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The dynamics of model colloidal gels under a steady shear flow is studied by means of a Brownian dynamics (BD) simulation while applying orthogonal superposition rheometry, which superimposes a small amplitude oscillatory flow orthogonal to the main flow direction. Orthogonal dynamic frequency sweep (ODFS) curves are obtained at various magnitudes of the main flow, which shows shear thinning behavior of the colloidal gel. The viscoelastic spectra of the ODFS can be superimposed onto a master curve by the horizontal shift factor, which is equivalent to particle viscosity. That is, the shear rate controls a single master clock for all viscoelastic spectra of the ODFS in the form of a time–shear rate superposition, which bears an analogy with the time–temperature superposition of polymeric systems. In the low-frequency region of the master curve, both orthogonal moduli are well superimposed onto a single master curve, whereas the loss modulus deviates slightly from the master curve in the high-frequency region, which coincides with the experimental findings. We observe spatial and time-varying structural properties in both low- and high-frequency regions on the ODFS curves by decomposing the pair distribution function. It is verified that each flow condition shifted onto the same stress level on the master curve shows identical spatial orthogonal moduli at all radial distances despite the differences in the aggregate size and average particle connectivity.

We propose a groove-embedded partitioned pipe mixer (GPPM) and conduct an in-depth numerical study on the flow and mixing characteristics of the GPPM in the creeping flow regime. The GPPM is a variant of a previously reported mixer, the barrier-embedded partitioned pipe mixer (BPPM), and is designed to achieve better energy-efficient mixing compared to the BPPM. In this paper, we first introduce the working principle of the GPPM and its mixing protocols. Then, the flow system affected by mixing protocols and geometrical parameters of the GPPM is investigated using Poincare sections. As for mixing characteristics, the flux-weighted intensity of segregation is employed for quantitative mixing analysis. It turns out that a GPPM with a proper set of design parameters can indeed lead to a globally chaotic mixing. More importantly, the best GPPM showed better mixing in terms of energy consumption compared to its counterpart, the best BPPM.

In order to investigate how particle aggregation affects tensile mechanical performance of composite, a ductile biopolymer (poly(caprolactone)) was melt-compounded with CaCO3 particles over a wide concentration range from 10 to 60 wt.%. The aggregation of CaCO3 particles in poly(caprolactone) (PCL) is investigated depending on particle concentration and surface modification (with stearic acid (2.5 wt.%)) based on rheological assessment. If the composite is mixed with a high concentration of particles (> 30 wt.%), morphological observations and a thermal behavior analysis do not find a difference in the particle aggregation regardless of particle surface modification. However, the linear viscoelastic moduli of the composites distinguishes the difference in particle aggregation regarding to surface modification, indicating induced aggregation behavior with surface-modified CaCO3 (sCC). The composite with sCC starts to form network structure of particles at a lower concentration (30 wt.%) than that with unmodified particles (40 wt.%). When particles form the network structure above the particle percolation threshold, the yield strength of the composite begins to decrease even though Young’s modulus is still increasing. In contrast to the expectation of the better dispersion of particles by surface modification as well as improved tensile mechanical performance with better dispersion, sCC rather induced aggregation with a lower concentration of particle than unmodified particles which resulted in decrease in yielding performance. This study showed that rheological study, especially for the composite with high concentration of particles, is useful to figure out the particle dispersion against a limit at morphology observation.

A systematic study using a model negative electrode slurry with poly(acrylic acid) as a binder is conducted aiming at the control of both dispersion quality and rheology in the electrode manufacturing process. Rheological properties of the model slurries vary considerably with the neutralization degree α. Optical microscope and Turbiscan measurements show that the rheological change is accompanied by the change in particle aggregation tendency. Adsorption and zeta potential measurements reveal that α-dependent adsorption of poly(acrylic acid) is the key factor that controls the rheology of the slurries. The difference in α of the slurry results in a significant difference in the surface roughness and the carbon black particle distribution in the electrode. From this study, it is concluded that the adjustment of neutralization degree of poly(acrylic acid)-based binder critically affects the heterogeneity of the electrode, which can influence the performance as well as the rheological stability in the electrode manufacturing process.

In this study, the transport and deposition of colloidal particles onto a patterned membrane surface are analyzed by both numerical simulation and experiment. The channel Reynolds number (Re) and the size ratio of the particle to the pattern (a/h) are chosen as the major simulation parameters. With an increase in Re and a/h, the number of deposited particles decreases and the rate of permeate flux decline is reduced. Under certain specific combinations of the design parameters, the suspended particles are impeded to access the patterned membrane surface. Based on the particle trajectory analysis, it is claimed that “inaccessible zones”, where the suspended particles cannot be accessed by the flow, are formed near the patterned membrane surface, with the increase in Re and a/h. Cross-flow microfiltration experiments using a poly(methyl methacrylate) (PMMA) particle suspension are also conducted to verify the trend in particle deposition observed in simulation. As the radius of the PMMA particle increases, the number of deposited particles is reduced and the critical flux for the onset of the particle deposition is increased, which qualitatively matches well with simulation. It is found that a patterned membrane can reduce tremendous amounts of colloidal fouling by prohibiting the access of the suspended particles to the membrane surface with the appropriate choice of design parameters such as Re and a/h.

We investigate the drying process of monodisperse colloidal film over a wide range of Péclet number (Pe) by using the Brownian dynamics simulation. We analyze the detailed process in three aspects; accumulation front, normal stress, and microstructure. The evolution of particle distribution is quantified by tracking the accumulation front. The accumulated particles contribute to the continuous increase of the normal stress at the interface. At the substrate, the normal stress first stays constant and then increases as the accumulation front touches the substrate. We quantitatively analyze the stress development by a scaled normal stress difference between the two boundaries. At all tested Pe, the stress difference increases to the maximum, followed by a decrease during drying. Interestingly, a mismatch is observed between the stress difference maximum and the initial stress increase at the substrate. The microstructural analysis reveals that this mismatch is related to the microstructural development at the substrate.

A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 &times, 10&minus, 2 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeter~aggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G&prime, ), high Young&rsquo, s modulus, high dielectric loss (&epsilon, &Prime, ), and negative&ndash, positive switching of dielectric constant at high frequency (of 103 Hz) of composite.

A binder plays a critical role in dispersion of coating liquids and the quality of coating. Poly(vinylidene fluoride) (PVDF) is widely used as a binder in cathode slurries, however, its role as a binder is still under debate. In this paper, we study the role of PVDF on the rheology of cathode battery slurries consisting of Li(Ni1/3Mn1/3Co1/3)O2 (NCM), carbon black (CB) and N-methyl-2-pyrrolidone (NMP). Rheology and microstructure of cathode slurries are systemically investigated with three model suspensions: CB/PVDF/NMP, NCM/PVDF/NMP and NCM/CB/PVDF/NMP. To highlight the role of PVDF in cathode slurries, we prepare the same model suspensions by replacing PVDF with PVP, and we compare the role of PVDF to PVP in the suspension rheology. We find that PVDF adsorbs neither onto NCM nor CB surface, which can be attributed to its poor affinity to NCM and CB. Rheological measurements suggest that PVDF mainly increases matrix viscosity in the suspension without affecting the microstructure formed by CB and NCM particles. In contrast to PVDF, PVP stabilizes the structure of CB and NCM in the model suspensions, as it is adsorbed on the CB surface. This study will provide a useful insight to fundamentally understand the rheology of cathode slurries.

In this paper we investigated numerically the flow and mixing characteristics of the barrier-embedded partitioned pipe mixer (BPPM) in non-creeping flow conditions. Numerical simulations are conducted for three mixing protocols of the BPPM, co-rotational, mirrored co-rotational, and counter-rotational protocols in the range of the Reynolds number (Re), 0.1≤Re≤300, focusing on the effect of the Reynolds number, the barrier height, and the mixing protocols on the mixing in the BPPM. Each mixing protocol creates two crosssectional flow portraits with crossing streamlines. Poincare sections were plotted to investigate the flow system affected by the Reynolds number and the barrier height. Mixing in a specific BPPM is characterized using the intensity of segregation in terms of the compactness and the energy consumption. The dependency of the barrier height and the Reynolds number on the final mixing state of the BPPMs was identified by mixing analyses. The co-rotational protocol results in an efficient mixing in the creeping flow regime. Meanwhile, mirrored co-rotational and counter-rotational protocols, which lead to poor mixing in the creeping flow regime, turned out to be efficient protocols in the higher Reynolds number regime.

We investigate the influence of inter-particle affinity on the microstructure and rheological behavior in the bimodal suspension systems. For this purpose, we design the suspensions using two kinds of polystyrene beads (PS, size ∼530 nm) as a large particle which are electrostatically stabilized and are different in surface properties only, while keeping unstable alumina coated silica (Al-silica, size ∼12 nm) as a small particle. To change the affinity, hydrogen bonding is induced by modifying surface of PS as poly (vinyl pyrrolidone) (PVP). The influence of affinity between large and small particles is investigated by observing the changes in rheological properties and microstructure. Even with the same, the formation of Al-silica cluster which connects large particles is dominant when sulfate modified PS is used and the affinity between the particles is not strong. On the contrary, the Al-silica particles cover the surface of large particles rather than making bridges when PVP modified PS is used and the affinity is strong. The phase map which shows fluid-gel transition according to the composition of the suspension is also obtained. The affinity is found to affect the shape of the phase map too. This research explains how the differences in affinity between large and small particles affect the bimodal suspensions according to the surface properties of the particles, and provides an insight on the complex behavior of particulate fluids.

In this study, we examine the complex interplay between particulate fouling and flow disturbance via particle simulation and microfluidic experiments. From the experiment, it is found that a particle is transported and deposited following the streamline, which is affected by the existing particle deposit. Inspired by this microfluidic observation, we develop a novel coarse-grained particle simulation, which continuously updates the flow field by considering the particle deposits, to investigate particulate fouling more intensively. Four physical factors are proposed to describe quantitatively the particulate fouling: effective collision, hydrodynamic boundary layer, inaccessible zone, and high shear stress region. In the initial stage of fouling, a number of particles are deposited within the growing hydrodynamic boundary layer, where effective collisions are readily achieved. In the latter stage of fouling, the inaccessible zone and high shear stress region are expanded, which causes the particle deposition rate to decrease. This result provides a comprehensive understanding of the particulate fouling through the combination of the four physical factors.

In this study, the clogging mechanism of poly(styrene) particles in the flow through a single micro-pore was investigated. Together with the microscopic observation, the pressure drop was also measured. The pressure drop fluctuated according to the amount of particles deposited inside the channel. When the particles deposited and blocked the channel, the channel was clogged and the pressure drop increased sharply. During the clogging process, the particles were often detached by the flow, and interesting behaviors, such as “rolling” and “stick and detach”, were found to be the key factors that determine whether the clogging completely occurs or not. Above a certain flow rate, the channel was not clogged and the pressure drop did not increase further. The particles deposited in the upstream had an influence on the flow path. When the particles were deposited in the upstream, the flow detoured and the vortex was formed. The effect of viscosity was examined by controlling the concentration of glycerol solution. As the viscosity and the flow rate increased, the shear stress applied to the particles became larger and it was more difficult for the particles to get accumulated. The normalized clogging pressure drop decreased exponentially with shear stress. It was unity above a certain shear stress, in which the particles did not clog the channel completely.

Time-dependent viscoelastic properties of Oldroyd-B fluid were investigated by lattice Boltzmann method (LBM) coupled with advection-diffusion model. To investigate the viscoelastic properties of Oldroyd-B fluid, realistic rheometries including step shear and oscillatory shear tests were implemented in wide ranges of Weissenberg number (Wi) and Deborah number (De). First, transient behavior of Oldroyd-B fluid was studied in both start up shear and cessation of shear. Stress relaxation was correctly captured, and calculated shear and normal stresses agreed well with analytical solutions. Second, the oscillatory shear test was implemented. Dynamic moduli were obtained for various De regime, and they showed a good agreement with analytical solutions. Complex viscosity derived from dynamic moduli showed two plateau regions at both low and high De limits, and it was confirmed that the polymer contribution becomes weakened as De increases. Finally, the viscoelastic properties related to the first normal stress difference were carefully investigated, and their validity was confirmed by comparison with the analytical solutions. From this study, we conclude that the LBM with advection-diffusion model can accurately predict time-dependent viscoelastic properties of Oldroyd-B fluid.

For melt-compounded poly(lactic acid) composites containing graphene nanoplatelets (GNPs) at low volume fractions, ϕGNP ≤ 0.34 vol. %, this study focused on correlation between the composite properties and a large-scale structure of GNPs formed by a strong alternating current electric field (with the frequency and intensity of 60 Hz and 1.75 kV/mm, respectively). The electric field was applied to the composite in a rheometer through the parallel plate fixture, so that the parallel plates served as the rheological measurement fixture as well as the electrodes. Optical microscopy, transmission electron microscopy, and two-dimensional wide-angle X-ray diffraction measurements revealed that almost randomly oriented, thin stacks of GNPs in the as-fabricated composites were aligned by the electric field in the field direction and further organized into an extended chain (or column) of stacks. This chained-stack structure bridged two parallel plate electrodes when ϕGNP was above a threshold value, ϕGNP* ≅ 0.17 v...

Butt-fusion welding is an effective process for welding polymeric pipes. The process can be simplified into two stages. In heat soak stage, the pipe is heated using a hot plate contacted with one end of the pipe. In jointing stage, a pair of heated pipes is compressed against one another so that the melt regions become welded. In previous works, the jointing stage that is highly related to the welding quality was neglected. However, in this study, a finite element simulation is conducted including the jointing stage. The heat and momentum transfer are considered altogether. A new numerical scheme to describe the melt flow and pipe deformation for the butt-fusion welding process is introduced. High density polyethylene (HDPE) is used for the material. Flow via thermal expansion of the heat soak stage, and squeezing and fountain flow of the jointing stage are well reproduced. It is also observed that curling beads are formed and encounter the pipe body. The unique contribution of this study is its capability of directly observing the flow behaviors that occur during the jointing stage and relating them to welding quality.

In this study, the effect of organoclay as a compatibilizer in immiscible poly(lactic acid) (PLA) and natural rubber (NR) blends was studied. Structural development of PLA90/NR10 blend was examined depending on the clay content (0.5–10 wt%). The drop size of the dispersed NR phase initially decreased and then remained constant as the clay content increased. Below the critical concentration (3 wt%), the clay was selectively localized mostly at the interface between the matrix phase (PLA) and the dispersed phase (NR), whereas the clay particles were additionally observed in the matrix phase above 3 wt%. XRD analysis revealed that the gallery structure of the clay was highly dependent on the concentration and selective location of the clays. The development of the structure and the physical properties of the blend were also investigated according to the clay contents by measuring the linear viscoelasticity and surface tension. The degree of clay exfoliation was analyzed quantitatively in terms of the modulus ratio of PLA/NR/clay and PLA/clay. The elongational behavior and mechanical properties of the blends were strongly dependent on the location of the clays. The clay worked as an efficient compatibilizer below the critical content, while it worked as a reinforcing filler above the threshold, making the matrix more rigid.

We explore the relaxation behavior of model colloidal gels under steady shear flow by means oforthogonal superposition rheometry. Fumed silica and carbon black dispersions in Newtonian matrices are used as a model system. As shear rate increases, the frequency dependent orthogonal moduli of the gels shift along the frequency axis without changing their shape, which finally can be superimposed to yield a single master curve. This indicates that the shear rate tunes a master clock for overall relaxation modes in the sheared colloidal gels to produce a ‘‘time-shear rate superposition (TSS)’’, as temperature does in polymeric liquids to produce a time-temperature superposition (TTS). The horizontal shift factor required at each shear rate to obtain the master curve is found to be directly proportional to the suspension viscosity for all the cases. From this result, we suggest that the suspension viscosity determines the overall relaxation time of the particles in the flowing colloidal gel. ispartof: Soft Matter vol:14 issue:42 pages:8651-8659 ispartof: location:England status: published

Silica nanoparticle (SiNP)-poly(vinyl alcohol) (PVOH) coating is an important material system in paper coating applications, where particle distribution critically affects coating performance. In the present study, the authors investigated a role of physicochemical interaction between SiNP surface and PVOH chain in SiNP distribution in the coating layer, with a comparison of the suspension at pH 3 (good interaction) and pH 10 (poor interaction) as PVOH concentration was varied. Rheological properties and sedimentation behavior of the suspensions showed the dispersion stability of SiNP at pH 3 was improved by the addition of PVOH, whereas it was independent of the PVOH concentration at pH 10. Scanning electron microscopy and small angle x-ray scattering intensity of dried coating layer showed the uniform and dense structure with homogeneous distribution of SiNPs at pH 3, where spatial arrangement of SiNPs depended on the addition of PVOH. However, non-uniform and porous structures with SiNP aggregates were observed at pH 10, where the spatial arrangement of SiNPs was independent to the addition of PVOH. The stress development during drying of the coating suggested that the mechanical property was related to the spatial arrangement of individual SiNPs at pH 3, whereas to the distribution of SiNPs aggregates at pH 10.

The formation of Taylor cone jet is a key process in electrohydrodynamic printing that is used to produce high resolution patterns. Even though the inks are complex fluids composed of particles, binder, and solvent, most of previous researches have assumed the ink as a Newtonian fluid. In this study, we investigate the effect of viscoelasticity of the ink on Taylor cone jet using two model systems designed to control the elasticity and viscosity of the ink independently. The elasticity and viscosity improve the stability by expanding the operating windows for Taylor cone jet. The results can be summarized in terms of two parameters: elasticity parameter, ξ, and viscosity parameter, χ. The increase in elasticity widens the range of voltage for Taylor cone jet zone, while the range of flow rate remains independent of elasticity. The effect of elasticity is dominant for ξ>1while it is nearly negligible for ξ1. This study will contribute to the optimal design of EHD printing ink by providing the operating window maps in terms of material properties. Keywords: Ink viscoelasticity, Taylor cone jet, Operating window map, Electrohydrodynamic printing

There have been many efforts to enhance the performance and the stability of Li-ion battery. It is crucial to develop a new material as well as to understand the mechanism of microstructure formation of the electrode in order to enhance the performance of the battery. In this study, the effect of sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) on the microstructure formation as well as on the rheological properties in the aqueous anode slurries is investigated. The graphite particles aggregate with each other due to their hydrophobicity and form a gel structure in an aqueous slurry. Both CMC and SBR induce the dispersion of the graphite particles by adsorbing onto the graphite surface. In the graphite/CMC/SBR slurry, the SBR can affect the dispersion of the graphite particles at low CMC concentration, while the microstructure is not changed regardless of added SBR at high CMC concentration because the SBR cannot adsorb on the graphite surface due to the presence of CMC. The microstructure of the slurry is also confirmed by the cryo-SEM images. Understanding the role of the binders on the microstructure formation will be helpful for the effective design of the battery slurries.

본 연구에서는 폴리프로필렌/아이오노머/클레이 삼상 복합체에서 클레이의 분산 및 위치에 따른 복합체의 구조변화와 물성을 연구하였다. 폴리프로필렌 90 wt%, 아이오노머 10 wt%의 블렌드에 클레이를 0~10 wt% 첨가하면서 물성변화를 관찰하였다. 클레이 함량 3%이하의 복합체에서 클레이는 아이오노머 상의 내부에 존재하는 반면, 클레이 함량이증가하면서 분산상에 클레이가 채워져 견고한 구조가 형성되며 추가적인 클레이는 계면에 존재하게 된다. 이에 따라계면에서의 상호작용은 폴리프로필렌과 아이오노머로부터 폴리프로필렌-클레이와 아이오노머-클레이의 상호작용으로변화하며 이에 따라 미세구조 및 유변물성이 변화한다. 복합체의 저장 모듈러스(G’)는 클레이가 분산상의 내부에 존재할 때는 거의 영향을 받지 않지만 클레이가 계면에 위치하면서부터 크게 증가한다. 또한 파단면의 모폴로지 역시 클레이가 복합체의 내부에만 존재할 경우에는 분산상의 상 경계가 뚜렷하게 관찰되고 분산상의 크기가 증가하지만, 클레이가 계면에 위치할 때는 분산상의 크기가 줄어들고 파단면의 모폴로지 역시 상의 경계가 뚜렷하게 관찰되지 않는 상용화된 모폴로지를 보인다. 우리는 복합체의 유변물성의 변화를 통하여 분산상 내부구조의 변화에 따른 클레이의 위치변화와 계면에서의 상호작용의 변화를 정량화 하였다. 또한 고체상태에서의 계면 접착량 측정을 통하여 계면에서의상호작용의 증가함에 따라 접착력이 증가하고, 미세구조상 클레이 입자가 계면에 존재할 때 결정화도가 낮아짐을 확인하였다.Abstract − In this study, structural developments of polypropylene / ionomer / clay ternary composites were investi-gated depending on the dispersion and localization of clay. The changes in physical properties were observed addingorganoclays 1~10wt% to 90% polypropylene and 10% ionomer blends. The organoclays were localized inside of thedispersed phase under the composition of 3wt%, however, over that composition, clay particles formed stiff networkstructure in the dispersed phase and additional clays were localized at the interface between two phases. According tothe developments of microstructure, the interaction of ternary composites changed from polypropylene-ionomer to poly-propylene-ionomer and ionomer-clay which affected rheological properties. The storage modulus (G’) of the compos-ites was similar to the blends when clays were localized inside of dispersed phase but increased when clays werelocalized at interface. Also, the fractured morphology of the composites showed phase boundary and growing radius ofdispersed phase depending on addition of fillers when clays were found inside. However, when fillers found at the inter-face between blends, the radius of the dispersed phase decreased and compatibilized morphology were observed. Theinterfacial interaction of the ternary composite was quantified depending on the structural development of dispersedphase and localization of clay particles by the rheological properties. The interaction of composites at solid state which

Patterned membranes have been proposed as a promising solution to membrane fouling in membrane processes for water treatment. CFD modeling studies were carried out to elucidate the anti-fouling effect of patterned membranes However, patterned membranes prepared usually by a phase inversion method are more likely to have broad pore size distributions and most modeling studies are based on two-dimensional space despite the three-dimensional pattern geometry. In this study, a patterned isopore membrane with reverse-pyramid patterns on its surface and a narrow pore size distribution was prepared from UV-curable polymer by the soft lithographic method. Factors affecting particle depositions on patterned isopore membranes were investigated during the crossflow microfiltration of different micro-sized particles and their mixture. The extent of particle deposition was largely dependent on crossflow velocity, pore water flux, and particle size. Particularly, the ratio of crossflow velocity to pore water flux mostly governed the extent of particle depositions (i.e., membrane fouling) on the patterned membrane surface and 3-D modeling based on computational fluid dynamics was also conducted to predict the formation of two distinct stream lines (bulk and vortex) and elucidate the mechanisms of anti-fouling characteristics of patterned membranes.

In this paper, the flow pattern of viscoelastic fluids flowing inside a 4:1 planar contraction microchannel was investigated and quantitatively analyzed. A wide range of Weissenberg number flows of poly(ethylene oxide) solutions were observed while maintaining low Reynolds number (0.01 > Re). As the shear rate or fluid elasticity was increased, a transition from steady to unsteady flow was observed. In the steady flow region, the flow pattern was Newtonian-like, progressed to a divergent flow where the upstream flow pattern was distorted due to elasticity, and then a vortex developed at the upstream corners. The vortex, which was stable at first, fluctuated with a certain period as the Weissenberg number increased. The oscillating vortex was symmetric at first and became asymmetric with various patterns. As the elasticity increased further, the vortex randomly fluctuated without any time period. The Lyapunov exponent for the change in vortex size was positive, meaning that the flow was spatially chaotic. This paper systematically analyzed the flow patterns of the elastic fluids in the micro-contraction flow, which included; Newtonian-like flow, divergent flow, oscillating flow with symmetry, oscillating flow with asymmetry, and chaotic flow.

Preheating of dental composites improves their flowability, facilitating successful restorations. However, the flowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied. The rheological properties of Z350 dental composites at 25, 45, and 60°C were measured by a strain-controlled rheometer. When a low strain (0.03%) was applied, the preheated composite exhibited greater shear storage modulus (G') and complex viscosity (η*) than a room-temperature composite. Oppositely, when a high strain (50%) was applied, G' and η* of a preheated composite were lower than those of a room-temperature composite. Preheating of dental composites might be helpful in clinical practice both to increase the slumping resistance when minimal manipulation is used (e.g., during the build-up of a missing cusp tip) and to increase flowability when manipulation entailing high shear strain is applied (e.g., when uncured composite resin is spread on a dentin surface).

Changes in flow pattern were investigated for a viscoelastic fluid (polyethylene oxide) in various-sized micro-fabricated planar 4:1 contraction channels. The flow pattern changed from a Newtonian-like flow to a flow with a vortex growth region, during which a divergent flow and lip vortex were also observed depending on the elasticity number (El) and aspect ratio. When the aspect ratio was large, the lip vortex was observed only in a limited number of cases, and the flow pattern occurring before the vortex growth was more diverse. When the elasticity number was large, the divergent flow was not observed unlike the cases in which the Elasticity number was small. The flow pattern in the contraction microchannel was found to be diverse and abundant depending on the aspect ratio and elasticity number.

Membranes with a patterned surface have become attractive for the mitigation of biofouling in membrane processes for water and wastewater treatment. However, previous studies have paid little attention to factors affecting pattern fidelity in the preparation of patterned membranes. Here, we examined several parameters such as the molecular weight and concentration of the polymer in the dope solution which might affect the pattern fidelity of prism-patterned membranes. Greater pattern fidelity was achieved as the molecular weight of the polymer decreased and its concentration increased. Pattern fidelity was also dependent on the work of adhesion of the replica mold and the polymer solution. In the crossflow filtration test, deposition of the GFP tagged P. aeruginosa PAO1 was decreased on the patterned membranes with a higher pattern height. The mechanisms involved in the preparation of patterned membranes with different fidelities were also investigated.

A vertically aligned carbon nanotube (VA CNT) membrane created from the successful fusion of nanotechnology and membrane technology has been stated to be a next generation membrane due to its fast water transport and antimicrobial properties. Although previous studies of the VA CNT membrane reported the potential for fast water transport or desalination by molecular dynamics simulation, this study is the first to report on the feasibility of using the VA CNT membrane for water purification. The VA CNT membrane (4.8 nm of pore diameter and 6.8×1010 #/cm2 of pore density) was fabricated and its flux, rejection performance, and membrane biofouling tendency were evaluated in comparison to the commercial ultrafiltration (UF) membrane. The VA CNT membrane appeared to have a water flux approximately three times higher than the UF membrane and water transport approximately 70,000 times faster than conventional no-slip flow. This higher flux was peculiarly observed in water, the most hydrophilic solvent, while other solvents showed that permeate flux decreased with higher viscosity. The rejection property of the VA CNT membrane as examined by the MWCO measurement was similar to the commercial UF membrane. Additionally, the VA CNT membrane showed better biofouling resistance with approximately 15% less permeate flux reduction and 2 log less bacterial attachment than the UF membrane. This study reports the high potential of the VA CNT membrane with antifouling property in the water purification process.

This paper aims at correlating the dispersion of multi walled carbon nanotubes (MWCNT) in natural rubber latex (NRL) medium with the rheological properties of nanocomposites. For this, MWCNTs were first treated with surfactants of different charges – anionic sodium dodecyl sulphate (SDS), cationic cetyl trimethyl ammonium bromide (CTAB) and non-ionic Tween 20 (TW) – prior to their latex dispersion by solution mixing. Simple techniques like UV visible spectroscopy and sedimentation index analysis are used to explore the better dispersion of surfactant/MWCNTs in aqueous medium, where the surfactants reduce the agglomeration and entanglement of the nanotubes and facilitate strong filler–polymer interfacial adhesion. Rheology of the NRL-MWCNT suspensions is applied to derive the CNT–latex interfacial interactions in a quantitative way. For this Maier-Goritz theoretical modeling is applied on the observed ‘Payne effect’. The effect of concentration of fillers, mixing time and temperature on the viscoelasticity of composites were also investigated. Contact angle measurements, transmission electron microscopy and Raman spectroscopy have been employed to substantiate the enhanced compatibility of surfactants wrapped MWCNTs with NRL where a promising dispersion and interfacial adhesion were achieved.

In this study, we report on a numerical study on design optimization for a microfluidic crossflow filtration system incorporated with the staggered herringbone micromixer (SHM). Computational fluid dynamics (CFD) and the Taguchi method were employed to find out an optimal set of design parameters, mitigating fouling in the filtration system. The flow and the mass transfer characteristics in a reference SHM model and a plain rectangular microchannel were numerically investigated in detail. Downwelling flows in the SHM model lead to backtransport of foulants from the permeable wall, which slows down the development of the concentration boundary layer in the filtration system. Four design parameters &mdash, the number of grooves, the groove depth, the interspace between two neighboring grooves, and the interspace between half mixing periods &mdash, were chosen to construct a set of numerical experiments using an orthogonal array from the Taguchi method. The Analysis of Variance (ANOVA) using the evaluated signal-to-noise (SN) ratios enabled us to identify the contribution of each design parameter on the performance. The proposed optimal SHM model indeed showed the lowest growth rate of the wall concentration compared to other SHM models.

The distinct structure and flow properties of capillary suspensions, i.e., ternary solid/fluid/fluid systems including two immiscible fluids, make these kinds of slurries promising candidates for the fabrication of Li-ion battery electrodes. Recently, aqueous graphite slurries have been introduced that have beneficial coating properties and yield high-capacity cells with a superior electrochemical performance. Here, we investigate how SBR particles, frequently used as a binder in graphite slurries, affect the structure and flow of the wet paste as well as the adhesion of the dry anode layer. Combining rheological, interfacial and structural investigations revealed that the SBR particles are located at the interface of both liquid phases, and the amount of added SBR and the energy input for dispersing the secondary fluid offer extra degrees of freedom for adjusting the flow properties and microstructure according to processing and product demands. Most importantly, at a given SBR content, the adhesion strength of the capillary-suspension-type graphite slurries to the current collector is substantially higher than for the anode layers made from conventional suspensions. This novel approach promises battery electrodes with extended durability at a low binder content and improved electrical conductivity. Further research on this highly technical highly demanding topic is needed to understand the underlying physics and its impact on electrochemical cell performance.

We used real-time fluorescence microscopy to investigate the migration of latex particles in drying battery slurries. The time evolution of the fluorescence signals revealed that the migration of the latex particles was suppressed above the entanglement concentration of carboxymethyl cellulose (CMC), while it was significantly enhanced when CMC fully covered the surfaces of the graphite particles. In particular, a two-step migration was observed when the graphite particles flocculated by depletion attraction at high CMC/graphite mass ratios. The transient states of the nonadsorbing CMC and graphite particles in a medium were discussed, and the uses of this novel measurement technique to monitor the complex drying processes of films were demonstrated.

In this study, the nonlinear response of polymer nanocomposites under large amplitude oscillatory shear (LAOS) flow was investigated. We first investigated polycaprolactone (PCL)/multiwall nanotube (MWNT) composites under LAOS flow using different analyzing methods including Lissajous plot analysis, stress decomposition, and Fourier transform rheology (FT-rheology). The nonlinear parameter Q (≡I3/1/γ02) was obtained from the FT-rheology as a function of strain amplitude, and the zero-strain nonlinearity Q0 (≡limγ0→0Q) was also calculated. We compared the linear and nonlinear viscoelastic properties as we increase MWNT concentration (ϕ). It was found that the zero-strain nonlinearity (Q0) was more sensitive to detect the effect of MWNT concentration than the linear viscoelastic properties. We also investigated the effect of particle shape on nonlinear viscoelastic properties of the polymer composites containing particles of different shape, e.g., PCL/MWNT (one-dimensional thread shape), PCL/organomodified ...

The presence of coarse particulate components in tailings streams poses significant challenges to the mineral processing industry. Suspensions with fast-settling coarse fractions make traditional rheological measurements tedious and inaccurate. These measurements are critical to the design and operation of mixing, dewatering, pumping and tailings equipment and operations. A methodology for predicting the gel point, close packing fraction and shear rheology of particulate slurries containing a binary mixture of fine and coarse material is presented. The model has validity subject to the constraint that the particle size of the coarse material is sufficiently distinct from that of the fine material. The model enables calculation of the gel point and close packing fraction of the mixture based on the gel points and close packing fractions of the pure fine and coarse materials in the suspension. The model predicts that the gel point (and close packing fraction) of the fine material increases with increasing coarse fraction until a maximum value is attained before decreasing to the gel point (or close packing fraction) of the coarse material. This relationship provides a subsequent basis for a yield stress model to accurately predict the yielding behaviour of binary mixtures of fine and coarse material. The model is useful in determining whether a sample exhibits yield stress behaviour through knowledge of the gel point and close packing fraction of the constitutive fine and coarse components. The model is exemplified using particulate mixtures containing coagulated aluminium oxide, calcium carbonate and coarse sand.

Patterned membranes for water treatment processes have been proposed to mitigate the detrimental effect of membrane fouling. Analysis of the effects of various pattern shapes on antifouling properties is required to achieve a higher resistance to fouling in these membranes. In this study, membranes for water treatment with unpatterned, pyramid, reverse-pyramid, and 45°-rotated pyramid patterns were prepared, and their antifouling effects were compared by measuring the extent of particle deposition during crossflow filtration. The 45°-rotated pyramid patterns were the most effective in reducing particle deposition. Computational fluid dynamics modeling was conducted for each membrane surface to elucidate the differences between the antifouling properties of various patterns in terms of shear stress and flow regime.

One of the key issues in membrane technology is to avoid fouling which is formed on the membrane surface. To get over this trouble, the use of a patterned surface was suggested as a way to reduce fouling. In this report, both the experimental and numerical studies were performed with a prism patterned membrane system. In our experiments, we observe the local distribution of microbials; more fouling in the lower part of the pattern and less fouling in the upper region. In the simulation, the vortex develops in the lower part of the pattern, in which the aggregates of solid components in the sludge can be easily formed, leading to a favorable fouling formation. It is also observed that the local wall shear stress is higher in the upper region of the pattern compared to the lower region where the vortex is formed. High shear stress facilitates detachment and prohibits attachment of solid components on the membrane surface. The simulation result (vortex formation in the lower region of the pattern and higher stress in the upper region) is in accordance with the experimental results on the distribution of microbials in the patterned membrane system (more fouling in the lower part of the pattern, and less fouling in the upper region). This indicates the importance of flow characteristics as well as the stress distribution to reduce the fouling in the patterned membrane system. In addition, it is emphasized that the pattern should be designed efficiently by considering the local flow and stress distribution in the cross flow membrane system.

We investigated the nonlinear and nonsymmetric responses of viscoelastic fluids under large amplitude oscillatory squeeze (LAOSQ) flow. The nonlinear and nonsymmetric stress response is a unique feature of oscillatory squeeze (OSQ) flow under larger deformation, but has rarely been investigated. The goal of this study is to systematically characterize the responses of viscoelastic fluids at larger deformation under oscillatory squeeze flow and to provide a platform for the analysis of nonsymmetric stress signals. We report a framework for the analysis of nonlinear-and-nonsymmetric stress signals at larger strain amplitude under oscillatory squeeze flow. The storage and loss modulus showed strain thinning behavior as the strain amplitude increases in both oscillatory shear and oscillatory squeeze flow. However the normal stress under LAOSQ was found to be nonsymmetric in both magnitude and shape unlike the shear stress under oscillatory shear flow. In addition the energy dissipation was found to be larger in extension than in compression. This study is expected to provide a platform to understand the nonlinear and nonsymmetric characteristics of complex fluids under LAOSQ flow.

Oscillatory shear flow has been widely used to investigate the flow properties of a wide range of complex fluids. The flow is useful because experimental platform is already fixed and its analysis has sound theoretical background. However it is too simple compared to the complex flows encountered in industry. Accordingly, the rheological response of complex fluids needs to be investigated in more complicated flow field. There were several reports on the superimposed flows in which oscillatory flow was applied either parallel or perpendicular to the steady shear flow. In this paper, we propose dynamic helical squeeze flow (DHSQ) which superimposes oscillatory shear and oscillatory squeeze between parallel plates. The nonlinear response in DHSQ was studied by comparing DHSQ with oscillatory shear (OS) and with oscillatory squeeze (OSQ) in terms of stress shape and Lissajous plot. In DHSQ, both stress curve and Lissajous plot of shear and normal stresses showed nonsymmetric characteristics unlike shear stress in large amplitude oscillatory shear (LAOS). The normal stress in DHSQ was more distorted than that of OSQ. The shear stress in DHSQ showed the onset of nonlinearity at lower strain amplitude than that of oscillatory shear flow (OS). It is due to the coupling of shear and squeeze flows, and the effect was more pronounced in the shear stress than in the normal stress.

Dynamic oscillatory shear flow tests, i.e. small, medium, and large amplitude oscillatory shear (SAOS, MAOS, and LAOS), are useful to study polymer composite systems. In this study, MAOS and LAOS tests were used to investigate the dynamic behavior of electrically activated polypropylene (PP)/Clay nanocomposites. The morphology of PP/Clay nanocomposites could be controlled by the applied time, type (AC and DC), and strength of the electric field. Various electrically activated PP/Clay nanocomposites were compared in terms of I3/1, which was determined from FT-Rheology within the MAOS and LAOS region. Nonlinear-Linear viscoelastic Ratio (NLR), which developed by Lim et al. (2011), was calculated to measure the dispersion quality of the PP/Clay nanocomposites.

Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background [1], [2], [3] and [4] and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ[subscript 0]) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G′(ω) and G″(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In the present review article, we first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations. We then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. We illustrate the utility and sensitivity of these protocols by investigating the nonlinear response of various complex fluids over a wide range of frequency and amplitude of deformation, and show that LAOS characterization is a rigorous test for rheological models and advanced quality control., Procter & Gamble Company, Schlumberger-Doll Research Center

In this study, we investigated drying process of silica/PVA suspensions. After measuring the amount of polymer adsorption and the stress evolution of a film during drying process, we could find a quantitative relationship between polymer adsorption and stress development, for silica/PVA suspensions of different pH and mixing time. For all the suspensions of different pH, both the amount of polymer adsorption (Γ) and the plateau stress of dry film (σ(p)) could be scaled onto a single master curve as a function of mixing time (t(m)). The scaling of mixing time for both Γ and σ(p) could be performed by the same scale factor, which implies that there is a one to one correlation between adsorption and stress. This correlation implies that we can control the microstructure and performance of dry film by adjusting the amount of polymer adsorption. The origin of adsorption kinetics of silica/PVA suspension was also discussed in terms of saponification of acetate groups in PVA, which facilitates hydrogen bonding between silica and PVA.

Dynamic self-assembly of droplets, regular structure formation of moving deformable objects in a confinement environment is a challenging problem in nonlinear dynamics and engineering patterned structure. In the current work, we investigated how the local kinematic history affects the dynamic self-assembly of picoliter-sized droplets near the expansion regions in microfluidic devices. The local kinematic history was controlled by the shape of the expansion region and characterized using computational fluid dynamics. Sizecontrolled aqueous droplets in light mineral oil were continuously generated at T-junction microchannel and transported toward the expansion region. The fast dynamics of the droplets was tracked using high-speed video microscopy. We found three types of dynamic droplet arrays: 1D, 2D zigzag, and irregular. The orderdisorder transition was associated not only with the droplet size, but also with the controlled local kinematic history, which results in the transient deformation of droplet and droplet-droplet interactions. The present results provide us with insight into the dynamic self-assembly of droplets and could be a useful guide for practical applications of droplet-based microfluidics.