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Broadband dielectric spectroscopy, rheology, and nuclear magnetic resonance spectroscopy are employed to study molecular dynamics in a nanoparticle organic hybrid material (NOHMs) system comprising...

We use broad-band dielectric spectroscopy (BDS) and small-angle X-ray scattering (SAXS) to investigate the impact of architectural asymmetry in the miktoarm star copolymer on the dielectric polymer...

Polymers exhibit deviations from their bulk physical properties in the vicinity of solid interfaces due to changes in configurations, entanglements, and relaxation dynamics at the interfacial regio...

During the course of studying silicon-containing diblock copolymers, it was discovered that poly(3,5-di(trimethylsilyl)styrene)-block-poly(3,4-methylenedioxystyrene) (PDTMSS-b-PMDOS) showed very un...

Ion dynamics in a series of imidazolium-based triblock copolymers (triblock co-PILs) are investigated using broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC) and compared to their homopolymer counterparts (homo-PILs). Two calorimetric glass transition temperatures (Tg) are observed corresponding to the charged poly(ionic liquid) (PIL) blocks and noncharged polystyrene (PS) blocks. Varying the counterion from Br– to NTf2– decreases the Tg of the charged block by over 50 °C, thereby increasing the room-temperature ionic dc conductivity by over 6 orders of magnitude. Interestingly, for a given anion, varying the volume fraction of the charged block, from ∼0.5 to ∼0.8, has very minimal effect on the dc ionic conductivity, indicating that the choice of counterion is the key factor influencing charge transport in these systems.

The impact of molecular structure on ion dynamics and morphology in ammonium- and imidazolium-based glassy polymerized ionic liquids (polyILs) is investigated using broadband dielectric spectroscopy (BDS), wide-angle X-ray scattering (WAXS), and classical molecular dynamics (MD) simulations. It is shown that ammonium-based polyILs exhibit higher dc ionic conductivity at their respective glass transition temperatures (Tg) compared to imidazolium systems. In addition, the length of the alkyl spacer has a more drastic impact on ionic conductivity at comparable time scales of segmental dynamics for ammonium than imidazolium polyILs. Agreement between the characteristic ion diffusion lengths estimated from the dielectric data and the ion-to-ion correlation lengths from the WAXS and all-atom MD simulations is observed. A recently proposed approach is employed to determine ionic mobility in a broad frequency range spanning 5 orders of magnitude below the Tg of polyILs studied, providing access to a regime of dif...

Broadband dielectric spectroscopy (BDS) is used to probe the chain and segmental dynamics of A2B2 and AB2 miktoarm star copolymers based on polystyrene (PS, A block) and polyisoprene (PI, B block) that display lamellar morphologies as determined using small-angle X-ray scattering (SAXS). While no changes in the distribution of PI segmental relaxation times are observed with variation of the molecular architecture, an unexpected increase in the normalized PI chain relaxation intensity is realized for AB2 miktoarm star copolymers as well as a change in the distribution of chain relaxation rates as compared to A2B2 and AB diblock copolymer systems. This result is attributed to asymmetry in the molecular architecture near the junction point, which affects the osmotic constraint of the tethered PI chains within the interfacial region of the lamellae. The results highlight the importance of macromolecular design on fundamental chain dynamics in phase-separated thermoplastic elastomers.

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. We observe that the characteristic rate of ion dynamics significantly slows down with decreasing film thicknesses above the calorimetric glass transition of the bulk polymer. However, the mean rates remain bulk-like at lower temperatures. These results highlight the increasing influence of the polymer/substrate interactions with decreasing film thickness on ion dynamics.

The effect of 2D confinement on the dynamics of the normal mode (chain mobility) and segmental relaxation in poly(propylene glycol) (PPG) has been studied with the use of broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). It is shown that both processes become faster with increasing degree of confinement. Interestingly, the crossover from VFT to the Arrhenius-like behavior of chain and segmental dynamics, observed in the examined system, is strictly related to the vitrification of the adsorbed polymers. We also report that the mean relaxation times of the normal, τNM, and segmental modes, τα, depend on the thermal history of confined PPG and can be significantly modified using different thermal treatments. It is demonstrated that annealing of the samples below the crossover temperature, Tc, leads to a systematic shift of the segmental relaxation and normal mode toward lower frequencies, resulting in an increase in the glass transition temperature of the spatially restrict...

The influence of swelling on the molecular dynamics of poly(2-vinylpyridine) (P2VP) brushes is measured by broadband dielectric spectroscopy (BDS) in a broad temperature (350–420 K) and spectral (0.1 Hz–1 MHz) range with nanostructured, highly conductive silicon electrodes, separated by 35 nm high insulating silica spacers. A “grafting-to” method is applied to prepare P2VP brushes with a grafting density σ = 0.12 nm–2 and a film thickness d = 7.3 nm as measured by ellipsometry. Swelling of the P2VP brushes is realized with tetrahydrofuran (THF) vapor using a flow cell. In the dry state, the segmental dynamics of the P2VP brushes coincides with the dynamic glass transition of the bulk system while in the swollen state it becomes faster by up to 1–2 decades due to the plasticizing effect of THF.

Fourier Transform Infrared and Broadband Dielectric Spectroscopies were applied to follow kinetics as well as molecular dynamics upon step-growth polymerization of bisphenol-A diglycidyl ether (DGEBA) with aniline both in bulk and in anodic aluminum oxide (AAO) membranes. For the first time the dynamics and kinetics of a curing epoxy system under confinement were analyzed and compared with the reaction in the bulk. As it turned out, polymerization is faster under confinement, compared to the analogous reaction carried out in the bulk system at the same temperature conditions. Additionally, the reaction speeds up with the degree of confinement. Furthermore, it was found that the initial step of the polymerization is significantly reduced or even suppressed in nanochannels; this is evident from the observation that kinetic curves do not follow sigmoidal shape that is characteristic for the autocatalytic type of chemical reactions. FTIR data showed unquestionably that the rate of reaction is slower at the surface of the pores with respect to the polymerization at the core of nanochannels. This finding is in tandem with Monte Carlo simulation reporting lower reactivity of the functional units close to the pore walls. Moreover, we found out that the activation barrier for the polymerization remains unchanged under confinement. Finally, dielectric measurements revealed that there is a characteristic change in the slope of segmental relaxation times plotted as a function of the time of reaction under confinement, a phenomenon whose comprehension demands further investigation.

Broadband dielectric spectroscopy (BDS) is employed to study the molecular dynamics of hydroxyl- (OH-) and amino- (NH2-) terminated polypropylene glycols (PPGs) of varying molecular weight. Besides the dynamic glass transition (α relaxation), a normal mode process and a secondary γ-relaxation is observed, the latter being assigned to librational fluctuations of the polar COC moiety. Additionally a further process is found and proven in two independent experiments (annealing PPGs at high temperatures and physical aging) to originate from residual H2O impurities in the sample and is therefore not related to the dynamics of PPG. It is occasionally, albeit incorrectly, discussed in the literature as Johari−Goldsten (JG) relaxation. Furthermore, aging in the systems under study is analyzed and found to follow the Nagel−Leheny equation.

Broadband dielectric spectroscopy (BDS), spectroscopic vis-ellipsometry (SE), X-ray reflectometry (XRR), and alternating current (ACC) as well as differential scanning calorimetry (DSC) are combined to study glassy dynamics and the glass transition in nanometric thin (≥5 nm) layers of polystyrene (PS) having widely varying molecular weights (27 500−8 090 000 g/mol). For the dielectric measurements two sample geometries are employed, the common technique using evaporated electrodes and a recently developed approach taking advantage of nanostructures as spacers. All applied methods deliver the concurring result that deviations from glassy dynamics and from the glass transition of the bulk do not exceed margins of ±3 K independent of the layer thickness and the molecular weight of the polymer under study. Our findings are discussed in the context of the highly controversial literature and prove that an appropriate sample preparation is of paramount importance.

International audience; Spectroscopic vis-ellipsometry and broadband dielectric spectroscopy (BDS) are combined to study the glassy dynamics of thin (>= 10 nm) layers of atactic poly(methyl methacrylate) (PM MA) annealed and measured under identical conditions. In order to unravel a possible effect of the underlying substrate, the interfacial interactions are systematically modified ranging from strong attractive interactions for covalently bonded PM MA brushes with high grafting density and for native silicon oxide (Si/SiO(x)) to weak and strong repulsive interactions as realized by Au-coated and HMDS-treated Si/SiO(x) surfaces, respectively. Down to the thinnest analyzed PM MA layers and independently from the applied substrate, both methods deliver-within the experimental accuracy (+/- 1 K for BDS and +/- 2 K for ellipsometry)-a coinciding result. The glassy dynamics arc not altered due to the one-dimensional confinement in these thin polymer layers. The results are discussed with respect to the highly controversial literature and the impact of the preparative conditions.