Evolution of viscosities and morphology for the two-phase system polyethylene oxide/poly(dimethylsiloxane)

Shear viscosities and oscillatory viscosities were measured for the two-phase system polyethylene oxide/poly(dimethylsiloxane) at 70 °C as a function of composition. This blend exhibits the usual droplet/matrix structures in the vicinity of the pure components and a region of co-continuity within which two droplet/matrix structures coexist. A stepwise reduction in the shear rate, , leads to a rapid increase in viscosity followed by a much slower exponential decay; plots of the corresponding rate constants as a function of composition exhibit two discontinuities marking the boundaries of co-continuity; a similar dependence is obtained for the time independent final viscosities . Keeping the blend composition constant and determining as a function of yields a curve that passes a distinct maximum, where the viscosities are very close to that of the less viscous pure component on both ends of this dependence. The dynamic mechanical measurements of the blends yield at low frequencies storage moduli G′ that are orders of magnitude larger than that of the components because of the deformation of the interfaces. At high frequencies, the loss moduli G″ reflect the increasing alignment of the drops suspended in the matrix phases. The composition dependencies of G′ and of the complex viscosities can again be used to determine the limits of co-continuity.     

高熵合金药型罩射流成型与稳定性

近年迅速兴起的多主元高熵合金因其具有很宽的成分-性能调控范围及一系列优异力学性能, 有望替代紫铜成为新一代药型罩材料. 本文基于CrMnFeCoNi五元高熵合金动态力学性能实验和数值模拟, 探索该合金用作药型罩的适用性. 基于分离式霍普金森拉杆和材料试验机研究了高熵合金不同应变率及温度下的力学行为, 获得了高熵合金Johnson-Cook热黏塑性动态本构. 利用流动速度与临界压垮角关系对凝聚性高熵合金射流形成边界进行界定. 结合数值模拟验证了高熵合金射流形成边界的合理性, 并进一步揭示了射流高速拉伸断裂演化规律. 研究表明: 射流断裂时间与材料强度成负相关, 材料动态强度增大, 将会引起射流断裂时间下降. 本工作可为新型高熵合金药型罩结构设计提供参考.      

Rheology as a tool for the analysis of the dispersion of carbon filler in polymers

The aim of this work is to validate the use of dynamic oscillatory measurements in the melt to characterize the dispersion of a filler in a matrix after melt blending. Polyethylene oxide (PEO) is used as a polymeric matrix. Active carbon is used as a filler at a constant filler volume content of 26.4%. The melt viscosity of the polymeric matrix is varied by melt blending of two miscible POE and polyethylene glycol (PEG) species having very different molecular weight distributions. This enables to obtain various matrix viscosities and in turn various states of dispersion of the filler that were characterized by optical microscopy and image analysis. Dynamic mechanical measurements in the melt in the terminal zone show a large increase of the moduli associated to the presence of the filler. Comparison with the results of optical microscopy shows that this increase is clearly related to the dispersion. The interparticle distance is likely to be the leading parameter rather than the number of particles. Characterization of the amount of bound polymer shows that the amount of bound polymer is nearly independent of the matrix composition. Futhermore, the composition of the bound layer reflects the matrix composition though PEO is slightly preferentially bound on the active carbon.     

Rheological properties of polyethylene/metaboric acid thermoplastic blends

The rheological properties of molten low-density polyethylene/metaboric acid blends were studied. It was found that the blend behavior can be rather different, depending on volume fraction of the inorganic component. Specifically, at some concentration of metaboric acid, the dynamic moduli and the Newtonian viscosity of the blends demonstrate a jump-like change. The concentration threshold depends on temperature and equals to 21.9 and 14.1 vol %, at 150 and 180 ^°C, respectively. In the concentration range below the threshold, the gain in the content of inorganic component results in an enhancement of the blend dynamic moduli and viscosity, without changing the general character of the rheological behavior of composition in the region of linear response. On the other hand, at higher concentrations of metaboric acid, the yield stress is observed, and the elastic modulus in the linear region of mechanical behavior becomes virtually independent of frequency. It was suggested that the rheological behavior of blends is related to a spontaneous change in their structure as well as planar molecular structure of the inorganic component.     

碳钢表面微弧氧化膜的制备及摩擦磨损性能研究

在碳钢表面利用微弧氧化技术分别在以铝酸盐和硅酸盐为主的电解液体系中制备了氧化膜.用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)研究了两种氧化膜的结构、元素含量及分布和相组成;用往复摩擦试验机评价了氧化膜的摩擦磨损性能,并对膜层和对偶表面的磨痕进行了表征.结果表明:铝酸盐体系中制得的微弧氧化膜主要由Fe3O4和铁铝尖晶石(Fe Al2O4)组成,而硅酸盐体系制得的微弧氧化膜成膜元素为Fe、Si和O,并且以非晶态存在.干摩擦条件下,铝酸盐体系中制备的微弧氧化膜具有比硅酸盐体系中制备的微弧氧化膜更低的摩擦系数和磨损率,这是由于铝酸盐中制备的氧化膜含有的Fe3O4在摩擦过程中向对偶发生了一定程度的转移,起到了减摩抗磨的作用.     

Rheological study of segmented polyurethane and polycaprolactone blends

The dynamic rheological properties of segmented polyurethane based on polycaprolactone diol (PU-PCL diol) and poly (ɛ-caprolactone) (PCL) blends were experimentally examined and theoretically analyzed using Palierne model. PU–PCL diol was melt blended with PCL in three different ratios of 20, 30, and 40%. Initial modeling attempts failed to fit the experimental data of these blends, as the model overpredicted their rheological data. This failure is believed to be due to partial dissolution of PCL in PU. According to our obtained results from differential scanning calorimetry and dynamic thermal mechanical analysis, pure PU–PCL diol is diluted by its homopolymer. By calculating the complex modulus of this diluted matrix using a simple mixing rule and its incorporation into the model, good fitting of the Palierne equation to the experimental data was obtained.     

一种基于电磁霍普金森杆的材料动态包辛格效应测试装置及方法

金属材料在复杂载荷条件下的动态力学行为研究一直备受关注,但受限于实验设备,金属材料的动态包辛格效应响应一直都难以获得。为了探究金属材料的包辛格效应与应变率效应之间的关系,本文中提出一种基于电磁霍普金森杆(electromagnetic split Hopkinson bar,ESHB) 的非同步加载实验技术,为测试金属材料在高应变率加载下的包辛格效应提供了一种有效的实验方法。本文中,首先介绍了非同步加载装置的主要特点,即可以用两列由脉冲发生器产生的应力波对受载试样进行连续的一次动态拉-压循环加载,且加载过程保证了应力波的一致性。分析了应力波对试样加载过程中的波传播历程,确保了加载过程的连续性。随后介绍了动态加载过程,数据处理方法和波形分离手段,并对动态加载过程进行应力平衡性分析,论证了实验装置的可靠性。最后采用该方法测试了5%预应变下6061铝合金动态压缩-动态拉伸的包辛格效应,并与准静态下的实验结果进行对比。实验结果表明,该材料单轴压缩没有明显的应变率效应,但其包辛格效应具有应变率依赖性,高应变率下材料的包辛格应力影响因子由0.07增大至0.17,具有显著的提升,这对传统意义上铝合金材料应变率不敏感的结论提出了挑战。     

Rheological properties of physical gel formed by hydrophobically modified urethane ethoxylate (HEUR) associative polymers in methanol–water mixtures

We investigated the effects of methanol on the two rheological properties, dynamic modulus and flow behaviour, for an aqueous solution of hydrophobically ethoxylated urethane (HEUR). When the added methanol constitutes 0–10 mol% of the sample, the gel relaxation time shortens; when it constitutes 20 mol% of the sample, the distribution of relaxation times broadens. Relaxation of the physical gel formed by a transient network is directly related to the lifetime of the crosslink points, i.e. flower micelles. We speculate that methanol addition shortens the relaxation time by changing the hydrophobic interactions in the flower micelles. The changed hydrophobic interactions then affect not only the relaxation time but also the shape of the HEUR-chain molecular associating structures which in turn affects the mechanical spectrum. Under constant shear flow, shear thickening increases with increasing methanol concentration, and the increase in stress under constant shear flow shows unusual behaviour. A possible contributing factor to this behaviour may be the non-cosolvency of methanol with polyethyleneoxide (PEO). At some critical concentration, methanol in PEO aqueous solution becomes a poor solvent, which then affects the properties of the PEO chains in the transient networks of HEUR aqueous solution. The rheological properties of the transient networks clearly affect the properties of both the crosslink points and the chains. In short, methanol addition induces complicated changes in gel mechanical properties.     

Characteristic-value analysis for plastic dynamic buckling of columns under elastoplastic compression waves

The characteristic-value analysis of plastic dynamic buckling is presented for columns under the action of elastoplastic compression wave caused by an axial-step load. Two critical conditions constituting a dynamic instability criterion are derived on the basis of transformation and conservation of energy. The governing equations, the boundary conditions and the continuity conditions derived by the use of the first critical condition are the same as those given by the adjacent-equilibrium criterion and are insufficient for determining two characteristic parameters involved in the governing equations. A supplementary restraint equation for buckling deformations at the plastic-wave front and the elastic-wave front is derived by the use of the second critical condition. Then, a couple of characteristic equations for two characteristic parameters are derived on the condition that the governing equations have non-trivial solutions satisfying the boundary conditions, the continuity conditions and the supplementary restraint equation. The critical-load parameters, dynamic characteristic parameter (exponent parameter of inertia term) and dynamic buckling modes are calculated from the solutions of the characteristic equations.     

Nonlinear viscoelastic characterization of molten thermoplastic vulcanizates (TPV) through large amplitude harmonic experiments

The so-called thermoplastic vulcanizates (TPV) are essentially blends of a crystalline thermoplastic polymer (e.g., polypropylene) and a vulcanizable rubber composition, prepared through a special process called dynamic vulcanization, which yields a fine dispersion of micron-size crosslinked rubber particles in a thermoplastic matrix. Such materials are by nature complex polymer systems, i.e., multiphase, heterogeneous, typically disordered materials for which structure is as important as composition. Correctly assessing their rheological properties is a challenging task for several reasons: first, even if the uniformity of their composition is taken for granted, TPV are indeed very complicated materials, not only heterogeneous but also with a morphology related to their composition; second, their morphology can be affected by the flow field used; third, the migration of small labile ingredients (e.g., oil, curative residue, etc.) can in the meantime significantly change the boundary flow conditions, for instance through self-lubrication due to phase separation of the oil, or wall slip, or both. The aims of the work reported were to investigate a series of commercial TPV through the so-called Fourier transform rheometry, a testing technique especially developed to accurately investigate the nonlinear viscoelastic domain. Results are tentatively interpreted in terms of material composition and structure. A shorter version of this paper was presented at the 3rd Annual European Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece.     

Viscoelasticity and diffusion in miscible blends of saturated hydrocarbon polymers

Linear viscoelasticity and tracer diffusion were investigated as functions of temperature, component molecular weight and blend composition for entangled, single-phase blends of nearly monodisperse poly(ethylene-alt-propylene) (PEP) and head-to-head polypropylene (HHPP). Both components are non-polar and, despite evidence for slight differences of component glass temperatures in their blends, the viscoelastic data obey time-temperature superposition rather well. The properties of the blends were compared at constant T-T _g (blend) with predictions of the tube-model theories. The composition dependence of viscosity agrees best with the double-reptation prediction, as had been found earlier for molecular weight blends. The variation in plateau modulus with composition is consistent with reptation, but the changes are too small to provide a definitive test. The tracer diffusion coefficients, D ^* _PEP and D ^* _HHPP are nearly independent of composition, consistent with the reptation prediction and in sharp contrast with tracer diffusion for blends with specific associations. Results for the recoverable compliance depart from this pattern, varying differently and much less strongly with composition than the predictions of either single or double reptation. It thus seems that microstructural blends may behave in significantly more complex ways than molecular weight blends even for components with only weak dispersive interactions and rather modest differences in glass temperature and plateau modulus.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.     

Manifestation of phase separation processes in oscillatory shear: droplet-matrix systems versus co-continuous morphologies

Phase separation processes in mixtures of poly-α-methylstyrene-co-acrylonitrile (PαMSAN) and poly-methylmethacrylate (PMMA) with lower critical solution temperature (LCST) behavior have been studied, focusing on the manifestation of the interface in oscillatory shear measurements. By using blends of different composition, systems with a droplet-matrix morphology or a co-continuous structure are generated during the phase separation process. The feasibility of probing this morphology development by rheological measurements has been investigated. The development of a disperse droplet phase leads to an increase in the elasticity of the blend at low frequency, showing up as a shoulder in the plot of storage modulus versus frequency. Here, the droplet growth is unaffected by the shear amplitude up to strains of 0.2; therefore the resulting dynamic data are suitable for quantitative analysis. In contrast, for blends in which phase separation leads to a co-continuous structure, the storage modulus shows a power law behavior at low frequency and its value decreases as time proceeds. For the latter systems, effects of the dynamic measurement on the morphology development have been observed, even for strain amplitudes as low as 0.01. To probe the kinetics of morphology evolution in droplet-matrix systems, measurements of the time dependence of the dynamic moduli at fixed frequency should be performed (for a whole series of frequencies). Only from such measurements, curves of the frequency dependence of the moduli at a well defined residence time can be constructed. From fitting these curves to the emulsion model of Palierne, the droplet diameter distribution at that particular stage in the phase separation and growth process can be obtained. It is not appropriate to use a simplified version of the Palierne model containing only the average droplet size, because a morphology with too broad a size distribution is generated. Received: 15 February 1999 Accepted: 20 May 1999     

微弧氧化一步制备石墨-PTFE共添加的自润滑膜层

在Na2SiO3-KOH基础电解液中添加不同的固体润滑微粒,利用微弧氧化技术在LY12铝合金上制备了含有固体润滑剂的微弧氧化膜层.利用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和扫描电子显微镜(SEM)研究了未添加、添加聚四氟乙烯(PTFE)和石墨-PTFE共添加微弧氧化膜层的组成和微结构.采用往复球-盘试验机评价了膜层的摩擦学性能.结果表明:加入到电解液中的固体润滑剂在微弧氧化过程中成功进入到膜层中,从而得到含有固体润滑剂的复合膜层.添加PTFE的微弧氧化膜层相较于未添加的膜层具有更小的摩擦系数,而石墨-PTFE共添加能够进一步降低膜层的摩擦系数.     

Scattering of SH-waves by an interacting interface linear crack and a circular cavity near bimaterial interface

An analytical method is developed for scattering of SH-waves and dynamic stress concentration by an interacting interface crack and a circular cavity near bimaterial interface. A suitable Green‘s function is contructed, which is the fundamental solution of the displacement field for an elastic half space with a circular cavity impacted by an out-plane harmonic line source loading at the horizontal surface. First, the bimaterial media is divided into two parts along the horizontal interface, one is an elastic half space with a circular cavity and the other is a complete half space. Then the problem is solved according to the procedure of combination and by the Green‘s function method. The horizontal surfaces of the two half spaces are loaded with undetermined anti-plane forces in order to satisfy continuity conditions at the linking section, or with some forces to recover cracks by means of crack-division technique. A series of Fredholm integral equations of first kind for determining the unknown forces can be set up through continuity conditions as expressed in terms of the Green‘s function. Moreover, some expressions are given in this paper, such as dynamic stress intensity factor (DSIF) at the tip of the interface crack and dynamic stress concentration factor (DSCF) around the circular cavity edge. Numerical examples are provided to show the influences of the wave numbers, the geometrical location of the interface crack and the circular cavity, and parameter combinations of different media upon DSIF and DSCF.     

The effects of chain conformation in the microfluidic entry flow of polymer–surfactant systems

An associative polymer–surfactant system has been used to observe the effects of chain conformation in the entry flow through a microfabricated planar 16:1:16 contraction–expansion geometry. The well-studied system of the flexible polymer poly(ethylene oxide) (PEO) and anionic surfactant sodium dodecyl sulfate (SDS) was used. Dilute polymer solutions with increasing SDS concentration were characterized in steady and dynamic shear, as well as capillary breakup extensional rheology. Based on this characterization, the primary quantitative difference is an increase in zero-shear viscosity as a result of the PEO chain expansion brought on by association of SDS surfactant micelles. However, these quantitatively similar solutions were observed to exhibit much more qualitatively different flow patterns via fluorescent streak imaging in the entry flow. In contrast to previous work on PEO solutions, the PEO–SDS systems were observed to transition to a steady viscoelastic flow regime characterized by stable lip vortices at much lower elasticity and Weissenberg numbers. The resulting insight gained regarding the utility of microfluidic flows in elucidating effects of subtle conformational changes further illustrates the potential for using microfabricated devices as rheometric tools for measuring the properties of dilute and weakly viscoelastic fluids.     

用焦散线法研究PP/PA6/POE-g-Ma的动态断裂性能

研究了由直接共混法制备而成的聚丙烯/尼龙6/马来酸酐接枝乙烯-辛烯共聚物(PP/PA6/POE-g-MA)三元共混体系的静、动态力学性能,并采用反射型动态焦散线方法对其动态断裂性能进行了实验研究。根据动态断裂实验过程中得出的I型裂纹尖端的焦散斑,测得PP/PA6/POE-g-Ma共混高聚物的动态断裂韧性和裂纹扩展速度。此外,本文通过扫描电镜对动态断裂截面的细观观测,进一步分析了材料损伤破坏的机理,并探讨了共混高聚物方法对材料抗断裂性能的影响。实验结果表明,动态焦散线方法为高聚物复合材料的动态断裂实验研究提供了一种可行的方法,并可为高聚物复合材料性能的改进提供依据。     

Thermorheological properties of LLDPE/LDPE blends

The thermorheological behavior of a number of linear low-density polyethylene and low-density polyethylene (LLDPE/LDPE) blends was studied with emphasis on the effects of long chain branching. A Ziegler–Natta, LLDPE (LL3001.32) was blended with four LDPEs having distinctly different molecular weights. The weight fractions of the LDPEs used in the blends were 1, 5, 10, 20, 50, and 75%. Differential scanning calorimetry (DSC) analysis has shown that all blends exhibited more than one crystal type. At high LDPE weight fractions, apart from the two distinct peaks of the individual components, a third peak appears which indicates the existence of a third phase that is created from the co-crystallization of the two components. The linear viscoelastic characterization was performed, and mastercurves at 150 °C were constructed for all blends to check miscibility. In addition, Van Gurp Palmen, zero-shear viscosity vs composition, Cole–Cole, and the weighted relaxation spectra plots were constructed to check the thermorheological behavior of all blends. In general, good agreement is found among these various methods. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, the SER universal testing platform from Xpansion Instruments. The blends exhibit strain-hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component.     

Dynamic rheology of the immiscible blends of liquid crystalline polymers and flexible chain polymers

Immiscible blends containing liquid crystalline polymers (LCP) as dispersed phases show different dynamic rheological properties than those composed of flexible polymers. The widely used Palierne’s model was shown by many authors to be insufficient to describe the frequency dependence of dynamic modulus of such blends. A new model was presented to describe the dynamic rheology of the immiscible blend containing LCP as a dispersed phase. The flexible chain polymer matrix was assumed to be a linear viscoelastic material under small amplitude oscillatory shear flow, and the LCP was assumed to be an Ericksen’s transversely isotropic fluid. The Rapini-Papoular equation of anisotropic interfacial energy was used to account for the effect of nematic orientation on the interfacial tension. It was found that the orientation of the director and the anchoring energy greatly influenced the storage modulus at the “shoulder” regime. The overall dynamic modulus of the blend can be well described by the model with suitable choice of the orientation of the director and anchoring energy of LCP.     

TC4合金微弧氧化膜的摩擦磨损性能及其失效机理研究

采用微弧氧化(PEO)技术在TC4合金(Ti6Al4V钛合金)表面制备了微弧氧化耐磨陶瓷膜层. 利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)和摩擦试验机分析测试了微弧氧化膜的结构与组成,考察了膜层在干摩擦和油润滑条件下的摩擦磨损性能及其磨损失效机理. 结果表明:基底材料的氧化和电解液化合物的沉积均对微弧氧化膜层的生长起重要作用;微弧氧化有效提高了材料的耐磨性,降低了材料在油润滑条件下的摩擦系数;在干摩擦条件下,摩擦力较大,剪切应力是导致膜层失效的主要因素,在油润滑环境中,压应力是导致膜层失效的主要因素;对微弧氧化膜层进行有效润滑可以极大地提高膜层的使用寿命.      

Influence of dispersion procedure on rheological properties of aqueous solutions of high molecular weight PEO

The linear and nonlinear viscoelastic behaviors of poly(ethylene oxide) (PEO) in aqueous media have been investigated as a function of concentration and molecular weight. A particular interest has been paid to study the effect of turbulent flow under stirring, inducing both shear and elongational stresses, on the rheological behavior of the polymer solutions. The comparison of intrinsic viscosity and viscoelastic properties between shaken and stirred PEO solutions is discussed at the molecular scale in terms of chain scission and aggregation. Results point out that the effect of the mechanical history on the rheological response of PEO solutions depends also on the concentration regime and molecular weight. Indeed, the influence of the dispersion procedure vanishes by decreasing both the concentration and the molecular weight.