Viscosity Eta Research Articles

Gel formation and low‐temperature intramolecular conformation transition of a triple‐helical polysaccharide lentinan in water

The gelation behavior of the triple-helical polysaccharide lentinan fractions having different molecular weights in water at 25 degrees C were studied by using a rheometer. The analysis of concentration and molecular weight dependence of shear stress and shear viscosity showed that aqueous lentinan is a typical shear-thinning fluid, possessing potential as a viscosity control agent, and that a weak gel with entangled network structure formed. The dynamic oscillatory behavior of lentinan in the temperature range of 1-15 degrees C was also investigated by rheologic method. The storage modulus G' and complex viscosity eta* increased first with decreasing temperature, and underwent a maximum centered at 7-9 degrees C, and then decreased with further decreasing temperature. This abnormal phenomenon was ascribed to formation of rigid structure in the gel state, which was confirmed by the experimental results from micro-DSC. The micro-DSC curves showed that an endothermic peak appeared at 7-9 degrees C for lentinan in water upon heating, which was attributable to the intramolecular order-disorder structure transition similar to triple-helical polysaccharide schizophyllan. Namely, at lower temperature, the side glucose residues of lentinan (triplix II) formed a well-organized triple-helical structure (triplix I) through hydrogen-bonding with the surrounding water molecules. Moreover, this conformation transition was proved to be thermally reversible.

Ion Association in [bmim][PF6]/Naphthalene Mixtures: An Experimental and Computational Study

Mixtures of room temperature ionic liquids (IL) with neutral organic molecules provide a valuable testing ground to investigate the interplay of the ionic and molecular-dipolar state in dense Coulomb systems at near ambient conditions. In the present study, the viscosity eta and the ionic conductivity sigma of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])/naphthalene mixtures at T = 80 degrees C have been measured at 10 stoichiometries spanning the composition range from pure naphthalene to pure [bmim][PF6]. The viscosity grows nearly monotonically with increasing IL mole fraction ( x), whereas the conductivity per ion displays a clear peak at x approximately 15%. The origin of this maximum has been investigated using molecular dynamics simulations based on a classical force field. Snapshots of the simulated samples show that the conductivity maximum is due to the gradual transition in the IL component from an ionic state at high x to a dipolar fluid made of neutral ion pairs at low x. At concentrations x < 0.20 the ion pairs condense into molecular-thin filaments bound by dipolar forces and extending in between nanometric droplets of IL. These results are confirmed and complemented by the computation of dynamic and transport properties in [bmim][PF6]/naphthalene mixtures at low IL concentration.

Crystal growth kinetics exhibit a fragility-dependent decoupling from viscosity

In this paper we establish the temperature dependence of the kinetic coefficient associated with crystal growth into the supercooled liquid for a wide range of organic and inorganic materials. We show that the kinetic coefficient for crystal growth scales with the shear viscosity eta as eta(-xi) and that the exponent depends systematically on the fragility of the liquid. The greater the fragility (i.e., deviation away from an Arrhenius temperature dependence for eta), the larger the difference 1-xi. We argue that this breakdown in scaling between the crystal growth kinetics and the viscosity is a manifestation of heterogeneous dynamics in supercooled liquids. In addition, we show that the absolute growth rate at intermediate viscosities is correlated with the entropy difference between the liquid and the crystal.

Small Shear Viscosity of a Quark-Gluon Plasma Implies Strong Jet Quenching

We derive an expression relating the transport parameter q and the shear viscosity eta of a weakly coupled quark-gluon plasma. A deviation from this relation can be regarded as a quantitative measure of "strong coupling" of the medium. The ratio T{3}/q, where T is the temperature, is a more broadly valid measure of the coupling strength of the medium than eta/s, where s denotes the entropy density. Different estimates of q derived from existing Relativistic Heavy Ion Collider data are shown to imply radically different structures of the produced matter.

A comprehensive, time-resolved SANS investigation of temperature-change-induced sponge-to-lamellar and lamellar-to-sponge phase transformations in comparison with 2H -NMR results

Time-resolved small-angle neutron scattering (TR-SANS) was employed to observe temperature-induced phase transitions from the sponge (L (3) to the lamellar ( L (alpha) phase, and vice versa, in the water-oil (n -decane)-non-ionic surfactant ( C(12)E(5) system using both bulk and film contrast. Samples of different bilayer volume fractions phi and solvent viscosities eta were investigated applying various amplitudes of temperature jump DeltaT . The findings of a previous (2)H -NMR study could be confirmed, where the lamellar phase formation was determined to occur through a nucleation and growth process, while it was concluded that the L (3) -phase develops in a mechanistically different and more rapid manner involving uncorrelated passage formation. Likewise, the kinetic trends of the nucleation and growth transition (decreased transition time with increase of phi and DeltaT were witnessed once again. Additionally, NMR and SANS data that demonstrate a strong dependency of that process on solvent viscosity eta are presented. Contrariwise, it is made evident via both SANS and NMR results that the L (alpha) -to-L (3) transition time is independent (within experimental sensitivity) of the varied parameters (phi , DeltaT , eta . Unusual scattering evolution in one experiment, originating from a highly ordered lamellar phase, intriguingly hints that a major rate determining factor is the disruption of long-range order. Furthermore, the bulk contrast investigations give insight into structure peak shifts/development during the transitions, while the film contrast experiments prove the bilayer thickness to be constant throughout the phase transitions and show that there is no evidence for a change in the short-range order of the bilayer structure. The latter was considered possible, due to the different topology of the L (3) and L (alpha) phases. Lastly, an unexpected yet consistent appearance of anisotropic scattering is detected in the L (3) -to- L (alpha) transitions.

Viscoelasticity of Dynamically Self-Assembled Paramagnetic Colloidal Clusters

Paramagnetic particles in a liquid above a solid dynamically self-assemble into two-dimensional (2D) viscoelastic clusters in a processing magnetic field if the precession angle exceeds the magic angle. Hexagonal clusters rotate with a frequency proportional to the precession frequency of the magnetic field. The rotation is explained by viscoelastic shear waves excited in the clusters that can be visualized slightly above the magic angle. The cluster rotation and the visualization of viscoelastic modes are independent techniques to probe the rheological properties of the cluster. We find agreement between both techniques when determining the 2D cluster viscosity eta(c) approximately 10(-11) N s/m.

Release of diclofenac sodium from polylactide-co-glycolide 80/20 rods

Due to inflammatory reactions complicating bioabsorbable devices, the aim of this study was to develop and characterize bioabsorbable implants with anti-inflammatory drug releasing properties. Polylactide-co- glycolide (PLGA) 80/20 was compounded with diclofenac sodium (DS) to produce rods. Thermal properties were analyzed using differential scanning calorimetry (DSC). Inherent viscosity (eta(inh)) was measured to evaluate the drug effect on the extrude polymer. Drug release measurements were performed using UV-spectrophotometer. Five parallel samples from each type of rods were examined, first at 6 hour intervals, then on daily basis, and later twice a week. DS was released in 110 days from thinner rods and in 150 days from thicker rods. Drug release comprised a starting peak, slow release phase, then a high release phase, and a burst release phase. DSC analysis showed that DS containing rods had crystallinity in their structure. In conclusions, it is feasible to combine PLGA 80/20 and DS by using melt extrusion. Released DS concentrations reached local therapeutic levels, but the release profile was complex and therapeutic levels were not reached all the time.

Critical Exponents and Self-Similarity for Sol-Gel Transition in Aqueous Alginate Systems Induced by in Situ Release of Calcium Cations

The sol-gel transition in aqueous alginate systems induced by in situ released calcium cations was monitored with rheology methods. Four alginate samples with different molecular weights and M/G ratios were used over the concentration C(Alg) of 2 approximately 6 wt % with different mole ratios f of Ca2+ to the alginate repeat unit. The scaling for the zero shear viscosity eta(0) before the gel point and the equilibrium modulus Ge after the gel point was described as eta(0) approximately epsilon(-k) and Ge approximately epsilon(z), respectively, where the relative distance to the gel point f(gel) was epsilon = (/f-f(gel)/)/f(gel). The relaxation critical exponent n was determined with Winter's criterion, and the critical exponents k and z estimated respectively from independent measurements of eta(0) and Ge gave n from z/(k + z). Before the gel point, the storage and loss moduli G' and G'' obtained at various epsilon can be superposed fairly well to form the master curve. The critical exponents n, k, and z were also evaluated from the shift factors and the structure self-similarity was found in the critical gel. The critical exponents evaluated with different methods agreed well with each other, suggesting two categories of the gelation as growth and cross-link. For the alginate with lower molecular weight, the critical exponents were almost independent of alginate concentration and close to the percolation prediction. For the alginate with higher molecular weight, the critical exponents, however, changed with alginate sample and concentration. The relative alginate concentration C(Alg)/C(Alg)* was found to serve as a criterion to divide these two transitions.

Structural relaxation and rheological response of a driven amorphous system

The interplay between the structural relaxation and the rheological response of a simple amorphous system {a 80:20 binary Lennard-Jones mixture [W. Kob and H. C. Andersen, Phys. Rev. Lett. 73, 1376 (1994)]} is studied via molecular dynamics simulations. In the quiescent state, the model is well known for its sluggish dynamics and a two step relaxation of correlation functions at low temperatures. An ideal glass transition temperature of Tc=0.435 has been identified in the previous studies via the analysis of the system's dynamics in the framework of the mode coupling theory of the glass transition [W. Kob and H. C. Andersen, Phys. Rev. E 51, 4626 (1995)]. In the present work, we focus on the question whether a signature of this ideal glass transition can also be found in the case where the system's dynamics is driven by a shear motion. Indeed, the following distinction in the structural relaxation is found: In the supercooled state, the structural relaxation is dominated by the shear at relatively high shear rates gamma, whereas at sufficiently low gamma the (shear-independent) equilibrium relaxation is recovered. In contrast to this, the structural relaxation of a glass is always driven by shear. This distinct behavior of the correlation functions is also reflected in the rheological response. In the supercooled state, the shear viscosity eta decreases with increasing shear rate (shear thinning) at high shear rates, but then converges toward a constant as the gamma is decreased below a (temperature-dependent) threshold value. Below Tc, on the other hand, the shear viscosity grows as eta proportional, etax 1/gamma, suggesting a divergence at gamma=0. Thus, within the accessible observation time window, a transition toward a nonergodic state seems to occur in the driven glass as the driving force approaches zero. As to the flow curves (stress versus shear rate), a plateau forms at low shear rates in the glassy phase. A consequence of this stress plateau for Poiseuille-type flows is demonstrated.

Bulk viscosity of high-temperature QCD

We compute the bulk viscosity zeta of high-temperature QCD to leading order in powers of the running coupling alpha_s(T). We find that it is negligible compared to shear viscosity eta for any alpha_s that might reasonably be considered small. The physics of bulk viscosity in QCD is a bit different than in scalar phi^4 theory. In particular, unlike in scalar theory, we find that an old, crude estimate of zeta as 15 ((1/3)-v_s^2)^2 eta gives the correct order of magnitude, where v_s is the speed of sound. We also find that leading-log expansions of our result for zeta are not accurate except at very small coupling.

Attenuation of acoustic normal modes in piezoelectric plates loaded by viscous liquids

Attenuation cac versus viscosity eta of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/lamda = 0.6 - 2.5. Two modes with an optimal combination of sensitivity (0.1 dB/mm x cP), insertion loss (<35 dB), and stop-band rejection (>15 dB) are found in liquid-loaded 128 degrees Y,X + 90 degrees - LiNbO3 with h/lamda = 1.67. Both modes are suited for viscosity measurements and other sensing tasks in viscous liquids. They have predominantly longitudinal displacement and large propagation velocity v(n), about 15,000 m/s.

Origin of Enhanced Crystal Growth Kinetics near Tg Probed with Indomethacin Polymorphs

Using three crystal polymorphs of indomethacin (IMC), we tested two interpretations of the enhanced crystal growth kinetics near the glass transition temperature Tg. This enhancement refers to the stronger temperature dependence of liquid viscosity eta than crystal growth rate (corrected for thermodynamic driving force). This enhancement is attributed in the first interpretation to an increase of the number of preferred interfacial growth sites with decreasing temperature and, in the second interpretation, to the breakdown of the Stokes-Einstein relation in deeply supercooled liquids. We measured the growth rates of the IMC polymorphs (alpha, gamma, and delta) from Tg + 9 K (Tg = 314 K) to near the respective melting points. From Tg + 19 K to Tg + 69 K, the growth rates of the polymorphs changed by 10(4) fold but displayed the same temperature dependence (eta-0.78) after corrections for thermodynamic driving forces. These results argue for a liquid-state origin of the enhanced growth kinetics. Below ca. Tg + 19 K, delta IMC continued to grow in the same spherulite morphology but alpha and gamma IMC grew in different, fiberlike morphologies and, if measured consistently, at faster rates. We conclude that the liquid dynamics of IMC controls its crystal growth kinetics over a wide range of temperatures but changes of growth morphologies near Tg also lead to apparent acceleration of growth of certain polymorphs. This work also extended a previous study of D-sorbitol to lower temperatures to enable a broader analysis of crystal growth kinetics of organic molecules near Tg.

Synthesis of Polyurethane Acrylate and Application to Ultraviolet-Curable Pressure-Sensitive Adhesive

ABSTRACT Synthesis of polyurethane acrylates (PUA) using dimer acid-based polyester diol and hydrogenated castor oil (HCO) and preparations of the UV-curable pressure-sensitive adhesive (PSA) were reported. The effect of hydroxyl from dimer acid polyester diol/hydroxyl from HCO ratio (OHDiol/OHHCO), hydroxyl from both HCO and DAPD/2-hydroxyethyl acrylate ratio (OHPolyol/HEA), and tackifying resin/PUA ratio on the dynamic viscoelastic properties and performance of UV-cured PSA were investigated. The study revealed that, with OHDiol/OHHCO and OHPolyol/HEA increased, the storage modulus (G′), the loss modulus (G″), and complex viscosity (Eta*) of UV-cured PSA increased, and so did the corresponding holding power (HP). Peeling strength, however, decreased. As increasing the tackifying resin/PUA ratio, G′, G″ and Eta* decreased, and so did HP, whereas the peeling strength increased. Catalysts affected the dynamic properties and the performance of PSA. In contrast with PSA corresponding to dibutyltin dilaurate (DBTDL), the PSA corresponding to organic bismuth (OB) had higher dynamic modulus, complex viscosity, and holding power, but lower peeling strength.

Critical behavior of 2,6-dimethylpyridine-water: Measurements of specific heat, dynamic light scattering, and shear viscosity

The specific heat C(p) at constant pressure, the shear viscosity eta(s), and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature T(c). The amplitude of the fluctuation correlation length xi(0)=(0.198+/-0.004) nm has been derived from a combined evaluation of the eta(s) and D data. This value is in reasonable agreement with the one obtained from the amplitude A(+)=(0.26+/-0.01) J(g K) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Gamma of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Gamma=(25+/-1)x10(9) s(-1). No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity eta(b), resulting from the treatment of eta(s) and D data, with the viscosity eta(s)(nu=0) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5-130 MHz using a novel shear impedance spectrometer.

Macro- and microdefinitions of fragility of hydrogen-bonded glass-forming liquids

In the present paper, the nature of the fragility of liquids with a developed H-bond network is investigated. It is shown that the effective activation energy of the shear viscosity eta and the fragility parameter defined as m=d log eta/d(Tg/T)|t=t+g are immediately connected with the average number nH(T) of the H-bond per molecule. The consistency of the macroscopic (m) and the microscopic [M=d(u(2)(0)/<u(-->2)>loc)/d(Tg/T)|T=T+8, where <u-->2>loc=<u-->2>anharm - <u-->2>harm] definitions of the fragility is established.

The influence of potential softness on the transport coefficients of simple fluids

This study explores the effects of interaction softness on the transport properties of simple fluids. The transport coefficients of soft-sphere fluids in which the particles interact via the potential, phi(r)=epsilon(rsigma)(-n), with n in the range from 6 to 1152, have been calculated by molecular-dynamics computer simulation. The self-diffusion coefficient D shear viscosity eta(s), bulk viscosity eta(b), and thermal conductivity lambda were computed over a wide packing fraction range. It was found that the Batschinski-Hildebrand expressions, in which D, eta(s) (-1), eta(b) (-1), and lambda(-1) are assumed to have a linear dependence on the molar volume, represent the data quite well for all n, although least well for the thermal conductivity. The density for which, on extrapolation, each of these quantities is zero, increases with the softness of the interaction (or approximately n(-1)), suggesting that the effective hard-sphere diameter decreases with increasing softness in the small n limit. This treatment leads to simple empirical formulas for the effect of density and n on the effective hard-sphere diameter and packing fraction (in an intermediate range) and the four transport coefficients of these fluids.

Effects of L. F04, the active fraction ofLycopus lucidus, on erythrocytes rheological property

To study the effects of L.F04, the active fraction of Lycopus lucidus, on erythrocytes rheological property so as to investigate its mechanism in promoting blood circulation and removing blood stasis. The effects of L.F04 (used for treatment for 10 days in different dosages) on deformability, aggregation and membrane liquidity of erythrocytes (MLE) as well as whole blood apparent viscosity (eta(b)) were examined on the basis of rat model of blood-stasis syndrome induced by venous injection of high molecular weight dextran. As compared with the normal control group, the model group's RBC deformability and MLE were lower, and the aggregation of erythrocytes and eta(b) were higher. Compared with the model group, both L.F04 0.612 g/kg and 0.306 g/kg showed significant effect in improving deformability and inhibiting aggregation of red blood cells (RBC) and reducing blood viscosity. The trend of improving MLE was also shown. L.F04 could significantly improve the abnormal rheological property of erythrocytes.

An Interstitialcy Theory of Structural Relaxation and Related Viscous Flow of Glasses

A theory of isothermal structural relaxation and creep of glasses below the glass transition temperature is given. According to the interstitialcy theory, the supercooled liquid state does not exist below a Kauzmann "pseudocritical" temperature T(k), which lies above the temperature T(K), commonly called the "Kauzmann temperature." Structural relaxation is simply a reduction with time of the interstitialcy concentration to the crystalline state for T<T(k), and to the metastable supercooled liquid state for T>T(k). The predicted viscosity eta is universal, given by eta=eta(0) + eta(T)t, in agreement with experiment. eta is continuous in T, with eta discontinuous at T(k) but linear in 1/T above and below T(k). The dependence of eta on the shear modulus directly connects kinetic and thermodynamic properties of glasses and liquids.

Damping of Acoustic Waves in Dilute Polymer Solutions

The shear viscosity eta_s(w) of dilute polymer solutions (of flexible coils) has been classically measured and interpreted in terms of the Zimm modes. We point out that the longitudinal viscosity eta_l(w) is the sum of two components eta_l=4*eta_s/3+eta_p, where eta_p is due to an effect of pressure on the coil size. We discuss eta_p for a crude model involving a dependence of both the Kuhn length a and the Flory parameter chi on pressure. We find that eta_p is comparable to eta_s for good solvent conditions, but that eta_p should dominate over eta_s near the theta point.

Viscoelastic characterizations of acellular dermal matrix (ADM) preparations for use as injectable implants

Viscoelastic characteristics of acellular dermal matrix (ADM) preparations with various additives were analyzed with creep curves, stress-strain relationships, and the storage modulus with reference to those of ADM preparations crosslinked with glutaraldehyde. Creep curves for all ADM preparations were determined to comply with the Kelvin-Voigt model. The stress-strain plots of all ADM preparations compared were described as linear. The storage modulus of all ADM preparations was maintained at a nearly constant level throughout the range of oscillating frequencies applied. ADM preparations crosslinked with glutaraldehyde showed that both Young's modulus (E) for the spring part and retardation time (tau) in the Kelvin-Voigt model, and hence viscosity (eta) for the liquid part, increased with an increasing concentration of glutaraldehyde. Higher Young's modulus and viscosity and a greater extent of the "solid" response of ADM preparations crosslinked with glutaraldehyde might have been responsible for the longer persistence that was demonstrated after implantation. The increase in ADM concentration and the addition of various additives to ADM preparations, including alpha-hydroxy acid (citric acid, lactic acid, and glycolic acid) and hyaluronic acid, resulted in similar effects on the viscoelastic characteristics of the ADM preparations, but they were less efficacious than those crosslinked with glutaraldehyde. Among them, increasing ADM concentration to >200 mg/mL and addition of glycolic acid at a concentration of >2% improved the viscoelastic characteristics of the resulting ADM preparations so that their level of persistence was closer to that of material crosslinked with glutaraldehyde. On the contrary, the influence on viscoelastic characteristics of adding PVP greatly differed from that of hyaluronic acid and was only apparent when adding concentrations of PVP of >10%. Similarly, viscoelastic characteristics of the ADM preparations examined were also so sensitive to temperature that the persistence of ADM preparations after implantation at body temperature would deteriorate.