Tack and Related Properties of Isopropyl Azodicarboxylate Modified Polybutadiene

1984 ◽  
Vol 57 (1) ◽  
pp. 227-242 ◽  
Author(s):  
G. R. Hamed ◽  
C-H. Shieh
Keyword(s):  
Initial Increase ◽  
Infrared Analysis ◽  
Additional Contribution ◽  
Great Loss ◽  
Entanglement Density ◽  
Green Strength ◽  
Chain Mobility ◽  
Modified Polymers ◽  
Slow Rise ◽  
Two Phases

Abstract Polybutadiene has been modified by reaction with isopropyl azodicarboxylate (IAD). The reaction is quite efficient, resulting in a structure in which there are pendant hydrazoester groups dangling from the BR backbone. The Tg's of the modified polymers increase with IAD content. Eventually, at high levels of modification, two Tg's are observed, indicating the presence of two phases. Infrared analysis indicates the presence of H-bonding within the modified polymers. The green strength of these polymers increases with IAD content, whereas, tack passes through a maximum with increasing IAD level. At low IAD levels, the increase in green strength is attributed to increased polar interactions between chains, whereas, at higher IAD levels, there appears to be an additional contribution from strain-induced phase separation (see Reference 1). This type of behavior is favorable for high tack. The initial increase in tack as IAD is incorporated is due, in part, to the enhanced green strength. A more important feature is that the green strength is enhanced without great loss of the molecular mobility needed to form a tack bond. This occurs because of 1) the slow rise in Tg and 2) a lowering of the entanglement density with modification. Blocky additions of the IAD contributes to the former effect as does the presence of the alkyl group (isopropyl) in the polar IAD moiety. Additionally, it is inferred that the IAD-BR molecules do not have to interdiffuse as far across the interface to develop a strong tack bond as do purely hydrocarbon BR chains. Evidence for this is the rapid initial increase in relative tack for the IAD modified elastomers. Finally, the loss of tack at high IAD levels is due to a severe decrease in chain mobility, thereby prohibiting the formation of an extensive tack bond.

The Chain End Distributions and Crosslink Characteristics in Black-Filled Rubbers

1998 ◽  
Vol 71 (5) ◽  
pp. 975-987 ◽  
Author(s):  
Asahiro Ahagon
Keyword(s):  
Average Molecular Weight ◽  
Chain Scission ◽  
Polymer Phase ◽  
Chain Mobility ◽  
Filled Rubber ◽  
Bound Rubber ◽  
Filled Rubbers ◽  
Carbon Gel ◽  
Two Phases ◽  
Chain Slippage

Abstract A black-filled rubber compound consists of two phases: the free polymer phase, where no particle exists, and the carbon black agglomerate phase, where highly concentrated particles are bound by a small amount of the polymer—so called bound rubber. The Charlesby—Pinner virtual linear number-average molecular weight Mn1 of the polymer in each phase is determined for black-filled compounds to obtain information about the chain end distribution in the compounds. The nominal crosslink density of the bound rubber is also measured by means of the swelling measurement of the “carbon gel” to characterize the crosslink variation in the vulcanizates. The results indicate that the chain end density is much higher in the agglomerate phase than in the free polymer phase due to enhanced chain scission during mixing. The enhancement of scission is considered due to the free radical crosslinking which imposes restriction to chain slippage in the flow field. This together with the previous findings suggests the features of the phase construction in the filled vulcanizates: tightly crosslinked free polymer phase with fewer chain ends, and loosely crosslinked agglomerate phase with more chain ends but, with rather suppressed chain mobility due to the dense nano-scale particles. The features match well with the energy dissipating and the toughened nature of the filled vulcanizates.

scholarly journals Layered Double Hydroxide Nanomaterial as Highly Efficient Adsorbent and its Recycling after Removal of a Carcinogenic Tartrazine Dye from Wastewater

2021 ◽  
Vol 12 (6) ◽  
pp. 7725-7740
Keyword(s):  
Layered Double Hydroxide ◽  
High Efficiency ◽  
Low Cost ◽  
Dye Adsorption ◽  
Infrared Analysis ◽  
Retention Capacity ◽  
Before And After ◽  
The Matrix ◽  
Two Phases ◽  
Double Hydroxide

In this work, the tartrazine dye is removed from the wastewater by the layered double hydroxide (LDH) [Zn2-Al-Cl]. LDH materials have proven to be highly effective in removing pollutants, with a low cost of synthesis, non-toxic, and they do not regenerate the sludge. Several parameters were studied, the retention of dye by LDH nanomaterial is optimized for a pH between 6 and 8, the equilibrium retention is obtained after 24 hours, and retention kinetics follows the pseudo-second-order model. The isotherms are the H type, and they follow the Langmuir model, retention capacity reaches 100% for a mass ratio (adsorbate/adsorbent) between 0.1 and 0.5, and the maximum amount retained of the dye is 740.35 mg/g for an initial concentration of tartrazine was 1200 mg/L and 100 mg of mass of LDH. X-ray diffraction (XRD) showed that the synthesized matrix is crystallized in a lamellar structure. Two processes affect the removal of the dye, adsorption of the surface of LDH, and intercalation between the layers. Infrared analysis indicated the appearance of the band's dye in the spectrum of the matrix after retention. Moreover, scanning electron microscopy showed the lamellar character of the two phases obtained before and after retention. The thermodynamics study showed that the process is endothermic, and the adsorption mechanism is governed by physisorption. The LDH nanomaterial is a good adsorbent with low cost, high efficiency, and recyclable.

scholarly journals Recent evolution and associated hydrological dynamics of a vanishing Tropical Andean glacier: Glaciar de Conejeras, Colombia

2018 ◽  
Author(s):  
Enrique Morán-Tejeda ◽  
Jorge Luis Ceballos ◽  
Katherine Peña ◽  
Jorge Lorenzo-Lacruz ◽  
Juan Ignacio López-Moreno
Keyword(s):  
Hydrological Cycle ◽  
Great Sensitivity ◽  
Glacier Retreat ◽  
Small Scale ◽  
Initial Increase ◽  
High Temporal Resolution ◽  
Special Focus ◽  
Hydrological Response ◽  
Great Loss ◽  
Loss Of Mass

Abstract. Glaciers in the inner tropics are rapidly retreating due to atmospheric warming. In Colombia, this retreat is accelerated by volcanic activity, and most glaciers are in their last stages of existence. There is general concern about the hydrological implications of receding glaciers, as they constitute important freshwater reservoirs and, after an initial increase in melting flows due to glacier retreat, a decrease in water resources is expected in the long term as glaciers become smaller. In this paper, we perform a comprehensive study of the evolution of a small Colombian glacier, Conejeras (Parque Nacional Natural de los Nevados), that has been monitored since 2006, with special focus on the hydrological response of the glacierized catchment. The glacier shows great sensitivity to changes in temperature and especially to the evolution of the ENSO phenomenon, with great loss of mass and area during El Niño warm events. Since 2006 it has suffered a 37% reduction from 22.45 ha to 12 ha in 2017, with an especially abrupt reduction since 2014. During the period of hydrological monitoring (June 2013 to December 2017) streamflows at the outlet of the catchment experienced a noticeable cycle of increasing flows up to mid-2016 and decreasing flows afterwards. The same kind of cycle was observed for other hydrological indicators, such as slope of the rising flow limb or the monthly variability of flows. We observed an evident change in the daily hydrograph: from a predominance of days with a pure melt-driven hydrograph up to mid-2016, to an increase in the frequency of days with flows less influenced by melt after 2016. Such a hydrological cycle is not directly related to fluctuations of temperature or precipitation; therefore, it is reasonable to consider that it is the response of the glacierized catchment to retreat of the glacier. Results confirm the necessity for small-scale studies at a high temporal resolution in order to understand the hydrological response of glacier-covered catchments to glacier retreat and imminent glacier extinction.

scholarly journals COVID-19 epidemics monitored through the logarithmic growth rate and SIR model

2021 ◽  
Author(s):  
Tomokazu Konishi
Keyword(s):  
Growth Rate ◽  
Real Data ◽  
Sir Model ◽  
Clear Correlation ◽  
Initial Increase ◽  
Number Of Patients ◽  
The Difference ◽  
Two Phases ◽  
Short Time ◽  
Logarithmic Growth

Background: The SIR model is often used to analyse and forecast the expansion of an epidemic. In this model, the number of patients exponentially increases and decreases, resulting in two phases. Therefore, in these phases, the logarithm of infectious patients changes at a constant rate, the logarithmic growth rate K. However, in the case of the coronavirus disease 2019 (COVID19) epidemic, K never remains constant but increases and decreases linearly; therefore, the SIR model does not fit that seen in reality. We would like to clarify the cause of this phenomenon and predict the occurrence of COVID19 epidemics. Methods: We simulated a situation in which smaller epidemics were repeated with short time intervals. The results were compared with the epidemic data from 279 countries and regions. Results: In the simulations, the K values increased and decreased linearly, similar to the real data. Because the previous peak covered the initial increase in the epidemic, K did not increase as much as expected; rather, the difference in the basic reproduction number R0 appeared in the slope of increasing K. Additionally, the mean infectious time τ appeared in the negative peaks of K. By using the R0 and τ estimated from the changes in K, changes in the number of patients could be approximated using the SIR model. This supports the appropriateness of the model for evaluating COVID-19 epidemics. By using the model, the distributions of the parameters were identified. On average, an epidemic started every eleven days in a country. The worldwide mean R0 was 2.9; however, this value showed an exponential character and could thus increase explosively. In addition, the average τ was 12 days; this is not the native value but represents a shortened period because of the isolation of patients. As τ represents the half-life, the infectious time varies among patients; hence, prior testing should be performed before isolation is lifted. The changes in K represented the state of epidemics and were several weeks to a month ahead of the changes in the number of confirmed cases. In the actual data, when K was positive on consecutive days, the number of patients increased a few weeks later. In addition, if the negative peaks of K could not be reduced to as small as 0.1, the number of patients remained high. Thus, the number of K-positive days and mean infectious time had a clear correlation with the total number of patients. In such cases, mortality, which was lognormally distributed, with a mean of 1.7%, increased. To control the epidemic, it is important to observe K daily, not to allow K to remain positive continuously, and to terminate a peak with a series of K-negative days. To do this, it was necessary to shorten τ by finding and isolating a patient earlier. The effectiveness of the countermeasures is apparent in τ. The effect of vaccination, in terms of controlling the epidemic, was limited.

Precipitation of NiHfsi phase in NiAl single crystals containing Hf

1995 ◽  
Vol 53 ◽  
pp. 532-533
Author(s):  
A. Garg ◽  
R. D. Noebe ◽  
R. Darolia
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
High Temperature Strength ◽  
Bridgman Technique ◽  
Shell Mold ◽  
Third Phase ◽  
Unknown Phase ◽  
Transmission Electron ◽  
Two Phases ◽  
Nial Matrix

Small additions of Hf to NiAl produce a significant increase in the high-temperature strength of single crystals. Hf has a very limited solubility in NiAl and in the presence of Si, results in a high density of G-phase (Ni16Hf6Si7) cuboidal precipitates and some G-platelets in a NiAl matrix. These precipitates have a F.C.C structure and nucleate on {100}NiAl planes with almost perfect coherency and a cube-on-cube orientation-relationship (O.R.). However, G-phase is metastable and after prolonged aging at high temperature dissolves at the expense of a more stable Heusler (β'-Ni2AlHf) phase. In addition to these two phases, a third phase was shown to be present in a NiAl-0.3at. % Hf alloy, but was not previously identified (Fig. 4 of ref. 2 ). In this work, we report the morphology, crystal-structure, O.R., and stability of this unknown phase, which were determined using conventional and analytical transmission electron microscopy (TEM).Single crystals of NiAl containing 0.5at. % Hf were grown by a Bridgman technique. Chemical analysis indicated that these crystals also contained Si, which was not an intentional alloying addition but was picked up from the shell mold during directional solidification.

Imaging of Al-Li-Cu alloys with a Scanning Ion Microprobe

1990 ◽  
Vol 48 (2) ◽  
pp. 314-315
Author(s):  
K.K. Soni ◽  
D.B. Williams ◽  
J.M. Chabala ◽  
R. Levi-Setti ◽  
D.E. Newbury
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Equilibrium Phase ◽  
Icosahedral Symmetry ◽  
Ion Microprobe ◽  
X Ray ◽  
Cu Alloys ◽  
Two Phases ◽  
The University ◽  
Secondary Ion

In contrast to the inability of x-ray microanalysis to detect Li, secondary ion mass spectrometry (SIMS) generates a very strong Li+ signal. The latter’s potential was recently exploited by Williams et al. in the study of binary Al-Li alloys. The present study of Al-Li-Cu was done using the high resolution scanning ion microprobe (SIM) at the University of Chicago (UC). The UC SIM employs a 40 keV, ∼70 nm diameter Ga+ probe extracted from a liquid Ga source, which is scanned over areas smaller than 160×160 μm2 using a 512×512 raster. During this experiment, the sample was held at 2 × 10-8 torr.In the Al-Li-Cu system, two phases of major importance are T1 and T2, with nominal compositions of Al2LiCu and Al6Li3Cu respectively. In commercial alloys, T1 develops a plate-like structure with a thickness <∼2 nm and is therefore inaccessible to conventional microanalytical techniques. T2 is the equilibrium phase with apparent icosahedral symmetry and its presence is undesirable in industrial alloys.

Defect structures of Nb1+αS2 sulfidation scales

1992 ◽  
Vol 50 (1) ◽  
pp. 38-39
Author(s):  
Chuxin Zhou ◽  
L. W. Hobbs
Keyword(s):  
Stacking Faults ◽  
Rhombohedral Structure ◽  
Stacking Sequence ◽  
Defect Structures ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plane Normal ◽  
Lower Case ◽  
Sulfur Layer ◽  
Two Phases

One of the major purposes in the present work is to study the high temperature sulfidation properties of Nb in severe sulfidizing environments. Kinetically, the sulfidation rate of Nb is satisfactorily slow, but the microstructures and non-stoichiometry of Nb1+αS2 challenge conventional oxidation/sulfidation theory and defect models of non-stoichiometric compounds. This challenge reflects our limited knowledge of the dependence of kinetics and atomic migration processes in solid state materials on their defect structures.Figure 1 shows a high resolution image of a platelet from the middle portion of the Nb1+αS2 scale. A thin lamellar heterogeneity (about 5nm) is observed. From X-ray diffraction results, we have shown that Nb1+αS2 scale is principally rhombohedral structure, but 2H-NbS2 can result locally due to stacking faults, because the only difference between these 2H and 3R phases is variation in the stacking sequence along the c axis. Following an ABC notation, we use capital letters A, B and C to represent the sulfur layer, and lower case letters a, b and c to refer to Nb layers. For example, the stacking sequence of 2H phase is AbACbCA, which is a ∼12Å period along the c axis; the stacking sequence of 3R phase is AbABcBCaCA to form an ∼18Å period along the c axis. Intergrowth of these two phases can take place at stacking faults or by a shear in the basal plane normal to the c axis.

Convergent-bceam diffraction studies on lead zirconate titanate Ceramics

1986 ◽  
Vol 44 ◽  
pp. 482-483
Author(s):  
M.L.A. Dass ◽  
T.A. Bielicki ◽  
G. Thomas ◽  
T. Yamamoto ◽  
K. Okazaki
Keyword(s):  
Lead Zirconate Titanate ◽  
Direct Proof ◽  
Lead Zirconate ◽  
Subsolidus Phase ◽  
Pzt Ceramics ◽  
Subsolidus Phase Diagram ◽  
Zirconate Titanate ◽  
Two Phases ◽  
Cbd Method ◽  
Titanate Ceramics

Lead zirconate titanate, Pb(Zr,Ti)O3 (PZT), ceramics are ferroelectrics formed as solid solutions between ferroelectric PbTiO3 and ant iferroelectric PbZrO3. The subsolidus phase diagram is shown in figure 1. PZT transforms between the Ti-rich tetragonal (T) and the Zr-rich rhombohedral (R) phases at a composition which is nearly independent of temperature. This phenomenon is called morphotropism, and the boundary between the two phases is known as the morphotropic phase boundary (MPB). The excellent piezoelectric and dielectric properties occurring at this composition are believed to.be due to the coexistence of T and R phases, which results in easy poling (i.e. orientation of individual grain polarizations in the direction of an applied electric field). However, there is little direct proof of the coexistence of the two phases at the MPB, possibly because of the difficulty of distinguishing between them. In this investigation a CBD method was found which would successfully differentiate between the phases, and this was applied to confirm the coexistence of the two phases.

The stabilization of B.C.C. Cu in Cu/Nb nanolayered composites

1996 ◽  
Vol 54 ◽  
pp. 228-229
Author(s):  
H. Kung ◽  
A.J. Griffin ◽  
Y.C. Lu ◽  
K.E. Sickafus ◽  
T.E. Mitchell ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Layer Thickness ◽  
Volume Fraction ◽  
Ion Beam ◽  
High Strength ◽  
Cross Sectional ◽  
Metastable Structure ◽  
High Resolution Tem ◽  
Potential Improvement ◽  
Two Phases

Materials with compositionally modulated structures have gained much attention recently due to potential improvement in electrical, magnetic and mechanical properties. Specifically, Cu-Nb laminate systems have been extensively studied mainly due to the combination of high strength, and superior thermal and electrical conductivity that can be obtained and optimized for the different applications. The effect of layer thickness on the hardness, residual stress and electrical resistivity has been investigated. In general, increases in hardness and electrical resistivity have been observed with decreasing layer thickness. In addition, reduction in structural scale has caused the formation of a metastable structure which exhibits uniquely different properties. In this study, we report the formation of b.c.c. Cu in highly textured Cu/Nb nanolayers. A series of Cu/Nb nanolayered films, with alternating Cu and Nb layers, were prepared by dc magnetron sputtering onto Si {100} wafers. The nominal total thickness of each layered film was 1 μm. The layer thickness was varied between 1 nm and 500 nm with the volume fraction of the two phases kept constant at 50%. The deposition rates and film densities were determined through a combination of profilometry and ion beam analysis techniques. Cross-sectional transmission electron microscopy (XTEM) was used to examine the structure, phase and grain size distribution of the as-sputtered films. A JEOL 3000F high resolution TEM was used to characterize the microstructure.

EELS white line intensities calculated for the 3d and 4d metals

1989 ◽  
Vol 47 ◽  
pp. 388-389
Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz
Keyword(s):  
Experimental Data ◽  
Line Intensity ◽  
Transition Probabilities ◽  
Initial Increase ◽  
White Line ◽  
Hartree Fock ◽  
Line Intensities ◽  
Integrated Intensity ◽  
X Ray Absorption ◽  
The Continuum

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.

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