Dynamics Of Poly Research Articles

Charge carrier dynamics in PMMA–LiClO4 based polymer electrolytes plasticized with different plasticizers

We have studied the charge carrier dynamics in poly(methylmethacrylate)-LiClO4 polymer electrolytes plasticized with different plasticizers such as ethylene carbonate (EC), propylene carbonate (PC), polyethylene glycol (PEG), and dimethyl carbonate (DMC). We have measured the broadband complex conductivity spectra of these electrolytes in the frequency range of 0.01 Hz–3 GHz and in the temperature range of 203 K–363 K and analyzed the conductivity spectra in the framework of the random barrier model by taking into account the contribution of the electrode polarization observed at low frequencies and/or at high temperatures. It is observed that the temperature dependences of the ionic conductivity and relaxation time follow the Vogel-Tammann-Fulcher relation for all plasticized electrolytes. We have also performed the scaling of the conductivity spectra, which indicates that the charge carrier dynamics is almost independent of temperature and plasticizers in a limited frequency range. The existence of nearly constant loss in these electrolytes has been observed at low temperatures and/or high frequencies. We have studied the dielectric relaxation in these electrolytes using electric modulus formalism and obtained the stretched exponent and the decay function. We have observed less cooperative ion dynamics in electrolytes plasticized with DMC compared to electrolytes plasticized with EC, PC, and PEG.

β-NMR measurements of molecular-scale lithium-ion dynamics in poly(ethylene oxide)-lithium-salt thin films.

β-detected NMR (β-NMR) has been used to study the molecular-scale dynamics of lithium ions in thin films of poly(ethylene oxide) (PEO) containing either lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoroacetate (LiTFA) salts at monomer-to-salt ratios (EO/Li) of 8.3. The results are compared with previous β-NMR measurements on pure PEO and PEO with lithium triflate (LiOTf) at the same loading [McKenzie et al., J. Am. Chem. Soc. 136, 7833 (2014)]. Activated hopping of 8Li+ was observed in all of the films above ∼250 K, with the hopping parameters strongly correlated with the ionicity of the lithium salt rather than the polymer glass transition temperature. The pre-exponential factor increases exponentially with ionicity, while the activation energy for hopping increases approximately linearly, going from 6.3±0.2 kJ mol-1 in PEO:LiTFA to 17.8±0.2 kJ mol-1 in PEO:LiTFSI. The more rapid increase in the pre-exponential factor outweighs the effect of the larger activation energy and results in 8Li+ hopping being fastest in PEO followed by PEO:LiTFSI, PEO:LiOTf, and PEO:LiTFA.

New dynamics in poly(propylene glycol) based glass-forming nanocomposites

Results of broadband dielectric spectroscopy and rheological studies of poly(propylene glycol)+SiO2 nanocomposites are presented. They show that the dynamics in high-concentrated composites is dominated by confinement and adsorption effects. The most notable finding is the impact of nanoparticles on fragility, the fractional translational – orientational decoupling and the shift of dynamics towards the pure Vogel-Fulcher-Tammann pattern, associated with the lack of local symmetry preferences.

Dynamics of poly(vinyl methyl ketone) thin films studied by local dielectric spectroscopy.

Local dielectric spectroscopy, which entails measuring the change in resonance frequency of the conducting tip of an atomic force microscope to determine the complex permittivity of a sample with high spatial (lateral) resolution, was employed to characterize the dynamics of thin films of poly(vinyl methyl ketone) (PVMK) having different substrate and top surface layers. A free surface yields the usual speeding up of the segmental dynamics, corresponding to a glass transition suppression of 6.5° for 18 nm film thickness. This result is unaffected by the presence of a glassy, compatible polymer, poly-4-vinyl phenol (PVPh), between the metal substrate and the PVMK. However, covering the top surface with a thin layer of the PVPh suppresses the dynamics. The speeding up of PVMK segmental motions observed for a free surface is absent due to interfacial interactions of the PVMK with the glass layer, an effect not seen when the top layer is an incompatible polymer.

Effects of interfacial interactions and of crystallization on rigid amorphous fraction and molecular dynamics in polylactide/silica nanocomposites: A methodological approach

We employ a partly new experimental approach to polymer nanocomposites (PNCs) based on a semicrystalline matrix, in order to distinguish between phenomena affiliated, on the one hand, to interactions between polymer and nanoparticles, and, on the other hand, to polymer crystals. Thus, effects of silica nanoparticles and of crystalline fraction (CF) on glass transition and segmental dynamics in poly (l–lactic acid) were investigated by means of differential scanning calorimetry (DSC) and broadband dielectric relaxation spectroscopy (DRS). Analysis of results involves combination of measurements on initially amorphous and on semicrystalline (annealed) samples. No change in the glass transition temperature by the filler is observed by DSC, whereas the heat capacity step decreases in the PNCs. The segmental α relaxation (dynamic glass transition) in DRS becomes, however, faster and weaker in the PNCs. Results are rationalized in terms of the rigid amorphous fraction (RAF) due to filler (interfacial polymer, RAFfiller) and due to polymer crystals (RAFcrystal). RAFfiller and RAFcrystal were disentangled from the total RAF via two assumptions: (a) assuming the same RAFcrystal to CF ratio in the neat matrix and the PNCs, and (b) assuming the same RAFfiller in amorphous and semicrystalline samples. Changes of the various polymer fractions with composition show similar trends in DSC and DRS. RAFfiller was found to increase with filler fraction, with a saturation for the largest loading (20 wt%), assigned to filler aggregation confirmed by morphological characterization. Both RAFcrystal and mobile amorphous fraction, MAF, were found within experimental error almost constant with filler loading. The overall results suggest that interfacial interactions (RAFfiller) in combination with changes in semicrystalline morphology dominate polymer dynamics in semicrystalline PNCs.

Dynamics of poly(vinyl butyral) studied using dielectric spectroscopy and 1H NMR relaxometry.

Dielectric Spectroscopy (DS) and 1H Fast Field-Cycling (FFC) NMR relaxometry were applied for understanding the dynamic behavior of the amorphous ter-polymer poly(vinyl butyral) (PVB) across the glass transition temperature (Tg = 70 °C by Differential Scanning Calorimetry). Above Tg, main chain segmental motions (α relaxation) were detected and characterized using both DS and FFC NMR relaxometry. The correlation times extracted by the analysis of DS and FFC NMR relaxometry data agreed within a factor of three and showed a Vogel-Fulcher-Tammann temperature dependence, with an associated Tg of 69 °C and a fragility of 155 for PVB glass. Below Tg, a secondary process (β relaxation) was revealed by DS, and was ascribed to reorientations of the vinyl alcohol dipoles due to local twisting motions with an associated activation barrier of 11 kcal mol-1. The β process was also found to contribute to 1H NMR relaxation above Tg.

Charge carrier extraction study of hole mobility and dynamics in poly(3-hexylthiophene) films subjected to photothermal aging

The evolution of charge carriers mobility μ and their concentration p in the diode devices with the architecture: indium tin oxide (ITO)/poly(3-hexylthiophene) (P3HT)/Al, subjected to photothermal aging in argon atmosphere was investigated using Current Extracted by the non-Linearly Increasing Voltage (CEnLIV) technique based on measuring charge carrier extraction under applied voltage pulses of arbitrary shape and limited amplitude. The kinetics of accumulation of radicals in the P3HT films was explored by the electron spin resonance (ESR) spectroscopy under similar conditions. A remarkable dynamics of μ and p in the system was observed after applying bias voltage to the photothermally aged P3HT-based diode devices. This process was shown to be fully reversible and the system undergoes relaxation to the original state after removal of the bias voltage. The experimental data reflecting the photothermal degradation of P3HT in the presence of trace amounts of oxygen trapped in the films were explained by the proposed kinetic scheme describing the interactions of free charge carriers with the donor-acceptor pairs.

Studies on the Temperature and Time Induced Variation in the Segmental and Chain Dynamics in Poly(propylene glycol) Confined at the Nanoscale

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...

Molecular dynamics simulation on the nanofiber formation of conducting polymers in solutions

ABSTRACTWe study the initial nucleation dynamics of poly (3-hexylthiophene) (P3HT) in solution, with particular regard to the effect of rigid backbone length on the ordering dynamics. We carried out Langevin dynamics simulation, and found that the initial nucleation processes of P3HT in solution begin with the ring ordering, followed by the main chain ordering. In the meantime, ordering of side chains was slow and induced by the packing of main chains. This basic ordering mechanism is common regardless of chain length of P3HT in this study, although the longer chain systems showed slower growth than the shorter chain systems. Our simulation results demonstrated the unique and universal ordering features of comb-like polymers with flexible side chains and rigid main chains in the initial crystallization processes.

Charge transfer dynamics in poly(3-hexylthiophene): nanodiamond blend films

The introduction of nanodiamond (ND) into regioregular poly(3-hexylthiophene) (P3HT) can vary the conformational structure of the polymer. The microstructure of the blend films was analyzed by various techniques, such as absorption spectra, Raman spectra and X-ray diffraction. It is shown that the presence of ND improves the crystallinity and increases the effective conjugation length of P3HT in the blend films. Furthermore, the photo-excited dynamics between P3HT and ND were studied by the steady-state and time-resolved photoluminescence techniques. An obvious fluorescence quenching in the blend films demonstrates the high efficiency of photoinduced charge transfer between P3HT and ND. The energy transfer dynamics could be excluded owing to the bandgap of ND is larger than P3HT. The morphology of the blend films was investigated by Kelvin probe force microscope and transmission electron microscopy. The interpenetrating network of P3HT fibrils and ND domains facilitates charge transfer between the two materials, resulting in the obvious fluorescence quenching of the polymer. The enhanced photocurrent in a prototypical device based on P3HT:ND blends may be correlated with the high efficiency of charge transfer from P3HT to ND.

Molecular ring rotation in poly(vinylferrocene)

We investigate the ring rotation dynamics in poly(vinylferrocene) (PVFc) using incoherent neutron spectroscopy. PVFc contains ferrocene units laterally attached to a polymer backbone, allowing for one cyclopentadienyl ring of the organometallic sandwich structure of ferrocene to undergo rotational jump diffusion. The barrier of rotation is found to be broadly distributed, but the dynamics can be well described using a rotation rate distribution model which is well known from the description of methyl group rotation in glassy polymers. As necessary information for the analysis of quasielastic scattering data, we measure the static structure factor of the polymer using polarized neutron diffraction. Neutron time-of-flight and backscattering data are then combined and consistently modeled over the large temperature range from 80 K to 350 K yielding an Arrhenius behavior of the jump rate distribution. The mean value of potential barrier distribution is found to be 〈EA〉 = 9.61(2) kJ mol-1 with a root mean square width of σE = 3.12(1) kJ mol-1, being the result of superposition of constant intramolecular and heterogeneous intermolecular rotational barriers.

Ultrafast Singlet Fission in a Push-Pull Low-Bandgap Polymer Film.

Excited-state dynamics in poly[4,6-(dodecyl-thieno[3,4-b]thiophene-2-carboxylate)-alt-2,6-(4,8-dioctoxylbenzo[1,2-b:4,5-b]dithiophene)] (PTB1) was studied by transient absorption spectroscopy. Upon photoexcitation at 400 nm, an additional transient species is promptly generated along with singlet excitons and survives up to nanoseconds, while singlet excitons disappear completely. In order to assign the long-lived species, we measured transient absorption spectra over the wide spectral range from 900 to 2500 nm. As a result, we found that the long-lived species is ascribed not to polarons but to triplet excitons, which is formed through the ultrafast singlet fission (SF). We discuss the ultrafast SF mechanism in push-pull low-bandgap polymer PTB1 films on the basis of the excited-state dynamics under various excitation wavelengths and intensities.

Probing the effects of external species on poly(acrylate acid) chain dynamics by using cationic AIE-active fluorophore

We report here our results on the investigation of the chain dynamics of poly(acrylic acid) in aqueous solution. The concentration of poly(acrylic acid) was approximately 3.8×10−4 mol/L, two orders of magnitude higher than that reported in the literature. The pH value of the solution was 3.9, and the hydrogen bonds between the intrinsic and ionized carboxylic acid groups formed dynamic networks, which captured aggregation-induced emission-active molecules (a tetra-quaternary ammonium modified tetraphenylethene derivative) inside the polymer coils and induced fluorescence emission. The hydrogen bonds can be classified as intra- or intermolecular; both can be probed based on the emission change of the tetra-quaternary ammonium modified tetraphenylethene probes. The effects of different external stimuli on the polymer chain dynamics were investigated using different metal cations (including Na+, Li+, Zn2+, Ni2+, Ca2+, and Co2+), different cation concentrations (1×10−6 to 4×10−4 mol/L), different poly(acrylic acid) molecular weights (5, 240, and 450 kDa), and different copolymers. The experimental results indicate that the long poly(acrylic acid) chains (high molecular weight) tend to form dense globular coils and exclude the probe molecules outside, which are robust and unsusceptible to water-soluble metal cations. However, the shorter poly(acrylic acid) chains tend to form intermolecular hydrogen bonds, which are helpful in capturing more probe molecules inside the networks, thus inducing stronger emission. Because of the dual functions of forming hydrogen bonds with carboxylic groups and acting as an acceptor of protons from the carboxylic acid group to form cationic species, copolymerization with acrylate amide [poly(acrylic acid)-co-poly(acrylamide)] can greatly affect the chain dynamics of poly(acrylic acid) segments, which is reflected by the drastically decreased emission intensity from the fluorescent probes.

Glass transition and segmental dynamics in poly(l-lactic acid)/graphene oxide nanocomposites

Effects of graphene oxide (GO) and GO modified with dodecylamine (org-GO) on glass transition and segmental dynamics of poly(l-lactic acid) (PLLA) were investigated by differential scanning calorimetry (DSC) and two dielectric techniques, broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) techniques. Measurements were performed on initially amorphous and on crystallization annealed samples. Isothermal crystallization in the neat matrix and the nanocomposites was followed by DSC and BDS with the same thermal protocol. No change in the glass transition temperature is observed by DSC, whereas the heat capacity step decreases in the nanocomposites. The segmental α relaxation becomes faster and broader in the nanocomposites and its dielectric strength decreases. The results were rationalized in terms of a fraction of interfacial polymer becoming immobilized in the nanocomposites. Changes of this interfacial polymer fraction with composition and functionalization show similar trends in DSC and BDS, absolute values are, however, larger by BDS.

PAT-seq: a method to study the integration of 3'-UTR dynamics with gene expression in the eukaryotic transcriptome.

A major objective of systems biology is to quantitatively integrate multiple parameters from genome-wide measurements. To integrate gene expression with dynamics in poly(A) tail length and adenylation site, we developed a targeted next-generation sequencing approach, Poly(A)-Test RNA-sequencing. PAT-seq returns (i) digital gene expression, (ii) polyadenylation site/s, and (iii) the polyadenylation-state within and between eukaryotic transcriptomes. PAT-seq differs from previous 3′ focused RNA-seq methods in that it depends strictly on 3′ adenylation within total RNA samples and that the full-native poly(A) tail is included in the sequencing libraries. Here, total RNA samples from budding yeast cells were analyzed to identify the intersect between adenylation state and gene expression in response to loss of the major cytoplasmic deadenylase Ccr4. Furthermore, concordant changes to gene expression and adenylation-state were demonstrated in the classic Crabtree–Warburg metabolic shift. Because all polyadenylated RNA is interrogated by the approach, alternative adenylation sites, noncoding RNA and RNA-decay intermediates were also identified. Most important, the PAT-seq approach uses standard sequencing procedures, supports significant multiplexing, and thus replication and rigorous statistical analyses can for the first time be brought to the measure of 3′-UTR dynamics genome wide.

Muon spin relaxation study of spin dynamics in poly(triarylamine)

Organic semiconductors (OSCs) have been of great interest over the last couple of decades on account of their mechanical flexibility, ease of processing and high tunability as well as being readily available. Polymers, in particular, possess the two desirable properties, print processing and electronic tunability. These properties are both necessary for the application of these materials in devices such as organic solar cells and spin valves being engineered for hard disks and logic devices. Much focus in recent years has been given to researching electron and hole dynamics, transport mechanisms and spin relaxation in order to utilise these OSCs in novel organic devices. Here the μSR technique is applied to perform an in depth study of the electron dynamics and spin relaxation in the commonly used poly(triarylamine) polymer (PTAA). Strong evidence shows that the electron wave function can be considered localised to the aromatic rings giving rise to a strong hyperfine coupling interaction with the attached muon. Additionally, an electron spin relaxation (eSR), similar to that previously reported in the small organic molecule series (in the order of 0.25μs−1), is shown to exist with a value of 0.31μs−1 at room temperature.

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. For the thin films, GISAXS and AFM reveal hexagonally packed cylinders of PS in a PI matrix. Three dielectrically active relaxation modes assigned to the two segmental modes of the styrene and isoprene blocks and the normal mode of the latter are studied selectively by BDS. The dynamic glass transition, related to the segmental modes of the styrene and isoprene blocks, is independent of the dimensionality and the finite sizes (down to 18 nm) of confinement, but the normal mode is influenced by both factors with 2D geometrical constraints exerting greater impact. This reflects the considerable difference in the length scales on which the two kinds of fluctuations take place.

Growth of Polymer Nanorods with Different Core–Shell Dynamics via Capillary Force in Nanopores

The dynamics of poly(n-butyl methacrylate) confined in porous anodic aluminum oxide (AAO) templates are investigated using differential scanning calorimetry (DSC) and fluorescence nonradiative energy transfer (NRET). Two glass transition temperatures (Tg,low and Tg,high) are obtained at higher infiltration temperatures via capillary force followed by slow cooling. Tg,low resembles the Tg of the bulk phase and represents the transition of the core layer. Tg,high represents the transition of the adsorbed layer in the confined polymer glass. The temperature threshold to form one or two glass transitions is determined by adjusting the infiltration temperatures and the pore diameters. It is shown that the adsorbed layer has increased interchain proximity relative to the bulk. In addition, the glass transition behavior is hypothesized to be mediated by the counterbalance of the size and interfacial effects in the confined space. The easily synthesized core–shell nanofibers with one glassy and one rubbery component without the need for block polymers have promising potential for use in several processing strategies.

Properties of PVDF-MCM41 Nanocomposites Studied by Dielectric, Raman and NMR Spectroscopy

To obtain information on the polymer-inorganic filler interactions and on the confinement effect of polymer chains we studied the properties of solution-cast poly(vinylidene fluoride)-MCM41 molecular sieve nanocomposites. The dielectric response of the nanocomposites was found to be determined generally by the response of the polymer matrix, whereas the polymer-filler interactions resulted in an increase of the relaxation rates of the local mode and segmental motions in the amorphous phase of the poly(vinylidene fluoride) matrix. The effect has been related to a reduction of intermolecular correlations between the segments and was confirmed by the dispersion of 1H spin-lattice relaxation times in PVDF-MCM41 composites. Moreover, the relaxometry experiments have shown that the dynamics of poly(vinylidene fluoride) chains confined to MCM41 molecular sieve channels can be described by tube/reptation model proposed by De Gennes, Doi and Edwards.

Confined dynamics in poly(ethylene terephthalate): a coherent and incoherent neutron scattering study

We show that the combination of dielectric relaxation with neutron spin echo and incoherent neutron backscattering measurements performed in deuterated and protonated poly(ethylene terephthalate) suggests that the intrinsic dynamics of semicrystalline polymers occurs in an homogeneous scenario, similar to that valid to describe the dynamics of totally amorphous polymers. The quasielastic neutron scattering data are satisfactorily described by a theoretical model that considers that the proton mobility follows a random jump-diffusion in a restricted environment.