Rheological Behavior of Dope Solutions of Poly(acrylonitrile‐co‐itaconic acid) in N,N‐dimethylformamide: Effect of Polymer Molar Mass

The rheological behavior of dope solutions of poly(acrylonitrile‐co‐itaconic acid) or poly(AN‐co‐IA) is important from the point of view of deriving the spinning conditions for good quality special acrylic fibers. The viscosity of the resin dope is dictated by the polymer concentration, molar mass, temperature and shear force. The dynamic shear rheology of concentrated poly(AN‐co‐IA) polymer dope solutions in N, N‐dimethylformamide, in the molar mass (M¯_v) range of 1×10⁵ to 1×10⁶ g/mol, was investigated in the shear rate (γ′) range of 1×10¹ to 5×10⁴ min^?1. An empirical relation between η and M¯_v was found to exist at constant shear rate. The dope viscosity was dependent on the molar mass and the shear rate at a given temperature (T) and concentration. The polymer molar mass index of dope viscosity (m) was calculated as functions of concentration (c), shear rate and temperature. The m values increased with shear rate and temperature. A master equation relating m, with shear rate and temperature was derived for a given dope concentration. At higher shear rates, m tends to the value of 3.4, which is close to the molar mass index of viscosity reported for molten thermoplastics. m increased significantly with shear rate and nominally with temperature, while an increase in concentration decreased it. The onset of shear thinning of the dope shifted to a lower shear rate regime with an increase in polymer concentration and the molar mass. For a given value of molar mass, the increase in viscosity of the dope solution with polymer concentration was dependent on the shear rate.     

Active3He activation analysis for carbon and oxygen

The surface and body concentrations of carbon and oxygen have been measured in various materials using prompt³He activation techniques. This target excitation functions were determined for (³He, p) reactions with carbon and oxygen over a³He energy range from 2.5 to 9.0 MeV. These data were used in the calculations of activation curves for various combinations of incident particle energy, impurity distributions, and material. Information on a computer code that was used in the analysis of the data is presented. Work done under the auspices of the U.S. Atomic Energy Commission.     

Thermodynamic interaction functions for 4He and 3He quantum liquids

The method of interaction functions is applied to quantum liquids. The interaction energies at 0 K are found as 14.3 cal/mole for ⁴He and 11.0 cal/mole for ³He. The interaction energy as a function of volume for all temperatures along the saturation line is deduced as an expression common to the two isotopes. The two isotopes have a region of anomaly in the interaction entropy, where the liquid appears less ordered than an ideal gas. These anomalies can be eliminated for ³He by allowance for the spin entropy and for ⁴He via the difference between the concentrations of the component with zero entropy in the liquid and Bose gas.     

Extraterrestrial3 He in marine polymetallic nodules: A potential method for measuring growth rate of nodules

The comparative measurements of helium isotope compositions between marine polymetallic nodules and their surrounding sediments, their magnetic fractions and bulk from C-C Zone of the East Pacific Basin are reported. The⁴He content and³He/⁴He ratio of polymetallic nodules and their surrounding sediments are extremely high; the³He,⁴ He concentrations and most³He/⁴He ratios of magnetic fractions in nodules and sediments are apparently higher than those in bulk. The helium isotope data points of nodules and sediments are all distributed along or closely to the mixing curve of the interplanetary dust particles (IDPs) and the terrigenous sediments in the chart of³He-³He/⁴He. In the same sampling site, the³He/⁴He ratios of nodules and their surrounding sediments are very similar, and the changes of both ratios are synchronous. It shows that the high³He/⁴He ratios in nodules and sediments may all result from IDPs. So, if the flux of extraterrestrial³He into the nodules and sediments is constant, the growth rate of polymetallic nodules and the sedimentation rate of sediments can be independently calculated according to the concentra-tion of extraterrestrial³He in nodules and sediments.

     

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

Poly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the range of 1 × 10⁵–1 × 10⁶ g mol^?1, has been investigated in the shear rate (γ′) range of 1 × 10¹–5 × 10⁴ min^?1. The zero shear viscosity (η₀) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔG_V) values were in the range 5–32 kJ mol^?1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔG_V value of the polymer solution of any and concentration (c) is suggested. The power law fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and was found to exist at constant shear rate, concentration and temperature. For each , the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Damage in Y-Ba-Cu-O films produced by4He ions

The question of destructibility of an ion beam technique applied to the analysis of high temperature superconductors is discussed, namely the influence of the often used analyzing⁴He ion beam on a monocrystalline YBa₂Cu₃O₇ film. The rate of irradiation defect production is measured for 1 and 3.07 MeV⁴He⁺ irradiation and compared with a Monte Carlo simulation. It is shown that the usual depth profiling by⁴He ion beams does not change the measured element profiles, but is destructive from the view point of the superconducting properties of a sample, due to the great number of defects produced. Using a large solid angle detector one can minimize the analyzing dose to avoid the destruction of superconducting properties.     

CURING AND RHEOLOGICAL BEHAVIOR OF VINYL ESTER RESINS PREPARED IN THE PRESENCE OF TERTIARY AMINES

Vinyl ester resins V₁, V₂ & V₃ of acid value (～6 mg KOH g^?1 solid) were synthesized using bisphenol-A epoxy and acrylic acid in the presence of triethyl-, tripropyl- and tributyl-, amines in 210, 270 and 340 minutes, respectively. The synthesized resins were characterized by FTIR spectroscopy and a new peak at 2360 cm^?1 was observed which is due to attachment of amines to resin structure by hydrogen bond. The curing behavior of synthesized resin containing 40% styrene (w/w) and 2% benzoyl peroxide was studied using DSC technique and found to be affected by presence of amines. Activation energy and frequency factor for the curing reaction increases from 14 Kcal mol^?1 to 23 Kcal mol^?1. Rheological behavior of resins containing 40% styrene was studied using a Haake Rotovisco RV20 viscometer, and viscosity was found to increase with shear rate up to 200 sec^?1. The average values of activation energy at constant shear stress (6-15 Pa) were 12.94, 13.20, 13.70 Kcal mol^?1 for V₁, V₂ and V₃, respectively. The activation energy at constant shear rate decreases with an increase in the shear rate.     

Extraterrestrial<Superscript>3</Superscript> He in marine polymetallic nodules: A potential method for measuring growth rate of nodules

The comparative measurements of helium isotope compositions between marine polymetallic nodules and their surrounding sediments, their magnetic fractions and bulk from C-C Zone of the East Pacific Basin are reported. The⁴He content and³He/⁴He ratio of polymetallic nodules and their surrounding sediments are extremely high; the³He,⁴ He concentrations and most³He/⁴He ratios of magnetic fractions in nodules and sediments are apparently higher than those in bulk. The helium isotope data points of nodules and sediments are all distributed along or closely to the mixing curve of the interplanetary dust particles (IDPs) and the terrigenous sediments in the chart of³He-³He/⁴He. In the same sampling site, the³He/⁴He ratios of nodules and their surrounding sediments are very similar, and the changes of both ratios are synchronous. It shows that the high³He/⁴He ratios in nodules and sediments may all result from IDPs. So, if the flux of extraterrestrial³He into the nodules and sediments is constant, the growth rate of polymetallic nodules and the sedimentation rate of sediments can be independently calculated according to the concentra-tion of extraterrestrial³He in nodules and sediments.     

Flow properties of branched polydisperse polymers

Viscosity and normal-stress difference as functions of shear rate were examined for poly(vinyl acetate) samples with various degrees of random branching in diethyl phthalate solution. At moderate concentration (c = 0.17 g/ml) the viscosities were depressed by branching, in fair accord with the Bueche theory. However, at higher concentrations (c = 0.35 g/ml) the data showed a progressive trend in the direction of viscosity enhancement by branching, a characteristic which has been observed by other workers in undiluted branched polymers. Accompanying viscosity enhancement was an increase in the temperature coefficient of viscosity, an increase in recoverable compliance (estimated from steady-state normal-stress data) and an early onset in the shear rate dependence of viscosity.     

Trace determination of oxygen in gold-copper alloys and in high purity gold using3He and4He activation analysis

Trace amounts of oxygen in gold-copper alloys and high purity gold have been determined by³He and⁴He activation analysis. Interferences from the matrix have been identified and the factors which can have an effect upon the precision and the accuracy of the method have been investigated. Thus a destructive technique has been choosen. The¹⁸F produced was chemically separated by steam distillation and precipitated as PbClF. The values of the oxygen concentration were found to range between 0.2 and 2 μg·g⁻¹ depending on the copper concentration and the thermal treatment applied to the samples. A possible mechanism of internal oxidation is presented.     

Rheology of (±)‐camphor‐10‐sulfonic acid doped polyaniline‐m‐cresol conducting gel nanocomposites

The rheological behavior of polyaniline‐(±champhor‐10‐sulfonic acid)_0.5‐m‐cresol [PANI‐CSA_0.5‐m‐cresol] gel nanocomposites (GNCs) with Na‐montmorillonite clay (intercalated tactoids) is studied. The shear viscosity exhibits Newtonian behavior for low shear rate (<2 × 10^?4 s^?1) and power law variation for higher shear rate. The zero shear viscosity (η₀) and the characteristic time (λ) increase but the power law index (n) decrease with increase in clay concentration. In the GNCs storage modulus (G′) and loss modulus (G″) are invariant with frequency in contrast to the pure gel. The G′ and G′ exhibit the gel behavior of the GNCs up to 105 °C in contrast to the melting for the pure gel at 75.7 °C. The percent increase of G′ of GNCs increases dramatically (619% in GNC‐5) with increasing clay concentration. The conductivity values are 10.5, 5.65, 5.51, and 4.75 S/cm for pure gel, GNC‐1, GNC‐3, and GNC‐5, respectively, promising their possible use in soft sensing devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 28–40, 2008     

Use of spin-labelling techniques to probe the dynamics of He(23 S) deexcitation at solid surfaces

Spin labelling techniques, specifically the use of electron-spin-polarized He(2³ S) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of He(2³ S) deexcitation at solid surfaces. Data for a clean Au(100) surface are presented that show that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization. The electrons involved in Auger neutralization are observed to be correlated in spin and possible reasons for this are discussed. Results obtained at Xe and NO films adsorbed on cooled Au(100) and Cu(100) substrates, respectively, show that He(2³ S) metastable atom deexcitation is analogous to gas-phase Penning ionization. Detailed differences are apparent that can be attributed to effects associated with the underlying substrate and interactions involving neighboring atoms in the film.     

Study on the flow of highly concentrated emulsions

An investigation was performed into the flow of highly concentrated water-in-oil emulsions. The viscosity of the low shear rate region in the downward curve was much higher than the viscosity of the upward curve due to the refining effect of the intensive shear. However, this refining effect lasted for just a short time. After that, the structure of highly concentrated emulsion (HCE) can return to its original state. The flow of HCE depends on the shear rate and droplet size of the dispersed phase. The viscosity curve of HCE, which is measured in the initial upward shearing sweep, had two platforms, whereas the region of shear rate was 10^?4?s^?1?～?10³?s^?1. The water-in-oil structure was destroyed by intensive shear and much solid ammonium nitrate (AN) was observed in the image of HCE. The small droplets can enhance the capacity of HCE to prevent the breakage of structure under shearing. The microstructure of HCE was closer to its original situation when the droplet size was small.     

Hyperfine structure of the 33 P state of3He and isotope shift for the 23 S-33 P 0 transition

The hyperfine structure of the³He 1s 3p ³ P state and the³He-⁴He isotope shift is determined by high precision measurements of the 1s2s ³ S ₁-1s 3p ³ p ³ P _J transition frequencies near 389 nm. A direct frequency measurement is made without the need for wavelength calibration by tuning a single laser to the atomic frequency, and using a novel heterodyne method to observe beat frequencies with a stable reference laser. A fit to a theoretical model of hyperfine structure is used to determine the hyperfine shifts. Additional off-diagonal mixing effects are investigated to resolve a possible systematic discrepancy in the hyperfine intervals. The final isotope shift without hyperfine structure of 42184308±165 kHz is used to deduce an rms nuclear charge radius for³He of 1.956±0.042 fm. This is in good agreement with other values obtained from atomic isotope shift measurements, and a recent theoretical value of 1.958±0.006 fm. The present result helps to resolve substantial differences in the³He nuclear radius derived from electron-nuclear scattering measurements, and it provides a significant test of the nuclear three-body problem.     

Rheology of hydroxypropylcellulose solutions

The rheology of hydroxypropylcellulose (HPC)—acetic acid solutions was investigated by using a cone-and-plate rheometer and a capillary rheometer, for polymer concentrations ranging from 10 to 80%. Isotropic solutions exhibit a Newtonian plateau followed at higher shear rates by a pseudoplastic zone. The apparent viscosity varies as C^5.2 if concentration C is less than 27% and as C¹³ for 27% < C < 30%. A biphasic interval (isotropic and cholesteric phases) exists between 30 and 35%. A maximum in viscosity is observed at C = 30%, the height of the viscosity peak being a decreasing function of shear rate. Anisotropic solutions are strongly viscoelastic. Both isotropic and anisotropic solutions give results (apparent viscosity, first normal-stress difference, relaxation time, etc.) which are not in good agreement with Doi's theory. This is understandable since the HPC chain cannot be modeled by a rigid rod. Upon heating, anisotropic HPC—acetic acid solutions undergo an anisotropic to isotropic phase transition which is easily detected by a maximum in the temperature dependence of the first normal-stress difference and of the apparent viscosity.     

Critical molecular weight for onset of non-newtonian flow and upper newtonian viscosity of polydimethylsiloxane

The flow curves of fractionated polydimethylsiloxanes of different molecular weights were obtained over a wide range of shear rates, from 3 × 10^?1 to 4.3 × 10⁶ sec^?1, by use of a gas-driven capillary viscometer designed to decrease the experimental error in high shear rate region. Non-Newtonian flow can occur at molecular weights below the critical molecular weight M_c for the entanglement of polymer chain. The critical molecular weight M′_c for the onset of the non-Newtonian flow is identical with that of the segment of viscous flow. For the polymer of molecular weights from M′_c to M_c, the upper Newtonian viscosity increases with an increase in molecular weight. Above M_c, the upper Newtonian viscosity is almost independent of the molecular weight.     

Rheological study of an aromatic polyamide-hydrazide

Rheological and rheo-optical data are reported for the poly(terephthalamide of p-aminobenzhydrazide), X-500, in dimethyl sulfoxide solutions in the concentration range 0.2 to 6.0 g/100 ml. The objective of these measurements is to seek evidence of shear-induced isotropic → nematic phase transition. Three types of measurement, Couette, cone and plate, and capillary rheometer, all indicate that this system exhibits flow instabilities at high shear rates and concentrations. In this region both the viscosity and the primary normal stress difference decrease with time under shear. In the capillary rheometer the apparent viscosity is smaller for shorter capillaries and, for short capillaries, there is a range of shear rates in which plug flow and a coiled extrudate are observed. These instabilities may arise from the existence of a mixture of isotropic and nematic phases. At lower shear rates, where the flow behavior appears normal, the concentration dependence of the flow birefringence increases at a critical polymer concentration C This value is in reasonable accord with the concentration corresponding to the change of slope of logη (measured at low shear rate) vs. logC_p. Both the latter measurements appear to be sensitive to the onset of the phenomenon, which may be due to a shear-induced transition or the rheological effect of chain entanglements.     

Viscosity Behaviors of Rapidly Curable Silica Sols

The viscosity behaviors of rapidly curable transparent silica aerogels, such as time at the onset point and the slope of viscosity increase, are investigated as functions of target density, water and catalyst content. Results were compared with the visually measured gel time. The effects of temperature and shear rate on the onset point and rate of the viscosity increase are also investigated with the selected samples. Experimental design and result analysis were also conducted using the Design of Experiment (DOE) method, and the Arrhenius relation was applied to predict the temperature dependence of viscosity. It is found that the target density and catalyst content played more important roles in determining gelation and viscosity behavior than water content did. As the target density increased, the gel time and the onset point appeared at significantly earlier times and the slope increased more rapidly, while there existed an optimum catalyst and water content for fast gelation and desirable viscosity behaviors. The temperature dependence of the viscosity behaviors of rapidly curable transparent silica sols can be expressed by the Arrhenius relation. The onset time of viscosity increase was little affected by the shear rate at a low shear rate range of up to 1.32 s⁻¹, and after that it linearly decreased with increasing shear rate, while the slope of viscosity increase continuously decreased with increasing shear rate. Overall, the viscosity measurement appears as a simple and reliable method for quantitatively measuring gel time, especially for the rapidly curable sol–gel process.     

Spectroscopy with sound on superfluid 3He B

Collective modes of superfluid ³He B have been studied by means of sound attenuation and sound velocity studies. A new sound attenuation peak has been observed in superfluid ³He B at ?ω ≈ Δ(T). This peak has been identified with the real squashing mode. Pulse time of flight methods has been used in these studies. At high sound amplitudes, interesting transient effects have been observed which have been tentatively identified with solitonlike behavior.