WAXS studies of global molecular orientation induced in nematic liquid crystals by simple shear flow

Global molecular orientation function coefficients for the nematic liquid crystal 4-cyano 4- n -pentylbiphenyl (5CB) in shear flow are presented, being extracted from 2-dimensional Wide-Angle X-ray Scattering data. A linear increase in orientation parameter P2 is observed with a logarithmic increase in shear rate. It is proposed that this arises from an increased number of LC directors aligning to the shear axis. Upon cessation of shear flow, the anisotropy is seen to relax away completely, over a time scale which is inversely proportional to the previously applied shear rate.     

Analysis of electroosmotic flow of power-law fluids in a slit microchannel

Electroosmotic flow of power-law fluids in a slit channel is analyzed. The governing equations including the linearized Poisson-Boltzmann equation, the Cauchy momentum equation, and the continuity equation are solved to seek analytical expressions for the shear stress, dynamic viscosity, and velocity distribution. Specifically, exact solutions of the velocity distributions are explicitly found for several special values of the flow behavior index. Furthermore, with the implementation of an approximate scheme for the hyperbolic cosine function, approximate solutions of the velocity distributions are obtained. In addition, a generalized Smoluchowski velocity is introduced by taking into account contributions due to the finite thickness of the electric double layer and the flow behavior index of power-law fluids. Calculations are performed to examine the effects of kappaH, flow behavior index, double layer thickness, and applied electric field on the shear stress, dynamic viscosity, velocity distribution, and average velocity/flow rate of the electroosmotic flow of power-law fluids.     

Viscosity studies of poly(DL‐lactic acid) in supercritical CO2

The effect of supercritical CO₂ on the viscosity and activation energy to viscous flow of P_DLLA is investigated, using a high pressure parallel plate rheometer, over a range of temperatures (50–140 °C) and pressures (5–12 MPa). The Cross model is fitted to the data to enable calculation of the zero shear viscosity and critical shear rate. A significant decrease in the viscosity is observed on increasing both variables; however, at high temperatures, the pressure effect becomes negligible. An increase in the critical shear rate is also observed on raising the pressure, indicative of a reduction in the relaxation time of the polymer. Manipulation of the Arrhenius equation shows a reduction in the activation energy to viscous flow as the pressure is increased. Together, these results show that the melt processing temperature of P_DLLA can be reduced in the presence of supercritical and high pressure CO₂. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Rheological Study on Polypropylene/Cycloolefin Copolymer Blends

Summary: Polypropylene, cycloolefin copolymer and their blends were characterized by means of melt flow analysis and capillary rheometry at temperatures between 190 and 230 °C in order to shed more light on COC fiber formation obtained in injection molding process. Melt viscosity and its activation energy as functions of blend composition show negative deviation from the expected additivity (Negative Deviating Blends). The COC/PP viscosity ratio increases with shear rate, but decreases with temperature. High temperature, low viscosity ratio and high shear rate seem to be favorable for fiber formation. Glass transition (from the reversible heat flow curve of modulated DSC) of dumbbell specimens produced by injection molding at 230 °C with COC minor component was 2–4 °C higher than that of grinded pellets obtained from mixing at 190 °C.     

Linear viscoelastic behaviors of polybutene-1 melts with various structure parameters

The effects of weight-average molecular(Mw), molecular weight distribution(MWD), and isotacticity on the linear viscoelastic behavior of polybutene-1 melts are studied. It is observed that the linear viscoelastic region becomes slightly narrower with increasing frequency. In frequency sweeps, the transition of the polymer melts flow from Newtonian flow to power-law flow can be observed. The melts with higher Mw and/or broader MWD, as well as higher isotacticity exhibit higher complex viscosity, zero shear viscosity, viscoelasticity moduli, relaxation modulus, broader transition zone, while lower critical shear rate, non-Newtonian index, and the frequency at which elasticity begins to play an important role. The relationship of zero shear viscosity on Mw has been established, which agrees with the classical power law. Furthermore, it is found that the cross-over frequency decreases with increasing Mw and the cross-over modulus increases with narrowing MWD.     

On the flow characteristics of highly concentrated oil-in-water emulsions

The laminar flow characteristics of oil-in-water emulsions with oil concentrations greater than 59% by volume have been investigated experimentally. Up to an oil concentration of 65% by volume, the emulsions exhibited power-law non-newtonian behaviour. At a higher oil concentration, of 72.21% by volume, a dramatic change in the flow behaviour of the emulsion was observed. The flow curve, i.e. shear stress vs. shear rate plot on a log-log scale, clearly exhibited the presence of a yield-stress.The rheological data on the emulsions were used to correlate the laminar pipeline transport data on the same emulsions. For power-law emulsions, values of the drop in pipeline pressure could be accurately predicted from simple rheological measurements. For a yield-stress emulsion, the experimental pipeline data deviated from the predicted values especially at low values of shear stress.     

Rheology-modulated alterations in electro-magneto-hydrodynamic flows in a narrow cylindrical capillary: Contrasting trends in high and low surface charge limits

We investigate electrokinetic transport of power-law fluids in a narrow cylindrical capillary in the presence of a transverse magnetic field. The governing equations including the full Poisson-Boltzmann equation and the Cauchy momentum equation with power-law constitutive behavior are solved numerically, without being restrictive to low surface potential limits. The influence of the power-law index, wall zeta potential, relative strength of electromagnetic force over viscous force (as represented by the Hartmann number), and the lateral electric field strength on the variation of the volumetric flow rate is analyzed. Our results reveal a significant augmentation in the net-throughput beyond the traditionally explored low surface-charge limits, especially for shear-thinning fluids, defying the established notions. These fundamental theoretical premises may act as essential precursors towards developing deeper insights on fluidic transport bio-nanopores under electro-magneto- hydrodynamic influences.     

水溶性聚酯浓溶液的流变特性

研究了由对苯二甲酸二甲酯、间苯二甲酸、间苯二甲酸二甲酯 5 磺酸钠与乙二醇等共缩聚合成的PET型水溶性聚酯浓水溶液 (质量浓度 3 0 % )的流变特性 .研究表明 ,溶液的表观粘度随切变速率的变化规律呈现一定的切力增稠特征 ,流动指数范围为 1 0 4～ 1 2 0之间 ;其lgηa τ曲线呈线性 ,零切粘度值为 1 5 8～3 5 2cP ,随分子量、分子结构和温度而异 ,其中分子链中间苯二甲酸乙二醇酯 5 磺酸钠链节含量对溶液粘度影响较大 ;粘流活化能因分子结构和切变速率而变 ,其值范围为 1 2 0～ 2 3 9kJ/mol.     

What is the flow activation volume of entangled polymer melts?

We evaluate the flow activation volume in polymer melts of isotactic polypropylene and atactic polystyrene with step-shear experiments at different melt temperatures. The melt is initially sheared with constant shear rate until the attainment of a melt state with nearly constant viscosity. Perturbations to this experiment, involving shear steps in short-time intervals with decreasing rates, are induced next. Measurements of the shear stress value at each shear rate step allow the evaluation of an experimental (apparent) flow activation volume. The true flow activation volume is evaluated by extrapolating the experimental data to infinite shear stress values. The value obtained is larger than the physical volume of the chain and agrees with the volume of a tube confining chains with a molecular weight between M _n and M _w. Besides supporting the validity of tube model, experiments based on this protocol may be used on model polymer samples, in composites with nanoparticles and in polymer blends to access the validity of mechanisms considered by flow models.     

Flow curves of an adsorbed protein layer at the saliva-air interface

At the air-liquid interface of human saliva a protein layer is adsorbed. An apparatus is described with which a flow curve of this layer was measured. In the majority of samples the viscosity of the surface layer changed gradually and could be described by a power-law dependence on the shear rate. The zero-shear viscosity was 1–100 MPa·s. In some saliva samples a sharp yield point was observed.     

Effect of Coriolis and buoyancy forces on three-dimensional flow of chemically reactive tangent hyperbolic fluid subject to variable viscosity

Thermophoresis effect has wide range of applications in electro-static precipitators and in biology for calculating single biological macro molecules, such as genomic-length DNA and HIV virus in the micro channels. Current study deal with effects of Coriolis and buoyancy forces on the three-dimensional boundary layer flow of tangent hyperbolic fluid with thermo-migration and haphazard motion of nano-sized particles. Arrhenius kind of chemical reaction is taken along an exponentially stretchable surface. The main focus of current exploration is to execute shear thinning nano-liquid flow past an exponentially rotating stretchable surface under the influence of variable viscosity, mixed convection and activation energy. We are motivated to explore the features of three-dimensional shear thinning model combined under the features of mixed convention, variable viscosity, and activation energy. The mathematical model is designed to generate PDEs and converted them into ODEs by employing fractious transformation. The numerical outcomes are exhibited via graphs by employing Bvp4c numerical technique whereas the values of skin friction coefficient are calculated by monopolizing shooting method. Characteristics of the parameters appearing in modeling like the viscosity parameter, power-law index, local Weissenberg number, mix convection parameter, rotation parameter, Prandtl number and chemical reaction parameter are comprehensively analyzed through graphical behavior. The impact of governing parameters on skin friction, heat and mass transfer rates is illustrated through tables. The detail analysis anticipates that the elevation in Weissenberg number and porosity caused decline in velocity. Further, the temperature behaves doppositely analogous to development Prandtl besides the thermophoresis parameter.     

A microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow

Biological cells in vivo typically reside in a dynamic flowing microenvironment with extensive biomechanical and biochemical cues varying in time and space. These dynamic biomechanical and biochemical signals together act to regulate cellular behaviors and functions. Microfluidic technology is an important experimental platform for mimicking extracellular flowing microenvironment in vitro. However, most existing microfluidic chips for generating dynamic shear stress and biochemical signals require expensive, large peripheral pumps and external control systems, unsuitable for being placed inside cell incubators to conduct cell biology experiments. This study has developed a microfluidic generator of dynamic shear stress and biochemical signals based on autonomously oscillatory flow. Further, based on the lumped-parameter and distributed-parameter models of multiscale fluid dynamics, the oscillatory flow field and the concentration field of biochemical factors has been simulated at the cell culture region within the designed microfluidic chip. Using the constructed experimental system, the feasibility of the designed microfluidic chip has been validated by simulating biochemical factors with red dye. The simulation results demonstrate that dynamic shear stress and biochemical signals with adjustable period and amplitude can be generated at the cell culture chamber within the microfluidic chip. The amplitudes of dynamic shear stress and biochemical signals is proportional to the pressure difference and inversely proportional to the flow resistance, while their periods are correlated positively with the flow capacity and the flow resistance. The experimental results reveal the feasibility of the designed microfluidic chip. Conclusively, the proposed microfluidic generator based on autonomously oscillatory flow can generate dynamic shear stress and biochemical signals without peripheral pumps and external control systems. In addition to reducing the experimental cost, due to the tiny volume, it is beneficial to be integrated into cell incubators for cell biology experiments. Thus, the proposed microfluidic chip provides a novel experimental platform for cell biology investigations.     

Evaluation of the melt stabilization performance of hydroxytyrosol (3,4-dihydroxy-phenylethanol) in polypropylene

The use of hydroxytyrosol (3,4-dihydroxy-phenylethanol) as a potential alternative to synthetic compounds in the melt stabilization of polyolefins is considered. Hydroxytyrosol was found to play a role in enhancing the oxidative stability of olive oil, and a similar reduction in polyolefins’ thermo-oxidative degradation during processing is expectable. Rheological tests (melt flow index and viscosity vs. shear rate) showed the good antioxidant performance of hydroxytyrosol during polypropylene processing as was also demonstrated by the increase in apparent activation energies and oxidation induction parameters after addition to polypropylene (0.1 wt%). Results were compared to those obtained for a commercial synthetic phenolic antioxidant and for a natural compound widely used in polymer stabilization (α-tocopherol). The main conclusion of this work is the good performance of hydroxytyrosol in polypropylene stabilization during processing and consequently the possibility of its use in formulations with improved resistance to oxidative degradation.     

表面活性单体DMBAC光聚合动力学研究

采用偶氮二异丁脒盐酸盐(AIBA)作为光引发剂,光引发聚合并研究了阳离子表面活性单体——甲基丙烯酰氧乙基二甲基苄基氯化铵(DMBAC)的均聚及其与丙烯酰胺(AM)共聚合反应的动力学行为,聚合反应均在高于DMBAC临界胶束浓度(CMC)的条件下进行.研究结果显示DMBAC均聚合反应速率与引发剂浓度的0.29次方以及单体浓度的0.89次方成正比,均聚合反应的表观活化能约为13.74 kJ/mo1;DMBAC与AM共聚合反应速率与引发剂浓度的0.82次方以及单体总浓度的0.83次方成正比,共聚合反应的表观活化能约为10.97 kJ/mo1;同时测得DMBAC与AM共聚合反应的单体竞聚率为r₁=0.27(AM)、r₂=2.00(DMBAC),说明AM趋向于形成共聚物,而DMBAC更趋向于形成均聚物.     

氯化聚氯乙烯/氯化聚乙烯共混体的流变性能

<正> 氯化聚氯乙烯(CPVC)是聚氯乙烯(PVC)的氯化产物。它具有优良的耐化学腐蚀、耐油、隔氧等性能。它的使用温度、抗张和弯曲强度与PVC相比有很大提高。这些特性加上氯元素资源丰富、价格便宜,使CPVC可望成为具有吸引力的热塑性工程塑料。有关CPVC共混体系的研究已有不少报道。然而多数的研究范围较窄,尤其是关于CPVC共混体系流变性研究很少见。本文首次广泛研究了不同组成的CPVC/CPE共混     

Critical fluctuations near the consolute point of n-pentanol-nitromethane. An ultrasonic spectrometry, dynamic light scattering, and shear viscosity study

Ultrasonic attenuation spectra, the shear viscosity, and the mutual diffusion coefficient of the n-pentanol-nitromethane mixture of critical composition have been measured at different temperatures near the critical temperature. The noncritical background contribution, proportional to frequency, to the acoustical attenuation-per-wavelength spectra has been determined and subtracted from the total attenuation to yield the critical contribution. When plotted versus the reduced frequency, with the relaxation rate of order-parameter fluctuations from the shear viscosity and diffusion coefficient measurements, the critical part in the sonic attenuation coefficient displays a scaling function which nicely fits to the data for the critical system 3-methylpentane-nitromethane and also to the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. The scaled half-attenuation frequency follows from the experimental data as Omega(1/2)emp= 1.8+/-0.1. The relaxation rate of order-parameter fluctuation shows power-law behavior with the theoretically predicted universal exponent and the extraordinary high amplitude Gammao= (187+/-2) x 10(9) s(-1). The amount of the adiabatic coupling constant /g/= 0.03, as estimated from the amplitude of the critical contribution to the acoustical spectra, is unusually small.     

RHEOLOGICAL BEHAVIOR OF POLYPHENYLENE SULFIDE/POLYAMIDE-66 BLENDS

Blends of polyphenylene sulfide (PPS) containing trace amounts of branching and/orcross-linking in chain and Polyamide-66(PA-66) have been prepared by melt blending. Therheological behavior of PPS/PA-66 blends has been studied by means of capillary rheo-meter, and compared with PPS. The effects of shear rate, shear stress and temperature onthe flow of PPS/PA-66 blends and PPS are discussed. The non-Newtonian indexes andthe activation energies of viscous flow are obtained. The results show that the apparentviscosity of PPS/PA-66 blends is not sensitive to shear rate and stress, but decreases withthe elevation of temperature. On the contrary, the apparent viscosity of the PPS decreasesobviously with the increasing of shear rate and shear stress, but it is increased by theelevation of temperatue.