drop-cast films from chloroform solutions are found to be preferentially oriented parallel to the substrates regardless of M{sub w}. However, the mesoscale nanocrystalline morphology of the drop-cast films is significantly affected by M{sub w}, exhibiting a distinctive morphological transition from short nanorods to long nanofibrils above a critical number-averaged M{sub w} ({approx} 3.6 kDa). This is probably due to the change in a conformation change from an extended-chain to a folded-chain, as M{sub w} of RR P3HT increases. In contrast, spin-casting of high M{sub w} RR P3HT produces less ordered films with a lower crystallinity and mixed parallel/perpendicular orientations of {pi}-conjugated planes. The crystallinity and parallel -conjugated orientation of RR P3HT in spin-cast films could be improved by thermal treatments at high-temperatures either (1) above the glass transition temperature or (2) above the melting temperature of RR 3PHT followed by recrystallization upon cooling under vacuum. However, the charge mobility of the spin-cast films for a field-effect transistor application is still lower than thatmore » of the drop-cast films. This would be attributed to the chain oxidation and the development of distinct grain boundaries between RR P3HT nanofibrils during the thermal treatments.« less
TL;DR: The relationship between the contact angles, surface tension, and surface roughness is reviewed in this article, where the Wenzel and Cassie-Baxter models are used as a guide to predict the superhydrophobic roughness of polymers.
Abstract: The relationship between the contact angles, surface tension, and surface roughness is reviewed. Numerical formulas related to the superhydrophobic rough surfaces of polymers are predicted with two approaches, the Wenzel and Cassie–Baxter models. With these models as a guide, an artificial superhydrophobic surface is created. Rough nylon surfaces mimicking the lotus leaf are created by the coating of a polyester surface with nylon-6,6 short fibers via the flocking process. Poly(acrylic acid) chains aregrafted onto nylon-6,6 surfaces, and this is followed by the grafting of 1H,1H-perfluorooctylamine onto the poly(acrylic acid) chains. Water contact angles as high as 178° are achieved. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 253–261, 2007.
TL;DR: In this article, the effect of 3-methacryloxypropyltrimethoxysilane (3-MPTS) functionalization on poly(propylene) composites was investigated by means of polarized optical microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction.
Abstract: Multi-walled carbon nanotubes (MWNTs) were functionalized with a silane coupling agent. The MWNTs were first coated with inorganic silica by a sol-gel process and then grafted with 3-methacryloxypropyltrimethoxysilane (3-MPTS). The effect of raw MWNTs and silane-functionalized MWNTs on the crystallization behavior of poly(propylene) (PP) was investigated by means of polarized optical microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. Results obtained from isothermal crystallization experiments indicate that 3-MPTS functionalization affects the crystallization and melting behavior of PP/MWNTs composites remarkably, which can be attributed to the fact that 3-MPTS functionalization of MWNTs leads to a uniform dispersion of MWNTs in PP matrix resulting in the good nucleating effect of MWNTs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1616–1624, 2007