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.     

钠型蒙脱土悬浮体和水解聚丙烯酰胺体系的负触变现象

由钠型蒙脱土悬 浮体和水解聚丙烯酰胺组成的体系有负触变现象, 对负触变性的形成条件和影响因素作了初步探讨. 并对微观结构作了一些推测.     

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.     

On the viscosity of composite suspensions of aluminum and ammonium perchlorate particles dispersed in hydroxyl terminated polybutadiene--New empirical model

The rheological properties of fuel suspensions with various solid loadings up to close their maximum packing fraction and suspending media having different viscosities are investigated using the rotational viscometer at relatively low shear rates in which suspensions behave as Newtonian fluids. Aluminum (Al) and ammonium perchlorate (AP) particles are major solid components of any solid fuel system which should be distributed uniformly inside a polymeric binder based on hydroxyl terminated polybutadiene (HTPB). The experimental data generated in this investigation indicates that the relative viscosity of the suspensions is independent of viscosity of polymer binder, but in addition to solid content, geometrical aspects of the solid particles affect strongly the relative viscosity of suspensions. Maximum packing fraction of filler is found to be suitable quantitative measure of filler characteristics such as size, size distribution, shape and structure. Consequently, it is revealed that the relative viscosity of fuel suspension is a unique function of reduced volume fraction (Phi). Based on analogy of viscosity enhancement of reactive resin with cure conversion and suspension with filler content, an empirical model with two adjustable parameters originated from resin gelation model is suggested. According to this model and experimental results obtained in this investigation, a generalized model is proposed to describe the relative viscosity as a function of solid content in which the adjustable parameters are found to be general constants. The generalized model which is expressed as mu(r) = (1-Phi)(0.3 Phi-2) is found to be quite accurate to predict the experimental data. Furthermore, the applicability and accuracy of the generalized model are evaluated using the viscosity data of some suspension systems reported in the literature.     

Study on the thixotropy of aluminum magnesium hydroxide– Na-montmorillonite suspension

 In this paper, the thixotropy of the aqueous suspension consisting of aluminum magnesium hydroxide (AMH) possessing permanent positive charges and Na-montmorillonite possessing permanent negative charges was studied. Besides positive thixotropy and negative thixotropy, a novel thixotropic phenomenon was found, i.e., a given system studied may display, early and late, positive M28.8nthixotropic character and negative thixotropic character, we describe it as “complex thixotropy”. The content of the suspension and electrolyte may influence the forms of thixotropy of the suspension studied. Received: 4 February 1997 Accepted: 15 October 1997     

UV-Raman and NMR spectroscopic studies on the crystallization of zeolite A and a new synthetic route

UV-Raman and NMR spectroscopy, combined with other techniques, have been used to characterize crystallization of zeolite A. In situ UV-Raman spectroscopy shows that the starting gel for crystallization of zeolite A contains a lot of four-ring (4R) building units and the appearance of six-ring (6R) building blocks is the signal for crystal formation. (29)Si NMR spectroscopy results suggest that the starting gel is double four-ring (D4R) rich and during crystallization of zeolite A both α and β cages appear. (27)Al NMR spectroscopy results indicate the absence of Al (2Si) species in the starting gel, suggesting the absence of single 4R building units in the starting gel. Furthermore, composition analysis of both solid and liquid samples shows that the solid rather than liquid phase predominates for the crystallization of zeolite A. Therefore, it is proposed that the crystallization of zeolite A mainly occurs in the solid phase by self-assembly or rearrangement starting from the zeolite building units mainly consisting of D4R. The essential role of D4R is directly confirmed by successful conversion from a solution of D4R to zeolite A in the presence of NaCl, and the importance of solid phase is reasonably demonstrated by the successful synthesis of zeolite A from a dry aluminosilicate gel. By considering that the solid phase has a major contribution to crystallization, a novel route was designed to synthesizing zeolite A from the raw materials water glass (Na(2)SiO(3) in aqueous solution) and NaAlO(2), without additional water and NaOH; this route not only simplifies synthetic procedures, but reduces water consumption.     

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.     

Characterization of Oil-Wax Gel with Higher Velocity Gradient

The properties of solid surface on oil-wax gel are one of the most important factors which decide the quality of products such as cosmetics. The thixotropic property of solid surface depends on the velocity gradient and it is increased with higher velocity gradient as controlling the morphology on solid surface of oil-wax gel. The morphological change of oil-wax gel in compliance with surface properties of wax matrix can cause different rheological behaviors. Rheological behavior of oil-wax gel regarding the surface transition range in accordance with shear strain was observed to characterize surface properties. In an earlier article, the morphological mechanism of causing surface transition range and the factors of influencing surface transition range were examined by studying the rheological behaviors of a solid-state emulsion. Here, we investigated, in the lattice structure terms, the morphological change of oil-wax gel by measuring surface transition range depending on velocity gradient, which could influence the hardness and sweating phenomenon. We confirmed that the morphological change of oil-wax gel was accompanied by crystal size, crystal conformation, the degree of crystallinity. Surface transition range depending on velocity gradient was shown in large and regular lattice structure of oil-wax gel better than small and irregular one.     

Mechanism of Reversible Thixotropic Transformation in Concentrated Suspensions of Monodisperse Spherical Silica Particles: Analysis in Terms of Colloidal Crystal Formation and Growth

The mechanism of thixotropic transformation of concentrated suspension of monodisperse spherical silica particles into gel made of blocks with regular structure was considered in terms of colloidal crystal formation and the Alder–Hoover model of phase transition. The kinetics of linear growth of colloidal crystals as structural blocks was experimentally studied. This process was shown to have the activation nature determined by the diffusion of structural units at the interface and can be described in terms of Frenkel's kinetic theory of liquids.     

超细改性碳酸钙浓悬浮体的正负触变性

以超细改性碳酸钙、氧化钙、邻苯二甲酸二辛脂组成的浓悬浮体为对象,用触变性和屈服应力来探测悬浮体的内部结构,结合悬浮体的分散稳定性能,讨论了正负触变性的形成、稳定性和可逆转变及触变性结构的强度,并考察了游离脂肪酸对悬浮体正负触变性转化的影响.     

Fe-Al-Mg-MMH/钠质蒙脱土分散体系触变性研究

研究了Fe-Al-Mg型混合金属氢氧化物(简称MMH)/钠质蒙脱土(简称MT)分散体系的触变性,发现在不同MMH/MT质量比(R)条件下,分散体系可分别呈现正触变性和负触变性.在所研究的R范围(0～0.091)内,随R增大,体系的触变性发生正触变性-复合触变性-负触变性的转化.考察了高速剪切分散后,测定粘度变化前的静置时间(ts)和测定粘度时的剪切速率(DL)对触变性的影响.探讨了各种触变性产生的原因,提出了“分散粒子-空间连续网络结构-密实聚集体”和“分散粒子-密实聚集体-密实聚集体簇”机理,较合理地解释了观察到的复合触变现象.     

聚苯胺溶液的凝胶化行为

通过流变学手段对聚苯胺溶液的凝胶化行为研究表明，在室温下，聚苯胺（ＰＡｎ）／Ｎ－甲基－２－吡咯烷酮（ＮＭＰ）溶液有一转折浓度Ｃｇ（０．０５ｇ／ｍＬ），浓度高于此值时，浴液凝胶化速度急剧增大，凝胶速度还与溶剂，ＰＡｎ分子量及溶液的温度有很大关系。溶液中不溶的ＰＡｎ的存在会加速凝胶化过程。ＰＡｎ／ＮＭＰ凝胶的假塑性和触变性明显地反映出ＰＡＶＮＭＰ溶液的凝胶化是溶剂参与的ＰＡｎ分子链间的物理交联过程。     

A metastable van der waals gel: transitioning from weak to strong attractions

Here we describe a method to create gels where the gel point is decoupled from gel elastic properties. Working with charge stabilized polystyrene latex particles with diameters, D, of 508-625 nm at ionic strengths of 0.1-1 M, the gel volume fraction is varied from 0.10-0.35 through the addition of less than monolayer coverage of hexaethylene glycol monododecyl ether (C6E12). At each surfactant concentration, the gel volume fraction depends on the background ionic strength. The changes in gel point with surfactant concentration suggest the strength of interparticle attraction decreases with increasing surfactant concentration. These changes are not reflected in the gel moduli, which are independent of surfactant concentration and ionic strength. We propose a model to describe this behavior based on gelation due to localization in a shallow truncated van der Waals minimum produced by the surfactant acting as a steric stabilizing layer. The surfactant remains mobile on the surface. Below the gel volume fraction, the time particles spend in the truncated well are not sufficient for the surfactant to be displaced such that the particles can only sample the shallow well. Above the gel volume fraction, particles are localized in the truncated van der Waals minima for sufficient periods of time to displace the surfactant layers with the result being that the particles fall into a primary van der Waals minimum. The result is gel points sensitive to surfactant concentration but moduli that are independent of the gel volume fraction.     

A stable single piece of unimolecularly pi-stacked porphyrin aggregate in a thixotropic low molecular weight gel: a one-dimensional molecular template for polydiacetylene wiring up to several tens of micrometers in length

An amide-type copper porphyrin gelator having alkyldiacetylene tethers gives very transparent gel in Decalin, and the gel shows unique thixotropic behavior. One-dimensional aggregates generated in the gel act as templates for unimolecularly segregated polydiacetylene wiring upon UV irradiation on the surface. The polymerization along the aggregation goes to at least several micrometers long.     

羧甲基纤维素钠/蒙脱土悬浮体系的流变性能及其影响因素

考察了蒙脱土(MT)质量分数(w)、羧甲基纤维素钠(CMC)/MT质量比(R)、电解质(NaCl、MgCl2和AlCl3)、pH值和温度对MT或CMC/MT悬浮体系流变性能和触变性的影响。 结果表明,随w增加,纯MT悬浮体系的流体类型由近牛顿流体向塑型流体变化,触变类型则由无触变、正触变向复合触变性转变;而CMC/MT悬浮体系仍保持MT体系的正触变塑型流体特征,但屈服值τ0和稠度指数K增加,滞后环面积S和电动电势|ζ|先增加后减小,表现出同步变化。 电解质和实验温度均不改变CMC/MT悬浮体系的正触变性塑型流体特征,但电解质使τ0和K增加,而温度增加使τ0和K减小。 随介质pH值的增加,CMC/MT体系由负触变性变为正触变性,|ζ|增大,S先增加后减小,且在pH=8.46时达到最大。     

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.     

Gelation of cellulose nanocrystal suspensions in glycerol

Aqueous suspensions of cellulose nanocrystals (NCC) produced by sulfuric acid hydrolysis of natural cellulose fibres display a number of unique properties. In addition to forming equilibrium chiral nematic phases above some critical concentration, cellulose nanocrystal suspensions tend to gel or aggregate if the stability of the suspension decreases, for example because of a decrease in the surface charge density of sulfate ester groups, or a change in the properties of the suspending medium. Direct incorporation of unmodified nanocrystals into organic media usually leads to aggregation. We have found that it is possible to circumvent this difficulty and form clear thixotropic gels of unmodified NCC in glycerol, by careful evaporation of water from aqueous glycerol suspensions of NCC. The physical gels form at a fairly low (<3 wt%) concentrations of cellulose. The initial composition of the suspension, the temperature and rate of evaporation, and the time resting at room temperature all influence the formation of thixotropic gels. Desulfation of the acid-form nanocrystals, enhanced in the glycerol-rich suspensions, is shown to be a key step in this gelation process.     

以拟薄水铝石为铝源合成的β沸石的表征和催化性能(英文)

考察了以拟薄水铝石为铝源、固体硅胶为硅源、四乙基氢氧化铵为模板剂时不同晶化混合液ＳｉＯ２／Ａｌ２Ｏ３比和不同晶化温度对β沸石合成的影响。ＸＲＤ、ＴＧＡ、ＩＣＰ及ＳＥＭ研究结果表明,在晶化混合液ＳｉＯ２／Ａｌ２Ｏ３比为２０至５０之间、晶化温度为１４０℃～１６０℃范围内能合成出高结晶度的β沸石,且β沸石硅铝比与晶化混合液硅铝比呈良好的线性关系：ＴＧＡ总失重量随β沸石硅铝比增加而增加,晶化温度对β沸石的晶粒度没有明显影响。此外,所制备的Ｈβ沸石对甲苯与Ｃ９芳烃歧化和烷基转移反应具有良好的催化性能。     

High-resolution electron microscopy study on the growth of zeolite L nanoclusters

The synthesis of zeolite L nanoclusters that starts from a clear mixture and proceeds through the formation of an amorphous gel phase is followed by high-resolution transmission electron microscopy (HRTEM). It is shown that by examining the solid products from partially crystallized samples, it is possible to deduce information concerning growth events at the nanometer scale. HRTEM studies reveal a definite link between the gel microstructure and the zeolite L nanocluster morphology. Moreover, it is demonstrated that a cautious interpretation of HRTEM information does not justify the conclusion that growth takes place by agglomeration of individual zeolite L nanocrystals but rather by propagation of more isolated nucleation events through the gel network.     

纳米富铝β沸石的合成与表征

以低硅铝比焙烧后的硅铝胶固体为初始原料,在含F-近中性与低含水量体系下晶化合成出相对高结晶度的纳米富铝β沸石。实验考察了合成条件、硅铝胶焙烧对晶化产物的影响和晶化过程中Al配位状况变化,并采用XRD、XRF、SEM/TEM2、7AlMAS NMR物化方法对晶化产物进行表征。结果表明,含F-离子、H2O/SiO2摩尔比为2.4～6.0以及高温焙烧硅铝胶有利于合成高结晶度的纳米富铝β沸石;硅铝胶固体焙烧后能产生易于转化为β沸石晶核的Al四配位结构,而部分六配位Al在晶化过程中缓慢溶入β沸石晶核中而最终生成纳米富铝β沸石。