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Nanoconfined polymer chains—as can be formed when polymers intercalate into layered inorganic materials—show remarkable bulk properties, many of which are connected to dynamical heterogeneity in the polymeric phase. Microscopically, it appears that slow dynamical modes are associated with the species in direct contact with the surface, with substantially more mobile species only a fraction of a nm away. In the more distant phase, larger angle and moderately fast dynamics (typically, ns– μ s ) grows in over a broad temperature range not well correlated to bulk phase transitions. In this work, we probe the slowest dynamical modes and apply one- and two-dimensional 2H exchange NMR experiments to study thin polymer layers intercalated between the flat inorganic faces of fluorohectorite (FH). One sample is created by intercalation of perdeuterated poly(ethylene oxide) into FH, and the second by intercalation of d 3 -poly(styrene) into a surface-modified FH. Large-amplitude reorientation of the PEO backbone is substantially hindered in the narrow two-dimensional layers, and reorientation is limited to small-amplitude steps at rates that are largely independent of temperature. Simulations of the two-dimensional exchange experiments suggest that dynamics in nanoconfined polymers is associated with small-angle rotational diffusion.

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.

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.

Characterization of dynamics of the charge-carrying species in polymer electrolytes has proven difficult. In this work we focus on a nanocomposite polymer electrolyte created when poly(ethylene oxide) (PEO) is intercalated into a layered silicate, Li–montmorillonite. We characterize both the Li+–silicate distance and the cation dynamics by analysis of the changes in 7Li nuclear magnetic resonance (NMR) line shape observed as the temperature is changed and cation diffusion is enabled. The observed spectra are compared to spectral simulations which emphasize the role of dipolar fields, associated with the static paramagnetic Fe3+ ions randomly distributed at the Al3+ lattice sites, interacting with the mobile cations. Low temperature line shapes are asymmetric, and not simply related to line shapes of more typical NMR interactions. Simulation of 7Li NMR spectra and comparison to experimental spectra shows that the Li+ interacts most strongly with the silicate surface layer, and all our evidence indicates th...

The grayish–black ternary nitride LixMn2−xN (x≈0.67) was prepared from lithium nitride, manganese powder and nitrogen. The phase adopts an anti-Rutile structural arrangement with lithium and manganese atoms disordered on one site: Space group P42/mnm (No. 136), a=4.68578(9) A, c=2.97762(9) A, Z=2. The electrical resistivity of a sintered pellet (ρ≈8.5·10−3 Ω cm at 250 K) increases slowly as the temperature is decreased (to about 1·10−2 Ω cm at 4 K). Magnetic susceptibility and solid state 6Li-NMR measurements suggest localized magnetic moments on the manganese atoms and probably an antiferromagnetic ordering at about 115 K.

We have measured both of the electrooptical and the Raman characteristics of polymer - stabilized cholesteric texture(PSCT) films fabricated with various polymer concentrations. Some correlations between these two characteristics were found. This indicates the Raman experiment could provide us another technique to analyze the PSCT films.

The grayish–black ternary nitride LixMn2−xN (x≈0.67) was prepared from lithium nitride, manganese powder and nitrogen. The phase adopts an anti-Rutile structural arrangement with lithium and manganese atoms disordered on one site: Space group P42/mnm (No. 136), a=4.68578(9) A, c=2.97762(9) A, Z=2. The electrical resistivity of a sintered pellet (ρ≈8.5·10−3 Ω cm at 250 K) increases slowly as the temperature is decreased (to about 1·10−2 Ω cm at 4 K). Magnetic susceptibility and solid state 6Li-NMR measurements suggest localized magnetic moments on the manganese atoms and probably an antiferromagnetic ordering at about 115 K.

A high-temperature liquid chromatographic technique is employed for the separation of commercially available polymer additives to enhance the resolution and speed. Separation efficiencies and elution behaviors for seven phthalate plasticizers and five antioxidants are evaluated at elevated column temperatures and with a thermal gradient. Diamondbond C18 (octadecylsilica), Zirchrom PS (zirconia-based polystyrene), and Zirchrom PBD (zirconia-based polybutadiene) columns are selected for the study because of their thermal stability. The temperature programming is controlled with a column oven in conjunction with an independent mobile phase preheater and a post-column effluent cooling assembly. Van't Hoff plots show that the reverse-phase liquid chromatography mechanism is maintained over a wide range of column temperatures. A 1% increase of acetonitrile in the mobile phase is estimated to have a comparable effect as a 7-7.5 degrees C column temperature increase on the retention time changes.

A novel cholesteric liquid crystal/polymer gel dispersion has been constructed which can be operated either in normal mode or reverse mode. The normal-mode cell is opaque in a field-OFF condition and clear in a field-ON condition. The reverse-mode cell is clear in a field-OFF condition and opaque in a field-ON condition. In the clear state, both cells are haze-free for all viewing angles. The cholesteric liquid crystal/polymer gel dispersion can be used to make normal-mode and reverse-mode light shutters. The reverse-mode shutter has very good electrooptical characteristics, exhibiting a sharp transition, small hysteresis, and fast dynamic response. >

We describe a new type of color display consisting of polymer‐dispersed droplets of chiralliquid crystal having negative dielectricanisotropy. In the field‐off state, the dropletsscatter light randomly. In the field‐on state the droplets selectively reflect a bright color. Measurements of reflectivities and switching times are presented and we discuss possible applications.

Noise spectroscopy has previously been demonstrated to provide broad-bandwidth excitation with minimal applied RF field strengths. Nonetheless, its application to broadline solid-state NMR spectroscopy has appeared limited by the need to have unrealistically short probe- and receiver-recovery times after pulses. In this Communication, we explain theoretically and demonstrate experimentally that accurate lineshapes can be observed in 2 H solid-state NMR spectroscopy even where the probe ringdown time greatly exceeds the required time between sampled data points. Moreover, accurate lineshapes can be observed to ±125 kHz using RF fields as weak as a few hundred hertz.

We have developed a polymer dispersed cholesteric liquid crystal which exhibits two stable states at zero field: reflecting planar texture and non-reflective focal conic texture. Both states have thresholds under driving voltage pulses. The material can be used to make multiplexed displays on passive matrix. Because the liquid crystal is encapsulated, the dispersion can be coated on plastic substrates to make large size displays. Furthermore, it can be used to make single layer full color displays by using a photo-tuning method.

We have developed two types of polymer stabilized cholesteric dichroic dye displays. In the first type, an anisotropic polymer network perpendicular to the cell surface was formed by photo-polymerization in the homeotropic texture in the presence of an electric field. The polymer network enhanced the hysteresis of the voltage-transmittance curve, and the material can be operated in bistable mode at a bias voltage in the hysteresis loop. In the second type, a random polymer network was formed by photo-polymerization in the isotropic phase at an elevated temperature. The polymer network suppressed the hysteresis, and the material can be operated in gray scale mode. The displays had high on-state transmittance, good contrast ratios, and were suitable for direct view display applications.

Sorption isotherms and diffusion coefficients of water in a 0.3-mil Kapton polyimide film at 30, 45, and 60°C are reported. The data are well described by the dual mode sorption and transport models at low activities. At high penetrant activities, clustering of water is suggested by a Zimm–Lundberg analysis of the sorption data and the fact that the diffusion coefficient for water decreases with increasing external vapor activity. The effect of temperature on the diffusion coefficients at infinite dilution and the dual mode sorption parameters kD, b, and C are presented and discussed. The magnitude of the activation energy of the diffusion coefficient at infinite dilution, 5.4 kcal/mol, is smaller than the corresponding activation energy in more flexible chain polymers, perhaps suggesting that rather small backbone motions are associated with diffusion of water through the Kapton matrix. The predictions for the isosteric enthalpy of sorption from the dual mode model are presented and compared with the values determined from graphical analysis of the sorption isotherms performed independently without reference to the dual mode sorption model.

The synthesis of (L)-(-)-4″-(2-methylbutylphenyl) 4″-(2-methylbutyl)-4-biphenylcar-boxylate (CE2) and related chiral liquid crystals has been discussed by Gray and McDonnell. We present here the first synthesis of the enantiomer of CE2 and we use it to measure the temperature-chirality phase diagram of the biue phases of CE2. This diagram is compared with that obtained using the CE2 “racemate” containing nonen-antiomeric optical isomers of CE2. The synthesis of (R)-(+)-2-methylbutan-l-ol which has been developed will be broadly useful for the preparation of other chiral liquid crystals having optically active (R)-2-methylbutyl sidechains.

Sorption kinetics and equilibria as well as permeabilities and diffusion time lags for CO2 in Kapton polyimide film have been studied at temperatures from 35 to 55°C and pressures up to 0.78 atm. The sorption/desorption cycles indicate that the diffusivity of CO2 increases with increasing local penetrant concentration in the polymer. Both the permeability and time lag decrease with increasing upstream CO2 pressure. All of these results are described well by theoretical expression based on the dual-mode theory of sorption and transport in glassy polymers.

We report a new metal‐semiconductor thin‐film diode with an I‐V characteristic similar to that of a p‐n junction. Its forward bias current is dominated by majority‐carrier tunneling, and its reverse breakdown voltage is over 50 V. The fabrication process, the I‐V curves, and the Auger depth profile of the interfacial layer are presented.

Gravimetric sorption and desorption data are reported for water and anhydrous ammonia in Kapton® at 30°C. The data for water at low activity are described well by Fick’s Law with a concentration dependent diffusion coefficient. At high vapor activity, evidence of small extents of chemical reaction of the water with imide groups was discovered. Even after exposure to a relative humidity of 81.4% for two weeks, however, only 0.31% of the imide structures were affected. Anhydrous ammonia, on the other hand, at rather low relative saturations (0.012 to 0.032) interacted strongly with some of the imide structures of Kapton®. Infrared and gravimetric sorption/desorption measurements were used to characterize the locus and extent of reaction. It was found that after exposure of a 0.5 mil sample to an ammonia relative saturation of 0.0316 for 16 days, roughly 17% of the imide structures were disturbed. Analysis of the coupled diffusion and chemical reaction suggests that only a fraction of the total number of imide groups (~20%) appear to become “activated” or “labilized” during the solid state curing step in which stresses may arise. Stress relief by the limited ammonolysis reaction presumably deactivates the remaining imide groups. The possiblity of using Kapton® as a combined protective barrier and scavenger coating or film is explored briefly.