Strain Sweep Tests Research Articles

Strain Sweep Fatigue Testing of Sand Asphalt Mortar to Investigate the Effects of Sample Geometry, Binder Film Thickness, and Testing Temperature

This study evaluated the viscoelastic fatigue behavior of binder using strain sweep fatigue testing of cylindrical sand asphalt mortar (SAM) samples. The SAM samples can represent the realistic film thickness (such as 10–70 μm thick) of the binder in mixtures, while testing repeatability-efficiency can still be met as a result of the use of a standard sand as a load carrier between binder films. A proper testing protocol is still under development, and one of the unknowns in the field is a set of testing conditions that can provide repeatable and case-sensitive test results. Toward that end, SAM samples with different dosages of binder in three geometries were tested at varying temperatures in this study. A PG 64-34 binder was used, and a strain sweep test using a dynamic shear rheometer was conducted to compare the test results from the different cases. Four parameters resulting from the SAM testing were examined: two accounting for material linear viscoelastic behavior and two accounting for fatigue damage characteristics. The parameters were incorporated with statistical analyses to quantitatively evaluate data variability and sensitivity influenced by the binder film thickness, SAM specimen geometry, and testing temperature. The coefficient of variation was less than 20% for all the cases, which indicated the validity of the SAM method attempted in this study. Results also indicated that fatigue behavior was independent of the SAM geometries used in this study, while binder film thickness and testing temperature significantly affected test results.

Ageing effects on the linear and nonlinear viscoelasticity of bituminous binders

ABSTRACT The paper investigates the effects of ageing on the linear and nonlinear viscoelastic properties of bituminous binders for paving applications. Four neat binders were analysed in their unaged state and after long-term ageing, which was simulated in the laboratory with the Rolling Thin Film Oven (RTFO) and the Pressure Ageing Vessel (PAV). Amplitude sweep tests and frequency sweep tests were performed to explore the response in the linear domain. Repeated strain sweep tests were carried out to isolate nonlinearity from other mechanisms related to damage. The time–temperature superposition principle and the generalised Maxwell model with a Prony series discretization were used to describe the overall viscoelastic response of binders, introducing strain-dependent shift factors to account for nonlinearity. Results indicate that the adopted experimental and modelling approach allows a proper assessment of the effects of ageing on viscoelasticity.

Rheological properties of peanut protein isolate aggregation suspension and acid-induced gel

The dynamic rheological properties of peanut protein isolate (PPI) suspension and acid-induced PPI gels were studied. In frequency sweep test, the storage modulus (G′) and the loss modulus (G″) of PPI aggregation suspensions at different concentrations increased with the increase of frequency. The steady state shear flow test showed that PPI aggregation suspension had a thinning behavior of the shear, and the image of steady shear curve fitted the Carreau model. After gel formation, acid-induced PPI gels showed a typical Type I behavior (strain thinning) in strain sweep test, meaning that PPI gel got easily broken down, and there was a very small opportunity for the protein molecules to re-establish the network. Compared with the strain sweep of PPI aggregation suspensions and gels, the range of the storage modulus existed a dramatic difference, which could get about tenfold. As the frequency increased, both elasticity and viscosity increased in frequency sweep test, which indicated that the frequency dependence of the storage modulus increased with the increase of concentration. Keywords: peanut protein isolate (PPI), aggregation suspension, acid-induced PPI gel, dynamic rheological properties DOI: 10.25165/j.ijabe.20211403.6021 Citation: Huang Z G, Wang X Y, Chi S Y, Hua Z, Bi C H. Rheological properties of peanut protein isolate aggregation suspension and acid-induced gel. Int J Agric & Biol Eng, 2021; 14(3): 255–260.

Fourier transform fatigue analysis of the stress in tension/tension of HDPE and PA6

AbstractMechanical fatigue under strain controlled tension/tension (T/T) of rectangular un‐notched and notched specimens of high density polyethylene and polyamide 6 was performed. Under large amplitude oscillatory elongation, the stress response is nonlinear asymmetric due to a different stress response during loading and unloading and was analyzed via discrete Fourier transform. Dynamic strain (ε0) sweep tests revealed odd (I3/1 α ε02) and even (I2/1 α ε01) harmonics in the stress, well described by the Neo‐Hooke's law. Before crack onset for the Nc specimens, the storage and loss moduli and I2/1 are constant, but I3/1 increases with fatigue. The first derivative of I3/1 (dI3/1/dN) and the cumulative nonlinearity Qf parameter (integral of I3/1/ε02) were found to be strong criteria predicting fatigue. To break the unnotched specimens in the low and high cycle fatigue regime, large strain amplitudes were applied, resulting for both materials in initial plastic deformation followed by buckling when a critical compression force is exceeded. This results in a different time evolution of the linear and nonlinear parameters, especially as a minimum in the I2/1 curve. Finally, a model is proposed to describe the nonlinear viscoelastic specimen response under T/T and the effect of buckling.

Evaluation of rheological behaviour of flowable dental composites reinforced with low aspect ratio micro-sized glass fibres

ObjectiveExperimental investigation is carried out to determine the flowability and stickiness of the developed composite material for dental restoration containing low aspect ratio (AR ≤ 100) surface treated micro-sized glass fibres. MethodsSpecimens are manufactured by mixing low AR (50/70/100) micro-sized glass fibres with two different weight fractions (5%/10%) into UDMA/TEGDMA based resin. Particulate filler composite (PFC) containing 55% glass fillers is used as the control group. Dynamic oscillatory strain sweep tests are conducted to analyse the linear viscoelastic behaviour. Solid-to fluidic transition behaviour of dental composites is also calculated in terms of flow and yield stresses. Furthermore, the oscillatory frequency sweep tests are conducted at three different strains (0.5%, 5% and 50%) resembling the positioning of unset paste onto restorations for different real-life clinical situations. Additionally, stickiness of dental composites with handling instrument (steel) and dentine covered with bonding agent is also evaluated. ResultsThe results suggested the all the FRC groups exhibited non-Newtonian, shear-thinning behaviour. It is further established that inclusion of 5% of 50/70AR fibres into dental composites does not affect the flowability. Simultaneously, stickiness with dentine covered with bonding agent is more for these two compositions as compared to that of handling instrument (steel). SignificanceThis study suggest that visco-elastic properties of dental composites are greatly affected by the type of filler (spherical shaped particulate fillers or rod-shaped fibres) as well as fibre weight fraction/fibre AR. This phenomenon can be attributed to the varying interactions between micro-sized fibres of different AR/weight fraction, particulate fillers and monomers.

Development of hydroxyapatite reinforced alginate–chitosan based printable biomaterial-ink

This study reports synthesis of sodium alginate/ chitosan/ hydroxyapatite (HAp) based biomaterial-ink. An ionic interaction between polyanionic alginate and polycationic chitosan has been observed that forms a physical gel. The dispersion of HAp has been achieved through ultra-sonication, and stability of HAp in the hydrogel system has been achieved through hydrogen bonding with chitosan. Post printing crosslinking has been carried out with a 10 w/v % aqueous calcium chloride (CaCl2) solution. The combinations of biomaterial-ink have been characterized through Attenuated Total Reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), Scanning Electron Microscope (SEM), contact angle measurements. Further, the inks were characterized to estimate the printability and rheological responses. ATR-FTIR study confirms the ionic interaction between alginate and chitosan and identifies the presence of HAp in the biomaterial-ink. SEM morphology depicted the post-printing shape retention ability of the bioprinted constructs and revealed the structure’s rough morphology. All the biomaterial-ink combinations depicted hydrophilic nature as confirmed by the contact angle measurements. Rheological studies of the printable ink with hydroxyapatite revealed shear thinning properties and acceptable viscosity, essential for extrusion during bioprinting. The biomaterial-ink comprised only sodium alginate, and chitosan also displayed shear thinning abilities and showed lower working viscosity resulting in poor printability. The addition of hydroxyapatite to the hydrogel revealed acceptable post-printing structural stability. However, beyond 0.2% by weight of HAp imparts brittleness in the final structure. The linear viscoelastic regime, elastic modulus, and viscous modulus of the inks have been determined through the oscillatory strain sweep test. Creep recovery study, essential for predicting material behaviour immediately after ejection from the nozzle, indicated the material’s viscoelastic behaviour. The power law model has been used to estimate the flow index that predicted shear thinning abilities of the biomaterial-ink, and a correlation between the experimental and theoretical model was established. Herschel–Bulkley empirical model was used to determine yield stress (minimum stress required for extrusion from the nozzle) of the biomaterial-ink. Rheological studies and printability studies indicated Ink 5% 2% 0.1% as a promising combination for tissue engineering applications.

Using Poloxamer® 407 as Building Block of Amphiphilic Poly(ether urethane)s: Effect of its Molecular Weight Distribution on Thermo-Sensitive Hydrogel Performances in the Perspective of Their Biomedical Application

Due to its hydroxyl terminal groups, Poloxamer® 407 (P407), a commercially available poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer can be used as macrodiol for the synthesis of high molecular weight amphiphilic poly(ether urethane)s (PEUs). This work was aimed at studying the effect of P407 purification by removing PEO-PPO diblock copolymer by-products on the chemical properties of PEU polymer and the physical properties of PEU hydrogels. Removal of PEO-PPO diblock copolymers (P407_P) was found to preserve the thermo-responsiveness of resulting hydrogels, although slightly lower gelation onset temperature (Tonset) was found for P407_P (15.3°C) vs. P407 (16.7°C) hydrogels (25% w/V) as assessed through temperature ramp test. P407 and P407_P were then reacted with 1,6-diisocyanatohexane and 1,4-cyclohexanedimethanol to synthesize two different PEUs, coded as CHP407 and CHP407_P, respectively. Lower Number Average Molecular Weight (Mn¯) and higher polydispersity Index (D) was measured for CHP407 (Mn¯: 34 kDa, D: 1.6) respect to CHP407_P (Mn¯: 40 kDa, D: 1.4) as a consequence of macrodiol purification. CHP407_P hydrogels formed bigger micelles (43.9 ± 4.1 nm vs. 28.7 ± 4 nm) while showed similar critical micellar temperatures (22.1°C vs. 21.6°C) respect to CHP407 formulations. Sol-to-gel transition of CHP407 and CHP407_P hydrogels was similar while CHP407_P gelation time at 37°C was longer as assessed by tube inverting test. The rheological analysis showed slightly lower Tonset for CHP407_P hydrogels (15% w/V), probably due to larger micelle size, promoting micellar assembly. However, CHP407_P hydrogels showed a significantly lower critical strain than CHP407 hydrogels, as assessed by strain sweep test, suggesting their higher brittleness due to a lower density of intermicellar bridge chains. Nano-scale hydrogel characterization by Low-Field Nuclear Magnetic Resonance spectroscopy supported previous findings, showing lower spin-spin relaxation time (i.e., 1,259 ms) for CHP407_P than for CHP407 hydrogels (i.e., 1,560 ms) at 37°C, which suggested the formation of a more tightly packed network for CHP407_P than CHP407 hydrogel. Finally, lower swelling capability and resistance against dissolution were measured for CHP407_P hydrogels. Overall, the here‐reported results suggested that the heterogeneous structure in the CHP407 hydrogel network caused by the presence of diblock copolymer-based macrodiols improved PEU hydrogel properties in light of their applicability in the biomedical field.

Mechanical Assessment and Hyperelastic Modeling of Polyurethanes for the Early Stages of Vascular Graft Design.

The material design of vascular grafts is required for their application in the health sector. The use of polyurethanes (PUs) in vascular grafts intended for application in the body appears to be adequate due to the fact that native tissues have similar properties as PUs. However, the influence of chemical structure on the biomechanics of PUs remains poorly described. The use of constitutive models, together with numerical studies, is a powerful tool for evaluating the mechanical behavior of materials under specific physiological conditions. Therefore, the aim of this study was to assess the mechanical properties of different PU mixtures formed by polycaprolactone diol, polyethylene glycol, and pentaerythritol using uniaxial tensile, strain sweep, and multistep creep-recovery tests. Evaluations of the properties were also recorded after samples had been soaked in phosphate-buffer saline (PBS) to simulate physiological conditions. A hyperelastic model based on the Mooney–Rivlin strain density function was employed to model the performance of PUs under physiological pressure and geometry conditions. The results show that the inclusion of polyethylene glycol enhanced viscous flow, while polycaprolactone diol increased the elastic behavior. Furthermore, tensile tests revealed that hydration had an important effect on the softening phenomenon. Additionally, after the hydration of PUs, the ultimate strength was similar to those reported for other vascular conduits. Lastly, hyperelastic models revealed that the compliance of the PUs showed a cyclic behavior within the tested time and pressure conditions and is affected by the material composition. However, the compliance was not affected by the geometry of the materials. These tests demonstrate that the materials whose compositions are 5–90–5 and 46.3–46.3–7.5 could be employed in the designs of vascular grafts for medical applications since they present the largest value of compliance, ultimate strength, and elongation at break in the range of reported blood vessels, thus indicating their suitability. Moreover, the polyurethanes were revealed to undergo softening after hydration, which could reduce the risk of vascular trauma.

A Study on the Influence of the Chemical Nature of Fillers on Rheological and Fatigue Behavior of Bitumen Emulsion Mastic.

Cold Bitumen Emulsion (CBE) mixture technologies have been recently developed to lower pavement construction temperatures to reduce environmental costs and control gas emissions. Due to its poor early mechanical strength, active fillers (i.e., cement) have been used to obtain high early stiffness in order to have the potential for timely construction of the next layer. There is, however, a lack of understanding about the impact of active fillers on the viscoelastic behavior and fatigue damage resistance of CBE mastics. This study, therefore, aims to identify the influence of active fillers on the rheological properties and the resulting fatigue behavior of CBE mastic, supported by chemical analysis for the filler-bitumen emulsion. For this aim, bitumen emulsion was mixed separately with seven fillers/blended fillers to prepare the CBE mastics. Various experiments, including continuous pH monitoring tests (chemical reactivity of filler-bitumen emulsion), Strain Sweep (SS) tests, Temperature-Frequency Sweep (TFS) tests, Time Sweep (TS) tests, and Linear Amplitude Sweep (LAS) tests were conducted on the CBE binder and the prepared mastics. Results show that the rheological performance and the fatigue damage resistance depend not only on the filler inclusions but also on filler type and chemistry. On this basis, the rise in complex shear modulus and the decrease in the viscous component is associated with a significant enhancement in fatigue performance for specific fillers.

Cellulose Nanocrystal (CNC)-Latex Nanocomposites: Effect of CNC Hydrophilicity and Charge on Rheological, Mechanical, and Adhesive Properties.

Cellulose nanocrystals (CNCs), a sustainable nanomaterial, are in situ incorporated into emulsion-based pressure-sensitive adhesives (PSAs). Commercially available CNCs with different surface hydrophilicity and surface charge (CNC101 and CNC103 from CelluForce) are used to explore their role in PSA property modification. Viscosity measurements and atomic force microscopy reveal differences in degree of association between the CNCs and the latex particles depending on the surface properties of the CNCs. The more hydrophilic and higher surface charge CNCs (CNC101) show less association with the latex particles. Dynamic strain sweep tests are used to analyze the strain-softening of the nanocomposites based on CNC type and loading. The CNC101 nanocomposites soften at lower strains than their CNC103 counterparts. This behavior is confirmed via dynamic frequency tests and modeling of the nanocomposites' storage moduli, which suggest the formation of CNC aggregates of, on average, 3.8 CNC101 and 1.3 CNC103 nanoparticles. Finally, PSA properties, i.e., tack, peel strength, and shear strength, simultaneously increase upon addition of both CNC types, although to different extents. The relationship between the PSA properties and CNC surface properties confirms that the less hydrophilic CNCs lead to improved CNC dispersion in the PSA films and therefore, enhance PSA properties.

Effects of Bloom number on phase transition of gelatin determined by means of rheological characterization

This study shows the impact of the Bloom number on the melting and gelation behavior of porcine gelatin. Different batches of gelatin were prepared in concentrations of 2, 3, and 5 wt% having Bloom numbers of 100, 180, 240, and 260. Using asymmetrical flow field-flow-fractionation, the molecular weight of gelatin was determined. It was observed that higher Bloom numbers correspond to higher molecular weights. Systematic strain and temperature sweep tests were conducted to determine the yielding point and the phase transition temperatures. The latter was established by the crossover point method and the Winter-Chambon criterion, and small differences between these two methods were recorded. By increasing the Bloom number, the dynamic moduli were increased, as well as the gelation and melting temperatures. The same trend is valid for the gelatin concentration. On the other hand, the Bloom number does not considerably affect the yielding phenomenon under large amplitude oscillatory shear deformations. In conclusion, the Bloom number has a similar rheological effect on gelatin as the molecular weight, and considerable alterations of the viscoelastic gel properties can be expected at significantly different Bloom numbers.

Azobenzene-grafted carboxymethyl cellulose hydrogels with photo-switchable, reduction-responsive and self-healing properties for a controlled drug release system

In this study, multifunctional hydrogels containing host-guest complex formation between azobenzene-grafted carboxymethyl cellulose (CMC-Azo) and β-cyclodextrin (CD) dimers connected by disulfide bonds with agarose for structural support were prepared. The obtained hydrogels exhibited self-healing properties by host-guest complexation as well as gel-sol phase transition in response to ultraviolet (UV) light and reducing agents. Photo-switchable properties of the hydrogels depend on changes in the complex formation of CD-dimers through the trans(450 nm) to cis(365 nm) photo-isomerization of azobenzene. The tensile and strain sweep tests confirmed that the hydrogel's self-healing ability was 79.44% and 81.59%, respectively. In addition, drug release from the hydrogels was controlled to accelerate to 80% in 3 h using UV light or reducing agent. Since the suggested photo-switchable, reduction-responsive, and self-healable hydrogels are non-cytotoxic, they can be potentially applied as biomedical materials in the development of hydrogel-based drug release systems.

Pickering emulsion fabricated smart polyaniline/clay composite particles and their tunable rheological response under electric field

Conducting polyaniline (PANI)/attapulgite (ATP) nanocomposite particle was fabricated via Pickering emulsion polymerization and adopted as a candidate material for a polymer/inorganic -based electrorheological (ER) fluid. Scanning electron microscope and transmission electron microscope demonstrated that the PANI were covered compactly with rod-shaped ATP. Flow, viscoelastic, and yielding characteristics of the PANI/ATP ER fluid, where the synthesized particle was dispersed evenly in silicone oil, were assessed by a rotational rheometer under applied external electric field. The PANI/ATP ER fluid was found to exhibited typical ER characteristics, and the flow curves were scaled appropriately using a modified Mason number for a qualitative description of the rheological behavior of the ER fluid. All three different yield stresses measured from different methods showed a conduction mechanism with a slope of 1.5. In addition, complex viscosity determined by both Cox-Merz rule and its modified Cox-Merz rule were compared with shear viscosity measured under a steady-shear condition. The equivalence between the shear and complex viscosities was also appeared in a strain sweep test for this ER fluid.

Effect of cohesive and adhesive parameters on the moisture resistance of thin friction course (TFC) with varying mix design parameters

Thin friction course (TFC), one typical pavement surface treatments (PSTs), is mixed with modified asphalt emulsion, fine aggregate, and cement. Moisture-induced damage is one of the main distresses usually occurring in TFC. To mitigate potential moisture damage, varying TFCs with different combinations of emulsion, SBR latex, and cement dosages were investigated by the wet track abrasion test (WTAT). Then, the adhesive strength and cohesive stiffness of corresponding residue emulsion-cement mastics were estimated based on the binder bond strength (BBS) test and the strain sweep test, respectively. The results indicated that the increased emulsion, SBR latex, and cement dosages are beneficial to the moisture resistance of TFC. The pull-off strength of BBS test shows poor correlation with the aggregate losses and the failure type is cohesion by observation, which means the adhesion strength of the residue mastic-aggregate bond is higher than the cohesive strength based on the limited data. Furthermore, based on the strain sweep test, it was found that the cohesive parameters, including the maximum shear stress and the complex modulus at the strain level of 7% could perfectly correlate with the average aggregate loss with a correlation coefficient of 0.8841 and 0.8678, respectively. Therefore, both SBR and cement modification could enhance the cohesive stiffness of the cement-binder mastics and then improve the moisture resistance of the TFC.

Fabrication and Characterization of Hydrogels Based on Gelatinised Collagen with Potential Application in Tissue Engineering.

Regenerative medicine is increasingly focused on the development of biomaterials that facilitate cell adhesion and proliferation through the use of natural polymers, which have better biocompatibility and biodegradability. In this way, the use of hydrogels has been considered as a potential option for tissue engineering due to their physical and chemical characteristics. However, few studies associate the raw materials properties and processing conditions with the final characteristics of hydrogels, which could condition their use as scaffolds for tissue engineering. In this context, the main objective of this work was the evaluation of type I collagen as raw material for the elaboration of hydrogels. In addition, gelation time, pH and temperature were evaluated as the most influential variables in the hydrogel processing method by rheological (time, strain and frequency sweep tests) and microstructural (Cryo-SEM) measurements. The results indicate that it is possible to obtain collagen hydrogels with adequate rheological and microstructural characteristics by selecting optimal processing conditions. However, further studies are necessary to assess their suitability for cell accommodation and growth.

Avaliação da influência do envelhecimento e da temperatura nas características viscoelásticas de ligantes asfálticos

As especificações SUPERPAVE (Superior Performing Asphalt Pavements) introduziram a caracterização reológica de ligantes asfálticos, atribuindo propriedades de engenharia aos mesmos. Devido à complexidade do comportamento viscoelástico dos ligantes, os parâmetros reológicos foram inicialmente propostos apenas na região viscoelástica linear (LVER). Sabe-se que a rigidez do material é influenciada diretamente pela frequência, temperatura e envelhecimento. Esse trabalho estudou o efeito da temperatura de ensaio e do nível de envelhecimento na região viscoelástica linear durante o ensaio de varredura de deformações usando o reômetro de cisalhamento dinâmico (DSR). O envelhecimento foi realizado em estufa de filme fino rotativo (RTFO). Foram avaliados três ligantes asfálticos: um ligante convencional, um 60/85-E modificado por SBS (copolímero em bloco de estireno-butadieno-estireno) e o outro altamente modificado (HiMA). Os resultados mostram que os ligantes têm sua região viscoelástica linear reduzida com o aumento do envelhecimento e a redução da temperatura. Os ligantes modificados apresentaram maiores LVER que o ligante convencional, principalmente em altas temperaturas.

New Studies on the Galactomannan Extracted from Trigonella foenum-graecum (Fenugreek) Seed: Effect of Subsequent Use of Ultrasound and Microwave on the Physicochemical and Rheological Properties

The effect of subsequent use of ultrasound and microwave on the physicochemical and rheological properties of galactomannan extracted from fenugreek seed (locally called as Shanbalileh) was investigated. Maximum yield of 18.54% was gained at optimized conditions: ultrasound power of 150 W, microwave power of 500 W, seed to water ratio of 1:30, and extraction time of 150 min. Chemical composition of the galactomannan was 7.03% (wb) moisture, 5.35% (db) ash, 0.85% (db) protein, 0.59% (db) lipid, and 85.89% (db) carbohydrate, respectively. FT-IR analysis admitted representative peaks of polysaccharide at 3400, 2920, 1620, 1400, and 1050/cm. Thermal analysis results revealed a melting range of 60–135 °C and degradation temperature of 280.54 °C. XRD pattern illustrated a large degree of crystallinity in the galactomannan structure. The results of SEM imaging indicated that the obtained galactomannan had a smooth surface. The steady shear flow experiments showed that the shear stress–shear rate, apparent viscosity–shear rate, and shear stress–time well fitted in Herschel–Bulkley, Carraeu, and Figuni–Shoemaker models. The samples with 0.5 and 1% w/v concentration demonstrated viscous-like and sample with 1.5% w/v indicated gel-like behavior upon strain and frequency sweep tests. Other parameters including bulk and tapped density, powder cohesiveness, powder compressibility index, DPPH-free radical scavenging activity, powder solubility, water holding capacity (WHC), and oil holding capacity (OHC) were also evaluated.

Influence of long‐term storage on the performance of polyamide‐based nanocomposites: Role of nanoclay fillers

AbstractThis work deals with the effects of long‐term storage on the properties of polyamide 12 filled with nanoclay mass fractions of 0, 3, and 5%. More precisely, such nanocomposites were prepared using internal mixer, and then stored in a room under ambient conditions, for 6 years, protected from light and temperature variations. The changes in their thermal, mechanical, and rheological properties were analyzed, in relationship with the microstructure changes. Various analyses and tests were conducted, including wide‐angle X‐ray diffraction experiments, water mass loss evaluation, differential thermal analyses, strain sweep tests on solid‐state specimens, as well as time sweep and oscillatory shear measurements on melt‐state specimens. The results mainly revealed the effects of the absorbed water on the changes of the aged nanocomposite performances and highlighted the positive role of nanoclay platelets in the preservation of processability and end‐use properties.

Rheological properties and the micromodel investigation of nanosilica gel-reinforced preformed particle gels developed for improved oil recovery

Preformed particle gels (PPGs) in solutions have been widely used to suppress excess water production in mature oil reservoirs and, in turn, to improve the amount of oil recovery in brown oil fields. In this study, PPG solutions were meticulously formulated and synthesized in order to be utilized in harsh environments in terms of pressure, temperature, pH, and salinity from a free radical polymerization process.In this work, nanosilica gel at different weight percentages was added to improve the mechanical and thermal stability properties of the PPG at harsh condition: high pressure, temperature, and strain. Moreover, the effects of nanosilica gel at various concentrations, ranging from 0.0 to 1.0 wt%, on the PPG swelling properties in a 100,000 ppm brine along with the viscoelastic behavior of acrylamide copolymer (AM) and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) with crosslinker of polyethylenimine (PEI) at 90 °C were studied. Having customized the formulation of the nanosilica-reinforced PPG, the solution was used to investigate the amount oil recovered in a water flooding process on a micromodel scale.The results for the recovery of oil obtained from the injection of PPG solutions were compared with those of water injection without PPG; i.e., the conventional water flooding. It should be stated that the microscopic images showed that nanosilica gel could affect the porous structure of the PPG and the X-ray Powder Diffraction (XRD) results confirmed the nanosilica particle distribution in the PPG pores with different diameters. Hence, the nanosilica-reinforced AM-AMPS/PEI with 1 wt% of the nanoparticles led in swelling of 8 g/g of the dried PPG. In addition, the strain sweep test at 90 °C suggest that increasing of nanosilica gel concentration from 0.2 to 1.0 wt% resulted in 3.34 times increase in the amount of elastic resistance of the PPG breakpoint and, thus, improvement in the complex modulus of initial PPG.In conclusion, the injection of PPG solutions, significant improvement in the oil recovery could be attained. The oil recovery factor increased from 32% under the conventional water flooding to 81% after injection of water with PPG containing only 1 wt% of nanosilica gel. Succinctly, the results confirmed that the tailored formulation had a great potential for field applications to enhance the oil recovery.

Nonlinear \u201coddities\u201d at the percolation of 3D hierarchical graphene polymer nanocomposites

The nonlinear rheology of a novel 3D hierarchical graphene polymer nanocomposites was investigated in this study. Based on an isotactic polypropylene, the nanocomposites were prepared using simple melt mixing, which is an industrially relevant and scalable technique. The novel nanocomposites stand out as having an electrical percolation threshold (≈0.94 wt%) comparable to solution mixing graphene-based polymer nanocomposites. Their nonlinear flow behavior was investigated in oscillatory shear via Fourier-transform (FT) rheology and Chebyshev polynomial decomposition. It was shown that in addition to an increase in the magnitude of nonlinearities with filler concentration, the electrical percolation threshold corresponds to a unique nonlinear rheological signature. Thus, in dynamic strain sweep tests, the nonlinearities are dependent on the applied angular frequency, potentially detecting the emergence of a weakly connected network that is being disrupted by the flow. This is valid for both the third relative higher harmonic from Fourier-transform rheology, I3/1, as well as the third relative viscous, v3/1, Chebyshev coefficient. The angular frequency dependency comprised non-quadratic scaling in I3/1 with the applied strain amplitude and a sign change in v3/1. The development of the nonlinear signatures was monitored up to concentrations in the conductor region to reveal the influence of a more robust percolated network.