Rheological Behavior of Fugitive Organic Inks for Direct-Write Assembly

2007 ◽  
Vol 17 (1) ◽  
pp. 10112-1-10112-8 ◽  
Author(s):  
Daniel Therriault ◽  
Scott R. White ◽  
Jennifer A. Lewis
Keyword(s):  
Rheological Behavior ◽  
Room Temperature ◽  
Complex Viscosity ◽  
Direct Write ◽  
Master Curves ◽  
Numerical Predictions ◽  
Beam Analysis ◽  
Storage And Loss Moduli ◽  
Temperature Superposition ◽  
Rheological Experiments

Abstract The rheological behavior of a fugitive organic ink tailored for direct-write assembly of 3D microfluidic devices is investigated. Rheological experiments are carried out to probe the shear storage and loss moduli as well as the complex viscosity as a function of varying temperature, frequency and stress amplitude. Master curves of these functions are assembled using time-temperature superposition. The fugitive ink, comprised of two organic phases, possesses an equilibrium shear elastic modulus nearly two orders of magnitude higher than that of a commercial reference ink at room temperature and a peak in the relaxation spectrum nearly six orders of magnitude longer in time scale. The self-supporting nature of extruded ink filaments is characterized by direct video imaging. Comparison of the experimentally observed behavior to numerical predictions based on Euler-Bernoulli viscoelastic beam analysis yield excellent agreement for slender filaments.

scholarly journals Study on Mechanical Relaxations of 7075 (Al–Zn–Mg) and 2024 (Al–Cu–Mg) Alloys by Application of the Time-Temperature Superposition Principle

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Jose I. Rojas ◽  
Jorge Nicolás ◽  
Daniel Crespo
Keyword(s):  
Temperature Region ◽  
Master Curve ◽  
Amorphous Materials ◽  
Superposition Principle ◽  
Mg Alloys ◽  
Loading Frequency ◽  
Master Curves ◽  
Storage And Loss Moduli ◽  
Temperature Superposition ◽  
Time Temperature Superposition

The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of the temperature (from 30 to 425°C) and the loading frequency (from 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven to be useful in studying mechanical relaxations and obtaining master curves for amorphous materials. In this work, the TTS principle is applied to the measured viscoelastic data (i.e., the storage and loss moduli) to obtain the corresponding master curves and to analyze the mechanical relaxations responsible for the viscoelastic behavior of the studied alloys. For the storage modulus it was possible to identify a master curve for a low-temperature region (from room temperature to 150°C) and, for the storage and loss moduli, another master curve for a high-temperature region (from 320 to 375°C). These temperature regions are coincidental with the stable intervals where no phase transformations occur. The different temperature dependencies of the shift factors for the identified master curves, manifested by different values of the activation energy in the Arrhenius expressions for the shift factor, are due to the occurrence of microstructural changes and variations in the relaxation mechanisms between the mentioned temperature regions.

Modeling of Shear Rheological Behavior of Uncured Rubber Melt

2020 ◽  
Vol 30 (1) ◽  
pp. 130-137
Author(s):  
Hengxiao Yang ◽  
Qimian Mo ◽  
Hengyu Lu ◽  
Shixun Zhang ◽  
Wei Cao ◽  
...  
Keyword(s):  
Shear Rate ◽  
Constitutive Model ◽  
Incompressible Fluid ◽  
Rheological Behavior ◽  
Rheological Characteristics ◽  
One Dimensional ◽  
Ptt Model ◽  
Rate Region ◽  
Proposed Model ◽  
Rheological Experiments

AbstractTo describe uncured rubber melt flow, a modified Phan–Thien–Tanner (PTT) model was proposed to characterize the rheological behavior and a viscoelastic one-dimensional flow theory was established in terms of incompressible fluid. The corresponding numerical method was constructed to determine the solution. Rotational rheological experiments were conducted to validate the proposed model. The influence of the parameters in the constitutive model was investigated by comparing the calculated and experimental viscosity to determine the most suitable parameters. The uncured rubber viscosity was 3–4 orders larger than that of plastic and did not have a visible Newtonian region. Compared with the Cross-Williams-Landel-Ferry (Cross-WLF) and original PTT models, the modified PTT model can describe the rheological characteristics in the entire shear-rate region if the parameters are set correctly.

Rheological Behavior and Microstructure of Flame Retardant Polypropylene Composites

2010 ◽  
Author(s):  
Guo Jiang ◽  
Kai Liao ◽  
Juan-Juan Han ◽  
De-Xian Feng ◽  
Han-Xiong Huang
Keyword(s):  
Magnesium Hydroxide ◽  
Shear Viscosity ◽  
Flame Retardancy ◽  
Rheological Behavior ◽  
Oxygen Index ◽  
Complex Viscosity ◽  
Test Results ◽  
Screw Extruder ◽  
Polypropylene Composites ◽  
Twin Screw

Polypropylene (PP)/magnesium hydroxide (MDH) composite was melt-mixed using a twin-screw extruder. Two types of MDH were used, one with the modification of silane and another without. The rheological behavior was measured by capillary and dynamical rheometer. Microstructure of these composites was observed by SEM. Their flame retardancy was characterized by oxygen index and Horizontal/Vertical burning test. Results showed that shear viscosity and complex viscosity of PP with modified MDH were lower than that of PP with non-modified MDH. SEM results also showed a better dispersion of silane modified MDH in PP matrix. With the increase of MDH content, the oxygen index of composites was increased. When the content was increased to 60 wt%, the composite was UL94 HB and V-1.

Deformation of Porous, Nanostructured Silver at Room Temperature and 150 °C

2013 ◽  
Vol 1513 ◽  
Author(s):  
Guillaume Noiseau ◽  
Michael F. Becker ◽  
John W. Keto ◽  
Desiderio Kovar
Keyword(s):  
Room Temperature ◽  
Local Strain ◽  
Direct Write ◽  
Compression Tests ◽  
Sufficient Energy ◽  
Starting Point ◽  
Mean Size ◽  
Constant Displacement ◽  
Patterned Films ◽  
Porous Silver

ABSTRACTPorous, nanostructured silver samples were produced using a direct-write method where a nanoparticle aerosol consisting of particles with a mean size of approximately 5 nm were accelerated to speeds of approximately 1000 m/sec and impacted onto a translating substrate [1]. The impacting particles have sufficient energy to stick to the substrate, allowing patterned thick films to be directly written from the aerosol without a mask. Unlike other low temperature processing routes for achieving patterned films, no organics are added that can interfere with postdeposition processing. Typical films are 5- 100 μm thick, up to several centimeters long, and have an as-deposited relative densities as high as 70% of bulk Ag. Compression tests were carried out in steps at room temperature and at 150°C under constant displacement rates. Local strain and densification were measured by optical profilometry between each compression step. The results can be used as a starting point to better understand the mechanisms that govern plasticity, creep, and sintering in nanostructured, porous silver at low processing temperatures.

Defects and AlSb Precipitate Nucleation in Laser Irradiated Aluminum

1981 ◽  
Vol 4 ◽  
Author(s):  
P. S. Peercy ◽  
D. M. Follstaedt ◽  
S. T. Picraux ◽  
W. R. Wampler
Keyword(s):  
Room Temperature ◽  
Laser Energy ◽  
Ion Beam ◽  
Threshold Energy ◽  
Single Pulse ◽  
Temperature Profiles ◽  
Beam Analysis ◽  
Slip Deformation ◽  
Precipitate Nucleation ◽  
Substrate Temperatures

ABSTRACTLattice defects and precipitates induced in unimplanted and Sb-implanted <110> single crystal Al by single pulse irradiation with a Q-switched ruby laser were studied using ion beam analysis and electron microscopy. The absorbed laser energy during irradiation is directly measured in these studies to allow precise numerical modeling of the melt times and temperature profiles. For unimplanted Al, slip deformation gives rise to increased channeled yields throughout the analyzed depth and occurs for energies well below the melt threshold energy of 3.5 J/cm2. Slip deformation is also observed for irradiation energies above the melt threshold energy, and melting is accompanied by a discontinuous increase in the minimum channeling yield, X min- Implanted Sb (to ∼2 at.% peak concentrations) is found to impede epitaxial regrowth and result in polycrystalline Al formation for laser energies such that the melt front is believed not to penetrate through the Sb-containing region. For deeper melt depths, a metastable alloy is formed with up to 35% of the Sb located in substitutional sites. AlSb precipitate formation in the melt was not observed for room temperature irradiations; however, randomly oriented AlSb precipitates are observed for irradiation at substrate temperatures of 100 and 200 °C These measurements yield an estimated time for nucleation of AlSb precipitates in molten Al of 5 nsec < tnuc < 25 nsec.

Laminar Flame Speeds and Strain Sensitivities of Mixtures of H2∕O2∕N2 at Elevated Preheat Temperatures

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
J. Natarajan ◽  
T. Lieuwen ◽  
J. Seitzman
Keyword(s):  
Kinetic Model ◽  
Temperature Dependence ◽  
Reasonable Agreement ◽  
Room Temperature ◽  
Laminar Flame ◽  
Flame Speed ◽  
Numerical Predictions ◽  
Hydrogen Flame ◽  
Measured Strain ◽  
Lean Conditions

Laminar flame speeds and strain sensitivities of mixtures of H2 and air or air highly diluted with N2 (O2:N2 1:9) have been measured for a range of equivalence ratios at high preheat conditions (∼700K) using a nozzle generated, 1D, laminar, wall stagnation flame. The measurements are compared with numerical predictions based on three detailed kinetic models (GRIMECH 3.0, a H2∕CO mechanism from Davis et al. (2004, “An Optimized Kinetic Model of H2∕CO Combustion,” Proc. Combust. Inst., 30, pp. 1283–1292) and a H2 mechanism from Li et al. (2004, “An Updated Comprehensive Kinetic Model of Hydrogen Combustion,” Int. J. Chem. Kinet., 36, pp. 566–575)). Sensitivity of the measurements to uncertainties in boundary conditions, e.g., wall temperature and nozzle velocity profile (plug or potential), is investigated through detailed numerical simulations and shown to be small. The flame speeds and strain sensitivities predicted by the models for preheated reactants are in reasonable agreement with the measurements for mixtures of H2 and standard air at very lean conditions. For H2 and N2 diluted air, however, all three mechanisms significantly overpredict the measurements, and the overprediction increases for leaner mixtures. In contrast, the models underpredict flame speeds for room temperature mixtures of H2 with both standard and N2 diluted air, based on comparisons with measurements in literature. Thus, we find that the temperature dependence of the hydrogen flame speed as predicted by all the models is greater than the actual temperature dependence (for both standard and diluted air). Finally, the models are found to underpredict the measured strain sensitivity of the flame speed for H2 burning in N2 diluted air, especially away from stoichiometric conditions.

Hygro-mechanical analysis of wood subjected to constant mechanical load and varying relative humidity

Holzforschung ◽  
2018 ◽  
Vol 72 (10) ◽  
pp. 863-870 ◽  
Author(s):  
Sabina Huč ◽  
Staffan Svensson ◽  
Tomaž Hozjan
Keyword(s):  
Relative Humidity ◽  
Rheological Behavior ◽  
Transport Model ◽  
Mechanical Load ◽  
Mechanical Analysis ◽  
Material Parameters ◽  
Fitting Procedure ◽  
Numerical Predictions ◽  
Shrinkage And Swelling

AbstractA hygro-mechanical (H-M) analysis of a wooden specimen sustaining a mechanical load while subjected to varying relative humidity was performed to predict the long-term rheological behavior of wood. The numerical analysis was based on the experimental results of total strains, monitored in two orthotropic material directions on oak wood specimens under constant uniaxial compression and with moisture content (MC) variation. For the moisture analysis, a multi-Fickian moisture transport model (MFMTM) was used to obtain temporal and spatial MC fields, which were the input data in the mechanical analysis. The presented mechanical model assumed a decomposition of the total strains into the elastic, viscoelastic and mechanosorptive strains and the strains due to shrinkage and swelling. The moisture and mechanical analyses required material parameters, which were taken from the literature or were empirically obtained by a fitting procedure. The performed H-M analysis gave accurate numerical predictions of the experimentally obtained total strains in two orthotropic directions simultaneously. Thus, the analysis developed has a high potential for predicting the long-term rheological behavior of timber structures, assuming that the material parameters are determined previously, based on specific, extensive, multidimensional experimental analyses.

Dynamic Mechanical Analysis of Fly Ash Filled Polyurea Elastomer

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jing Qiao ◽  
Alireza V. Amirkhizi ◽  
Kristin Schaaf ◽  
Sia Nemat-Nasser
Keyword(s):  
Glass Transition ◽  
Fly Ash ◽  
Dynamic Mechanical Analysis ◽  
Volume Fraction ◽  
Loss Modulus ◽  
Mechanical Analysis ◽  
Temperature Dependent ◽  
Dynamic Mechanical ◽  
Storage And Loss Moduli ◽  
Temperature Superposition

In this work, the material properties of a series of fly ash/polyurea composites were studied. Dynamic mechanical analysis was conducted to study the effect of the fly ash volume fraction on the composite’s mechanical properties, i.e., on the material’s frequency- and temperature-dependent storage and loss moduli. It was found that the storage and loss moduli of the composite both increase as the fly ash volume fraction is increased. The storage and loss moduli of the composites relative to those of pure polyurea initially increase significantly with temperature and then slightly decrease or stay flat, attaining peak values around the glass transition region. The glass transition temperature (measured as the temperature at the maximum value of the loss modulus) shifted toward higher temperatures as the fly ash volume fraction increased. Additionally, we present the storage and loss moduli master curves for these materials obtained through application of the time-temperature superposition on measurements taken at a series of temperatures.

The Effect of Nanoclay on the Rheological Properties of Polylactic Acid/Polyhydroxybutyrate-Valerate Blends

2015 ◽  
Author(s):  
Haibin Zhao ◽  
Xiangfang Peng
Keyword(s):  
Injection Molding ◽  
Polylactic Acid ◽  
Strong Interaction ◽  
Rheological Behavior ◽  
Full Range ◽  
Complex Viscosity ◽  
Polymer Chains ◽  
Wide Range ◽  
Strong Shear ◽  
Microcellular Injection Molding

In this article, the effects of nanoclay (CN) on the rheological behavior of polylactic acid (PLA)/polyhydroxybutyrate–valerate (PHBV) blends was investigated. The rheological behavior of PLA/PHBV blends showed a Newtonian plateau that converted to strong shear thinning behavior over the full range of frequency by the incorporation of nanoclay. The results indicate that the storage modulus and complex viscosity of PLA/PHBV blends were sensitive to nanofillers. An obvious pseudo-solid-like behavior over a wide range of frequency in PLA/PHBV/CN nanocomposites showed that the strong interaction between the PLA/PHBV blend and the nanoclay restricted the relaxation process of the polymer chains. Therefore, the PLA/PHBV/CN nanocomposites possess a higher modulus and greater melt strength, which are desirable for creating an improved foamed structure when manufactured via microcellular injection molding.

Solvent and Curing Effects on Diffusion at Polyimide Interfaces

1989 ◽  
Vol 154 ◽  
Author(s):  
S. F. Tead ◽  
E. J. Kramer ◽  
T. P. Russell ◽  
W. Volksen
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Spin Coating ◽  
Room Temperature ◽  
Ion Beam ◽  
Complete Conversion ◽  
Thermally Activated ◽  
Post Annealing ◽  
Analysis Technique ◽  
Beam Analysis

AbstractInterdiffusion at interfaces between deuterated polyamic acid (d-PAA) and polyimide (PI) films was investigated with forward recoil spectrometry, an ion beam analysis technique. The PI films were prepared by spin – coating a solution of PAA on a silicon substrate, followed by an anneal at a temperature Ti, which produced partial or complete conversion of the PAA to PI. An overlayer of d-PAA was added in one set of samples by spin – coating from solution and in another set by transferring (in the absence of solvents) a dry d- PAA film onto the PI surface. The bilayer samples were then either annealed at a temperature Td or allowed to stand at room temperature. Bilayers prepared by spin – coating d-PAA from solution directly on partially cured PI films had interdiffusion distances w that decreased with increasing values of Ti to immeasurable levels by Ti = 200 °C. The decrease in w with increasing Ti is thought to be caused by a positive Flory parameter between PAA and PI which increases with the imide fraction in the PI film; the result is an increasing immiscibility between the swollen polymer layers. No interdiffusion occurred in the solventless – transfer samples for any combination of temperatures Ti or Td from room temperature up to 400 °C. Post – annealing of spin – coated bilayers at a temperature Td up to 400 °C was ineffective in producing any additional interdiffusion. Both of these results indicate that thermally activated interdiffusion (even for initially unimidized samples) does not exist in the absence of solvents, an effect attributed to the rapid increase of the glass transition temperature of the polymer with imidization.

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