Poly(vinylidene fluoride) (PVDF) is a strongly anisotropic electroactive polymer whose piezoelectric and fer roelectric properties comes from the way dipoles align cooperatively in the polar /i and y crystalline phases. However, producing these phases and controlling their orientation to favor a texturation during melt processing is still a challenge. This study demonstrates a combined approach using a quaternary ammonium-modified mont morillonite (Dellite (R) 67 G) and high-temperature electrical poling to promote PVDF phase selection and induce microstructural texturation. PVDF nanocomposites containing 0.5-10 wt.% clay were prepared via twin-screw extrusion, ensuring repro ducible dispersion. Differential scanning calorimetry and polarized optical microscopy show that the organoclay enhances nucleation, helping PVDF to crystallize faster. That heterogeneous crystallization increases the crystal lization temperature by up to 15 degrees C. WAXD and FTIR analyses reveal that the clay stimulates the formation of polar y and /i phases even at low loadings. A main objective of this work is to investigate the synergy between clay-induced nucleation and electric-field-induced chain and dipole alignment. Contact poling at 160 degrees C maximizes this coupling, yielding 92 % electroactive phase content in the nanocomposite, compared with 85 % in neat PVDF. This enhancement is attributed to ion-dipole interactions at the clay interfaces and the way the electric field drives PVDF chains into aligned conformations. Overall, this study provides a reproducible melt-processing route that allows control over PVDF's crys talline phase by exploiting the combined action of nanofillers and electrical poling at elevated temperatures. This approach establishes a foundation for the scalable production of highly anisotropic, high-performance electroactive materials for sensing, energy harvesting, and actuation applications.

In this article, we contrast laser ablation propulsion with photon pressure propulsion. LAP must use repetitive short pulses (~100 ps) for best performance, while PPP requires GW-level continuous (CW) lasers and a lightsail to receive the beam and drag the payload to relativistic speeds.

The crystallization of organic-based materials occurs under conditions far from equilibrium, leading to patterns that grow as propagating waves into the surrounding unstable fluid medium. This problem was reformulated considering the concept of thermal forces of preexisting 2D patterns. A new finite difference numerical scheme was tested. Dendritic islands were distributed in the liquid-viscous fluid. It induced a heterogeneous thermal distribution nearby the dendritic islands. The evolution of the isoline of the temperature versus time reveals fractal patterns within the inter-dendritic liquid. The physical origin of the fluctuations is guided by the proximity of the dendrites, i.e. lack of space. Moreover, the gradient of temperature is depicted by isocline pictures. Fractal patterns may be considered advantageous and be taken as a key point to the next step, i.e. the crystal growth in an environment subjected to rapid variations of temperature.

Crystal morphologies of different binary and ternary "model mixtures" were investigated using different cooling conditions (with cooling rates from 0.1 to more than 300 degrees C min-1). Needle-like crystals tend to form in binary mixtures under fast cooling, while uncommon spherulitic crystals were observed in ternary mixtures under slow cooling. These differences in crystal morphology lead to distinct mechanical behavior of the "model mixtures". As shown by cone penetration tests, mixtures with spherulitic crystals exhibit a lower mechanical strength than those with densely arranged needle-like crystals. In addition, nanoindentation tests demonstrated that Young's modulus and plasticity limit of mixtures are higher upon faster cooling. Lipstick-shaped cast samples were studied, in which cooling rates are much higher at the surface than at the center. A gradual change in crystal morphology was observed from surface to center, correlating to the hard surface and the soft center as revealed by nanoindentation tests. This work illustrates the relationship between process thermal control, microstructure morphology, and mechanical properties for wax-oil mixtures, paving the way to the monitoring of sensorial properties by control of mixture composition and process control.

The Al-51 at% Zn alloy shows a total transformation of the eutectoid mixture at this concentration. It is therefore ideal for studying the evolution of the alpha and beta phases as a function of temperature. In the present work, we have clearly demonstrated a correlation between the evolution of the microstructure observed by scanning electron microscopy (SEM) and the results obtained by isothermal mechanical spectroscopy (IMS) [1]. IMS measurements on this alloy were carried out over a very wide frequency range (10(-5 )-50 Hz) and the results obtained show that it exhibits different relaxation peaks as a function of temperature between ambient and 540 K. Upon heating, two peaks P1 and P2 appear below the eutectoid transition temperature (550 K). Both peaks are thermally- activated; P1 decreases and disappears with increasing measurement temperature while P2 appears and increases continuously until the eutectoid transition temperature. These peaks have been associated with thermally induced diffusion of atoms across the alpha-beta interface; this could correspond, according to the literature, to a change in the shape of the lamellar interface between the alpha and beta phases [1]. The SEM observations were performed after several quenches at different temperatures (385 K, 433 K and 493 K after a holding time of 2 h 30 min) chosen in the temperature range of the internal friction peaks evolution. The results obtained allowed us to associate the P1 peak to the lamellar structure whose destruction leads to the collapse of P1. On the other hand, the P2 peak is associated to the globules coalescence and as this coalescence increases the amplitude of this peak becomes more important. The analysis of our SEM observations has clearly highlighted the transformation mechanisms of this eutectoid mixture by specifying without ambiguity the passage from the lamellar structure to the globular structure and then the collapse of the latter. (C) 2021 Elsevier B.V. All rights reserved.

This paper aims at a better understanding of the polypropylene (PP) physical extrusion foaming process with the objective of obtaining the lowest possible foam density. Two branched PPs were compared to the corresponding linear ones. Their shear and elongation viscosities were measured as well as their crystalline properties. Trials were conducted in a single screw extruder equipped with a gear pump and a static mixer cooler to adjust the melt temperature at the final die. The effect of decreasing this temperature on the PP foamability and on the pressure drop in the die was analyzed. The foam density of branched PPs varies from high to low values while decreasing the foaming temperature. In the same processing conditions, the foam density of linear PPs does not decrease so much, as already evidenced in the literature. The foamability transition coincides with an increase of the pressure drop in the die. The originality of the work lies in the thermomechanical analysis of the polymer flow in the die which allows the identification of the relevant physical phenomena for a good foamability. The comparison of the experimental pressure drops in the die and the computed ones with the identified purely viscous behavior points out the influence of the foaming temperature and of the PP structure. At high foaming temperature the discrepancy between experimental measurements and the computed pressure drops remains limited. It increases when decreasing the foaming temperature, but the mismatch is much more important for branched PPs than for linear ones. This difference is analyzed as a combination of the activation energy of the viscosity, the elongational viscosity in the convergent geometry of the die which is much more important for branched PPs than for linear ones, and the onset of crystallization which occurs at higher temperature for branched PPs than for linear PPs.

High pressure facilitates crystallization of isotactic polypropylene (iPP) in the orthorhombic ??-form, differing in structure and properties from the ??-form, in which iPP crystallizes under common processing conditions. In the study, the effect of high pressure on crystallization of iPP nanocomposites was examined. The iPP nanocomposites with 1-5 wt.% of well dispersed either o-MMT (PP/MT) or MWCNT (PP/CN) were prepared by mixing molten iPP with the nanofillers. The nanocomposites and neat iPP were crystallized during cooling under pressures up to 300 MPa. Regardless of crystallization pressure, the crystallization temperatures were similar whereas the sizes of the polycrystalline aggregates were only slightly smaller in PP/MT compared to those of neat iPP. On the contrary, the presence of MWCNT elevated the crystallization temperature of PP/CN by 8-13 K compared to that of neat iPP, and strongly decreased the grain size. This evidenced the nucleating activity of MWCNT during high-pressure crystallization of iPP in the ??-form. The higher crystallization temperature allowed a larger portion of the polymer to crystallize in the ??-domain before the ??-domain was reached. As a result, PP/ CN, especially crystallized under 50-100 MPa, contained more ??-form than neat iPP and PP/MT.

Characterization and modelling of wax crystallization must be carefully addressed to understand wax-oil organogels formation. During casting process of wax-based mixtures, wax crystallization occurs under concomitant non-constant and high cooling rates. In this study, the crystallization kinetics of two representative wax-based materials were studied by power-compensated Differential Scanning Calorimetry (DSC) with moderate-high cooling rates (from − 20 to − 200 °C min−1) in constant cooling rate (isokinetic) conditions and in simplified non-constant cooling rate (non-isokinetic) conditions. Analyses based on the evolution of the mass fraction of solid wax calculated from heat flow (DSC signal) show similar kinetics trend and enthalpy of crystallization for the different isokinetic conditions, but with a significant influence on the supercooling effects. Considering the limits of the classic Avrami kinetics modelling for high aspect ratio crystals and complex mixtures, a semi-empirical modelling approach of non-isokinetic cooling conditions in a differential form is proposed. The modelling shows a good correlation with experimental results.

A better understanding of elastomers’ behavior during Rapid Gas Decompression (RGD) requires advanced knowledge of what is happening during gas sorption and desorption. This will offer to improve numerical simulation phenomena to consider a real environmental use of an O-ring, as for thermal applications. A previous experimental study developed testing protocols to investigate the performance of elastomeric O-rings. The non-contact measurement technique has been validated to identify the swelling and shrinking coefficients during sorption and desorption of carbon dioxide (CO2) from a Hydrogenated Nitrile Butadiene Rubber (HNBR) O-ring. The present work describes the effect of CO2 pressures on Fluorocarbon rubber (FKM) seals behavior coupled with temperature. To evaluate the effect of reinforcing the HNBR and FKM matrices with nanofillers, experimental tests were carried out and compared with those of the two elastomers without fillers. The four materials’ CO2 sorption and desorption coefficients are identified, and their swelling upon decompression is measured. It appears that HNBR is the best candidate under the applied service conditions. On the other hand, the nanofillers introduced in the elastomers may cause some early damages under RGD conditions.

Ceramic is among the complicated materials to use in the design of fine objects. Complex shapes without any major defect are not easy to produce. In most of the cases, the production of ceramic parts is the results of three steps. Firstly, the "sculpture" of the raw piece by adding raw materials to lead to the final object. Secondly, the "drying" and finally the "high temperature oven-dry" of the dried raw object to transform the granular dough into a nice consistent compact material. Exploiting the special characteristics of ceramic is not only a thing of the past. Nowadays new possibilities, i.e., shapes and styles, can be offered in the use of ceramics, and especially where it concerns the application of the Additive Manufacturing (AM) concept. The combination of Computer Aided Design (CAD) to AM opens a completely new means of finding novel ways of processing final objects. By choosing to use kaolin clay without any chemical additions (or improvers) as "a model material," the ability to produce controlled structures with freedom in design by additive deposition modeling is exposed. Discussions relate to the concomitant control of the process parameters, the kaolin hydration and the complexity of printed structures. The optimization of process parameters (nozzle speed, layer thickness, wall thickness) were defined with the calibration of the material flow. Both windows adjusting water content in dough (%wt) and imposing pressure in the tank of the 3D printer have been defined accordingly. The role of layer impression support was also found to be important. This study credits to use the state-of-the art technique (3D printing) to explore sustainable manufacturing of potteries.

The present study investigates the triggering and acceleration of xylitol crystallization for its use as a short-term TES. The combined effect of seeding and the action of shear on xylitol crystallization at a supercooled temperature has been investigated by direct observations under shear (rheo-optical approach) and by rheometry. The initial seed is an agglomerate of crystals of xylitol. In addition to the more classical erosion and rupture mechanisms leading to the dispersion of crystals, shear has shown to induce the detachment of crystalline dust adhered to the initial seed into the supercooled xylitol. These crystal fragments then serve as sites for secondary nucleation and subsequent crystallization. Rheo-optical observations have allowed the determination of shear conditions to control the size of crystals by dispersion. A second part has been dedicated to the effect of shear on crystallization of xylitol by seeding by means of rheology. The measurements, although not reproducible, clearly show that seeding in presence of shear (for the investigated conditions) is very efficient to trigger and accelerate the crystallization of xylitol. Post-mortem DSC and XRPD analyses of the final crystallized seeded and sheared samples have not shown any effect on the xylitol crystallinity degree.

In this paper, we review practical limitations to laser space propulsion that have been discussed in the literature. These are as follows: (1) thermal coupling to the propelled payload, which might melt it; (2) a decrease in mechanical coupling with number of pulses, which has been observed in some cases; and (3) destruction of solar panels in debris removal proposals that might create more debris rather than less. Previously, lack of data prevented definite assessments. Now, new data on multipulse vacuum laser impulse coupling coefficient Cm on several materials at 1064 nm, at 1030 nm, and at 532 nm are available. We are now able to compare the results for single and multiple pulses on materials that have been considered for laser ablation space propulsion (LASP), or that are likely space debris constituents, and decide whether LASP is a practical idea. Laser space propulsion and debris removal concepts depend on thousands or hundreds of thousands of repetitive pulses. Repetitive pulse mechanical coupling as well as thermal coupling (which can melt the target rather than propel it) are both important considerations. Materials studied were 6061T6 aluminum, carbon-doped polyoxymethylene (POM), undoped POM, a yellow POM copolymer, and a mixture of Al and POM microparticles combined and pressed, containing a 50%/50% mixture of the two materials by mass. We address 6 and 70 ps pulses because of the availability of data at these pulse durations. We also briefly consider continuous wave (CW) laser propulsion. Finally, we consider a recent paper concerning solar panel destruction from a positive perspective.

A key problem in the modeling of polyurethane (PU) foaming is the determination of relevant physical parameters for the viscosity, the gas expansion, and the curing rate. Indeed, it is difficult to measure the chemical kinetics parameters as well as the viscosity of industrial PU formulations (polyol-isocyanate-water mixture) because the time scales of gas production and PU crosslinking are very short and hardly compatible with the installation of the sample in characterization devices such as differential scanning calorimetry and parallel plates rheometer. A FOAMAT (R) system has been developed to get these experimental data but the relationship between measurements and the rheo-chemical parameters has not been clearly established. In this paper, an analytical model of the foaming process is developed in the cylindrical FOAMAT geometry, which allows identifying the parameters of the curing and gas production kinetics equations, as well as the viscosity. This analytical model is based on a set of simplifying hypotheses which validity is checked using the finite element computation software REM3D dedicated to foaming modeling and applicable for injection-molding processing.

1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the α- form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the γ- polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2–1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (Tc) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic γ- form. As a consequence, Tc and the γ- form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of Tc and the decrease of grain size under high pressure of 200–300 MPa required higher content of DMDBS than the nucleation of the α-form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity.

As thermal energy storage is becoming more important, new materials are being studied. Sugar-alcohols (SA) are very promising as phase change materials (PCM) because they are non-toxic, affordable and their latent heat is high. However, undercooling and low crystallization rates are some of the problems present in these materials. The SA studied in this work is xylitol, and using a microscope connected to a transparent counter-rotating shear cell, the effect of secondary nucleation is studied, as well as the crystallization rate of xylitol and how undercooling affects it. From the results, it is deduced that a proper seed preparation and handling is needed. The crystal structure is also studied, using XRPD diffractograms and differential scanning calorimetry.