Migration and Settling of Particulates in Filled Epoxies

2003 ◽  
Author(s):  
Lisa Mondy ◽  
Rekha Rao ◽  
Eric Lindgren ◽  
Amy Sun ◽  
Robert Lagasse ◽  
...  
Keyword(s):  
Particle Concentration ◽  
Particle Migration ◽  
Polymerization Reaction ◽  
Temperature Dependent ◽  
Filled Polymers ◽  
Post Test ◽  
Manufacturing Applications ◽  
Microscopy Data ◽  
Suspension Model ◽  
Epoxy Systems

Manufacturing applications for filled polymers include encapsulation of microelectronics and injection molding of composite parts. Predictive tools for simulating these manufacturing processes require knowledge of time- and temperature-dependent rheology of the polymer as well as information about local particle concentration. The overall system rheology is highly dependent on the particle concentration. The local particle concentration can change due to gravity, convection and shear-induced migration. For the epoxy systems of interest, an extent of reaction can be used to track the degree of cure. We couple the curing model with a diffusive flux suspension model [Zhang and Acrivos 1994] to determine the particle migration. This results in a generalized Newtonian model that has viscosity as a function of temperature, cure and concentration. Using this model, we examine settling of the particulate phase in both flowing and quiescent curing systems. We focus on settling in molds and flow in wide-gap counter-rotating cylinders. The heat transfer, including the exothermic polymerization reaction, must be modeled to achieve accurate results. The model is validated with temperature measurements and post-test microscopy data. Particle concentration is determined with x-ray microfocus visualization or confocal microscopy. Agreement between the simulations and experimental results is fair.

Nuclear Magnetiic Resonance Imaging (NMRI) of Flow-Induced Microstructure of Concentratied Suspensions

1992 ◽  
Vol 289 ◽  
Author(s):  
A. W. Chow ◽  
S. W. Sinton ◽  
J. H. Iwamiya
Keyword(s):  
Particle Concentration ◽  
Particle Distribution ◽  
Leading Edge ◽  
Particle Migration ◽  
Fall Velocity ◽  
Resonance Flow ◽  
Liquid Suspensions ◽  
Induced Changes ◽  
Solid Liquid ◽  
Neutrally Buoyant

AbstractThe application of nuclear magnetic resonance flow imaging (NMRI) to the study of Couette and falling-ball viscometry of solid/liquid suspensions is described. The suspension consisted of non-Brownian, monodisperse, neutrally-buoyant spheres of 50 vol%. NMRI data demonstrated flow-induced changes in the particle distribution in the suspension that strongly influence the accuracy in viscosity measurements using these flow geometries. In Couette flow, direct correlation between stress measurements and particle concentrations at various locations in the flow cell as a function of shear strain can be made. Our data directly confitrm the shearinduced particle migration theory proposed by Leighton and Acrivos.[1] In the falling-ball experiments, increased particle concentration at the leading edge and decreased concentration at the trailing edge of the ball was observed when the falling ball is big compared to the cylinder containing the suspension. This change in particle distribution can be directly related to the changes in fall velocity of the ball as a function of position in the cylinder.

Electrokinetic Particle Migration in Heterogeneous Electrolyte Systems

2003 ◽  
Author(s):  
Shankar Devasenathipathy ◽  
Juan G. Santiago ◽  
Takahiro Yamamoto ◽  
Yohei Sato ◽  
Koichi Hishida
Keyword(s):  
Electric Field ◽  
Particle Concentration ◽  
Colloidal Particles ◽  
Transverse Electric ◽  
Flow Direction ◽  
Velocity Fields ◽  
Particle Migration ◽  
Preliminary Evaluation ◽  
Software Code ◽  
Electrokinetic Process

This paper presents a preliminary evaluation of an electrokinetic process for the buffer transfer and stacking of charged colloidal particles in solution. The mechanism exploits the effects of particle stacking across stacking across streamlines in a flow with electrical conductivity gradients transverse to the flow direction. Particle velocity fields and particle concentration measurements in a T-shaped microchannel system are presented. Upon application of an electric field, negatively charged particles are extracted from a low conductivity stream and stacked into a high conductivity stream. A simplified numerical model of the process with a commercial software code captures the generation of a transverse electric field.

Experimental and Numerical Investigation Into the Heat Transfer Study of Nanofluids in Microchannel

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Pawan K. Singh ◽  
P. V. Harikrishna ◽  
T. Sundararajan ◽  
Sarit K. Das
Keyword(s):  
Heat Transfer ◽  
Particle Concentration ◽  
Volume Fraction ◽  
Particle Migration ◽  
Experimental Investigations ◽  
Heat Transfer Behavior ◽  
Discrete Phase ◽  
Transfer Behavior ◽  
Set Up ◽  
Transfer Study

There are very few detailed experimental investigations about the heat transfer behavior of nanofluids in microchannel. The heat transfer behavior of nanofluids in microchannel is investigated. Two microchannels with hydraulic diameters 218 and 303 μm are fabricated by wet etching process on silicon wafer. An experimental set-up having provision of flow in the channel and temperature measurement along with bottom wall temperature is built-up. Alumina nanofluids with concentrations of 0.25 vol. %, 0.5 vol. %, and 1 vol. % with 45 nm are prepared, stabilized, and characterized by standard methods. The thermal conductivity and viscosity used in the study were measured and analyzed. The base fluids used are water and ethylene glycol. The effect of volume fraction, channel size, particle size, and base fluids are presented and analyzed. An important phenomenon of dispersion is observed. In addition, numerical modeling is carried out by using discrete phase approach. Shear induced particle migration is identified to be the reason of difference for dispersion of particles. The Brownian and thermophoretic forces are responsible for major changes in particle concentration and their movement. Also, it was found that better heat transfer characteristics can be obtained by higher concentration of nanofluids and by low viscous base fluids.

Temperature Dependent Fluorescence of Nanocrystalline Ce-doped Garnets For Use as Thermographic Phosphors

2008 ◽  
Vol 1076 ◽  
Author(s):  
Rachael Hansel ◽  
Steve Allison ◽  
Greg Walker
Keyword(s):  
Combustion Synthesis ◽  
Synthesis Method ◽  
Emission Spectra ◽  
Blue Shift ◽  
Transmission Electron Microscopy Data ◽  
Temperature Dependent ◽  
Quenching Temperature ◽  
Transmission Electron ◽  
Efficient Combustion ◽  
Microscopy Data

ABSTRACTFour samples of (Y1−xCex)3(Al1−y Gay)5O12 (where x=0.01, 0.02 and y=0, 0.5) were synthesized via the simple, efficient combustion synthesis method in order to determine the effect of substituting Ga3+ for Al3+ on the temperature-dependent fluorescent lifetime. X-ray diffraction shows that the Ga-doped samples have longer lattice constants and transmission electron microscopy data show that each sample consists of nanocrystallites which have agglomerated in micron-sized particles. Photoluminescence data reveal that the addition of gallium into the YAG:Ce matrix induces a red shift in the absorption spectra and a blue-shift in the emission spectra. The laser-induced fluorescent lifetime was determined as a function of temperature over the range of 0-125°C using two different emission filters. Increasing the amount of dopant ultimately results in a decrease of the fluorescent lifetime. The quenching temperatures for the Ga-doped samples were lower than the samples without gallium. The results of this work show that combustion synthesis is viable method for making highly luminescent, nanocrystalline TGPs. In addition, these results show that the quenching temperature of YAG:Ce can be altered by substituting ions which alter the location of the charge transfer state and by changing the morphology of the sample.

Studies in polymerization XIV. The solid-state polymerization of acrylic and methacrylic acids

1963 ◽  
Vol 271 (1346) ◽  
pp. 357-378 ◽  
Keyword(s):  
Free Radicals ◽  
Acrylic Acid ◽  
Methacrylic Acid ◽  
Ultra Violet ◽  
Polymerization Reaction ◽  
Temperature Dependent ◽  
Compressive Stresses ◽  
Spin Resonance ◽  
Optical Retardation ◽  
No Free Radicals

Crystalline acrylic and methacrylic acids can be polymerized by ultra-violet irradiation a t temperatures not far removed from their melting points. In both cases the reaction proceeds in such a way as to give non-crystalline and disoriented polymer. Irradiation of methacrylic acid under these conditions gives a measurable free radical concentration, whereas no free radicals are detectable by electron spin resonance in irradiated acrylic acid. The production of observable free radicals in methacrylic acid crystals is very temperature dependent, decreasing with reduction in temperature. The polymerizations have been studied in some detail by observing the changes in the optical retardation of thin single crystals while undergoing reaction. In this way a post-irradiation reaction was observed with methacrylic acid but not with acrylic acid samples. The most striking observations were those obtained when the crystals were subjected to small mechanical compressive stresses, when the polymerization reaction was generally retarded or stopped. To account for the results obtained it is suggested that the polymerization reaction takes place in association with crystal dislocations. The effect of mechanical stress is considered to arise from the displacement of dislocations. Two possible mechanisms, depending on the properties of crystal dislocations, have been suggested. Although more experimental data are required it is thought that the observed pressure effect will be of considerable importance in the elucidation of the details of the polymerization.

scholarly journals Temperature-Dependent Enhancement Effects for TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-ene) with 2-Methylimidazole-Intercalated α-Zirconium Phosphate as a Latent Thermal Initiator in the Reaction of Glycidyl Phenyl Ether

Inorganics ◽  
2019 ◽  
Vol 7 (7) ◽  
pp. 83 ◽  
Author(s):  
Osamu Shimomura ◽  
Suguru Sasaki ◽  
Kaori Kume ◽  
Atsushi Ohtaka ◽  
Ryôki Nomura
Keyword(s):  
Catalytic Activity ◽  
Zirconium Phosphate ◽  
Storage Conditions ◽  
Phenyl Ether ◽  
Polymerization Reaction ◽  
Temperature Dependent ◽  
Catalytic Effects

The catalytic effects of 1,1,3,3-Tetramethylguanidine (TMG), 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), 7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) in the reaction with glycidyl phenyl ether (GPE) at 40 °C were investigated. For the reaction, the %conversion of GPE was only 11%, carried out at 40 °C over 14 days in the presence of TBD.Additionally, there was little catalytic activity for the same reaction performed under typical storage conditions at 25 °C. The effect of TBD with 2-methylimidazole-intercalated α-zirconium phosphate (α-ZrP∙2MIm), as a latent thermal initiating system in the reaction with GPE, was then examined. The reaction did not proceed within 1 h at 80 °C. On increasing the temperature to 120 °C, the %conversion reached 75% for reaction at 1 h. Under typical storage conditions (7 days at 25 °C), the %conversion of GPE was only 7%. With addition of TBD to α-ZrP∙2MIm, reagent stability was maintained, and the polymerization reaction proceeded rapidly with the application of heat.

Complex Rheology in Particle-Laden Composite Materials

2003 ◽  
Author(s):  
Rekha R. Rao ◽  
Douglas B. Adolf ◽  
Lisa A. Mondy
Keyword(s):  
Composite Materials ◽  
Constitutive Equation ◽  
Particle Concentration ◽  
Model System ◽  
Fiber Spinning ◽  
Hysteretic Behavior ◽  
Manufacturing Processes ◽  
Colloidal Systems ◽  
Couette Viscometer ◽  
Epoxy Systems

The rheology of curing composite materials is important to many manufacturing processes. At Sandia, we work with particle-filled epoxy systems for a variety of applications. One particular system, designated as “459,” exhibits complex, counter-intuitive rheological dependence on temperature, flow history and particle-concentration. Despite the particles being relatively large (10 μm), 459 exhibits shear-thinning hysteretic behavior reminiscent of colloidal systems. It is hypothesized that the thixotropy arises from reaction of the 459 curative with the surface of the particulates. Under certain conditions, the addition of filler offsets the effect of epoxy polymerization on the viscosity, resulting in a viscosity that is constant with time. For this reason, we have developed an experimental model system that can be used to separate the effects of particle aggregation from the effects of cure on the viscosity. We have done experiments with this model suspension to determine its time-dependent response in step shear. In addition, we are working on a computational model that can be used to predict the behavior of the aggregating suspension. Preliminary modeling efforts focus on using a generalized Newtonian constitutive equation that relates the viscosity to the local aggregate concentration, defined by a dimensionless structure factor, to capture the time-dependence. Results from this constitutive equation are presented and compared to the experimental data from step-shear experiments in a Couette viscometer. Modeling results are also presented for a transient fiber spinning problem where the free surface evolves as the viscosity develops over time.

scholarly journals Active and Passive Application of the Phosphoric Acid on the Bond Strength of Lithium Disilicate

2016 ◽  
Vol 27 (1) ◽  
pp. 90-94 ◽  
Author(s):  
Tatiana Cardona Giraldo ◽  
Vanessa Roldan Villada ◽  
Mauricio Peña Castillo ◽  
Osnara Maria Mongruel Gomes ◽  
Bruna Fortes Bittencourt ◽  
...  
Keyword(s):  
Phosphoric Acid ◽  
Bond Strength ◽  
Lithium Disilicate ◽  
Resin Cement ◽  
Scanning Electron Microscopy Data ◽  
Post Test ◽  
Group A ◽  
Microscopy Data ◽  
Microshear Bond Strength ◽  
One Way Anova

Abstract The objective of this study was to evaluate the effect of passive or active phosphoric acid (PA) application after hydrofluoric acid (HA) treatment on the microshear bond strength of lithium disilicate. Thirty ceramic discs were made with IPS Emax 2 (10 mm thick and 10 mm diameter). The specimens were divided into 3 groups, A: 9.6% HA application; AF: 9.6% HA application + cleaning with 37% PA in passive mode and AFF: 9.6% HA application + cleaning with 37% PA in active mode. For the microshear test, four tygons (0.9 mm diameter and 0.2 mm high) were filled with resin cement (RelyX Ultimate) and placed on the ceramic disks. After testing, the fracture modes were examined under scanning electron microscopy. Data were analyzed by one-way ANOVA and Tukey's post test (α=0.05). The bond strength values were significantly higher in Group AFF (11.0±2.5 MPa) compared with group A (8.1±2.6 MPa) (p<0.002). AF group was not statistically different (9.4±2.5 MPa) from Group A. It was concluded that the active application of 37% PA after 9.6% HA increases the microshear bond strength values between the resin cement and lithium disilicate ceramic.

APPLICATION OF ELECTRICAL CAPACITANCE TOMOGRAPHY FOR DENSE CROSS-SECTIONAL PARTICLE MIGRATION IN A MICROCHANNEL

2015 ◽  
Vol 77 (17) ◽  
Author(s):  
Nur Tantiyani Ali Othman ◽  
Masahiro Takei
Keyword(s):  
Particle Concentration ◽  
Solid Phase ◽  
Particle Migration ◽  
Experimental Result ◽  
Tikhonov Regularization Method ◽  
High Yield ◽  
Electrical Capacitance Tomography ◽  
Electrical Capacitance ◽  
Cross Sectional ◽  
Capacitance Tomography

In microfluidic applications, in order to produce the high yield of desired product, the study of particle migration is very important to enhancement and increases the efficiency of positioning and sorting process. One of an effective and robust method for visualization imaging, passively positioning and sorting microparticles and cells without the assistance of sheath fluid is electrical capacitance. In this study, to study the behavior of particle migration, a fine particle concentration in a cross-sectional microchannel is determined for the high dense initial particle concentrations (ξ=10.0%) and small particle diameters (dp= 2.1 μm) by using a high speed multiplexer and 12 multi-layer electrical capacitance tomography (ECT) sensing to discuss the stream migration along five cross-sections. The polystyrene particles as solid phase and non-conductive deionized water as a liquid phase are non-uniformly injected into the inlets microchannel. From the electrical capacitance distribution, the tomography images that show the equilibrium particle migration is reconstructed by used the Tikhonov regularization method. It has been observed that the particle concentration at the wall vicinity area is increased as ξ and dp are increased while the particle concentration at the center area is decreased. It shows the particles are moved away from the center towards wall vicinity area and particles migrated towards the wall increased in the outlet area as the particles move along the cross-sectional microchannel. The experimental result is verified with the COMSOL simulation.

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