Conductivity and dielectric relaxation of Li salt in poly(ethylene oxide) and epoxidized natural rubber polymer electrolytes

Two types of polymer electrolytes were studied: poly(ethylene oxide) (PEO) and epoxidized natural rubber (ENR) both filled with lithium perchlorate. Universal dielectric behavior and impedance relaxation were investigated at room temperature over a wide range of salt concentration. Complex impedance plots exhibit one semicircle in some cases (PEO polymer electrolytes) with an extended spike at low frequencies. This implies a double layer capacity strongly influences conductivity at low frequencies. In the ENR–salt system, semicircles can be obtained only at very high concentrations. This points towards stable resistor dominated networks only develop at very high salt concentrations for this system. Centers of the semicircles lie below real axis indicating non-Debye dielectric relaxation. The relaxation peak broadens and shifts to higher frequencies with increasing salt content. It indicates that the relaxation time of polarization relaxations decreases with ascending salt content. Relaxations occur at extremely low salt concentrations in PEO and only at very high salt concentrations in ENR. Hence, conductivity of ENR–salt is one to two orders of magnitude lower as for PEO–salt.     

表面张力对PEO稀溶液粘度行为的影响

测定了不同分子量聚氧化乙烯 (PEO)在水和苯溶剂中的粘度 ,发现在低浓度区PEO水溶液的比浓粘度出现负偏离 ,PEO苯溶液比浓粘度与浓度之间依旧满足线性关系 .表面张力测定结果表明 ,PEO分子显著降低了水的表面张力 ,而苯的表面张力则不受影响 .PEO水溶液和纯溶剂水表面张力的不同干扰了高分子溶液和溶剂在粘度计中流过时间的测量 ,导致低浓度区PEO水溶液比浓粘度出现负偏离 .利用PEO水溶液和水表面张力测定结果 ,结合乌式粘度计的几何尺寸 ,定量分析了PEO水溶液和纯溶剂水表面张力的差异对粘度测量结果的影响 ,计算结果与实验结果基本相符 .如果用PEO水溶液流过时间对浓度作图的外推值t0 计算相对粘度 ,可以完全消除PEO水溶液和水表面张力差异对粘度测量的影响     

A Rheological Study of Xanthan Polymer for Enhanced Oil Recovery

This study explored the potential application of xanthan gum as a polymer-flooding agent for oil recovery applications in a specific Devonian oil field. Rheological measurements using oscillatory and steady shear were carried out to examine the change in shear viscosity when the polymer was applied under reservoir conditions. The xanthan rheological properties were described by the Herschel–Bulkley and Ostwald models to characterize its non-Newtonian behavior. As expected, the results showed that higher xanthan concentrations raised the polymer viscosity and increased the degree of shear thinning. Addition of alkalis caused the viscosity of the xanthan solutions to decrease, but they maintained their shear-thinning properties. Polymer solutions in typical oil field brine increased in viscosity by ca. 400% for 720 hours storage time. On the other hand, as expected, the solutions lost their viscosity gradually with increasing temperature. However, at reservoir temperature (68°C), the polymer solutions kept more than 60% of their initial viscosity. In oscillatory deformation tests it was observed that all the measured viscoelastic properties were influenced by temperature and confirmed that xanthan solution behaved as a weak-gel. An order-disorder transition exists within the xanthan-brine solutions which responds to changes in solution concentration, temperature and alkalis.     

Ultrasonic-assisted de-agglomeration and power draw characterization of silica nanoparticles

Breakage of nanoparticle cluster require high-intensity devices for stable and uniform distribution of aggregates. The ultra-sonication process is a high energy-intensive technique that produces cavitation effect to break the aggregates. In the present study, ultra-sonication is used for the de-agglomeration of fumed silica nanoparticles in low to high viscosity liquids. Water- and glycerol-based dispersion has been investigated at different solid loadings (up to 10 wt% for water-based dispersion and 5 wt% in glycerol-based dispersion) and viscosity of continuous phase (1–100 mPa.s). Breakup mechanism and kinetics have been studied at optimized operating conditions and no significant effect is found at different solid loadings on breakup mechanism. Particle size measurements are reported and found that volume of fine generation increased with an increase in sonication time. Further, it is observed that the stability of dispersion in the liquid is very high even at high concentration of solid used. Larger agglomerates are found at high viscosity of continuous phase and a lag is also observed for 100 mPa.s glycerol solution even at low solid loading (1 wt%). From, rheological characterizations it is found that the behavior of dispersed solution changed with time, temperature and solid loading. Erosion is found to be the breakup mechanism and further, validated with scattering light characterization. Furthermore, power draw increased with an increase in the viscosity of continuous phase, however, no significant effect of solid loading is observed. It is also observed that process is more energy-efficient at higher solid loading as the volume of fine produced is more as compared to low solid loading. Therefore, it can be concluded that the stable and uniform dispersion of nanoparticles can be achieved using an ultra-sonication device at high solid loading in viscous liquids.     

High Pressure High Temperature Dynamic Rheometry of Sulfonated Polyacrylamide Solutions in Electrolyte Media as Used for Oil Recovery Applications

Sulfonated polyacrylamide (SPAA) solutions were prepared and the effects of pressure, polymer concentration, and water temperature, pH and salinity on their rheological behavior were investigated using a concentric cylinder dynamic rheometer equipped with a high pressure cell. According to the rheological flow curves the shear stress of SPAA solutions increased less than in proportion to their shear rates; that is, a shear thinning effect occurred. For polymer solutions containing 15,000 ppm of SPAA, shear viscosity, and stress were nearly insensitive to pressure. However, the shear viscosity and stress of SPAA solutions were affected by temperature and this effect was more evident at lower pressure. The flow curves indicated the shear viscosity and stress of the samples increased with increasing SPAA concentration and pH of the water, but were decreased with increasing water salinity and temperature.     

Structural and rheological properties of chitosan semi-interpenetrated networks

The local structure and the viscoelastic properties of semi-interpenetrated biopolymer networks based on cross-linked chitosan and poly(ethylene oxide) (PEO) were investigated by Small Angle Neutron Scattering and rheological measurements. The specific viscosity and the entanglement concentration of chitosan were first determined, respectively, by capillary viscosimetry and steady-state shear rheology experiments performed at different polymer concentrations. Mechanical spectroscopy was then used to study the gelation process of chitosan/PEO semi-interpenetrated networks. By fitting the frequency dependence of the elastic and loss moduli with extended relations of relaxation shear modulus around the sol-gel transition, it was shown that the addition of PEO chains had a significant effect on the viscoelastic properties of aqueous chitosan networks but no effect on the gelation time. The improvement of mechanical properties was in accordance with the correlation length decrease deduced from Small Angle Neutron Scattering experiments.     

Rheological and Mechanical Characterization of Multi-Walled Carbon Nanotubes/Polypropylene Nanocomposites

The rheology and morphology of multi-walled carbon nanotube (MWNT)/polypropylene (PP) nanocomposites prepared via melt blending was investigated. The minor phase content of MWNT varied between 0.25 and 8 wt%. From morphological studies using a scanning electron microscopy technique a good dispersion of carbon nanotubes in the PP matrix was observed. The rheological studies were performed by a capillary rheometer, and mechanical properties of the nanocomposites were studied using a tensile and flexural tester. Both PP and its nanocomposites showed non-Newtonian behavior. At low shear rates the addition of MWNT content causes an increase in viscosity; however, viscosity is less sensitive to addition of MWNT content at higher shear rates. Flow activation energy for the nanocomposites was calculated using an Arrhenius type equation. From this calculation it was concluded that the temperature sensitivity of nanocomposites was increased by increasing of nanotube content. An increase in tensile and flexural moduli and Izod impact strength was also observed by increasing the MWNT content. From rheological and mechanical tests it was concluded that the mechanical and rheological percolation threshold is at 1.5 wt%.     

Rheological Behavior of Some Cationic Polyelectrolytes

The rheological behavior of some cationic polyelectrolytes in aqueous solution is presented. The polyelectrolytes under study consist of polycations that have positive charges (N,N-dimethyl-2-hydroxypropylenammonium chloride) located along the main chain with or without nonpolar side chains (PCA₅D₁ and PCA₅, respectively). This investigation mainly considers the influence of oscillation frequency and temperature on their rheological behavior in salt-free aqueous solution at three polymer concentrations (c_p = 2%, 4%, and 6%) as well as in the presence of low molar mass salt (NaCl). The results indicate the main effect of these parameters was to modify the hydrophobic interactions between the side nonpolar groups of the modified polyelectrolyte. The comparison between the complex viscosity values, at the same polymer concentration, c_p = 4%, for PCA₅D₁ and PCA₅ shows higher values in the whole interval of temperatures under study and a pseudoplastic behavior at temperatures greater than 50°C for the former system.     

Viscosity and dispersion state of magnetic suspensions

We investigate the viscosity behavior of a magnetic suspension in which magnetic particles are dispersed in a mixture of polyacrylic liquids. The size of magnetite particles is nearly 300 nm and the volume fraction of the magnetic particles is in the range of 0.003-0.03. The particle concentration dependence of the suspension viscosity yields the intrinsic viscosity [η], which varies from 25.6 at 5 s⁻¹ to 5.1 at 400 s⁻¹. The yield stress and the infinite shear viscosity of the suspension increase non-linearly as the particle concentration ? increases. We examine the effect of process conditions such as milling time and amount of dispersant on the viscosity behavior of the suspension. As milling time elapses, yield stress and low shear viscosity decrease and then reach constant values while the infinite shear viscosity remains constant. When oleic acid is added as a dispersant, the yield stress and low shear viscosity of the suspension show minimum values as the amount of oleic acid increases. These results agree with experimental results of sedimentation tests, which enable us to estimate the aggregate size of magnetic suspension. The yield stress and the low shear viscosity of the magnetic suspension are found to be useful in evaluating the dispersion state of the magnetic suspension.     

Mechanical Properties and Flow Behavior of Polymers for Enhanced Oil Recovery

The mechanical properties and flow behavior in porous media of three different polymer systems including a hydrophobically modified acrylamide-based copolymer (HMSPAM), a partially hydrolyzed polyacrylamide (HPAM), and a polysaccharide (xanthan gum) were evaluated to establish their functional differentiation as mobility control agents in enhanced oil recovery (EOR). The rheological properties of the polymers were described by the power-law model to investigate their non-Newtonian behavior. The first normal stress difference (N₁) and Weissenberg number (W_e) were also used to compare their elastic properties. The experimental results showed that, at comparable shear viscosity, HMSPAM exhibited significant elasticity compared to HPAM and xanthan gum. Shear resistance tests indicated that all of the polymers experienced an extra stress when converging into a capillary tube due to the “entrance effect.” Xanthan gum was the most mechanically stable polymer. Moreover, HMSPAM showed the superior reformability which was quantified by the regained viscosity with relaxation time. This could be explained by the rapid re-association of the hydrophobic interactions. Sandpack flood tests indicated that HMSPAM rendered extremely high mobility control ability during polymer flooding suggesting its potential in EOR. However, this polymer also experienced significant retention within the porous media (potential injectivity and plugging problems), which may be attributed to the formation of bulky associative polymer networks. In this work, UV spectrometry was employed to monitor the concentration of the produced polymer solutions and quantify the polymer retention within porous media. This analytical approach offers great reliability and simplicity. It was concluded that the use of a particular polymer system depends on the oil reservoir conditions and the target EOR application.     

Impedance spectra of polymer electrolytes

The authors present a phenomenological view on dielectric relaxation in polymer electrolytes. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The following is based on systems with high molar mass poly(ethylene oxide) (PEO) and epoxidized natural rubber with 25 mol% of epoxide content (ENR-25) filled with lithium perchlorate (LiClO₄). Dielectric properties of these systems have been studied as a function of salt content at room temperature. Additionally, properties of neat low molar mass PEO were studied as function of temperature. Relaxation-coined dielectric behavior rules the system with PEO in the frequency that ranged up to 10⁶ Hz. Imaginary parts of impedance, tangent loss, and electric modulus spectra show distribution of relaxation times. Comparison of tangent loss (tan δ) spectra and imaginary part of electric modulus (M″) spectra reveals that localized motion dominates long-range motion of dipoles in the low-frequency range. However, discrepancy between them decreases with growing salt content. Scaling of tan δ spectra demonstrates that distribution of relaxation times does not depend on salt content in the range of low frequencies. The ENR-25 system exhibits solely relaxation like a macroscopic dipole. In conclusion, the system with PEO is characterized by individual relaxation of well-interacting dipoles, whereas the system based on ENR-25 is coined by immobilized dipoles that lead in the state of high-salt content to the relaxation behavior of a macroscopic dipole.     

Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate

The Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate in dioxane was investigated at different temperatures. The viscosity data were analyzed in terms of Martin's and Fedor's relationships and also generalized in terms of reduced variables. The rheological behavior of cellulose acetate butyrate solutions in the whole range of concentrations is determined by the parameter (K_MC [n]). The temperature dependence of viscosities was expressed by the Arrhenius-Frenkel-Eyring equation and the activation energy of viscous flow of polymer solutions (ΔGv) was calculated. ΔGv increases with concentration of polymer solution and is independent of temperature. The preexponential factor, A, related to activation entropy, decreases with concentration of polymer solution. The thermodynamic parameter of viscous flow for cellulose acetate butyrate (CAB)-dioxane solutions is indicative of moderately stiff structure for CAB in solutions.     

The fusion of ethylene oxide polymers

Summary Calorimetric measurements by DSC technique have been made in pure polyethylene glycol (PEG) and oxide (PEO) polymers having a very wide molecular-weight range (from 600 to 4000 000) and in PEO (MW 600 000)-NaSCN complexes. It was found that the melting temperature increases with increasing molecular weight, ranging from 293 K in the polymer with MW=600 to 340 K in that with MW=4000 000. The behaviour of the heats of fusion with increasing molecular weight reflects the trend expected in systems, in which the increase of the main chain length produces a relevant growth of the degree of crystallinity. A distinct maximum of the heat of fusion has been found at about MW=10000, this result being an evidence of the high amount of crystalline regions building up the structure of that system. The dependence of the melting temperature on molecular weight has been nicely accounted for by using the expression of Flory, deduced from the statistical theory of polymers having the most probable molecular-weight distribution. The addition of sodium thiocyanate to PEO modifies the morphology of the host polymer and, for salt concentrations higher than 0.03 molar fraction, gives rise to the formation of a PEO-salt crystalline complex characterized by a high melting temperature. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.     

Study on Steady Shear Rheological Behavior of Concentrated Suspensions of Sulfonated Polyacrylamide/Na-Montmorillonite Nanoparticles

Concentrated suspensions of sulfonated polyacrylamide (SPA)/Na⁺-montmorillonite (Na-MMT) were prepared and their stability and steady shear rheological properties were described as a function of nanoparticle and polymer concentration and temperature. The results showed that the Na-MMT nanoparticles suspensions were stable in the absence and presence of SPA and no sedimentation was seen. The Z-average particle sizes for the SPA/Na-MMT suspensions increased in the presence of SPA. Rheological investigations showed that the SPA solutions and SPA/Na-MMT suspensions displayed non-Newtonian behavior in almost the whole range of shear rate. All the suspensions exhibited a shear-thinning flow character as shear rate increased. The flow curves indicated the shear viscosity and stress of the samples were decreased with increasing nanoparticles concentration up to 1.5 wt%, but for Na-MMT loading greater than 1.5 wt% there was an increase in shear viscosity and stress of the suspensions. Increasing of SPA concentration had more effect on increasing the rheological properties of SPA/Na-MMT suspensions than increasing of nanoclay content. Shear viscosity and stress of the suspensions increased with increasing SPA concentration and decreased with increasing temperature from 50°C to 70°C.     

分散介质和温度对纳米二氧化硅胶体剪切增稠行为的影响

对分散介质和温度对纳米二氧化硅胶体剪切增稠行为的影响进行了系统研究. 用四种液体分散介质(乙二醇, 聚乙二醇400, 丙二醇, 聚丙二醇400)制备的纳米二氧化硅胶体表现出不同的连续剪切增稠或者跳变剪切增稠行为. 温度上升降低了分散介质的黏度, 进而降低了胶体的表观黏度. 剪切增稠的临界黏度与温度的关系符合“Arrhenius”公式的描述. 胶体黏度与分散介质黏度的比值用来归一化不同温度下的稳态剪切流变曲线. 在低剪切速率的剪切变稀阶段, 剪切变稀现象与分散介质黏度没有明显相关性, 而与分散介质的化学性质密切相关. 在高剪切速率的剪切增稠阶段, 分散介质黏度越高, 胶体剪切增稠现象越强烈.     

Improvement in properties of coal water slurry by combined use of new additive and ultrasonic irradiation

Coal water slurry (CWS) was prepared with a newly developed additive from naphthalene oil. The effects of ultrasonic irradiation on coal particle size distribution (PSD), adsorption behavior of additive in coal particles and the characteristics of CWS were investigated. Results showed that ultrasonic irradiation led to a higher proportion of fine coal in CWS and increased the saturated adsorption amount of additive in coal particles. In addition, the rheological behavior and static stability of CWS irradiated by ultrasonic wave were remarkably improved. The changes on viscosity of CWS containing 1% and 2% additive are qualitatively different with the increasing sonication time studied. The reason for the different effect of sonication time on CWS viscosity is presented in this study.     

Rheology of nanosized hairy grain suspensions

Suspensions of nanosized hairy grains have been prepared by grafting long polydimethylsiloxane chains (molecular weight ) onto silica particles (radius ), dispersed into a good solvent of PDMS. Depending on the particle volume fraction, different rheological behaviors are observed. In the very dilute regime, the suspensions are perfectly stable and the particles behave almost as hard spheres: flow penetration inside the corona is then very weak. When the particle volume fraction goes to the close packing volume fraction, the suspension viscosity does not diverge as for hard spheres due to the increase of flow penetration inside the corona and to corona entanglements. The particles have then the same behavior as polymer stars having an intermediate number of arms (). Finally, in the concentrated regime (), the suspensions form irreversible gels. We shown that this unexpected gelation phenomenon is related to the presence of the silica cores: grafted PDMS chains can adsorb onto different particles and form irreversible bonds between the cores. The viscosity and elastic modulus evolutions during gelation are well described by the scalar percolation model of sol-gel transition. Received 23 March 1998     

Mechanism of Electrospinning for Poly(amic acid)/Polyacrylonitrile Fiber Fabrication

A poly(amic acid) (PAA) solution in xylene was prepared for electrospinning in order to fabricate fibers. However, jet breaking occurred at the point of the occurrence of whipping instability, resulting in forming micro-particles. This was an exceptional jet behavior compared with the general electro-spraying process that occurs directly from the surface of the polymer droplet. It is important to understand the mechanism of electrospinning and the instability of PAA in order to form fibers for mat deposition. Thus, the behavior of the jet breaking was clearly observed by a high-speed camera and the dynamic behavior of the jet was explored by an image analysis technique. Furthermore, polyacrylonitrile (PAN) was added to the PAA/xylene solution with various concentrations to change the elongation viscosity. Uniform diameter fibers were obtained by increasing the content of PAN to the level that the drag force between the polymer chains increased enough to overcome the drawing force. As a result the optimum content ratio of the PAA/PAN mixed solution to obtain the desired fiber spinning and deposition was determined as being 5:5.