Mass Transfer in a Flat Gas/Liquid Interface using non‐Newtonian Media

Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients.     

Improvement of the deflocculating power of polyacrylates in ceramic slips by small additions of quaternary ammonium salts

In this work, we examine the effect of small additions of cationic quaternary ammonium salts (QAS) of different molecular weight on the rheology of an industrial ceramic suspension deflocculated with sodium polyacrylate and sodium metasilicate. The observed shear thinning behaviors obey the typical power law of fluid rheology. In order to characterize the rheological behavior of these slurries, three new parameters are introduced: a low shear rate consistency index and two transient viscosities, distant from the equilibrium, after increasing and decreasing the shear rates. These parameters vary with polyacrylate molecular weight and on additions of small quantities of QAS, which we found to be useful for decreasing the slurry viscosity.     

Structure and dynamics of dipolar fluids under strong shear

Molecular dynamical simulation has been carried out to investigate the structure and dynamics of a dipolar fluid under strong shear. Dipolar fluid consists of polarizable particles, which have an induced dipole moment in the applied field direction. Shear stress is perpendicular to the field direction. When shear stress is small, the flow has a flowing-chain structure. If shear stress increases to pass a critical value, flowing-chain structure changes to flowing layer structure. Each layer is parallel to the flow direction and shear direction. Within one layer, particles form strings in the flow direction.     

Investigation of the relationships between the chain organization and rheological properties of atactic poly(vinyl alcohol) hydrogels

The structure and rheological behavior of atactic poly(vinyl alcohol) (a-PVA) hydrogels prepared by freeze/thaw cycles were investigated as a function of polymer concentration and number of freeze/thaw cycles. The presence of phases with different mobilities was observed using ¹³C CP/MAS and DP/MAS NMR experiments. The degree of crystallinity of the a-PVA-rich phase was determined by ¹H NMR free decay experiments. Measurements of the shear storage and loss modulus were performed at a fixed frequency of 1 Hz and a strain value of 0.1%, i.e. under conditions where the deformation imposed on the gel structure is entirely reversible. Results thus obtained showed that an increase in the number of freeze/thaw cycles induces an increase in the degree of crystallinity in the polymer-rich phase together with an increase in the storage modulus. The a-PVA hydrogels became more fragile as the number of freeze/thaw cycles was increased. Moreover, both the percentage of protons in a rigid environment measured by ¹H NMR and the storage modulus values tended to a limiting value after six freeze/thaw cycles. These results show that the first five or six freeze/thaw cycles play a very important role in determining the hydrogel structure and rheological properties. A more detailed comparison of NMR and rheological data led to the conclusion that the storage modulus is mainly controlled by the a-PVA crystallinity while the hydrogen bond interactions have a much smaller contribution.     

外加剂混凝土动态与静态坍落度损失的流变特性

本文对动、静态下混凝土坍落度损失的规律进行了研究,并从流变学的角度分析了外加剂对动、静态下混凝土坍落度损失的影响坍落度损失存在差别的原因.     

Mixture-proportioning of high-performance concrete

The paper presents a new approach to design concrete mixtures. It is based upon a set of models relating composition and engineering properties of concrete, to be implemented into software, linked with a material database. The principles underlying the various models are summarized, most of which focus on the granular structure of fresh/hardened concrete. A global approach to concrete is promoted, where performance specifications can be formulated in terms of fresh concrete (yield stress, plastic viscosity, slump and air content), hardening concrete (adiabatic temperature rise and autogenous shrinkage) and hardened concrete (compressive strength at any age, tensile strength, elastic modulus, creep and shrinkage). This approach is illustrated through the design of a special high-shrinkage high-performance concrete (HPC) for road application. To date, durability is lacking in the model and requires further research.     

Properties of paper coated with kaolin: The influence of the rheological modifier

The first part of this paper analyses the influence of the molecular weight and concentration of carboxymethyl cellulose (CMC) and of kaolin concentration on rheology of the coating colours and on paper properties coated with ultra lightweight coatings (ULWC). In the second part, relationships between the rheological characteristics of the coating colour formulations and coated paper surface quality was also studied.New indexes on paper roughness at micro-scale are presented (RZI and SRI). In general, they show good correlation with sheet gloss. A new gloss index (SGI) is presented, accounting for the contribution of gloss from machine direction (MD) and cross direction (CD). Porosimetry was used to access microstructural characteristics in order to correlate them with light scattering and gloss properties. The former property is closely related to Hg intrusion volume of the coated layer while gloss is related to surface porosity with pore diameters in the range of 7–15 μm as measured by Hg intrusion volume.     

Ring-opening polymerization of decamethylcyclopentasiloxane initiated by a superbase: Kinetics and rheology

The use of phosphazene bases in combination with water was proved to be efficient in order to obtain polysiloxane polymers from cyclic monomers. Only a few minutes are necessary to obtain polymer chains with a monomer concentration of 5% at the equilibrium. For that purpose the space which is between a rheometer's plates is the most convenient device to monitor this reaction concerning a chemical and viscoelastic point of view. Therefore, here is proposed a chemo-rheology study that leads in the same time to the chemical kinetics equations and to the variation of the viscoelastic functions during the polymerization. In this way different catalysts are used and their efficiencies are compared as a function of their “basicity tank”. Whatever the experimental conditions involved are, viscosity versus polymer concentration or conversion shows a master curve for catalysts suitable to be used under extrusive conditions. Thus, only a few experiments are needed in order to develop a model which can be used to foresee the variation of the viscosity during the reaction.     

Synthesis of polymeric pour point depressants for Nada crude oil (Gujarat,India) and its impact on oil rheology

Five flow improvers have been synthesized to study rheological properties of Nada crude oil (Gujarat, India). Anhydride copolymers were prepared making use of the copolymerization of acrylates of different alkyls with maleic anhydride and the Poly (n-alkyl acrylates-co-N-hexadecylmaleimide) were prepared by the reaction of copolymer with hexadecylamine. The additives were purified and characterized by FTIR, GPC. The prepared polymeric additives shows dual function both as wax dispersants and flow improvers and all of them acts as good pour point depressants. Yield stress and the viscosity of the crude oil at different temperatures and concentrations of additives were evaluated by zero friction advanced rheometer AR-500 of TA instrument. Comparison of morphologies and structures of wax crystals or aggregates in waxy crude oils beneficiated with and without a PPD was also done by micro photographic studies which show the modification in wax crystal morphology due to additives.     

粘合剂流变特性的研究(待续)

本文从流变学的观点出发,分析粘合剂在配制及粘结过程中,反映出不同的流变特性,而粘合剂本身的流动、粘度、触变性与涂胶及其粘合的质量关系重大。