低密度聚乙烯熔体的非线性依时性流变特性及表征

进行了一种低密度聚乙烯 (LDPE ,PE FSB 2 3D0 2 2 Q2 0 0 )熔体的触变环实验 ,实验结果表明该LDPE的粘弹力学特性具有复杂的非线性依时特性 ;进一步的应力增长实验表明在定常剪切速率 5s- 1 下应力会随着剪切时间的延长而明显下降 .文中用一个变型的Huang方程表征了实验得到的触变环 ,模型计算与各实验结果基本吻合 ;但同时注意到模型的参数不具有通用性 ,没有全面反映LDPE(Q2 0 0 )熔体的粘弹力学特性 ,此外 ,变型Huang方程也无法预测材料在剪切之后的应力松弛 .     

Survival analysis of microarray expression data by transformation models

Many microarray experiments involve examining the time elapsed prior to the occurrence of a specific event. One purpose of these studies is to relate the gene expressions to the survival times. The Cox proportional hazards model has been the major tool for analyzing such data. The transformation model provides a viable alternative to the classical Cox's model. We investigate the use of transformation models in microarray survival data in this paper. The transformation model, which can be viewed as a generalization of proportional hazards model and the proportional odds model, is more robust than the proportional hazards model, because it is not susceptible to erroneous results for cases when the assumption of proportional hazards is violated. We analyze a gene expression dataset from Beer et al. [Beer, D.G., Kardia, S.L., Huang, C.C., Giordano, T.J., Levin, A.M., Misek, D.E., Lin, L., Chen, G., Gharib, T.G., Thomas, D.G., Lizyness, M.L., Kuick, R., Hayasaka, S., Taylor, J.M., Iannettoni, M.D., Orringer, M.B., Hanash, S., 2002. Gene-expression profiles predict survival of patients with lung adenocarcinoma. Nat. Med. 8 (8), 816-824] and show that the transformation model provides higher prediction precision than the proportional hazards model.     

电感耦合等离子体发射光谱法(ICP-AES)测定黄禾和谷子中15种元素

摘 要：提出了用等离子体发射光谱对通辽地区产黄禾和谷子中Na,Ca,Sn,Cu,Zn,Al,Mg,Fe,P,Si,K,Ba,Se,Mo,Mn 15种元素含量同时进行测定的方法,并对各元素作了加标回收实验,黄禾和谷子中各元素的平均回收率为96.67%～104.00%,RSD为0.78%～2.86%。方法简便、快速、准确地测定了黄禾和谷子中的元素。结果显示,在黄禾和谷子中K,P,Mg含量高,谷子中Ca,Mg,Fe,Zn和Mn的含量较黄禾中的高。黄禾和谷子中富含丰富的Na,Ca,Zn,Fe等元素,从微量元素角度看谷子中对身体有益的元素较黄禾高。     

分数Maxwell模型应用于PTFE松弛模量的研究

用分数Maxwell模型对聚合物PTFE(Polytetrafluoethylene)的应力松弛过程进行了研究. 分数Maxwell模型的渐近行为是确定其参数的基本依据, 但根据实验数据确定的松弛时间与渐近解成立的条件并不自恰. 通过适当选定松弛时间, 利用起始时段的实验数据确定初始松弛指数和松弛模量, 并适当优化末端松弛指数, 分数Maxwell模型可以对粘弹性应力松弛过程给出非常好的描述.     

电感耦合等离子体原子发射光谱法(ICP-AES)测定黄禾和谷子中15种元素

提出了用电感耦合等离子体原子发射光谱法对通辽地区产黄禾和谷子中Na,Ca,Sn,Cu,Zn,Al,Mg,Fe,P,Si,K,Ba,Se,Mo,Mn 15种元素含量同时进行测定的方法,并对各元素作了加标回收实验,黄禾和谷子中各元素的平均回收率为96.67%~104.00%,相对标准偏差RSD均小于5%。方法简便、快速、准确地测定了黄禾和谷子中的元素。结果显示,在黄禾和谷子中K,P,Mg含量高,谷子中Ca,Mg,Fe,Zn和Mn的含量较黄禾中的高。黄禾和谷子中富含丰富的Na,Ca,Zn,Fe等元素,从微量元素角度看谷子中对身体有益的元素较黄禾高。     

盐酸胍/Ⅰ型胶原分散体系的流变性

采用胃蛋白酶降解法从猪皮中提取了胶原蛋白,用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDSPAGE)确定为Ⅰ型胶原;红外及紫外光谱表明胶原分子中存在三螺旋结构.分别采用小幅振荡剪切法、恒定剪切速率法及滞后环法研究了盐酸胍浓度及作用时间对Ⅰ型胶原蛋白体系流变性的影响.研究表明,随盐酸胍浓度的增大及作用时间的延长,盐酸胍/胶原分散体系由假塑性流体逐渐接近于牛顿流体.在所研究的盐酸胍浓度范围(0~6.0 mol/L)内,盐酸胍/胶原分散体系的触变性类型随盐酸胍浓度的增大发生正触变性-复合触变性-负触变性的转变;随盐酸胍作用时间的延长(6~48 h),盐酸胍浓度为1.0 mol/L的胶原分散体系的触变性类型发生复合触变性-负触变性的转变.本文的研究结果有助于加深对触变性产生机理的认识.     

Hysteresis and strain hardening in the creep response of a polyaniline ER fluid

The electrorheological creep response of PANI/silicone oil suspensions near the yield point is investigated using parallel plate rheometry. Controlled-stress, thixotropic loop experiments exhibit a pronounced hysteresis, from which we determined the static yield stress (sigma(y(static))), as the stress where onset of flow occurs on the upward part of the loop, and a dynamic yield stress (sigma(y(dynamic))), defined as the stress at which flow ceases on the downward part of the loop. The magnitude of the hysteresis, as characterized by the area under the loop, increases substantially with applied field strength and particle concentration, but decreases with increase of temperature. Consistent with literature data, the creep compliance shows an evolution from viscoelastic to viscoplastic to viscous flow behavior as the applied stress increases through the yield point. In the viscoplastic regime, the apparent equilibrium compliance, J(e)(app), shows a discrete pre-yield transition to higher values, indicating a seemingly-enhanced ductility as the applied stress nears the yield point. Measurement of the static yield stress following these creep experiments suggests that the origin of this transition is a pronounced strain-hardening effect. We conclude that strain-hardening contributes to the hysteresis observed in the thixotropic loop test.     

黄原胶水凝胶的分子网络模型

本文结合二次采油中作为压裂液的黄原胶水凝胶,从其成胶机理着手分析,以Carreau-Bird模型为基点,在分子网络模型中引进了吸附反应动力学项以及计及流体触变性质的函数f(t),并把自由链、迷向链及破碎网络对应力的贡献模拟成牛顿性,从而导出本构方程。方程中的参数值由凝胶的粘弹性性质及非线性物质函数决定,用有约束的优化方法进行优化后得到,模型计算的结果与实验数据大致相符。     

Shear-induced topology changes in liquid crystals of the soybean lecithin/DDAB/water system

The viscoelastic behavior of the two different liquid crystalline lamellar phases and the liquid crystalline cubic phase of the mixed soybean lecithin/DDAB system in water was studied through rheology, with mechanical parameters studied as a function of composition. The swollen or diluted lamellar region is formed by vesicles, and its characteristic flow curve presents two-power law regions separated by a region where viscosity passes through a maximum. Yield stress and shear-dependent flow behavior were also observed. The microstructure suffers transformation under shear stress, and rheological response shifts from thixotropic to antithixotropic loops. Similar rheological behavior has been observed for samples in the collapsed or concentrated lamellar region, at the water-rich corner of the phase diagram. Vesicle formation may therefore occur by shearing the initial stacked and open bilayers. However, concentrated lamellar samples in the water-poor part of the phase diagram are less sensitive to shear effects and show plastic behavior and thixotropy. All lamellar samples manifest high elasticity. The dynamic responses of both lamellar topologies, i.e., vesicles and open bilayers, are comparable and exhibit an infinite relation time. The bicontinuous cubic, liquid crystalline phase is highly viscous. Its dynamic response cannot be modeled by a Maxwell model.     

Thixotropic organogels based on a simple N-hydroxyalkyl amide: rheological and aging properties

The thixotropic properties ofthermoreversible organogels composed ofN-3-hydroxypropyl dodecanamide and various apolar fluids have been investigated by X-ray scattering, light microscopy, and rheo-optics experiments. This revealed that gel formation occurs via a precipitation process. Depending upon the cooling rate, large interconnected aggregates are formed and induce an elastic behavior. When submitted to a shear flow, these aggregates disentangled and became aligned in the direction of the velocity. Nevertheless, shear does not alter the structure of the individual aggregate and connections between the aggregates are quickly rebuilt due to gravity and thermal fluctuations when the applied flow is stopped. The alignment under flow and the reformation of the connections after the cessation of the shear induces the thixotropic behavior.     

The Role of Viscoelastic Adhesive Contact in the Sintering of Polymeric Particles

The sintering of polymeric particles is analyzed by considering the growth of contact between viscoelastic spheres driven by adhesive intersurface forces. This process is dominant during the initial phase of sintering and is succeeded by a viscous sintering step that is driven by surface tension and accommodated by viscous flow. The intersurface forces in this work are described by a cohesive zone model. A new formulation of adhesive contact that does not require the cohesive zone to be smaller than the contact radius, together with finite element simulations is used to study the growth of contact. The results of this paper establish conditions that determine the dominant mechanism of contact growth during sintering. These conditions are described using a "deformation map". For a Maxwell material, if particle radius R(max),相似文献   

A hybrid rheological model for particulate suspension in zeolite crystal growth

A hybrid constitutive model is developed to represent the thixotropic behavior of particulate suspension during zeolite crystallization from solution. This model is valid over the complete solid fraction range typical for such a process. It employs two internal variables, agglomeration and contiguity, to describe the degree to which the gel particles form short- and long-range networks. The contiguity is used to weigh the effects of hydrodynamic to chain-like network deformation on the suspension viscosity. Heterogeneous nucleation and surface reaction-controlled crystal growth are assumed to describe the evolution of microstructure and solid fraction of gel and crystals. Such a model successfully captures the thixotropic behavior of zeolite particulate suspension by comparison of the predictions with a set of experimental data.     

Influence of Electrolytes on the Thixotropy of Ferric Aluminum Magnesium Hydroxide‐Montmorillonite Suspensions

Abstract

The thixotropy of suspensions consisting of ferric aluminum magnesium hydroxide (Fe‐Al‐Mg‐MMH) and Na‐montmorillonite (MT) is examined with special emphasis on the influence of electrolytes. When NaCl or MgCl₂ is added into the Fe‐Al‐Mg‐MMH/MT suspension, the thixotropy of the suspension may change (if positive) from positive and complex into negative, but NaCl or MgCl₂ can't alter the thixotropic type of a negatively thixotropic suspension. When AlCl₃ was added to positive thixotropic system can be transformed to a complex one, whereas a complex and negative thixotropic suspension remains unchanged, for additions less than 0.01 mol/L; when the addition level of AlCl₃ increases, all types of thixotropic systems are changed to non‐thixotropic. In addition, NaCl and MgCl₂ make the initial viscosity measured after cessation of intensive shearing increase, but the value of the viscosity decreased rapidly with time. The equilibrium viscosity of the suspension decreased gradually with increasing concentrations of NaCl and MgCl₂ in the suspension. With increasing concentration of AlCl₃, the equilibrium viscosities of the positive thixotropic suspension and the complex thixotropic suspension increase at first, but decrease later, and the equilibrium viscosity of negative thixotropic suspensions decrease gradually.     

国内外PVB材性研究

主要介绍了国内外研究PVB(聚乙烯醇缩丁醛)材性的现状。国内外研究表明,PVB是应变率及温度敏感材料。应变率增加,弹性模量变大;温度升高,弹性模量和剪切模量均下降。同时,国内外进行了少量的实验,研究PVB的本构模型。总结发现,PVB的本构模型可描述为线弹性、弹塑性、线性粘弹性和非线性粘弹性四种,但本质上PVB是非线性粘弹性材料,不同的环境条件与计算要求可选择不同的本构模型。目前,国内外学者比较认可的是用超弹性考虑其非线性,用Maxwell模型考虑其粘弹性。     

用Wagner型本构方程表征低密度聚乙烯熔体的粘弹性及其非线性依时特性的预测

通过实验研究了一种低密度聚乙烯 (LDPE ,PE FSB 2 3D0 2 2 /Q2 0 0 )熔体的粘弹性 ,并用KBKZ类本构方程中的Wagner模型进行了表征 .用Wagner模型预测了LDPE的非线性依时粘弹特性 ,并同已报道的变型Huang方程的结果进行了比较 .在最大剪切速率 5s- 1 下 ,KBKZ方程预测的短剪切时间下的触变环与实验结果吻合较好 ,当剪切时间加长时 ,KBKZ方程的预测结果比实验值偏高 .KBKZ方程能够较好地预测应力增长和应力松弛特性 ,即能够真实地反映出实验中的应力过冲以及应力松弛的过程 ,而变型Huang方程则不能 .变型Huang方程中的参数是孤立地、片面地反映材料在特定条件下的流变特性 ,而KBKZ方程中描述材料流变性质的参数能基本上反映出该LDPE的粘弹性 .因此 ,KBKZ方程描述和预测依时性粘弹特性的综合能力强于变型的Huang方程 .结果还表明KBKZ方程仍不能准确、完整地描述LDPE Q2 0 0的依时性粘弹性 .     

触变性含蜡原油等温胶凝过程特性及模型研究

综合利用理论推导和流变实验方法对触变性含蜡原油的等温胶凝过程进行了详细的研究, 采用结构参数法建立了静态结构恢复模型, 并经实验结果证明该模型对多种原油的结构变化曲线均有较高的拟合精度. 同时以青海原油为例, 根据实验数据和拟合参数分析了含蜡原油等温胶凝过程特性. 结果表明, 随着温度的升高、预剪切速率的增大以及预剪切时间的增加, 原油在恒温静止过程中形成的结构强度均会减弱. 测量温度越高, 预剪切时间越长, 则原油的结构参数变化速率越大; 而预剪切速率越高, 原油结构参数变化速率在初始阶段越大, 在最终阶段反而越小, 但与未经剪切油样相比, 原油受剪切后其结构参数变化速率在整个测量时间范围内均偏大.     

盐酸胍/Ⅰ型胶原分散体系的流变性

采用胃蛋白酶降解法从猪皮中提取了胶原蛋白, 用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)确定为Ⅰ型胶原; 红外及紫外光谱表明胶原分子中存在三螺旋结构. 分别采用小幅振荡剪切法、 恒定剪切速率法及滞后环法研究了盐酸胍浓度及作用时间对Ⅰ型胶原蛋白体系流变性的影响. 研究表明, 随盐酸胍浓度的增大及作用时间的延长, 盐酸胍/胶原分散体系由假塑性流体逐渐接近于牛顿流体. 在所研究的盐酸胍浓度范围(0~6.0 mol/L)内, 盐酸胍/胶原分散体系的触变性类型随盐酸胍浓度的增大发生正触变性-复合触变性-负触变性的转变; 随盐酸胍作用时间的延长(6~48 h), 盐酸胍浓度为1.0 mol/L的胶原分散体系的触变性类型发生复合触变性-负触变性的转变. 本文的研究结果有助于加深对触变性产生机理的认识.     

Rheological behavior of self-assembling PEG-beta-cyclodextrin/PEG-cholesterol hydrogels

The rheological properties of a recently developed self-assembling hydrogel system composed of beta-cyclodextrin (betaCD)- and cholesterol-derivatized 8-arm star-shaped poly(ethylene glycol) (PEG8) were investigated. To understand and predict the gel rheological properties, data fitting with the Maxwell model as well as comparing the system's concentration-dependent behavior with Cates' model for reversibly breaking chains were performed. To investigate the influence of the polymer architecture, networks were also prepared by replacing the cholesterol-derivatized 8-arm star-shaped PEG by linear bifunctional PEG-cholesterol or by using 4-arm instead of 8-arm polymers. Rheological analysis showed that the 8-arm polymer-based mixtures yielded tight viscoelastic networks, but their storage and loss moduli significantly deviated from those predicted by the Maxwell model. The scaling of the plateau moduli, relaxation times, and zero-shear viscosities with concentration for gels composed of 8-arm cholesterol- and betaCD-derivatized PEG followed a power law with exponents higher than predicted by Cates' model. On the other hand, hydrogels in which linear bifunctional PEG-cholesterol was used instead of 8-arm star-shaped PEG-cholesterol or which were based on 4-arm polymers showed a substantially better fit with the Maxwell model and reduced differences between empirical and Cates' theoretical scaling exponents. Rheological analysis also showed that the hydrogels were thermoreversible. At low temperatures, the gels showed viscoelastic behavior due to slow overall relaxation of the polymer chains. At higher temperatures, however, a reduced number of betaCD/cholesterol complexes and concomitant faster chain relaxation processes eventually led to liquid-like behavior. The relationship between temperature and the relaxation time was used to determine an activation energy of 46 kJ/mol for breaking and reptation of the polymers.     

Some applications of the AMPC model of the shear yield stress of particulate fluids

The AMPC structural model of shear yield stress of single component suspensions is extended to three important rheological phenomena encountered in particulate fluids. These are shear yield stress of multi-component systems, time dependent shear yield stress of thixotropic suspensions, and compressive yield stress of particulate fluids. The shear yield stress of multi-component suspensions is modeled by summing the interparticle interactions due to all possible combinations of particle sizes and solid constituents. The time dependent shear yield stress of thixotropic muds is simulated by invoking the proportionality between yield stress and interparticle bond density across the shear plane. The compressive yield stress of particulate fluids is calculated by assuming that consolidation occurs by shear but at a narrower gap between the particles. The ability of the model to describe these diverse phenomena reasonably well seemingly validates its basic premise, namely, a 3-dimensional space-filling network of particles whose mechanical properties can be estimated from the theory of strength of particulate assemblage.     

Thixotropy of Aqueous Suspensions Containing Mg‐Al Hydrotalcite‐like Compound and Low‐substituted Cationic Starch: Comparison between Oscillatory Shear and Thixotropic Loop Measurements

The rheological properties of aqueous suspensions consisting of positively charged aluminum magnesium hydrotalcite‐like compound (HTlc) and low‐substituted cationic starch (LCS) were investigated. Special emphasis was placed on the thixotropic phenomenon. Thixotropic behavior was investigated by two thixotropic methods: thixotropic loop and oscillatory shear measurements. LCS molecules could be adsorbed onto HTlc particles due to the hydrogen bonding between ether groups or hydroxyl groups of LCS and hydroxyl groups of HTlc. The elastic dynamic response of the HTlc/LCS suspension increased with increasing mass ratio (R) of HTlc and a three‐dimensional network structure could be formed in the suspension with higher R value. The thixotropic type of the HTlc/LCS suspension transformed from negative to positive and then to complex thixotropy when R changed from 0 to 0.5. By comparing between the thixotropic results obtained by thixotropic loop and oscillatory shear measurements, it was validated that the thixotropic loop for the suspension showing complex thixotropy had a crossover point.