Interfacial Dynamics in Supported Ultrathin Polymer Films-From the Solid to the Free Interface.

Molecular dynamics in ultrathin layers is investigated using nanostructured electrodes to perform broadband dielectric spectroscopy measurements, and by atomistic molecular dynamics simulations. Using poly(vinyl acetate) as the model system and taking advantage of access to the distribution of relaxation times in an extended temperature range above the glass transition temperature, , we demonstrate that while the mean rates of the segmental relaxation remain bulklike down to 12 nm film thickness, modified molecular mobilities arise in the interfacial zones. Combining results from simulations and experiments, we show unambiguously that both the slow relaxations arising from adsorbed polymer segments and the faster modes attributed to segments in the vicinity of the free interface have non-Arrhenius temperature activation.

Isocyanate- and solvent-free synthesis of melt processible polyurea elastomers derived from urea as a monomer.

Polyurea elastomers are utilized for a myriad of applications ranging from coatings and foams to dielectric materials for capacitors and actuators. However, current synthetic methods for polyureas rely on highly reactive isocyanates, solvents, and catalysts, which collectively pose serious safety considerations. This report details the synthesis and characterization of melt processible, poly(tetramethylene oxide) (PTMO)-based segmented polyurea elastomers utilizing an isocyanate-, solvent-, and catalyst-free approach.

Elucidating the impact of extreme nanoscale confinement on segmental and chain dynamics of unentangled poly(cis-1,4-isoprene).

Broadband dielectric spectroscopy is employed to probe dynamics in low molecular weight poly(cis-1,4-isoprene) (PI) confined in unidirectional silica nanopores with mean pore diameter, D, of 6.5 nm. Three molecular weights of PI (3, 7 and 10 kg/mol) were chosen such that the ratio of D to the polymer radius of gyration, R, is varied from 3.

Charge transport and dipolar relaxations in phosphonium-based ionic liquids.

The role of anions in charge transport and localized dipolar relaxations in tributyloctylphosphonium ionic liquids is investigated by broadband dielectric spectroscopy and rheology. The dielectric spectra are quantitatively described by a combination of the random barrier model which accounts for ion transport and empirical Havriliak-Negami functions to characterize dipolar relaxations. Two secondary relaxations are observed at temperatures below the calorimetric glass transition temperature, where the primary structural relaxation is essentially frozen at the relevant experimental time scales.

Probing Nanoscale Ion Dynamics in Ultrathin Films of Polymerized Ionic Liquids by Broadband Dielectric Spectroscopy.

Continuous progress in energy storage and conversion technologies necessitates novel experimental approaches that can provide fundamental insights regarding the impact of reduced dimensions on the functional properties of materials. Here, we demonstrate a nondestructive experimental approach to probe nanoscale ion dynamics in ultrathin films of polymerized 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide over a broad frequency range spanning over 6 orders of magnitude by broadband dielectric spectroscopy. The approach involves using an electrode configuration with lithographically patterned silica nanostructures, which allow for an air gap between the confined ion conductor and one of the electrodes.

Confinement for More Space: A Larger Free Volume and Enhanced Glassy Dynamics of 2-Ethyl-1-hexanol in Nanopores.

Broadband dielectric spectroscopy and positron annihilation lifetime spectroscopy are employed to study the molecular dynamics and effective free volume of 2-ethyl-1-hexanol (2E1H) in the bulk state and when confined in unidirectional nanopores with average diameters of 4, 6, and 8 nm. Enhanced α-relaxations with decreasing pore diameters closer to the calorimetric glass-transition temperature (T(g)) correlate with the increase in the effective free volume. This indicates that the glassy dynamics of 2D constrained 2E1H is mainly controlled by density variation.

Structure and Dynamics of Asymmetric Poly(styrene-b-1,4-isoprene) Diblock Copolymer under 1D and 2D Nanoconfinement.

The impact of 1- and 2-dimensional (2D) confinement on the structure and dynamics of poly(styrene-b-1,4-isoprene) P(S-b-I) diblock copolymer is investigated by a combination of Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Grazing-Incidence Small-Angle X-ray Scattering (GISAXS), and Broadband Dielectric Spectroscopy (BDS). 1D confinement is achieved by spin coating the P(S-b-I) to form nanometric thin films on silicon substrates, while in the 2D confinement, the copolymer is infiltrated into cylindrical anodized aluminum oxide (AAO) nanopores. After dissolving the AAO matrix having mean pore diameter of 150 nm, the SEM images of the exposed P(S-b-I) show straight nanorods.

The kinetics of mutarotation in L-fucose as monitored by dielectric and infrared spectroscopy.

Fourier Transform Infrared Spectroscopy and Broadband Dielectric Spectroscopy are combined to trace kinetics of mutarotation in L-fucose. After quenching molten samples down to temperatures between T = 313 K and 328 K, the concentrations of two anomeric species change according to a simple exponential time dependence, as seen by an increase in absorbance of specific IR-vibrations. In contrast, the dielectric spectra reveal a slowing down of the structural (α-) relaxation process according to a stretched exponential time dependence (stretching exponent of 1.

Glassy dynamics and physical aging in fucose saccharides as studied by infrared- and broadband dielectric spectroscopy.

Fourier Transform Infra Red (FTIR) and Broadband Dielectric Spectroscopy (BDS) are combined to study both the intra- and inter-molecular dynamics of two isomers of glass forming fucose, far below and above the calorimetric glass transition temperature, T(g). It is shown that the various IR-active vibrations exhibit in their spectral position and oscillator strength quite different temperature dependencies, proving their specific signature in the course of densification and glass formation. The coupling between intra- and inter molecular dynamics is exemplified by distinct changes in IR active ring vibrations far above the calorimetric glass transition temperature at about 1.

Glassy dynamics in condensed isolated polymer chains.

In the course of miniaturization down to the nanometer scale, much remains unknown concerning how and to what extent the properties of materials are changed. To learn more about the dynamics of condensed isolated polymer chains, we used broadband dielectric spectroscopy and a capacitor with nanostructured electrodes separated by 35 nanometers. We measured the dynamic glass transition of poly(2-vinylpyridine) and found it to be bulk-like; only segments closer than 0.