Rheological Criteria Research Articles

Evaluation of mechanical anisotropy induced by 3D printing process for earth-based materials

Due to the high energy consumption of cement-based materials, debates are increasing to develop new composites using natural resources. As a result, there are more investigations on bio-based and earth-based materials in the literature thanks to their capability to reduce carbon dioxide gas emissions (CO2). Accordingly, earth has a strong potential since it hardens by drying rather than by hydraulic setting, it is also infinitely repairable and recyclable, without generating greenhouse gas. This work investigates the manufacturing of earth-based material using 3D printing process. In the first step the water content was found according to the rheological criteria target allowing the material to be extruded at a continuous and regular flow rate. The corresponding dosage ensures a sufficient yield stress allowing the deposit of the printed layers without collapsing and the possibility to support the upper layers. In the second step, prismatic specimens were printed using two different nozzle outputs. The samples were cut and sanded to extract normalized specimens. After mass stabilization, mechanical tests were conducted, the work included three-point bending tests, compression tests and shear tests. The findings were compared with the results obtained on cast specimens. As printed elements are made layer after layer, the manufacturing method had an impact on the behavior, the quality of the material and exhibited an apparent anisotropy. Consequently, for each test, the loading was applied in the longitudinal, transverse, and normal directions regarding the printed layers. It has been found that the resistances of the printed samples were of the same order of magnitude as those measured on cast ones, especially when the loading was perpendicular to the printed layers. On the other hand, the resistances were significantly reduced when the loading led to expansion or tension perpendicular to the layers.

POWDER-ACTIVATED CONCRETE WITH A GRANULAR SUR-FACE TEXTURE

In recent years, self-compacting concrete mixtures have been widely used. Such mixtures are characterized by high workability without the use of vibration exposure. The application of innovative technologies allows manufactoring of various materials and products for architectural and construction purposes with improved decorative properties. The paper provides the results of a study on the selection of compositions for decorative-finishing powder-activated concrete with a granular surface texture according to rheological properties, strength and frost resistance had been adopted.
 The following components were adopted for the research. Egyptian white cement was used as a binder, microquartz as a microfiller, screenings of crushing granite and cooper slag of 0–0.63 mm fraction was used as a finely dispersed component, granite cuts 0.63–5.0 mm and cooper slag of 0.63–2.5 mm fraction as an aggregate sand. A new generation superplasticizer of domestic and foreign productionplasticized the mixtures. Structural and rheotechnological parameters of powder-activated concretes were calculated.
 From the obtained values of the conditional rheological criteria of powder-activated concretes, it follows that all of them are much greater than unity and characterize a significant excess of the volumes of rheological matrices over the volumes of fine-grained, coarse-grained components that fit into them with large separation of particles and grains.
 Strength as a complex mechanical characteristic, including a combination of strength, reliability and durability criteria, is the most important quality parameter of the concrete structure as an active and the most massive building material for structural purposes. A significant number of facilities made of concrete and reinforced concrete are being built in the southern and northern regions, characterized by extreme climatic conditions. Buildings and structures are exposed to cyclic loadings of various types and climatic influences, characterized by cyclic manifestations of negative and alternating temperatures. The research revealed high indicators of strength and frost resistance of decorative powder-activated concretes with a granular surface texture.

Rheology of Polymer Processing in Spain (1995-2020).

The contribution of Spanish scientists to the rheology involved in polymer processing during the last 25 years is investigated. It is shown that the performed research covers, at different levels, all industrial polymeric materials: thermoplastics, thermosets, adhesives, biopolymers, composites and nanocomposites, and polymer modified bitumen. Therefore, the rheological behaviour of these materials in processing methods such as extrusion, injection moulding, additive manufacturing, and others is discussed, based on the literature results. A detailed view of the most outstanding achievements, based on the rheological criteria of the authors, is offered.

Rheological criteria for distinguishing self-healing and non-self-healing hydrogels

Owing to the structural resemblance of synthetic hydrogels to biological tissues, numerous self-healing wet materials have recently emerged, based on either chemical or physical motifs. With a plethora of novel synthetic hydrogels, a reliable characterisation strategy to assess self-healing is necessary. Herein, we therefore propose rheological criteria to distinguish self-healing hydrogels by comparing two types of poly (vinyl alcohol) hydrogels prepared via freezing/thawing (FX) or borax addition (BX). Non-self-healing FX and self-healing BX hydrogels exhibit incompatible features for three rheological characteristics: 1) Bingham behaviour without a lower Newtonian flow region (LNFR) (FX) versus pseudoplastic behaviour with a LNFR (BX), 2) infinite chain flow relaxation time (τf) versus finite τf on a reasonable time scale, and 3) drastic gel-sol transition with heating versus negligible transition. The plotting of modulus master curves confirms the terminal flow behaviour of the self-healing BX hydrogels, in contrast to the rubbery nature of the FX gels. The flowability of the self-healing hydrogels is ascribed to the pseudo-state of the gel network, due to the dynamic nature of the borate-diol bonds. Thus, the rheological criteria provide a sound theoretical background for self-healing material characterisations.

Rheological rationalization of in situ nanofibrillar structure development: Tailoring of nanohybrid shish-kebab superstructures of poly (lactic acid) crystalline phase

The key rheological parameters for in situ development of poly (butylene terephthalate) nanofibrils (PBT NFs) in poly (lactic acid) (PLA) matrix using a tuned melt spinning process were studied. Observation of ellipsoidal PBT domains oriented along a short die was attributed to a low interfacial tension between the blend constituents and fulfilled melt rheological criteria for fibrillation in a simple shear flow. The stability of the deformed droplets under the shear and elongational flows was studied by comparing the droplet breakup time and residence time in each flow field. It was demonstrated that the deformed droplets (ellipses) with an increased robust interface underwent coalescence through pinch-off in the subsequent elongational flow field, and transformed to the nanofibrils with an average diameter comparable to the gyration radius (Rg) of PLA chains. In the fabricated isotropic in situ nanofibrillar composites (NFCs), a random orientation of 2D nanohybrid shish-kebab (NHSK) superstructure was observed as a result of the orthogonal pattern of melt crystallized PLA nanodomains on the PBT NFs surface. The NHSK superstructure established in quiescent bulk through mechanism of geometric confinement (soft epitaxy) enabled us to tailor the crystalline morphology via annealing temperature. In a constant nanofibril content, increasing the isothermal temperature (Tiso) up to 114 °C led to an increase in the kebabs length and interlocking of the adjacent superstructures. A transition to spherulitic crystal morphology was observed due to further temperature increase (Tiso≥117 °C). The observed transition indicated that at higher Tiso, the fewer raw nuclei, which were initiated by soft epitaxy mechanism of PLA chain segments on the PBT NFs at the early stage of nucleation, could conduct self-nucleation and 3D lateral growth. The Avrami model was found to be applicable for interpreting variations of crystallite morphology, crystallization rate, and nucleation mechanisms with PBT NF content and isotherm temperature.

Modified Marshall Test assessment for emulsified asphalt cold mixes

Asphalt cold mixes are attractive to transportation agencies for their simplicity in set-up, less energy requirement, ease of application, and environmentally friendliness, though it suffers setbacks in terms of lack of a universally acceptable mix campaign, high water susceptibility, and low mechanical strength at initial stages of construction. However, they are widely used for rehabilitation and maintenance works, and to a lesser extent construction in low-trafficked roads. Notable among the cold mixtures is polymer modified emulsified asphalt micro-surfacing, which is used as a thin non-structural layer for the restoration of skid resistance and waterproofing. Marshall test is used to assess its performance similar to a structural wearing course layer. This study assessed the mechanical performance of cold mixtures by a modified Marshall mix employing a low viscosity cationic quick set emulsion (CQS-1h) and a cationic rapid set emulsion (RS-1k) and a 60/70 penetration grade binder. Rheological criteria assessment was conducted on both emulsions including particle charge, residue by evaporation, settlement and storage stability, solubility in inorganic solvent sieve test, and Saybolt Furol viscosity, while the residue from evaporation was tested for microstructural and mechanical performance, 65% and 63% residue by evaporation, dissolved in trichloroethylene at 95% and 100% for CQS-1h and RS-1k respectively.

Rheological criteria assessment of a rapid setting emulsion as compared to quick set for emulsified asphalt cold mixes

Pavement deterioration is inevitable on roads. Unlike structural failures that can only be remedied by total reconstruction, road’s functional failures are corrected through effective maintenance works. Preventive maintenance in the form of an emulsified asphalt cold slurry micro-surfacing is considered superior to corrective maintenance – which is a reactive approach. Exploring alternative(s) to the normal quick setting emulsion used for pavement preservation maintenance will make it more robust and cost-effective. This study conducted an assessment of the key parameters specified by the department of public works (Jabatan Kerja Raya) JKR-2008 and International Slurry Surfacing Association (ISSA A143) specifications for emulsified asphalts emulsions used for cold mixes, specifically, emulsified asphalt micro-surfacing mixtures used for pavement maintenance. Cationic quick set (CQS-1h) and Rapid Set (RS-1k) emulsions were tested in the Transportation laboratory of UTM under controlled laboratory conditions. Tests include settlement and storage stability, particle charge, residue by evaporation, sieve test, and Say bolt Furol viscosity, while the residue from evaporation was tested for microstructural and mechanical performance, results were compared with JKR-2008 and ISSA A143 standard specifications. The result indicated that although the desirability for opening traffic within 1hr is not guaranteed with RS-1k, yet, it gives promising similar properties with CQS whilst satisfying cold mix requirement.

A methodology for the mix design of earth bedding mortar

Earth masonry is a good alternative to more conventional materials in order to reduce the environmental impact of building materials. However earth construction techniques mostly rely on bricklayers’ experience, which is a hindrance to industrial development of this traditional know-how. This article proposes a methodology for the mix design of unstabilized earth bedding mortar based on mechanical criteria of the masonry and rheological criteria of fresh mortar. A test to characterize the shear strength of the masonry interface is specially investigated. The mechanical performances of the formulated mortar are then validated with laboratory scale characterization.

RSM-based modeling and optimization of self-consolidating mortar to predict acceptable ranges of rheological properties

Using a high or low amount of cementitious material, water-cement ratio (W/C), and superplasticizer (SP) cause instability and reduction in compressive strength of concrete according to their impact factor and interaction. However, making a concrete with the optimum amount of variables could improve its properties. So, optimization of concrete ingredient due to absence of proper mix design code is required. The remarkable features of response surface method (RSM) are modeling and optimization. This study was carried out with the aim of investigating rheological and hardened properties of self-consolidating mortar (SCM) using RSM with four factors (silica fume, slag, SP and W/C). Rheological criteria of EFNARC code were used to specify the optimum restriction. According to statistical analysis and validation of equations, it can be concluded that RSM is a confident and efficient method to evaluate the properties of SCM. In addition, according to model, the silica fume increased EFNARC code limitation ranges by improving the rheological properties, however, slag had an almost neutral role. In the best case, the addition of silica fume, reduced the segregation up to 5 times. Although silica fume increased the compressive strength up to 45%, slag totally decreased the compressive strength.

Electrospinning of poly(lactic acid): Theoretical approach for the solvent selection to produce defect‐free nanofibers

ABSTRACTIn this study an integrated methodology was proposed for the selection of solvent systems to produce electrospinnable solutions that form defect‐free poly(lactic acid) (PLA) fibers with narrow diameter distributions. The solvent systems were chosen using a thermodynamic approach, combined with electrical and rheological property criteria. More specifically, the three step methodology includes (1) initial choice of solvent by solubility evaluation to meet thermodynamic criteria, (2) electrical properties, that is, conductivity and dielectric constant adjustment by using solvent mixtures to meet electrical property criteria, and (3) critical entanglement concentration (Ce) determination by viscosity measurements, supported by elastic and plastic moduli measurements, followed by concentration adjustment to meet rheological criteria. All three criteria need to be met to ensure defect‐free nanofiber morphology. The methodology was demonstrated using PLA solutions that were characterized in terms of thermodynamic properties, conductivity, surface tension, and viscosity measurements. These data were analyzed and related to the nanofiber morphology and diameter as determined from scanning electron microscopy (SEM). Measurements of the elastic (G′) and the plastic (G″) moduli of PLA solutions showed a sharp increase of G′ at the chain entanglement concentration. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2016,54, 1483–1498

Ex vivo lung graft perfusion

This review proposes an update of the state of the art and the ongoing clinical trials of ex vivo lung perfusion for lung transplantation in patients. Ex vivo lung perfusion techniques (EVLP) can be used to evaluate a lung graft outside of the body. The goal of EVLP is to study the functional status of lung grafts that were first rejected for transplantation because they did not match all criteria for a conventional transplantation. After an EVLP evaluation, some of these lungs may be requalified for a possible transplantation in patients. This article proposes an overview of the developments of EVLP techniques. During EVLP, the perfusion and ventilation of the isolated lung preparation are very progressive in order to avoid oedema due to ischaemia-reperfusion injuries. Lung evaluation is mainly based on gasometric (PaO2/FiO2) and rheological criteria (low pulmonary arterial resistance). Several series of patients transplanted with EVLP evaluated lungs have been recently published with promising results. EVLP preparations also allow a better understanding of the physiopathology and treatments of ischaemia-reperfusion injuries. Organ procurements from “non-heart-beating” donors will probably require a wider application of these ex vivo techniques. The development of semi-automated systems might facilitate the clinical use of EVLP techniques.

Linear rheology of nanofilled polymers

The linear rheology of nanoparticle filled polymer (NPFP) melts has been a quite charming but controversial topic of long standing. This article reviews recent research advances to provide a general understanding of its universal appearance and underlying mechanism. This work summarizes the rheological criteria for determining the so-called liquid-to-solid transition with increasing filler content, the contradictory ideas of four kinds of time-concentration superposition principles proposed for constructing master curves of linear rheology, and a wide range of constitutive and phenomenological models focused on creating rheological contributions of the polymer, filler, and interface region from different perspectives. Controversies about microstructures of NPFPs including filler structure and chain dynamics of the matrix are briefly described. Several open questions are highlighted to outline the most likely general framework for the further investigation of the linear rheology of NPFP melts.

Effect of ultrasound, low-temperature thermal and alkali pre-treatments on waste activated sludge rheology, hygienization and methane potential

Waste activated sludge is slower to biodegrade under anaerobic conditions than is primary sludge due to the glycan strands present in microbial cell walls. The use of pre-treatments may help to disrupt cell membranes and improve waste activated sludge biodegradability. In the present study, the effect of ultrasound, low-temperature thermal and alkali pre-treatments on the rheology, hygienization and biodegradability of waste activated sludge was evaluated. The optimum condition of each pre-treatment was selected based on rheological criteria (reduction of steady state viscosity) and hygienization levels (reduction of Escherichia coli, somatic coliphages and spores of sulfite-reducing clostridia). The three pre-treatments were able to reduce the viscosity of the sludge, and this reduction was greater with increasing treatment intensity. However, only the alkali and thermal conditioning allowed the hygienization of the sludge, whereas the ultrasonication did not exhibit any notorious effect on microbial indicators populations. The selected optimum conditions were as follows: 27,000 kJ/kg TS for the ultrasound, 80 °C during 15 min for the thermal and 157 g NaOH/kg TS for the alkali. Afterward, the specific methane production was evaluated through biomethane potential tests at the specified optimum conditions. The alkali pre-treatment exhibited the greatest methane production increase (34%) followed by the ultrasonication (13%), whereas the thermal pre-treatment presented a methane potential similar to the untreated sludge. Finally, an assessment of the different treatment scenarios was conducted considering the results together with an energy balance, which revealed that the ultrasound and alkali treatments entailed higher costs.

Rheological analysis of stabilized cerium-gadolinium oxide (CGO) dispersions

Abstract The objective of the present work is to generate general rheological criteria to investigate high solid loading dispersions suitable for the shaping of homogeneous ceramic bodies. Systematic analysis of the rheological properties of moderately low specific surface area (SSA) Ce 0.9 Gd 0.1 O 3-δ (CGO10) dispersions was performed in rotational and oscillatory modes. The dispersant content was optimized to attain fully stabilized dispersions. A critical upper limit for the ceramic content was introduced and denoted ϕ h . It defines the limit to non-Newtonian flow and corresponds to the highest feasible volume fraction to which reproducible dispersions are achieved. The method proposed for its determination is based on the analysis of the flow index as function of the ceramic volume fraction. For the CGO dispersions formulated in this work, ϕ h was found to be around (0.34 ± 0.04). The maximum volume fraction ( ϕ m ) was also estimated and found to be (0.55 ± 0.01).

Caracterização meso e microscópica de bandas de deformação em arenitos porosos: um exemplo nas tectonossequências Paleozoica, Pré- e Sin-rifte da Bacia do Araripe, Nordeste do Brasil

Deformation bands are narrow tabular volumes developed in porous sandstones. Although these structures are a product of brittle deformation, they may have internally a continuous displacement gradient. When granular cataclasis is the dominant deformation mechanism, the initial properties of their host rocks (i.e., porosity and permeability) can change significantly. The deformation bands in sandstones from the pre- and syn-rift of the Araripe Basin were studied in meso and microscale in order to classify them and to understand the deformation mechanisms involved during their nucleation and development. Their geometric-spatial, kinematic, and rheological criteria allowed establishing relations between the origin of deformation bands and lithification of their host rocks. Additionally, some inferences on their influence to the fluid flow in the reservoir-scale were outlined. Moreover, the study of deformation bands contributed to the understanding of the tectonic evolution of the studied basin. Accordingly, the study of deformation bands can support research on local and regional aspects of the tectonosedimentary evolution of sedimentary basins.

Spontaneous Gelation of a Novel Histamine H4 Receptor Antagonist in Aqueous Solution

Low molecular weight hydrogelators typically require a stimulus such as heat, antisolvent, or pH adjustment to produce a gel. This study examines gelation of a novel histamine H4 receptor antagonist that forms hydrogels spontaneously at room temperature. To elucidate the mechanism and structural moieties responsible for this unusual gelation, hydrogels were characterized by rheology, optical microscopy, and XRD. SEM was performed on xerogels; NMR measurements were conducted in gelator solutions in the presence of a gel-breaker. The influence of temperature, concentration, pH, and ionic strength on elastic and viscous moduli of the hydrogels was evaluated; gel points were established via thorough rheological criteria. The observed are "true" gels with a fibrillar texture and lamellar microstructure. On a molecular level, the gels are composed of aggregates of partially ionized species stabilized by hydrophobic interactions of aromatic moieties. The gel-to-sol transition occurs at physiologically relevant temperatures and is concentration-, pH-, and ionic strength-dependent. We hypothesize that this spontaneous gelation is due to the so-called "spring" effect, a high energy salt form that transiently increases aqueous solubility above its equilibrium limit. Upon equilibration, this supersaturated system undergoes aggregation that avoids crystallization and produces a hydrogel.

Historical evolution of oil painting media: A rheological study

Rheology is the science of flow, which is a phenomenon found in every painting operation, such as decorative paintings or protective coatings. In this article, the principles of rheology as applied to paintings and coatings are recalled in a first part and the rheological criteria required in the paint industry presented. Indeed, different flow behaviours leads to different finishes. The same procedure and techniques as in industry can be employed to explain some evolutions in oil painting aspects over the centuries. The first recipes for oil painting indicate the use of treated oil, resins and spirits. This article deals with the evolution of the composition of these systems as media for oil painting, according to rheological clues. During the Renaissance period, the media used were Newtonian or slightly shear thinning and allowed one a perfect levelling. Then techniques changed, paints became more opaque with less addition of oil/resin media, and brushstrokes appeared visible. Some preparations containing lead, oil and mastic resin, whose flow behaviour is closed to those required in industry, may have appeared during the 17th century and are still used and sold today. To cite this article: L. de Viguerie et al., C. R. Physique 10 (2009). La rhéologie, science de l'écoulement, est à ce titre présente dans toute opération de peinture. Nous proposons dans une première partie un bref rappel des principes et définitions en rhéologie ainsi que les différents critères définis dans l'industrie pour la formulation. Les propriétés rhéologiques conditionnent en effet le rendu final de la peinture. Un même type de raisonnement peut être appliqué tant pour la mise au point des peintures industrielles où il s'agit d'ajuster la formulation en fonction des critères requis, que pour l'étude des peintures de chevalet où le rendu final donne des informations sur la rhéologie et donc la composition de la peinture utilisée. Les premières recettes de liants et mediums pour la peinture à l'huile indiquent l'utilisation d'huile, de résines, et d'essence. En partant de l'étude rhéologique de ces systèmes nous proposons de suivre l'évolution de leur composition et de leur utilisation en tant que médiums pour la peinture à l'huile. Pendant la Renaissance, des systèmes newtoniens ou légèrement rhéofluidifiants permettant un nivellement complet de la surface, ont du être utilisés. Progressivement les techniques se modifient : la touche de l'artiste devient visible. Les traces de pinceaux apparaissent, la peinture est utilisée opaque (et non plus transparente en glacis) et les mediums huiles/résines sont moins employés. Des préparations à base d'huile additionnée de plomb, et de résine mastic apparaissent, au XVIIe siècle d'après certaines sources. Ces préparations, dont les propriétés rhéologiques sont proches de celles recherchées par l'industrie, sont encore préparées et vendues de nos jours. Pour citer cet article : L. de Viguerie et al., C. R. Physique 10 (2009).

Rheology and morphology change with temperature of SEBS/hydrocarbon oil blends

The effect of hydrocarbon oil incorporation on the rheological and phase behaviors of poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) has been investigated. SEBS-A1 (neat SEBS) shows a presence of very long relaxation time mode even at the highest temperature carried out here. On the other hand, G′ of SEBS-A3 (oil concentration = 50 wt %) drastically decreases with increase of temperature at a critical temperature, which can be assigned to be order–disorder transition (ODT). The critical temperature was determined by two rheological criteria. Incorporation of hydrocarbon oil affects the ODT temperature. The rheological response is very sensitive to a few temperature increases around the ODT temperature. Above the critical temperature, G′ finally yields the terminal flow in the low frequency range. The morphological observation at various temperatures was determined using atomic force microscopy (AFM) equipped with environmental controller. This enabled in situ observation of structural change of SEBS induced by temperature and phase transition. We found that the layered texture, mostly aligned along the surface can be seen for SEBS-A1 ranging from room temperature to 230 °C, though the image contrast reduced by an increase of temperature. SEBS-A3 showed sphere domains at room temperature and also remains the structure at a critical temperature. The phase separated structure disappeared almost completely above ODT temperature, which was confirmed by the rheologial criteria. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 955–965, 2009

Phase inversion and viscoelastic properties of phase-separated polymer blends

The morphologies and viscoelastic properties of the phase-separated poly(styrene-co-maleic anhydride)/poly(methyl methacrylate) bends have been investigated using TEM and rotational rheometry. Various rheological criteria based on the viscoelastic properties of the blends have been used to evaluate the phase inversion. By correlating the rheological results to data from morphological analysis by TEM, it is found that the maximum of the storage modulus and the viscosity at low shear rate are most suitable for determining the phase-inversion composition of the present phase-separated polymer blends. While the data from the maximum of the shear viscosity at high shear rate and from the shear-thinning extent proposed by Ziegler et al. slightly deviate from that from TEM micrograph, which indicates that shear-induced structure lie. Moreover, the prediction using various rheological models, as the viscosity ratio of the two coexisting phases is substituted for that of the pure components, is in nearly good agreement with that from TEM observation.

Crystallization of Polymers from Stressed Melts

In the last decade, there have been several investigations into the route by which a polymer melt that has been subjected to flow transforms into a crystalline state. Crystallization of polymers from flowing or stressed melts is a technologically important problem since most thermoplastics are subjected to intense flow fields during normal processing operations. The renewed interest in this problem is due to the availability of new experimental tools that, coupled with advances in modeling and simulations, are beginning to yield insights into the molecular characteristics that control the crystallization pathways adopted by a stressed polymer melt. Recent evidence conclusively implicates the high molecular weight tail in promoting crystallization on shearing. It appears that the formation of oriented nuclei in polydisperse melts is controlled by chain orientation of a small fraction of high molecular weight chains in a melt. Thus, it is the rheological criteria for “critical” chain orientation that govern flow‐induced acceleration and orientation in polymer crystallization. This review summarizes the literature on the effect of shearing on polymer crystallization, and focuses on recent advances in understanding the role of molecular parameters that couple polymer crystallization to flow and melt orientation.