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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.

Deformation and breakup of a single agglomerate exposed to pure planar extensional flow in a cross-channel were experimentally investigated. Aggregation was generated by applying shear with destabilized polystyrene particles, and the fractal dimension, df, of the agglomerate was 2.25. The aggregation focused on the center of the channel by sheath flow was rotated while approaching stagnant point. Then, the aspect ratio increased as it deformed close to the stagnant point. The probability of the breakup and the fragment distribution were dependent upon the viscosity and flow rate and were superimposed on a master curve as a function of applied stress. With the increase in stress, the projected area of the fragment that was split by the flow decreased with a power-law relationship, and the exponent was in agreement with the model prediction.

The effect of particles on the development of instability patterns during the capillary thinning process of a poly(ethylene oxide) solution has been experimentally studied in an effort to clarify the filament breakup behavior of particulate systems. We focus on breathing and formation of the first bead in particular, which as this bead initiate blistering. Changes in instability patterns due to an addition of PMMA particles are investigated by observing the evolution of a filament undergoing capillary thinning. The addition of particles accelerates breathing and the formation of the first bead. By comparing the extensional properties of a PMMA/PEO suspension to those of glycerin/PEO solutions which has the same shear viscosity, surface tension and polymer concentration, it was found that the addition of particles has little effect on the behavior of polymer chains under an extensional flow. Meanwhile, the flow becomes heterogeneous with the fluctuation of the local particle concentration, inducing rapid thinning at the neck region, which propagates throughout the filament as capillary thinning proceeds. The addition of particles also influences the position of the first bead. For a pure polymer solution and a polymer solution with a small amount of particles (∼2 wt.%), the first bead mostly appears near the upper neck. However, as the particle concentration increases to 10 wt.%, the first bead appears at random locations along the filament, with similar probabilities. The randomization of the position of the first bead is attributed to the non-uniform distribution of particles inside a thinning filament due to the fluctuation of the local particle concentration.

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.

Current heterogeneous cell assembly techniques in coculture systems rely on irreversible cell layering or a cell separation membrane. However, the techniques possess major drawbacks of inefficiency in direct interactions of the assembled cell layers and cell separation following coculture, which hamper characterization and therapeutic applications of the cells following coculture. Here, we develop a reversible cell layering platform for assembly of heterogeneous cells that allows both active direct cell–cell interactions and facile cell separation. Anionic maleimide-chondroitin-sulfate is grafted onto the surface membrane of myogenic C2C12 cells and human mesenchymal stem cells (hMSCs) to modify the surface charge of the cells without cytotoxicity. A highly porous chitosan thin film is formed in situ interspacing between the heterogeneous cell layers via ionic cross-linking of cationic chitosan and anionic functionalized cells, forming compactly assembled double-layered cell constructs. The chitosan film ...

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.

Air pollution is one of the most serious problems facing mankind because of its impact on ecosystems and human beings. Although particulate matter (PM) consists of both filterable PM (FPM) and condensable PM (CPM), most research has focused on eliminating only FPM. In this work, we introduce a filter system that removes both FPM and CPM from pollution source with high efficiency. The system consists of two reduced graphene oxide (rGO) filters and a condenser between them that can remove the usual FPM and at the same time CPM-induced FPM that typically leaves the pollution source unabated. The filters, quite effective in removing the PM with their three-dimensional structure, retain the removal capability even at high temperature and in acidic condition that prevail at the pollution source. The proposed rGO system could provide a complete solution for removal of both FPM and CPM from the pollution source.

The compatibilizing effect of organoclay in immiscible poly(lactic acid) (PLA) and natural rubber (NR) blends was investigated through small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) tests by varying clay concentrations, mixing conditions, and types of clay. A quantified nonlinear parameter (I3/1) from FT-rheology and complex moduli (|G*|) were used to analyze the structural development of the PLA/NR blends in response to added clays. The nonlinear–linear viscoelastic ratio (NLR ≡ normalized nonlinear viscoelastic property/normalized linear viscoelastic property) was also introduced to describe morphological changes in the blends. Observation of the TEM images revealed that the drop size of natural rubber decreased as the clay content increased from 0.5 to 3 wt %. However, the NR size did not change above 3 wt % of the clay. The NLR value increased up to 3 wt % and then reached a plateau. The drop size reduction due to increased mixing rates was reflected in the NLR v...

Particle shape is one of the most important parameters that can influence the characteristics and properties of dispersion systems. In this study, we have developed a straightforward and facile method to generate oblate spheroidal particles via a film squeezing process. Representative methods so far developed to prepare oblate spheroidal particles, such as film blowing and mechanical stretching based on a biaxial process, have serious problems, including being difficult methods to adopt, very low yield, and non-uniform particle size. Our film squeezing process involves simply squeezing a sandwiched array comprised of an arbitrarily shaped film with embedded polymer spheres between two identical circular elastomeric sheets, on the basis that homogeneous deformation is possible in the mid-plane of simple squeeze flow. This method utilizes a unified uniaxial process for producing both prolate and oblate spheroidal particles. The advantages of the method are easier access, much higher yield, and more uniform sizes and shapes than previously reported methods. This process can be helpful for the fundamental studies utilizing oblate spheroidal particles with controlled geometries.

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.

We investigate the filament thinning behavior of the suspensions under extensional flow in the final stage of filament breakup process. Under the extensional flow, the particles dispersed in a Newtonian medium induce complex behaviors; in particular, the particles cause non-uniform filament thinning when the minimum neck diameter (W) of the filament becomes as thin as the length scale of the particle. We suspend 20 wt% of 10 μm poly(methyl methacrylate) (PMMA) particles in a silicone oil, and compare the filament thinning of the suspension with that of silicone oil having the same viscosity and surface tension. In this way, the effect of the particles on the thinning filament can be confirmed while eliminating differences in the rheological properties of the two fluids. The particles begin to affect filament shape when the filament becomes thinner than W = 10 D (D = 10 μm; particle diameter). The filament surface is rough and the shape of the filament is random for W

A systematic study has been performed to investigate the effect of surface potential of nanoparticles on the rheological behavior of bimodal suspensions, using a model system consisting of polystyrene latex (primary size ∼530 nm) and alumina-coated silica (primary size ∼12 nm) particles. The surface potential of small particles was tuned by varying the solution pH, causing them to be repulsive to each other, attractive to each other, and oppositely charged to the large particles, while the large particles remained electrostatically stabilized. We found that the rheological properties could be dramatically changed from viscous to gel-like depending on the surface potential and concentration of small particles. A colloidal gel was induced by small particles when the small particles had the opposite charge to the large particles and a volume fraction of 10(-4)ϕsmall10(-3), and when the small particles were attractive to each other above a critical threshold, ϕsmall10(-4). Cryo-SEM distinguished the gel structures to be either short bridging gels produced by oppositely charged small particles or long bridging gels or dense gels produced by attractive small particles. On the basis of this rheological behavior and microstructure, we prepared a phase diagram of highly size-asymmetric bimodal colloids with respect to the surface chemistry and concentration of small particles.

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

Colloidal dispersions in polymer solution are important material systems in coating and printing applications. Understanding the role of polymers in drying process is important to obtain the desired performance of the solid film. In this study, we investigated the role of polymers in stress development during drying of aqueous silica and poly(vinyl alcohol) (PVA) suspensions, and the microstructure of solid film. Adsorbed polymers were found to affect the spatial organization of silica particles, which reduces the size of aggregates and the increase in stress development. The effect of adsorbed polymers on the stress development was hindered as the amount of non-adsorbed polymer increased. The role of adsorbed and non-adsorbed PVA in stress development was found to be generalized to yield a single master curve independent of polymer concentration.

We investigate the effect of particles dispersed in a Newtonian medium on the filament breakup of suspensions under extensional flow. In particular, we focus on the final stage of the breakup process: 10 μm poly(methyl methacrylate) (PMMA) particles with 0∼20 wt% are dispersed in silicone oil and the effects of the added particles on the thinning dynamics of the filament are observed with time-dependent changes in the minimum neck diameter (W). The particles decelerate the breakup process until the minimum thickness (W) of the filament becomes 5 d (d = 10 μm: particle diameter), and then they accelerate the process rapidly until the pinch-off. When the thinning dynamics and filament shape of the 20 wt% PMMA suspension are compared with those of a silicone oil with the same viscosity and surface tension, the particles affect the thinning dynamics by changing the breakup velocity under W∼35 d compared with the viscosity-matched silicone oil. When the filament becomes thinner than W∼10 d, the particles induce different surface shapes compared with those of the viscosity-matched silicone oil. When the filament becomes thinner than W∼5 d, the roughness of the filament surface increases. Thus, the effect of the particles in the final stage of filament breakup is more complicated than that in the initial stage, and we demonstrate that the particles dispersed in a Newtonian medium induce complex behaviors in the final stage of filament breakup.

The effect of sodium carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) on film formation was evaluated by analyzing both drying stress and pore size distribution. We discovered that the SBR in a graphite/SBR slurry filled the voids among the graphite particles with the increase in SBR concentration. In addition, the CMC in the graphite/CMC slurry was adsorbed onto the graphite surface, which caused the graphite particles to coalesce. In the graphite/CMC/SBR slurry, a large amount of SBR was needed to increase the mechanical strength of the film in the low concentration region of CMC. However, in high concentration region of CMC, the SBR did not affect the mechanical strength of the film any longer. On the basis of the drying stress measurements, we could draw a processing window map that clearly shows the effect of CMC and SBR on the mechanical strength of the film, which will be useful in the design of anode slurries.

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.

Metallic nanowires with excellent electrical conductivity and high aspect ratio are critical in the preparation of conductive polymer nanocomposites. In this work, highly conductive polystyrene/silver nanowire (PS/AgNW) nanocomposites were prepared by latex blending, and their electrical and rheological properties were investigated. A high yield of long and thin AgNWs was synthesized with the polyol method. AgNWs were incorporated with highly monodisperse PS microspheres to produce polymer nanocomposites with a nanowire network structure providing electrical pathways. An electrically conductive network of AgNWs was obtained at an electrical percolation threshold of 0.49 vol % AgNW, and an electrical conductivity of 10(2) S/m was obtained at 1 vol %. The dynamic rheological properties evaluated at 1 vol % also confirmed that the AgNWs were physically connected to one another at this concentration.

This article presents a characterization method that could be useful for evaluating the performance of ink in electrohydrodynamic jet printing. The ink contains pigment particles and polymer (stabilizer for pigments) and has a low viscosity and a low elasticity. Depending on the medium (hydrocarbon for oil-based inks and glycol ether for polar solvent-based inks) and the type of pigment (exhibiting different colors), vast differences were found in the dielectric properties even when the viscosities of the inks were almost identical. These differences between the two series of inks were related to differences in the ion concentration n and ion mobility μ estimated from an analysis of the complex dielectric constant e* (= e′ – ie″) on the basis of Macdonald theory. These differences between the polar solvent- and oil-based inks are discussed in relation to the performances of the inks in electrohydrodynamic inkjet printing.

We report the effect of flow-induced dynamical heterogeneity on the nonlinear elastic modulus of weakly aggregated colloidal gels that have undergone yielding by an imposed step strain deformation. The gels are comprised of sterically stabilized poly(methyl methacrylate) colloids interacting through short-ranged depletion attractions. When a step strain of magnitude varying from γ = 0.1 to 80.0 is applied to the quiescent gels, we observe the development of a bimodal distribution in the single-particle van Hove self-correlation function. This distribution is consistent with the existence of a fast and slow subpopulation of colloids within sheared gels. We evaluate the effect of incorporating the properties of the slow, rigid subpopulation of the colloids into a recent mode coupling theory for the nonlinear elasticity of colloidal gels.

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.

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.

Applying an electric field is an efficient way to fabricate polymer/clay nanocomposites. It helps to achieve a good dispersion of nanoclays which improves the performance of the polymeric system. In this study, the effect of an alternating current (A.C.) electric field was investigated on clay exfoliation with various combinations of polymer/clay nanocomposites. Three different types of organoclays (Cloisite 10A, 20A, 30B) were introduced in polypropylene (PP) and poly(lactic acid) (PLA) matrices. Their rheological properties showed that the A.C. electric field was effective in enhancing the dispersion of organoclays in both the PP/clay and PLA/clay composites. The efficiency of the A.C. field varied depending on the combination of polymer and clay nanoparticles. In the case of PP, the best combination was PP/C20A followed by PP/C10A and PP/C30B. In contrast, PLA/clay showed an opposite trend. This difference arises from the different affinities between the polymers and the functional groups of the clays. The Hansen solubility parameter was introduced to quantify the affinities between the polymer and clay. The electric field was more effective for polymer/clay combinations that had less difference in the Hansen solubility parameter. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43582.

Stable drop jettability is mandatory for a successful, technical scale inkjet printing, and accordingly, this aspect has attracted much attention in fundamental and applied research. Previous studies were mainly focused on Newtonian fluids or polymer solutions. Here, we have investigated the drop jetting for zinc oxide (ZnO) particulate suspensions. Generally, the inverse Ohnesorge number Z = Oh–1, which relates viscous forces to inertia and surface tension, is sufficient to predict the jettability of single phase fluids. For the inkjet printer setup used here, jetting was possible for Newtonian fluids with 2.5 < Z < 26, but in the identical Z-range, nonjetting and nozzle clogging occurred for certain suspensions. A so-called ring-slit device, which allows for simultaneous formation and detection of aggregates in strongly converging flow fields, and single particle detecting techniques, which allow for an accurate determination of the number and size of micrometer-sized aggregates in suspensions of nanopa...

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.

To compare the rheological characteristics of structurally different hyaluronic acid (HA)-based biomaterials that are presently used for phonosurgery and to investigate their influence on the viscoelastic properties of vocal folds after implantation in an in vivo rabbit model.In vitro and in vivo rheometric investigation.Experimental laboratory, Inha and Seoul National Universities.Viscoelastic shear properties of 3 HA-based biomaterials (Rofilan, Restylane, and Reviderm) were measured with a strain-controlled rheometer. These biomaterials were injected into the deep layers of rabbit vocal folds, and viscoelastic moduli of the injected vocal folds were determined 2 months after the injection. The vocal fold specimens were observed using a light microscope and a transmission electron microscope.All HA-based biomaterials showed similar levels of shear viscosity, which were slightly higher than that of human vocal folds reported in previous studies. Compared with noninjected control vocal folds, there were no significant differences in the magnitudes of both elastic shear modulus (G') and viscous modulus (G") of injected vocal folds among all of the materials. Light microscopic images showed that all materials were observed in the deep layers of vocal folds and electron scanning images revealed that injected HA particles were homogeneously distributed in regions of collagenous fibers.HA-based biomaterials could preserve the viscoelastic properties of the vocal folds, when they were injected into vocal folds in an in vivo rabbit model. However, further studies on the influence of the biomaterials on the viscoelasticity of human vocal folds in ECM surroundings are still needed.

Linear polymers are restricted to use in processes that involve severe extensional deformation, such as fiber spinning, film blowing, and thermoforming. To extend their applicability, the extensional properties of polymer melts should be enhanced such that strain hardening, which is defined as an increase in extensional viscosity under a large strain that deviates from the linear viscoelastic curve, is pronounced. In this study, a novel preparation method of linear polymer/inorganic nanocomposites was proposed with a main focus on enhanced melt strength. The design of molecular structure consists of three components—linear polymer, compatibilizer, and surface-modified particles. High-density polyethylene was used as a linear polymer while polyethylene grafted with maleic anhydride was used as a compatibilizer. Silica particles were synthesized and modified on their surfaces by 3-aminopropyltriethoxysilane. The strain hardening behavior of the surface-modified silica composites was pronounced. However, such a result was not observed for the composites of the same composition with pure-silica. In addition, the dispersion of the modified silica was much better than that of pure-silica.

The addition of organically modified layered silicates (organoclay) to highly immiscible polypropylene/polystyrene, PP/PS, blends leads to a significant change in blend morphology and rheology. In this study, the kinetics for morphological development of the blend nanocomposites was studied by two mixing methods (internal batch mixing and continuous mixing), with a focus on the mechanism of dispersion of the silicate layers and its dependence on mixing conditions. Through the use of a twin-screw co-rotating extruder specially modified with sampling ports along its length it was possible to study, for the first time, the kinetics of morphology developed upon mixing. The results show that the evolution of silicate layer dispersion during morphology occurs by and large relatively early in the mixing process and that the most favorable breaking process of the dispersed phase occurs initially due to the breaking up of the initial silicate tactoids into thinner ones and also due to their presence inside it. As a consequence of these sequential processes, the organoclay layers end up at the interface between the PP and the polystyrene phases and stabilize the morphology.

The dynamic rheological behavior and phase morphology of Polytrimethylene terephthalate (PTT) and ethylene propylene diene monomer (EPDM) uncompatibilized blends and those compatibilized with maleic anhydride grafted EPM (EPM-g-MA) were investigated. Effects of blend ratio and reactive compatibilization on the morphology and rheological properties of compatibilized and uncompatibilized blends have been analyzed. The viscosity ratio between the polymers was found to be sensitive to frequency which gave an indirect idea about the unstable morphology. The complex viscosity and dynamic modulus increased with increase in compatibilizer addition up to critical micelle concentration. Palierne and Choi-Schowalter models were used to calculate the interfacial tension between the polymers. The interfacial tension decreased with the addition of compatibilizer up to CMC. It was also found that the minimum value of interfacial tension was found at CMC beyond that a levelling off is observed. The rheological properties of both compatibilized and uncompatibilized blends are found to be closely related to their phase morphology. POLYM. ENG. SCI., 50:1945–1955, 2010. © 2010 Society of Plastics Engineers

The slurries comprising LiCoO 2 powder, carbon, and polymeric binder are prepared by two different mixing processes, and their rheological properties are compared. In the multi-step process, the solvent is added into solid mixture in stepwise, whereas the total amount at once in the one-step process. The former process gives the slurry that is more suitable for electrode preparation with fluid-like behavior and more uniform dispersion of solid ingredients as compared to those prepared from the letter. In the composite electrode prepared from the former, the LiCoO 2 and carbon particles are homogeneously distributed without agglomeration. Indebted to this favorable feature, this electrode exhibits a better electrochemical performance for cyclability and rate capability. It is very likely that the contact resistance and charge transfer resistance for lithiation/de-lithiation are smaller in the former electrode due to the homogeneous distribution of LiCoO 2 and carbon particles, which leads to a less significant electrode polarization.

Motivated by the previous studies (Lee et al., Lab Chip 10:1160–1166, 2010; Link et al., Phys Rev Lett 92:054503-1–054503-4, 2004), the droplet dynamics passing through obstructions in confined microchannel was explored both numerically and experimentally. The effects of obstruction shape (cylinder and square), droplet size, and capillary number (Ca) on droplet dynamics were investigated. For the size control, due to an obstruction-induced droplet breakup, the cylinder obstruction was found to be advantageous over square type for practical purposes. The thread breakup was attributed to both normal and shear components of velocity gradients near the obstruction, in particular, near the corners of the square. As a result, the square obstruction was considered to generate more non-trivial satellite droplets. The droplet size showed little influence on the droplet dynamics. Considering the wetting process on the cylinder surface, we explored the droplet dynamics passing through two successive cylinder obstructions, where more complicated dynamics was observed depending on Ca (capillary number ~ viscous force / interface tension), cylinder interval, and droplet size. Here, we propose two requirements for independent wetting on each cylinder: (i) low Ca droplet should be manipulated, and (ii) cylinder interval should be larger than channel width. That is, low Ca droplet could intrude the region between two cylinders if the cylinder interval was far enough, while the droplet could not intrude due to geometric hindrance for close obstructions. In the numerical viewpoint, the proposed requirements were also valid for multi-cylinder obstructions up to 6. In addition, we propose a novel design of array structure of cylinders for a selective wetting, which might be useful to fabricate Janus particles. We hereby prove by both simulation and experiments that the wetting on the obstruction is controllable by changing Ca and cylinder design in the multilayer deposition process.

Key microstructural properties of particulate coatings such as porosity and particle order are established during drying. Therefore, understanding the evolution of particulate distributions during drying is useful for designing coating properties. Here, a 1D model is proposed for the particle distribution through the coating thickness at different drying times and conditions, including Brownian diffusion, sedimentation, and evaporation. Effects of particle concentration on diffusion and sedimentation rates are included. Results are condensed onto a drying regime map which predicts the presence of particle surface accumulation or sediment based on two dimensionless numbers: the Peclet number and the sedimentation number. Cryogenic scanning electron microscopy (cryoSEM) is used to image the transient particulate distributions during the drying of a model system comprised of monodisperse silica particles in water. Particle size and evaporation rates are altered to access various domains of the drying map. There is good agreement between cryoSEM observations and model predictions. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Dispersion of nano-sized particles at high solid content has attracted attention in many industrial applications such as printed electronic products. However, the material design and processing heavily depends on experience with little quantitative measure. For fabrication of thinner dielectric layers, Ni size is getting smaller when used as an inner electrode in multilayer chip capacitor (MLCC). In the present study, we investigate the rheological properties and printing performance of the pastes with two different sizes of Ni particles in the same incompatible binder mixtures of ethyl cellulose (EC) and polyvinyl butyral (PVB). The difference in particle size causes different microstructural heterogeneity and highly nonlinear rheological properties upon the external flow field. The printing pattern and the surface profile are also analyzed by confocal images after screen printing. For smaller particle size of Ni, the more heterogeneous microstructure is observed with increasing PVB content, which is evidenced by the screen printing images as well as its rheological behavior. We explain the difference of spatial heterogeneity in terms of different interactions between particle–particle and particle–polymer. This work is believed to contribute to better design of inner electrodes and processing in MLCC manufacturing.

Ethylene-methacrylic acid ionomer (Surlyn) with concentration up to 20 wt% based on total weight of polymer resin was added into polypropylene (PP)/organoclay hybrids. The microstructure, rheological properties, crystallization properties and mechanical properties of the obtained nanocomposites have been investigated. The addition of ionomer markedly enlarged interlayer spacing of the platelets and led to an improved degree of exfoliation. Moreover, clay silicates were found to selectively disperse either inside the ionomer phase or at the phase boundary. Compared to the binary immiscible blends, an improved interfacial adhesion was achieved for PP/Surlyn/OMMT hybrids. Unlike PP/Surlyn binary blends, the viscoelastic properties of the hybrids significantly increased with increasing Surlyn concentration, which could be attributed to the improved clay dispersion and the contribution of silicate layers at the interface between PP and Surlyn. A synergistic role between Surlyn and clay was also found to suppress the crystallization of PP matrix. In addition, PP/Surlyn/OMMT hybrids exhibited superior tensile strain compared to the corresponding PP/PP-g-MA/OMMT. Both tensile strength and elongation at break showed maximum at Surlyn concentration of 5 wt%. By comparing the experimental tensile yield strength with model prediction, it was suggested that the clay platelets localized at the interface could play a role of interfacial activation to some extent.

We performed numerical and experimental studies on the viscous folding in diverging microchannel flows which were recently reported by Cubaud and Mason (Phys Rev Lett 96:114501, 2006a). We categorized the flow patterns as “stable”, “folding,” and “chaotic” depending on channel shape, flow ratio, and viscosity ratio between two fluids. We focused on the effect of kinematic history on viscous folding, in particular, by changing the shape of diverging channels: 90°, 45°, and hyperbolic channel. In experiments, the proposed power–law relation ( $$ f\sim \dot{\gamma }^{1},$$ where f is the folding frequency, and $$ \dot{\gamma }$$ is the characteristic shear rate) by Cubaud and Mason (Phys Rev Lett 96:114501, 2006a) was found to be valid even for hyperbolic channel. The hyperbolic channel generated moderate flows with smaller folding frequency, amplitude, and a delay of onset of the folding compared with other two cases, which is considered to be affected by compressive stress when compared to the simulation results. In each channel, the folding frequency increases and the amplitude decreases as the thread width decreases since higher compressive stress is applied along the thin thread. The secondary folding was also reproduced in the simulation, which was attributed to locally heterogeneous development of compressive stresses along the thread. This study proves that the viscous folding can be controlled by the design of flow kinematics and of the compressive stresses at the diverging region.

The particle/polymer/solvent suspension system shows complicated microstructure. When the suspension system experiences an industrial process such as coating and drying, the system experiences microstructural change. In this study, we investigated the microstructural change during the drying of a silica/polyvinyl alcohol (PVA) suspension, with an emphasis on suspension stability. We controlled the amount of PVA adsorption on the silica surface by adjusting the pH (1.5, 3.6, and 9) of the silica/PVA suspension. The amount of adsorption was measured to increase with decreasing pH, and the degree of flocculation in the silica/PVA suspension became stronger with decreasing pH. However, through the measurement of stress development during drying and the observation of film microstructure after drying, we found that the more strongly flocculated suspension became a more disperse, close-packed film after drying. By evaluating the potential energy, we could suggest the role of adsorbed polymers in structural change during the drying of the silica/PVA suspension. As pH decreases, the adsorbed polymers could bridge the particles and lead to a flocculated suspension before drying. As the solvent evaporates during drying, the adsorbed polymers introduce steric repulsion between approaching particles, leading to a change from flocculated to dispersed microstructure. This implies that the required silica/PVA film performance and the microstructure of the silica/PVA suspension can be tailored through controlling the polymer adsorption in suspension.

Recently, we reported how viscoelasticity affects drop dynamics in a microchannel flow using the finite element-front tracking method (FE-FTM). In this work, we investigate drop dynamics for a wider range of parameters: viscosity ratio between droplet and medium ( χ ) , capillary number ( Ca ), droplet size, and fluid elasticity. The Oldroyd-B model is adopted as the constitutive equation for the viscoelastic fluid. We observe that the drop deformation in a microfluidic channel is dependent on Ca , which is more pronounced for smaller χ values. The present work shows that viscoelasticity plays an important role in drop dynamics with increasing χ values for Newtonian droplet in viscoelastic medium, which can be attributed to high normal stress developed in narrow film thickness between droplet and channel for higher χ values. We also study circulation problem inside droplets, which is important in practice, such as in droplet reactor application. The present work shows that circulation intensity is enhanced with decreasing χ values. We find that the relevance of viscoelastic effects on internal circulation is dependent on χ values, and the circulation intensity is distinctively decreased with increasing elasticity for high χ values for Newtonian droplet in viscoelastic medium. We expect that the present work be helpful not only in controlling droplets but also to improve our physical insight on drop dynamics in microchannel flows.

The surface of silica nanoparticles was modified with poly(ethylene glycol) methacrylate (PEGMA) or poly(propylene glycol) methacrylate (PPGMA) in order to improve the dispersion of nanoparticles in a polymer matrix. Nanosized silica particles were synthesized by the Stober method with tetraethyl orthosilicate (TEOS). Silica nanoparticles were treated with triethoxyvinylsilane (VTES) as a coupling agent to introduce reactive groups and the PEG or PPG were then grafted onto the particle surface via UV-photopolymerization. Various analytical methods, i.e., scanning electron microscopy (SEM), thermogravimetry (TG), zeta potential measurement, and water vapor adsorption measurement were used to comprehensively characterize the unmodified(pure) and modified silica particles. The SEM images of the pure and modified particles demonstrated that both particles have a spherical shape and a uniform size without agglomeration. The silica particles modified with polymers showed higher weight loss than unmodified silica particles because of the decomposition of the organic polymers grafted onto the particles. The surface modification of silica particles with polymers decreased the zeta potential values of the silica surface. Modified silica particles had lower water vapor adsorption due to the hydrophobic surface property resulting from the polymers grafted onto the silica surface. In addition, we have developed an electrical conductivity measurement as a novel method to analyze the surface properties of silica nanoparticles. The modified silica particles had lower electrical conductivity than that of unmodified silica particles.

Since biofilms show strong resistance to conventional disinfectants and antimicrobials, control of initial bacterial adhesion is generally accepted as one of the most effective strategies for preventing biofilm formation. Although electrical methods have been widely studied, the specific properties of cathodic, anodic, and block currents that influence the bacterial detachment and inactivation remained largely unclear. This study investigated the specific role of electric currents in the detachment and inactivation of bacteria adhered to an electrode surface. A real-time bacterial adhesion observation and control system was employed that consisted of Pseudomonas aeruginosa PAO1 (PAO1) with green fluorescent protein as the indicator microorganism and a flow cell reactor mounted on a fluorescent microscope. The results suggest that the bacteria that remained on the electrode surface after application of a cathodic current were alive, although the extent of detachment was significant. In contrast, when an anodic current was applied, the bacteria that remained on the surface became inactive with time, although bacterial detachment was not significant. Further, under these conditions, active bacterial motions were observed, which weakened the binding between the electrode surface and bacteria. This phenomenon of bacterial motion on the surface can be used to maximize bacterial detachment by manipulation of the shear rate. These findings specific for each application of a cathodic or anodic electric current could successfully explain the effectiveness of block current application in controlling bacterial adhesion.

In this study, we investigated clay migration and its localization in multiphase blend nanocomposite systems during the evolution of blend morphology to elucidate how a hydrodynamic stress and chemical affinity between the polymer and clay induce them. To observe the morphology evolution, a multilayered blend, alternatively superposed poly(butylenes terephthalate) (PBT) and polystyrene (PS)/clay films or PBT/clay and PS films, was subjected to homogeneous shear flow, 1 s−1. Furthermore, the morphology was observed at different shear rates 1 s−1. When the PBT/(PS/clay) multilayered blend is subjected to flow, the clay dispersed in the PS layer first migrates to the interface depending on the amount of applied strain. The clay at the interface causes the average drop size of blend morphology to become smaller and the blend morphology becomes more stable because of the coalescence suppression effect. As more shear is applied, the clay at the interface moves further into more compatible phase, PBT, although the viscosity of PBT is higher than PS. On the contrary, the clay in the PBT layer does not migrate to the PS phase at any shear rate, which means that its chemical affinity is strong enough to prevent shear-induced migration. The clay increases the viscosity of the PBT phase and results in a different morphology with a droplet, cocontinuous structure. As a result, when the clay is induced to migrate by hydrodynamic stress, it migrates into thermodynamically more stable positions at the interface or in the chemically more compatible phase, depending on the applied strain. Once it is located at a thermodynamically more stable position, it is difficult to push it out only by hydrodynamic stress. The location of clay is significantly affected by the morphology during evolution, which means that the blend morphology can control the droplet form and cocontinuous structure by control of the clay migration kinetics. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Macromolecules 49(23), 9068 - 9079(2016). doi:10.1021/acs.macromol.6b01939, Dispersions of nanoparticles (NPs) in a polymer matrix are a key element to set various properties of solution-cast polymer nanocomposite films. While the dispersion state of NPs in nanocomposite films has been extensively studied over the past decades, the structural development during drying and the relation of liquid and solid structure still remains poorly understood. In the present work, we study how NP dispersions develop during drying in polymer nanocomposite films, particularly focusing on the role of particle–polymer interaction in the structural development. Aqueous dispersions of nanosilica and poly(vinyl alcohol) are used as model NP/polymer mixtures, where the particle–polymer interaction can systemically be varied via the pH. A novel vertical small-angle X-ray scattering technique enables us to directly observe the development of the NP’s dispersion state during drying. At a high pH 10, where silica particles have a poor affinity to PVA, SAXS intensity evolution shows phase separation during drying, resulting in the formation of dense aggregates of bare particles in the solid film. On the other hand, at a low pH 3, where silica particles have a good affinity with PVA, the SAXS data indicate a gradual densification of the NPs while maintaining a constant interparticle distance, which is originating from adsorbed PVA. The resulting solid film after drying exhibits an improved dispersion of NPs. The evaluation of the interparticle interaction suggests that the adsorbed polymer plays generally a key role in the uniform distribution of NPs in solid films, as it sterically stabilizes NPs over short ranges during all drying stages whereas depletion attraction dominates at longer ranges., Published by Soc., Washington, DC

We control the hydrophobicity of submicrometer silica spheres by modifying their surface with -CH3, -CH=CH2, -(CH2)(2)CH3, -CH2(CH2)(4)CH2-, -C(6)H(5), -(CH2)(7)CH3, and -(CH2)(11)CH3 groups through a modified one-step process. The scanning electron microscopy (SEM), quasi-elastic light scattering (QELS), UV-visible spectra, nitrogen sorption, and water vapor adsorption methods are used to characterize the particles. The SEM micrographs of the particles demonstrate that the modified particles are uniformly spherical, monodisperse, and well-shaped with the particle size ranging from 130 to 149 nm depending on the modified organic groups. In aqueous solution, the particles modified with phenyl groups have an obvious UV absorption peak at around 210 nm, whereas the other modified particles and unmodified particles do not have any UV-visible absorption peaks. There exist obvious differences in the amount of water vapor adsorbed depending on the type of surface functional groups of the modified particles. Compared with the unmodified particles, the modified particles have a lower water vapor adsorption because of the improved hydrophobicity of the particle surface. As a potential application, we prepared polystyrene/SiO2 nanocomposites by blending polystyrene with the synthesized particles. Water contact angle measurements show that the surface of the composite prepared with the modified particles are more hydrophobic. Confocal microscopy demonstrates that the particles are less agglomerated in the nanocomposite as the particles become more hydrophobic. These comprehensive experimental results demonstrate that the hydrophobicity of the particles can be easily controlled by surface modification with different organosilanes through a modified one-step process.

Linear viscoelastic and dielectric measurements were conducted for a blend of polyisoprene (PI, M = 19.9 × 103) and poly(4-tert-butyl styrene) (PtBS, M = 69.5 × 103) with a PI/PtBS composition of 8/2 (w/w). In general, PI and PtBS exhibit the lower-critical-solution-temperature (LCST) type phase behavior. At temperatures examined, T ≤ 70 °C, our PI/PtBS blend was in a statically homogeneous state. The PI chain has the so-called type-A dipoles parallel along the backbone, and its large-scale (global) motion activates prominent dielectric relaxation, while the PtBS chain has no type-A dipoles and its global motion is dielectrically inert. In fact, at angular frequencies ω between 101 s-1 and 105 s-1 and at T ≤ 70 °C, the dielectric signal of the blend was exclusively attributed to the PI chains therein. The time−temperature superposition failed for the dielectric loss e‘ ‘ of the PI chains, despite the fact that the blend was statically homogeneous. This result suggested that the frictional environment for ...

In this study, polypropylene (PP)/clay nanocomposites containing different concentrations of ethylene-methacrylic acid ionomer (i.e. Surlyn®) were prepared, and the effect of ionomer on clay dispersion was studied via WAXD, rheology, SEM, and TEM. The role of the ionomer in the nanocomposites was compared with that of maleic anhydride grafted PP (PP-g-MA), which has been widely used as a compatibilizer in making PP/clay nanocomposites. With an increase in the concentration of compatibilizer, the position of d001 peak of OMMT shifted toward a lower angle for PP-g-MA system, while the position remained almost unchanged for Surlyn system, in which a larger interlayer spacing (d001) was found with respect to the former. In rheology, the addition of the ionomer led to a gradual increase in both moduli and complex viscosity, and the nonterminal behavior at low frequency was observed in both systems. In addition, the ternary hybrid containing 20 wt % Surlyn achieved the largest enhancement in relative viscosity, which was more than that of the nanocomposite prepared from pure Surlyn or pure PP, presumably indicative of the existence of strong interaction between the components. Finally, SEM and TEM micrographs demonstrated that exfoliated structure was preferred for PP/Surlyn/OMMT hybrids, while intercalated morphology for PP/PP-g-MA/OMMT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4024–4034, 2007

BACKGROUND It remains to be elucidated whether exposure to air pollutants aggravates atopic dermatitis (AD). OBJECTIVES This study aimed to evaluate the effects of exposure to formaldehyde for 1 h and 2 h on skin barrier function in both the control and the AD groups. METHODS In 41 patients with AD and 34 healthy children, a provocation test was performed in which two different areas of normal-appearing skin on the forearm were stimulated with airborne formaldehyde at 500 μg m(-3) or placebo for 2 h. We measured transepidermal water loss (TEWL) and skin pH, and calculated the percentage change from baseline. RESULTS Exposure to formaldehyde increased TEWL in the control group [P < 0·001; median of difference 1·4; interquartile range (IQR) 0·9-1·6] and in the AD group (P < 0·001; median of difference 2·5; IQR 2·0-3·6). The percentage change of TEWL after formaldehyde exposure in the AD group was higher than in the control group (P < 0·001), whereas exposure to placebo showed no differences between both groups. The AD group also demonstrated a higher percentage increase in skin pH after exposure to formaldehyde than the control group (P < 0·001). CONCLUSIONS Short-term exposure to formaldehyde causes skin barrier dysfunction in both healthy children and children with AD, and this effect is more prominent in children with AD.