Korea-Australia Rheology Journal最新文献

In this work, a one-step reactive extrusion method was adopted to improve comprehensive properties of poly(butylene adipate-co-terephthalate) (PBAT) by melt blending with two chain extenders, including polycarbodiimide (PCDI) and multi-functional epoxy polymer (ADR). Their influences on rheological behaviors, aging properties, and thermal stability of PBAT were explored, and the detailed mechanisms were also discussed. It was found that the terminal carboxyl content of PBAT decreased with addition of PCDI and ADR. When 1.0 wt% PCDI was added, the terminal carboxyl content deceased by 70.3%. This indicated that the reaction between the two chain extenders and the terminal hydroxyl and carboxyl groups of PBAT enhanced to perform the chain extension, which increased the molecular weight, storage modulus, loss modulus, and complex viscosity of PBAT, and different relaxation processes were observed for different samples by Han and Cole–Cole plots. Damp-heat aging resistance measurements showed correlation with terminal carboxyl content in PBAT. And reducing the terminal carboxyl content in PBAT was shown to increase hydrolytic stability. For PBAT with 1.0 wt% PCDI blend, the tensile strength and elongation at break retention were above 70%. In addition, the thermal stability of PBAT was also improved due to the chain extension in the blends, which retarded degradation. The analysis results indicated that the comprehensive performance of modified PBAT was the best when 1.0 wt% PCDI was added.

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The research introduces a numerical method for solving the problem of an axisymmetric rigid smooth body indenting an incompressible elastic layer. This study proposes a computational approach with the deformed mesh interface in the COMSOL Multiphysics software, which allows the discretized interior nodes to move by solving PDEs for the mesh displacements with the given slope boundary condition. The proposed method is applied to the indentation problems with spherical and conical smooth axisymmetric indenters. The results are in a good agreement with the analytical solutions, and the method shows rapid convergence.

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The spreading behavior of droplets impacting solid surfaces is of significant importance in numerous industrial and medical applications. This study specifically focuses on the droplet impact behaviors of shear-thinning fluids. Extensive impact experiments were conducted using high-speed visualization techniques. Image sequences in the DI water and xanthan gum solution droplets impact process are captured at a We range of around 3.2–388 and Re_n of 18–8145. The morphologies of spreading droplets on hydrophilic, moderate, and hydrophobic surfaces was observed with temporal evolution. The experimental results showed that the spreading behavior of shear-thinning droplets varies with the impact velocity, surface wettability, and fluid concentration. The droplets spread more widely and rapidly at larger We with the time evolution of the spreading factor. In addition, the spreading of the droplets becomes suppressed on a hydrophobic surface or with a higher xanthan concentration. With the increase of We, the effect of fluid viscosity gradually surpasses the surface wettability. The fluid viscosity with the shear-thinning properties has more influence on the spreading behavior at high We. Furthermore, the experimental data of the maximum spreading factor could be scaled with the We and Re_n at low and high We, respectively. Finally, the maximum spreading of shear-thinning droplets was correlated with a universal rescaling model. The correlation shows good accordance with the experimental results of droplet impact from this study and the literature in a wide range of impact conditions and shear-thinning properties.

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Silica/PEG200 shear thickening fluids (STFs) are widely used smart fluids. There is often residual water during the STF preparation process because of the strong water adsorbability due to the abundant hydroxyl group on the silica surface. Residual water usually influences the shear-thickening behavior of STFs. How much influence the residual water has during the preparation processes on the properties of STFs is still a problem. In this paper, six preparation processes were designed, and the influence of residual water content on the shear thickening behavior due to different preparation processes is analyzed. Firstly, three drying processes were used to prepare STFs, i.e., three kinds of silica powder, which were obtained from spray, freeze, or oven drying of the silica dispersion, were dispersed in PEG200 to obtain STFs. Secondly, three wet processes were used to prepare STFs, i.e., three kinds of silica slurry, which were obtained by centrifuging and washing through water, ethanol, or tetrahydrofuran of the silica dispersion, were directly dispersed into PEG200 and dried to obtain STFs. All the silica dispersion used in these six preparation processes was prepared using the Stöber method. The properties, microstructure, and residual water content of the STFs prepared by the six preparation processes were explored. The results showed that the preparation processes have a big influence on the properties of related STFs. The silica’s residual water content derived from different preparation processes is the critical factor that affects STFs’ shear thickening performance. The drying process using silica powder from spray drying of the silica dispersion resulted in the lowest water content and led to the best shear-thickening performance of the corresponding STFs. Meanwhile, the wet process using a slurry obtained by centrifuging and washing through tetrahydrofuran of the silica dispersion could also prepare STFs with good shear thickening behavior.

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Nonsolvent-induced phase separation is a widely used technique in the manufacture of polymeric separators. This method involves fine-tuning porous structures through the phase separation of polymer solutions in Li-ion secondary battery systems. The phase separation properties and kinetics of heat-resistant poly(vinylidene fluoride-co-hexafluoropropylene) polymer solutions were characterized by adjusting the weight ratio of N-methyl-2-pyrrolidone (NMP) as a solvent and water as a nonsolvent using both macro- and micro-rheological techniques. The viscoelastic moduli, measured with a rotational rheometer as a macro-rheological technique, and autocorrelation functions describing the fast movements of tracer ceria particles within polymer solutions—quickly detected using the micro-rheological light scattering technique of multi-speckle diffusing wave spectroscopy—offered a comprehensive assessment of the phase separation status and its kinetics during changes in the NMP/water ratio. These results are expected to play a fundamental role in understanding and controlling the pore structures of actual separator membranes applied in Li-ion battery systems.

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Recent experimental observation in thermal-induced gelation of silica-based shear thickening fluids (STFs) has necessitated the efforts to address the thermal instability of the STFs. The shear thickening behavior of hydrophilic fumed silica/PEG disappeared after thermal treatment. Hydrophobic surface is demonstrated to enhance thermal stability of the fumed silica/PEG system under the same thermal treatment. Dynamic temperature sweep experiments reveal a temperature-induced sol–gel transition of the hydrophilic silica/PEG. Meanwhile, hydrophobic silica/PEG does not undergo such gelation and still displays viscosity thickening after thermal treatment. This gelation process is found to be concentration-dependent and irreversible, with enhanced gelation at higher specific surface areas of hydrophilic silica particles. The small-angle X-ray scattering (SAXS) studies suggest that this sol–gel transition is likely attributed to the reduction of solvation layer which could be highly influenced by particle surface hydrophilicity. Comprehensive experiments, including Soxhlet extraction and rheology, confirm that the resulting stable three-dimensional structure is not formed by chemical crosslinks but behaves as a physical network. It is demonstrated how tailoring particle–medium interactions through controlling particle surface characteristics can be used to improve thermal stability of silica-based STFs.

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In the current study, cellulose nanocrystal (CNC) reinforced cyclic olefin copolymer (COC) composite film was fabricated via spin-coating. For the application to the transparent and flexible substrate, the physical characteristics of the composite film were investigated, such as transparency, coefficient of thermal expansion (CTE), thermal properties and scratch resistance. COC was used as a matrix due to its high optical transparency, and CNC was utilized as a filler to lower CTE and enhance the thermal and mechanical properties. As the CNC loading increased, the tensile strength and elastic modulus increased significantly. In addition, the CNC/COC film exhibited a high transparency of 85%.

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Carbon fiber-reinforced plastics (CFRPs) have attracted attention as lightweight materials with exceptional properties, making them suitable for applications in industries where enhanced fuel efficiency and vibration-damping effects are required. However, as CFRP applications expand beyond the mobility sector, the demand for additional functionalities, particularly electrical conductivity, has emerged. In this study, we employed a multi-drop filling process (MDF) to produce hybrid CFRP with imparted electrical conductivity. This approach enables precise resin drop and simultaneous curing, addressing the challenges associated with conventional CFRP production processes. Based on filtering effects during MDF, additives, such as carbon nanotubes (CNTs) and graphene, could concentrate on the surface while resin impregnated the fiber reinforcement, resulting in CFRP with surface-concentrated electrical conductivity (ScEC). We dispersed CNTs and graphene in the resin to induce a bridge effect between the additives. Resin dispersion was achieved using surfactants and solvents, preserving the enhanced electrical conductivity and mechanical properties of the CFRP. The structure, electrical conductivity, and mechanical properties of the fabricated CFRP were evaluated. The results show that the hybrid CFRPs possess the intended structure and exhibit ScEC. This study paves the way for the fabrication of CFRPs with different functionalities, thereby promoting their applications in various industries.

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The use of machine learning to predict rheological properties of polymers has great potential to facilitate the characterization of novel materials. Here, we have suggested the analogy between the double reptation (DR) and the deep neural network model. The double reptation model itself can be the special case of the deep learning method; linear activation function, and identical sets of weights for the two hidden layers are the characteristics of the double reptation model. The identical sets of weights in the double reptation model are related with the molecular weight distribution (MWD). We first generated ground truth data based on double reptation model. Then, we analyzed the dataset with reptation-guided deep neural network (RGDNN). We showed that the RGDNN model is available to determine entanglement molecular weight (plateau modulus), and monomeric friction factors from the simulated experimental rheological data (prepared using DR model) without any additional information. Overall, a noteworthy conceptual improvement in the determination of major factors that determine the rheological behavior of ultrahigh molecular weight polyethylene (UHMWPE) gels has been achieved.

The deformation capacity conditions several processes in cement-based materials, including workability and structural build-up. However, the origins of this deformation capacity present some ambiguities. This paper aims to contribute to improving the comprehension of the deformation capacity of fresh cement pastes. For this, the effect of water-to-cement ratio (w/c) and superplasticizer (SP) dosage on the viscoelastic properties of cement paste is examined using oscillatory rheology and yield stress measurements. It appears that water to cement ratio affects slightly the critical strain at the end of the linear viscoelastic domain (LVED) and strongly the storage modulus. The addition of superplasticizer seems to have a strong effect on the critical strain. In addition, it was shown that the critical strain at the end of the LVED is associated with strong physical forces (colloidal forces enhanced by early hydrates formation), while the transition strain at the flow onset is due to large structural reorganizations.