Plateau Value Research Articles

Influence of long chain branching on fiber diameter distribution for polypropylene nonwovens produced by melt blown process

In this work, linear isotactic polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) miscible blend, both having comparable weight average molecular weight, zero-shear viscosity, and polydispersity index, were used to produce nonwovens via melt blown technology in order to understand the role of long chain branching in the fiber diameter distribution. Basic morphological characteristics of produced nonwoven samples have been determined using digital image analysis of scanning electron microscope images considering different magnifications to capture nanofibers as well as microfibers. At the same air flow rate, polymer flow rate, and temperature, the average fiber diameters were the same, 1.6 μm, but the coefficient of variation, CV, was greater for the linear PP than for the blend. Material elasticity was assessed by reptation-mode relaxation time, λ, determined by fitting of deformation rate dependent shear viscosity by Cross and Carreau-Yasuda models as well as via fitting of frequency dependent loss and storage moduli master curve by a two-mode Maxwell model. It was found that λ is higher for LCB-PP in comparison with L-PP and the Cross model gives a meaningful relaxation time while the Carreau-Yasuda model does not despite giving a better numerical fit. Extensional rheology was assessed by the strain rate dependent uniaxial extensional viscosity (estimated from the entrance pressure drop using the Gibson method). The infinite shear to zero-shear shear viscosity ratio η∞/η0 (obtained directly from the shear viscosity data measured in a very wide shear rate range) was shown to be proportional to the maximum normalized extensional viscosity at very high extensional strain rates, ηE,∞/(3η0). η∞/η0 was related to temperature and basic molecular characteristics of given polymers via simple equation. It was observed that extensional viscosity for both samples first decreases with increased extensional strain rate to its minimum value at 200 000–400 000 1/s and then increases to plateau value, ηE,∞ (corresponding to the maximum chain stretch) at about 2 ⋅ 106 1/s. At low deformation rates, extensional viscosity is higher for LCB-PP in comparison with L-PP, but the trend is switched at very high deformation rates; ηE,∞ (and also ηE,∞/3η0) becomes lower for LCB-PP in comparison with L-PP. These results suggest that high stability of LCB-PP blend can be explained by its higher stretchability at very high deformation rates (occurring at the die exit where an intensive fiber attenuation takes the place) and its lower stretchability at medium and low deformation rates, at which melt/air inertia driven bending instability called whipping occurs.

Experimental characterisation of fatigue damage in foamed bitumen stabilised materials using dissipated energy approach

Abstract Foamed bitumen stabilisation (FBS) of degraded pavements has become popular in recent times. Although the common failure mechanism of FBS materials under repeated heavy traffic loads has been identified as bottom-up fatigue cracking, further research is required to better model their performance characteristics. In this study, the four-point bending test was performed under both stress-controlled and strain-controlled modes to characterise the flexural fatigue performance of FBS beams. The dissipated energy (DE) approach was adopted to describe the flexural fatigue behaviour of FBS materials. This paper presents the issues in conventional DE calculation methods and suggests new empirical equations to more accurately determine the DE, the ratio of DE change, the plateau value and the cumulative dissipated energy (CDE) of FBS materials. The analysis of experimental results revealed that the CDE and the number of load cycles to the final flexural fatigue rupture of FBS beams are highly correlated.

The role of stress softening in crack propagation of filler reinforced elastomers as evaluated by the J-Integral

A recently developed micromechanical model of stress softening and hysteresis of filled rubber is used to calculate the energy density- and stress distribution around the crack tip for a given displacement field, which is determined by digital image correlation. This allows for a quantitative evaluation of stress-softening influences on the J-Integral, J1. In addition, the gradients of stress, strain and energy close to the crack tip are evaluated and compared to predictions of purely elastic material behaviour. The J-Integral is determined for carbon black filled truck tire tread compounds based on natural rubber (NR) and phase separated blends of NR with butadiene rubber (BR) and/or styrene-butadiene rubber (SBR). Dependent on the compound used, J1 is found to decrease significantly with decreasing contour radius r, indicating that most of the energy flux into the crack tip is dissipated due to stress softening and is not available for crack growth. For larger distances r, when the energy field becomes isotropic, plateau values are obtained for the J-Integral, which coincide with global tearing energies calculated by simple thermodynamics.

Water chemistry, solution resistivity, and oxygen reduction reaction in simulated primary coolant of pressurized water reactors

AbstractThe effect of temperature (25 °C–300 °C) on the ohmic potential drop (ΔEΩ) and resistivity (Rsol) of a simulated primary coolant of the pressurized water reactors was investigated using electrochemical impedance spectroscopy (EIS) and galvanostatic potentiometry. The variations in the conductivity and pH of the solution showed that by increasing the temperature the magnitude of the Rsol and therefore ΔEΩ of the system first decreases rapidly (until ~150 °C) and then reaches a relatively stable plateau value. Increasing the pressure of the system decreased the magnitude of the Rsol in the oxygenated coolant. Investigation of the oxygen reduction reaction (ORR) on platinum (Pt), 316L stainless steel (SS), Alloy 690, and carbon steel revealed the great effect of water chemistry, in particular pH on the rate of the ORR on these materials. OH− adsorption on Pt reduced the rate of the ORR on this metal at temperatures higher than ~100 °C. Finally, it was found that higher H3O+ concentrations reduce the rate of the ORR on iron‐ and nickel‐based alloys, while increasing the OH− concentration at temperatures higher than ~150 °C accelerates the rate of the ORR on these alloys.

A Numerical Investigation on Tidally Induced Sediment Transport and Morphological Changes with Changing Sea Level in South-East England

The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale.

Transconductance Distribution in Program/Erase Cycling of NAND Flash Memory Devices: a Statistical Investigation

A new method for characterizing the evolution of oxide charge ( ${Q}_{T}$ ) generation during program/erase (P/E) cycles is developed. The concentration of ${Q}_{T}$ can be separated from the floating gate charge ( ${Q}_{\text {FG}}$ ) by statistically analyzing the distribution of transconductance reduction ( $\Delta {G}_{m,\text {max}}$ ) after P/E cycles. The effect of the number and position of discrete ${Q}_{T}$ on the distribution of $\Delta {G}_{m,\text {max}}$ is studied. The cycling dependence of the ${Q}_{T}$ generation is given by a fractional equation that includes a power of the number of P/E cycles in the denominator. For fewer than 30k cycles, the equation can be simplified as a power-law equation in the number of cycles with a power factor of 0.58. For more than 30k cycles, the ${Q}_{T}$ generation gradually goes to a plateau value ${Q}_{{0}} = {1.5}\times {10}^{{20}}$ cm−3. It is indicated that the ${Q}_{T}$ generation is limited by the concentration of inherent weak bonding points inside SiO2 or the Si/SiO2 interface. The temperature dependence of the ${Q}_{T}$ generation is also provided. The activation energy ( ${E}_{A}$ ) of the ${Q}_{T}$ generation is approximately 0.1 eV, which is compatible with the ${E}_{A}$ value of electron traps creation in SiO2.

The optimal incubation time for in vitro hemocompatibility testing: Assessment using polymer reference materials under pulsatile flow with physiological wall shear stress conditions.

During hemocompatibility testing, activation products may reach plateau values which can result in less distinction between hemocompatible and hemo‐incompatible materials. Of concern is an underestimation of the blood activation caused by the biomaterial of interest, which may result in a false assessment of hemocompatibility. To elucidate the optimal incubation time for in vitro hemocompatibility testing, we used the Haemobile circulation model with human whole blood. Blood from healthy volunteers was in vitro incubated under pulsatile flow with physiological wall shear stress conditions at 37°C for 30, 60, 120, or 240 min. Test loops containing low‐density polyethylene and polydimethylsiloxane served as low and high reference materials, that is, hemocompatible and hemo‐incompatible biomaterials, respectively. In addition, empty loops served as a negative reference. Thrombogenicity, platelet function, inflammatory response, coagulation, and hemolysis between references and incubation times were compared. We found that thrombogenicity and platelet function were significantly affected by both the duration of incubation and the type of material. In particular, thrombogenicity and platelet function assessments were affected by incubation time. We found that an exposure time of 60 min was sufficient, and for almost all variables an optimal incubation time to discriminate between the low and high reference material. © 2019 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2335–2342, 2019.

Evaluation of fatigue behavior of asphalt binders containing reclaimed asphalt binder using simplified viscoelastic continuum damage approach

Several fatigue damage analysis approaches have been introduced for asphalt binders and mixtures. In this study, using three modifiers including softer bitumen, a rejuvenator and waste polymer modified bitumen, fatigue behavior of RAB-containing binder mixes was evaluated based on the simplified viscoelastic continuum damage mechanics (S-VECD). In addition, correlations between the S-VECD parameters and the other fatigue failure criteria were investigated. For this purpose, the time sweep test was used to evaluate fatigue behavior of various asphalt binders in controlled-strain mode. Results showed that the rejuvenator and softer bitumen had the greatest effect in terms of prioritization on the improvement of the fatigue resistance of the RAB-containing binder mixes. Moreover, the results showed that good unique relationships between plateau value (PV) and Nf50 and between rate of change of total released pseudo strain energy (GR) and Nf50 were established in the RAB-containing binder mixes. Furthermore, there was a good relationship between the two concepts of the dissipated energy approach used for determination of the PV and the dissipated pseudo strain energy approach which used for calculation of the GR values.

Exhaled breath temperature as a tool for monitoring asthma control after an attack in children.

Exhaled breath temperature (EBT) has been suggested as a non-invasive marker of airway inflammation in asthma. There have been no studies examining longitudinal changes in EBT following asthma attacks. To investigate changes in EBT during and after an asthma attack and to relate these changes to changes in respiratory physiological measurements. We evaluated 38 hospitalized children aged 5-18 years diagnosed with an asthma attack. Spirometry was performed upon hospitalization. During hospitalization, EBT, peak expiratory flow rate (PEFR), and asthma score were measured daily. These tests were repeated 1 week and 1 month after discharge. The overall PEFR change, temporal changes in plateau values at the end of expiration, and time-dynamic associations were evaluated using linear mixed models. FEV1 was lower at admission than at discharge (63.3 ± 24 vs 99.5 ± 14 percent of predicted, P < 0.001). The EBT was higher at admission than at 1 week after discharge (34.1°C [range: 33.9-34.8°C] vs 33.6°C [range: 33.0-34.2°C], P = 0.007); overall, EBTs decreased over time (P = 0.007). Among individual subjects, decreased EBT was correlated with increased PEFR over time. Furthermore, plateau values at the end of expiration had a time-dependent, dynamic association with the PEFR during hospitalization (P = 0.005) and between asthma attack onset and asthma status stabilization (P = 0.032). The EBT was elevated during asthma attacks and gradually decreased until asthma was well controlled. The EBT may be a useful, non-invasive tool for monitoring asthma control in children.

Brownian dynamics investigation of the Boltzmann superposition principle for orthogonal superposition rheology

The most general linear equation describing the stress response at time t to a time-dependent shearing perturbation may be written as the integral over the past history t' of a time dependent relaxation modulus, depending on t - t', multiplied by the perturbing shear rate at time t'. This is in agreement with the Boltzmann superposition principle, which says that the stress response of a system to a time dependent shearing deformation may be written as the sum of responses to a sequence of step-strain perturbations in the past. In equilibrium rheology, the Boltzmann superposition principle gives rise to the equality of the shear relaxation modulus, obtained from oscillatory experiments, and the stress relaxation modulus measured after a step-strain perturbation. In this paper, we describe the results of Brownian dynamics simulations of a simple soft matter system showing that the same conclusion does not hold when the system is steadily sheared in a direction perpendicular to the probing flows, and with a gradient parallel to that of the probing deformations, as in orthogonal superposition rheology. In fact, we find that the oscillatory relaxation modulus differs from the step-strain modulus even for the smallest orthogonal shear flows that we could simulate. We do find, however, that the initial or plateau levels of both methods agree and provide an equation relating the plateau value to the perturbation of the pair-function.

Microgels as viscosity modifiers influence lubrication performance of continuum.

Biocompatible microgels have been demonstrated to act as excellent lubricants, however, the influence of the continuum on their overall mechanical performance has been neglected so far. In this work, the mechanical performance of colloidal whey protein microgels (hydrodynamic diameter ∼100 nm measured using dynamic light scattering and atomic force microscopy) of different rigidity dispersed in Newtonian (buffer and corn syrup) or complex non-Newtonian fluids (xanthan gum) is investigated for the first time via rheology and soft tribology. Dispersions of both soft microgels (G' ∼ 100.0 Pa) and hard microgels (G' ∼ 10.0 kPa) were observed to act as thickeners in buffer as well as in low viscosity corn syrup and correspondingly reduced the friction, latter decreased as a function of the increased rigidity of the microgels. Differently, in high viscosity continuum, the microgels acted as thinning agents and increased the friction. In the lubrication limit, microgels in buffer or corn syrup behaved as Newtonian fluids with effective viscosity corresponding to their second Newtonian plateau value (η∞). However, the lubrication performance of the microgels dispersed in the complex fluid (xanthan gum) could not be described quantitatively by η∞. For the low viscosity xanthan gum, the microgels had no influence on friction. Nevertheless, for the high viscosity counterparts, the soft microgels acted as thinning agents whilst the hard microgels accelerated the onset of elastohydrodynamic regime. This study demonstrates that microgels act as viscosity modifiers directly influencing the tribological performance, depending upon a subtle interplay of rheological properties of the particles and continuum.

Internal Energy Distribution of Secondary Ions Under Argon and Bismuth Cluster Bombardments: "Soft" Versus "Hard" Desorption-Ionization Process.

The emission/ionization process under massive argon cluster bombardment was investigated by measuring the internal energy distributions of a series of benzylpyridinium ions. Argon clusters with kinetic energies between 10 and 20keV and cluster sizes ranging from 500 to 10,000 were used to establish the influence of their size, energy, and velocity on the internal energy distribution of the secondary ions. It is shown that the internal energy distribution of secondary ions principally depends on the energy per atom or the velocity of the cluster ion beam (E/n ∝ v2). Under low energy per atom (E/n˂10eV), the mean internal energy and fragmentation yield increase rapidly with the incident energy of individual constituents. Beyond 10eV/atom impact (up to 40eV/atom), the internal energy reaches a plateau and remains constant. Results were compared with those generated from bismuth cluster impacts for which the mean internal energies correspond well to the plateau values for argon clusters. However, a significant difference was found between argon and bismuth clusters concerning the damage or disappearance cross section. A 20 times smaller disappearance cross section was measured under 20keV Ar2000+ impact compared to 25keV Bi5+ bombardment, thus quantitatively showing the low damage effect of large argon clusters for almost the same molecular ion yield. Graphical Abstract ᅟ.

Nature of Asphaltene Aggregates

The size and fractal dimension of asphaltene aggregates were investigated for two Western Canadian bitumens diluted with n-heptane at concentrations above the onset of precipitation. Asphaltene aggregate size distributions were measured over time using focused beam reflectance and micrographic methods in a series of batch experiments at different n-heptane contents and shear rates. The fractal dimensions of the aggregates were determined from the volume of the settled aggregates. The asphaltenes formed approximately log-normal size distributions with volume mean diameters of tens to hundreds of micrometers, depending mainly upon the n-heptane content. The distributions were established in less time than the first measurement could be obtained (about 30 s) and changed relatively little afterward. The average aggregate size increased with an increasing n-heptane content but reached a plateau value at 70–80 wt % n-heptane. The fractal dimension reached a maximum at a similar n-heptane content. Micrographic i...

Modelling of rheological and chemical properties of asphalt binder considering SARA fraction

Modelling the rheological properties and chemical characteristics of asphalt material has been a hotspot. In this study, 20/40 and 60/80 pen grade asphalt binders named binder A and binder B were used to blend eleven binder samples. After that, a novel column chromatography was applied to collect sufficient SARA (Saturates, Aromatics, Resins and Asphaltenes). The Dynamic Shear Rheometer (DSR) test was used to develop the viscoelastic master curves for binders and their subsets. The Fourier Transform Infrared Spectroscopy (FTIR) test was conducted to identify and semi-quantitatively analyze the notable functional groups. Linear combination models were conducted between rheological model parameters and chemical components. It was found that the contents of Asphaltenes and Saturates increased, while those of Resins and Aromatics decreaed with the addition of binder A, resulting in the increased colloidal instability index (CII) values. In addition, the Saturates had constant value of phase angle, while the phase angle master curves of Aromatics and Resins showed plateau values of 80°. Resins containing more aromatic structures had a lower frequency (high temperature) value at this plateau value. Furthermore, the main findings were that ICC and ICH of Aromatics as well as ICH and ISO of Resins had significant relationships with binder A content. Statistically, several parameters such as CResins, CAsphaltenes, CII, ICC of Aromatics, ICH of Aromatics, ICH of Resins, and ISO of Resins had significant effects to develop multiple linear regression model on asphalt rheological properties.

Micellization of a weakly charged surfactant in aqueous salt solution: Self-consistent field theory and experiments

Self-consistent field (SCF) calculations and light scattering experiments were performed to study the pH and salt response of micelles composed of surfactants with a single weak acid group in aqueous salt solution. To this end, the common surfactant Brij 35 was oxidized to yield a polyoxyethylene alkyl ether carboxylic acid with a single terminal weakly charged carboxylic acid group in alkaline media. At low pH values, the micellar hydrodynamic radii (Rh) are independent of the salt concentration. By contrast, at pH values around the acid dissociation constant (pH ≈ pKa ± 1), the micellar radius decreases upon increasing pH until a salt-dependent plateau value is reached. The reduction in micellar size is more pronounced for lower salt concentrations. The SCF computations are in qualitative agreement with the experimental results and further reveal a limiting value for Rh corresponding approximately to the Debye length λD. Self-assembly into micelles is suppressed for low salt concentrations that would yield Rh < λD. Instead, the surfactants remain as unimers in solution. The results are summarized in a state diagram displaying the preferred surfactant configuration in solution as a function of Rh/λD, pH and salt concentration.

New insights into the adsorption behavior and mechanism of alginic acid onto struvite crystals

Struvite crystallization is one of the most promising routes for phosphorus recovery from phosphorus-rich sludge. However, the adsorption of alginic acid, a surrogate of extracellular polymeric substances in phosphorus-rich sludge, on struvite crystals has been proved to significantly inhibit struvite crystallization. To comprehensively understand the inhibitory mechanism, the adsorption behavior was evaluated at various adsorption time, the concentration of alginic acid, pH and ionic strength in the present study. Subsequently, adsorption equilibrium isotherm, kinetic and thermodynamics models were employed to fit the adsorption data. Interestingly, the adsorption mechanism was explored by X-ray photoelectron spectra (XPS) and Fourier transform infrared spectroscopy analysis (FTIR), which was further elucidated by triple-layer model (TLM). The results indicated that the adsorption capacity of struvite crystals almost reached a plateau value within the first 30 min. Meanwhile, the adsorption capacity was significantly reduced with increasing pH, but slightly increased with increasing ionic strength. Moreover, the adsorption process obeyed pseudo-second order kinetic model and Langmuir adsorption isotherm model, whereas intra-particle diffusion was a main rate-limited step. Furthermore, hydrogen bonding and surface complexation between alginic acid and struvite crystals dominated the adsorption mechanism. Additionally, alginic acid underwent surface reactions by virtue of two outer-sphere surface complexes and one inner-sphere surface complex. The findings presented herein will facilitate understanding of the inhibitory mechanism of organic matters on struvite crystallization from phosphorus-rich sludge.

Neutral pion and η meson production at midrapidity in Pb-Pb collisions at sNN=2.76 TeV

Neutral pion and η meson production in the transverse momentum range 1 <pT< 20 GeV/c have been measured at midrapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semicentral Pb-Pb collisions at sNN = 2.76 TeV. These results were obtained using the photon conversion method as well as the Photon Spectrometer (PHOS) and Electromagnetic Calorimeter detectors. The results extend the upper pT reach of the previous ALICE π0 measurements from 12 to 20 GeV/c and present the first measurement of η meson production in heavy-ion collisions at the LHC. The η/π0 ratio is similar for the two centralities and reaches at high pT a plateau value of 0.457 ± 0.013stat ± 0.018syst. A suppression of similar magnitude for π0 and η meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of Next to Leading Order (NLO) pQCD predictions and hydrodynamic models. The measurements show a stronger suppression than observed at lower center-of-mass energies in the pT range 6 <pT< 10 GeV/c. For pT< 3 GeV/c, hadronization models describe the π0 results while for the η some tension is observed.1 MoreReceived 21 March 2018DOI:https://doi.org/10.1103/PhysRevC.98.044901Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.©2018 CERN, for the ALICE CollaborationPhysics Subject Headings (PhySH)Research AreasNuclear reactionsRelativistic heavy-ion collisionsNuclear Physics

2D PIC-MCC simulations of magnetron plasma in HiPIMS regime with external circuit

2D particle simulations of plasma evolution in high power impulse magnetron sputtering (HiPIMS) are very scarce. Short HiPIMS unipolar pulses ( plateau at constant ) are applied on a planar magnetron cathode with a metal target operated in pure argon at . The model begins with a pre-ionised gas before the pulse, defined as a typical direct current (DC) discharge (). Applying the voltage pulse leads to a sharp increase in the current. The external circuit is reduced to a simple resistance connected in series with the discharge. Both the discharge and the resistance are fed by the HiPIMS power supply. HiPIMS voltage and current evolution during the pulse and the near afterglow are self-consistently obtained from the particle-in-cell Monte Carlo collision (PIC-MCC) simulation. Results for three values of the external resistance (, and ) show that, at least for this range, the pulse current plateau value is inversely proportional to the resistance, exceeding for the lowest resistance for target diameter. Comparison with experiment shows that by reducing the external resistance to the pulse current exceeds , in agreement with the discharge voltage and current waveforms found in the model. The microscopic PIC-MCC approach gives access to a set of plasma parameters, some of which, close to the target, have never been explored before. Generally, the voltage drop across the ionisation region (IR) is found to be higher than the voltage in the cathode sheath (CS), in line with the prediction of the ionisation region model (IRM), emphasising the importance of Ohmic heating in HiPIMS. Additionally, the model shows that a transitory double layer separates the IR from the CS, as is also seen with probe measurements. The ambipolar diffusion feeds the diffusion region volume with a plasma density which is typically one order of magnitude below the average density in the IR that exceeds for the external resistance. The electron energy distribution function is composed of at least two Maxwell distributions during the pulse. The temperatures of different electron populations relax along the pulse plateau and tend to approximately the same value. The electron temperature is highest during the sharp increase in current, characterised by a peak in the electron density at this instant, even though the current is far below its plateau value. This increase in density is consistent with experimental findings by optical emission spectroscopy. The ions bombarding the target are spread out on a larger race track compared to the DC case and the typical average ion energy is approximately half of the cathode–anode voltage, due to the voltage drop being split between the CS and the IR. The evolution of the plasma parameters and the effect of the power are also discussed.

Expanding the application of the van Gurp-Palmen plot: New insights into polymer melt rheology

We report on an extension of the van Gurp-Palmen (vGP) plot [van Gurp, M. and Palmen, J., Rheology Bulletin, 1998, 67(1), 5–8.] developed through a compilation of literature data for polymer melts with different topological structures: linear (pure and blend), ring, comb, and bottlebrush. We introduce a new parameter: the reciprocal of complex modulus at the first minimum moving from the terminal regime (1/Gδmin,1∗) and compare it with the steady-state recoverable compliance Js. Results show that 1/Gδmin,1∗ and Js while related to each other in that they follow similar dependences on the molecular weight (linear and bottlebrush polymers), weight fraction of high molecular weight content (linear blends), and backbone concentration (comb polymer), there are also differences. For example, in the unentangled regime both Js and 1/Gδmin,1∗ increase with increasing molecular weight but reach different plateau values as entanglement coupling sets in. In the case of ring polymers, the molecular weight dependences of 1/Gδmin,1∗(∼Mw1) and Js(∼Mw2) show very different scaling with molecular weight and do not reach a plateau value even for molecular weights as high as approximately 15 times the entanglement molecular weight of the linear counterpart. Furthermore, examination of the impact of linear additives on the vGP plots of the rings potentially provides a new way to assess their freedom from linear contamination. Also, because 1/Gδmin,1∗ occurs in the frequency regime above that of the terminal regime and Js requires either very good estimates of terminal behavior in dynamic measurements or direct determination from creep and recovery measurements, 1/Gδmin,1∗ is easier to obtain. The work shows that detailed analysis of the van Gurp-Palmen plot has the potential to provide new insights into the rheological response of polymer melts over what is obtained conventionally from viscoelastic characterization methods.

Simple and Reliable Method for Studying the Adsorption Behavior of Aquivion Ionomers on Carbon Black Surfaces.

A better understanding of the interactions of carbon black and perfluorinated sulfonic acid (PFSA) ionomer helps to improve the effectiveness of polymer electrolyte membrane fuel cells. We present a simple and fast method for quantitative PFSA ionomer analysis based on suspension density measurements. After validation of the reliability of our method by thermogravimetric analysis and isothermal titration calorimetry (ITC), we investigate the adsorption equilibrium of short-side-chain PFSA ionomers of different equivalent weights (EW) and polarities on carbon black. The measured adsorption isotherms exhibit a plateau in the ionomer surface concentration for ionomer equilibrium concentrations ≤2 g/L. In this concentration range, the adsorption isotherms are described by the Langmuir model, whereby the surface concentrations in the plateau region are between 0.041 and 0.070 g/g. The plateau value of the ionomer surface concentration increases with EW and therefore with decreasing number of side chains with terminal sulfonic acid group per ionomer molecule, while the amount of adsorbed sulfonic acid groups remains constant for all investigated ionomers, resulting in similar ζ-potentials and sedimentation stability of the suspensions. The free energies of adsorption Δ G calculated from the association constants of the adsorption isotherms agree well with Δ G values obtained by isothermal titration calorimetry (ITC) and thus validate the adsorption isotherm measurement method. From the values of adsorption enthalpy Δ H ((-7.3 ± 0.8) kJ/mol) and entropy Δ S (ca. 100 J/(mol K)), which were extracted from ITC, we conclude that the ionomer adsorption on carbon black is a spontaneous physisorption process.