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The knowledge of the thermo-mechanical response of polymers during crystallization is of seminal importance for process control and modeling. Among the other subtle findings, the crystallinity-rheological simplicity, resembling the thermo-rheological one, was frequently reported, based on the observation that the same amount of crystallinity induces the same rheological hardening to the polymer, regardless the crystallization conditions. The crystallization kinetics, which is a fundamental issue in polymer science, is investigated with differential scanning calorimetry (DSC) measurements. However, the poor agreement of calorimetric data with data coming from rheological investigation remains a debated issue. The crystallization kinetics of a commercial poly-ethylene-vinyl-acetate copolymer (EVA) is here investigated both with DSC and rheological measurements. EVA is a nice model system since its melting point is below 100[degrees]C, thus allowing avoiding all the experimental shortcomings related to thermal degradation. We show that DSC and rheological crystallization data satisfactorily agree for the investigated copolymer and thus we conclude that all the discrepancies found in the literature must be principally due to experimental artifacts. Moreover, the observed agreement between DSC and rheological data confirms that the rheological hardening is proportional to the volume of crystallites only and not to the modality in which the crystallization takes place., INTRODUCTION The process technologies of semi-crystalline polymers require a deep understanding of crystallization kinetics that dominate the quality and the performances of the final products. Depending on the processing techniques [...]

Ethylene vinyl acetate (EVA) is a random copolymer of ethylene and varying amounts of vinyl acetate that interfere with poly-ethylene chain packing reducing crystallinity, thus improving transparency and lowering the melting temperature to 40[degrees]C-60[degrees]C. The material viscoelastic properties in its working conditions may thus depend on the crystallinity degree. The crystallization process is here rheologically studied in non-isothermal conditions and the frequency spectra are measured at different temperatures to investigate the viscoelasticity of EVA. Coupling the crystallization kinetics and the viscoelastic spectra at different temperatures, that is, at different degree of crystallinity, we here determine two independent shift factors, one for the timecrystallinity shift, the other for the time-temperature shift, so to propose a new time-temperature-crystallinitysuperposition to reconcile all the data on a single master curve. In this way, the experimentally observable frequency range has been widened significantly so to detect all the relaxation times of the material from the shortest to the largest ones., INTRODUCTION In polymer processing, like injection molding, fiber spinning, film casting, and so on, a forming step of the melt is followed by solidification due to cooling. This implies that [...]

Wettability, typically estimated through the contact angle, is a fundamental property of surfaces with wide-ranging implications in both daily life and industrial processes. Recent scientific interest has been paid to the surfaces exhibiting extreme wettability: superhydrophobic and superhydrophilic surfaces, characterized by high water repellency and exceptional water wetting, respectively. Both chemical composition and morphology play a role in the determination of the wettability "performance" of a surface. To tune surface-wetting properties, we considered coatings of carbon nanoparticles (CNPs) in this study. They are a new class of nanomaterials synthesized in flames whose chemistry, dimension, and shape depend on combustion conditions. For the first time, we systematically studied the wettability of CNP coatings produced in a controlled rich ethylene/air flame stabilized over a McKenna burner. A selected substrate was intermittently inserted in the flame at 15 mm above the burner to form a thin coating thanks to a thermophoretic-driven deposition mechanism. The chemical-physical quality and the deposed quantity of the CNPs were varied by opportunely combing the substrate flame insertion number (from 1 to 256) and the carbon-to-oxygen ratio, C/O (from 0.67 to 0.87). The wettability of the coatings was evaluated by measuring the contact angle, CA, with the sessile drop method. When the C/O = 0.67, the CNPs were nearly spherical, smaller than 8 nm, and always generated hydrophilic coatings (CA < 35°). At higher C/O ratios, the CNPs reached dimensions of 100 nm, and fractal shape aggregates were formed. In this case, either hydrophilic (CA < 76°) or superhydrophobic (CA ~166°) behavior was observed, depending on the number of carbon nanoparticles deposed, i.e., film thickness. It is known that wettability is susceptible to liquid surface tension, and therefore, tests were conducted with different fluids to establish a correlation between the flame conditions and the nanostructure of the film. This method offers a fast and simple approach to determining mesoscale information for coating roughness and topographical homogeneity/inhomogeneity of their surfaces. [ABSTRACT FROM AUTHOR]

We study the shear rheological behavior of a commercial stereolithography paste containing ≈ 50 vol. % of zirconia particles (diameter ≈ 100 nm) with the aim to clarify physical mechanisms occurring during the "scraping" step of this yield stress fluid. Beyond a flow curve characterized by a high zero-shear viscosity accompanied with an overall shear-thinning behavior, we investigate in a systematic way the transient regime through start-up experiments. We demonstrate that a structural transition occurs between 10 − 2 and 10−1 s−1, resulting in an apparent interruption of the shear-thinning. The corresponding transient response presents a pronounced extra-growth of the shear stress before to stabilize at high strain amplitude and a negative first normal stress difference peak, both effects become stronger at higher shear rates. These observations are rationalized based on the high interparticle friction owing to the polyhedral shape and the roughness of the particles. In addition, relaxation tests following the start-up experiments reveal that the samples submitted to shear rates higher than 10−1 s−1 cannot relax the shear stress to the same level as in low shear rate experiments, suggesting a durable structural modification likely to impact the quality of the parts prior to their debinding and densification. Finally, we utilize orthogonal superposition rheology to illustrate how the application of an oscillatory deformation during the scraping procedure could help to reduce the shear-thinning interruption and improve the stereolithography processing as already observed empirically during scraping. [ABSTRACT FROM AUTHOR]

A soil depleted of its organic carbon content is typically destabilized, i.e., its capacity to maintain its microstructure intact under various stress conditions weakens, and consequently, landslides and mudflows can be triggered and propagated more easily. In a previous work, we showed with a rheological analysis that the removal of the sole water-soluble organic carbon "destabilized" the slurry very similarly to what occurs with the removal of the vast majority of soil organic carbon. In principle, the water-soluble organic carbon can be dissolved by rainfall, during which water can infiltrate the soil, eventually leaving it either by percolation or evaporation. These two processes are mimicked here with two different soil water wetting procedures. The stability of the treated (wetted) soils is studied with rheological and granulometric experiments. The former run on concentrated suspensions, while the latter run on very diluted ones. Despite this, the results agreed very well, indicating that the two wetting procedures induce the same destabilization of the soil which behaves as the one depleted by the whole water-soluble organic carbon. Our results concluded that a soil destabilized by a wetting procedure, i.e., by a rainfall event, will be more prone to trigger a landslide that will propagate more swiftly and will stop with more difficulties. [ABSTRACT FROM AUTHOR]

Hydroxypropyl methylcellulose (HPMC) is a polymer made of a cellulose backbone with etherified methoxy and hydroxypropyl substitutions that undergoes a reversible inverse thermo‐gelation upon heating. The thermo‐gelation follows a two‐step mechanism: first, phase separation occurs, then fibrils, formed in the polymer‐rich phase, entangle to form the three‐dimensional gel network. This work aims at understanding the influence of degree (DS) and molar substitution (MS) on the thermo‐gelation process. DS is the number of methyl groups, and the MS is the hydroxypropyl content per anhydroglucose unit. The thermo‐gelation process is here rheologically investigated for two HPMC samples, which have similar molecular weight but different MS and DS: thermal ramps are coupled with time sweep tests at selected temperatures and with frequency sweep experiments. Results show an important effect not only on the transition temperatures (beginning of the phase separation, beginning of the gelation) but also on the kinetics of the different phases of the process. [ABSTRACT FROM AUTHOR]

A non-Brownian, inertialess, dense suspension of rigid hollow glass spheres is studied with time sweep oscillatory experiments. The measured apparent complex viscosity is shown to depend on the amplitude of the applied strain, in agreement with the literature, and, unexpectedly, also on the angular frequency. Two different regimes are individuated depending on the applied strain. For values smaller than 1, when the structure evolution is driven by the shear-induced diffusion, the complex viscosity depends on the frequency, for values larger than 1, it is rate independent. In the first regime, the dependence on the applied strain amplitude and the angular frequency can be lumped into a single parameter: The maximum shear rate, the applied strain amplitude times the angular frequency. The results obtained are quite surprising since in a non-Brownian, inertialess, dense suspension, the particle interactions do not have a characteristic time scale and, consequently, the governing equations of motion result rate independent. Only the presence of a nonhydrodynamic force can introduce a characteristic time. We observe that this nonhydrodynamic force must be so small to be neglected in simple shear, since the behavior of the investigated suspension in the steady shear flow is found to be rate independent, and it must show its effects only in oscillatory experiments with strain amplitude smaller than 1. The frequency dependence is also observed with two less concentrated suspensions and all the data collapse on a single master curve, proving that the physics underneath the rate dependence is independent of the concentration. [ABSTRACT FROM AUTHOR]

This paper describes and discusses experimental results on the absorption of sulphur dioxide in electrified water sprays, either when the polluted gas is treated as is or when the gas is exposed to a corona source to ionize the sulphur dioxide. The experiments revealed that an electrified spray with a charge‐to‐mass ratio of 50 μC · kg−1 enabled the absorption rate of droplets to double, regardless of their polarities. Corona charging gave rise to an increase in the SO2 depletion rate over the scrubber wall, while negligible effects appeared on the actual droplets absorption rate. These findings suggested that faster absorption rates mostly, though not uniquely, depend on the modifications on the morphological and interfacial properties of the sprayed droplets induced by the free electric charge imposed on their surface. Conversely, the absorption rates were negligibly affected by the electrical interactions between droplets (either charged or uncharged) and the sulphur dioxide ions/radicals originating from the corona source. [ABSTRACT FROM AUTHOR]