Effect of Surface-Active Substances on the Rheological Properties of Silicon Carbide Suspensions in Paraffin

In this paper, the possibility of stabilization of SiC suspensions in paraffin (hot-molding slips) was investigated from the colloid science point of view. By considering the surface properties of finely dispersed silicon carbide, surface-active agents (fatty amine and alkylsuccinimide) which are suitable for surface modification by chemical adsorption on SiC were selected. Adsorption of fatty amines and alkylsuccinimide was carried out in model experiments in chloroform. Increasing the length of the carbon–hydrogen chain caused the adsorption to decrease, and the adsorption area of one molecule in the saturated adsorption layer to increase. The stabilizing effect of surface-active agents resulted in improved flow behavior of hot-molding slips. The efficiency of surface-active agents increased with increased adsorption layer thickness. In highly concentrated SiC hot-molding slips, a combination of alkylsuccinimide and fatty amine proved to be very efficient. This synergistic effect of long- and short-chained surface-active agents is discussed in terms of an adsorption layer model.     

Effects of Ammonium Chloride on the Rheological Properties and Sedimentation Behavior of Aqueous Silica Suspensions

The influence of ammonium chloride (NH₄Cl) on the rheological properties and sedimentation behavior of aqueous silica (SiO₂) suspensions of varying solids volume fraction (φ_s) was studied. SiO₂ suspensions with low NH₄Cl concentration (≤0.05 M , pH 5.2) exhibited Newtonian behavior and a constant settling velocity ( U ). The volume fraction dependence was well described by the Richardson–Zaki form, U = U ₀(1 −φ_s) ⁿ , where n = 4.63 and U ₀= 1.0419 × 10⁻⁵ cm/s. At higher NH₄Cl concentrations (0.07–2.0 M , pH 5.2), suspensions exhibited shear thinning and more complicated sedimentation behavior due to their aggregated nature. For all suspensions studied, however, the apparent suspension viscosity, characteristic cluster size, and initial settling velocity were greatest at ∼0.5 M NH₄Cl and exhibited a similar dependence on salt concentration. Above 0.5 M NH₄Cl, considerable restabilization was observed. This behavior cannot be explained by traditional DLVO theory.     

Drying Suspensions in a Pulsed Fluidized Bed of Inert Particles

The drying of carbohydrate suspensions on polypropylene particles in a pulsed fluidized bed was studied by means of a 2⁵ experimental design, to determine the effect of the air flow and temperature, suspension flow rate, and free section and rotating speed of the rotary plate on the Nusselt number, the moisture content of the product, and the percentage of solids retained inside the bed (which were minimized to 4.9 and 14.4%, respectively) with an air flow of 600 m³/h at 90°C and 720 mmHg, a suspension flow rate of 6 L/h, and a plate with 6% free section, rotating at 50 rpm.

Additionally, the effects of temperature, air flow, and suspension flow rate on the residence time distribution (RTD) were determined, using the stimulus-response methodology. The RTD was represented by 1.1 to 2 tanks in series, according to this model. The mean residence time of the dried carbohydrate particles was between 5.4 and 8.2 min.

Finally, an egg suspension could be dried at 4 L/h, with air at 90°C, with a mean residence time about 50% longer that that found for drying carbohydrate suspensions.     

Drying Suspensions in a Pulsed Fluidized Bed of Inert Particles

The drying of carbohydrate suspensions on polypropylene particles in a pulsed fluidized bed was studied by means of a 2⁵ experimental design, to determine the effect of the air flow and temperature, suspension flow rate, and free section and rotating speed of the rotary plate on the Nusselt number, the moisture content of the product, and the percentage of solids retained inside the bed (which were minimized to 4.9 and 14.4%, respectively) with an air flow of 600 m³/h at 90°C and 720 mmHg, a suspension flow rate of 6 L/h, and a plate with 6% free section, rotating at 50 rpm.

Additionally, the effects of temperature, air flow, and suspension flow rate on the residence time distribution (RTD) were determined, using the stimulus-response methodology. The RTD was represented by 1.1 to 2 tanks in series, according to this model. The mean residence time of the dried carbohydrate particles was between 5.4 and 8.2 min.

Finally, an egg suspension could be dried at 4 L/h, with air at 90°C, with a mean residence time about 50% longer that that found for drying carbohydrate suspensions.     

Electrokinetic and Rheological Properties of Aqueous TiN Suspensions with Ammonium Salt of Poly(methacrylic acid)

The study illustrates how rheology and electrokinetics can be utilized in the investigation and optimization of the properties of ceramic suspensions. Zeta potential studies show that the isoelectric point of TiN particulates is at pH=4, and for the pH range used, PMAA–NH₄ addition results in a more negative zeta potential value. The rheological behavior of titanium nitride in the presence of PMAA–NH₄ is strongly dependent on pH and three rheological types have been defined.     

In Situ Rheological Investigation of the Coagulation in Aqueous Alumina Suspensions

Electrostatically stabilized alumina suspensions can be destabilized by the enzyme-catalyzed decomposition of urea (direct coagulation casting). Depending on the conditions, this reaction can shift the pH of a suspension to the buffer pH of the reaction products or increase the ionic strength at the buffer pH. The coagulation for both mechanisms was investigated using in situ rheological measurements. Using a vane tool in oscillation mode, the measuring conditions were optimized to find a reasonable method for time-dependent measurements. Constant parameters (stress or strain) proved to be unsuitable, because the linear viscoelastic region shifted considerably during the coagulation. Furthermore, the gel structure produced on coagulation via increase of ionic strength (Δ I ) was very sensitive to the oscillation. Therefore, for long-time experiments, a short continuous measurement with a low strain was followed by amplitude sweeps with increased intervals to determine the linear values of G ' and G ". In this way, the increase of the moduli G ' and G " could be followed for longer times, and it was possible to demonstrate two results. First, the final G ' of the network was about 10 times higher for Δ I -coagulated material than for suspensions coagulated via pH shift (ΔpH). Second, particle rearrangement processes took place in Δ I -coagulated networks even after the chemical changes were finished, whereas ΔpH-coagulated samples were "frozen-in" when approaching the isoelectric point and showed no further physical changes afterward.     

微嵌段缔合聚合物溶液的线性粘弹性

通过高级流变仪测试了不同微嵌段长度的缔合聚合物溶液的剪切稀释特性和线性粘弹性。测试结果表明,在临界缔合浓度之上,其幂律指数和松弛时间在NH=30.8时出现极值,证实缔合聚合物的非牛顿特性和线性粘弹性并不是随嵌段长度增加而单调增加的,这与一般缔合聚合物的规律不一致;在临界缔合浓度以下,其非牛顿特性和线性粘弹性随着嵌段长度增加而逐步增加。因此嵌段长度通过影响缔合效应的强度进而影响缔合聚合物的粘弹性。     

Viscoelastic behavior of hydrogel-based xanthan gum/aluminum lactate with potential applicability for conformance control

Gel systems composed of biopolymers can be used, which block the regions of high water permeability during a previously established period, through the in situ formation of a gel inside the rock pores. Among the biopolymers studied, xanthan gum has attracted the greatest attention due to its viscosifying power and good stability in reservoirs subject to severe salinity and temperature from 27 to 90°C. Xanthan chains have the ability to build up physical networks with metals such as aluminum lactate to form hydrogels. Therefore, the objective of this study was to prepare and evaluate, hydrogels made from xanthan gum (XG) cross-linked with aluminum lactate. Initially, the influence of the gel formulation (biopolymer concentration and cross-linker) and the reservoir conditions (pH, temperature, salinity) of the gel strength of the system and the injectivity of the gel systems was investigated through rheological tests. Subsequently, was analyzed the morphology of the systems for 30 days by scanning electron microscopy (SEM). The results showed that the systems based on xanthan gum cross-linked, were able to form strong gels at pH 8, temperature of 70°C and salinity of 29,940 mgL⁻¹ TDS. In general, the evaluated parameters (pH, temperature, salinity, polymer concentration, and cross-linker) had a direct effect on the initial strength of the gel. However, after aging for 30 days, a drop in gel resistance was observed, since all systems have similar tan (δ) values and these parameters no longer show significant influence The aging analysis of hydrogel systems by SEM showed a difference in the surface microstructure of the dry hydrogel over the 30 days.     

Time-Dependent Adhesion-Induced Phenomena: Viscoelastic Creep of a Substrate Polymer Over Rigid Particles

The adhesion of micrometer-size particles to an alternating block copolymer composed of polydimethyisiloxane and polyester was found to be accompanied by substantial viscoelastic flow of the substrate polymer. This flow gave rise to contact radii, which were substantially larger than those predicted by the JKR theory. Moreover, tensile-induced creep of the substrate resulted in anomalously large menisci that actually flowed up several particle heights. The flow of the material occurred over a period of days and, in some instances, the observed contact radii were greater than a critical radius for substantial engulfment of the particles by the substrate. Craters were left behind after particle removal, suggesting plastic-rather than elastic response of the substrate polymer to the surface-force-induced stresses. Size-exclusion chromatography has identified the presence of lower molecular weight polydimethylsiloxane-rich copolymer species in the n-hexane soluble mobile phase responsible for the unexpected behavior exhibited by this polymer substrate.     

Effect of 2-Phosphonobutane-1,2,4-tricarboxylic Acid Adsorption on the Stability and Rheological Properties of Aqueous Nanosized 3-mol%-Yttria-Stabilized Tetragonal-Zirconia Polycrystal Suspensions

2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) was evaluated as a dispersant for nanosized 3-mol%-Y₂O₃-stabilized tetragonal-ZrO₂ polycrystal (3Y-TZP) suspensions. The adsorption of PBTCA was characterized using the decolorization method of ferric 5-nitrosalicylate complexes. Maximum adsorption of the dispersant on the 3Y-TZP powder was found to occur at pH 3.0. At pH >3.0, the adsorbed amount decreased with increased pH. Semiquantitative analysis using auger electron spectroscopy showed that PBTCA adsorbed irreversibly on the powder. The surface charge of the powder was evaluated by measuring the zeta-potential in dilute powder suspensions. The suspension was most effectively stabilized at high pH by the high charge induced by the adsorption of PBTCA. Rheological properties of the suspension were evaluated as a function of dispersant amount and solids loading. The optimum amount of dispersant increased with increased solids loading for solids loading >20 vol%. A stable suspension of 35 nm 3Y-TZP particles with a solids loading as high as 32 vol% was obtained using PBTCA as dispersant, in contrast to 28 vol% when using ammonium polyacrylate (NH₄PAA). Theoretical calculations of the interaction between 3Y-TZP particles showed that the stabilization of the suspensions was attributed to a combination of the electrostatic repulsion and a steric barrier caused by the adsorbed PBTCA. Induced coupling plasma analysis showed that PBTCA could be completely burned out during sintering, which confirmed its suitability as a dispersant for 3Y-TZP.     

Adipose Tissue-Derived Stromal Cells Alter the Mechanical Stability and Viscoelastic Properties of Gelatine Methacryloyl Hydrogels

The extracellular matrix provides mechanical cues to cells within it, not just in terms of stiffness (elasticity) but also time-dependent responses to deformation (viscoelasticity). In this work, we determined the viscoelastic transformation of gelatine methacryloyl (GelMA) hydrogels caused by adipose tissue-derived stromal cells (ASCs) through mathematical modelling. GelMA-ASCs combination is of interest to model stem cell-driven repair and to understand cell-biomaterial interactions in 3D environments. Immortalised human ASCs were embedded in 5%, 10%, and 15% (w/v) GelMA hydrogels and evaluated for 14 d. GelMA had a concentration-dependent increase in stiffness, but cells decreased this stiffness over time, across concentrations. Viscoelastic changes in terms of stress relaxation increased progressively in 5% GelMA, while mathematical Maxwell analysis showed that the relative importance (R_i) of the fastest Maxwell elements increased proportionally. The 10% GelMA only showed differences at 7 d. In contrast, ASCs in 15% GelMA caused slower stress relaxation, increasing the R_i of the slowest Maxwell element. We conclude that GelMA concentration influenced the stiffness and number of Maxwell elements. ASCs changed the percentage stress relaxation and R_i of Maxwell elements transforming hydrogel viscoelasticity into a more fluid environment over time. Overall, 5% GelMA induced the most favourable ASC response.     

In Situ Surface Modification of Silicon Carbide Particles Using Al3+ Complexes and Polyelectrolytes in Aqueous Suspensions

Silicon carbide (SiC) particles were modified in situ , using Al³⁺ complexes in aqueous media, via control of Al(NO₃)₃concentration and pH. The Al³⁺ formed hydrolyzed complexes that adsorbed onto the charged sites on the SiC particle surfaces. As a result, the surface-modified SiC particles behaved in an alumina-like manner in the approximate pH range 5–8. The modified SiC particles were further treated with two types of polyelectrolytes that were sequentially adsorbed onto the particle surface, to give a maximum surface charge. As a result of this surface-modification process, the SiC could be dispersed with Al₂O₃in aqueous media without heteroaggregation.     

Influence of Acidity on the Stability and Rheological Properties of Ionically Stabilized Alumina Suspensions in Ethanol

The ionic stability of alumina particles in moderately concentrated ethanol suspensions is studied. Surface chemistry and interparticle forces are manipulated by controlling the acidity of the suspensions without dispersants. The acidity of ethanol solution is determined using ion transfer functions, wherein the relationships between acidity, alumina particle surface charge, zeta-potential, stability, and suspension rheological behavior are established. Positive isoelectric point (IEP) shift is observed for alumina in ethanol on increasing the solids concentration. However, dilute and concentrated aqueous suspensions of alumina give the same IEP. The viscosity and flow curves for alumina/ethanol suspensions are acidity dependent. The flow curves of the suspensions follow the Casson model, and the Casson yield value is used to evaluate suspension stability.     

Properties of a semi-crystalline and an amorphous thermotropic liquid crystalline polymer

The physical properties, thermal stability, rheology and tensile properties of a commercial semi-crystalline and an amorphous thermotropic liquid crystalline polymer (TLCP) have been investigated. Analysis by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) confirm the presence of a small melting endotherm and a glass transition in the former material. The as-received amorphous TLCP exhibits no obvious melting endotherm and a strong glass transition is detected. The flow and tensile properties of the semicrystalline polymer are dominated by the presence of the crystalline to nematic transition temperature. The properties of the amorphous TLCP appear to be governed by increasing mobility afforded by increasing temperature. Based on flow behaviour and further DSC analysis it has been shown that under appropriate annealing conditions the as-received amorphous TLCP can develop solid crystalline order.     

一种线型聚合物的合成及荧光性质

采用Heck缩聚反应合成了一个新的线型聚合物,聚[蒽-2,5-二(苯基)-1,3,4-噁二唑]交替共聚物(An-OXD)。化合物的结构经过红外光谱,核磁共振表征。An-OXD在二氯甲烷中最大吸收波长位于315 nm;荧光发射峰位于412 nm。线型聚合物An-OXD具有很强的荧光发射能力。     

Comparisons of the rheological behaviors of polypropylene and polymethyl methacrylate in a capillary die

In this study, the rheological characteristics of polypropylene (PP) melt at 210, 220, and 230 °C and polymethyl methacrylate (PMMA) melt at 230, 240, and 250 °C in a micro die were investigated. The experiments were performed over a shear rate range of 3 × 10² to 5 × 10³ s^?1 using an advanced twin‐bore capillary rheometer. Dies with diameters of 1.0, 0.5, and 0.25 mm were used. The results indicated that the geometric dependences of the PP and PMMA viscosities were not identical at different shear rates and temperatures and that the micro size effect had a profound influence on the PP viscosity. The analysis demonstrated that the variations in the shear viscosity of the PP and PMMA melts in the micro die were partially attributed to the contribution of the pressure applied to the polymer melts. Additionally, the effect of wall slip on the PP and PMMA viscosities in the tested dies was investigated based on the modified Mooney method. The results implied that wall slip easily occurred in the PP melt flowing through the 0.25 mm die at 210 °C due to the distinct size effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44617.     

Linear Viscoelastic Characteristics of Poly(trimethylene terephthalate)/Polycarbonate Blends in the Melt State

Summary: Blends of poly(trimethylene terephthalate) (PTT) and polycarbonate (PC) over full composition range were prepared using a twin‐screw extruder. A glycidyl methacrylate‐based terpolymer was used to modify the interface of the blends. Morphological examinations were carried out using transmission electron microscopy (TEM) and confirmed the biphasic structure of the blends. Dynamic rheological response of the blends was recorded in the linear viscoelastic region. It was observed that addition of the terpolymer to the system increases the dynamic shear moduli and complex viscosity of the blends, which is attributed to interactions of the terpolymer at the interface of two phases leading to a restricted chain mobility of the blend components. The Veenstra model was found to be able to describe dynamic shear modulus of the PTT/PC 50/50 blend; however, for the compatibilized blend of PTT/PC 50/50, the fit is not as good as that of uncompatibilized system, which is believed to be due to formation of micelles in this system.

Dynamic storage modulus of the compatibilized and uncompatibilized PTT/PC blends.     

Storage modulus of polybutadiene core in acrylonitrile–butadiene–styrene polymers with different degrees of grafting

The linear viscoelastic behavior of acrylonitrile‐butadiene‐styrene (ABS) polymers in the molten state, with different degrees of grafting, was investigated within the framework of Palierne's emulsion model. The main aim of the present study is to quantitatively analyze the effect of grafting degree on the storage modulus G′ of the polybutadiene (PB) rubber core dispersed in ABS polymers. According to our model calculations, the degree of grafting significantly affects the G′ values of the PB core and, hence, the viscoelastic properties of ABS polymers. Our calculations showed that the Palierne model is very useful to calculate the storage modulus of the rubber particles dispersed in rubber‐modified polymeric materials, at least in the high‐frequency region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 924–930, 2001     

Rheology of cubic particles in a concentrated colloidal dispersion suspending medium

The flow behavior of mixtures of micron‐sized cubic particles suspended in a concentrated colloidal dispersion is investigated across a broad range of cubic particle concentrations. In the semi‐dilute regime, the qualitative shape of the dynamic moduli and flow curves reflect those of the underlying colloidal dispersion medium. These curves are superimposed with the underlying colloidal dispersion using shift factors that are found to be larger than those obtained in a recent study of suspensions of non‐colloidal spherical particles in the same colloidal dispersion medium. At higher concentrations of cubic particles, deviations from this shifting procedure are apparent. Scaling calculations suggest depletion interactions are responsible for the increase in the low shear viscosity and confinement of the underlying colloidal dispersion can be expected to enhance the shear thickening behavior at high shear stresses. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1091–1101, 2017     

团聚硼颗粒在HTPB富燃料推进剂中的流变特性

为了探索球形团聚硼颗粒的制备效果,对端羟基聚丁二烯(HTPB)黏合剂、不同类型的团聚硼颗粒与HTPB黏合剂以一定质量配比形成的悬浮液,以及含团聚硼颗粒HTPB富燃料推进剂流变特性进行了对比研究。结果表明,HTPB黏合剂的表观黏度随温度的升高而降低,最终趋于某一定值;在一定温度下,无定形硼粉经团聚改性后,团聚硼颗粒与HTPB形成悬浮液的表观黏度和屈服值较团聚前降低,且两者均随时间的增加而增加;采用含团聚硼颗粒的富燃料推进剂药浆的流变特性大大改善,有利于含硼富燃料推进剂能量的提高和燃烧性能的改善。