High Viscosity Region Research Articles

Plane strain fracture toughness of polyphenylene sulfide

AbstractThe plane strain fracture toughness of polyphenylene sulfide (PPS), tested with different molecular structures such as linear PPS, heat‐treated PPS, and branched PPS, was investigated over a wide range of melt viscosity and crystallinity and compared with other mechanical properties. The fracture toughness of linear PPS increased with increasing melt viscosity, and it reached the highest fracture toughness calculated from linear elastic fracture mechanics (LEFM) observed in this study. In this high melt viscosity region, the linear PPS specimen showed slow crack growth instead of brittle fracture. Although the tensile properties of heat‐treated PPS and branched PPS are the same as those of linear PPS, the fracture toughness of linear PPS is superior. The fracture toughness is affected by the crystallinity of the specimen, and the effect of crystallinity on fracture toughness is smaller than that of melt viscosity and molecular structure.

Kinetic theory and molecular dynamics simulations of microscopic flows

This study aims at the understanding of the viscosity distributions near a solid wall in microscopic pores. The pair-correlation function is derived from the density distribution function, which in itself is obtained from molecular dynamics simulations. The revised Enskog equation for the shear flow of strongly inhomogeneous hard-sphere fluids is solved by the Chapman–Enskog method and the viscosity coefficients are obtained by keeping all the high-order derivatives of the density and pair-correlation functions. The molecular dynamics method is used in order to simulate the Couette flow of a Lennard-Jones fluid in a micropore, with weak or strong wall–fluid interactions. Under the weak interaction, slip is observed near the wall and the fluid in the contact layer exhibits higher viscosity than the fluid in other regions. Under the strong interaction, a layer of fluid always adhered to the wall is observed. A low viscosity valley often exists next to the high viscosity region, where apparently the flow commences. It is observed that the molecular dynamics simulations predict higher viscosity than the kinetic theory of the hard-sphere model, as it is expected. However, the distributions obtained from both methods are in qualitative agreement. The present study suggests that, provided the bulk viscosity and appropriate boundary conditions are used, the Navier–Stokes equations are valid at a distance of two to three molecular layers from the wall.

Pressure Tuning of Solvent Relaxation Time for the Excited Intramolecular Charge-Transfer Kinetics in 4-(N,N-Dimethylamino)triphenylphosphine in Alcohol

The dynamic solvent effect on the excited state intramolecular charge-transfer (ICT) reaction of 4-(N,N-dimethylamino)triphenylphosphine (DMATP) in alcohol solvents is examined by a high-pressure method. In order to deduce the solvation effect on the ICT reaction of DMATP, the picosecond time-dependent Stokes shift (TDSS) of coumarin 153 (C153) in alcohols is measured as a function of pressure. The resulting high-pressure solvent relaxation time (τs) is in excellent agreement with the longest longitudinal relaxation time (τL) of alcohols from low-temperature sources. In the low-viscosity region at low pressures, the rate of the ICT formation correlates with τs (or τL), while in the high viscosity region at high pressures, it becomes noticeably faster than τs (or τL).

Rotational Behavior of N-(2-Naphthylmethyl)carbazole in a 1,2-Dichloroethane/Poly(ethylene oxide) Mixture Measured by a Time-Resolved Fluorescence Depolarization Method

Abstract Stationary and nanosecond time-resolved fluorescence depolarization spectroscopy has been used to detect the rotational behavior of N-(2-naphthylmethyl)carbazole as a function of the solvent viscosity. The variation in the viscosity was effected by the addition of poly(ethylene oxide), and the range of the variation was 0.78 N m−2 s−1 to 33 × 10−3 N m−2 s−1. The viscosity dependence of the rotational diffusion coefficient (Dr) in the high-viscosity region was different from that in the low viscosity region. Radii of gyration of N-(2-naphtylmethyl)carbazole in the low and high viscosity regions were about 8 and 4 Å, respectively. The former agrees with the total size of N-(2-naphthylmethyl)carbazole, and the latter with the size of the cabazolyl group. The crossover point of the rotational motion of N-(2-naphthylmethyl)carbazole was at a concentration of 0.6 g ml−1 of poly(ethylene oxide), which coincided with the overlap concentration of poly(ethylene oxide) molecules. Therefore, the rotational mode of N-(2-naphthylmethyl)carbazole varies from the whole to the carbazolyl group by the addition of poly(ethylene oxide).

Ultrasonic investigation of the viscosity dependence of the rate constants of rotational isomerism of dibromoethane and dibromopropane in solution

Ultrasonic relaxation spectra due to the rotational isomerism of 1,2-dibromoethane and 1,2-dibromopropane in n-hexane and diisobutyl phthalate have been measured as a function of solution viscosity. The rate constant of the rotational isomerism was determined by analysis of the frequency dependence of the ultrasonic absorption or sound velocity. The reaction rate constants of the rotational isomerism increased with decreasing solution viscosity. The viscosity dependence of the rate constant for 1,2-dibromoethane solutions is well interpreted in terms of Kramers' model. For 1,2-dibromopropane, the pre-exponential factors predicted by Kramers' model are in agreement with experimental results in the low-viscosity region, while in the high-viscosity region deviation from Kramers' theory was found in the pre-exponential factor. The deviation is considered to be due to the strong interaction between 1,2-dibromopropane and diisobutyl phthalate.

A simple model of plate generation from mantle flow

SUMMARY A simple model of non-Newtoniancreepingflow is used to evaluate classes of rheologieswhichallow viscous mantle flow to becomeplate-like. The model describes shallow-layerlithosphericmotion driven by sources and sinks. The sources represent spreading ridges while the sinks rep-resent subduction zones; the sources and sinks thus also prescribe the poloidal component ofthe surface flow field. The toroidal (strike-slip) component of the flow field is found via thesolution of the Stokes equation with non-Newtonian rheology. As a first basic investigation ofthe model, the horizontal divergence from the two-dimensional rectangular velocity field ofOlson & Bercovici (1991) is used for the source-sink field. The degree to which the inducedfluid flow reproducesthe rectangularplate is used to measure the success of differentrheologiesin generating plate-like flows. Results indicate that power-law rheologies, even in the limit ofvery high power-law indexν, can only produce modest plate-like flow. For example, the ratioof toroidal to poloidal kinetic energy for a source-sink field derived from a square plate is atbest 0.65, whereas a perfect square plate has a ratio of 1.0. Moreover, the power-law rheologyappears to reach an asymptotic limit in its ability to produce plate-like behavior. This impliesthat plate tectonics is unlikely to arise from a power-law rheology even in the limit of very highν. A class of rheologies that yield significantly more promisi ng results arise from the Carreaupseudo-plastic rheology with the power-law index taken to be ν < 0. One rheology in thisclass is the continuum model for stick-slip, earthquake behavior of Whitehead & Gans (1974),which is essentially the Carreau equation with ν = −1. This class of rheologies, referred to asthe stick-slip rheologies, induces a toroidal to poloidal kinetic energy ratio for a square plates’ssource-sink function which can be as high as0.9. The viscosity (or strength) distribution forthis class of rheologies also appears more plate-like, showing fairly uniform high viscosity re-gions (pseudo-plates) and sharply defined low viscosity zones (pseudo-margins). In contrast,even the most nonlinear power-law rheology produces spatially varying high viscosity regionsand relatively smooth low viscosity margins. The greater success of the stick-slip rheologiesin producing plates is attributed to a self-lubricating mechanism in which the transfer of mo-mentum from regions of high shear to low shear is inhibited. In contrast, even in the limit ofinfinite power-law index, a power-law rheology can retard but never prohibit momentum trans-fer. This feature is essential to the sharpening of velocity profiles into plate-like profiles, whichis illustrated with a simple boundary-layertheory.Key words: Plate tectonics, mantle convection, non-Newtonian flow, toroidal-poloidal cou-pling.

A low-cost surface laser light scattering spectrometer

A low-cost surface laser light scattering spectrometer for measuring interfacial tension and viscosity has been built and tested. The spectrometer is based on a cheap multimode semiconductor laser and an ordinary Si photodiode. In the case of fluids with moderate viscosities (e.g. hexane, ethanol and water) the spectrometer provides an accuracy as least as good as that obtained with the high-cost light scattering spectrometers proposed so far. Possible improvements of the spectrometer for expanding its range into the high viscosity region are discussed.

Storage of erasable laser induced holographic gratings in low molar mass cholesteric liquid crystals

Abstract We succeeded in storing optical information with low-molecular-weight cholesteric liquid crystals. Nematic mixtures of glassy compounds which are chiralized by the addition of small amounts CB15 (BDH) have been used. Reversible optically induced holographic gratings were stored both below the glass transition temperature and above the glass transition in the temperature region of high viscosity. Erasure can be achieved by local heating of the sample making possible to use the material for multiple storage processes. A mechanism to explain the formation of the grating is discussed.

Glass-like behaviour of proteins as seen by Mössbauer spectroscopy

Mössbauer spectroscopy reveals a strong analogy in the dynamic properties of 57Fe in glycerol and in myoglobin crystals. Above about 200 K, the shape and the area of the spectra can be explained by a jump diffusion model with a jump time distribution according to Cole-Davidson. In the high-viscosity region well below 200 K, the myoglobin molecules have a similar but not an identical structure indicating a highly degenerated ground state energy of the molecules.

The heat source of Ruapehu crater lake; deductions from the energy and mass balances

Regular observations of temperature, outflow rates and water chemistry of Crater Lake, Mt. Ruapehu, New Zealand have been made for the last 25 years. These data have been used to derive a model of the dynamics of the lake, and determine the input of energy, mass, and chloride from the volcano to the Crater Lake. The recent, relatively quiescent state of the volcano, when virtually no heat has been input to the lake, has also enabled an assessment to be made of the surface heat loss characteristics, which play an important role in the model of the lake. The modelling suggests that since about 1982 the ratio of the volcanic heat to mass added to the base of the lake is about 6 MJ/kg, which is not compatible with heating of the lake by magmatic steam alone. Thus, only about 50% of the heating has been by magmatic steam. It is suggested that heat could be transferred from a magmatic source to the region below the lake by a heat-pipe mechanism, commonly associated with geothermal systems. The simultaneous upward movement of vapour phase, and downward movement of liquid phase from condensed vapour allows efficient heat transfer without overall mass transfer. The permeability necessary to supply the required heat is of the order of 10 darcy, and is consistent with a rubble filled vent. For at least the last five years, there has been a characteristic pattern in the Crater Lake temperature record, with alternate heating and cooling phases. The heating phase generally lasts for one or two months, while the cooling phase lasts for six months to a year. A possible explanation for this cyclic behaviour is the presence of a layer of liquid sulphur under Crater Lake, acting as a partial barrier between the heat-pipe and the lake. The unusual variations of the viscosity of liquid sulphur with temperature will mean that at temperatures greater than 160°C, the layer of sulphur becomes highly viscous and would block any upwards steam flow and hence stop the heat input to Crater Lake, so producing a cooling phase. This blockage would last until the heating from below raised the temperature of the sulphur beyond the high-viscosity region, so gases could again pass through the sulphur.

A new apparatus for measuring high viscosities

A new viscometer especially designed for the high viscosity region is presented. The magnetoviscometer uses Stokes' falling sphere principle, where the gravitational force is substituted by a magnetic one. The working principle and set-up of the apparatus are described; some results obtained on technical polymers are given and special features of the magnetoviscometer (such as measurement under pressure and the use of disposable cells) are emphasised.

Transient natural convection in a square cavity of a fluid with temperature-dependent viscosity

A study is made of unsteady natural convection in a square cavity of a fluid with a temperature-dependent viscosity. The flow is driven by instantaneously raising the temperature at one vertical wall and lowering the other. The viscosity variation is modeled by an exponential form, v v o = exp(−CT) . Two boundary conditions at the horizontal walls are used: insulating walls and highly conducting walls. Numerical solutions to the governing time-dependent equations at large reference Rayleigh numbers are acquired. The evolutions of the flow patterns and isotherms are presented under various parameter settings. When the viscosity are large, convective activities are facilitated in the region of low viscosity and suppressed in the region of high viscosity. The global impact is to enhance the flow and heat transfer in the cavity. A representative time history of the velocities is shown. A heatup time scale is corroborated. The transient behavior of the Nusselt number at the walls is scrutinized. During the transient phase, the effect of variable viscosity is such that the heat inflow to the cavity exceeds the heat outflow from the cavity. In effect, the cavity acts as a receiver of net heat input during the transient process.

Stabilization of Metallic Glasses by Irradiation with Picosecond Laser Pulses.

IntroductionGlassy metallic alloys are usually formed by bringing a small amount of the melt mechanically into good thermal contact with a heat conducting medium. Cooling rates of the order of 106K/sec can thereby be obtained. Despite the extensive use of laser treatment in many areas of technology the idea of using ultra short laser pulses to increase the cooling rate by many orders of magnitude is relatively new. The rates obtainable in metals as a result of laser irradiation have been estimated to be of the order of 1010 K/sec (for nanosecond laser pulses) in the critical temperature region of high nucleation rate and low viscosity. Some less sophisticated estimates for laser annealing of silicon with picosecond pulses yield values of 1012 – 1013 K/sec.. The recent measurements of the surface colour temperature in laser irradiated metals suggest cooling rates of the order of 1010K/sec in both nanosecond and picosecond regimes.

Falling sphere viscometry in gravitational and magnetic fields

The classical falling sphere method based onStokes' law is well known. Using gravitational forces, however, restricts the range of measurements considerably. This advantage can be overcome by applying iron spheres in a magnetic field, which allows to measure polymer melts with viscosities up to η0=109 Pa s (with very strong magnets available even more). A special measuring cell designed for application in the magnetic field is tested with several silicon oils in the gravitational field too. In both cases wall and end corrections toStokes' law have to be considered and are of main concern. Another important point is a reliable temperature measurement. Results especially for the high viscosity region of polymer melts are given.

Secular rotational motions and the mechanical structure of a dynamical viscoelastic Earth

We give a survey of the analytical methods for computing the linear responses of the rotational axis of a layered viscoelastic Earth to surface loading. The two classes of eigenspectra involving isostatic relaxation of the mantle and readjustment of the spin axis are emphasized as being essential for a uniformly valid description of polar wander. The rotational responses due to the application of an equilibrium phase or a chemically layered boundary condition at the 670 km discontinuity are studied. The displacement fields associated with rotational deformation are affected to a much greater extent by the amount of chemical enrichment than are the eigenfunctions associated with isostatic relaxation. The present polar motion data from International Latitude Service (I.L.S.) can be fit equally well by a pure chemical or an equilibrium phase boundary with a 9% change in density across the interface. On the other hand, responses from models with a smaller amount of chemical stratification, <7%, are not compatible with the data. The secular variation of the Earth's gravitational harmonic J 2 is insensitive to the chemical nature of the 670 km discontinuity. From the rotational data it is not possible to rule out the existence of a high viscosity region with values of O(10 23)P at the bottom 500 km of the mantle, although a solution with a relatively uniform viscosity profile, O(10 22P), still can be found. Inferences of the globally averaged thickness of the elastic lithosphere from rotational data are not affected too much by the particular density stratification used for the lithosphere and upper mantle. They lie in the range between 120 and 170 km.

Studies on the Solution Properties of Anionic Surfactants, Alkanamide Poly (oxyethylene) Sulfates I.

In the present work, the surface viscosities, closely related to the practical characteristics such as properties of foam, have been measured to depict the iso-surface-viscous curves on the triangular diagrams for alkanamide poly (oxyethylene) sulfate/N, N-diethanoldodecanamide (thickener) /water systems (concentration 00.1%). The surfactants used were sodium dodecanamide, tetradecanamide and hexadecanamide poly (oxyethylene) sulfates, and sodium dodecyl poly (oxyethylene) sulfate for comparison. Consequently, the following informations were obtained. (1) There lie 3 high surface viscosity regions, where the thickener is added slightly in the surfactant solutions (α), the surfactant is added slightly in the thickener solutions (β), and the thickener is added comparably to or more than the surfactants (γ). (2) While, with increase in the number of oxyethylene units in the surfactant molecule, α region is shifted to higher concentration of the surfactant and becomes more contracted, this region is shifted to lower concentration of the surfactant and surface viscosity increases remarkably with increase in alkane chain length. (3) As to, β region, no noticeable difference is found among the surfactants used. (4) γ region is the most extensive of 3 regions, and especially in the case of hexadecanamide poly (oxyethylene) sulfate it extends much more toward the water corner. (5) with increase in the number of oxyethylene units and in alkane chain length, surface viscosity in γ region increases, and in the latter case this region is shifted to higher concentration of the thickener. (6) In the case of dodecyl poly (oxyethylene) sulfate, α region is situated in higher concentration of the surfactant and more contracted than in corresponding alkanamide poly (oxyethylene) sulfate. However, γ region is more extensive and surface viscosity is higher.

Study of molecular motions in liquids by ESR and relaxation measurements. III. Temperature dependence of g of semiquinones in alcohols

The g values of 1,4-benzosemiquinone and durosemiquinone anions in methanol, ethanol, and n-butanol have been measured at temperatures T, above the freezing point of the solvents. The rapid variation of g with T in the high-viscosity region has been assigned to slow tumbling effects. The gradual increase of g with an increase in T has been assigned to an equilibrium between the hydrogen-bonded and non-hydrogen-bonded semiquinones. This has been confirmed from a study of g of DSQ in ethanol-DME, ethanol-acetonitrile, and ethanol-DMSO mixtures. Combining the results of the earlier electron spin relaxation studies with the estimated fraction of the time for which the semiquinone is not hydrogen-bonded and the enthalpy change associated with the above-mentioned reaction (∼1 kcal mole −1), it was concluded that in alcohols (i) in the temperature range studied there is a greater probability of finding the semiquinone in the hydrogen-bonded state; (ii) it can go to a non-hydrogen-bonded state without requiring energies of the order of hydrogen-bonding energies; (iii) only a fraction of the non-hydrogen-bonded sate corresponds to a state of free rotation; (iv) this free rotation is different from the large-step motion associated with the reorientation; (v) the descriptions of the hindered rotation of the semiquinone in alcohols in the liquid state and the frozen state are likely to be similar. The value 1 kcal mole −1 corresponds to the energy difference between the two hydrogen-bonded states of an alcohol molecule in the neighborhood of the semiquinone. In the first hydrogen-bonded state it is bonded to the semiquinone, while in the second hydrogen-bonded state it is bonded to neighboring alcohol molecules, forming a polymer but leaving the semiquinone nonhydrogen-bonded.

Effects of iron oxidation state on viscosity, lunar composition 15555

The viscous flow behavior of a 9.6-kg lunar rock containing 22.5 wt.% FeO was studied in the temperature ranges from 620 to 700 C and from 1215 to 1400 C. The material was synthesized under mildy reducing conditions to simulate the Fe(2+)/total Fe ratio of the lunar environment. The effect of iron oxidation state on flow behavior in the high viscosity region is studied for specimens of the 15555 composition with Fe(2+) concentration ratios of 0.94, 0.76, and 0.20. A change in ratio from 0.94 to 0.76 had no observable effect on viscosity, whereas a change from 0.76 to 0.20 was accompanied by a drastic increase in viscosity (some three orders of magnitude) at a given temperature, but without changing the form of the variation of viscosity with temperature. The flow behavior is analyzed as a function of the structural features of the glasses.

High-temperature flow behavior of glass-forming liquids: A free-volume interpretation

High-temperature viscous flow data are reported for three relatively simple organic liquids: o-terphenyl, salol, and α-phenyl-o-cresol. The results are combined with previous flow data on the same liquids to obtain viscosity-temperature relations over some 15 orders of magnitude. For each liquid, as well as for tri-α-naphthylbenzene, the free-volume theory of Turnbull and Cohen is found to provide a close representation of the data for viscosities between 10−2 P (the high-temperature limit of the data) and about 104 P. Over this range, even the pre-exponential factors derived from fitting the experimental results are in close agreement with those predicted by the theory. At lower temperatures, the free-volume expression overestimates the difficulty of flow. For all four organic liquids, the fractional free volumes at the points of departure, TB, of the experimental data from the free volume predictions are close to 0.015. An empirical high-temperature flow relation of the free-volume form is suggested as η ≈ [(MkT)1/2/a02] exp {0.25/[0.015 + Δ α (T - TB)]}, where M is the mass of the molecule, a0 is its diameter, and Δα is the difference in thermal expansion coefficient between liquid and glass. It is suggested again that free-volume theories be used to represent flow behavior in the fluid range rather than in the high-viscosity region as the glass transition is approached.

Viscous flow behavior of selenium

The viscosity of 99.99% pure selenium has been determined over the available range of temperature where crystallization could be avoided. A bending beam viscosimeter was used to obtain data in the high viscosity region, and a rotating cylinder instrument was employed for the low viscosity range. Also determined was the stress dependence of the viscosity at temperatures of 31.5 and 29.6°C. The critical stress for non-Newtonian flow was found to lie in the range of hundreds of psi, which is appreciably smaller than that for oxide liquids in a similar range of viscosity.