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We investigated the rheological behaviors and orientation of three different types of layered silicate composite systems under external flow: microcomposite, intercalated and exfoliated nanocomposites. Rheological measurements under shear and uniaxial extensional flows, two-dimensional, small-angle X-ray scattering and transmission electron microscopy were conducted to investigate the properties, as well as nano- and micro-structural changes, of polymer/layered silicate nanocomposites. The preferred orientation of the silicate layers to the flow direction was observed under uniaxial extensional flow for both intercalated and exfoliated systems, while the strain hardening behavior was observed only in the exfoliated systems. The degree of compatibility between the polymer matrix and clay determined the microstructure of polymer/clay composites, strain hardening behavior and spatial orientation of the clays under extensional flow.

This study investigated the microstructural evolution of PP/clay nanocomposites under electric field. The storage modulus, which is a kind of mirror of the microstructure, increases while an electric field (both AC and DC) is applied. It was found that time and the electric field strength can be superposed to yield a single mastercurve that is independent of the type and strength of the electric field. In addition, the shift factor scaled differently according to the field type. The SAXS and TEM data revealed that the AC field induces the microstructural evolution of the nanocomposites toward an exfoliated structure, while the DC field induces the alignment of silicate layers. In a DC field, the alignment process occurs as a result of dielectrophoretic motion. However, in an AC field, dielectric relaxation analysis showed that an exfoliation process arises as a result of the breakup of the charge balance.

In this study, linear and branched polypropylenes (PP) were compared under medium strain amplitude oscillatory shear (usually strain amplitude range from 10 to 100%) with Fourier-transform rheology (FT rheology). On a log–log diagram, the third relative intensity (I 3/I 1), which is a parameter to represent nonlinearity, shows a linear relationship with the strain amplitude in the range of medium strain amplitude. The slope of I 3/I 1 of linear PP with various molecular weight and molecular weight distribution was 2 as most constitutive equations predict, while that of branched PP was 1.64, which is lower than that of linear PP. When the linear and branch PP were blended, the slope of I 3/I 1 was proportional to the composition of the branch PP. Therefore, it is suggested that the degree of branching can be defined in terms of the slope of I 3/I 1 under medium amplitude oscillatory shear.

In this study, we investigated the effect of organically modified nanoclay (organoclay) on the morphology of immiscible polymer blends (PBT/PE) with various compositions of PBT ranging from 1 to 90 wt%. When a small amount of organoclay between 1 and 3 phr is added to the blend, the thin clay tactoids of the thickness of the order of 10 nm are located at the interface between PBT and PE phase. As its content is increased, the additional organoclay positions in a specific component depending on its affinity with the component. The addition of a small amount of organoclay results in the effective size reduction for PBT/PE blend. The organoclay located at the interface forms the interfacial phase with a non-homogeneous distribution of clay along the interface and changes the interfacial tension, which result in the coalescence suppression of the droplets. Rigid organoclay with a high aspect ratio allows the blend morphology with long-term thermal stability by suppressing the Brownian motion. This ability of the organoclay to suppress the coalescence of the droplets effectively reduces the droplet size. On the other hand, additional organoclay results in the rheological properties of particular component being increased, which means the change in the viscosity ratio. The change in the viscosity ratio, together with the coalescence suppression effect, affects the determination of the droplet size, depending on the location of the organoclay. Therefore, the organoclay suppresses the coalescence of the droplets at the interface, while simultaneously influencing the breakup of the droplets due to the change of viscosity ratio. q 2006 Elsevier Ltd. All rights reserved.

Rheological properties of long-chain-branched isotactic polypropylene (PP) via copolymerization with a very small amount of nonconjugated α,ω-diene monomer using metallocene catalyst system in both linear and nonlinear regions were investigated, comparing with conventional linear and long-chain-branched PP modified at postreactor. Although comonomer incorporation was equal to 0.05 mol% or less, it caused high molecular weight, broad molecular weight distribution, and long-chain branching. A detailed study on the effect of diene incorporation on the polymer properties was conducted, comparing with modified PP in postreactor. Polymer chain microstructures were characterized by gel permeation chromatography with multiangle laser light scattering (MALLS), differential scanning calorimetry, and rheological means: dynamic viscoelasticity, step-strain, uniaxial elongational flow measurements, and large amplitude oscillatory shear. The PP, which incorporated a small amount of diene monomer, showed significantly improved viscoelastic behaviors. The diene-propylene copolymer containing long-chain branches showed extremely long relaxation mode under shear and outstanding viscosity increase under elongational flow, so-called strain hardening. The difference in microstructure of diene-propylene copolymer with modified PP with long-chain branches is investigated by MALLS and rheological characterizations.

We investigate the rheological behavior of the polymer blends with fibril morphology, with special focus on the effect of fibril morphology on the extensional properties under uniaxial extension. We add a small amount of the dispersed phase to the matrix, and control the blend morphology by changing the viscosity ratio. When the fibril morphology is maintained, the blend shows not only a significant increase of the extensional viscosity but the strain hardening behavior. The extensional viscosity increases depending on the aspect ratio of the fibers, while the strain hardening behavior originates from the restricted stretching of deformable fibers, which has been confirmed theoretically by introducing the concept of rigidity of the fiber. It suggests a way to induce the strain hardening behavior by introducing deformable fibrils into the matrix, that is, by the design of polymer blends with a small amount of dispersed phase such that the fibril structure is maintained.

Rheological properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer solution in both linear and nonlinear regions have been investigated. PEO-PPO-PEO triblock copolymer solution shows a dramatic change in mechanical properties as temperature changes. PEO-PPO-PEO triblock copolymer undergoes a transition from sol to gel with increase of temperature. During this transition the copolymer solution passes through three different stages, namely sol, soft gel, and hard gel. In our previous research (Hyun et al. in J Non-Newtonian Fluid Mech 55:51–65, 2002), large amplitude oscillatory shear (LAOS) behavior was found to be very sensitive to the generated microstructures. In this study, we investigated the relationship between the LAOS type and the microdomain structure. Newtonian behavior is observed in sol region, while there appear two kinds of LAOS types in the soft gel region. One is type I (G′, G′′ decreasing) and the other is a combination of type I and type IV (G′, G′′ increasing followed by decreasing). Type III (G′ decreasing, G′′ increasing followed by decreasing) is observed in the hard gel region. We compared the shape of stress curves, Lissajous pattern, and Fourier transform (FT) rheology of hard gel and soft gel under LAOS, and tried to relate the complex LAOS behavior with the microstructural change. From these investigations, it was found that the LAOS behavior and the stress pattern at large strain are closely related to the microdomain structure of PEO-PPO-PEO triblock copolymer, and provide a lot of useful information on the microstructures induced by large deformation.

In this work, we present high-resolution solutions for viscoelastic 4:1 planar contraction flow problems using a transient finite element method based on the fractional step method (FSM) and stabilization techniques (DEVSS-G/DG) with linear equal-order interpolation function. The Oldroyd-B model was used as the constitutive equation. A parallel multi-frontal algorithm was implemented to enhance computational speed and all solutions were obtained on a parallel machine. The vortex intensity and the re-attachment length of corner vortex show good mesh-convergent behavior and are compared with previous results from the literature. In particular, the present results are in good agreement with the predictions of the high-resolution finite volume method of Alves et al. [15]. This may be the first case that quantitative agreement is obtained between studies using different numerical methods for the benchmark problem of 4:1 planar contraction flow. As there has been little quantitative agreement in the previous investigations and only few simulation results with highly refined meshes exit, this study may well be regarded as accurate and meaningful in the sense that reasonable convergence is achieved for prediction of 4:1 planar contraction flow using transient finite element methods.

In this work, we have prepared bioartificial polymer blends using hyaluronate (HA) as a biological component and poly(vinyl alcohol)–borax association (PVAs) as a synthetic component, and investigated the rheological properties as well as morphology of the blends. When plotted against the blend composition, the rheological properties showed both positive and negative deviation from the linear additive mixing rule depending on thermal history. The blend showed enhanced viscosity at the composition of 20 wt% of HA and 80 wt% of PVAs, when PVA was dissolved at high temperature. The viscosity enhancement was caused by the network formation of HA aggregates in the micrometer scale. In addition, the network structure of HA aggregates was found to be fractal with the fractal dimension of 1.7. As PVA system also forms a network structure in the nanometer scale between hydroxyl groups of PVA and borate anions, the blend system is unique in that it has network structures in both micrometer and nanometer scales in one material. On the contrary, HA formed aggregates but not any network structure in the blend of the same composition but of the negative deviation. In conclusion, we showed that HA/PVAs blend system may have diverse morphology as well as very broad spectrum of rheological properties, and could suggest that the rheology and morphology of HA/PVAs blends can be designed not only by controlling composition but also by controlling thermal and deformation history of the components.

Although the stress of oscillatory shear flow can be decomposed into elastic and viscous parts in the linear regime, it is not yet known how to decompose the stress of a large amplitude oscillatory shear (LAOS) flow. We developed a method of analyzing LAOS data, which decomposes the stress into elastic and viscous components on the basis of a sound mathematical and physical foundation. This method is based on the symmetry of the stress and is a generalization of linear viscoelasticity from the viewpoint of geometry. The proposed method is more powerful than previous methods such as Fourier transform analysis and the Lissajous plot, in that it is more sensitive to the presence of nonlinearities and it is easier to determine nonlinear parameters.

The effect of flow conditions on the “negative wake” generation (longitudinal velocity overshoot behind a cylinder in the viscoelastic fluid flow along the centerline) has been investigated. FENE-CR model that predicts constant shear viscosity and controlled extensional viscosity was considered as a constitutive equation. The discrete elastic viscous split stress-G/streamline upwind Petrov–Galerkin (DEVSS-G/SUPG) formulation was employed and the high-resolution solutions were obtained with an efficient iterative solver based on the incomplete LU(0)-type preconditioner and BiCGSTAB. We found that the “negative wake” generation was more obvious in uniform flow conditions than in Poiseuille flow, which suggests that the experimentally unrevealed “negative wake” generation of Boger fluids could be partially attributed to the geometrical effect of Poiseuille flow. The “negative wake” generation was more discernable at low extensibility and high value of viscosity ratio, which agrees well with the previous studies. In addition, we could observe an undershoot phenomenon in Poisseuille flow condition, which has never been reported.

In this study, we have investigated morphology evolution of polymer blends during extrusion. By choosing two polymers, high density polyethylene (PE) and poly (1,4-butylene terephthalate) (PBT), having a large difference in melting temperature, we could control the viscosity ratio of the blend as well as the morphology. The morphology of the dispersed phase evolved from film to fibril and to droplet structure depending on thermal and deformation history. We could maintain the film or fibril structure in a final product by keeping the dispersed phase deformable and rigid enough to avoid the relaxation that is related with instability originating from the interfacial tension. The anisotropic structures (film and fibril) were found to enhance the rheological properties significantly, but in different manners under shear and extensional flow fields. This study shows that diverse morphology can be obtained by controlling processing conditions, and the rheological properties can be dramatically enhanced by morphology control.

Vortex enhancement mechanism in 4:1 planar contraction flow of a viscoelastic fluid has been investigated, where the Oldroyd-B model was considered as a constitutive equation. Finite element method was used based on the fractional step method for time marching and DEVSS/DG as a stabilizing scheme. The prediction of vortex dynamics agreed well with the experimental results. At first, a lip vortex was generated at the reentrant corner at low Weissenberg number (We). As We increases, the size of the salient corner vortex becomes reduced, while the lip vortex becomes more pronounced and finally takes over the corner vortex. The trajectory of a lip vortex at high We was found to follow the steady state positions of the lip vortex at lower We, which means that the fluid has a memory and there exists a simple relationship between We and time. Accordingly, a simple universal behavior was found to dominate the vortex enhancement mechanism in the 4:1 planar contraction flow of the Oldroyd-B fluid.

An efficient iterative solution method is developed to obtain high-resolution solutions of viscoelastic flow problems, and the accuracy as well as the performance is investigated for highly refined finite elements. The formulation is based on DEVSS-G/SUPG, and the problem size is expanded up to the extremely large-scale problem composed of 1,362,480 unknowns with 84,531 finite elements, much more than the previous results [F.P.T. Baaijens, An iterative solver for the DEVSS/DG method with application to smooth and non-smooth flows of the upper convected Maxwell fluid, J. Non-Newtonian Fluid Mech. 75 (1998) 119; A.E. Caola, Y.L. Joo, R.C. Armstrong, R.A. Brown, Highly parallel time integration of viscoelastic flows, J. Non-Newtonian Fluid Mech. 100 (2001) 191]. An iterative solver [Y.S. Nam, H.G. Choi, J.Y. Yoo, AILU preconditioning for the finite element formulation of the incompressible Navier–Stokes equations, Comput. Methods Appl. Mech. Eng. 191 (2002) 4323] with a mixed formulation originally developed for Newtonian flow simulation and BiCGSTAB method is implemented as the solution method. The preconditioner of adaptive incomplete LU [Y.S. Nam, H.G. Choi, J.Y. Yoo, AILU preconditioning for the finite element formulation of the incompressible Navier–Stokes equations, Comput. Methods Appl. Mech. Eng. 191 (2002) 4323] is modified for DEVSS-G/SUPG. The modified adaptive incomplete LU(1)/BiCGSTAB with the variable reordering scheme is excellently applicable for a wide range of Weissenberg numbers (We) with the finest mesh ( We ∼ 0.875). The solution method is applied to the well-known two-dimensional Oldroyd-B fluid flow past a confined cylinder problem. The obtained dimensionless drag with different meshes varies within 0.013% at all converged We and shows a mesh convergent behavior of extra stresses in the wake region up to We = 0.7. At We larger than 0.7, complete mesh convergence is not achieved, but the prediction of dimensionless drag agrees well with some of the previous reports based on other methods. As there exists a discrepancy in the prediction of drag at high We among the research groups, it is meaningful that some of the results agree well with each other, even though they are computed from different methods. In addition, we could observe a singular behavior of extra stresses at high elasticity with highly refined meshes, and this singular behavior is suspected to be the origin of the failure of convergence at high We. This may be related with the unboundedness of the extensional viscosity in the Oldroyd-B model or with other numerical origin in the very refined meshes. To figure out whether this singular behavior or the failure originates from the constitutive equation or from other numerical origin in the very refined meshes, it will be necessary to solve the problems with other constitutive equations or with much more refined meshes. © 2004 Elsevier B.V. All rights reserved.

A dry-base electrorheological (ER) fluid was prepared by dispersing synthesized semiconducting polyaniline (PANI) particles into silicone oil, and its viscoelastic properties were investigated under applied electric fields using a rotational rheometer. Within the linear viscoelastic region, the ER fluid was observed to be elastic, due to columnar structure of PANI particles sustaining the deformation. Its rheological functions (G′ and G″) were interpreted based on the dimensional analysis, and they showed roughly linear electric-field dependence of the dimensional collapse of the viscoelastic behavior with frequency suggesting that the interactions between highly irregular particles are saturating even at these relatively low values of the dielectric mismatch. Furthermore, the recovery percentage obtained from the creep and recovery experiments increased with applied electric fields.

The normal concept is that the critical molecular weight (MC) is about twice as large as the entanglement molecular weight (Me). However, experimental data have shown considerable deviations from MC ≈ 2Me. Furthermore, a determination of MC requires samples with a wide range of molecular weights, including weights lower than MC and higher than MC. In this article, we suggest a simple method for determining MC from the loss moduli of nearly monodisperse linear polymers with M ≫ MC. We consider two characteristic relaxation times, which correspond to the local maximum and minimum of the loss modulus. MC is determined from the intersection of two phenomenological relaxation times as a function of the molecular weight. The method precisely agrees with MC ≈ 2Me, which is not shown by conventional methods. Moreover, our method provides a determination of relaxation time τe, at which chain segments first feel the constraints imposed by the conceptual tube, without the measurement of the tube diameter and the monomeric friction coefficient, which may be determined by complicated procedures with a lot of data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2724–2729, 2004

High impact polystyrene has been a typical thermoplastic to improve the impact strength and toughness of polystyrene. One of the main factors affecting these properties is the particle size and size distribution of the rubber phase. The rubber-phase particle size is related to the prepolymerization time that is determined by the phase inversion between polystyrene and rubber phases. However, the phase inversion in highly viscous oil-in-oil emulsions proceeds with a transitional fashion, not a catastrophic inversion. It has been tried to elucidate this inversion point by using viscosity, conversion and conductivity measurement techniques. They are used to find the point of phase inversion, indicative of the end of phase inversion, but they cannot produce its progression consecutively. In this study, a laser light scattering technique is utilized to characterize the evolution of the rubber particle size distribution depending on reaction time as well as to find the point of phase inversion. The progression of phase inversion during polymerization is monitored by this technique, which in turn is used to establish the proper prepolymerization time. Comparisons, limitations, and applications are dealt with.

We suggest a universal plot that superposes linear viscoelastic data of nearly monodisperse polymers on a single curve, regardless of the molecular weight, temperature, and species of polymers. The plotting method is based on the time–temperature superposition and rescaling of viscoelastic functions with terminal behavior. Without any information from molecular theories, the plot supports the fact that the molecular theories of the linear viscoelasticity of monodisperse polymers are independent of the species of polymers. Although an appropriate scaling may show universality by separately extracting the reptational mode and the Rouse mode from the whole set of viscoelastic data, our plotting method shows universality in a unified manner that scales the viscoelastic functions measured over the whole frequency range. We explain the origin of the universality of the plot in terms of molecular theory, the phenomenological spectra of the relaxation time (the BSW and CW spectra), and the principle of time–temperature superposition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2730–2737, 2004

High-impact polystyrene (HIPS) was prepared by the bulk or low-solvent polymerization of styrene in the presence of dissolved rubber and characterized to measure the dispersed particle size of the rubber phase. Before preparation, the prepolymerization time was established by measuring the evolution of particle size distribution of the dispersed phase as a function of reaction time. The measurement technique by laser light scattering was found to be efficient enough not only to lead to the right prepolymerization time but also to predict rubber-phase particle size distribution. Polymerization experiments were then conducted to investigate the effect of solvent contents on the particle size distribution of the rubber phase, in which ethylbenzene was introduced as a solvent at levels of 0, 3, 10, and 15%. As the solvent content increased, the size of rubber-phase particles initially increased, reaching a maximum, and then decreased. It is speculated that a decrease in the molecular weight of the matrix, a decrease in the viscosity ratio between polybutadiene to polystyrene phases, and a change in rubber morphology all contributed to the change in the rubber particle size of HIPS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3672–3679, 2003

Large amplitude oscillatory shear (LAOS) behavior of electrorheological (ER) fluids has been investigated using three-dimensional particle-level dynamics simulation. As an ER device usually operates in a dynamic mode with large deformation, it is important to understand the LAOS behavior as well as its underlying mechanism for the development of an effective ER fluid. Simulation predicted most of the experimental observations including strain overshoot, distorted stress signal, dogbone-type Lissajous curve, and stripe pattern formation, to list a few. By careful investigation of cluster statistics as well as microstructures, we found that the strain overshoot phenomenon, which is often observed in complex fluid systems with little explanation, arises from the cluster reformation process in addition to a slight rearrangement within a cluster. Fourier transformation analysis was also performed, and the scaling behavior of the intensities of higher harmonics was investigated. The intensities of higher harmon...

Large amplitude oscillatory shear (LAOS) behavior of complex fluids, which form microstructures depending on their deformation history, has been investigated by using a network model. According to recent experimental observations, the LAOS behavior of complex fluids could be classified by at least four types: type I, strain thinning (G � , G �� decreasing); type II, strain hardening ( G � , G �� increasing); type III, weak strain overshoot ( Gdecreasing, G �� increasing followed by decreasing); type IV, strong strain overshoot ( G � , G �� increasing followed by decreasing). To understand such complex behavior, we have applied a general network model. As there is little information available on the form of creation and loss rates of network junctions, we have modeled the creation and loss rates as exponential functions of shear stress. By adjusting the model parameters that define the creation and loss rates, the types of LAOS behavior observed in the experiments could be reproduced. Despite highly simplistic modeling, the model reproduced the types of LAOS behavior observed in the experiments, which means that the behavior can be explained in terms of the model parameters, that is, the creation and loss rates of network junctions. It is also suggested that the LAOS behavior can be effectively used as a tool for classifying complex fluids. © 2003 Elsevier B.V. All rights reserved.

A novel approach to fabricate poly(propylene)/clay nanocomposites under an electric field without adding any compatibilizer was proposed. The electrically activated poly(propylene)/clay nanocompsites show enhanced rheological properties with the disapearance of the characteristic peak in X-ray diffraction. Transmission electron microscopy was used to confirm the microstructural changes of the nancomposites. Electric field was found to facilitate destruction of the layer-stacking and separation of the silicate layers.

We study the mechanism of depletion stabilization and the resultant microstructure of aqueous suspensions of nano-sized silica and poly(vinyl alcohol) (PVA). Rheology, Small Angle Light Scattering (SALS) and Small Angle X-ray Scattering (SAXS) techniques enable us to analyse the microstructure at broad length scale from single particle size to the size of a cluster of aggregated particles. As PVA concentration increases, the microstructure evolves from bridging flocculation, steric stabilization, depletion flocculation to depletion stabilization. To our surprise, when depletion stabilization occurs, the suspension shows the stabilization at the cluster length scale, while maintaining fractal aggregates at the particle length scale. This sharply contrasts previously reported studies on the depletion stabilization of micro-sized particle and polymer suspensions, which exhibits the stabilization at the particle length scale. Based on the evaluation of depletion interaction, we propose that the depletion energy barrier exists between clusters rather than particles, due to the comparable size of silica particle and the radius gyration of PVA. ispartof: Langmuir vol:31 issue:6 pages:1892-1900 ispartof: location:United States status: published

Particle depositions on patterned membrane surface were experimentally measured and compared with those of non-patterned membranes. Prism patterns introduced to membrane surface significantly reduced particle deposition. A larger pattern was less effective against particle deposition than a smaller pattern under low Reynolds number, but was very successful in mitigating particle deposition under high Reynolds number at faster crossflow velocity. The particle deposition and anti-fouling mechanisms were analyzed using computational fluid dynamics simulation. A vortex was formed in the valley region between prism patterns, proposing that particles entering the valley region because of permeation drag had a chance to return back to bulk crossflow stream during flowing along with the vortex. The distance between the vortex and bulk stream was shorter under high Reynolds number than under small Reynolds number, suggesting that the return of particles in the valley region into the bulk stream was quite enhanced by increasing crossflow velocity. To further mitigate particle deposition on the valley region, new patterns were developed by introducing intervals to prism patterns and showed much improvement in antifouling ability by enhancing the vortex and reducing the portion of permeation stream in the valley region.

Rheological properties of some polymer solutions in both the linear and non-linear regions have been investigated. The solutions include poly(vinyl alcohol) solution (with and without sodium borate), hyaluronic acid solution, and xanthan gum solution; some of which form microstructures depending on their deformation history, and thus can be classed as complex fluids. Among the rheological properties, the large amplitude oscillatory shear (LAOS) behavior was found to be very sensitive to the interactions or the shear-induced formation of microstructures. Depending on the interactions between the microstructures, it was found that there exist at least four types of LAOS behavior: type I, strain thinning (G′, G″ decreasing); type II, strain hardening (G′, G″ increasing); type III, weak strain overshoot (G′ decreasing, G″ increasing followed by decreasing); type IV, strong strain overshoot (G′, G″ increasing followed by decreasing). It is suggested that the LAOS behavior can be effectively used as a tool for classifying the complex fluids.

The effect of graft ratio on the dynamic moduli of ABS (Acrylonitrile-Butadiene-Styrene Copolymer) has been investigated. Unlike previous papers, the storage modulus at low frequency shows both minimum and maximum as graft ratio increases, and the rubber particles do not agglomerate significantly at high graft ratios. The dependence of the rheological properties on the graft ratio is quite complicated. This arises from its morphological change that leads to different interactions between the rubbery phase and the matrix phase. The minimum has been reported previously, and is explained in terms of rubber dispersion. However, the maximum at high graft ratio has never been reported. The origin of maximum seems to come from the repulsive forces between the long graft chains of neighboring rubber particles. Analogy between our experimental results and simulation results has been discussed to deduce the mechanism of maximum storage modulus at high graft ratio.

Three-dimensional numerical simulation of viscoelastic coextrusion process has been performed and numerical results were compared with the experimental data of Karagiannis et al. (1990). By varying the magnitude of the second normal stress difference and its ratio of Fluid I and Fluid II, we were able to control the interface profile and the degree of encapsulation along the downstream direction. By increasing the parameter α (αFluid I=αFluid II) from 0.1 to 0.4 in the Giesekus model and increasing the α ratio (αFluid IαFluid II) between Fluid I and Fluid II from 2.0 to 4.0 in the permissible range of realistic polymeric systems, the interface profile and the degree of encapsulation along the downstream direction were fitted with the experimental results. There was little difference between the numerical results and the experimental data in the interface profile and the degree of encapsulation along the downstream direction when the α ratio was set to 3.0 (0.3:0.1). Fluid I with larger magnitude of the second normal stress difference protrudes into Fluid II with smaller magnitude of the second normal stress difference around the symmetric plane, while Fluid II wraps around Fluid I near the side walls. As the ξ 1 ratio (ξ 1 ,Fluid Iξ 1 ,Fluid II) increases from 1.0 to 3.0 for the two-mode Phan-Thien and Tanner model, it was found that the curvature of the interface profile increased, and the difference between the numerical results and the experimental data in the interface profile and the degree of encapsulation along the downstream direction was almost negligible when the ξ 1 ratio was set to 3.0 (0.54:0.18). Although the parameters of viscoelastic models were fitted by using the shear viscosity data only, quantitative agreements between the numerical results and the experimental coextrusion data were quite satisfactory.

The homogeneous polycarbonate/poly(acrylonitrile-butadiene-styrene) (PC/ABS) nanocomposite thin films were prepared by a facile solvent casting method using phenylene modified-mesoporous silica materials as additives and dichloromethane as a solvent. The physicochemical analyses using small-angle X-ray scattering, nitrogen adsorption–desorption, solid-state 13C and 29Si nuclear magnetic resonance, and scanning electron microscope were investigated to provide clear physical and chemical properties for modified-mesoporous materials and nanocomposite films. Tensile tests were performed at room temperature according to ASTM D638. Rheological properties were also analyzed to observe any variance of solid–liquid property. As a compatibilizer and a reinforcing filler, mesoporous (organo-)silicas showed enhanced features in rheological and mechanical properties. The sound absorption coefficient was measured by the impedance tube up to 6400 Hz according to ISO 10534-2. It was found that the PC/ABS nanocomposites containing mesoporous materials can be used as a sound-proofing support material depending on fabrication process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45777.

The oscillational motion of bacteria and non-biological particles on a positively polarized substrate surface were investigated in this study using several bacterial species ( Staphylococcus epidermidis ATCC12228 and Pseudomonas aeruginosa PA14) and polystyrene particles (modified with sulfate or carboxylate) that have different cell/particle size, surface potential, surface ionizable functional group, and surface appendage with respect to the mean square displacement (MSD) and motion trajectory. The attractive/repulsive interactions between the bacteria/particle and a positively polarized substrate surface are further discussed with the results of the motion analysis based on the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. As our major findings, all the bacterial species and particles showed oscillational motion, a kind of sub-diffusive motion that is more limited than the Brownian motion of the suspended bacteria/particles, on a positively polarized substrate surface. However, the motion properties among the bacteria/particles were found to differ in motion radius and MSD. As the size and negative surface potential of the bacteria/particle got smaller, the oscillational motion became more active, which may result from a decrease in attractive interactions such as van der Waals interaction and electrostatic attractive interaction. In the case in which some surface functional group (e.g., sulfate group) contributed to the formation of a strong Lewis acid–base interaction, the oscillational motion was significantly reduced regardless of the surface potential of the particle. The bacterial surface appendages were found to have no influence in explaining motion differences between the bacteria and non-biological particle.

Flow-induced instabilities that lead to non-uniform stationary flow profiles have been observed in many different soft-matter systems. Two types of instabilities that lead to banded stationary states have been identified, which are commonly referred to as gradient- and vorticity-banding. The molecular origin of these instabilities is reasonably well understood. A third type of instability that has been proposed phenomenologically [Europhys. Lett., 1986, 2, 129 and Phys. Rev. E, 1995, 52, 4009] is largely unexplored. Essential to this “Shear-gradient Concentration Coupling” (SCC-) instability is a mass flux that is induced by spatial gradients of the shear rate. A possible reason that this instability has essentially been ignored is that the molecular origin of the postulated mass flux is not clear, and no explicit expressions for the shear-rate and concentration dependence of the corresponding transport coefficient exist. It is therefore not yet known what types of flow velocity- and concentration-profiles this instability gives rise to. In this paper, an expression for the transport coefficient corresponding to the shear-gradient induced mass flux is derived in terms of the shear-rate dependent pair-correlation function, and Brownian dynamics simulations for hard-spheres are presented that specify the shear-rate and concentration dependence of the pair-correlation function. This allows to explicitly formulate the coupled advection–diffusion equation and an equation of motion for the suspension flow velocity. The inclusion of a non-local contribution to the stress turns out to be essential to describe the SCC-banding transition. The coupled equations of motion are solved numerically, and flow- and concentration-profiles are discussed. It is shown that the SCC-instability occurs within the glass state at sufficiently small shear rates, leading to a banded flow-profile where one of the bands is non-flowing.

We numerically investigated the dynamics of short double-stranded DNA molecules moving through a deep-shallow alternating nanofilter, by utilizing Brownian dynamics simulation. We propose a novel mechanism for high-throughput DNA separation with a high electric field, which was originally predicted by Laachi et al. [Phys. Rev. Lett. 2007, 98, 098106]. In this work, we show that DNA molecules deterministically move along different electrophoretic streamlines according to their length, owing to geometric constraint at the exit of the shallow region. Consequently, it is more probable that long DNA molecules pass over a deep well region without significant lateral migration toward the bottom of the deep well, which is in contrast to the long dwelling time for short DNA molecules. We investigated the dynamics of DNA passage through a nanofilter facilitating electrophoretic field kinematics. The statistical distribution of the DNA molecules according to their size clearly corroborates our assumption. On the other hand, it was also found that the tapering angle between the shallow and deep regions significantly affects the DNA separation performance. The current results show that the nonuniform field effect combined with geometric constraint plays a key role in nanofilter-based DNA separation. We expect that our results will be helpful in designing and operating nanofluidics-based DNA separation devices and in understanding the polymer dynamics in confined geometries.

We numerically investigated the dynamics of short double-stranded DNA molecules moving through a deep-shallow alternating nanofilter, by utilizing Brownian dynamics simulation. We propose a novel mechanism for high-throughput DNA separation with a high electric field, which was originally predicted by Laachi et al. [Phys. Rev. Lett. 2007, 98, 098106]. In this work, we show that DNA molecules deterministically move along different electrophoretic streamlines according to their length, owing to geometric constraint at the exit of the shallow region. Consequently, it is more probable that long DNA molecules pass over a deep well region without significant lateral migration toward the bottom of the deep well, which is in contrast to the long dwelling time for short DNA molecules. We investigated the dynamics of DNA passage through a nanofilter facilitating electrophoretic field kinematics. The statistical distribution of the DNA molecules according to their size clearly corroborates our assumption. On the other hand, it was also found that the tapering angle between the shallow and deep regions significantly affects the DNA separation performance. The current results show that the nonuniform field effect combined with geometric constraint plays a key role in nanofilter-based DNA separation. We expect that our results will be helpful in designing and operating nanofluidics-based DNA separation devices and in understanding the polymer dynamics in confined geometries.

The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions. Shear thickening was successfully captured for highly concentrated suspensions at high particle Reynolds number, and both the local rheology and local structure of the suspensions were analyzed. It was also found that the linear correlation between the local particle stress and local particle volume fraction was dramatically reduced during shear thickening. These results clearly show how the change in local structure of suspensions influences the local and bulk rheology of the suspensions.

Three-dimensional numerical simulation of coextrusion process of two immiscible polymers through a rectangular channel has been performed using the finite element method. The upper convected Maxwell (UCM) model and the Phan-Thien and Tanner (PTT) model were considered as viscoelastic constitutive equations. The elastic viscous stress splitting (EVSS) method was adopted to treat the viscoelastic stresses, and the streamline upwinding (SU) method was applied to avoid the failure of convergence at high elasticity. The problem arising from the ambiguous outlet boundary condition that has previously been used in the three-dimensional simulation of a viscoelastic coextrusion process could be avoided by introducing the open boundary condition (OBC) method. The abrupt change or deviation of contact line position near the outlet that was observed when the fully developed outlet boundary condition was applied could be clearly removed by using the OBC method. The effects of viscoelastic properties, such as the shear viscosity ratio, the elasticity, the second normal stress difference, and the extensional viscosity on the interface distortion, the interface curvature, and the degree of encapsulation along the downstream direction have been investigated. The shear viscosity ratio between the polymer melts was the controlling factor of the interface position and the encapsulation phenomena. The interface distortion seems to increase as the elasticity ratio increases under constant shear viscosity, even though it is not so large. The degree of encapsulation seems to increase with increasing the ratio of the second normal stress differences. The extensional viscosity had minor effect on the encapsulation phenomena. The second normal stress difference was found to have a great influence on the increasing of the degree of encapsulation along the downstream direction as compared to the effect of the first normal stress difference.

We have developed a numerical algorithm based on 2D/3D finite element method for solving non-Newtonian fluid flow with the moving free surface encountered in polymer processing. The power law model is considered as a rheological constitutive equation. The standard Galerkin finite element formulation/penalty formulation are applied to discrctize the governing equations, the volume-of-fluid (VOF) scheme is used to track the moving free surface, and the donor-acceptor model introduced by Hirt and Nichols is modified and implemented on FEM. We applied the numerical scheme to simulate fountain flow and viscous buckling problems. For fountain flow, the numerical prediction of this study is in good agreement with the experimental results of other investigators. For viscous buckling, both 2D and 3D numerical simulations show that the shear thinning effect retards buckling. As this algorithm is very effective in treating moving free surface problems and requires less memory than previous algorithms, it may help solve challenging problems in polymer processing such as transient visroelastic flow simulations with moving free surfaces.

The weldline morphology of modified-poly(phenylene-oxide)/polyamide-6 blends has been investigated. A distinct contacting layer consisting of fine spherical particles was observed from the V-notch at the surface to the center of the molded part for the low viscosity ratio blend. In contrast, such small particles were not found and a slight deformation was observed near the part's surface for the high viscosity ratio blend. The weldline morphology was found to be dominated by the deformation, the breakup, and the relaxation of the dispersed modified-poly(phenylene oxide) phase. The effect of injection conditions on the weldline morphology has also been investigated. The morphology of the meldline was quite complicated. Distorted multi-layered structures were observed. It was found that those structures arise from the subsequent flow after merging of the two flow fronts. Weldlines and meldlines have been studied separately, and their formation mechanisms were found to be basically similar.

High Impact Polystyrene (HIPS) polymers varying widely in the degree of graft, size of the rubber particles and volume fraction of the rubber phase have been tested in uniaxial tension. From these tests, it is shown that the yield stress and tensile modulus decrease as the degree of graft increases up to about 120%, and then increase. Increasing the rubber volume fraction and the size of the rubber particles also reduces the yield stress. A dynamic test is conducted and it is verified that the glass transition temperature of the rubber phase increases with increasing the degree of graft. In addition to this, the maximum tan δ increases with increasing the degree of graft up to about 120%, and then decreases. It is also shown that the yield stress and tensile modulus of HIPS have a relationship with the dynamic behavior of the rubber phase, i.e. the yield stress and tensile modulus decrease almost linearly as the maximum tan δ increases.

The effect of injection molding conditions and reactive compatibilization on the morphology of maleic anhydryde-modified poly(phenylene oxide)/polyamide-6 blends was investigated. The injection flow rate primarily influenced the position of the subskin layer, and the injection temperature affected the aspect ratio of the dispersed phase. A reduction of the size of the dispersed phase occured during the converging flow in the barrel-to-sprue zone. The reactive compatibilization reduced the flow induced deformation, the coalescence and the breakup of particles and improved the dispersion of the minor phase.

The morphology of injection molded poly(phenylene oxide)/polyamide-6 blends was investigated. A distinct skin layer, subskin layer, and core region were found across the part thickness, and the morphology of the skin layer was clearly observed. The shape and size of the dispersed phase depended on the position across the part thickness and the viscosity ratio of the component polymers. For low viscosity ratios, small and large particles coexisted in the subskin layer, implying that both coalescence and breakup of the dispersed phase occurred in that layer. For high viscosity ratios, an intermediate zone, in which little deformation of the dispersed phase occurred, was found between the skin layer and the subskin layer. These findings are expected to help foster understanding of the mechanism of morphology evolution during the filling and cooling stages of the injection molding process.

Electrorheological (ER) properties of ER suspensions composed of silica particles and silicone oil under the squeezing flow have been investigated experimentally by changing experimental conditions such as applied electric field, volume concentration of silica particles, medium viscosity of silicone oil, and water content in silica. ER behavior in the squeeze flow is unique in several ways compared to that in the shear flow. Electric field and volume concentration increase as the squeezing proceeds, which increases the strength of chain structures formed between the electrodes. High yield stress and normal stress can be obtained in the case of high voltage, high volume fraction, low medium viscosity, and high water content. As the squeezing proceeds, the normal stress increases, showing some fluctuation due to the deformation of chain structures in the suspension. The fluctuation observed in the stress grows so violent under a certain condition, which seems to be caused partly by macroscopic rearrangement...

The Partial Frame Process (PFP) is a kind of gas-assisted injection molding, in which the void core is generated by imposing low pressure air into the molded part just after the resin is completely filled, after which the void grows as it compensates the volume shrinkage of resin. It resembles a secondary gas penetration step of gas-assisted injection molding, but has more advantages, such as its simplicity, design flexibility, ease of control, and cheap utilities. In this study, modeling of the void growth in PFP was carried out. By comparing the results with the experimental data, basic assumptions have been justified and the mechanism of the void growth could be explained in terms of the process parameters such as mold temperature, melt temperature, and the channel size. An experimental approach was also taken. As there are many factors affecting the process, the method of design of experiments was adopted, and the effects of the process parameters on the void growth length and the mechanism of the void growth were investigated. The results are expected to help in mold design and the determination of the operating conditions, as well as our understanding of this new process.

We have considered two dimensional electrons further confined in an inhomogeneous magnetic field which is B =0 for r r 0 and B ≠0 elsewhere. We have noticed, through the exact evaluation of the single particle energy spectra, the existence of current-carrying edge states near the dot boundary circulating either clockwise or counterclockwise. These magnetic edge states are shown to have quite different properties from those originated from electrostatic confinements.

Modeling of the void growth in Partial Frame Process (PFP) was carried out by assuming that the shrinkage due to temperature difference is compensated by the growth of void, and the results will be presented in the talk. By comparing the results with the experimental data, basic assumptions will be justified and the mechanism of the void growth will be explained in terms of the process parameters. Experimental study has also been carried out based on the design of experiments (DOE) to see the effects of the process parameters on the void growth length.

The formation of magnetic edge states is investigated for magnetic quantum structures with inhomogeneous magnetic fields such as a magnetic quantum dot (B=0 for r

The harmony of ink and printing method is of importance in producing on-demand droplets and jets of ink. Many factors including the material properties, the processing conditions, and the nozzle geometry affect the printing quality. In electrohydrodynamic (EHD) printing where droplets or jets are generated by the electrostatic force, the physical as well as the electrical properties of the fluid should be taken into account to achieve the desired performance. In this study, a systematic approach was suggested for finding the processing windows of the EHD printing. Six dimensionless parameters were organized and applied to the printing system of ethanol/terpineol mixtures. On the basis of the correlation of the dimensionless voltage and the charge relaxation length, the jet diameter of cone-jet mode was characterized, and the semicone angle was compared with the theoretical Taylor angle. In addition, the ratio of electric normal force and electric tangential force on the charged surface of the Taylor cone was recommended as a parameter that determines the degree of cone-jet stability. The cone-jet became more stable as this ratio got smaller. This approach was a systematic and effective way of obtaining the Taylor cone of the cone-jet mode and evaluating the jetting stability. The control of the inks with optimized experimental parameters by this method will improve the jetting performance in EHD inkjet printing.

We report a first application of vertical small angle X-ray scattering to investigate the drying process of a colloidal suspension by overcoming gravity related restrictions. From the observation of the drying behavior of charge-stabilized colloidal silica in situ, we find the solidification of the colloidal particles exhibits an initial ordering, followed by a sudden aggregation when they overcome an electrostatic energy barrier. The aggregation can be driven not only by capillary pressure but also by thermal motion of the particles. The dominating contribution is determined by the magnitude of the energy barrier at the transition, which significantly decreases during drying due to an increased ionic strength. ispartof: Langmuir vol:29 issue:32 pages:10059-10065 ispartof: location:United States status: published