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This study assesses the impact of Treated Distillate Aromatic Extract (TDAE) oil, at concentrations of 0–20 parts per hundred rubber (phr), on the glass transition temperature (T g) of High Vinyl/Low Styrene Styrene-Butadiene Rubber (HVLSS-SBR), polybutadiene rubber (BR), and their blends with weight ratios of 70/30 and 50/50. Using Dynamic Mechanical Analysis, Broadband Dielectric Spectroscopy, and Positron Annihilation Lifetime Spectroscopy, we found that TDAE modifies T g and fractional free volume (F v) differently across materials. In HVLSS-SBR, TDAE reduced T g by approximately 10 °C and increased F v by 0.8 %. In BR, TDAE raised T g by 5–7 °C without altering F v. The 70/30 blend showed no T g change but a 0.6 % F v increase. For the 50/50 blend, one Havriliak-Negami equation indicated a T g rise of 2–3 °C and a 0.4 % F v increase. A two-equation analysis revealed a 6 °C T g increase and 0.9 % F v boost in the BR-rich phase, versus a 2 °C rise and 0.3 % F v uptick in the HVLSS-SBR-rich phase. The sequence of compatibility, influenced by TDAE, is crystalline BR > amorphous BR > HVLSS-SBR >70/30 blend >50/50 blend. This study provides valuable insights into the behavior of TDAE oil in rubber blends and can serve as a basis for further research in this field. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work we synthesized and studied a series of linear polylactides (PLA) with a fixed L/ d -lactide stereoisomer ratio, covering together the wide range of molecular weights, M n , from ∼6 to ∼80 kg/mol. The basic aims are the segmental mobility mapping, in terms of time scale and fragility, the recording of the M n dependences of the glass transition temperature and fragility, and, finally, the comparison with corresponding findings from the literature. Obviously, the direct M n effects on T g are assessed by preserving PLA at the amorphous state, i.e., via melting and relatively fast cooling. The segmental mobility is studied by conventional and temperature modulated calorimetry, whereas the molecular dynamics is assessed employing the technique of broadband dielectric spectroscopy in combination with proper critical analysis and evaluation routes. The calorimetric and dielectric T g (M n) trends were found consistent between each other as well as with previous findings in similar systems, both with respect to experimental findings and theoretic predictions for PLAs of similar L/D ratio. The M n threshold of entanglements seems to lay between 13 and 28 kg/mol. The fragility index of the α relaxation, i.e., the dielectric analogue of the glass transition, exhibits a similar dependence to that of T g (M n). When decreasing M n to very low values, the high fragility (∼150) drops down to 0 (M ñ 6 kg/mol), denoting the vanishing of the polymer chains' cooperativity. Qualitatively interesting alternations are recorded in the dielectric strength of the α relaxation and the relaxation times width. The effects are discussed in terms of the various parameters co-affecting the polymer dynamics, namely, chain lengths, free volume and dynamical heterogeneities. [Display omitted] • Preparation and molecular dynamics investigation of linear PLA with from ∼6 to ∼80 kg/mol. • Recording of the M n dependence of the calorimetric/dielectric T g and of the fragility index of α relaxation. • The M n threshold for entanglements is estimated between 13 and 28 kg/mol. • Consistent findings with previous experimental ones and theoretic predictions for PLAs of similar L/D ratio. [ABSTRACT FROM AUTHOR]

In this paper, we studied for the first time the impact of the molecular weight, M n , and the topology on the molecular dynamics of a series of grafted poly(poly(dimethylsiloxane methacrylate)) (polyPDMSMA). The behavior of grafted (molecular brushes) polyPDMSMA and their three-armed counterparts of tailor-made properties prepared by Atom Transfer Radical Polymerization (ATRP) was monitored by means of broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and comprehensive rheology analysis. Surprisingly, the dielectric loss spectra of all studied polyPDMSMA exhibit the presence of two dielectric relaxation processes above their glass transition temperature, T g. A comparison of dielectric, calorimetric and mechanical data indicated that the faster and slower relaxation processes identified in loss spectra can be related to the segmental and chain dynamics, respectively. Interestingly, we observed that the "local" segmental dynamics of studied polyPDMSMA, involving the mobility of few repeatable units creating a segment, is almost unaffected by neither the length of polymer chain, number of grafts nor its topology. This is also reflected in a weak molecular weight-dependences of T g of studied polyPDMSMA independently to their topology. On the other hand, the time-scale separation between segmental and the chain modes as well as the amplitude of the latter process increase with growing M n of all examined polyPDMSMA. Additionally, it should be mentioned that the mechanical data collected for samples characterized by high molecular weight (of M n > 280 kg/mol) reveal the emergence of additional process (most likely related to the grafts and/or the star arm relaxation) at the intermediate regime, independently to their topology. Interestingly, this mode was observed to be much slower for the star-shaped macromolecules when compared to the grafted polymers, despite their lower M n. This implies that the observed differences are not a result of different molecular weights, but rather originate from a various molecular mechanism due to the different topology of the studied samples. In this context, one can assume that in the case of high-molecular-weight macromolecules, the backbone architecture has a significant influence on the behavior of polymers, including their molecular dynamics. [Display omitted] • Increase of the glass transition of studied polyPDMSMA with their molecular weight. • Loss spectra of polyPDMSMA exhibit multiple dielectric relaxation processes. • Observed dielectric processes were assigned as the chain and segmental modes. • Presence of grafts/arms relaxation (or entanglement segments) in mechanical data. [ABSTRACT FROM AUTHOR]

Rubber compounds are usually vulcanized in order to improve their mechanical properties. Although vulcanization has been largely studied in the literature, it is not completely clear how the different additives interact among them and how these affect the final properties of the compounds. Here, we present a systematic study using a combination of different experimental techniques, which allows a deeper understanding of the vulcanization mechanisms. We have studied different compounds, with and without silica filler, prepared with styrene butadiene rubber (SBR) of different microstructures and functional end groups. The dielectric response of cured and uncured samples was measured at different temperatures in a wide frequency range. In addition, we analysed the calorimetric and mechanical properties for selected compounds as well as the crosslink density. Furthermore, we performed in-situ vulcanization (in the dielectric cell) to analyse the evolution of different contributions to the dielectric spectrum during cure. Based on our results we conclude that the dielectric response of these SBR compounds is strongly affected by the presence of one of the cure accelerators used in the formulation, namely diphenyl guanidine (DPG). However, this does not affect the segmental relaxation time nor the structure of the crosslink network or the mechanical properties. This study shows the potential of broadband dielectric spectroscopy for monitoring and understanding the vulcanization mechanisms. Image 1 • Understanding vulcanization mechanisms using molecular dielectric dyes. • Effect of the vulcanization additives on the dielectric response of rubber compounds. • Filler-accelerator interaction in vulcanized rubber compounds. • In situ monitoring of vulcanization process by means of dielectric spectroscopy. [ABSTRACT FROM AUTHOR]

Blends of poly(vinylidene fluoride) (PVDF) and ionic liquids (ILs) with different cations and anions have been prepared by solvent casting. The IL content was the same in all blends of the series. Molecular relaxation and ionic conductivity have been systematically studied by broadband dielectric relaxation spectroscopy (BDS) in wide frequency (0.1 Hz–1 MHz) and temperature ranges (−120 to 150 °C) and the results have been analysed in terms of dielectric modulus M*(ω) and conductivity σ*(ω) formalisms. The main relaxation process (β-relaxation) of the amorphous phase of the blend that integrates amorphous polymer chain segments and IL molecules was observed. Significant differences in the Vogel-Fulcher-Tammann (VFT) fitting parameters in the PVDF/IL blends with different anions were detected. The conductivity σ*(ω) formalism shows that it is strongly dependent on the miscibility of the IL with the amorphous PVDF chains and the type of anion. The Barton-Namikawa-Nakajima (BNN) relation σ 0 ∼ ω c is fulfilled for all PVDF/IL blends except for that containing 1-ethyl-3- methylimidazolium hydrogen sulfate, [Emim][HSO 4 ]. The activation energy of the ac conductivity, calculated according to the Dyre model, decreases for all PVDF/IL blends with respect to neat PVDF. The structure of the cation of the IL has been found to exert less influence on the dielectric and conductivity properties of the blends. Image 1 • The electrical response of PVDF/IL blends with different anions and cations is reported. • The miscibility between IL and PVDF is homogeneous in the amorphous phase. • The structure of the cation of the IL has little influence on dielectric response and ionic conductivity. • Anion size strongly affects ionic conductivity behavior and mobility parameters. [ABSTRACT FROM AUTHOR]

The molecular dynamics of poly(1-trimethylsilyl-1-propyne) in the presence of N 2 , CO 2 , CH 4 and C 2 H 4 , is assessed in situ with broadband dielectric and solid state NMR spectroscopies. The measurements of the dielectric permittivity and the analysis of the dielectric spectra show two secondary β relaxations and the absence of a glass transition. These relaxations could be associated to highly flexible and disordered regions (β 1), and to more rigid and ordered ones (β 2). The E a of β 1 observed in the presence of CO 2 was the highest among the four gases studied, suggesting an increased presence in disordered regions. The results of 13C T 1 NMR relaxation measurements provide complementary information on the polymer backbone dynamics. The T 1 s of main chain carbons increase as the concentration of gas sorbed in the polymer increases, indicative of a decrease in chain mobility. The combination of both spectroscopies afforded additional insight toward the understanding of gas transport in glassy microporous polymers. [Display omitted] • PTMSP is a glassy microporous polymer with high free volume fraction and permeability to gases. • BDS and solid state NMR provide information in situ on the molecular dynamics in PTMSP-gas systems. • Carbon dioxide tends to occupied free volume in dense regions of PTMSP membranes. • Increasing concentration of sorbed gas leads to decreasing mobility of polymer chains. [ABSTRACT FROM AUTHOR]

Inhomogeneous network construction is a useful strategy to solve the trade-off between mechanical strength and creep in vitrimer rubbers. But it is still lack of tools to tune the mechanical properties and network dynamics of this new system. In this paper, uneven distribution of functional groups was realized by sequential coordination polymerization of myrcene and isoprene and epoxidation. The following epoxidation and curing generated VMI-x samples with inhomogeneous network. Polyisoprene was used to prepare control samples called VPI-x with homogeneous network. Different lengths of dicarboxylic acid crosslinkers (SA = succinic acid, HA = heptanedioic acid, DA = decanedioic acid) were used to probe their effects on dynamic behaviors, mechanical properties and recyclability. Morphological test and nanomechanical mapping confirmed the inhomogeneous feature of VMI-x samples. For both inhomogeneous and homogeneous samples, SA and DA crosslinkers brought higher tensile strength and modulus, earlier SIC phenomenon and higher orientation percentage of amorphous molecular chains than those of HA, which are ascribed to extra permanent cross-linking existing in SA samples and transition entanglements existing in DA samples. However, the constrain effect of SA crosslinker is too strong in inhomogeneous network to sacrifice the extensibility, which is much smaller than those of HA and DA. SA and DA samples also present restricted segmental motion and superior creep resistant properties compared to HA samples according to the results of broadband dielectric spectroscopy and DMA test. Differently, at high temperature above 130 °C, the stress relaxation, topology freezing transition temperature (Tv) and recycling efficiency of strength are dominated by the crosslinker length monotonically, probably due to the disentanglement of DA crosslinkers. Compared to homogeneous network, inhomogeneous ones showed obvious enhanced mechanical properties, lower hysteresis, quicker segmental relaxation, lower creep and quicker network relaxation. This work demonstrates that crosslinker lengths could tune the vast aspects of vitrimer elastomers and is a non-negligible factor to determine their properties, especially for those with inhomogeneous networks. [Display omitted] • Inhomogeneous vitrimer elastomers were built by varying crosslinker length. • The mechanical properties and creep resistance can be finely tuned. • Stress relaxation and recyclability are related to crosslinker length monotonically. [ABSTRACT FROM AUTHOR]

One of the greatest goals of modern polymer science can be considered the production of high-performance polymer nanocomposites from renewable sources due to the growing interest in environmental and sustainability issues. Within that scope, a good strategy is to pair the processability of thermoplastic materials with the outstanding characteristics of 2D nanomaterials. However, the final performance of the produced nanocomposite is mainly attributed to the interphase, i.e., the volume fraction of the bulk polymer that has its molecular dynamics affected by interactions with the surface of the filler. Therefore, we aim to investigate how different 2D nanomaterials, i.e., graphene oxide (GO), hexagonal-boron nitride (h-BN), and molybdenum disulfide (MoS 2) affect the molecular dynamics of a fully bio-based polyamide 1010 (PA 1010) by a new correlation between experimental results from differential scanning calorimetry, broadband dielectric spectroscopy, and dynamic mechanical analysis. For that, nanocomposites based on single and hybrid-fillers were produced through melt mixing. It was observed that, although all nanofillers seem to hinder the molecular relaxation of the polymer chains, GO and h-BN were more effective than MoS 2. This remained true when the fillers were applied individually and in the hybrid form. This effect has been attributed to the following aspects: (I) higher enthalpy related to the melting of the polyamide crystals after the Brill transition, which indicates lower thermal motion being gained before the transition takes place; (II) higher activation energy of the glass transition, which was estimated from the fitting of the dielectric spectra to the Havriliak-Negami function and then to the Vogel-Fulcher-Tammann model; (III) lower values of the "adhesion factor", which is calculated from the decrease in intensity of the mechanical tan(δ) in the nanocomposites with respect to the neat polymer, indicating higher adhesion for the composites filled with GO and h-BN. To confirm the trends observed experimentally for each nanomaterial, molecular dynamics simulations, which enabled the investigation of the adhesion force as a function of nanosheet displacement, were also carried out. The simulations corroborated with the experimental observations, in which h-BN leads to a more intense force of separation, followed by GO, and lastly by MoS 2. Since the level of interfacial interactions is what mainly dictates the performance of polymer nanocomposites, it is suggested that GO, and especially h-BN, might present greater promise for novel bionanocomposites based on PA 1010. [Display omitted] • Development of polymer nanocomposites using a biopolyamide as matrix; • Investigation of how graphene oxide, hexagonal-boron nitride, and molybdenum disulfide affect the Brill transition of bio-based polyamide 1010; • Determination of the nanocomposites' glass transition activation energy by fitting the dielectric loss curves to the Havriliak-Negami function and then applying the Vogel-Fulcher-Tammann model; • Estimation of the interfacial strength by calculating the "adhesion factor" as a function of nanofiller and content; • Simulation of the energy necessary to separate each nanosheet from a mass of polyamide 1010 through molecular dynamics. [ABSTRACT FROM AUTHOR]

PEO films were prepared on glass substrates from dissolved PEO powder in methanol using the solution casting technique. The investigation of these PEO films involved the utilization of Atomic Force Microscopy, Dielectric Relaxation, and Nuclear Magnetic Resonance techniques to explore alterations in the morphology of the polyethylene oxide polymer films as a response to consecutive thermal cycling at various heating and cooling rates. The dielectric loss curve dependency on frequency for each temperature point within the thermal cycles was fitted with a Havriliak–Negami function with an electrical conductivity contribution. The relaxation times associated with the α- and β-relaxation processes were determined by applying the Arrhenius temperature law, enabling the calculation of the respective activation energies. The study reveals the influence of heating rates on the reversibility of dielectric permittivity, dielectric loss, and dielectric strength, which remains consistent at 2 K/min but not at 0.35 K/min. It also emphasizes the impact of crystallinity on the electrical conductivity of PEO films, highlighting the significance of the amorphous state. The investigation of activation energies for β-relaxation and α-relaxation reveals values of 0.40 eV and 0.74 eV, respectively, in line with similar materials. 1H NMR spectra were studied to differentiate between the crystalline and amorphous phases. The peaks corresponding to the crystalline phase exhibit broad NMR signals with overlapping characteristics attributed to the diverse crystalline structural environments that are present. [Display omitted] • PEO films were prepared from dissolved PEO powder in methanol using the solution casting technique on glass substrates. • The alterations in the morphology of the PEO films as a response to consecutive thermal cycling at various heating and cooling rates were investigated. • The electrical conductivity of PEO films notably increases as the degree of crystallinity decreases, highlighting the importance of the amorphous state for enhanced conductivity. • The utilization of 1H NMR spectra proved successful in distinguishing between the crystalline and amorphous phases within PEO films. • The amorphous-to-crystalline ratio increases with temperatures during thermal cycling and decreases upon cooling, demonstrating full recoverability. [ABSTRACT FROM AUTHOR]

In this paper, we synthesized five self-crosslinked polymerized ionic liquids (S-PILs) containing distinct ion spacers but identical mobile counterions. The structural characterization of these S-PILs was carried out using Fourier transform infrared spectroscopy and wide-angle X-ray scattering. The electrorheological (ER) effect was investigated using rheological measurement and broadband dielectric spectroscopy. The results showed that the ER effect of S-PIL with phosphorus-containing ion spacers was the weakest, that of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers was increased, and that of S-PIL with amino-containing ion spacers was the strongest. Dielectric spectra analysis showed that the interfacial polarization time of S-PIL with phosphorus-containing ion spacers was the longest, resulting in its weakest ER effect. The interfacial polarization times of S-PIL with imidazole-containing ion spacers and S-PIL with pyridine-containing ion spacers were increased but their conductivities were relatively large, which led to strong electrode polarization and weakened their ER effect. S-PILs with amino-containing ion spacers had moderate conductivity and suitable polarization time, so they had the strongest ER effect. Finally, we discussed the reasons for these different conductivity and dielectric polarization by combining the dissociation degree of counterions calculated by Raman spectroscopy and the activation energy of ion movement calculated by conductivity data. The study provides a molecular-level understanding for the rational design and preparation of S-PILs with high ER performance. Self-crosslinked polymerized ionic liquids (S-PILs) containing different types of ion spacers were prepared and showed a significant dependence of electrorheological effect on the type of ion spacers. [Display omitted] • Self-crosslinked PILs with different types of ion spacers were prepared. • ER effect of S-PILs depended on the type of ion spacers. • ER effect of S-PILs with amino-containing ion spacers was the strongest. • Conductivity and dielectric property of S-PILs depended on the type of ion spacers. • Ion dissociation degree and activation energy of S-PILs depended on the type of ion spacers. [ABSTRACT FROM AUTHOR]

With the help of Broadband Dielectric Spectroscopy, it has been possible to study the molecular dynamics of disentangled Ultra High Molecular Weight Polyethylene in a wide temperature and frequency range. Catalytic ashes of aluminum oxide act as dielectric probes, allowing the identification of five different processes: an α c -process due to movements in the crystalline phase, two γ-processes attributed to amorphous chain portions close to the crystalline lamellae, and two β-processes that we have attributed to the disentangled and entangled amorphous phases. The entanglement formation has been followed by isothermal runs and a model that predicts the energy spent to form entanglements as a function of time and temperature is thereby proposed. This model allowed us to calculate the associated activation energy of the entanglement process. Our work advances further the understanding of entanglement dynamics of ultra-high molecular weight polymers, and the proposed model could prove useful to describe other similar processes such as cross-linking. [ABSTRACT FROM AUTHOR]

Nanoparticles significantly reinforce polymers and enhance rheological nonlinearity while the mechanisms are far from being clear. We herein provide a novel strategy to prepare silica network (SN) by burning silica filled ethylene propylene rubber compounds and SN composites by absorbing unentangled polypropylene glycol (PPG) liquid. The SN is explored as the first experimental model imitating the “filler network” in nanocomposites. We investigate rheological responses of SN and its nanocomposites. We find that SN exhibits the soft glassy behavior and dominates the reinforcement and nonlinear behavior of the nanocomposites. On the other hand, by using modulated differential scanning calorimetry and broadband dielectric spectroscopy, we show that a part of PPG chains form glassy and restricted fractions in the interfacial fraction of the nanocomposites. The interfacial fraction contributes additionally to the reinforcement and dominates the dissipation above 10 rad/s. The present study can be helpful for understanding the roles of the interface and filler network in reinforcement and nonlinear behaviors of nanocomposites. [ABSTRACT FROM AUTHOR]

Polymer Single-chain nanoparticles (SCNPs) with different cross-linking densities were synthetized from poly (methyl methacrylate-co-(2-acetoacetoxy) ethyl methacrylate) (PMMA-co-PAEMA) random copolymers, and the molecular dynamics of SCNPs was investigated using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The DSC results show that the glass transition temperature (T g) of SCNPs formed after intra-molecular cross-linking is higher than that of linear precursor, and increases with increasing the cross-linking density. The BDS results reveal that the segment (α) relaxation of SCNPs is significantly inhibited, as evidenced by an increase in the relaxation time and a decrease in the dielectric strength. This is due to the intra-molecular topological constraints which limits the mobility of the polymer segments. Moreover, the distribution width of α relaxation is broader, indicating a more pronounced dynamical heterogeneity. The relaxation time of Johari-Goldstein β (β JG) relaxation increases slightly, neither the dynamics nor the peak width of β JG relaxation is affected by intra-molecular cross-linking. [Display omitted] • The intra-molecular cross-linking significantly affects T g and segmental dynamics of SCNPs. • The α relaxation of SCNPs is significantly inhibited, as evidenced by an increase in the relaxation time, a decrease in the dielectric strength. • Neither the dynamics nor the peak width of β JG relaxation is affected. [ABSTRACT FROM AUTHOR]

We elucidate the influence of composition (weight ratios of 89/11, 76/24 and 49/51) and morphology (spherical, cylindrical and lamellar) on the dielectric and viscoelastic properties in shear and elongation of anionically synthesized polystyrene- block -poly(4-vinylpyridine) (PS- b -P4VP) diblock copolymers in the microphase-separated state. The temperature dependence of the response in both experiments is compared. The analysis of the linear regime shows the appearance of composition (superposition of moduli) and interfacial effects caused by microphase separation (low frequency shoulder, plateau and ω 1 / 2 regime for dynamic moduli and Maxwell-Wagner-Sillars polarization in dielectric experiments). In shear and extensional flows with a constant deformation rate, a pronounced strain-softening behavior in case of a cylindrical and a lamellar morphology appears. For a high weight fraction of the majority phase and a spherical morphology, respectively, strain-softening is observed to a lesser extent. Consequently, strain-softening of diblock copolymer melts can be tuned by the weight/volume ratio of the two blocks. [ABSTRACT FROM AUTHOR]

This work presents the molecular dynamics of both fully amorphous and semicrystalline poly(butylene 2,5-furanoate) (PBF). Broadband dielectric spectroscopy experiments were combined with temperature modulated differential scanning calorimetry measurements. The results showed that the subglass molecular dynamics is characterized by the existence of two dielectric relaxation processes, being the faster one associated to the glycolic subunit, whereas the slower relaxation was assigned to the link in between the ester group and the furan ring. Crystallization affected differently the contribution of these two components. Additionally, crystallization had a stronger effect on the α relaxation process, related to the segmental dynamics of the amorphous phase. In the semicrystalline state, the PBF amorphous phase was described as being composed by different fractions, including a completely rigid one, with distinctly slower mobilities and reduced contributions to the dielectric relaxation, compared to the fully amorphous polymer. [ABSTRACT FROM AUTHOR]

The accurate and convenient characterization of the interfacial layer is a crucial prerequisite for understanding the relationship between structure and macroscopic properties in polymer nanocomposites (PNCs). Herein, enthalpy relaxation and interfacial layer properties estimated from temperature-modulated differential scanning calorimetry (TMDSC) and broadband dielectric spectroscopy (BDS) of model PNCs with attractive interactions are investigated. We demonstrate that enthalpy relaxation enables the accurate quantification of the volume fraction of the interfacial layer (φ int) as TMDSC and BDS. The parameter (χ int) corresponding to the decreased degree of enthalpy hysteresis (Δ H R) related to the contribution of the interfacial layer, is identical with φ int estimated from BDS, while presents only similar dependence on nanoparticle loading with φ int estimated from TMDSC. This interesting phenomenon can be ascribed to the consistency between enthalpy and dielectric relaxation, which both characterize the dynamic change of polymer mainly originating from segmental relaxation. Such an unexpected correlation between enthalpy and dielectric relaxation provides a new approach to characterize the interfacial layer properties of PNCs and understand its impact on the glass transition behavior. [Display omitted] • The decreased degree of Δ H R increases monotonically with increasing nanoparticle loading after excluding the contribution of nanoparticle. • The decreased degree of Δ H R related to the contribution of the interfacial layer is identical with the volume of interfacial layer (φ int) estimated from BDS. • The correlation between enthalpy and dielectric relaxation provides a new strategy to characterize φ int in PNCs. [ABSTRACT FROM AUTHOR]

Matrimid and Matrimid/PhenethylPOSS nanocomposites films were prepared by solution casting. They can be considered as potential membrane materials for gas separation. Their dielectric properties were investigated using Broadband Dielectric Spectroscopy (BDS) in combination with standard techniques. Matrimid shows one relaxation process assigned as β*-relaxation and a conductivity contribution. The relaxation process has a high activation energy of 99 kJ/mol. Thus this process is supposed to be of cooperative nature due to a π–π stacking of the phenyl rings of Matrimid. The influence of the thermal history on Matrimid was analyzed with BDS as well where an annealing effect is found. The Matrimid nanocomposites show up to a concentration of about 4 wt% PhenethylPOSS a miscibility on a molecular level. For higher concentrations a phase separated structure was indicated. The conductivity of both systems is explained by π–π stacking of the phenyl rings which enhances charge transport. [ABSTRACT FROM AUTHOR]

A green and cheap silicone-based elastomer has been developed. Through the simple mixing-in of biodiesel-originating glycerol into commercially available polydimethylsiloxane (PDMS) pre-polymer, a glycerol-in-PDMS emulsion was produced. This counterintuitively stable mixture became a basis for obtaining elastomeric composites with uniformly distributed glycerol droplets. Various compositions, containing from 0 to 140 parts of glycerol per 100 parts of PDMS by weight, were prepared and investigated in terms of ATR-FTIR, broadband dielectric spectroscopy, mechanical properties as well as optical and scanning electron microscopy. The materials were proven additionally to exhibit a strong affinity to water, which was investigated by simple water absorption tests. Incorporating glycerol into PDMS decreased the Young's modulus of the composites yet the ultimate strain of the elastomer was not compromised, even in the presence of very high loadings. The conducted experiments highlight the great potential of this new type of elastomer and reveal some possible applications. [ABSTRACT FROM AUTHOR]

Results by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) are presented in this work, monitoring the interplay between confined, interfacial, and bulk polymer dynamics in silica–gel/polydimethylsiloxane (PDMS) systems. Confined and bulk mobility could be distinguished by recording two well separated glass transition steps in DSC. For low content of adsorbed PDMS (40 wt%), two contributions to segmental dynamics were detected by BDS, arising from the polymer in the interfacial layer on the surfaces of nanoparticles ( α int relaxation) and from polymer chains confined in the pores (∼6–20 nm in diameter) of silica–gel ( α p ), while no bulk segmental relaxation was detected. Nanozirconia grafted onto inner and external surfaces of silica–gel resulted, on the one hand, in reduction of the number of polymer–filler contact points and, on the other hand, in more severe spatial confinement of the polymer in pores. Two additional processes contribute to the dielectric response for the higher polymer loading (80 wt%), arising from the bulk–unaffected amorphous polymer chains ( α relaxation) and the constrained polymer mobility between condensed crystal regions ( α c ). Thermal annealing suppressed the interfacial and bulk (via crystallization) polymer mobility, whereas the confined polymer dynamics remained completely unaffected. The interfacial characteristics could be described well in terms of bimodal conformations of polymer chains, similarly to polymers adsorbed on flat solid surfaces, and in terms of changes in apparent interfacial layer thickness. [ABSTRACT FROM AUTHOR]

Filler–filler and filler–matrix interactions in polymer composites increase with filler concentration and strongly influence the mechanical and rheological properties of polymer composites. By means of the spouted bed spray granulation process polymer composites with an extremely high concentration of inorganic fillers can be prepared. In this work, the viscoelastic properties of highly filled composites of poly(vinyl butyral) (PVB) and alumina particles are studied in the glassy, entanglement and terminal flow regime of poly(vinyl butyral). Ceramic-polymer composites with a volume concentration of inorganic particles between 61 vol% and 77 vol% were prepared. Such large filler fractions imply a strong effect of filler–filler interactions on the viscoelastic properties of the composite. Dynamic-mechanical thermal analysis reveals that the composites are characterized by a predominantly elastic behaviour below and above the glass transition temperature of the polymer phase because of strongly pronounced filler–filler and polymer–filler interactions. A phenomenological equation is proposed in order to describe the reinforcement effect which implies an increase of storage modulus by a factor of up to four orders of magnitude. The results of frequency and strain sweeps in the oscillatory mode show that the polymer phase strongly influences the deformation of the contact network of inorganic particles. Differential scanning calorimetry and broadband dielectric spectroscopy indicate that the glass transition temperature of poly(vinyl butyral) does not significantly differ within experimental resolution for pristine PVB and the PVB phase in the composites. [ABSTRACT FROM AUTHOR]

In this work we present a dielectric relaxation study of Acrylic/Polyurethane polymers synthesized via miniemulsion photo-polymerization. Three different samples, both parts of the synthesized hybrid latex (SOL and GEL fractions) and a full acrylic sample as reference have been considered. Besides dielectric experiments using Broadband Dielectric Spectroscopy (BDS) technique, complementary Differential Scanning Calorimetry measurements have been performed. The thermodynamic characterization outcomes evidence very similar characteristics of the glass transition phenomena among the investigated samples without any signature of melting/crystallization. However BDS experiments show three well resolved dielectric relaxation processes above Tg, two of them evidence marked differences among the samples. A detail study allows us to provide a molecular origin for these three dielectric relaxation processes in connection with the sample characteristics. In particular, our results show that the characterization of these hybrid Acrylic/PU by BDS can provide access to some of the structural features that would ultimately influence the adhesives properties. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy (BDS) is employed for the study of the dielectric response of Polyoxymethylene/boehmite alumina (POM/alumina) and Polyoxymethylene/Layered Silicates (POM/LS) semi-crystalline nanocomposites, together with the response of pure POM. The compilation of the dielectric responses of all systems reveals the existence of five dielectric relaxation mechanisms assigned, in terms of decreasing temperature at constant frequency, as IP (interfacial polarization), α-, β-, γ- and δ-relaxations. IP, α- and γ-relaxations are detected in all studied systems and they are well documented in the literature. δ-relaxation, been the fastest mechanism, is present only in the POM/LS system and is associated with defect dipoles in the crystalline phase of POM. Finally, β-relaxation is present only in the POM/alumina nanocomposite and its dynamics obey Vogel–Fulcher–Tamann temperature dependence. This work presents a complete mapping of the dielectric relaxation mechanisms of POM and signifies the connection of β-mode with the glass to rubber transition of POM, confirming its cooperative character. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the motional dynamics and relaxation behavior of a series of model poly(dimethylsiloxane)-co-meta-carborane (PDMS-co-CB) hybrid elastomers have been studied in depth, using Broadband Dielectric Spectrometry over a temperature range of −130 to 100 °C and a frequency window of 10−1 to 107 Hz. The segmental α-relaxation of both the PDMS and carborane chain segments has been characterized at specific carborane backbone incorporation levels. A direct correlation between the ratio of PDMS to carborane segments and the motional constraint of the network as a whole was observed. In addition to the study of the α-motional modes associated with local intra-segmental motions and the onset of cooperative motion, we have also identified and studied a higher order cooperative (normal-mode) motion of extended segments of the carborane–siloxane co-polymer chains at elevated temperatures. These normal mode motions have been shown to follow an Arrhenius temperature dependence, are sensitive to the local chemical environment and have not been previously reported in this class of polysiloxane copolymer. The motional dynamics of the PDMS-co-CB networks have been compared and contrasted with those of a series of conventionally filled PDMS–Boron Nitride (PDMS–BN) composite systems. While the effects of the chemically bound carborane segment on the PDMS chain dynamics, local order and global network properties have been shown to be directly correlated, significant and predictable, the effects of the BN filler on the PDMS matrix are significantly less so and the results suggest that the filler material may in fact be disrupting the network order, with a consequently negative impact on the properties of the composite. [Copyright &y& Elsevier]

Over the past decades, polysiloxane-based dielectric elastomers (DEs) have attracted significant research attention; however, the low dielectric constant and poor breakdown strength of polysiloxane limit its application in DEs. In this study, the effect of phenyl side groups on the dielectric properties and unique dielectric relaxation behavior of polymethyl phenyl siloxane (PMPS) was investigated. The dielectric constant of PMPS was slightly improved from 3.45 to 3.60 by introducing appropriate amount of the phenyl side groups into polysiloxane. Moreover, the electrical breakdown strength of PMPS increased from 31.70 to 35.91 kV mm−1. The contribution of the α - and β -relaxations significantly increased the dielectric loss of PMPS. To better understand the effect of the phenyl side groups on these properties, the dielectric relaxation behavior of copolymers with different phenyl contents was studied in detail via broadband dielectric spectroscopy and thermally stimulated depolarization current measurements. This study paves a new path to design and prepare polysiloxane-based soft materials with high dielectric constant and improved electrical breakdown strength. [Display omitted] • 1, Polymethyl phenyl siloxanes random copolymers were synthesized. • 2, Breakdown strength of polysiloxanes were significantly improved. • 3, The relationship between polymer chains structure and dielectric behavior was revealed. [ABSTRACT FROM AUTHOR]

Abstract: Filler-polymer interactions in reinforced rubbers are mainly governed by a thin layer of polymer around the filler particles. The dynamics of this layer has long been a matter of intense investigation. Some researchers suggest that this “interacting layer” is immobilized and possesses slower dynamics compared to the bulk, whereas some others consider it equally mobile. In this work, we address this problem by studying the macroscopic characteristics of reinforced rubber using Broadband Dielectric Spectroscopy (BDS) and by measuring its local dielectric behavior using a new AFM based approach: nano-dielectric spectroscopy. This new approach enables us to study the dielectric response of the interacting polymer layer and the bulk dynamics locally, with a spatial resolution of about 20–30 nm. The total amount of interacting polymer within the compounds was also obtained by analyzing the local mechanical properties. Both macro- and nano-measurements show no differences in the polymer local dynamics for the compounds here analyzed. We propose that, for our particular system, the interacting polymer layer shares the same local relaxation dynamics with the bulk rubber due to the presence of a flexible link between the polymer chains and the nanoparticles. [Copyright &y& Elsevier]

Abstract: Molecular dynamics of miktoarm star copolymers consisting of poly(n-butyl acrylate) PBA and polyethylene oxide (PEO) arms was studied by means of Broadband Dielectric Spectroscopy (BDS) and Nuclear Magnetic Resonance (NMR) methods. The spectroscopic studies were performed for three types of copolymers differing in the composition, namely materials containing 76%, 46% and 16% molar fraction of PBA arms. The local processes, described by the Arrhenius law (e.g. the anisotropic rotation of methyl groups and the anisotropic local motions in the PEO chain), were observed for the studied systems below the glass transition temperature. It was found that the investigated PBA/PEO miktoarm star copolymers are characterized by single glass transition, which may result from similar values of glass transition temperatures of the PBA and PEO polymers. The segmental dynamics in the studied systems was quantitatively described by using the Vogel-Fulcher-Tammann (VFT) relation applied to combined NMR and BDS data. Moreover, above the glass transition temperature the interfacial polarization and conductivity phenomena were detected with the BDS method for all systems under study. [Copyright &y& Elsevier]

Abstract: Poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) (PMMA/SMA) blends with various compositions were prepared through solution casting and melt blending. Two preparation routes, solution casting and melt blending, were used to achieve different degrees of molecular entanglement in the samples with solution casting giving rise to a lower degree of entanglement. Therefore, the effect of molecular entanglement on molecular dynamics and phase-separation kinetics of PMMA/SMA blends was investigated by using broadband dielectric spectroscopy and small-angle laser light scattering (SALLS). Molecular entanglement is found to have a pronounced effect on the α-relaxation process. The glass transition temperature (Tg ) is related to the degree of entanglement and a higher degree of entanglement can result in a higher Tg which shifts to a higher temperature after annealing. The relaxation time (τ) of the α-relaxation process is lower for lower degrees of entanglement. Neither the dynamics nor the distribution width of the β-relaxation process is affected by degree of entanglement, regardless of the blend composition. The kinetics of phase-separation by spinodal decomposition (SD) in PMMA/SMA blends are however significantly influenced by the degrees of entanglement with decomposition rate being higher at lower degrees of entanglement. [Copyright &y& Elsevier]

Abstract: The physical aging process, namely the spontaneous evolution of the thermodynamic state occurring in glasses, has been monitored in poly(methyl methacrylate) (PMMA)/silica and polystyrene (PS)/silica nanocomposites following the time evolution of the enthalpy by means of differential scanning calorimetry (DSC). The effect on physical aging of the content of silica particles has been investigated in detail varying it over a wide range. Our results indicate accelerated physical aging in the nanocomposites in comparison to the corresponding pure polymer. Furthermore the acceleration is generally more pronounced in nanocomposites presenting a high silica content. This result cannot be attributed to a difference in molecular mobility of the polymers in the nanocomposites in comparison to pure PMMA and PS, since broadband dielectric spectroscopy (BDS) indicates no effect of silica nanoparticles on the polymer segmental dynamics. Moreover, calorimetric measurements reveal a reduction of the heat capacity jump at Tg for the nanocomposites, as well as lower experimentally recoverable enthalpy values. This may result from the faster non-isothermal evolution of the glass state when cooling down the samples from their liquid state. To account for these experimental results the acceleration of physical aging has been rationalized in the framework of the diffusion of free volume holes model as previously proposed. This is able to adequately catch the dependence of the physical aging rate on silica content, determining the area of nanoparticles to the volume of polymer, that is the relevant variable within the diffusion model. [Copyright &y& Elsevier]

Abstract: The phase transition observed by various methods in poly(vinyl methyl ether)/water systems at around 18 °C has been assigned by some investigators to the pre-melting of water and by others to a glass transition of the polymer. In this study, broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry were used to identify this transition in radiationally crosslinked poly(vinyl methyl ether) hydrogels, as well as to analyse sub-zero relaxation processes in such a three-phase (polymer/ice/liquid water) system. The process at 18 °C was related to the pre-melting of water induced by the segmental motions of the polymer; however, it was seen to be one transition due to the cooperative motions of both compounds. The atypical (two regimes) temperature dependence of the segmental motion process was observed and was related to confinement of the polymer chains between ice clusters below approximately −24 °C; furthermore, the main dielectric process of hexagonal ice was identified and a Maxwell-Wagner effect was observed. [Copyright &y& Elsevier]

Abstract: The changes induced in the amorphous regions of poly(ethylene terephthalate) as a consequence of recrystallization processes, taking place after cold-crystallization at T c =100°C, are analyzed by means of isothermal dynamical mechanical spectroscopy and microindentation hardness. Overall, a recrystallization process at either 115 or 125°C causes an increase of the rigidity within the amorphous domains confined by the crystals. Microhardness measurements carried out at room temperature reveal that recrystallization leads to an enhanced mechanical performance of the amorphous regions. The analysis of isothermal segmental relaxation patterns recorded in a frequency interval of 10−3–60Hz indicates the appearance of two distinct contributions, which find correspondence with observations by broad band dielectric spectroscopy on the same systems. The faster one is ascribed to segmental relaxation within the amorphous domains where the confinement by crystals is relatively weak. The slow relaxation mode is associated with regions where the conformational dynamics is strongly restricted by the crystals. A relative increase of the slow process is detected upon recrystallization. A recently developed relaxation function model is employed to estimate the size of the static cooperatively rearranging regions for both, the slow and the fast modes. It is found that this size increases either upon decreasing the temperature or as an effect of recrystallization. In addition, the number of monomers involved in a conformational rearrangement turns out to be significantly larger in the regions associated to the slow mode process. [Copyright &y& Elsevier]

Abstract: We study the effect of in situ synthesized 10 nm silica nanoparticles on the glass transition and dynamics of natural rubber networks using differential scanning calorimetry, broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents. Even in the absence of specific polymer-filler interactions, polymer segments within a few nanometers of the filler particles exhibit relaxation times up to 2–3 orders of magnitude slower and reduced heat capacity increment at the glass transition compared to bulk natural rubber. These effects are only observed when the nanoparticles are uniformly distributed in the polymer matrix. [Copyright &y& Elsevier]

Abstract: The molecular dynamics of solutions of poly(2-vinylpyridine) (P2VPy) and a series of low molecular weight phenols containing from one to six hydroxyl groups were investigated using broadband dielectric spectroscopy (DRS). Dynamic mechanical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering and wide-angle X-ray diffraction were employed in a complementary role. Segmental relaxation times for the α processes of all solutions follow expectations from T gs derived from DSC experiments. For three of the model mixtures at 30 and 50mol% [i.e., those containing bis (4-hydroxyphenyl) methane, 2,6 dihydroxynaphthalene, and 2,2-methylenebis[6-(2-hydroxy-5-methylbenzyl)-p-cresol] significantly broadened dielectric α relaxation time distributions were observed, indicating dynamic heterogeneity. On the other hand, 4-ethyphenol–P2VPy solutions display dynamic homogeneity. P2VPy with 10mol% 2,3,3,4,4,5-hexahydroxybenzophenone behaved differently than all mixtures investigated in this study: it displayed a T g (and T α) significantly higher than that of the neat components, a small SAXS scattering peak, and an additional dielectric relaxation that we propose originates from Maxwell–Wagner–Sillars interfacial polarization. We propose that this behavior is a result of a phase separation of different types of hydrogen-bonded complexes, one rich in P2VPy and the other involving the type of 2,3,3,4,4,5-hexahydroxybenzophenone hydrogen-bonded structures found in the neat state. Intermolecular hydrogen bonding in all of the P2VPy–phenol mixtures suppresses, in some cases completely, the local P2VPy β relaxation by decreasing the mobility of the pyridine side groups. [Copyright &y& Elsevier]

Solvent-free double network elastomers have excellent mechanical properties and stability. However, there are few studies on ion transport in solvent-free double network elastomers. In this paper, we prepared a kind of poly(ionic liquid) (PIL)-based solvent-free elastomer with double network structure by using crosslinked poly[2-(methacryloyloxy)ethyl] trimethyl ammonium bis(trifluoromethanesulfonyl) imine (P[VBTMA][TFSI]) network as brittle network and crosslinked poly(ethyl acrylate) (PEA) as stretchable network. The mechanical properties and the ion transport of samples as a function of elongation strain were investigated by stress-strain curves and broadband dielectric spectroscopy, respectively. The results show the double network elastomer has medium elastic modulus of 0.4–0.9 MPa, high elongation strain of 1700–2300% and ionic conductivity of 1.04 × 10−7 S·m−1 at room temperature. When the sample does not yield, stretching almost does not affect the ion transport in the network. As the strain exceeds the yield point, the conductivity relaxation time of the samples with low crosslinking degree of PIL network increases little, while the conductivity relaxation time of the samples with high crosslinking degree increases significantly. This is because the former network breaks uniformly, while the latter appears phase separation when yielding. The result improves the understanding of ion transport in double network polyelectrolyte elastomers. Solvent-free DN elastomers composed of PIL/PEA are prepared, which show medium elastic modulus and high elongation strain. Stretching does not affect ion transport in the DN elastomers before yield, while stretching affects ion transport in the DN elastomers after yield due to phase separation. [Display omitted] • Solvent-free DN elastomers composed of PIL/PEA are prepared. • The DN elastomer has medium elastic modulus and high elongation strain. • Stretching does not affect ion transport in the DN elastomers before yield. • Stretching affects ion transport in the DN elastomers after yield due to phase separation. [ABSTRACT FROM AUTHOR]

In this work, we synthesized and investigated five linear and –OH terminated poly(ε -caprolactone)s, PCL, prepared by ring opening polymerization. The samples cover the molar mass, M n , range from ∼4 to ∼70 kg/mol. These biobased polyesters are studied combining a sum of experimental techniques for the structure (infra-red spectroscopy, X-ray diffraction), thermal transitions (calorimetry), semicrystalline morphology (polarized microscopy) and molecular dynamics (broadband dielectric spectroscopy). In particular, upon subjecting the samples to carefully selected thermal conditions, involving extreme cases of crystal memory, namely preserved against erased memory, interesting effects were revealed. The role of M n in PCL is initially reflected on the crystallization and, indirectly, on molecular mobility via crystallinity. For the lower M n s, the formation of interchain interactions, in particular, between the backbone carbonyls (–C O) and the chain end groups (–OH) seems to dominate, exhibiting larger temperature widths of self-nucleation (SN). On the other hand, for larger M n s the increased chain-chain entanglements (physical crosslinks) govern, resulting in favored nucleation, however suppressed SN width. The preservation of melt memory is documented by various physical processes to arise from increased fraction of bound carbonyls and result to altered crystals structuring. Then, next to presenting the effect of M n and crystalline fraction on both the static and the dynamic glass transition, we assess in depth the molecular origins of local dynamics. We demonstrate that the expected interchain associations could be directly correlated with changes on the dielectric strength of local γ relaxation, being luckily strong in PCL, due to the involvement of the carbonyl groups, rather than on segmental dynamics (α relaxation). The latter was affected only in terms of strength and fragility, by the tight or loose semicrystalline morphology, within which the crystals may act both as factors that impose constraints to chains diffusion (low M n) as well as spatial confinement (higher M n). Overall, our findings demonstrate the ability to tune the final PCL properties related to crystallization (permeability, mechanical performance), which is desired envisaging future applications (e.g., biomedical, packaging). [Display omitted] • Linear –OH terminated PCL prepared by Ring Opening Polymerization and investigated. • For high molar mass (M n) the chain entanglements govern nucleation, however, do not favor melt memory. • For low lower M n , the chain-chain interactions, between backbone –C O and end –OH, govern melt-memory. • Evaluation of inter-chain interactions and self-nucleation by various and in principle different techniques. • Denser upon preservation of melt memory and spatial nano-confinement (for high M n). [ABSTRACT FROM AUTHOR]

Abstract: The miscibility and molecular dynamics of nanostructured maleated polypropylene (mPP)/polycarbonate (PC) blends prepared by in situ polymerization of macrocyclic carbonates with polypropylene modified with 0.5wt% of maleic anhydride-reactive groups were investigated over a wide range of frequencies (10−2–0.5×107 Hz) at different constant temperatures using broadband dielectric spectroscopy and scanning transmission electron microscope (STEM). The molecular dynamics of the glass relaxation process of the blend (α-relaxation process) appeared at a lower temperature range compared with that of the pure PC. This shift in the molecular relaxation process is attributed to the partial miscibility of the two polymer components in the blends as previously confirmed by the morphology via STEM. Nanoscale morphologies with average domain diameters as small as 50nm were obtained for the different blend compositions studied. The STEM photographs show that the graft mPP-g-PC prefers to locate at the interfaces as previously reported. The relaxation spectrum of pure PC and mPP/PC blends was resolved into α- and β-relaxation processes using the Havriliak–Negami equation and ionic conductivity. The dielectric relaxation parameters, such as relaxation peak broadness, maximum frequency, f max, and dielectric strength, Δɛ (for the α- and β-relaxation processes), were found to be blend composition dependent. The kinetics of the α-relaxation processes of the blends were well described by Vogel–Fulcher–Tammann (VFT) equation. The local process of PC was resolved into two relaxation processes β1 and β2, associated with the carbonyl groups'' motion and the combined motions of carbonyl and phenylene groups, respectively. Only β2 shifted to lower frequency in the blend while β1 was relatively not affected by blending. The electric modulus of the blends was used to get a sufficient resolution of the different relaxation processes in the samples, i.e., α-, β-relaxation processes, ionic conductivity, and interfacial polarization. In addition, the blending method used was found to increase the d.c. conductivity without affecting the charge carrier transport mechanism, making it possible to develop novel polymer blends with tunable dielectric properties and morphology from existing polymers. [Copyright &y& Elsevier]

Abstract: Broadband dielectric spectroscopy was used to examine carboxylic acid-terminated poly(d,l-lactide) samples that were hydrolytically degraded in 7.4 pH phosphate buffer solutions at 37°C. The dielectric spectral signatures of degraded samples were considerably more distinct than those of undegraded samples and a T g-related relaxation associated with long range chain segmental mobility was seen. For both degraded and undegraded samples, a relaxation peak just beneath a DSC-based T g was observed, which shifts to higher frequency with increasing temperature. Thus, this feature is assigned as the glass transition as viewed from the dielectric relaxation perspective. Linear segments on log–log plots of loss permittivity vs. frequency, in the low frequency regime, are attributed to d.c. conductivity. An upward shift in relaxation peak maximum, f max, observed especially after 145d of immersion in buffer, implies a decrease in the time scale of long range segmental motions with increased degradation time. Permittivity data for degraded and undegraded materials were fitted to the Havriliak–Negami equation with subtraction of the d.c. conductivity contribution to uncover pure relaxation peaks. Parameters extracted from these fits were used to construct Vogel–Fulcher–Tammann–Hesse (VFTH) curves and distribution of relaxation time, G(τ), curves for all samples. It was seen that the relaxation times for the α-transition in both degraded and undegraded samples showed VFTH temperature behavior. G(τ) curves showed a general broadening and shift to lower τ with degradation, which can be explained in terms of a broadening of molecular weight within degraded samples and faster chain motions. [Copyright &y& Elsevier]

Abstract: Phosphate glass (Pglass)/polymer hybrids are a relatively new class of materials that combine the advantages of classical polymer blends and composites without their disadvantages. In the case of highly interacting Pglass/polymer (i.e., polyamide 6) hybrids, counter-intuitive properties that are difficult to explain are often observed. To shed light into the origins of the special behavior of the hybrids, we investigated the molecular relaxation processes in the hybrids using broadband dielectric spectroscopy. The dielectric loss spectra were fitted with the Havriliak–Negami equation and the characteristic relaxation times of the hybrid and the pure components were observed. The temperature dependence of the characteristic relaxation times was described using either the Vogel–Fulcher–Tammann, for the α-relaxations, or an Arrhenius type equation, for the β- and γ-relaxations. The addition of Pglass greatly accelerated both the α- and β-relaxations of the polyamide 6. However, the γ-relaxation was found to be independent of Pglass composition. This suggests partial miscibility in the solid state, which was confirmed via NMR spectroscopy. The unexpected dramatic change in the β-relaxation process in the 10vol.% Pglass hybrid suggests that blending can change the local environment of polyamide 6 due to the nanoscale morphology of this system as confirmed by TEM and NMR. It is thought that the fraction of miscible Pglass disrupts the hydrogen bonding between polyamide 6 chains and thereby reduces coordinated, multiple chain motion. In turn, this produces a plasticization effect and possible modification of the polyamide 6''s crystalline structure in the Pglass/polyamide 6 hybrids. [Copyright &y& Elsevier]

Abstract: The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-T g relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites. [Copyright &y& Elsevier]

Abstract: Molecular mobility in the films of chromophore-containing copolymethacrylates was studied by dielectric spectroscopy. Near the glass transition temperature α- and δ-relaxation processes were observed, being related to segmental mobility and the reorientation of chromophore-containing side groups, respectively. It was shown that the temperature dependences of relaxation times in the range of the δ-process are linear or curvilinear for copolymers with 20 or 50% molar fraction of chromophore-containing units, indicating that the local or cooperative character of chromophore mobility was due to the absence (presence) of inter-chromophore interactions. These data are very important for optimizing the chromophore molar content in NLO polymers since the inter-chromophore dipole–dipole interactions usually lead to the formation of centrosymmetric anti-parallel aggregates which cannot be oriented by external electric fields. It was shown that the δ-process occurs at higher temperatures than the α-process. This fact is of great importance for optimizing the poling temperature at which macroscopic non-centrosymmetric orientation of chromophore occurs under the external electric field applied across a polymer film. The poling temperature should be at least not lower than the glass transition temperature for the δ-process. [Copyright &y& Elsevier]

Abstract: Structural relaxation processes in poly(methyl-para-tolyl-siloxane) (PMpTS) polymers of three molecular weights were studied using dynamic light scattering. Two relaxation processes: the usual α and an additional slow one α′ were observed and studied as function of temperature and molecular weight. Contrary to the structural relaxation, we find that in a plot T–T g the relaxation times for the α′ process for all molecular weights do not collapse to a single curve. For one of the samples the light scattering correlation functions were compared with the corresponding functions obtained by means of mechanical relaxation, dielectric spectroscopy and computer simulations. The simulations show that the bimodal distribution, i.e. the α relaxation and the slow (α′) process are contained in the correlation functions of most of the probes (optical anisotropy, dipole moment, chain bond, density) in agreement with experimental observations. [Copyright &y& Elsevier]

Abstract: Several non-conventional polyurethane (PU) networks crosslinked with hyperbranched polyester (Boltorn®H40) were synthesised with an aim to determine an influence of the PU chain length on molecular relaxations in such systems. The PU chain length was regulated by changing the macrodiol length or by changing the number of the repeating macrodiol/diisocyanate units n. Molecular dynamics were investigated by broadband dielectric spectroscopy and by dynamic mechanical analysis. It was found that the macrodiol length has a strong influence on the glass transition and the α-relaxation, and also on the crystallization. By contrast, the changes of n practically do not affect the molecular relaxations. This effect was explained by the formation of a physical network by hydrogen bonds between urethane groups, controlling the molecular mobility. The rheological measurements have shown, that at temperatures above 150°C, when hydrogen bonds were thermally destroyed, not only macrodiol length but also n had strong influence on the flowing point. [Copyright &y& Elsevier]

Abstract: The molecular dynamics in a variety of poly(ethylene isophthalate)s (PEIs) is studied by broadband dielectric spectroscopy (BDS). The materials comprise non-substituted main chain polyesters and polyesters with semifluorinated (oxydecylperfluorodecyl) side chains. Combining temperature-dependent small angle X-ray scattering (T-SAXS), differential scanning calorimetry (DSC) and BDS it can be shown that the microphase separated semifluorinated polymers exhibit independent dynamic glass transition relaxations taking place in the separate microphases. Additionally in the glassy state, the non-substituted polymers show an Arrhenius-type relaxation whose activation energy decreases gradually from 52 to 40kJ/mol with increasing main chain flexibility. The semifluorinated polymers exhibit a relaxation assigned to fluctuations of the perpendicular component of the fluoroalkyl end group with activation energies between 38 and 40kJ/mol. With increasing flexibility of the main chain, the dynamics of the backbone becomes faster for the non-substituted polymers while an opposite trend is observed in the oxydecylperfluorodecyl substituted side-chain materials. A detailed explanation of the molecular origin of the relaxations is provided. [Copyright &y& Elsevier]

Abstract: The segmental dynamics of bisphenol-A-polycarbonate (BPA-PC) are studied as a function of temperature (in the range from 143 to 473K) and pressure (0.1–300MPa) within the frequency range from 3×10−3 to 1×106 Hz using dielectric spectroscopy aiming at extracting the more relevant parameter associated with the liquid-to-glass transition. Rheological measurements are also made in the temperature range from 408 to 513K for comparison. The dynamic results coupled with the equation of state reveal that both density and thermal energy control the segmental dynamics with density being the most important variable in the vicinity of the transition. This is documented by independent estimates of the value of the dynamic ratio EV ∗/H ∗ (∼0.44). This low value of the dynamic ratio is discussed in terms of the packing irregularities and large monomer volume of BPA-PC. In addition, the pressure coefficient of T g (dT g/dP ∼0.52K/MPa) is one of the highest for a polymeric substance. [Copyright &y& Elsevier]

Abstract: The dynamic behaviour of a set of copolyesters made of 1,4-butanediol, terephthalic acid and 5-tert-butyl isophthalic acid, as well as the two parent homopolymers was studied. Although the insertion of the tert-butyl isophthalate units in the main chain of poly(butylene terephthalate) modified the glass transition, the β relaxation did not change dramatically. By using broadband dielectric spectroscopy we have obtained a detailed picture of the dynamic behaviour of these systems. In all cases, a strong correlation between the α relaxation and the β relaxation above T g was observed in accordance with recent proposals based on the coupling model. [Copyright &y& Elsevier]

Abstract: The influence of the development of crystalline structure on the segmental dynamics of the amorphous phase in poly(butylene isophthalate) (PBI) has been studied by a combination of relaxation and scattering techniques. By means of dielectric spectroscopy (DS) the dynamics of both amorphous and semicrystalline PBI samples has been observed in a wide frequency and temperature range. The evolution of the crystalline phase with time has been studied in a range of temperatures, starting from initially glassy PBI by simultaneous small and wide angle X-ray scattering (SWAXS). By using a state-of-the-art setup designed specifically for the in situ study of both DS and SWAXS simultaneously (SWD), the crystallization of initially amorphous PBI has been followed in real time from both the structural and dynamics points of view. The obtained results support a model based on two different regimes on crystallization and a heterogeneous distribution of lamellar stacks. During the first regime the primary stacks cause the apparition of a rigid amorphous phase (RAP), i.e. a phase of amorphous chains lacking segmental motion. During the second regime, however, no more RAP is observed, indicating that the new lamellae that appear during this stage are nearly individual and not forming lamella stacks. [Copyright &y& Elsevier]

Abstract: Broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarisation currents (TSDC), differential scanning calorimetry (DSC) and to a lesser extent water uptake measurements, were employed to investigate molecular mobility, morphology and crystallization/melting events of PEG in poly(imide-amide)–polyethylene glycol hybrid networks (PIA–PEG) with short (M n=1000g/mol) and long (M n=3400g/mol) PEG crosslinks. The results obtained suggest long range connectivity of the PEG component in the hybrids with short PEG crosslinks at PEG content higher than 40wt% and in these with long PEG crosslinks at PEG content higher than 20wt%. Crystallization of the PEG component is observed by DSC in the hybrids with the longer crosslinks at sufficiently high content of PEG, only. The glass transition temperature, T g, of PEG component in the hybrids with the shorter PEG crosslinks is shifted to higher temperatures compared to that of the hybrids with longer PEG crosslinks, while suppression of the glass transition of the PEG component is observed in the hybrids with the shorter PEG crosslinks at PEG content lower than 40wt%. The results are discussed in terms of constraints to segmental motion of the PEG crosslinks, imposed by fixed PEG chain ends on the rigid PI chains. [Copyright &y& Elsevier]

Abstract: Polycarbonate/poly(ε-caprolatone), PC/PCL, amorphous miscible blends with 90/10 and 80/20 composition in weight, have been studied by X-ray diffraction and broad-band dielectric spectroscopy. The molecular dynamics for the high T g component segmental mobility have been followed by analyzing the isothermal dielectric losses as a function of frequency with Havriliak–Negami distributions. The PCL plasticization effect is observed as a lowering of the Vogel–Tammann–Fulcher terminal temperature without any significant change in the other relaxation parameters. The isothermal crystallization process of the 90/10 PC/PCL blend has been studied in real time both by following the decrease of mobile amorphous material from the variation of the dielectric losses, and by wide angle X-ray scattering to follow the crystal growth. Quantitative comparisons show the disappearance of much higher amounts of mobile amorphous chains than those that are transferred to the crystallites. The existence of a rigid amorphous phase in the blend is established in non-negligible amounts as the isothermal crystallization of PC develops. The remaining mobile amorphous phase has unchanged dynamics. [Copyright &y& Elsevier]

RAFT-made poly(ionic liquid) chains (PIL), poly(1-[2-acryloylethyl]-3-methylimidazolium bromide) (Poly [AEmim][Br]), have been mixed with a ionic liquid (IL), namely butylmethylimidazolium chloride ([C4mim][Cl].) The similarities in terms of structure and polarity of these molecular and macromolecular imidazolium derivatives led to homogeneous and transparent solutions. The influence of the chain molar mass and the concentration was examined through rheology investigation. It was established that the steady-shear viscosity of the solutions, and the viscoelastic properties can be finely tuned by these two parameters and by temperature. The thermal-dependence of the rheological features allowed for determining high activation energies (E a) (around 80 kJ/mol), compared to analogous PIL aqueous solutions. Such E a values reflect high cohesion in PIL/IL solutions, related to the formation of multiple strong interactions, such as hydrogen bonds, van der Waals forces and Coulomb interactions between ionic species. Wide-angle and small-angle X-ray scattering experiments as well as scanning electron microscopy analysis evidenced a multi-scale local homogeneity of the PIL/IL solutions, which additionally exhibit high ionic conductivity (ca. 10−3 S/cm at 30 °C), as measured by broadband dielectric spectroscopy. [Display omitted] • Never described mixtures composed of poly([AEmim][Br]) and [C4mim][Cl] were investigated and characterized. • The rheological properties were tuned both by the molar mass and the concentration of poly(ionic liquid). • A reinforced cohesion, due to H-bonds and electrostatic interactions, was obtained within the mixtures. • High ionic conductivity can be reached, offering applicative potential notably in the field of energy devices. [ABSTRACT FROM AUTHOR]