表面活性剂对TiO2水悬浮体稳定及流变性质的影响

在陶瓷的制备过程中,通常需将陶瓷粉末分散于水中形成陶瓷浆后再浇铸成型.研究表明[1],陶瓷浆的分散、稳定及流变性质直接影响到成品的性能.因此,研究分散稳定剂对该浆料性质的影响有着重要意义.本文利用电泳和流变学方法研究了TiO2在表面活性剂的水溶液中浓浆体的分散稳定性及流变性质.     

添加剂对TiO2/水分散体流变性的影响

研究了TiO₂生产中有关助剂对其流变性能的影响,得到了TiO₂/水分散体的流变性能与三乙醇胺用量之间的关系,并找到了最佳用量.实验发现,六偏磷酸钠为分散剂时,其使用效果有时间依赖性;碳酸铵作絮凝剂时则对分散体的流变性能和形成的絮凝体有影响.     

Non-linear viscoelastic behavior of fumed silica suspensions

Suspensions of fumed silica exhibit a wide range of rheological properties depending on the nature and magnitude of the interparticle forces. In a non-polar fluid, the particles interact through hydrogen bonding and can form a three-dimensional network. The microstructure formation is responsible for the non-linear viscoelastic behavior of fumed silica suspensions, even at very small strain. These non-linear rheological properties have been studied in small amplitude oscillatory experiments as a function of particle size, surface treatment of particles, suspending medium polarity and solids concentration. The non-linear viscoelastic behavior is characterized by a non-sinusoidal waveform of the signal response. For suspensions in a non-polar fluid, both the elastic and the loss moduli are shown to be sensitive to the strain amplitude: the elastic modulus is decreasing with increasing strain whereas the loss moduli is initially increasing with strain. We have chosen to examine the dissipated energy which is clearly related to the breakup of the suspension structure. A comparison of model predictions and the experimental data shows the limitations of these models, recently proposed in the literature to describe the behavior of colloidal suspensions. Received: 9 March 1998 Accepted: 17 November 1998     

RHEOLOGICAL BEHAVIOR OF ERWINIA GUM IN AQUEOUS SOLUTION*

Erwinia (E) gum, an extracellular polysaccharide, is composed of fucose, galatose, glucose andglucuronic acid. Its viscosity behavior was investigated by a low-shear-rate multiball viscometer and arotational viscometer. Its weight-average molecular weight M_w and intrinsic viscosity [η] in 0.2 mol/L NaClaqueous solution were measured by light scattering method at 35℃and viscometry at 25℃and found to be1.06×10~6 g/mol and 1050 mL/g, respectively, and its aggregates in aqueous solution were proved by gelpermeation chromatography (GPC). These results indicated that E gum in water has exceedingly highviscosity and exhibits Binham fluid behavior, owing to its aggregation. The viscosity of E gum decreasedwith increasing temperature, and the turning point appeared at 38℃for dilute solution and 80℃forconcentrated solution suggesting that the aggregates of E gum in water started to disaggregate under thesetemperatures. In addition, the aggregates can be disrupted by adding either acid or base. The experimentalresults indicated that the E gum is a good thickening agent, and its fluid behavior is similar to xanthan.     

Assessment of morphology in transient and steady state regimes resulting from phase separation in polystyrene/poly(vinyl methyl ether) blend

Morphology development after phase separation in polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend was assessed both in transient and in steady state regimes. Phase segregation was evaluated by various techniques including optical microscopy, light transmission, dynamic scanning calorimetry and rheological analyses. The steady state particle size resulted from phase separation was determined experimentally and then compared to the predictions of both the emulsion models that assume zero-thickness interfacial boundaries and to the asymptotic value of the Cahn–Hilliard theory that assumes rather a diffuse interphase.     

有机蒙脱土对端羧基聚丁二烯凝胶流变行为的影响

在恒定剪切速率下,利用旋转流变仪研究端羧基聚丁二烯/蒙脱土纳米复合凝胶的流变行为,同时利用X-射线衍射(XRD)和透射电镜(TEM)等表征手段研究其微观结构.研究结果表明,该体系在26～116℃的升-降温过程中,观察到不可逆转变和可逆转变两种流变行为,其中不可逆转变流变行为归因于蒙脱土片层的剥离过程,而可逆转变流变行为...     

疏水改性低分子量阳离子聚丙烯酰胺抑制剂的制备及性能评价

针对现有阳离子类抑制剂与钻井液配伍性、抑制性较差的不足,本文以丙烯酰胺、甲基丙烯酰氧乙基三甲基氯化铵、丙烯酸十八酯为原料,以乙醇和乙酸丁酯的混合物作溶剂,采用沉淀聚合法,制备出了疏水改性低分子量阳离子聚丙烯酰胺BJX-1页岩抑制剂。通过研究不同反应条件对BJX-1分子量的影响规律,得出溶剂组成对BJX-1分子量影响最大,可通过调节溶剂组成实现BJX-1分子量的控制。当分子量为1.45×10~5g/mol~1.87×10~5g/mol时,BJX-1的抑制性最好,页岩岩屑120℃热滚回收率约为78%;增加BJX-1中疏水结构单元含量至2%~4%时,可进一步提高BJX-1抑制性,使页岩岩屑120℃热滚回收率高于90%;此时的最佳反应条件为:以乙醇和乙酸丁酯按体积比90∶10~100∶0组成的混合物作为溶剂,引发剂质量分数为0.1%,单体质量分数为3%,在80℃下反应7h。通过对比研究发现,当加量为1%时,BJX-1所对应的页岩岩屑120℃热滚回收率分别比常用小分子阳离子化合物JA-1和高分子量阳离子聚合物DY-1高27.85%和50.06%。BJX-1更能提高钻井液的综合流变性能,使钻井液流变性更加稳定,而且具有优良的高温高压降滤失性。     

Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.     

Surface modification of colloidal silica particles

Colloidal silica particles in organic solvents were grafted, using several reagents, in order to make them hydrophobic. The hydrophobicity of the beads could be easily varied. Quasielastic light scattering and transmission electron microscopy experiments showed that no aggregation occurs during the reaction when monofunctional agents are used. Elemental analysis and solid-state NMR measurements gave us the rate of surface modification of the silanol groups. We also studied the rheological behaviour of the grafted particles as a function of the volume fraction in solvents of various hydrophobicity. Hexamethyldisilazane-grafted particles display hard-sphere behaviour in polar solvents such as 2-propanol, but not in alkanes, whereas dimethyldodecylchlorosilane-grafted particles flocculated in polar solvents but could easily be dispersed in apolar solvents. Received: 15 March 2000 Accepted: 11 July 2000     

Nonlinear Couette Flow in a Low Density Granular Gas

A model kinetic equation is solved exactly for a special stationary state describing nonlinear Couette flow in a low density system of inelastic spheres. The hydrodynamic fields, heat and momentum fluxes, and the phase space distribution function are determined explicitly. The results apply for conditions such that viscous heating dominates collisional cooling, including large gradients far from the reference homogeneous cooling state. Explicit expressions for the generalized transport coefficients (e.g., viscosity and thermal conductivity) are obtained as nonlinear functions of the coefficient of normal restitution and the shear rate. These exact results for the model kinetic equation are also shown to be good approximations to the corresponding state for the Boltzmann equation via comparison with direct Monte Carlo simulation for the latter.