Rheological studies of fumed silica–polydimethylsiloxane suspensions

In this study, dynamic mechanical measurements and transmission electron microscopy are used to examine the behavior of fumed silica/polydimethylsiloxane (PDMS) suspensions. The work focuses on three aspects: (i) the modulation of the interactions between silica and PDMS through a controlled silylation of the silica surface; (ii) the effect of the process used to graft the silica surface; (iii) the effect of the silica volume fraction used in the dispersions. A relation between the silica grafting ratio, the aggregate size and the rheological properties has been established and the results have interpreted through a model of fractal clusters.     

Rheological behavior of thermoreversible kappa-carrageenan/nanosilica gels

The rheological behavior of silica/kappa-carrageenan nanocomposites has been investigated as a function of silica particle size and load. The addition of silica nanoparticles was observed to invariably impair the gelation process, as viewed by the reduction of gel strength and decrease of gelation and melting temperatures. This weakening effect is seen, for the lowest particle size, to become slightly more marked as silica concentration (or load) is increased and at the lowest load as particle size is increased. These results suggest that, under these conditions, the particles act as physical barriers to polysaccharide chain aggregation and, hence, gelation. However, for larger particle sizes and higher loads, gel strength does not weaken with size or concentration but, rather, becomes relatively stronger for intermediate particles sizes, or remains unchanged for the largest particles, as a function of load. This indicates that larger particles in higher number do not seem to increasingly disrupt the gel, as expected, but rather promote the formation of stable gel network of intermediate strength. The possibility of this being caused by the larger negative surface charge found for the larger particles is discussed. This may impede further approximation of neighboring particles thus leaving enough inter-particle space for gel formation, taking advantage of a high local polysaccharide concentration due to the higher total space occupied by large particles at higher loads.     

硅溶胶在水性聚氨酯中的流变性能

用离子交换法由工业级水玻璃制得不同粒径的单分散稳定硅溶胶。硅溶胶稀溶液的特性粘数为０．０２ｄＬ／ｇ，与硅溶的粒径无关；硅溶胶中加入电解质，分散体系由牛顿型流体变为非牛顿型流体；水溶性聚氨酯的稀溶液是胀流型流体，加入硅溶胶，分散体系的表现粘度下降；     

Rheological Behavior for Mica-filled Polypropylene Composite Melts

The study on rheological properties of a series of mica-filled polypropylene (PP) composites was carried out. The influence of surface-treatment of mica particles on dynamic rheological behavior of the composites were dealt with. The viscosity (η) and dynamic modulus ( G‘ ) of the composite melts were higher than those of PP matrix, especially those for systems treated with silane, which was attributed to the interfacial adhesion enhancement. However, surface-treatment of mica by titanate resulted in lower η and G‘, as compared with the treatment by silane. The reason for this is believed to be the formation of the mono-molecular layer on the mica surface.     

PS-b-PAA两亲性嵌段聚电解质在水溶液中的聚集行为及其流变特性

以两嵌段共聚物聚苯乙烯-b-聚丙烯酸(PS-b-PAA)为研究对象,采用动态光散射(DLS)及透射电镜(TEM)表征了胶束及聚集体的结构,采用应力控制型旋转流变仪AR-G2研究了体系的流变特性.着重考察了聚电解质浓度、pH值以及外加盐(KBr)浓度对其在水中聚集行为的影响及对体系流变特性的影响.发现随着外加盐和聚电解质浓度的增高,体系中的胶束发生聚集,形成更大的聚集体.而pH值对胶束的聚集形态无明显的影响.胶束乳液均呈现明显的剪切变稀特征.然而,随着聚电解质浓度增加,低剪切速率下体系的表观粘度增高;高剪切速率时体系粘度趋于同一值(0.01Pa·s).与纯胶束乳液相比,外加盐的存在导致体系粘度增加;当外加盐浓度增加至4.31g/L,在低剪切速率下,体系出现牛顿平台区.溶液pH值对体系粘度无显著影响.     

流变和光学法研究PAN/DMSO/H_2O体系的凝胶化和相分离行为

碳纤维是非常重要的增强材料,在军工以及高档民用产品中用途广泛。因为聚丙烯腈原丝的结构会"遗传"到最终的碳纤维结构中,因此原丝结构对碳纤维的性能影响很大。原丝的结构是纺丝液在凝固浴中的相分离和凝胶化两个过程决定的,因此研究这两个过程的规律并进一步控制它们的进程,达到调控原丝结构的目的是非常重要的。本文介绍了本课题组利用流变学及光学的方法研究PAN/DMSO/H2O体系凝胶化及相分离行为的最新研究成果,主要探索了PAN/DMSO/H2O浓溶液中凝胶化行为,发现了二次自相似结构的形成并对其机理进行了分析,并对PAN/DMSO/H2O亚浓溶液中凝胶化与相分离的耦合过程进行了研究,分析了最终凝胶的结构特性及Winter-Chambon模型在此过程中的适用性。最后,对PAN/DMSO/H2O体系凝胶化及相分离行为的下一步研究进行了展望。     

Rheological Behavior of Epoxy Resin Concentrated Dispersions

IntroductionWaterbornedispersionsofpolymerresinswithlow(orzero)contentofvolatileorganiccompoundshavereceivedmuchat'tentionowingtoincreasinglystrictenvironmentalandecologicalregulations.BisphenolAepoxyresinisacondensationpolymerofanextensivescopeofapplicationssuchasincomposites,coatings,adhesives.Therefore,thepreparationoftheepoxyresinwaterbornedispersionsisveryinteresting.Recently,wehavesuccessfullypreparedtheepoxyresinwaterbornedispersionswithhighsolidcontentbyphaseinversionemulsificationtec…     

影响高浓度氧化石墨烯分散液流变行为的重要因素及群体平衡动力学分析

氧化石墨烯(GO)片的基面和边缘上存在大量的含氧官能团,能很好地分散在水中,因而具有很好的加工性和广阔的应用前景。在较高浓度范围下,GO水分散液中存在着强烈的竞争性相互作用,从而对流变行为产生较大影响。在本文中,通过稳态、动态等流变实验以及理论分析,研究了pH值、温度和不同的有机溶剂对GO分散液流变行为的影响。结果表明,降低pH值、适当增加温度以及加入吡啶均可促进GO水分散液从粘弹性液体到凝胶态的转变。利用DLVO (Deryagin-Landau-Verwey-Overbeek)理论,探讨了GO片之间的范德华作用力以及双电层排斥作用的相互关系,及其对流变性能的影响。通过群体平衡模型(PBE)分析了GO分散液的屈服应力与体积分数的正相关关系。同时,通过蠕变和松弛实验发现,高浓度的GO分散液中结构变化及流变行为在很多方面与高聚物相似,利用Poyting-Thomson模型能较好地拟合其粘弹性行为。上述研究结果为深入研究复杂的GO分散体系提供理论支撑和实验依据。     

Rheological behaviors of a series of hyperbranched polyethers

Hyperbranched polyethers with different structures and molecular weights(MW) were synthesized using the A2+B3 approach by varying monomer ratio, A2 structure, and reaction time. Effects of backbone structure and MW on melt rheological behaviors were investigated by both small amplitude oscillatory shear and steady shear measurements. Master curves were constructed using the time-temperature superposition principle and compared. In the reduced frequency range covered, lg G″~lg(ω·aT) always show a slope of 1.0, suggesting a terminal zone behavior; in contrast, unexpected step changes or plateaus are observed on lg G′ master curves. Effects of backbone structure and MW on master curves were discussed. The Cox-Merz rule was tested at different temperatures and was found to be applicable when flow instability was absent.     

Rheological properties of microfibrillar suspension of TEMPO-oxidized pulp

The rheology of cellulose microfibril suspensions from TEMPO-oxidized pulp was investigated. The suspension showed a pseudo-plastic and thixotropic behavior, slowly evolving with time under a given shear rate. The viscosity was proportional to the concentration up to the critical concentration of 0.23%. Above it, the viscosity followed a power law with exponents from 2 to 6 depending on the shear rate, and the system showed shear thinning behavior and behaved gel-like. Below this concentration, the system was more Newtonian. Birefringence measurement of 0.44% and 0.78% suspension showed that microfibrils alignment saturated at a small shear rate with a Herman’s orientation parameter below 0.65 probably due to the interconnection of microfibrils.     

Rheological characterization of polysaccharide-surfactant matrices for cosmetic O/W emulsions

Rheometrical techniques can be profitably used for polysaccharide matrices in order to evaluate their suitability for the preparation of stable cosmetic O/W emulsions. In particular, the rheological properties of aqueous scleroglucan systems were investigated under continuous and oscillatory shear conditions in a polymer concentration range (0.2-1.2% w/w) embracing the sol/gel transition. The effects due to the addition of two different surfactants (up to 10% w/w) were examined at constant polymer concentration (0.4% w/w). The selected additives are a nonionic polymeric siliconic surfactant (dimethicone copolyol) and a cationic surfactant (tetradecyltrimethylammonium bromide), respectively. Polysaccharide-surfactant interactions leading to complex formation were detected also through rheology. The combined action of both nonionic and cationic surfactants in the polymer solution was examined at two different surfactant concentration levels (5 and 10% w/w), demonstrating the beneficial effects produced on the mechanical properties of the polymer matrix by the coexistence of both surfactants. Such beneficial effects are confirmed by the stability and rheology shown by the emulsions prepared. In this way, the results point out the good agreement between the rheology of the continuous phase and the final characteristics of the emulsion obtained.     

Novel Method for Preparation of Polypropylene Blends with High Melt Strength by Reactive Compounding

Ultrafine full-vulcanized polybutadiene rubber(UFBR) with particle sizes of ca.50―100 nm were used for modifying mechanical and processing performances of polypropylene(PP) with PP-g-maleic anhydride(PP-g-MA) as a compatibilizer for enhancing the interfacial adhesion between the two components.The morphology,dynamical rheology response and mechanical properties of the blends were characterized by means of SEM,rheometer and tensile test,respectively.The results show that the ternary PP/UFBR blends compatibil...     

嵌段共聚物对SiO_2溶胶-凝胶过程的修饰行为

近年来,人们利用对溶胶凝胶(ＳｏｌＧｅｌ)化学的认识,通过表面活性剂调控硅醇盐水解缩聚反应过程和对溶胶表面进行修饰以获得在一定范围内可控结构和可控粒度的纳米材料［１,２］,但对ＳｉＯ２溶胶凝胶过程的改性机理尚待深入研究。在溶胶凝胶过程中,溶胶粒子和网络结构主要受该体系中晶核形成与生长机制以及颗粒之间作用力所控制,这是实施溶胶网络结构形貌控制的理论依据。本文考察了聚氧乙烯醚(ＰＥＯ)聚氧丙烯醚(ＰＰＯ)聚氧乙烯醚(ＰＥＯ)嵌段共聚物(简称ＥＰＥ)作为改性剂对ＳｉＯ２溶胶凝胶化过程的修饰行为,探讨了改性ＳｉＯ２溶胶…     

CPVC／SMA共混体的流变性能

CPVC有许多优良的物理和力学性能,但是它的热分解温度和熔融温度相距太近,加工性能很不好,Krishnan等人最先研究了CPVC的流变性能,我们近几年研究了其共混体的流变性,发现通过共混方法可以有效地改善CPVC的加工特性.CPVC与苯乙烯-马来酸酐共聚物(SMA)共混体的流变性的研究则未见报道.本文研究了CPVC/SMA共混体的流变特性,为CPVC材料加工工艺参数的制定提供了依据.     

Rheological evidence for the existence of subphases in the liquid crystalline 4-n-alkoxybenzoic acids

The rheological behaviour of the homologous series, the alkyloxybenzoic acids, has been studied at steady flow and small amplitude oscillatory shear. The temperature dependencies of the viscosity were compared with differential scanning calorimetry data in order to estimate pretransitional phenomena in mesophases. The values of the viscosity and flow activation energy (E) can be indicative of the mesophase state. 4-n-pentyloxybenzoic acid yields a classic nematic (N) phase while the next homologues show a cybotactic nematic phase having a higher E value. The N phase is a Newtonian fluid of lower viscosity than that of the isotropic phase. The cybotactic nematic phase by its rheological properties takes an intermediate position between the N phase and a smectic C (SmC) phase. The SmC phase is a viscoelastic and viscoplastic medium. The SmC phase of 4-n-octyloxy-, 4-n-nonyloxy-, 4-n-decyloxy- and 4-n-dodecyloxybenzoic acid can exist in high- and low-ordered states. The more ordered smectic phase is characterised by higher stiffness, viscosity and yield stress than those of the less ordered. The SmC phase of 4-n-hexadecyloxybenzoic acid is characterised by the only state with unstable value of apparent viscosity. The phase state and the transition temperature can be dependent on the thermal history of the sample and a mechanical shear.     

聚合物长支链的流变学表征方法

在聚合物中引入长支链能够显著地提高熔体强度,改善聚合物在拉伸流场中的加工性能,因此对长支链的表征显得十分重要。流变学被证实是一种非常有效且敏感的表征手段,近来受到普遍关注。本文总结了近年来国内外关于长支链聚合物流变学表征研究的最新进展,比较了不同类型流场下对长支链的流变学判断方法,尽量结合高分子链段分子结构解释了各种表征现象的含义,阐述了借助流变学对大分子拓扑结构的定性表征以及对长支链含量的定量表征方面的应用。     

Rheological properties of deionized Chinese ink

Rheological properties for Chinese ink in exhaustively deionized aqueous media were carefully examined. In the steady shear measurement, the shear viscosities of the ink could be well explained by considering the “effective” volume fraction of the particles in the ink including the electrical double layers and by using Einstein's equation for dilute suspension viscosity, when the particle volume fraction was substantially low. In the case that the volume fraction was higher, the shear viscosities showed extremely higher than those from Einstein's prediction, though the ink remained a Newtonian liquid. In the stress-strain measurement, the shear moduli were observed at strain smaller than 0.2. The “weak” aggregation among the particles in the ink under no shear or low shear rates was supported. It should be noted that the glue in the suspension plays an important role for the good liquidity of the ink and for the “weak” bridges among the particles resulting its good dispersion stability.     

Rheological studies of aqueous alkylpolyglucoside surfactant solutions

Alkylpolyglucosides (C _Y G _X ) are industrial products of mixtures consisting of a hydrocarbon chain with Y carbon atoms linked to X sugar residues. Based on detailed analytical investigation of technical grade alkylpolyglucosides (C_8–10G _X , C_12–14G _X and C_8–16G _X )/water systems using high-performance liquid chromatography in combination with a special kind of mass spectroscopy their rheological behaviour is discussed and compared to the rheological behaviour of pure alkyl monoglycosides (C₈G₁ and C₁₀G₁) in water. The rheological properties that exhibit a dependence on the alkyl chain length, Y, and the degree of polymerisation, X, are investigated by rotation and oscillation experiments over an extended concentration range. The Maxwell model fits the frequency dependence of the dynamic functions fairly well. The viscosity shows an Arrhenius-like dependence on temperature. A comparison is drawn between the monoglucosides and the polyglucosides, which shows that the rheological properties are more sensitive to the a change in chain length than in the degree of polymerisation. Phase transitions, especially liquid-crystalline to isotropic solutions, phase split into two coexisting liquid phases, and could be followed using visual observation and rheology. Depending on the difference in the rheological properties of the corresponding phases, viscoelastic measurements showed these transitions clearly. Additionally, the changes in viscosities were measured after addition of a second surfactant. Received: 4 January 1999 Accepted in revised form: 12 April 1999     

Rheological studies of diatom encapsulation in silica gel

The mutual influence of the mineral and biological components of a specific bio-hybrid system consisting of diatom cells entrapped in a silica gel was studied by rheological methods. Small amplitude shear stress oscillatory measurements indicate that the culture medium alone has a strong impact on the silica network formation and viscoelastic properties. In contrast, the presence of diatoms does not significantly perturb the sol–gel process, and leads to a moderate change in the gel elasticity. Compression tests show that a large difference exists between the mechanical properties of silica gels and diatom shells, suggesting a limited impact of the gel strength on the diatom survival rate. We also show that the biological activity of entrapped diatoms can modify the structural evolution of the silica gel. This work indicates that rheological methods may be important tools for the optimization of whole cells encapsulation procedures and further confirms that encapsulated diatoms are able to interact with the surrounding silica materials.     

Rheological properties of asphalt/SBS/clay blends

The effect of the addition of clay as a third component in polymer modified asphalts has been investigated. After a preliminary investigation on the binary asphalt/clay and polymer/clay blends, the tertiary blends were prepared by adding the clay and polymer to the asphalt, either separately or in the form of a premixed master batch. Intercalated nanocomposites with comparable interlayer distances and glass transition temperatures were obtained in both cases. However, the results show that the mixing procedure significantly affected the final rheological properties. The master curves built in the linear viscoelastic range and represented in both the frequency and the temperature domains help to visualize and evaluate such differences.