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A systematic series of ethylene-propylene-diene (EPDM) elastomer/carbon-black composites were studied to quantify the effect of additional ceramic fillers, especially of the interfacial contributions, on the dielectric properties of the composites. Substantial interfacial contributions to the composites’ dielectric properties were present in all systems. For all composites studied—using ceramic fillers with varied dielectric nature and spanning orders of magnitude in dielectric constants—the interfacial contributions overwhelmed the ceramic filler k-values and dominated the dielectric performance of the composites. Non-trivial interplays between the carbon black and the ceramic fillers were also manifested, casting doubts on the validity of standard models used for the prediction of dielectric permittivities of such composites.

In general, dielectric multifiller polymer composites have the potential to achieve enhanced performances by integrating the desirable properties of each filler. However, the improvement in thermophysical and dielectric properties is often accompanied by a deterioration of electrical breakdown strength (EBD). Here, we explore a two-filler polymer nanocomposite structure, based on polyolefins with montmorillonite and calcium carbonate fillers, and present an effective approach to obtain enhanced EBD by tailoring the composite morphology (by designing the pseudo-two-dimensional nanoclays to preferentially physisorb on the surfaces of calcium carbonates, so as to change the nature of the filler/polymer interfaces). It is shown that, in these structured polymer nanocomposites, the breakdown performance is substantially improved, exceeding the performance of the unfilled polymers and of the respective single-filler composites. The enhanced dielectric behavior originates from the specific composite morphology, ...

Emerging energy and insulation applications require dielectric materials that can operate at high electric fields and meanwhile possess low leakage currents. For dielectric polymer nanocomposites, beyond filler dispersion, tailoring hierarchical structures offers a promising, yet largely untapped, approach to reach this goal. Here, we demonstrate that the controlled arrangement of pseudo-2D nanofillers and polymer crystals in polyethylene/montmorillonite nanocomposites can be used as an effective approach to achieve nontrivial highly enhanced dielectric performances, far beyond what is feasible with conventional (macroscopic, isotropic) composites. In particular, it is shown that aligned nanofillers can increase the breakdown strength, while, at the same time, reducing the leakage current, in these dielectric nanostructured composites. The orientation of the nanosized pseudo-2D fillers increases the path tortuosity for charge transport, acting as an effective geometric barrier, in the same way and in addi...

The high field electric breakdown of polyethylene/montmorillonite nanocomposites was studied in detail, and compared to the unfilled respective films. The electric breakdown strength (EBD) of ‘aligned’ composite films (i.e., films with fillers oriented parallel to the film surface) is much higher than the EBD of the respective ‘isotropic’ composites (i.e., films with fillers of random orientation) and of the unfilled polymer films. This behavior suggests a barrier mechanism as the origin of electric strength improvement, a supposition that was investigated in detail here and is supported by: (a) EBD is not related to filler-induced or strain-induced polymer crystallinity changes; (b) EBD decreases with modulus, but improves with toughness for these films; (c) there is no change in the polymer EBD for a small temperature jump (ΔT from 25 °C to 70 °C), but there is a definitive change in the composite EBD for the same ΔT. All these, support the postulation that the electrical breakdown of these systems is predominately through thermal degradation mechanisms, which can be affected by the existence of oriented inorganic nanofillers (and of oriented polymer crystallites). Thus, the controlled orientation of nanofillers is shown to be an effective approach to substantially improve the electric breakdown strength of PE dielectric/insulating films.

This chapter summarizes studies on the nanostructure-property interdependencies in tailored/structured polymer nanocomposites, and explains the nanoscale principles leading to the design and synthesis of high-performance nanomaterials for energy storage applications. It provides clues on the mitigation of such detrimental effects, which are commonly responsible for the poor dielectric performance of the composites. Three key factors are emphasized for synthesizing multifunctional nanocomposites: Nanoparticle functionality, Self-assembly of desired nano structures, and Hierarchical nanostructures. The chapter discusses fundamental interrelationships between the nanoscale dielectric properties and the macroscopic properties of the nanocomposites with an emphasis on the dielectric breakdown strength. It describes spectroscopic studies for composites with potential dielectrical applications and with promise to store electrostatic energy. Nanoparticle functionality and nanoparticles with controlled size have shown notable benefits against detrimental effects associated with the interfaces; however, certain applications may necessitate the integration of two or more inorganic phases.

Nano-sized MoS 2 particles have been synthesized and polystyrene (PS) and poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using solution mixing techniques. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of the nanocomposites. Thermal stability and fire properties of nanocomposites were studied by thermogravimetric analysis and cone calorimetry. Mechanical properties were investigated by dynamical mechanical analysis and tensile testing. The PS/MoS 2 nanocomposites showed enhanced thermal stability in comparison to neat polystyrene, as exhibited by the increase of temperature of 50% mass loss point by over 30 °C in the best case. Reduction in the peak heat release rate was observed in all PS/MoS 2 nanocomposites and even more pronounced effects were found in PMMA/MoS 2 nanocomposite.

Composites of ethylene–vinyl acetate copolymer with two different layered double hydroxides have been obtained by melt blending and these have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, thermogravimetric analysis connected to mass spectroscopy and cone calorimetry. There is some small difference in dispersion between the zinc-containing and the magnesium-containing layered double hydroxides in EVA, but both these are microcomposites with good dispersion at the micrometer level and relatively poor dispersion at the nanometer level. There is a good reduction in the peak heat release rate at 10% LDH loading. In addition to chain stripping, which involves the simultaneous loss of both acetate and a hydrogen atom, forming acetic acid, and the formation of poly(ethylene-co-acetylene), side chain fragmentation of the acetate group also occurs and may be the dominant pathway of thermal degradation in the first step. The presence of the LDH causes acetone, rather than acetic acid, to be evolved in the initial step of the degradation.

Previous work in this laboratory has shown that bitumen and oil can be readily separated from sand, using ionic liquids at ambient temperatures. To probe the mechanism underlying the relative ease of separation, atomic force microscopy (AFM) has been used to study interaction forces and adhesion between bitumen surfaces and a silica probe in the presence of liquid media. The energy of adhesion between bitumen samples obtained from both Canadian and U.S. oil sands are approximately an order of magnitude smaller in an ionic liquid medium than in aqueous solution. This behavior was traced to the ability of ionic liquids to form layered charge structures on surfaces. Although interactions between the silica probe and an aged crude oil sample could not be determined, because the probe adhesion to the oil film exceeded the force capacity of the AFM, thermodynamic considerations indicate that the energy of separation of silica from aged oil is also significantly smaller in an ionic liquid medium than in aqueous ...

This manuscript reports on the direct identification of four states of water in hydrated Nafion ionomer polymers, including a quantitative measurement of their dynamics, as previously published in the Journal of the Electrochemical Society, 155, B163-B171 (2008). Here, we provide further details on the dynamics of these water states and we underline still-open scientific questions, towards stimulating further fundamental research in the field.

The microwave dielectric properties of perfluorosulfonic acid membranes are characterized by a two-port transmission line technique. Two dielectric relaxation modes are observed in the microwave region (0.045-26 GHz) at 25{degree sign}C. The higher frequency process observed is identified as the cooperative relaxation of bulk-like water, whose amount was found to increase linearly with water content in the polymer. The lower-frequency process, characterized by longer relaxation times (20-70 picoseconds), is attributed to water molecules that are loosely bound to sulfonate groups. The loosely bound water amount was found to increase with hydration level at low water content, and levels-off at higher water contents. Flemion SH150, which has an equivalent weight of 909 g/equiv, displays higher dielectric strengths for both of these water modes compared to Nafion 117 (equivalent weight of 1100 g/equiv).

Dielectric spectra of dimethyl sulfoxide (DMSO)/water mixtures, over the entire concentration range, were measured using the transmission line method at frequencies from 45 MHz to 26 GHz and at temperatures of 298-318 K. The relaxation times of the mixtures showed a maximum at an intermediate molar fraction of DMSO. A water structure "breaking effect", manifested by a reduced average number of hydrogen bonds per water molecule, was observed in dilute aqueous solutions based on the dielectric relaxation dynamics analysis. The increase in the dielectric relaxation time in DMSO/water mixtures was attributed to the spatial (steric) constraints of DMSO molecules on the hydrogen bond network, rather than being due to hydrophobic hydration of the methyl groups. The interactions between water and DMSO molecules in DMSO-rich mixtures are also discussed.

A series of five oleate-containing layered double hydroxides with varied ratios of zinc to magnesium, i.e., with the general formula Zn2−yMgyAl(OH)6 [CH3(CH2)7CHCH(CH2)7COO]·nH2O, were synthesized and used to prepare nanocomposites of polypropylene (PP). The nanomaterials were characterized by elemental analysis, attenuated total reflection-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the composites were characterized by XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. The zinc-containing LDH showed better dispersion in the polymer at the micrometer level than did the magnesium-containing LDH while both are equally well-dispersed at the nanometer level. The magnesium-containing composites led to more thermally stable systems in TGA experiments, while the zinc systems gave greater reductions in heat release rate during combustion. Dispersion was also affected by the amount of PP-g-MA which was present. More PP-g-MA gave better dispersion and a significantly reduced peak heat release rate, i.e., enhanced fire performance.

Copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) were prepared by partial hydrolysis of PMMA in bad solvent. These copolymers evidently have a blocky comonomer distribution –strands of predominantly MMA or MAA across the polymer– and show sharp transitions in aqueous solution upon pH change. Additionally, their hollow microcapsules show an exceptional and prolonged stability at acidic conditions (pH 2) and pH-triggered release at physiological conditions.

The melt rheological properties of layered silicate nanocomposites with maleic anhydride (MA) functionalized polypropylene are contrasted to those based on ammonium-terminated polypropylene. While the MA functionalized PP based nanocomposites exhibit solid-like linear viscoelastic behavior, consistent with the formation of a long-lived percolated nanoparticle network, the single-end ammonium functionalized PP based nanocomposites demonstrated liquid-like behavior at comparable montmorillonite concentrations. The differences in the linear viscoelasticity are attributed to the presence of bridging interactions in MA functionalized nanocomposites. Further, the transient shear stress of the MA functionalized nanocomposites in start-up of steady shear is a function of the shear strain alone, and the steady shear response is consistent with that of non-Brownian systems. The weak dependence of the steady first normal stress difference on the steady shear stress suggests that the polymer chain mediated silicate network contributes to such unique flow behavior.

Nanocomposites of poly(vinyl chloride) have been prepared using both hectorite- and bentonite-based organically-modified clays. The organic modification used is tallow-triethanol-ammonium ion. The morphology of the systems was investigated using X-ray diffraction and transmission electron microscopy and these systems show that true nanocomposites, both intercalated and exfoliated systems, are produced. The mechanical properties have been evaluated and the modulus increases upon nanocomposite formation without a significant decrease in tensile strength or elongation at break. Thermal analysis studies using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis were conducted. Thermal stability of the PVC systems was assessed using a standard thermal process evaluating the evolution of hydrogen chloride and by color development through the yellowness index. Cone calorimetry was used to measure the fire properties and especially to evaluate smoke evolution. The addition of an appropriately-modified bentonite or hectorite nanoclay leads to both a reduction in the total smoke that is evolved, and an increase in the length of time over which smoke is evolved. Along with this, a reduction in the peak heat release rate is seen. It is likely that the presence of the clay in some way interferes with the cyclization of the conjugated system formed upon HCl loss.

The heat sealing behavior of novel polyethylene-based nanocomposite films was investigated, as they relate to flexible packaging of fresh-cut vegetables, processed foods and biomedical devices. Appropriately designed sealant nanocomposites, which include dispersed montmorillonite nanofillers and ethyl vinyl acetate copolymer, produce a hermetic but peelable heat seal across a broad, 30–40°C, range of heat sealing temperatures, outperforming optimized commercial polyethylene-based sealants that achieve peelable seals in a much narrower heat sealing temperature range, of less than 15°C. Appropriate nanocomposite design leads to a general easy-open/peelable character of heat seals, which is: (a) independent of sealing conditions and apparatus — ranging from long dwell times at very high sealing pressures to very short heat impulses at very low sealing pressures; (b) markedly independent of the opposite side of the heat seal — for example, when sealed on itself, on unfilled sealant, or on high density polyeth...

A novel heat-sealing performance is achieved by polyethylene (PE) nanocomposites reinforced by ethylene vinyl acetate (EVA) and montmorillonite (MMT). Appropriate nanocomposite design leads to hermetic seals with a general peelable/easy-open character across the broadest possible sealing temperature range. Observations of the fracture seal surfaces by infrared spectroscopy and electron microscopy reveal that this behavior originates from a synergistic effect of the EVA copolymer and the montmorillonite clay nanofiller. Namely, the combination of EVA-copolymers and MMT nanofillers provides sufficiently favorable interactions for nanocomposite formation and mechanical robustness, but weak enough interfacial adhesion to promote a general cohesive failure of the sealant at the EVA/MMT interfaces.

The aqueous solution phase behavior of (ethylene oxide)/ethylene copolymers with varying degree of hydrophobicity is explored using an equation of state approach. The general formalism of the lattice-fluid with hydrogen-bonding theory is employed after a minor adjustment to account for multiple types of hydrogen bonds. The theoretical model is shown to be effective in describing the phase behavior of these systems, and the model parameters seem to be transferable between different homologous copolymer series. Despite limitations of the model, the calculated phase diagrams and the dependence of lower critical solution temperature (LCST) on the hydrophilic/hydrophobic content of the polymer show good correspondence with the available experimental data.

Nanocomposites of polystyrene (PS), acrylonitrile–butadiene–styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays.

Nanocomposites of polyethylene, ethylene–vinyl acetate copolymer and polystyrene with single- and multi-wall carbon nanotubes, organically modified montmorillonites and layered double hydroxides were prepared by melt blending. Their morphologies were assessed by X-ray diffraction and transmission electron microscopy, while the flammability properties were evaluated by thermogravimetric analysis and cone calorimetry. The relative amounts and the identity of the degradation products are changed when both well-dispersed cationic and anionic clays are used, but there is no difference in the degradation products when carbon nanotubes were utilized. When the nano-dimensional material is not well-dispersed, the degradation products are not changed. Unlike their smectite counterparts, polymer/layered double hydroxide nanocomposites give reasonably good reductions in peak heat release even when good nano-dispersion has not been obtained. These data suggest that the enhancement in the fire behavior must be, at least in part, due to different mechanisms for montmorillonite, layered double hydroxides and carbon nanotube-based nanocomposites.

The thermal degradation of poly(methyl methacrylate) and its nanocomposite has been studied to determine if the presence of clays (anionic and cationic) or carbon nanotubes has an effect on the degradation pathway. Nanocomposite formation has been established by X-ray diffraction and transmission electron microscopy, thermal degradation has been investigated by cone calorimetry and thermogravimetric analysis (TGA), and the products of degradation have been studied with TGA/FT-IR and gas chromatography/mass spectrometry (GC/MS). There are no marked differences in the degradation products of the polymer and its nanocomposites, but the degradation of the nanocomposite occurs at higher temperatures. The most likely explanation is that poly(methyl methacrylate) degrades by only a single route, so the clay cannot promote one pathway at the expense of another. This observation bears important implications for the barrier mechanism, which is currently used to explain the reduction in the peak heat release rate of nanocomposites. Copyright © 2006 John Wiley & Sons, Ltd.

The addition of inexpensive montmorillonite clay to a silicone resin employed as preceramic polymer was found to be advantageous for the production of SiOC glass matrix composites. Dense SiOC based monoliths were achieved with the addition of a substantial amount of calcined clay (30 wt.%) to the preceramic polymer; these composites exhibited remarkable hardness and fracture toughness, higher than those of SiOC glasses reported in the literature, due to the very small dimensions of silica and mullite crystal inclusions deriving from the decomposition of clay. Microcellular SiOC glass based microcellular foams were also produced, from composites filled by both calcined and organically functionalized clay. The inclusions from the decomposition of clay provided for the retention of the microcellular structure even after oxidation at 1200 and 1450 °C. Functionalized clay showed a more pronounced effect in limiting the extent of the densification and collapse of microcellular shape than calcined clay. In both cases, the crushing strength after oxidation was found to be particularly remarkable.

Poly(ethylene terephthalate) (PET)/clay nanocomposites were prepared by melt blending and their morphologies and properties were investigated through X-ray diffraction, bright field transmission electron microscopy, thermogravimetric analysis and cone calorimetry. Three clays were comparatively studied—montmorillonite, hectorite and magadiite—all organically modified with thermally stable surfactants developed in this laboratory. Two such organic modifications were investigated, alkyl-quinolinium surfactants and vinylbenzyl-ammonium containing copolymers; both organic modifications combine high enough degradation temperature to allow for melt processing with PET, and also favorable thermodynamics for nanocomposite formation with PET. All nanocomposites showed about the same value for the peak heat release rate (PHRR). The amount of char increases after nanocomposite formation and this could account for the PHRRs. Copyright © 2006 John Wiley & Sons, Ltd.

We report on the rapid formation of hydrophilic silicone elastomer surfaces by ultraviolet/ozone (UVO) irradiation of poly(vinylmethyl siloxane) (PVMS) network films. Our results reveal that the PVMS network surfaces render hydrophilic upon only a short UVO exposure time (seconds to a few minutes). We also provide evidence that the brief UVO irradiation treatment does not cause dramatic changes in the surface modulus of the PVMS network. We compare the rate of formation of hydrophilic silicone elastomer surfaces made of PVMS to those of model poly(dimethyl siloxane) (PDMS) and commercial-grade PDMS (Sylgard-184). We find that relative to PVMS, 20 times longer UVO treatment times are needed to oxidize the PDMS network surfaces in order to achieve a comparable density of surface-bound hydrophilic moieties. The longer UVO treatment times for PDMS are in turn responsible for the dramatic increase in surface modulus of UVO treated PDMS, relative to PVMS. We also study the formation of self-assembled monolayers (SAMs) made of semifluorinated organosilane precursors on the PVMS-UVO and PDMS-UVO network surfaces. By tuning the UVO treatment times and by utilizing mono- and tri-functional organosilanes we find that while mono-functionalized organosilanes attach directly to the substrate, SAMs of tri-functionalized organosilanes form in-plane networks on the underlying UVO-modified silicone elastomer surface, even with only short UVO exposure times.

Polyamide-6 (PA-6)/graphite nanocomposites were prepared by melt blending, using a variety of graphites, including virgin graphite, expandable graphites and expanded graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of graphite layers in the polymer matrix, and the dispersion depends on the graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties.

Stiff thin films on soft substrates are both ancient and commonplace in nature; for instance, animal skin comprises a stiff epidermis attached to a soft dermis. Although more recent and rare, artificial skins are increasingly used in a broad range of applications, including flexible electronics, tunable diffraction gratings, force spectroscopy in cells, modern metrology methods, and other devices. Here we show that model elastomeric artificial skins wrinkle in a hierarchical pattern consisting of self-similar buckles extending over five orders of magnitude in length scale, ranging from a few nanometres to a few millimetres. We provide a mechanism for the formation of this hierarchical wrinkling pattern, and quantify our experimental findings with both computations and a simple scaling theory. This allows us to harness the substrates for applications. In particular, we show how to use the multigeneration-wrinkled substrate for separating particles based on their size, while simultaneously forming linear chains of monodisperse particles.

Molecular dynamics computer simulations are used to study the structure and dynamics of 1-nm wide films of poly(ethylene oxide) (PEO) confined between mica-type layered silicates of different cation exchange capacities (CEC). The simulation setup mimics experimental systems formed by intercalation of PEO in montmorillonite alumino-silicates with varied inherent charges. It is shown that the presence and population of lithium has a significant influence on the behavior of the system, in addition to the confinement-induced effects caused by the extreme spatial restriction. The structural features of the confined PEO are strongly altered with the number of Li+, which determines the polymer/inorganic interactions. The combination of the nanoconfinement and the presence of lithium preclude regular ordered arrangements of PEO, similar to those observed in the bulk unconfined polymer. The segmental dynamics of PEO in confinement are also greatly influenced by the presence of lithium, because of the strong interaction between Li+ and the oxygen of the PEO backbone. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3460–3477, 2005

Monoalkyl- and dialkyl-imidazolium surfactants were used to prepare organ- ically modified montmorillonites with markedly improved thermal stability in comparison with their alkyl-ammonium equivalents (the decomposition temperatures increased by ca. 100 °C). Such an increase in the thermal stability affords the opportunity to form syndio- tactic polystyrene (s-PS)/imidazolium-montmorillonite nanocomposites even under static melt-intercalation conditions in the absence of high shear rates or solvents. Upon nano- composite formation, s-PS exhibited an improvement in the thermal stability in compari- son with neat s-PS, and the -crystal form of s-PS became dominant. This crystallization response agrees with previous studies of s-PS/pyridinium-montmorillonite hybrids and is tentatively attributed to a heterogeneous nucleation action by the inorganic fillers. © 2003

We employ atomistic computer modeling to investigate the structure and morphology of poly(ethylene oxide) (PEO) chains confined in 1-nm slit pores defined by montmorillonite silicate layers. Molecular dynamics computer simulations reveal the Li cations to be located in the immediate vicinity of the silicate surfaces and PEO to adopt highly amorphous conformations in a liquidlike bilayer across the slit pores. Despite the orienting influence of the parallel stacked silicate walls, PEO shows no indication of crystallinity or periodic ordering; in fact, for all temperatures simulated, it is less ordered than the most disordered bulk PEO system. These amorphous PEO film configurations are attributed to the combination of severe spatial confinement and the strong coordination of ether oxygens with the alkali cations present in the inter- layer gallery. These conclusions challenge the picture traditionally proposed for inter- calated PEO, but they agree with a plethora of experimental observations. Indicatively, the simulation predictions are confirmed by wide-angle neutron scattering and differ- ential scanning calorimetry experiments on PEO/montmorillonite intercalates. © 2003

The crystallization behavior of poly(ethylene oxide) (PEO) was studied in the presence of an inorganic filler surface (sodium montmorillonite) with DSC, as well as isothermal cross-polarization optical microscopy. Crystallization of PEO is found to be inhibited, exhibiting a decrease of spherulite growth rate and crystallization temperature. However, the overall crystallization rate increases with silicate loading as a result of extra nucleation sites, which occur in the bulk PEO matrix (i.e., far from the silicate surfaces). PEO differs from other systems, where crystallinity is typically enhanced next to such surfaces, in that the polymer is amorphized near the montmorillonite surfaces. This behavior is attributed to the specific way that PEO interacts with Na+ montmorillonite, where strong coordination of PEO to the surface Na+ cations promotes noncrystalline (ether crown) PEO conformations.

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s-PS), and elastomers, such as poly(ethylene-co-1-octene) and poly(ethylene-co-styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ∼270 °C to low glass-transition temperature ∼−60 °C. The chemistry involves two reaction steps, including the preparation of a borane group-terminated polyolefin by the combination of a metallocene catalyst and a borane chain-transfer agent as well as the interconversion of a borane terminal group to an anionic (O−K+) terminal group for the subsequent ring-opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α-olefins to the ring-opening polymerization of ethylene oxide. The well-defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (Mw/Mn < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002

Molecular-Dynamics computer simulations were used to study 2 nm wide polystyrene films confined in slit pores, defined by inorganic crystalline surfaces. The simulated systems mimic experimentally studied hybrid materials, where polystyrene is intercalated between mica-type, atomically smooth, crystalline layers. A comparison between the experimental findings and the simulation results aims at revealing the molecular origins of the macroscopically observed behavior, and thus provide insight about polymers in severe/nanoscopic confinements, as well as polymers in the immediate vicinity of solid surfaces. Pronounced dynamic inhomogeneities are found across the 2 nm thin film, with fast relaxing moieties located in low local density regions throughout the film. The origins of this behavior are traced to the confinement-induced density inhomogeneities, which are stabilized over extended time scales by the solid surfaces.

Molecular dynamics simulations are used to explore poly(ethylene oxide)/Li+ complexes, comparing bulk and nanoscopically confined systems. We focus on lithium ion dynamics, so as to elucidate the molecular mechanisms of ionic motion in these two environments. The confined systems mimic 0.8 nm thin intercalates between mica-type layers (montmorillonite). Simulations of the Li+/bulk PEO system show a clear change in the ion transport mechanism from a hopping fashion, at low temperatures, to a random Brownian-like diffusion, at higher temperatures. In sharp contrast, the intercalated, nanoconfined, systems display a single hopping mechanism throughout the same temperature range, dictated by the unique nature of the lithium coordination to the mica-type surfaces and the confined PEO.

This paper discusses an effective route in the functionalization of s-PS polymer that involves the direct copolymerization of styrene with a borane-containing styrenic monomer, i.e., 4-[B-(n-butylene)-9-BBN]styrene (B-styrene). The reactivity ratios of the two comonomers are quite close, with r1 = 0.9 for styrene and r2 = 1.2 for B-styrene in the Cp*Ti(OMe)3/MAO catalyst system. A broad composition range of syndiotactic poly(styrene-co-B-styrene) copolymers has been prepared with narrow molecular weight and composition distributions. The random copolymer structure was further evidenced by DSC and 13C NMR analyses. With increasing B-styrene concentration, the copolymers show a systematic decrease in glass transition temperature, melting point, crystallization temperature, and crystallinity. At above 8.4 mol % B-styrene content, the crystallinity of the copolymer completely disappears. In turn, the borane groups in the copolymer are very versatile and can be quantitatively converted to other functional grou...

Extrusion blown polyethylene and polyethylene/montmorillonite nanocomposite films were cold stretched to various ratios to quantify the influence of the crystal orientation and the nanofiller alignment on their dielectric breakdown performance. It was found that the crystal orientation could increase the breakdown strength (EBD) in the stretched blown films. The aligned pseudo-2D inorganic nanoclays provided additional strong improvements in EBD that can be superimposed to any EBD enhancement due to the polymer crystal orientation. At high filler loadings and high stretching ratios, the onset of percolation was observed through a substantial improvement in the dielectric breakdown strength.

Crystallization of poly(vinyl alcohol) in the presence of an inorganic filler surface (sodium montmorillonite, MMT) was observed and compared to the crystallization of the neat polymer. For this purpose, several atomic force microscopy modes, providing spatial resolution between amorphous and crystalline polymer, are employed to observe filled and unfilled PVA films. The various AFM modes utilized are detailed, with the emphasis on how they can contrast stiff (crystalline) and softer (amorphous) domains on a polymer surface. The study revealed changes in the PVA crystal morphology, with bulk crystallites growing to sizes of more than 5 μm, whereas next to the inorganic surfaces grow to only 1−2 μm in size. Moreover, complementary X-ray diffraction and DSC investigations indicate a new crystal structure formed next to the MMT surfaces, at the expense of the bulklike crystal.

The synthetic routes and materials properties of polypropylene/montmorillonite nanocomposites are reviewed. The nanocomposite formation is achieved in two ways: either by using functionalized polypropylenes and common organo-montmorillonites, or by using neat/unmodified polypropylene and a semi-fluorinated organic modification for the silicates. All the hybrids can be formed by solventless melt-intercalation or extrusion, and the resulting polymer/inorganic structures are characterized by a coexistence of intercalated and exfoliated montmorillonite layers. Small additionstypically less than 6 wt %of these nanoscale inorganic fillers promote concurrently several of the polypropylene materials properties, including improved tensile characteristics, higher heat deflection temperature, retained optical clarity, high barrier properties, better scratch resistance, and increased flame retardancy.

Molecular Dynamics (MD) simulations are used to explore the structure and dynamics of polystyrene confined in 2 nm slit pores, between parallel, crystalline, mica-type surfaces. The systems simulated resemble experimentally studied intercalated nanocomposites, where polystyrene is inserted between layered-silicate layers. The molecular modeling perspective complements the experimental findings and provides insight into the nature of polymers in nanoscopic confinements, especially into the molecular origins of their macroscopic behavior. Namely, a comparison between simulation and NMR studies shows a coexistence of extremely faster and much slower segmental motions than the ones found in the corresponding bulk polymer at the same temperature. The origins of these dynamical inhomogeneities are traced to the confinement induced density modulations inside the 2 nm slits. Fast relaxing phenyl and backbone moieties are found in low density regions across the film, and preferentially in the center, whereas slow relaxing moieties are concentrated in denser regions in the immediate vicinity of the confining surfaces. At the same time, the temperature dependence of the segmental relaxations suggests that the glass transition is suppressed inside the confined films, an observation confirmed by scanning calorimetry. © 2001 Elsevier Science B.V. All rights reserved.

The motion of confined polymers is measured experimentally between parallel, atomically smooth solid surfaces, separated by 2 nm. In particular, the kinetics of intercalation of monodispersed polystyrene in alkylammonium modified mica-type silicates were studied using X-ray diffraction. The kinetics of the neat polymers and their functionalized derivatives were measured as functions of molecular weight, extent of functionalization, and silicate surface organic modification, at various temperatures. Selective corroborative studies were also performed using in-situ small-angle neutron scattering (SANS). The kinetic data are interpreted in terms of an effective diffusion coefficient (Deff) of the polymer, which undergoes a dramatic decrease with stronger silicate surface-polymer interaction. This interaction is varied by either changing the silicate surface modification or by increasing the extent of functionalization of the polystyrene chains. Furthermore, the diffusion coefficient exhibits an inverse dependence on chain length (N), i.e., Deff ∝ N -1 , for chains up to 900 000 molecular weight.

Poly(vinyl alcohol)/sodium montmorillonite nanocomposites of various compositions were created by casting from a polymer/silicate water suspension. The composite structure study revealed a coexistence of exfoliated and intercalated MMT layers, especially for low and moderate silicate loadings. The inorganic layers promote a new crystalline phase different than the one of the respective neat PVA, characterized by higher melting temperature and a different crystal structure. This new crystal phase reflects on the composite materials properties. Namely, the hybrid polymer/silicate systems have mechanical, thermal, and water vapor transmission properties, which are superior to that of the neat polymer and its conventionally filled composites. For example, for a 5 wt % MMT exfoliated composite, the softening temperature increases by 25 °C and the Young's modulus triples with a decrease of only 20% in toughness, whereas there is also a 60% reduction in the water permeability. Furthermore, due to the nanoscale d...

Monte Carlo and molecular dynamics computer simulations are used to explore the atomic scale structure and dynamics of intercalated PEO/montmorillonite nanocomposites. Particular attention is paid ...

Our continuing study of the mechanism of flammability reduction of polymer−layered-silicate nanocomposites has yielded results for polypropylene-graft-maleic anhydride and polystyrene−layered-silicate nanocomposites using montmorillonite and fluorohectorite. Cone calorimetry was used to measure the heat release rate and other flammability properties of the nanocomposites, under well-controlled combustion conditions. Both the polymer−layered-silicate nanocomposites and the combustion residues were studied by transmission electron microscopy and X-ray diffraction. We have found evidence for a common mechanism of flammability reduction. We also found that the type of layered silicate, nanodispersion, and processing degradation have an influence on the flammability reduction.

Fluids in nanoscopic confinements possess a variety of unusual properties, and in particular, remarkable dynamical heterogeneities which vary on length scales as short as a fraction of a nanometer. While the surface forces apparatus provides an experimental probe of macroscopic properties of fluids in contact with atomically smooth solid surfaces, few experimental probes are available which test the microscopic origins of these heterogeneities. In this article we describe our recent efforts to apply nuclear magnetic resonance spectroscopy to nanoscopically confined poly(styrene) (PS) created by intercalation into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin–echo experiments which probe the entire organic layer suggests that PS in the center of the nanopores is more mobile than the bulk at comparable temperatures, while chain segments which interact with the surface are dynamically inhibited.

The full potential of nanoparticles in imparting new functionalities in polymer nanocomposites remains largely untapped. A widely applicable, two-solvent processing approach provides a hierarchical structure, affording unparalleled composite performance enhancement.