A study of interfacial dilational properties of two different structure demulsifiers at oil-water interfaces

The interfacial dilational viscoelastic properties of two demulsifiers with straight chain (SP-169) and branched chain (AE-121) at the oil-water interfaces were investigated by means of the longitudinal waves method and the interfacial tension relaxation method, respectively. The results obtained by the longitudinal waves method showed that the dilational viscous component for AE-121 and SP-169 also passed through a maximum value with increasing concentration. It was found that the maximum value appeared at different demulsifier concentrations during our experiment frequency; and the higher is the dilational frequency, the lower is the concentration. The influences of AE-121 and SP-169 on the dilational viscoelastic properties of the oil-water interface containing surface-active fraction from Iranian crude oil have been measured. The results clearly stated that both demulsifiers could obviously decrease the dilational elasticity of oil-water interface containing surface-active fraction. At low concentration, because of stronger adsorption ability, SP-169 has stronger ability to decreasing the dilational modulus than AE-121. We also found that the dilational modulus of the interface contained surface-active fraction passed through a minimum value with increasing demulsifier concentration for both demulsifiers. This result indicated the dosage of demulsifier had an optimum value. The results obtained by means of interfacial tension relaxation method showed that the slow relaxation processes involve mainly rearrangement in the conformation of the molecules appeared with increasing demulsifier concentration.     

Dewatering of crude oil emulsions 2. Interfacial properties of the asphaltic constituents of crude oil

The importance of the interfacial rheology in determining the stability of water-in-Buchan crude oil emulsions has been demonstrated in part 1 of this series of papers (R.A. Mohammed, A.I. Bailey, P.F. Luckham and S.E. Taylor, Colloids Surfaces A: Physicochem. Eng. Aspects, 80(1993)223). In part 2, interfacial tensions of crude oil, and solutions of asphaltenes and resins in a model oil have been investigated. Surface pressure vs. area (Π—A) curves of monolayers of asphaltenes, resins and their mixtures have been established. In its dependence on the ratio of resins to asphaltenes, the pseudostatic dilatational modulus has high values for low resin-to-asphaltene ratios and low values for high resin-to-asphaltene ratios. This is expected to throw light on the cause of the enhanced stability of water-in-crude oil emulsions.     

界面张力弛豫法研究不同分子量原油活性组分界面扩张粘弹性

采用界面张力弛豫法研究了不同分子量原油活性组分在正癸烷-水界面上的扩张粘弹性质,阐述了界面扩张模量的弹性和粘性随扩张频率的变化规律.研究发现,随着原油活性组分分子量的增大,极限扩张粘度明显增大,而极限扩张弹性逐渐增大;当分子量大于某一数值后,极限扩张弹性变化不明显.对界面张力弛豫实验结果进行拟合得到的参数表明,界面上和界面附近的微观弛豫过程的数目随原油活性组分分子量的增加而增加,弛豫过程的特征频率也呈规律性变化.不同原油活性组分的界面扩张粘弹性质可从其不同特征的微观弛豫过程得到解释.     

Polyelectrolyte/surfactant mixtures in the bulk and at water/oil interfaces

Stabilization of emulsions by mixed polyelectrolyte/surfactant systems is a prominent example for the application in modern technologies. The formation of complexes between the polymers and the surfactants depends on the type of surfactant (ionic, non-ionic) and the mixing ratio. The surface activity (hydrophilic–lipophilic balance) of the resulting complexes is an important quantity for its efficiency in stabilizing emulsions. The interfacial adsorption properties observed at liquid/oil interfaces are more or less equivalent to those observed at the aqueous solution/air interface, however, the corresponding interfacial dilational and shear rheology parameters differ quite significantly. The interfacial properties are directly linked to bulk properties, which support the picture for the complex formation of polyelectrolyte/surfactant mixtures, which is the result of electrostatic and hydrophobic interactions. For long alkyl chain surfactants the interfacial behavior is strongly influenced by hydrophobic interactions while the complex formation with short chain surfactants is mainly governed by electrostatic interactions.     

Comparison of rheological properties of cross-linked and thermal-mechanically degraded HDPE

Rheological properties of a high-density polyethylene (HDPE) subjected to thermal-mechanical degradation were compared with those of the HDPE degraded by the addition of small quantities of peroxides as free radical initiator. The high molecular weight fraction of HDPE changes quantitatively during processing, which has a remarkable effect on the rheological properties of the material, when the MWD narrows and the HMW tail decreases. The molecular weight distribution, especially the highest molecular weight fraction, is concluded to be more important than the long chain for HDPE rheology. © 1995 John Wiley & Sons, Inc.     

褐煤中水分对油煤浆流变性质的影响

针对云南褐煤,用真空干燥脱水和恒温恒湿箱处理获得了不同含水率的褐煤,在常温常压(t=19.3℃,p=1.01×105Pa)条件下研究了褐煤含水率对油煤浆流变特性的影响。研究表明,原料煤含水率对油煤浆黏度和流变特性有一定的影响。随褐煤含水率增加,油煤浆黏度先减小后增加。油煤浆浓度不同,剪切速率不同,黏度出现最低值的含水率值wmin也不同。浓度为45.45%的油煤浆,剪切速率小于4.4 s-1时,wmin为9.20%;剪切速率大于4.4 s-1时,wmin为7.80%。浓度为55.56%的油煤浆,剪切速率小于1.32 s-1时,wmin为7.40%;剪切速率大于1.32 s-1时,wmin为10.00%。随剪切速率变化,油煤浆黏度上下行曲线之间形成滞后环,表明油煤浆体系有触变性,并且不同含水率煤浆体系触变性不同,含水率越大,触变性越明显。实验中不同含水率褐煤油煤浆都属于假塑性流体,且含水率对模型参数有一定的影响。     

Impedance spectroscopy of reactive polymers. 3. Correlations between dielectric,spectroscopic, and rheological properties during cure of a trifunctional epoxy resin

An investigation was carried out of correlations between dielectric, vibrational spectroscopic, and rheological properties during cure of a thermoset formulation composed of trifunctional epoxy resin and tetrafunctional amine. Experimental techniques utilized include impedance spectroscopy, near-infrared spectroscopy, steady shear, and dynamic mechanical measurements. Reaction kinetics obtained from dielectric and spectroscopic results were in excellent agreement. Gelation and vitrification times determined by dielectric and rheological measurements were also found to agree very well, despite the empirical nature of such correlations. A characteristic pattern in plots of imaginary impedance as a function of reaction time was reported for the first time in the open literature, and it was suggested that it could be used to identify gelation and vitrification during the network formation. A realization of the full potential of dielectric impedance spectroscopy in monitoring the progress of chemophysical changes in reactive polymers, however, hinges upon a development of fundamental scientific correlations between dielectric and chemorheological phenomena during cure.     

Measurement of rheological properties of corn stover suspensions

Corn stover is currently being evaluated as a feedstock for ethanol production. The corn stover suspensions fed to reactors typically range between 10 and 40% solids. To simulate and design bioreactors for processing highly loaded corn stover suspensions, the rheologic properties of the suspension must be measured. In systems with suspended solids, rheologic measurements are difficult to perform owing to settling in the measurement devices. In this study, viscosities of corn stover suspensions were measured using a helical ribbon impeller viscometer. A calibration procedure is required for the impeller method in order to obtain the shear rate constant, k, which is dependent on the geometry of the measurement system. The corn stover suspensions are described using a power law flow model.     

Impact of imidazolium-based ionic liquid surfactant additions on dilational rheology properties of different protein adsorption layer

The interfacial behavior of β-casein and BSA solutions have been investigated in the presence of imidazolium-based ionic liquid surfactant ([C₁₄mim]Br) at the decane/water interface with the oscillating the drop and interfacial tension relaxation measurements. Both the electrostatic and the hydrophobic interaction between protein and [C₁₄mim]Br played crucial roles as [C₁₄mim]Br concentration increases. Furthermore, it was found that the dilational rheology parameters provided information of the adsorbed layers structure, and the dynamics properties of the adsorbed layers depend on the bulk [C₁₄mim]Br concentration. Moreover, with the concentration of [C₁₄mim]Br increasing, β-casein in the interfacial layer was subject to conformational changes where it gave space to [C₁₄mim]Br molecules in the form of co-adsorb; for BSA/[C₁₄mim]Br solutions, the globule protein BSA deformed and then co-adsorb with [C₁₄mim]Br molecules at the decane/water interface. These results will contribute to elucidation of the influence of the surfactant on the different structure proteins and the wide applications of protein/surfactant systems in practice.     

聚丙撑碳酸酯的流动性能表征

本文研究了聚丙撑碳酸酯的流动性能及其影响因素，实验表明聚丙撑碳酸酯为假塑性流体，它的表观粘度随着温度升高而降低，流动活化能随着剪切速率增加而变小，并得到了表观粘度与粘均分子量之间的定量关系．     

The rheological and thickening properties of cationic xanthan gum

In the present study, cationic xanthan gum (CXG) was synthesized to enhance the rheological property of xanthan gum (XG) by attaching quaternary amine groups to the backbone of XG. The efficacy of the substitution was confirmed by FT-IR spectra and ¹³C NMR. The surface morphology was changed considerably as demonstrated by SEM. The examined rheological properties of XG and CXG include steady-state and dynamic rheological properties. The results show that quaternary amine groups are successfully grafted onto the XG molecule. Apparent viscosity, storage modulus, and loss modulus of CXG solutions are greater than those of XG solutions under the same conditions. It is moreover found that apparent viscosity and viscoelasticity increase with the degree of substitution. The data indicate that the modified XG has much better heat resistance.     

Surface dilational moduli of polymer and blended polymer monolayers spread at air-water interfaces

Surface dilational moduli of polymer monolayers, blended polymer monolayers, and polymer particle monolayers spread at air–water interfaces are reviewed, focusing on measurements using surface pressure isotherm, surface pressure relaxation, and oscillating barrier methods. Differences between the surface dilational moduli of condensed polymer monolayers and expanded polymer monolayers are explored. Moreover, the features of the surface dilational moduli in blended polymer monolayers are discussed in terms of their miscibility.     

Effect of carbon dioxide on rheological properties and structure of polyacrylamide solutions

The effect of CO₂ on rheological properties and structure of polyacrylamide solutions was studied as a function of pressure, treating time, polymer type and presence of inorganic electrolytes and natural formation rocks. It was found that the serious deterioration of the solution viscosity can be attributed mostly to the change of the solution structure, while the actual molecular degradation plays negligible role in the process. The phenomena are explained by modification of the dissociation equilibrium of poly-electrolytes in presence of high hydrogen ion concentration. The experimental results may contribute significantly to elaboration of new stabilization concepts in special enhanced oil recovery technologies based on joint application of carbon dioxide and polymers.     

Mechanical properties of glassy polymers with controlled NP spatial organization

Industrially viable processes enabling effective control of nanoparticle (NP) spatial organization in polymers are vitally important for achieving potential of nano-composites as building blocks of dynamic composites. Here, we report on the small and large strain mechanical properties of glassy polymers with spatial organization of spherical NPs controlled by the balance of the (polymer-NP)/(NP-solvent) interfacial attraction and mixing conditions. While strong polymer-NP attraction yielded good NP dispersion regardless of the mixing rate, weak polymer-NP attraction and low shear rate mixing resulted in chain bound NP clusters. Polymers with individually dispersed NPs exhibited the largest elastic moduli and strength while polymers filled with deformable chain bridged NP clusters possessed the largest ductility, at the same NP content. Hybrid systems, consisting of chain bridged NP clusters embedded in a polymer with individually dispersed NPs, exhibited simultaneous enhancement of stiffness, strength and ductility with its extent tunable by the cluster content. Our results confirm the pivotal role of NP spatial organization in translating the nano- and micro-scale phenomena to macro-scale mechanical response of polymer nano-composites. The obtained knowledge enables the design of additive fabrication technologies capable of employing polymer nano-composites in manufacturing of lightweight, functional engineering structures.     

Injectable poloxamer/graphene oxide hydrogels with well‐controlled mechanical and rheological properties

Although significant progress has been made in the design and application of injectable hydrogels for biomedical applications, concurrent control of rheological and mechanical properties of injectable hydrogels has remained as an open challenge to the researchers. In this work, we introduce and put into practice a photo‐curable poloxamer (also known as Pluronic)/graphene oxide (Plu/GO) injectable hydrogel with well‐controlled rheological and mechanical properties. Acrylate group was anchored to hydrogel structure to endow photo‐crosslinking ability through decelerating degradation rate of poloxamer hydrogels after injection. It was found that the modified Plu remains stable in biological media for a long‐term period without significant weight loss. Rheological properties of hydrogels were also carried out as essential prerequisite for an ideal injectability via frequency sweep, flow curve, recovery, and yield stress before and after modification, signifying shear‐thinning behavior of Plu/GO hydrogels with high recoverability. The viscosity of shear‐thinning‐like hydrogels dropped at higher shear stress, which facilitated injection process. Moreover, mechanical behavior of Plu was optimized by manipulating the content of Plu, degree of modification with reactive precursor, curing, and particularly incorporation of GO without deteriorating effects on rheological behavior of Plu.     

原油活性组分油水界面膜扩张粘弹性研究

研究了用超临界萃取分馏法（SFEF）从伊朗重质原油中分离的两个具有不同平均分子量的原油界面活性组分在正癸烷/水界面的扩张粘弹性行为以及温度对体系扩张粘弹性的影响.研究发现平均分子量大的样品能在油水界面形成更为牢固的界面膜.从扩张模量幅度对扩张频率的双对数曲线和扩张模量相角的频率依赖关系可以推断所有实验体系界面膜的主要的弛豫过程不是扩散弛豫,而可能主要是通过吸脱附势垒的弛豫过程.温度对两个样品的扩张粘弹性参数都有强烈的影响.升高温度可以降低膜的强度和粘度,并且改变相角的频率响应.     

Dispersion stabilities and rheological properties of fumed silica suspensions

Herein, we have reviewed fumed silica suspensions in dispersing fluids, polymer melts, and polymer solutions, focusing on their dispersion stability and rheological properties as a function of the surface character of fumed silica powders and the silica volume fraction, ?. Hydrophilic fumed silica powders are well dispersed at ? < 0.01 in polar dispersing fluids or polar polymer melts, and their phase states change from sol to gel with increasing ?. Such changes should also be strongly related to the rheological responses of the hydrophilic fumed silica suspensions, which change from Newtonian flow behavior to gel-like elasticity with increasing ?. On the other hand, hydrophobic fumed silica powders are stabilized in both polar and nonpolar dispersing fluids, depending on the interactions between the surface hydrophobic moieties and the dispersing fluids, in addition to those between the residual surface silanol groups and dispersing fluid, except for the particle–particle interactions. Moreover, the effects of the adsorption and desorption of polymers, as well as of non-adsorbing polymers on the dispersion stability and rheological behavior of fumed silica suspensions are discussed, by taking account of their optical microscopic observation and SANS curves.     

Effect of nano‐polystyrene (nPS) on thermal,rheological, and mechanical properties of polypropylene (PP)

Polystyrene nanoparticles (nPS) in the range of 10–100 nm with spherical shape were synthesized by oil/water (o/w) microemulsion process. In this process ammonium persulfate (APS) as an initiator, sodium dodecyl sulphate as a surfactant and n‐pentanol as cosurfactant were used. Isolated nPS was characterized by FTIR and ¹H NMR spectroscopy. DSC studies of nPS showed higher T_g as compared to bulk PS. The effect of lower weight percentage (wt%) of nPS on the mechanical, rheological, and thermal properties of PP was investigated. The blends were prepared individually on brabender plastograph by incorporating nPS of ～60 nm with different wt% of loading (i.e., 0.10–0.5%). It was shown from the experimental results that thermal, rheological, and mechanical properties were increased as the polymer particles blended with PP. Blends with 0.25 wt% loading of nPS exhibit better properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of PP chains as recorded by improvement in crystallinity of PP with the addition of nPS as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.     

Developments of the spin labelling study of polymers at interfaces

The spin labelling method has been used in a large variety of situations, in the broad field of polymers at solid interfaces. The relevance of the method is confirmed on linear neutral chains of poly (ethylene oxide) (PEO) in well defined situations and compared with the simple theoretical calculations of a mean field theory or some scaling arguments. Both theories have their own strengths and weaknesses. Then the fact, that polymers at solid liquid interfaces are three components systems, is considered and successively the effect of varying the polymer architecture, the solid surface and the solvent is studied. In all these cases specific results are obtained by Electron Paramagnetic Resonance (EPR) showing the usefulness and the versatility of the method.