Viscosity Of Matrix Research Articles

Growth of sputtered silver nanoparticles on a liquid mercaptan matrix with controlled viscosity and sputter rate

Abstract A sputtering deposition of metals over liquid matrixes has been investigated as a novel and environmentally friendly method to generate stable colloidal metal nanoparticles. We have expanded this method by using the liquid monomers with mercapto groups in order to prepare more stable, uniform and size-controllable nanoparticles. Here we report the systematic investigation on the growth mechanism of silver nanoparticles on pentaerythritol tetrakis(3-mercaptopropionate) (PEMP) matrix under the varied viscosities controlled by temperature. The diameter of obtained nanoparticles increased from 1.8 to 2.3 nm as the viscosity of the liquid matrix increased, and at higher viscosity region we obtained a thin deposited film on the liquid surface but no nanoparticles formed. The effect of viscosity on the particle diameter was much smaller than previous works using ionic liquids or polyethylene glycol, and then the phenomenon was understood by the structure of these matrixes where PEMP has four mercapto groups however ionic liquids or polyethylene glycol does not have any functional groups that introduce strong interaction with metals. These demonstrations suggest that the sputtering over mercaptan liquid matrix is a more favorable method for the stable preparation of uniform very small nanoparticles.

Effects of matrix viscosity, mixing method and annealing on the electrical conductivity of injection molded polycarbonate/MWCNT nanocomposites

Effects of the compounding equipment, the viscosity of the matrix, and the annealing on the electrical resistivity of polycarbonate (PC)/MWCNT nanocomposites were investigated. Two different types of compounding equipment (a batch mixer and a twin screw extruder) produced a huge difference in the resistivity in an injection molded PC/MWCNT nanocomposite while the resistivity of compression molded samples showed only small differences. It was also observed that the viscosity of the PC matrix affected the resistivity of the injection molded nanocomposites to a great extent. The resistivity of the nanocomposites increased with the viscosity of the PC matrix. This is attributed to two factors. When the PC/MWCNT nanocomposites are fabricated, interpenetration of the PC matrix into MWCNT bundles is easier for a less viscous matrix. Another factor is that lower viscosity PC induces less orientation of MWCNTs.

Deciphering the Effect of Substrate Viscoelasticity on Hepatic Stellate Cell Function and Differentiation in the Context of Liver Fibrosis

Hepatic stellate cells (HSC) are mechanosensitive cells able to differentiate in vivo into myofibroblasts in stiff environments. Liver fibrosis is a pathological context condition characterized by increasing liver stiffness, and myofibroblastic differentiation, but the balance between the contribution of both the stiffness and the viscosity of the cellular matrix to this phenomenon remains to be determined. In order to evaluate the influence of substrate viscosity on HSC phenotype we developed a custom system of acrylamide gels with varying viscoelastic properties. Plating primary murine HSC on such acrylamide gels of varying stiffness, viscosity and biological functionalization reveals how the cellular phenotype is induced by each of these parameters and their respective influence on HSC function. Creation of substrates in which both the magnitude of elastic modulus and its rate of relaxation can be tuned can help define the time scales over which cellular mechanosensing occurs.

Mechanical Analysis of Single Myocyte Contraction in a 3D Viscoelastic Gel

Objective: Under congenital or acquired pathological conditions, excessive mechanical stress in myocardium leads to arrhythmias and heart failure, yet mechano-chemo-transduction (MCT) mechanisms are poorly understood at the single cell level during heart disease development. We recently developed a novel Cell-in-Gel system, embedding isolated live myocytes in a constraining hydrogel, to study MCT mechanisms under various mechanical scenarios.Methods: A mechanical model is used to calculate time-varying displacement, strain, and stress fields present during ongoing Cell-in-Gel experiments. Our previous 3D analytical solution of a single contracting myocyte embedded in an infinite elastic matrix (based on the Eshelby Inclusion problem) is extended to include the effects of Gel (matrix) viscosity. The model is calibrated by viscoelastic characterization of the Gel of various cross-linker densities using a dynamic rotary rheometer.Results: The analytical model enables quick parametric studies to establish trends with Gel stiffness and viscosity. As previously found for a purely elastic matrix, the stress state within the cell is multi-axial and uniform, yet cell surface tractions are quite non-uniform, and a typical cardiomyocyte in a gel of similar stiffness can contract only 20% of its load-free fractional shortening. The presence of Gel viscosity, however, adds a time lag between strains and stresses in both the cell and Gel and causes an increase in energy and mechanical power requirements for cell contraction.Conclusions: The mechanical model provides a baseline prediction (without up-regulation of Ca2+ transients) of the response of the myocyte during contraction in-gel. With preload or afterload, Cell-in-Gel data show stronger fractional shortening than predicted, so the model effectively quantifies this contractility enhancement (related to the Anrep effect). Thus, our analysis method can be used to quantitatively inform ongoing MCT studies that link mechanical stress to cardiac function and remodeling.

Magnetic response of gelatin ferrogels across the sol-gel transition: the influence of high energy crosslinking on thermal stability.

As emerging responsive materials, ferrogels have demonstrated significant potential for applications in areas of engineering to regenerative medicine. Promising techniques to study the behavior of magnetic nanoparticles (MNPs) in such matrices include magnetic particle spectroscopy (MPS) and magnetorelaxometry (MRX). This work investigated the magnetic response of gelatin-based ferrogels with increasing temperatures, before and after high energy crosslinking. The particle response was characterized by the nonlinear magnetization using MPS and quasistatic magnetization measurements as well as MRX to discriminate between Néel and Brownian relaxation mechanisms. The effective magnetic response of MNPs in gelatin was suppressed, indicating that the magnetization of the ferrogels was strongly influenced by competing dipole-dipole interactions. Significant changes in the magnetic behavior were observed across the gelatin sol-gel transition, as influenced by the matrix viscosity. These relaxation processes were modeled by Fourier transformation of the Langevin function, combined with a Debye term for the nonlinear magnetic response, for single core MNPs embedded in matrices of changing viscosities. Using high energy electron irradiation as a crosslinking method, modified ferrogels exhibited thermal stability on a range of timescales. However, MRX relaxation times revealed a slight softening around the gelatin sol-gel transition felt by the smallest particles, demonstrating a high sensitivity to observe local changes in the viscoelasticity. Overall, MPS and MRX functioned as non-contact methods to observe changes in the nanorheology around the native sol-gel transition and in crosslinked ferrogels, as well as provided an understanding of how MNPs were integrated into and influenced by the surrounding matrix.

炭素繊維強化ポリカーボネートの成形

In the molding of the carbon fiber reinforced thermoplastic (CFRTP), impregnation of the carbon fiber (CF) bundle is one of the important issues. In this study, we discussed the influence of the melting viscosity of matrix polycarbonate (PC) resin into the CF fabric substrate on the impregnation behavior, and also discussed the influence of the viscosity of the PC and molding time on the formation mechanism of the void. The CF/PC composites were prepared by using the CF plain fabric and PC film using film stacking method by changing the molding temperature and the molding time. According to the photograph of CF/PC surface, the PC resin into the CF bundle flowed in the chink of the CF bundle and crossing point of CF fabrics. The voids were formed by the PC resin impregnated as surrounding the aggregateofCF.Thesizeofvoids becomes smaller by impregnation of the PC resin into inside of the aggregate of CF. Therefore, when the matrix viscosity of PC is low, resin is easy to flow and the size of voids is easy to become smaller.

Functional pressure‐sensitive adhesive tapes for local anodization of aluminium surfaces

A novel, pressure‐sensitive adhesive tape for local anodization of aluminium surfaces was developed. The main difference between this tape anodization and conventional bath anodization is the viscosity of the anodization medium. While the viscosity of industrial anodization baths is similar to that of water, the viscosity of the adhesive matrix is higher by six orders of magnitude. To achieve a reliable application of tape anodization, the differences between bath and tape anodization were examined. This included the impact of process parameters on the morphology of anodic oxide layers. A decrease in the speed of the transport processes in the liquid phase because of the higher viscosity leads to changed rates of growth and the dissolution of the anodic oxide layer. The morphology of anodic oxide layers formed under conditions of high viscosity is presented. Layer thickness, pore density and pore area were obtained by statistical analysis of SEM images. The results are complemented by current–time response measurements during the anodization process. Practical tests of the applicability of the anodization tape for local pre‐treatment of aluminium surfaces prior to bonding or painting were successfully performed. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of nanoparticles on the morphology and properties of PET/PP in situ microfibrillar reinforced composites

In this work, the effect of SiO2 nanoparticles on the morphology and properties of PET/PP in situ microfibrillar reinforced composites (MFC) obtained from slit die extrusion and hot stretching‐quenching was investigated. The scanning electron micrographs revealed that the nanoparticles could have different effects on microfibril formation of PET/PP MFC depending on their concentration. Addition of appropriate content of nanoparticles (e.g., 1.6 and 8 wt%) facilitated the PET droplet‐fibril transition during stretching due to the presence of nanosilica in the PP matrix, which increased the viscosity of PP matrix and then improved the droplet deformability. However, at higher loading (e.g., 12 wt%), the aggregation of silica nanoparticles around the PET droplets prevented disperse phase coalescence during drawing and then reduced the fibrillation ability of PET minor phase. The dynamic rheological test performed at 190°C showed that the increased spatial restriction of the nanoparticles improved the viscoelastic moduli and complex viscosity of PET/PP MFC. DSC results indicated that nanosilica had little heterogeneous nucleation effect on the PP matrix of PET/PP MFC. Additionally, nanoparticles could present drastic improvement in the degradation behavior of PET/PP MFC under thermo‐oxidative conditions and increased the modulus of PET/PP MFC. POLYM. COMPOS., 38:2718–2726, 2017. © 2015 Society of Plastics Engineers

Hybrid Molecular and Spin Dynamics Simulations for Ensembles of Magnetic Nanoparticles for Magnetoresistive Systems.

The development of magnetoresistive sensors based on magnetic nanoparticles which are immersed in conductive gel matrices requires detailed information about the corresponding magnetoresistive properties in order to obtain optimal sensor sensitivities. Here, crucial parameters are the particle concentration, the viscosity of the gel matrix and the particle structure. Experimentally, it is not possible to obtain detailed information about the magnetic microstructure, i.e., orientations of the magnetic moments of the particles that define the magnetoresistive properties, however, by using numerical simulations one can study the magnetic microstructure theoretically, although this requires performing classical spin dynamics and molecular dynamics simulations simultaneously. Here, we present such an approach which allows us to calculate the orientation and the trajectory of every single magnetic nanoparticle. This enables us to study not only the static magnetic microstructure, but also the dynamics of the structuring process in the gel matrix itself. With our hybrid approach, arbitrary sensor configurations can be investigated and their magnetoresistive properties can be optimized.

Experimental study on penny-shaped fluid-driven cracks in an elastic matrix

When a pressurized fluid is injected into an elastic matrix, the fluid generates a fracture that grows along a plane and forms a fluid-filled disc-like shape. We report a laboratory study of such a fluid-driven crack in a gelatin matrix, study the crack shape as a function of time and investigate the influence of different experimental parameters such as the injection flow rate, Young’s modulus of the matrix and fluid viscosity. We choose parameters so that effects of material toughness are small. We find that the crack radius R ( t ) increases with time t according to t α with α =0.48±0.04. The rescaled experimental data at long times for different parameters collapse based on scaling arguments, available in the literature, showing R ( t )∝ t 4/9 from a balance of viscous stresses from flow along the crack and elastic stresses in the surrounding matrix. Also, we measure the time evolution of the crack shape, which has not been studied before. The rescaled crack shapes collapse at longer times and show good agreement with the scaling arguments. The gelatin system provides a useful laboratory model for further studies of fluid-driven cracks, which has important applications such as hydraulic fracturing.

The influence of processing techniques on the matrix distribution and filtration of clay in a fibre reinforced nanocomposite

A nano-modified matrix based on an epoxy resin and montmorillonite (MMT) layered silicates, was successfully infiltrated through 10 ply of carbon fibre preform. A combined fabrication process of a vacuum assisted resin infusion method (VARIM) followed by a rapid heating rate and mechanical vibration during cure, facilitated the infiltration of the nano-modified matrix through the preform. This was achieved by dispersing the MMT clay in the resin and ensuring that the viscosity of the nano-modified matrix remained low during fabrication. SEM-EDX (energy dispersive X-ray spectroscopy) spectra showed that chemical constituents within MMT clay including silicon, aluminium and magnesium elements had permeated through the fibre preform and were detected throughout the laminate. A homogeneous resin/particle distribution was achieved with the size of clay particles ranging from 100 nm to 1 μm.

Tribology of particle suspensions in rolling-sliding soft contacts

We investigate the lubrication of microsphere suspensions between compliant substrates, and probe the influence of matrix viscosity, particle phase volume, surface roughness and wetting, and slide-to-roll ratio (SRR). In general, the suspensions behave as a continuum in the elastohydrodynamic regime provided the film thickness, which is predicted from the product of speed and viscosity, is greater than the particle diameter. Below this, the frictional response is characteristic of the mixed and boundary regimes. In the boundary regime, friction is independent of phase volume above 5% and it is governed by the rolling friction associated with particles being entrained into the contact that is independent of SRR, which is made possible by substrate deformation. This study provides a benchmark for soft-tribology and biotribology studies involving more complex particle suspensions and particle-containing soft materials.

Thermal Composites of Biobased Polyamide with Boron Nitride Micro Networks

With the growing awareness of the damage sustained by environment, and the nearly-ubiquitous impulse to minimize and counteract this damage, the use of renewable (green) resources is becoming increasingly popular. Electronic industry continues to produce millions of electronic devices daily and the rapid growth of modern technology reduces these devices’ useable life spans. As a result, it has become increasingly imperative to find solutions for recycling these devices. Furthermore, since electronic devices are constantly becoming smaller and more powerful, accumulating heat concentration further reduces efficiency. Therefore, heat dissipation plays a very important role in modern electronic packaging applications. Bio-based high thermally conductive Polymeric composites seem to be potentially suitable replacements for current electronic packaging. These composites promise improved thermal management of electronics as well as protection from non-recyclable oil-based products in the environment. In this research, parametric study on partially bio-based polyamide (PA) in composite with micron size hexagonal boron nitride (hBN) platelets were performed. High viscosity PA90 and low viscosity PA30, both in composites with high thermally conductive hBN, were compared to determine the effect of matrix viscosity on mobility and arrangement of hBN particles, as well as effective thermal conductivity of the composite. Low viscosity PA30 consistently maintained higher values of thermal conductivity than the PA90. However PA90 shows higher mechanical properties. Furthermore, by narrowing down the filler content difference of the sample an interesting nonlinear trend between filler content and effective thermal conductivity of the composite is observed.

Electric-field induced filler association dynamics and resulting improvements in the electrical conductivity of polyester/multiwall carbon nanotube composites

The effects of electric fields on the filler response dynamics and electrical percolation of poly(ethylene succinate)/multiwall carbon nanotube (MWCNT) composites are studied. When subjected to AC electric fields in their melt state, PESu/MWCNT composites exhibit dramatic improvements in their transverse electrical conductivity. More importantly, the elevated conductivity values are preserved after matrix solidification. Overall, the experimental results show that the electrified composites exhibit the same electrical conductivity levels as their non-electrified counterparts at approximately threefold less filler content. The dynamics of the insulator-to-conductor transition under an electric field also are studied for these composites and correlate reasonably well with operating parameters, such as electric field intensity, matrix viscosity, and filler content through a relatively simple model. Such a model can serve as an enabling tool in the determination of process conditions for the manufacturing of electrically conducting MWCNT/polymer composites. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Effects of magnetic field input cycle and peptizer on the MR effect of magneto‐rheological elastomer based on natural rubber

The magneto‐rheological (MR) effect of magneto‐rheological elastomers (MREs) depends on the degree of orientation of carbonyl iron particles, which are dispersed in the elastomeric matrix. In this study, viscosity and molecular weight of NR matrix decreased with the addition of peptizer, and resulted in an increase of MR effect because of the efficient orientation of carbonyl iron particles. Also, the optimum conditions for applying a magnetic field to orient carbonyl iron particles were defined by the input duration time of the magnetic field, rather than the number of input times. Ideal input duration time to induce the orientation of carbonyl iron particles on the elastomeric matrix was 15 minutes. In this system, the MR effect of MRE decreased significantly above 20,000 cycles of cyclic deformation because of interfacial failure between the carbonyl iron particles and the matrix. It was expected that the dynamic property of MRE would increase if the interfacial interaction between carbonyl iron particles and the matrix improved. POLYM. ENG. SCI., 55:2669–2675, 2015. © 2015 Society of Plastics Engineers

Enhanced oxidation resistance of carbon fiber reinforced lithium aluminosilicate composites by boron doping

Carbon fiber reinforced lithium aluminosilicate matrix composites (Cf/LAS) modified with boron doping were fabricated and oxidized for 1h in static air. Weight loss, residual strength and microstructure were analyzed. The results indicate that boron doping has a remarkable effect on improving the oxidation resistance for Cf/LAS. The synergism of low viscosity of LAS matrix at high temperature and formation of graphite crystals on the surface of carbon fibers, is responsible for excellent oxidation resistance of the boron doped Cf/LAS.

Process-Oriented Determination of Preform Permeability and Matrix Viscosity during Mold Filling in Resin Transfer Molding

The resin transfer molding (RTM) offers great conditions for mass production of fiber reinforced plastics. In this process, preformed fiber textiles are infiltrated with matrix material (for example: epoxy resin). During the infiltration, the matrix material starts a curing process until the complete consolidation. After the de-molding and a short post-processing step, the final part is ready to use. To reduce the cycle time for the RTM manufacturing, it is necessary to model and predict the flow behavior of the matrix material in a realistic way. An important parameter is the preform permeability, which characterizes the flow resistance of fibers against the flowing matrix material.In this study a new measurement setup is presented, which is able to determine the permeability directly during the manufacturing process, with integrated pressure and temperature sensors. This approach has many advantages against conventional measurement setups, that try to recreate the RTM process with a simple replication. With these replicas, it is only possible to simulate low flow velocities and pressures. Dynamic effects that occur at higher velocities cannot be regarded. Furthermore, the new setup has the advantage that measurement artifacts, like capillarity, have a lower impact. In addition to that, the infiltration can be done with a constant viscosity test fluid as well as with reactive matrix material. Thus, it allows further determination of the time depending viscosity.

Preparation of Poly(phenylene oxide)/Polyamide-6 Nanocomposites with High Tensile Strength and Excellent Impact Performance

Organo-montmorillonite (OMMT) was introduced into SEBS-g-MA toughened poly(phenylene oxide)/polyamide-6 (PPO/PA6) blends simply by melt extrusion. The effects of OMMT on morphology, rheology, and mechanical behaviors of toughened PPO/PA6 nanocomposites were studied by scanning electron microscope, transmission electron microscope, capillary rheometer and mechanical tests. The addition of OMMT could decrease the size of dispersed PPO domains in PA6 matrix and melt viscosity of the toughened PPO/PA6 nanocomposites. Besides, exfoliated OMMT also brought significant improvement of tensile properties and heat deflection temperature (HDT), simultaneously. For nanocomposites with exfoliated OMMT, OMMT induced more core–shell toughening particles with the optimized size, and thus, elastomer-OMMT synergistic toughening was achieved in the PPO/PA6 nanocomposites. Consequently, PPO/PA6 nanocomposites with high tensile strength, excellent impact performance, improved HDT, and good processability were obtained.

A novel method for the determination of polymeric micro-fiber distribution of cementitious composites exhibiting multiple cracking behavior under tensile loading

A methodology is proposed to measure the micro-fiber distribution of high tenacity polypropylene fiber reinforced engineered cementitious composites (HTPP-ECC). For this purpose, scanning electron microscope (SEM) images of failure section were captured at backscattered electron mode (BEC) and analyzed via a consecutive set of image processing algorithms. Fiber distribution coefficients and fiber density maps of each section were determined. The validity of fiber distribution parameters is checked by comparing the multiple cracking potential of two distinctive HTPP-ECCs from the view point of tensile ductility (M24: 3.1%, M37: 0.8%) and matrix rheology (modified Marsh cone flow time; M24: 23s, M37: 40s). Results showed that a better fiber distribution at failure section and relatively porous matrix structure improved the multiple cracking potential of composites. The proposed methodology is capable of detecting the fiber distribution variation at micro-scale. Relatively high matrix viscosity was found responsible for the undesirable polymeric micro-fiber distribution of HTPP-ECCs.

Reduced percolation concentration in polypropylene/expanded graphite composites: Effect of viscosity and polypyrrole

ABSTRACTWith the goal to obtain material combining electrical and thermal conductivity at low filler loadings, composites based on polypropylenes (PP) and expanded graphite (EG) have been prepared. The effects of matrix viscosity and of coating the EG particles with polypyrrole (PPy, EG/PPy = 37.5/62.5 by weight) on the EG dispersibility and formation of percolation structures have been analyzed. When increasing the EG amount from 6 to 8 wt %, the electrical conductivity of PP/EG composites increased by 7–9 orders of magnitude, independent of matrix viscosity. When EG‐PPy is added, percolation was observed between 8 and 12 wt % EG‐PPy (3 and 4.5 wt % EG) in case of PP with higher viscosity and 6 wt % EG (2.25 wt % EG) in case of PP with lower viscosity, exhibiting a strong synergistic effect of EG and PPy in the latter case. In contrast, PPy does not contribute to reduction of thermal percolation concentration. Thermal percolation is observed at 8 wt % EG in PP/EG composites, but no percolation was found in PP/EG‐PPy composites with EG‐PPy contents of up to 20 wt %, corresponding to 7.5 wt % EG. Analyzing the melt rheology it becomes clear that the contribution of PPy to the formation of a filler network is strongly dependent on the matrix viscosity. The comparison of thermal, electrical and rheological percolation reveals that PPy participates in electron transport reducing the electrical percolation but not to heat transport. Overall, we found a good correlation between electrical, thermal, and melt rheological percolation concentrations. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41994.