聚丙烯腈/二甲基亚砜溶液的流变学性质

用HAAKE公司RSl50L型流变仪研究了PAN／DMSO溶液的流变学性质．讨论了温度、溶液浓度及PAN的分子量对流动曲线的影响。结果表明,在较低的剪切速率下,随温度的升高、浓度的降低及分子量的减小,流动曲线下移,并且开始向非牛顿区转变的临界切变速率增大．在较高剪切速率下,初始粘度低的溶液的粘度最高．在一定的浓度和剪切速率下溶液的粘度随温度的变化符合Arrhenius方程式．溶液在非牛顿区存在粘度突变现象．     

硫氰酸钠水溶液体系的聚丙烯腈溶液凝固行为

硫氰酸钠（NaSCN）溶剂路线是国外制备高性能聚丙烯腈（PAN）基碳纤维原丝成熟的纺丝工艺路线，该技术在国内碳纤维领域尚处于发展阶段。文中采用流变仪、红外光谱研究了PAN在不同质量分数NaSCN水溶液中形成的聚合物溶液的流变性能和PAN大分子状态；溶液中NaSCN质量分数的提高，PAN溶液的黏度先减小后增大，在51%NaSCN溶液中PAN溶液的黏度最低、，用光学显微镜和X射线衍射研究了NaSCN水溶液为溶剂的PAN溶液凝固行为。研究发现，51%NaSCN溶液中，PAN大分子以最舒展状态存在，PAN分子链的31螺旋构象更多，这与溶液中硫氰酸根主要以异硫氰酸根（—N=C=S）存在有关，PAN的氰基与异硫氰酸根的—N=C形成桥键结构。随着聚合物溶液中NaSCN质量分数增加，凝固剂水在PAN溶液中的扩散速率增加，PAN溶液凝固结晶程度先增大后减小，在质量分数为51%的NaSCN水溶液中，PAN的凝固结晶规整度更优异，这与PAN以解缠伸展状态存在相关，由于流动活化能更低，PAN溶液更易发生相转变。     

木质素/聚丙烯腈共混溶液的制备及其性能研究

为了探索木质素对丙烯腈聚合原液的性能影响，用两种不同的木质素与聚丙烯腈(PAN)进行了不同配比的共混实验，并对共混后的溶液进行黏度、稳态流变性能、固含量、分子量等一系列测试。结果表明，共混溶液的黏度随着温度的升高而下降，60℃左右时相对稳定；随着两种木质素含量的增加，A木质素/PAN共混溶液黏度显著增加，B木质素添加量超过40%后溶液黏度降低；木质素添加量为40%时，L_A溶液黏度较纯PAN溶液黏度增加了192%,L_B溶液黏度大幅提升了133%。这些都与溶液内分子链形态的变化有关，由于木质素添加后，共混溶液表现出典型切力变稀的性质，共混溶液的温度、木质素添加量等因素都会影响溶液切力变稀的临界剪切速率。实验发现，固含量降低没有影响溶液黏度，且A木质素/PAN共混溶液分子量大，分散度也较平均。不同木质素在添加少量时对PAN原液的流变性能影响几乎相近，因此共混溶液中加入30%～40%A木质素较适宜。     

超声波振动在静电纺丝技术中的应用

使用自行设计的振动静电纺丝设备分别对聚丙烯腈（PAN）和聚氧乙烯（PEO）进行了振动纺丝实验，实验结果表明，使用具有振动力场作用的静电纺丝设备，对于普通静电纺丝可以纺的溶液，纺出的纤维直径明显降低；对于粘度过高普通静电纺不能纺丝的聚合物溶液，可以进行纺丝。     

高分子量微生物纤维素LiCl/DMAc纺丝溶液流变性研究

微生物纤维素溶液流变性能对其纺丝工艺研究具有重要的指导意义,以8%LiCl/DMAc为溶剂采用旋转流变仪对不同分子量、不同固含量溶液的稳态流变及动态流变进行了测定。结果表明:微生物纤维素的LiCl/DMAc溶液属于非牛顿假塑性流体;高分子量的溶液比低分子量的溶液黏度要高;随温度的升高,溶液表观黏度不断下降,高浓度的溶液在低剪切速率下对温度更敏感,且浓度越高,结构黏度指数越大,纺丝难度越大。通过动态流变得知,溶液浓度越高,体系弹性强度及黏滞力越大,但对外部剪切力越敏感,其物理稳定性越弱。     

梯形聚苯基倍半硅氧烷/聚甲基丙烯酸甲酯溶液浇注共混物的相容性

用溶液浇注法制备了具有不同质量配比的高分子量、低分子量梯形聚苯基倍半硅氧烷（ＰＰＳＱ）与聚甲基丙烯酸甲酯（ＰＭＭＡ）的共混物。用扭辫分析技术研究了不同分子量ＰＰＳＱ与ＰＭＭＡ间的相容性及热历史对其相容性的影响。ＰＰＳＱ、ＰＭＭＡ在其溶液浇注膜中是部分相容的。红外光谱分析表明，低分子量的ＰＰＳＱ（Ｙ）与ＰＭＭＡ间有较强的相互作用，故其与ＰＭＭＡ的相容性比高分子量ＰＰＳＱ的好。热历史对该类溶液浇注共混体系的相容性影响较大，加热使ＰＰＳＱ（Ｙ）／ＰＭＭＡ共混物分相，但加热可增加高分子量ＰＰＳＱ与ＰＭＭＡ间的相容性。     

丁二烯-苯乙烯嵌段共聚物溶液粘度的测定和研究

采用NEX－1型锥板粘度计和HAAK－100型锥板粘度计测定了丁二烯－苯乙烯嵌段共聚物（SBS）两种型号SBS1401和SBS4402的环己烷溶液和甲苯溶液的粘度,温度范围为20℃-60℃,浓度范围为1％－25％。研究了各种因素对溶液粘度的影响,并计算出了运动粘度。8％以下溶液呈现牛顿流体的性质,粘度基本不随剪切速率改变。浓度从10％起,溶液呈现出非牛顿性,粘度随剪切速率呈幂率变化,粘流活化能随剪切速率的增加而增高。在本文的测量范围内,绝对粘度与浓度呈三次多项式的关系,运动粘度与浓度呈指数关系。     

羧甲基纤维素系列高分子表面活性剂在溶液中分子形态的研究

通过激光光散射和粘度法研究了羧甲基纤维素（ＣＭＣ）与烷基醇聚氧乙烯醚丙烯酸酯（ＡＲ１２ＥＯｎ）的超声共聚物在溶液中的分子形态。结果表明，随活性大单体支链增长，共聚物分子尺寸增大；水溶液中的胶束粒子随共聚物的疏水性增强而增大，ＣＭＣ－ＡＲ１２ＥＯ３体系胶束聚集数最大；共聚物分子与胶束均呈棒状结构。共聚物水溶液的粘度主要取决于分子量和胶束缔合数，盐水溶液中的粘度异常行为与共聚物中引入的大单体活性及形成的胶束结构有关。     

PAN超滤膜的性能改进

本文简要地报导了聚丙烯腈(PAN)超滤膜的性能改进新方法,即用含无机阳离子的凝胶浴的凝胶化工艺来制备高通量的PAN膜。为了探讨作用机理,研究了无机阳离子对PAN—DMF溶液体系流态特性的影响。结果表明在稀溶液情况下,由于无机阳离子的加入而使溶液结构指数变小;而在较浓溶液中,由于无机阳离子的加入而使结构指数增大;在某一合适的无机阳离子浓度下,随PAN浓度增加,溶液结构指数呈现出先下降而后回升增大的趋势。这种变化与无机阳离子在周期表中所处的位置有一定联系。此外还讨论了无机阳离子的加入对膜形态结构的影响。经红外光谱测定表明这种影响可能与无机阳离子与聚合物之间的作用有关。     

微支化型高分子量PPS树脂的合成及表征

用硫磺、对二氯苯为原料，在极性有机溶剂中，以１，２，４－三氯苯作共聚反应第三单体，共缩聚制得了微支化型高分子量聚苯硫醚（ＰＰＳ）树脂，在缩聚反应中，第三单体量一定时，一定时间内聚合物对数低切变粘度值与反应时间具有线性关系。聚合物经元素分析，红外光谱分析、Ｘ射线衍射分析、激光拉曼光谱分析以及热分析表明，微量（＜１．０％）三氯苯引入分子链对ＰＰＳ的组成和结构影响不大，产品仍为结晶性高聚物，不含双硫键。由于分子量提高，聚合物的热稳定性得到提高，根据不同需要合成的一定分子量范围的微支化型高分子量ＰＰＳ树脂不经热氧交联处理即可直接挤出造粒，用于注射成型和挤出成型。     

Synthesis and characterization of matrix metalloprotease sensitive-low molecular weight hyaluronic acid based hydrogels

Hyaluronic acid is a naturally derived glycosaminoglycan (GAG) involved in biological processes. A low molecular weight hyaluronic acid (50 kDa)-based hydrogel was synthesized using acrylated hyaluronic acid. Matrix metalloproteinase (MMP) sensitive hyaluronic acid-based hydrogels were prepared by conjugation with two different peptides: cell adhesion peptides containing integrin binding domains (Arg-Gly-Asp: RGD) and a cross-linker with MMP degradable peptides to mimic the remodeling characteristics of natural extracellular matrices (ECMs) by cell-derived MMPs. Mechanical properties of these hydrogels were evaluated with different molecular weights of acrylated hyaluronic acid (10 kDa and 50 kDa) cross-linked by MMP sensitive peptides by measuring elastic modulus, viscous modulus, swelling ratio and degradation rate. The MMP sensitive hydrogel based on the 50 kDa hyaluronic acid showed a 31.5-fold shorter gelation time, 4.7-fold higher storage modulus and 0.51-fold smaller swelling ratio than those of the hydrogel based on the 10 kDa. Degradation rate was dependent on MMP sensitivity of the peptide cross-linker. MMP sensitive hyaluronic acid based hydrogels were degraded faster than MMP insensitive-hyaluronic acid-based hydrogels. Human mesenchymal stem cells (MSCs) were cultured in MMP-sensitive or insensitive hyaluronic acid-based hydrogels (50 kDa hyaluronic acid) and/or immobilized cell adhesive RGD peptides. Cells cultured in the MMP-sensitive hydrogel with RGD peptides showed dramatic cell spreading compared with that of the control, which remained round. This MMP-sensitive low molecular weight hyaluronic acid-based hydrogel could be useful in tissue engineering by improving tissue defect regeneration and tissue remodeling.     

Thermal stability and melt rheology of poly(<Emphasis Type="Italic">p</Emphasis>-dioxanone)

Melt viscosities of poly(p-dioxanone) (PPDO) samples having different molecular weights were studied using a controlled-strain rotational rheometer under a nitrogen atmosphere. First, PPDO’s thermal stability was evaluated by recording changes in its viscosity with time. The result, that samples’ viscosities decreased with time when heated, demonstrated that PPDO is thermally unstable: its degradation activation energy, obtained by using a modified MacCallum equation, was a relatively low 71.8 kJ/mol K. Next, viscoelastic information was acquired through dynamic frequency measurements, which showed a shear thinning behavior among high molecular weight PPDOs, but a Newtonian flow behavior in a low molecular weight polymer (M _w = 18 kDa). Dynamic viscosity values were transferred to steady shear viscosities according to the Cox–Merz rule, and zero shear viscosities were derived according to the Cross model with a shear thinning index of 0.80. Then flow activation energy (48 kJ/mol K) was extrapolated for PPDO melts using an Arrhenius type equation. This activation energy is independent of polymer molecular weight. A linear relationship between zero shear viscosity and molecular weight was obtained using a double-logarithmic plot with a slope of 4.0, which is near the usually observed value of 3.4 for entangled linear polymers. Finally, the rheological behaviors of PPDO polymer blends having bimodal molecular weight distributions were investigated, with the results indicating that the relationship between zero shear viscosity and low molecular weight composition fraction can be described with a Christov model.     

Influence of viscosity on chondrogenic differentiation of mesenchymal stem cells during 3D culture in viscous gelatin solution-embedded hydrogels

Differentiation of human bone marrow-derived mesenchymal stem cells(hMSCs)is regulated by a variety of cues of their surrounding microenvironments.In particular,mechanical properties of cell culture matrices have been recently disclosed to play a pivotal role in stem cell differentiation.However,it remains elusive how viscosity affects the chondrogenic differentiation of hMSCs during three-dimensional(3 D)culture.In this study,a 3 D culture system that was established by embedding viscous gelatin solution in chemically cross-linked gelatin hydrogels was used for 3 D culture of hMSCs in gelatin solutions with different viscosities.The influence of solution viscosity on chondrogenic differentiation of hMSCs was investigated.Viscous gelatin solutions promoted cell proliferation in the order of low,middle and high viscosity while elastic hydrogels restricted cell proliferation.High viscosity gelatin solution led to increased production of the cartilaginous matrix.Under the synergistic stimulation of chondrogenic induction factors,high viscosity was beneficial for the chondrogenic differentiation of hMSCs.The results suggested the role of viscosity should be considered as one of the dominant mechanical cues affecting stem cell differentiation.     

Non-equilibrium Thermodynamic Model for the Estimation of the Soret Coefficient in Dilute Polymer Solutions

In the present work a theoretical model based on linear non-equilibrium thermodynamics and the concept of Eyring’s activation energy of viscous flow is developed to estimate the Soret coefficient in dilute polymer solutions. The model is capable of predicting a sign change in the Soret coefficient, when the polymer molecular weight changes. The key part of the model is the way that the net heat of transport of the polymer molecules is simulated. Employing the Mark–Houwink equation, which correlates the polymer solution intrinsic viscosity with its molecular weight, the net heat of transport of the polymer is correlated with the activation energy of viscous flow of the polymer’s monomer in the liquid state, the Mark–Houwink solution parameter, and the polymer molecular weight. The model is evaluated against the experimental data, where qualitative and in some cases quantitative agreement is found.     

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

The effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO₂) and calcium carbonate (CaCO₃) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO₃ suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO₂ suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO₂ suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO₃ ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.     

Environmental effects of silicone oil on mechanical properties of low and high molecular weight PMMA

The influence of a silicone oil environment on deformation modes and tensile behaviour of poly(methylmethacrylate) were investigated. Tests were made on samples coated with oils of varying viscosity, ranging from 5 to 1000 cSt. To investigate the effects of polymer molecular weight on environmentally induced craze growth and stability, tests were conducted on an extruded grade of relatively low molecular weight and on a cast grade of high molecular weight. All of the silicone oils acted as crazing agents and tensile strength and ductility were reduced in value as the viscosity of the oil was lowered. The low molecular weight polymer failed in a brittle manner in all environments but developed earlier and more intensive crazing as the liquid viscosity was reduced. The high molecular weight material underwent a ductile-brittle transition when the environment was changed from air to low viscosity silicone oils. The flow of the oil into existing flaws and crazes was sufficiently impeded at 1000 cSt viscosity so that both necking and surface crazing were observed under these conditions. To illustrate the various deformation and fracture modes that were observed, micrographs of free and fracture surfaces are presented and discussed.     

Rheological Characterization of Tear Substitutes

The steady state viscosity as a function of shear rate was determined for eight commerical tear substitutes and compared with data for high molecular weight sodium hyaluronate solutions. The Zero shear viscosity at steady state varied more than 100-fold from about 2 to 300 cP. Many samples were Newtonian, while some samples exhibited a varying degree of shear thinning (psedudoplastic) behaviour. The results are discussed in realation to the rheological behaviour of normal tears and mucin.     

Copolymerization of dimethylaminoethylacrylate-methyl chloride and acrylamide in inverse emulsion

The inverse emulsion copolymerization of acrylamide (AM) with dimethylaminoethylacrylate methyl chloride (Q9) using redox initiation with low surfactant concentration in an isoparaffinic solvent has been studied. The kinetics of conversions of inverse-emulsion polymerizations were investigated by HPLC method. It was an interesting way to know rapidly the conversion of each monomer with high reproducibility. In all experiments the monomer concentration was 25% respect the total weight or higher and the experiments were carried out at 50^∘C. The effects of initiator concentration, composition of the monomer mixture and monomer concentration on the polymerization conversion and viscosity of copolymers solutions have been examined. For copolymer characterization, the results of viscosity were compared with commercial copolymer viscosities. The formulations with 3,000 ppm of initiator were the most interesting of all copolymer compositions since they presented very high conversions and their viscosities were higher than those of commercial copolymer solutions. The analysis of monomer concentration was carried out with 3,000 ppm and the conversion and viscosity were higher when the monomer concentration was increased.     

原位聚合PA11/GO纳米复合材料的流变性能研究

采用原位聚合法制备了PA11(尼龙11)/GO(GO)纳米复合材料,并采用XLY-Ⅱ型毛细管流变仪研究了共混物的流变特性。结果表明:PA11及其复合材料均为假塑性流体,呈现切力变稀的现象;非牛顿指数n均小于1。随着GO含量的增加,PA11/GO纳米复合材料的表观黏度升高,粘流活化能下降,表明共混材料的表观黏度对温度的敏感性降低,易于加工成型。     

Ionic Strength Effects in Aqueous Solutions of Gelatin and Sodium Dodecylsulphate

Abstract

The interaction between the anionic surfactant sodium dodecylsulphate and the polyampholyte gelatin in aqueous solution has been studied by viscosity and fluorescence. Three different gelatin molecular iveights, a polydisperse gelatin and two fractionated samples derived from it, have been examined at two ionic strengths. On addition of sodium dodecylsulphate SDS, the viscosity of a low molecular weight fractionated (o.) gelatin increases smoothly with SDS concentration, unlike the polydisperse (standard) and high molecular zveight (HMW) fractionated gelatins which show maxima. The viscosity increase at the maximum increases with gelatin molecular weight. On addition of 0.1 M salt, the viscosities of the gelatin-surfactant mixtures are lower than the equivalent no-salt cases. Fluorescence studies suggest that the SDS micelles adsorbed onto these various gelatins under two different ionic strengths are remarkably similar.