Network Formation by Association of Polar Groups in Elastomers

1989 ◽  
Vol 62 (2) ◽  
pp. 343-356 ◽  
Author(s):  
N. Nakajima ◽  
C. D. Huang ◽  
J. J. Scobbo ◽  
W. J. Shieh ◽  
E. R. Harrell
Keyword(s):  
Polymer Chain ◽  
Simple Shear ◽  
Network Formation ◽  
The Other ◽  
Chain Entanglement ◽  
Acrylonitrile Copolymer ◽  
Polar Groups ◽  
Other Hand ◽  
Chemical Crosslinks

Abstract If an elastomer containing polar groups forms interchain associations, can we observe them independently from the effect of chain entanglement? Polyethylacrylate and polyepichlorohydrin are polar elastomers. Our previous deformational study indicated that these elastomers contain interchain associations, which are stronger than the physical entanglements. The conclusion was based on the results of large, unidirectional extension and small simple shear measurements. On the other hand, butadiene—acrylonitrile copolymer (NBR) containing 33% acrylonitrile did not indicate a presence of such a strong interchain association. In this work, we examined NBRs containing 40% acrylonitrile. The polar association, though weak, was detected with these elastomers. This indicates that the effective association involves a number of polar groups closely placed along the polymer chain. Also, in this work, nonpolar elastomers, SBRs, were chemically crosslinked and used as models. The polar association turned out to be not as strong as the chemical crosslinks. This indicates that the polar association disengage and reengage during the deformation.

Effect on Polymer Chain Structure Caused by the Molar Fraction of 4-Hydroxybutyrate in Poly(3-hydroxybutyrate- co -4-hydroxybutyrate)

2012 ◽  
Vol 602-604 ◽  
pp. 776-780
Author(s):  
Zhi Qiang Li ◽  
Mei Li ◽  
Wei Jia Fan
Keyword(s):  
Molecular Weight ◽  
Intrinsic Viscosity ◽  
Polymer Chain ◽  
Molar Fraction ◽  
Chain Structure ◽  
The Other ◽  
Mean Square ◽  
Polarizing Microscope ◽  
Other Hand ◽  
The Mean

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)copolymer [P(3HB-co-4HB)] is a kind of biodegradable high molecular polymer produced by bioaccumulation. Because of the good biodegradability and biocompatibility, P(3HB-co-4HB)s have attracted wide attention . At first, the intrinsic viscosity[η] in good solvent of P(3HB-co-4HB) s with varying contents of 4HB was investigated in different temperature. Second, observed the changes of crystallization gathered state caused by the varying contents of 4HB by polarizing microscope. The results show that to the P(3HB-co-4HB)s in same molecular weight, the intrinsic viscosity[η] in good solvent barely changes when the mole fractions of 4HB increase. On the other hand, the mean square end to end distances[0] of macromolecular flexible chains increase with the mole fractions of 4HB. At the same time, the states of aggregation change from spherulites to dendrites. In this investigation, we discuss the reasons of the differences in depth.

The rheology of a semi-dilute suspension of swimming model micro-organisms

2007 ◽  
Vol 588 ◽  
pp. 399-435 ◽  
Author(s):  
TAKUJI ISHIKAWA ◽  
T. J. PEDLEY
Keyword(s):  
Shear Flow ◽  
Flow Field ◽  
Simple Shear ◽  
Apparent Viscosity ◽  
The Other ◽  
Surface Velocity ◽  
Simple Shear Flow ◽  
Other Hand ◽  
Dilute Suspension ◽  
Micro Organisms

The rheological properties of a cell suspension may play an important role in the flow field generated by populations of swimming micro-organisms (e.g. in bioconvection). In this paper, a swimming micro-organism is modelled as a squirming sphere with prescribed tangential surface velocity, in which the centre of mass of the sphere may be displaced from the geometric centre (bottom-heaviness). Effects of inertia and Brownian motion are neglected, because real micro-organisms swim at very low Reynolds numbers but are too large for Brownian effects to be important. The three-dimensional movement of 64 identical squirmers in a simple shear flow field, contained in a cube with periodic boundary conditions, is dynamically computed, for random initial positions and orientations. The computation utilizes a database of pairwise interactions that has been constructed by the boundary element method. The restriction to pairwise additivity of forces is expected to be justified if the suspension is semi-dilute. The results for non-bottom-heavy squirmers show that the squirming does not have a direct influence on the apparent viscosity. However, it does change the probability density in configuration space, and thereby causes a slight decrease in the apparent viscosity atO(c2), wherecis the volume fraction of spheres. In the case of bottom-heavy squirmers, on the other hand, the stresslet generated by the squirming motion directly contributes to the bulk stress atO(c), and the suspension shows strong non-Newtonian properties. When the background simple shear flow is directed vertically, the apparent viscosity of the semi-dilute suspension of bottom-heavy squirmers becomes smaller than that of inert spheres. When the shear flow is horizontal and varies with the vertical coordinate, on the other hand, the apparent viscosity becomes larger than that of inert spheres. In addition, significant normal stress differences appear for all relative orientations of gravity and the shear flow, in the case of bottom-heavy squirmers.

Linear Thermal Expansion of Elastomers in the Range 300° to 76° K

1964 ◽  
Vol 37 (1) ◽  
pp. 154-168 ◽  
Author(s):  
R. F. Robbins ◽  
Y. Ohori ◽  
D. H. Weitzel
Keyword(s):  
Thermal Expansion ◽  
Linear Thermal Expansion ◽  
The Other ◽  
Thermal Contraction ◽  
Cryogenic Temperatures ◽  
Design Data ◽  
Polar Groups ◽  
Other Hand ◽  
Commercial Sources ◽  
Ceramic Fillers

Abstract From the relations between Tg's of the component homopolymers with that of the resulting copolymer, one sees that the limit of the Tg of copolymers is that of the homopolymers. To obtain a low Tg one must avoid polymers with polar groups and/or bulky groups. Polar groups afford opportunities for intermolecular links which hinder rotation necessary for “rubberyness.” Bulky groups cause stiffness, and also serve as obstructions to contractions. On the other hand, the same reasons that polar and bulky groups raise Tg serve to lower overall thermal contraction, since αr is always greater than αg. Fillers can be used to lower contraction, and new ceramic fillers with negative coefficients of expansion might be combined with specific polymers to obtain a material with a desired contraction. The authors feel that the data presented here, together with design data available from commercial sources, should enable the design engineer to find many new uses for elastomers at cryogenic temperatures.

The Degradation of Main Chains and Crosslinks in the Aging of Vulcanizates

1961 ◽  
Vol 34 (3) ◽  
pp. 922-924
Author(s):  
L. I. Lyubchanskaya ◽  
A. S. Kuzminskiĭ
Keyword(s):  
Thermal Decomposition ◽  
Three Dimensional ◽  
The Other ◽  
Polymeric Chain ◽  
Oxidative Destruction ◽  
Dimensional Lattice ◽  
Other Hand ◽  
Chemical Relaxation ◽  
Chemical Crosslinks ◽  
The Difference

Abstract In sulfur vulcanizates the energy of the bond between the atoms of sulfur in the crosslinks may differ essentially from the energy of the bonds in the main chains of the polymer since, as is known, the thermal decomposition of the polysulfide bonds may be brought about at considerably lower temperatures than the decomposition of the main chains. It was found by one of the present authors2 that the thermal decomposition of the sulfur bonds brings about an inhibition of the oxidation which develops in the chains of the polymer. Consequently we must not regard the destruction of the chains and the decomposition of crosslinks as independent processes. Nevertheless the difference in the rates of destruction and decomposition is so great that these processes may be separated. There are in the literature different views as to which elements in the structure of the vulcanizates the processes of aging extend to. Tobolsky asserts that the chemical relaxation of stress is caused by oxidative destruction of the polymeric chain of the vulcanizate independently of its structure. On the other hand Watson and coworkers consider that the decomposition of the lattice of the vulcanizate is the result of scission of chemical crosslinks. In the present investigation it was established that, depending upon the composition of the vulcanizate and the conditions of the experiment, the process of aging may involve both the chains of polymer and the crosslinks, forming a three-dimensional lattice of the vulcanizates.

Wrap, tilt and stretch of vorticity lines around a strong thin straight vortex tube in a simple shear flow

1997 ◽  
Vol 353 ◽  
pp. 115-162 ◽  
Author(s):  
GENTA KAWAHARA ◽  
SHIGEO KIDA ◽  
MITSURU TANAKA ◽  
SHINICHIRO YANASE
Keyword(s):  
Shear Flow ◽  
Simple Shear ◽  
Vortex Tube ◽  
Axial Direction ◽  
The Other ◽  
Simple Shear Flow ◽  
Streamwise Vortices ◽  
Other Hand ◽  
Cyclonic Vortex ◽  
Vortex Tubes

The mechanism of wrap, tilt and stretch of vorticity lines around a strong thin straight vortex tube of circulation Γ starting with a vortex filament in a simple shear flow (U=SX2Xˆ1, S being a shear rate) is investigated analytically. An asymptotic expression for the vorticity field is obtained at a large Reynolds number Γ/ν[Gt ]1, ν being the kinematic viscosity of fluid, and during the initial time St[Lt ]1 of evolution as well as St[Lt ](Γ/ν)1/2. The vortex tube, which is inclined from the streamwise (X1) direction both in the vertical (X2) and spanwise (X3) directions, is tilted, stretched and diffused under the action of the uniform shear and viscosity. The simple shear vorticity is on the other hand, wrapped and stretched around the vortex tube by a swirling motion, induced by it to form double spiral vortex layers of high azimuthal vorticity of alternating sign. The magnitude of the azimuthal vorticity increases up to O((Γ/ν)1/3S) at distance r=O((Γ/ν)1/3 (νt)1/2) from the vortex tube. The spirals induce axial flows of the same spiral shape with alternate sign in adjacent spirals which in turn tilt the simple shear vorticity toward the axial direction. As a result, the vorticity lines wind helically around the vortex tube accompanied by conversion of vorticity of the simple shear to the axial direction. The axial vorticity increases in time as S2t, the direction of which is opposite to that of the vortex tube at r=O((Γ/ν)1/2 (νt)1/2) where the vorticity magnitude is strongest. In the near region r[Lt ](Γ/ν)1/3 (νt)1/2, on the other hand, a viscous cancellation takes place in tightly wrapped vorticity of alternate sign, which leads to the disappearance of the vorticity normal to the vortex tube. Only the axial component of the simple shear vorticity is left there, which is stretched by the simple shear flow itself. As a consequence, the vortex tube inclined toward the direction of the simple shear vorticity (a cyclonic vortex) is intensified, while the one oriented in the opposite direction (an anticyclonic vortex) is weakened. The growth rate of vorticity due to this effect attains a maximum (or minimum) value of ±S2/33/2 when the vortex tube is oriented in the direction of Xˆ1+Xˆ2∓ Xˆ3. The present asymptotic solutions are expected to be closely related to the flow structures around intense vortex tubes observed in various kinds of turbulence such as helical winding of vorticity lines around a vortex tube, the dominance of cyclonic vortex tubes, the appearance of opposite-signed vorticity around streamwise vortices and a zig-zag arrangement of streamwise vortices in homogeneous isotropic turbulence, homogeneous shear turbulence and near-wall turbulence.

Influence of Temperature and the BZ Substrate on Aggregation-Disaggregation Self-Oscillation of a Polymer Chain

2011 ◽  
Vol 467-469 ◽  
pp. 1472-1477
Author(s):  
Yusuke Hara ◽  
Rumana A. Jahan
Keyword(s):  
Polymer Solution ◽  
Polymer Chain ◽  
Life Time ◽  
The Self ◽  
The Other ◽  
Sodium Bromate ◽  
Bz Reaction ◽  
Influence Of Temperature ◽  
Other Hand ◽  
Increasing Temperature

We synthesized a self-oscillating polymer chain with a negatively charged moiety. The polymer chain caused the aggregation-disaggregation self-oscillation under the constant temperature induced by the Belousov-Zhabotinsky (BZ) reaction. In this study, we investigated the influence of temperature and the concentration of sodium bromate on the aggregation-disaggregation self-oscillation of the polymer solution (1.0 wt%) in a strongly acidic condition. As a consequence, we clarified that the life-time of the self-oscillation increased with decrease in the concentration of sodium bromate. On the other hand, the lifetime of the self-oscillation decreased with increase in temperature. In high temperature condition (48 and 60 °C), the amplitude of the self-oscillation was significantly inhomogeneous. Moreover, the frequency of the self-oscillation increased with increasing temperature. On the other hand, the frequency decreased with increase in the concentration of sodium bromate. This tendency was opposite to that in the acid-free condition and the 2.0 wt% AMPS-containing polymer solution.

Inhibition of Protein Aggregation: SAXS Study on the Role of the αC Region of Fibrinogen in the Fibrin Polymerization

2011 ◽  
Vol 497 ◽  
pp. 41-46
Author(s):  
Kenji Kubota ◽  
Kaori Wakamatsu ◽  
Nobukazu Nameki ◽  
Yoshiharu Toyama
Keyword(s):  
Network Formation ◽  
The Other ◽  
Second Step ◽  
Hydrodynamic Diameter ◽  
Cross Sectional ◽  
Fibrin Polymerization ◽  
Other Hand ◽  
E Region ◽  
Fibrinogen Molecule

Fibrin polymerization proceeds in a stepwise manner. In the first step, fibrinogen-to-fibrin conversion is triggered by the enzymatic fibrinopeptide release and protofibril formation/growth proceeds. In the following second step, lateral aggregation of the protofibrils occurs resulting in the network formation. Switchover from the first step to the second one can regulate the resultant network structure, and the lateral aggregation is considered to be induced by the interaction between the αC regions of two adjacent protofibrils. In order to clarify the characteristics of this interaction, we examined the cross-sectional diameter DCin addition to the hydrodynamic diameter (Stoke diameter) of fibrinogen molecule in various solution conditions. Cross-sectional diameter of intact fibrinogen was 4.7 nm in agreement with the molecular structure. On the other hand, fragment-X, in which the αC regions are deleted, had smaller DCof 4.2 nm. This means that the αC regions snuggle up to the molecular backbone, which is consistent with the model that the termini of the αC regions are tethered to the central E-region in the intact fibrinogen. On the other hand, fibrinogen at pH 3 had a cross-sectional diameter of 4.0 nm, which is further smaller than that of fragment-X. This is accounted for by the scheme that the αC regions are released from the central region, because side chains of Asp and Glu residues have neutral charge at pH 3. With the increase of ionic strength up to 150 mM at pH 3, fibrinogen molecules become to aggregate resulting in huge aggregated particles. Our results suggest that the released αC regions can interact attractively with each other through the hydrophobic interaction, which supports the proposed scheme of fibrin polymerization.

scholarly journals Kinetic Assembly of a Thermally Stable Porous Coordination Network

2014 ◽  
Vol 70 (a1) ◽  
pp. C1246-C1246
Author(s):  
Hakuba Kitagawa ◽  
Hiroyoshi Ohtsu ◽  
Masaki Kawano
Keyword(s):  
Network Formation ◽  
Covalent Bond ◽  
The Other ◽  
Helical Chain ◽  
Network Synthesis ◽  
Thermally Stable ◽  
Slow Cooling ◽  
Coordination Network ◽  
Other Hand ◽  
Metal Sources

The advantage of porous coordination network synthesis is designability by changing metal sources and ligands.[1] Therefore, not only many commercially available ligands but also newly synthesized ones were used for networking. On the other hand, most of metal sources are common reagents or stable metal moieties because they can be more predictable as a metal connector. So far, there is no report focusing on usage of labile metal sources for selective network formation. One of the promising methods to produce unique networks with such labile metal sources is kinetic control[2] because labile metal sources produce various species in solution. In this talk, we will introduce selective syntheses of thermally stable porous coordination networks using a labile Cu4I4 cubane cluster [Cu4I4(PPh3)4] (1) and a rigid tetradentate Td-symmetry ligand tetra-(4-(4-pyridyl)phenyl)methane (2) by kinetic and thermodynamic control.[3] On heating the mixture of 1 and 2 in DMSO at 453 K, a homogenous colorless solution was obtained. Rapid cooling (~20 Kmin-1) of the solution produced yellow needle crystals, {[(CuI)2(2)]·solvent}n (3a) that shows novel CuI helical chain unit, in 99% yield (Fig. A). On the other hand, slow cooling (~3 Kmin-1) produced orange block crystals, {[(Cu2I2)(2)]·solvent}n (3b) that shows rhombic Cu2I2 dimer unit, in 95% yield. Both the network crystals can keep the crystallinity up to 673 K under N2 atmosphere. In kinetic product 3a, due to the unique structure, iodides of the CuI chains facing to 1D channel, the network crystal shows chemisorption of I2 by making a covalent bond with an iodide of part of the CuI chains to form an I3– group (Fig. B). On the other hand, in thermodynamic product 3b, Cu2I2 dimer units are hindered by bridging ligand 2. That is why network crystal 3b shows only physisorption of I2, even though network has 1D channel similar to 3a.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

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