Rheology of nematic solutions of rodlike chains: Comparison of theory and experiment

The rheological properties of nematic solutions of rodlike polymers are discussed, giving comparisons between theoretical results and certain experiments. Most of the theoretical treatments are based on application of the Leslie-Ericksen constitutive equation. The experimental data considered include distortion in a magnetic field and flow in shearing deformation over a range of shear rate, including rheo-optical observations. In general, it appears that the available theory does not describe a number of the features observed.     

Rheology of active filament solutions

We study the viscoelasticity of an active solution of polar biofilaments and motor proteins. Using a molecular model, we derive the constitutive equations for the stress tensor in the isotropic phase and in phases with liquid crystalline order. The stress relaxation in the various phases is discussed. Contractile activity is responsible for a spectacular difference in the viscoelastic properties on opposite sides of the order-disorder transition.     

Structural evidence of charge renormalization in semi-dilute solutions of highly charged polyelectrolytes

We show experimentally that Manning counterion condensation also leads to a renormalization of the charge density at high concentrations of highly charged, flexible, hydrophilic polyelectrolytes. Investigations by small angle neutron and X-ray scattering of semi-dilute solutions of poly(acrylamide-co-sodium-2-acrylamido-2-methylpropane sulfonate) at different charge densities above the condensation threshold, show that the scattering function is invariant with the charge density. Received 16 June 1998     

Effect of Compatibilizer Content on the Shear and Extensional Rheology of Polypropylene/Clay Nanocomposites

The shear and extensional rheology of polypropylene (PP)/organoclay nanocomposites in the presence of various maleic anhydride grafted polypropylene (PP-g-MA) compatibilizer concentrations were investigated. The PP nanocomposites were prepared via direct melt intercalation in an internal mixer. The structures of the nanocomposites were characterized by X-ray diffraction (XRD) and scanning electron microscopy. It was found that both the compatibilized and uncompatibilized nanocomposites could form an intercalated structure. However, the organoclay particles can disperse well only in the compatibilized systems. The linear viscoelastic properties, including the storage modulus G′ and complex viscosity η* were very sensitive to the microstructure of the nanocomposites. The extensional viscosities of PP nanocomposites were enhanced under a low deformation rate with increasing compatibilizer content and displayed a lack of superposition for different strain rates. It was proposed that the lack of superposition might originate from the formation of a three-dimensional organoclay network, which decreased in its complexity and strength as the deformation rate increased.     

Lattice Boltzmann Simulations of Blood Flow: Non-Newtonian Rheology and Clotting Processes

The numerical simulation of thrombosis in stented aneurysms is an important issue to estimate the efficiency of a stent. In this paper, we consider a Lattice Boltzmann (LB) approach to bloodflow modeling and we implement a non-Newtonian correction in order to reproduce more realistic flow profiles. We obtain a good agreement between simulations and Casson’s model of blood rheology in a simple geometry. Finally we discuss how, by using a passive scalar suspension model with aggregation on top of the LB dynamics, we can describe the clotting processes in the aneurysm     

Precursor Based on Polyborylborazine for BN Fiber: Preparation and Rheology Properties

A polyborylborazine precursor for hexagonal boron nitride (h-BN) was obtained by reaction of boron trichloride with methylamine and its structure was characterized by ¹¹BNMR, ¹³CNMR, ¹HNMR, and FTIR. The results show that the molecular precursor consists of borazine rings connected via a cross-linked network. The results of shear rheological tests indicated that the polymer is capable of being melt spun at moderate temperature, which implies that the structure of the molecular chains of the precursor polymer is branched. The precursor polymer was spun into a continuous polymer fiber in the melt state and then subsequently heat-treated under NH₃ up to 1000°C for conversion into BN fibers. Its surface morphology was observed by scanning electron microscopy (SEM); the fiber was free of defects and cavities.     

高煤级煤岩流变作用的谱学研究

为研究高煤级煤岩在不同流变条件下大分子结构的变化特征,对沁水盆地南部高煤级原生结构煤岩及其变温变压流变实验后的煤岩进行了FTIR和激光拉曼光谱测试和分析。结果表明：不同温压条件形成的不同类型流变煤岩的大分子结构和组成具有明显的差别。煤岩变温变压流变实验(温度300～400 ℃、围压50～100 MPa、应变小于10%和应变速率10-4～10-7·s-1)会使其大分子结构产生改变,并实现化学结构重组：当温度为300或350 ℃,高煤级煤岩易形成脆性流变或脆韧性流变,机械能转化为热能,一些键能较弱的支链和官能团断裂并且结构脱落,产生裂解小分子,其过程以应力降解作用为主,而芳香结构增多,同时出现应力缩聚;而温度上升至400 ℃以上,高煤级煤岩即可发生韧性流变,次生缺陷发育,机械能转化为应变能,脱落的小分子优先嵌入或吸附在大分子结构的缺陷或表面,脂肪和芳香结构的变化,其过程既有应力降解作用又有应力缩聚作用,而且以应力缩聚作用为主;围压和样品注水状态对大分子结构影响不明显。     

Rheology of the Cu-H2O nanofluid in porous channel with heat transfer: Multiple solutions

Dynamics of nanofluid comprising a base fluid (water) with copper (Cu) nanoparticles have been considered in channel with porous walls under magnetic field influence. The channel walls are considered to be permeable in order to analyze the wall mass transfer phenomenon. Relevant mathematical modelling has been performed and the derived PDEs are converted into coupled nonlinear ODEs by using suitable transformations. Computations have been made numerically by employing the shooting technique. It is noted that multiple solutions occur for the variation of suction Reynolds number, solid volume fraction and magnetic parameters which are interpreted in detail.     

Rheology Study of Chlorinated Polyethylene with Various Cl-Contents and Carbon Nanotube Composites

Composites of chlorinated polyethylene with various Cl-contents and carbon nanotubes (CNT) were produced and their rheological behaviors were characterized by capillary viscometry. For polyethylene (PE)/CNT composites with CNT loadings of 3 wt% and 5 wt%, the melt viscosity was higher than that of PE alone. However, the PE/CNT composite with CNT loading of 2 wt% gave a much lower melt viscosity than that of PE alone. The melt viscosity of chlorinated polyethylene (PECl)/CNT composites prepared also depended on the amount of added CNT and chlorine content. PECl/CNT composites with higher chlorine content displayed lower melt viscosities than that of PECl alone. A mechanism was proposed.     

Impact of Dose-Rate on Rheology,Structure and Wear of Irradiated UHMWPE

Ultrahigh molecular weight polyethylene (UHMWPE) is used as a bearing material in total joint replacements (TJR). UHMWPE for TJR is usually modified by irradiation and thermal treatment to increase wear resistance. We modified UHMWPE in three ways, differing in radiation dose-rate and/or atmosphere during irradiation. Rheological properties before and after irradiation were determined by means of oscillatory shear measurements. Structural changes were followed by X-ray diffraction, infrared spectroscopy, electron spin resonance, and solubility measurements. Wear resistance of selected samples was obtained by the pin-on-disk method. Rheological properties changed sensitively with modification conditions including radiation dose rate. Moreover, rheological results correlated well with both crosslinking extent and wear resistance. Finally, it was demonstrated that the optimal radiation dose, i.e. the dose leading to maximum crosslinking density and wear resistance, was different for each of the three modification procedures.     

Influence of Surfactant Functional Groups on Morphology and Rheology of Polypropylene/Organoclay Nanocomposites

Three surfactants, with the same long alkyl tail but varying in functional groups, were selected to modify two pristine clays with different cation exchange capacities (CEC). Each of the modified clays was melt-mixed with polypropylene (PP) to prepare nanocomposites. The microstructure of the resultant nanocomposites was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and rheological techniques. The results showed that the surfactant structure had remarkable effects on the morphology and shear rheology of the nanocomposites based on the high-CEC organoclay: use of benzyl functional groups led to the highest extent of intercalation and highest enhancement of shear properties, while use of 2-hydroxyethyl groups had the opposite effect. Nanocomposites based on low-CEC organoclay all exhibited poor dispersion and their shear behavior was changed only slightly in comparison to the polymer matrix. In the case of extensional rheology, strain hardening was observed only in the two nanocomposites containing surfactants with 2-hydroxyethyl groups, regardless of the dispersion state of the nanoparticles.     

Morphology,Rheology, and Mechanical Properties of Polylactide/Poly(Ethylene-co-octene) Blends

Polylactide (PLA)/poly(ethylene-co-octene) (POE) blends containing ethylene-glycidyl methacrylate copolymer (EGMA) as a compatibilizer were prepared by melt blending. An immiscible, two-phase structure with POE dispersed in the PLA matrix was observed by scanning electron microscopy. It was found that the POE particle size was significantly decreased by the addition of EGMA, and the POE particle size and distribution decreased with the increase of the compatibilizer content up to 2% EGMA, beyond which the POE particle size and distribution remained unchanged. The reactions between the epoxy groups of EGMA and carboxylic or hydroxyl groups of PLA were elucidated by the Fourier transform infrared spectroscopy. Rheological results showed that the G′(ω), G″(ω), and complex viscosity of PLA/POE blends significantly increased at low frequencies with the addition of EGMA. The failure mode changed from brittle fracture of the neat PLA to ductile fracture of the PLA/POE blends.     

SiO2 Reinforced EVM/TPU Blends: Bound Rubber and Rheology Behavior

Silica is shown to be a more active filler than carbon black for the reinforcement of EVM/TPU blends. The static rheology of EVM/TPU blends is considerably influenced by a tightly bound rubber structure developing between the TPU and silica that was identified by a tetrahydrofuran extraction test and SEM observations. Dynamic rheology behavior corroborated the development of bound rubber and indicated the existence of the Payne effect because of filler-filler networks in the blends. The silica-TPU interaction is thermally unstable at 190°C and mechanically unstable at a shear frequency of 1 Hz.     

Dynamic Rheology of Poly(3-hydroxybutyrate-co-4-Hydroxybutyrate) /Clay Biocomposites

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] composites filled with clay were prepared by a melt blending process. Dynamic rheology of the composites was measured by means of a rotational rheometer. The results showed that the interlayer spacing of the clay increased owing to the presence of the P(3HB-co-4HB) melt in the interlayer regions of the clay. The storage and the loss moduli of the composite samples increased with the increasing frequency, and decreased with the increasing temperature. The addition of the clay enhanced the oscillatory thinning behavior of the composite melts, and improved the processability of the P(3HB-co-4HB) melt. The decrease of the viscosity by increasing both frequency and temperature was feasible and effective for the composites with the clay contents of 1 and 2 wt.%.     

Investigation of Phase Separation in a Partially Miscible Polymer Blend by Rheology

The phase boundary and phase‐separation dynamics of a binary poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase‐separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase‐separation mechanisms.     

Gelation Rheology and Water Absorption Behavior of Semi-Interpenetrating Polymer Networks of Polyacrylamide and Carboxymethyl Cellulose

Gelation rheology and swelling behavior of novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on polyacrylamide are described. These hydrogels were prepared by solution cross-linking of partially hydrolyzed polyacrylamide and carboxymethyl cellulose (CMC), using chromium triacetate. Effects of CMC content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels increased with increasing CMC content. Enhancement of storage modulus was more than two times for the semi-IPN gels containing 50 wt% CMC. It was also found that increasing the CMC content decreased the loss factor, indicating that the elastic properties of this gelling system increase more strongly than the viscous properties. The swelling ratio of the semi-IPN gels in tap water, NaCl and CaCl₂ solutions, and synthetic oil reservoir water slightly decreased as the concentration of the CMC increased. The improved storage modulus and slightly decreased swelling capacity in oil reservoir water make these semi-IPN hydrogels potentially good candidates for excess water treatment in oil recovery applications.     

Wealth Rheology

We study wealth rank correlations in a simple model of macroeconomy. To quantify rank correlations between wealth rankings at different times, we use Kendall’s τ and Spearman’s ρ, Goodman–Kruskal’s γ, and the lists’ overlap ratio. We show that the dynamics of wealth flow and the speed of reshuffling in the ranking list depend on parameters of the model controlling the wealth exchange rate and the wealth growth volatility. As an example of the rheology of wealth in real data, we analyze the lists of the richest people in Poland, Germany, the USA and the world.     

高温高压下矿物流变强度与深源地震机制

利用高压原位同步辐射X射线衍射和衍射谱宽的分析,测量了地幔主要矿物橄榄石（olivine, α相）、卫思里石(wadsleyite,β相）、林伍德石(ringwoodite,γ相)及钙钛矿相(perovskite)高温高压下的流变强度.实验结果证明,上地幔和过渡层的矿物与下地幔矿物有非常不同的特点.橄榄石、β相和γ相的流变强度都对温度十分敏感,但唯有橄榄石强度在相对低温时就显著减弱,在873K时,橄榄石的强度只有β相的三分之一.与此相反,钙钛矿相的流变强度对温度的敏感度极低.地幔主要矿物流变强度（即矿物积累应力的能力）的特征及其对温度的敏感性可以帮助解释深源地震的发生频率随深度变化的规律.     

射线引起DNA双链断裂的统计分布

辐射过程引起的生物细胞的DNA双链断裂是一种很重要的细胞损伤过程.射线在细胞中能量沉积比较大时,DNA双链断裂的碎片分布会偏离随机断裂模型给出的结果,为此发展了新的模型分析方法-统计碎裂模型.根据统计物理学的原理和方法，放射性射线照射细胞后，将射线的能量传递给细胞中的DNA分子，当沉积的能量比较大时，体系会经过一个弛豫过程，DNA碎片大小l按照统计规律分布.体系熵值取极大的分布是最可几的分布，从而得到了辐射导致DNA双链断裂后碎裂片段随其大小l的分布函数exp(αl+βl²)，它对应于 两种成分，一种成分随碎裂片段的大小l的增大而迅速减小，这对应于分布函数中的exp(βl ²)项，对于质量比较小的碎裂片段，这种成分是主要贡献；另外一种成分随碎 裂片段的大小l的增大而缓慢减小，这对应于分布函数中的exp(αl)项，对于质量比较大的 碎裂片段，这种成分是主要贡献.根据实验所测的碎裂片段分布，通过数值解法解积分方程 ，将热力学参数α，β解出，与实验结果进行比较，实验的结果支持了DNA双链断裂后碎裂 片段分布的统计碎裂模型. 关键词： 熵 统计碎裂模型 DNA双链断裂     

The charge transfer via a double helix DNA

This paper reports a double helix model of charge transfer in DNA molecule. The calculated results show that the transmission characteristics of DNA are not only related to the longitudinal transfer but also to the helicity of molecule. It finds that there are four transmission bands centred at 0.92, 3.07, 7.75 and 8.87eV, also the width and intensity of bands corresponding to the helix direction are less than that of the longitudinal direction. With the increase of hopping energy, transmission bands become wide so that the transmission ability is enhanced.