Dynamic Stability of Heavy Crude Oil-in-Water Emulsions

The transport of heavy oil as concentrated oil-in-water (O/W) emulsions is one of the most promising pipeline techniques, and how to ensure a steady flow is the key to the successful application of this technology. Most of the previous studies focused on the static stability of the emulsions. However, the stability changes constantly with time and external shearing in the transportation. In this paper, a stable O/W emulsion was prepared for its dynamic stability to be tested by three methods of small-scale flow loop, rheology and stirring, respectively. The results indicated that the O/W emulsion with 30 vol.% water and 0.2 wt.% OP-10 could well satisfy the transport requirement. A critical temperature existed to make the rheological property of the emulsion rapidly deteriorate. For low-Reynolds-number turbulent pipe flow, an appropriate increase of temperatures and shear rates was conducive to the flocculation-dissociation balance of the internal phase, which could effectively reduce the apparent viscosity of the emulsion and the flow frictional resistance. High flow rate of O/W emulsions could be transported at relatively low temperatures to ensure great dynamic stability, and low flow rate of that could be done at relatively high temperatures to obtain low apparent viscosity.     

Alteration of Interfacial Stability of Oil-in-Water Emulsions Using Bio-Derived Additives

Oil-in-water (O/W) emulsions are widely used in the preparation of many cosmetics, foods, and pharmaceutical products. Microstructure and stability of such emulsions are of utmost importance for their acceptability by the end user. In the present work, we studied the O/W emulsions to know the effects of two bio-derived additives—juice of Coriander sativam L., and milk of Cocos nucifera L, which have good nutrient value for their use in food emulsions. Addition of Cocos nucifera L. milk resulted in enhanced stability with decrease in the polydispersity of dispersed droplets in the emulsions due to the presence of proteins in it. Addition of Coriander sativam L. provided better stability against pH variation from 4 to 8.     

Flocculation and Coalescence of Oil-in-Water Poly(dimethylsiloxane) Emulsions

The stability of poly(dimethylsiloxane) (PDMS) oil-in-water emulsions has been investigated in the presence of added NaCl as well as in the presence of added surfactant. The emulsions were prepared using a combination of nonionic (C(x)E(y), x and y represent the number of methylene (C) and ethylene oxide (E) groups, respectively) and cationic (quarternary alkylammonium) surfactants. The droplets were observed to exhibit weak flocculation in the presence of high NaCl concentration (1 M). Phase separation and optical microscopic observations revealed that the principal mechanism for emulsion destabilization at high salt concentration was coalescence, which was accelerated at elevated temperature (50 degrees C). The effective coalescence rate for diluted emulsions was investigated using photon correlation spectroscopy. The small effective Hamaker constant for PDMS is the primary reason for the slow rate of coalescence observed for the emulsions at neutral pH in the presence of NaCl. The stability of PDMS emulsions to flocculation is qualitatively similar to that reported for low Hamaker constant dispersions (e.g., microgel particles). Addition of cationic surfactants (cetyltrimethylammonium chloride and dodecyl dimethylbenzylammonium chloride) to the negatively charged droplets after preparation was shown to decrease the emulsion stability once the surfactant concentration exceeded the CMC. Electrophoretic mobility measurements showed that added cationic surfactant changed the sign of the droplet charge from negative to positive at concentrations well below the CMC. Charged micelles of the same sign as the droplets are electrostatically excluded from close approach to the droplet surface within a distance (varepsilon) which results in depletion flocculation. Copyright 2000 Academic Press.     

Analysis of the Rheological Behavior of Copper Metal Injection Molding (MIM) Feedstock

Metal Injection Molding (MIM) technique allows for the production of highly porous metallic foams with porosity levels up to 90%. It makes use of the pressure built up by the decomposition of a foaming agent which is incorporated in a foamable precursor copper material obtained by powder compaction. Rheological is one of the key factors to ensure the successful of MIM technique and to predict failure, whether due to the binder component and compositions, powder loading or unsuitable process parameters. The balanced ratio feedstock contains of 63 vol.% of copper powder, different percentage of potassium carbonate; Batch 1 (0.4 vol.%), Batch 2 (0.5 vol.%) and Batch 3 (0.6 vol.%), and the remaining volume percentage of binder system has been mixed to form copper feedstock. The rheological behaviors were investigated using a capillary rheometer (CFT-500D, Shimadzu) at various temperature and loads. From the experiments, it was concluded that the MIM feedstock exhibit a shear thinning or pseudo-plastic behavior based on the trend of graph which is suitable for MIM process. This result is within the ideal range of viscosity theoretical for MIM feedstock which is in the range of between 10 Pa.s to 1000 Pa.s at all temperature tested. The viscosity of a pseudo-plastic substance decreases as the shear rate increases (shear thinning). This could be due to particle orientation and ordering with flow as well as breakage of particle agglomerates released together with the binder.     

Rheological characterization of functional walnut oil-enriched butters stabilized by the various polysaccharides

Dynamic rheological measurements provide a valid determination of the ability of polymeric ingredients to compensate the reduced contribution of fat to texture and mouthfeel, as well as provide an emulsion that easily breaks down in commercial low-fat butters. In this study, the linear effects of pectin (PE, 0.5%) and xanthan gum (XG, 0.1%) and their interactions with locust bean gum (LBG, 0.2% and 0.4%), sodium-alginate (ALG, 0.2% and 0.4%), and modified starch (MS, 0.2% and 0.4%) on the flow behavior, dynamic rheological characteristics, and stability of reduced-fat butters containing 10% walnut oil (WO) were investigated. Results showed that the power law model can adequately fit the shear-rate/shear-stress data (0.888?≤?r?≤?0.992, p?G′?>?G″ at all frequencies. The samples prepared with PE–LBG (0.2% and 0.4%) and XG–ALG (0.4%) had the highest G′ values. The phase angle (G″/G′) decreased with increasing frequency from 0.03 to 15?Hz. The maximum apparent viscosity and stability were, respectively, found for WO butters formulated with XG–0.2% ALG and PE–0.4% LBG.     

Optimization of Oil-in-Water Emulsion Stability: Experimental Design,Multiple Light Scattering,and Acoustic Attenuation Spectroscopy

To find an optimal formulation of oil-in-water (O/W) emulsions (φ_o = 0.05), the effect of emulsifier nature and concentration, agitation speed, emulsifying time, storage temperature and their mutual interactions on the properties and behavior of these dispersions is evaluated by means of an experimental design (Nemrodw software). Long-term emulsion stability is monitored by multiple light scattering (Turbiscan ags) and acoustic attenuation spectroscopy (Ultrasizer). After matching surfactant HLB and oil required HLB, a model giving the Sauter diameter as a function of emulsifier concentration, agitation speed and emulsification time is proposed. The highest stability of C₁₂E₄-stabilized O/W emulsions is observed with 1% emulsifier.     

取代度和金属平衡离子对羧甲基纤维素热行为的影响

低取代度(DS<0.8)的NaCMC具有纤维素(Ⅱ)型的晶型结构,随DS增加结晶度迅速下降,DS>1时为无定形结构。其T_(?)随DS增加而降低,但DS=1.55的CMC的T_(?)则稍有提高。其起始分解温度(T_(?))随DS增加而增加,而分解活化能则与DS没有规律性的关系。CMC链上的平衡离子H~+、Na~+、Mg~+、Ca~+和Al~(3+)等对其结晶形态的破坏能力不同,对相同价数的离子,随离子半径增大,破坏力增强,而对半径相近的离子,高价的比低价的破坏作用明显。NaCMC的分解活化能E=251～293 kJ/mol,而高价平衡离子的CMC的E=105 kJ/mol左右。     

Rheological properties of carboxymethyl cellulose (CMC) solutions

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.     

pH-Dependent Aggregation Behavior and Emulsion Stability of Comb-Like Surfactant Containing PEO Grafts

The aggregation behavior of the comb-like surfactant, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA-M), prepared via the one-pot method, at surface and in solution, was investigated by equilibrium surface tension, rheological technology, and transmission electron microscopy (TEM). The emulsion prepared from n-decane/water/C₁₃E₇ was used as a model system to determine the influence of SMA-M on the stability of the emulsion. The equilibrium surface tensions of SMA-M solution with various pH were measured. The adsorption data, that is, the saturation surface excess concentration (Γ_max) and the minimum area (A _min) were evaluated using the average monomeric molecular weight (M _nA ). The results showed that Γ_max decreased with the increase of pH, but the A _min enlarged with the increase of pH. The results of the steady-state shear experiment indicated that the aggregate structure of the as-prepared comb-like surfactant SMA-M in aqueous solution evolved from interlinked micelle-like aggregates to isolated inflated micelle-like aggregates, then to rod-like aggregates with the increasing pH, which were confirmed by the TEM images. The investigation of the stabilization of n-decane/water/C₁₃E₇/SMA-M emulsion system indicated that SMA-M obviously slows down the phase separation, and the most effectively stabilized sample was obtained at pH 5.0. Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.     

Thermal and Rheological Behavior of Collagen. Chitosan blends

Collagen:chitosan blends in 1:1 ratio were prepared and characterized by Fourier transform infrared spectroscopy, thermal (DSC, TG) and rheological studies. Apparently each material maintains its behavior and addition of chitosan does not denature collagen fibers. The rheological behavior showed that adding chitosan to collagen causes a decrease of storage modulus (G’),viscous loss modulus (G”) and apparent viscosity when measured as a function of frequency. Both anionic and native collagen presented more solid-like behavior than fluid-like viscoelastic behavior. Collagen:chitosan blends exhibits a more fluid-like viscoelastic behavior. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Emulsifier Type on the Crystallization Kinetics of Oil-in-Water Emulsions Containing a Mixture of Solid and Liquid Droplets

Measurements of the ultrasonic velocity as a function of time (at 6.0°C) have been used to monitor the kinetics of crystallization of oil droplets in n -hexadecane-in-water emulsions containing a mixture of solid and liquid droplets. Crystallization is induced in liquid droplets when solid droplets are present. Induced crystallization is probably caused by crystals, protruding from solid droplets, penetrating into liquid droplets during collisions and thus acting as nucleation sites for crystal growth. The rate of induced crystallization depends strongly on the type of emulsifier used to stabilize the emulsion droplets. For the series of emulsifiers used in this study the rate decreased in the following order: Tween 20 > SDS > β-lactoglobulin > β-casein. Differences in rate can be explained by considering the influence the emulsifiers have on the interactions between droplets.     

CMC/PNIPAAm半互穿网络水凝胶的溶胀动力学研究

以羧甲基纤维素钠(CMC)和N-异丙基丙烯酰胺(NIPAAm)为原料,制备了具有温度和pH敏感性的半互穿网络(CMC／PNIPAAmsemi-IPN)水凝胶,并研究了水凝胶在不同温度和pH值条件下的溶胀行为。结果表明：在弱碱性(pH-7．4)条件下,凝胶的溶胀速率和溶胀度都随着凝胶中CMC含量的增加而增大;而在酸性(pH-1．O)条件下则相反。在弱碱性条件下,水分子在凝胶中的扩散行为都可用non-Fickian扩散来描述,水分子在凝胶中的扩散系数D随着凝胶溶胀速率的增大而增大;在酸性条件下,20℃时凝胶的溶胀过程符合non-Fickian扩散规律,而37℃时凝胶的溶胀过程符合Fickian扩散规律,但水分子的扩散系数D相差不大。     

Water Sorption to Hydroxyl and Carboxylic Acid Groups in Carboxymethylcellulose (CMC) Studied with NIR-spectroscopy

In carbohydrate systems which contain polar groups such as hydroxyl and carboxylic acid groups, water molecules are adsorbed in a specific way which varies with the type of polar group. Near infrared Spectroscopy (NIR) combined with multivariate statistical analysis was used to study the interactions between water molecules and carboxymethylated cellulose (CMC) with various degrees of substitution of the carboxylic acid groups, in two ionic forms (CMC-Na and CMC-Ca). The adsorbed water molecules were clearly influenced by the counterion; i.e. the nature of the ion-pair. A principle component analysis (PCA) identified variations in the registered spectra related to: the nature of the counter-ion, the degree of substitution (DS), the relative humidity (RH) and the type of polar group to which water was adsorbed. It was, possible furthermore, through the use of partial least square analysis (PLS), to extract spectral information related to the non-freezing bound water adsorbed on hydroxyl and carboxyl groups respectively. Loading spectra indicated that the obtained spectral information indeed correlated to the two kinds of polar groups studied (hydroxyl groups and carboxylic acid groups). The results support the view that, in the humidity range of 0–100%, water molecules are specifically adsorbed to individual polar groups, which characteristics are dependent on the nature of the polar group.     

Double Emulsions Stabilized by Xanthan in the Absence of Hydrophilic Surfactant

The preparation of double water-in-oil-in-water (W/O/W) emulsions containing xanthan gum (XG) in the absence of hydrophilic surfactant was investigated. The emulsions were prepared by the two-step emulsification process. The stability of these systems was evaluated through the evaluation of physicochemical and rheological properties. Microscopic observations in combination with particle size analysis were also performed. The obtained results show that it is possible to prepare stable double emulsions with a single polysaccharide by using the indirect process. The stability depends on the viscosity of the continuous phase and hence the concentration of XG. The apparent viscosity of the emulsions increased with the increase of XG concentration. Particle size analysis shows that the droplet sizes are directly related to XG concentration.     

Synthesis and performance of a Mono (dodecafluoroheptyl) acetate surfactant

A novel fluorinated surfactant, sodium 1?H, 1?H, 7H-dodecafluoro-1-heptyloxy acetate (DFHAS), was synthesized via a facile two-step synthetic procedure. The structure of product on each step was characterized by ^1?H NMR, ^19?F NMR, ¹³C NMR, FT-IR, and mass spectrum (MS). Ultraviolet absorption (UV) and ring measurements were performed to obtain detailed information of its surface properties. The results demonstrated that the novel surfactant possessed very low critical micelle concentration (CMC, 7.94?mM) and surface tension (20.01?mN/m). Furthermore, the surfactant had preferable thermal stability compared with other perfluorocarboxylates characterized by thermal gravimetric analysis (TGA). The practical application performance of DFHAS was finally validated through the emulsion polymerization of vinylidene fluoride (VDF) by means of its excellent emulsifying activities. It is expected that this versatile synthetic strategy may help fabricate satisfying green surfactant systems for the application in fields of emulsion polymerization, drug delivery and greases.GRAPHICAL ABSTRACT     

Characterization of gamma irradiated carboxymethyl cellulose (CMC) films loaded with metal salts and fertilizers

Carboxymethyl cellulose (CMC) films loaded with different metal ions and fertilizers have been successfully prepared by the solution casting technique. The prepared films were subjected to different doses of gamma radiation at room temperature. The preparation conditions such as effect of type of metals, fertilizers and radiation dose on gel fraction (%) and swelling (%) were investigated. The maximum value of gel fraction was obtained at 10 kGy radiation dose. The formation of CMC/metal complexes was confirmed by X-ray diffraction (XRD), infrared spectroscopy and scanning electron microscope (SEM) which confirm the existence of possible interaction between CMC and metal ions. The loading of various metal ions to CMC films were found to enhance the mechanical properties of the prepared films. The results provided confirmation that metal coordination between the metal cation and the carboxylate group of CMC occurred.     

Voltammetric Behavior of Uranium(VI) in Sulfuric Acid Solutions Containing Pyridine

It was shown that 8.8 × 10^–5 to 4.4 × 10^–3 M uranium(VI) in sulfuric acid solutions containing pyridine give a clearly defined cathodic peak with a height proportional to uranium(VI) concentration. Under the specified conditions, the electroreduction of uranium(VI) is irreversible and involves one electron, the limiting current of uranium(VI) is diffusion- and kinetically controlled. The kinetic parameters of the process under study were determined, and the effect of concomitant elements on the voltammetric behavior of uranium(VI) in pyridine-containing sulfuric acid supporting electrolytes was estimated.     

扩张流变法研究表面活性剂在界面上的聚集行为

近年发展起来的界面流变测定技术在研究界面性质方面具有许多独特之处.本文结合我们的工作,总结了近年来有关该技术在表面活性剂界面聚集行为研究中的应用,讨论了扩张频率、表面活性剂浓度及疏水链长、无机盐和温度对表面扩张流变行为的影响,同时探讨了小分子表面活性剂与高分子表面活性剂表面扩张流变行为的区别以及小分子表面活性剂在气/液界面与液/液表面的扩张流变性的差异.大量研究表明,借助于界面流变性的测定不仅可以研究发生在界面上和界面附近的微观弛豫过程,而且可以探讨界面上超分子聚集体的形成,进而为乳状液和泡沫等分散体系的稳定性提供依据.     

Experimental Investigation of Rheological and Morphological Properties of Water in Crude Oil Emulsions Stabilized by a Lipophilic Surfactant

Rheological behavior of two crude oils and their surfactant-stabilized emulsions with initial droplet sizes ranging from 0.5 to 75 µm were investigated at various temperatures under steady and dynamic shear testing conditions. In order to evaluate the morphology and Stability of emulsions, microscopic analysis was carried out over three months and average diameter and size distribution of dispersed droplets were determined. The water content and surfactant concentration ranged from 10 to 60% vol/vol and 0.1 to 10% wt/vol, respectively. The results indicated that the rheological properties and the physical structure and stability of emulsions were significantly influenced by the water content and surfactant concentration. The crude oils behaved as Newtonian fluids over a wide range of shear rates, whereas the emulsions behaved as non-Newtonian fluids, indicating shear-thinning effects over the entire range of shear rates. The viscosity, storage modulus and degree of elasticity were found to be significantly increased with the increase in water content and surfactant concentration. The maximum viscosity was observed at the point close to the phase inversion point where the emulsion system changes from water-in-oil emulsion to oil-in-water emulsion. The results also indicated that the rheological properties of crude oils and their emulsions are significantly temperature-dependent.