Importance of the morphology and structure of the primary aggregates for the dispersibility of carbon nanotubes in polymer melts

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Some aspects of the liquid water thermodynamic behavior: From the stable to the deep supercooled regime

Liquid water is considered to be a peculiar example of glass forming materials because of the possibility of giving rise to amorphous phases with different densities and of the thermodynamic anomalies that characterize its supercooled liquid phase. In the present work, literature data on the density of bulk liquid water are analyzed in a wide temperature-pressure range, also including the glass phases. A careful data analysis, which was performed on different density isobars, made in terms of thermodynamic response functions, like the thermal expansion αP and the specific heat differences CP − CV, proves, exclusively from the experimental data, the thermodynamic consistence of the liquid-liquid transition hypothesis. The study confirms that supercooled bulk water is a mixture of two liquid “phases”, namely the high density (HDL) and the low density (LDL) liquids that characterize different regions of the water phase diagram. Furthermore, the CP − CV isobars behaviors clearly support the existence of both a liquid–liquid transition and of a liquid–liquid critical point

Dispersing hydrophilic nanoparticles in hydrophobic polymers: HDPE/ZnO nanocomposites by a novel template-based approach

The efficiency of a novel template-based approach for the dispersion of hydrophilic nanoparticles within hydrophobic polymer matrices is investigated. The procedure envisages the permeation of a well dispersed nanoparticle suspension inside a micro-porous matrix, obtained through selective extraction of a sacrificial phase from a finely interpenetrated co-continuous polymer blend. Specifically, a blend of high density polyethylene (HDPE) and polyethylene oxide (PEO) at 50/50 wt% is prepared by melt mixing. The addition of small amounts of organo-clay promotes the necessary refinement of the blend morphology. Once removed the PEO, the micro-porous HDPE matrix is dipped in a colloidal suspension of zinc oxide nanoparticles which exhibits low interfacial tension with HDPE. A system prepared by traditional melt mixing is used as reference. Melt- and solid-state viscoelastic measurements reveal a good quality of the filler dispersion despite the uneven distribution on micro-scale. The latter can be capitalized to minimize the filler content to attain a certain improvement of the material properties or to design nano-structured polymer composites. © BME-PT

Tailoring chitosan/lta zeolite hybrid aerogels for anionic and cationic dye adsorption

Chitosan (CS) is largely employed in environmental applications as an adsorbent of anionic dyes, due to the presence in its chemical structure of amine groups that, if protonated, act as adsorbing sites for negatively charged molecules. Efficient adsorption of both cationic and anionic dyes is thus not achievable with a pristine chitosan adsorbent, but it requires the combination of two or more components. Here, we show that simultaneous adsorption of cationic and anionic dyes can be obtained by embedding Linde Type A (LTA) zeolite particles in a crosslinked CS‐based aerogel. In order to optimize dye removal ability of the hybrid aerogel, we target the crosslinker concentration so that crosslinking is mainly activated during the thermal treatment after the fast freezing of the CS/LTA mixture. The adsorption of isotherms is obtained for different CS/LTA weight ratios and for different types of anionic and cationic dyes. Irrespective of the formulation, the Langmuir model was found to accurately describe the adsorption isotherms. The optimal tradeoff in the adsorption behavior was obtained with the CS/LTA aerogel (1:1 weight ratio), for which the maximum uptake of indigo carmine (anionic dye) and rhodamine 6G (cationic dye) is 103 and 43 mg g−1, respectively. The behavior observed for the adsorption capacity and energy cannot be rationalized as a pure superposition of the two components, but suggests that reciprocal steric effects, chemical heterogeneity, and molecular interactions between CS and LTA zeolite particles play an important role

Reconstructing Native American Population History

The peopling of the Americas has been the subject of extensive genetic, archaeological and linguistic research; however, central questions remain unresolved1–5. One contentious issue is whether the settlement occurred via a single6–8 or multiple streams of migration from Siberia9–15. The pattern of dispersals within the Americas is also poorly understood. To address these questions at higher resolution than was previously possible, we assembled data from 52 Native American and 17 Siberian groups genotyped at 364,470 single nucleotide polymorphisms. We show that Native Americans descend from at least three streams of Asian gene flow. Most descend entirely from a single ancestral population that we call “First American”. However, speakers of Eskimo-Aleut languages from the Arctic inherit almost half their ancestry from a second stream of Asian gene flow, and the Na-Dene-speaking Chipewyan from Canada inherit roughly one-tenth of their ancestry from a third stream. We show that the initial peopling followed a southward expansion facilitated by the coast, with sequential population splits and little gene flow after divergence, especially in South America. A major exception is in Chibchan-speakers on both sides of the Panama Isthmus, who have ancestry from both North and South America

Recent Trends in Waterborne and Bio-Based Polyurethane Coatings for Corrosion Protection

Polyurethanes (PUs) have been extensively exploited for the production of protective coatings thanks to the versatility of their chemistry, which allows to adjust the coating properties depending on the final application. In the last decade, the concerns on the negative impact on the environment and human health of traditional petroleum-based and solvent-borne PUs have fostered the research on more environmentally friendly alternatives. This review article provides an overview of the recent approaches that have been profitably pursued for the development of green PUs coatings for the protection of metal surfaces from corrosion. In particular, waterborne and bio-based polyurethane coatings are addressed, highlighting the main strategies adopted to enhance their anticorrosion ability. Finally, relevant data on the protective performances of green PU coatings are collected and critically discussed

Linear Viscoelasticity of Polymer-Graphite Nanoplatelets(GNPs) Nanocomposites

We prepare well dispersed nanocomposites based on Graphite Nanoplatelets (GNPs) and polystyrene (PS) through a combination of solution and melt mixing techniques. The samples are subjected to morphological, electrical, and rheological investigations. Electron microscopy analyses show that GNPs are well dispersed, and the presence of few nanometers thick GNPs is noticed. The electrical conductivity of the polymer dramatically increases at a critical content of particles of Φ~4 wt.%, indicating that electrical percolation has occurred. The existence of a percolating network induces a marked elastic connotation in the melt state. We show that the elasticity of GNP networks in samples at different composition can be scaled on a single master curve. This allows for the accurate estimation of the rheological percolation threshold. In addition, using the master curve we can infer the elasticity of GNP networks which are too tenuous to be appreciated via conventional rheological measurements

Elasticity and structure of weak graphite nanoplatelet (GNP) networks in polymer matrices through viscoelastic analyses

The elasticity and structure of graphite nanoplatelets networks in polymer matrices are studied through linear viscoelastic analyses. GNPs-filled polystyrene nanocomposites at different filler content are prepared through a combination of solution and melt mixing techniques. Electrical volume conductivity experiments prove that a continuous path of conductive nanoplatelets builds up across the matrix above a critical filler content. GNP networks, however, are too tenuous to be detected through conventional dynamic-mechanical spectroscopy in the melt state. Nevertheless, we are able to estimate their elasticity by exploiting the predictive feature of a simple two-phase rheological model. Our approach, validated through the building of a master curve of the elastic modulus of samples at different composition, allows to isolate the elastic contribution of the bare GNP network, whose dynamics reveal that its elasticity follows critical behaviour as predicted by percolation theory

Tuning the Morphology of HDPE/PP/PET Ternary Blends by Nanoparticles: A Simple Way to Improve the Performance of Mixed Recycled Plastics

Due to a very low mixing entropy, most of the polymer pairs are immiscible. As a result, mixing polymers of different natures in a typical mechanical recycling process leads to materials with multiple interfaces and scarce interfacial adhesion and, consequently, with unacceptably low mechanical properties. Adding nanoparticles to multiphase polymeric matrices represents a viable route to mitigate this drawback of recycled plastics. Here, we use low amounts of organo-modified clay (Cloisite® 15A) to improve the performance of a ternary blend made of high-density polyethylene (HDPE), polypropylene (PP), and polyethylene terephtalate (PET). Rather than looking for the inherent reinforcing action of the nanofiller, this goal is pursued by using nanoparticles as a clever means to manipulate the micro-scale arrangement of the polymer phases. Starting from theoretical calculations, we obtained a radical change in the blend microstructure upon the addition of only 2-wt.% of nanoclay, with the obtaining of a finer morphology with an intimate interpenetration of the polymeric phases. Rather than on flexural and impact properties, this microstructure, deliberately promoted by nanoparticles, led to a substantial increase (>50 °C) of a softening temperature conventionally defined from dynamic-mechanical measurements

Mechanically coherent zeolite 13X/chitosan aerogel beads for effective CO2capture

The constant increase of CO2 concentration in the atmosphere is recognized worldwide to severely impact the environment and human health. Zeolites possess a high adsorption capacity for CO2 removal, but their powdery form prevents their use in many practical applications. When binding agents are used, a partial occlusion of the porosity can severely compromise the adsorption capacity. In this regard, a great challenge is producing compact composite adsorbents while maintaining a high specific surface area to preserve the pristine performance of zeolites. Here, this goal was achieved by preparing beads with a high content of zeolite 13X (up to 90 wt %) using a chitosan aerogel as the binding agent. A facile preparation procedure based on the freeze-drying of hydrogel beads obtained by phase inversion led to a peculiar microstructure in which a very fine polymeric framework firmly embeds the zeolite particles, providing mechanical coherence and strength (compressive strain >40% without bead fragmentation, deformation <20% under 1 kgf-load) and yet preserving the powder porosity. This allowed us to fully exploit the potential of the constituents, reaching a high specific surface area (561 m2 g-1) and excellent CO2 uptake capacity (4.23 mmol g-1) for the sample at 90% zeolite. The beads can also be reused after being fully regenerated by means of a pressure swing protocol at room temperature