Stability of Dispersions

The importance of the production and application of disperse systems in industry is steadily growing, while colloidal systems surround us every day (for example foodstuffs, pharmaceuticals etc.). Understanding the forces and mechanisms of interaction allows the development of new materials and improvement of available systems. The stability of such systems is one of the central research points. One of the well‐known physical models of colloid stability is given by DLVO‐Theory. With this theory we have a tool to influence the stability of such dispersion systems. In this paper, electrokinetic methods are used to investigate interaction forces in disperse systems. The influence of pH‐value, electrolyte concentration and valency is shown with suitable examples. However, in some cases the DLVO‐model is not satisfactory, and reasons for this behavior will also be discussed.     

Application of sodium benzoyl thiosulphate from aqueous solution to wool and its effect on substantivity of disperse dyes. Part 1: synthesis and characterisation of sodium benzoyl thiosulphate

The introduction of bulky aryl residues into wool fibres not only enhances their disperse dyeability but also improves their settability, shrink resistance and imparts easy‐care properties. It would be highly desirable for colourists to achieve such effects when dyeing or printing wool from an aqueous solution as wool/polyester blend fabrics could be dyed and printed with the same dye; furthermore, in the case of an all‐wool fabric pretreated with such arylating systems, following dyeing or printing with disperse dyes, dye fixation can be achieved by dry heat procedures. A water‐soluble, fibre‐reactive arylating agent, sodium benzoyl thiosulphate, was therefore synthesised, characterised and its stability to hydrolysis in aqueous media was examined.     

Whey Protein Isolate Coated Liposomes as Novel Carrier Systems for Astaxanthin

In this work, whey protein isolate (WPI)‐coated astaxanthin‐loaded liposomes are prepared by combining the fabrication of liposomes with the layer self‐assembly deposition technique. The physical properties of such composite carriers are evaluated by zeta potential, particle size, distribution, encapsulation efficiency, and morphology. WPI‐ coated astaxanthin‐loaded liposomes display homodisperse distribution and high encapsulation efficiency with a WPI coating layer surrounding the surface of conventional liposomes by the electrostatic interaction. Fourier transform infrared spectroscopy and X‐ray diffraction analysis reveal that WPI interacts with the lipid bilayer via hydrophobic forces and hydrogen bonding, which result in the successful coating. Based on experimental results of differential scanning calorimetry and thermogravimetric analysis, it is demonstrated that thermal stability of astaxanthin‐loaded liposomes benefits from the formation of surface modification of the WPI‐layer. In addition, the physical stability of WPI‐coated astaxanthin‐loaded liposomes under heating and light is significantly improved as compared with uncoated liposomes. This research might provide scientific guidance for the development of WPI‐coated liposomes as efficient carrier systems for bioactive substances in food and pharmaceutical industry. Practical Applications: To improve lipid membrane stability and to prevent the leakage of encapsulated astaxanthin, a novel carrier system based on WPI coated on the surface of liposomes is prepared through the layer self‐assembly deposition technique. This research suggests that WPI‐coated liposomes represent an effective and stable delivery system for astaxanthin. WPI‐coated liposomes could be developed as efficient carrier systems for bioactive compounds in the food and pharmaceutical industries.     

Rates of the colloid coagulation in the presence of irreversibly adsorbing and non‐adsorbing polymers

We have developed an analytic self‐consistent field theory of the effective interactions between nano‐ colloids mediated by irreversibly adsorbing polymers and non‐adsorbing polymers having a gyration radius much larger than that of colloids. By making use of this theory, we have calculated the potential of the polymer‐mediated forces for the above cases of polymer adsorption. On the basis of the obtained results for the polymer‐mediated potentials, we have obtained the stability ratio and rate of the coagulation in the presence of adsorbing and non‐adsorbing polymers. As a final result of our studies, we constructed the coagulation diagram that quantifies the combined effect of the Van der Waals and polymer‐mediated forces on the rate of colloid coagulation. Kinetic stability of the material‐specific colloid systems is discussed. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Evaluation of a New High‐Pressure Dispersion Unit (HPN) for Emulsification

Emulsification plays an important role in the formulation of lipophilic pharmaceutical agents. These substances are often included in the disperse phase of an oil‐in‐water emulsion. To reach a high bioavailability and a good long‐term stability, drop sizes much less than 1 micron are required. For the generation of such emulsions, energy densities of a quality which can only be reached in high‐pressure systems, are necessary. Actually available apparatus, such as high‐pressure homogenizers fitted with valves, microfluidizer or jet disperser, reach particle sizes of about 0.2 micron in continuous processes. It is indispensable to produce emulsions with smaller globules in order to receive a maximum of diversity in application. Therefore, dispersion units with a higher efficiency in drop breakup are needed. Especially in the case of parenterally administered medicament formulations an average particle size between 0.04 and 0.1 microns is requested which is up to now not reachable by continuous emulsification. In this study the drop breakup behavior of a new high‐pressure nozzle is investigated with the example of oil‐in‐water emulsions and compared to the breakup behavior of a state‐of‐the‐art nozzle and to available data published.     

Colloidal dispersions: Structure, stability and geometric confinement

The structure, stability, wetting, spreading, and adhesion behavior of suspensions of nanometer-sized particles depend highly on the many-body interaction forces between the particles and between the particles and the confining geometry. Such is especially the case in concentrated colloidal dispersions when particles are more likely to come in close contact with one another and are confined, where their structural properties are strongly modified in comparison to their bulk properties. The last decade has seen an intensified interest in understanding the role of many-body interactions, which result in attractive depletion and structural forces in fluid-particle systems. This perspective highlights the role of such forces in current and emerging technologies.     

Colloidal stability of high‐solids polystyrene and polyvinyl acetate latices

Commercial emulsion polymerization processes are often done with high‐solids recipes (e.g., about 50 wt % monomer), resulting in relatively viscous, pseudoplastic reaction mixtures. The change in rheological behavior during high‐solids emulsion polymerization complicates the operation in terms of imperfect mixing, increasing heat transfer resistance and reactor fouling. In this article, we report the influence of solids content on the colloidal stability of polystyrene (PS) and polyvinyl acetate (PVAc) latex systems. For the systems investigated, solids content up to 50 wt % had no influence on the colloidal stability of the latex. The influence of recipe on colloidal stability is more pronounced than the influence of operating conditions. Brownian coagulation dominates over shear coagulation for both low‐ and high‐solids systems, although in some cases the operating conditions appear to have some effect on the course and outcome of high‐solids emulsion polymerization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1780–1791, 1999     

THE STABILITY OF RADIALLY BOUNDED THIN FILMS

The linear stability of radially bounded thinning free films is examined for the case in which the surfaces of the film are initially plane and parallel. The two-dimensional time-dependent drainage flow computed by lubrication theory constitutes the base state. The linear stability of this flow with respect to axially symmetric varicose disturbance is treated in the quasistatic approximation. For thin films, disperse London-van der Waals attractive forces play a key role in determining the critical thickness at rupture, and the results are presented as predictions of critical film aspect ratio as a function of two dimensionless groups which are ratios of the important physical-chemical forces on the film. Predicted critical thicknesses are seen to agree well with the limited available experimental data.     

Improving the dyeability of polyimide by pretreatment with alkali

Polyimide fabric, as a high‐performance fabric, possesses advantageous properties, such as outstanding thermal stability and chemical resistance, but has poor dyeability. In this paper, polyimide fabric was dyed successfully with disperse dyes by high‐temperature and high‐pressure dyeing in the presence of a swelling agent and auxiliaries. Under optimal dyeing conditions, it is pretreated with NaOH 6 g l^?1 and dyed with disperse dyes 5% o.w.f., NaCl 1 m , benzyl alcohol 60 ml l^?1 at 135 °C for 45 min to obtain a satisfactory colour yield with good washing fastness and dry rubbing fastness with 93.3% strength retention. The experimental results demonstrate that the Nernst adsorption isotherm is a favourable model for polyimide fabric dyeing with disperse dyes.     

THE STABILITY OF RADIALLY BOUNDED THIN FILMS

The linear stability of radially bounded thinning free films is examined for the case in which the surfaces of the film are initially plane and parallel. The two-dimensional time-dependent drainage flow computed by lubrication theory constitutes the base state. The linear stability of this flow with respect to axially symmetric varicose disturbance is treated in the quasistatic approximation. For thin films, disperse London-van der Waals attractive forces play a key role in determining the critical thickness at rupture, and the results are presented as predictions of critical film aspect ratio as a function of two dimensionless groups which are ratios of the important physical-chemical forces on the film. Predicted critical thicknesses are seen to agree well with the limited available experimental data.     

A stable silicon/graphene composite using solvent exchange method as anode material for lithium ion batteries

Current research has demonstrated the combination of the high theoretical capacity offered by silicon nanoparticles (Si NPs) with graphene-based matrices in order to produce a high energy density and stable lithium ion battery system. However, Si NPs do not mix well with graphene oxide aqueous suspensions and thus create severe segregation of the materials. In this letter, we propose a simple, cost-effective and commercially-viable solvent exchange process to improve the interaction of the Si NPs in poor solvent environments such as in aqueous media. Using N-methylpyrrolidone (NMP) to disperse the Si NPs and followed by a solvent exchange process, we are able to improve the dispersion and stability of Si NPs in aqueous graphene oxide aqueous suspension. Consequently, this also improves the output and the stability of the lithium ion battery using the aforementioned composite system.     

膜乳化过程中流体流动对液滴受力和乳化效果的影响

分析了膜乳化过程中流体流动状况和分散相液滴的受力情况,以及二者的密切关系.在一定条件下计算了液滴所受的力,结果表明,表面张力引起的力、液滴内外静压差产生的力、平行于膜表面的流动曳力和运动浮力是主要的力;在此基础上,探讨了液滴的形成过程.实验考察了壁面剪应力和膜两侧压差与液滴平均直径及分散相通量的关系,结合受力计算讨论了分散相和连续相流动状况对膜乳化效果的影响.     

A new generation of refractory concretes colloid-chemical aspect of their technology

Some peculiarities of the technology of new refractory concretes (ceramoconcretes, low-cement refractory concretes, and vibrocompacted thixotropic fluid refractory pastes) are analyzed from the standpoint of modern colloid chemistry. Interactions of disperse particles and the aggregation stability of disperse systems are discussed. Using a highly concentrated binding suspension (HCBS) of quartz glass as an example, a diagram of the regions of stability and coagulation of particles depending on the pH index of the suspension has been constructed. The state and form of the bonds of water in disperse systems are analyzed. It is shown for clays and HCBS of a number of materials that the strength properties of binders depend on the electrokinetic potential of the initial disperse system. A correlation between the acid — basic properties of the solid phase and the characteristics of the binder is demonstrated. The effects of heterocoagulation in systems with a mixed solid phase are also discussed.Translated from Ogneupory, Vol. 35, No. 1, pp. 4–12, January, 1994.     

Physicochemical properties of cellulose nanocrystals treated by photo‐initiated chemical vapour deposition (PICVD)

Cellulose nanocrystals (CNCs) are novel nanomaterials produced by the pulp and paper industry. The surface properties of CNCs are key factors for their dispersion in solvents. These polar materials disperse readily in water, but not in organic solvents. The ability to disperse into typically non‐polar organic matrices is an indispensable requirement to exploit the growing market for nanocomposite materials. We present an innovative approach for modifying the surface of CNCs through scalable, gas‐phase photo‐initiated chemical vapour deposition (PICVD). Using syngas as a treatment precursor, we demonstrate the effectiveness of this technique to render the surface of the CNCs compatible with mildly polar and non‐polar solvents, evidenced by contact angle measurements. Further proof of this successful modification is given through dispersion assays, showing for example the ability to disperse treated CNC in toluene (whereas untreated samples do not disperse). Suspensions in organic solvents remain stable in excess of two weeks. Chemical characterization through XPS and FTIR confirms the presence of an oxygen‐containing coating on the CNC surface.     

Design of gold nanoparticle-based colorimetric biosensing assays

Gold nanoparticle (AuNP)-based colorimetric biosensing assays have recently attracted considerable attention in diagnostic applications due to their simplicity and versatility. This Minireview summarizes recent advances in this field and attempts to provide general guidance on how to design such assays. The key to the AuNP-based colorimetric sensing platform is the control of colloidal AuNP dispersion and aggregation stages by using biological processes (or analytes) of interest. The ability to balance interparticle attractive and repulsive forces, which determine whether AuNPs are stabilized or aggregated and, consequently, the color of the solution, is central in the design of such systems. AuNP aggregation in these assays can be induced by an "interparticle-crosslinking" mechanism in which the enthalpic benefits of interparticle bonding formation overcome interparticle repulsive forces. Alternatively, AuNP aggregation can be guided by the controlled loss of colloidal stability in a "noncrosslinking-aggregation" mechanism. In this case, as a consequence of changes in surface properties, the van der Waals attractive forces overcome interparticle repulsive forces. Using representative examples we illustrate the general strategies that are commonly used to control AuNP aggregation and dispersion in AuNP-based colorimetric assays. Understanding the factors that play important roles in such systems will not only provide guidance in designing AuNP-based colorimetric assays, but also facilitate research that exploits these principles in such areas as nanoassembly, biosciences and colloid and polymer sciences.     

Analysis of Mobility Effects in Particle-Gas Flows by Particle-Resolved LBM-DEM Simulations

Particle-resolved direct numerical simulations are performed to simulate the flow through particle assemblies that are either static or freely moving to demonstrate the influence of particle mobility. To obtain a comprehensive understanding for this influence essential parameters such as the Reynolds number, solids volume fraction, particle-fluid density ratio, collision parameters and particle shape are varied. The influence of particle mobility is assessed by evaluating the particle-fluid forces, the particle ensemble structure and particle velocities. It is found that the ability of existing correlations for static particle systems to predict drag and lift forces correctly in dynamic particle-gas flows is limited and that drift forces perpendicular to the drag force play an important role.     

Transferable intermolecular potentials for carboxylic acids and their phase behavior

Transferable step potentials are characterized for 39 carboxylic acids. The reference potential is treated with discontinuous molecular dynamics, including detailed molecular structure. Thermodynamic perturbation theory is used to interpret the simulation results and to provide an efficient basis for molecular modeling and characterization of the attractive forces. Four steps are used for representation of the attractive forces with only the first and last steps varied independently. The two middle steps are interpolated such that each site type is characterized by three parameters: the diameter, σ, the depth of the inner well, ε₁, and the depth of the outer well, ε₄. The depths of the attractive wells are optimized to fit experimental vapor pressure and liquid density data. Generally, the vapor pressure is correlated to an overall 43% average absolute deviation (% AAD) and the liquid density to 5% AAD. The deviations tend to be largest for the higher molecular weight acids. These deviations are larger than the errors previously encountered in characterizing organic compounds, but carboxylic acids present exceptional challenges owing to their peculiar dimerization behavior. Simultaneous correlation of vapor pressure, vapor compressibility factor, and phase equilibria of water + carboxylic acids place several constraints on the nature of the potential model, with the parameters of the present model representing a reasonable tradeoff. In other words, our model represents minimal deviations for vapor pressure, vapor compressibility factor, and phase equilibria of all acids simultaneously while varying the parameters σ, ε₁, ε₄, ε^CC(dimerizing site bonding energy), ε^AD(acceptor‐donor bonding energy), and K^HB(hydrogen bonding volume) for the acid O? and OH site types. The present model is characterized by one acceptor and one dimerizing site on the carbonyl oxygen and one acceptor and one donor site on the hydroxyl oxygen. The acceptor and donor are capable of interacting with water while the dimerizing site is not. With this model, the saturated vapor compressibility factor of acids with seven or fewer carbons is near 0.5 while higher carbon ratios lead to a compressibility factor approaching 1.0. To compensate for the high vapor pressure deviations of the transferable potential model, a correction is introduced to customize the molecule‐molecule self interaction energy. This adaptation results in deviations of 3.1% for vapor pressure of the pure acid database. To validate the behavior of the model for carboxylic acids in mixtures, 33 binary solutions were considered. Acids in this database ranged from formic to hexadecanoic. The average absolute deviation in bubble pressure for aqueous acid systems is 4.4%, 10.5% for acid + acid systems, and 4.7% for acid + n‐alkane systems without a customized interaction correction. When applying the correction, deviations were 2.4% for aqueous systems, 2% for acid systems, and 2.8% for acid + n‐alkane systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Coaxial Flow Contactors as Alternative to Double T-Contactors for Triphasic Slug Flow Generation

Triphasic gas-liquid-liquid slug flow systems have great application potential in flow chemistry and are normally generated with a double T-junction where the continuous phase and one disperse phase form a two-phase flow and the second disperse phase is added at the second junction. This design is limited to high disperse phase ratios when a regular and uniform flow is desired. The use of coaxial contactors allows overcoming most of these restrictions. The slug generation, stability, and regularity of the generated triphasic flow were experimentally characterized.     

MIXING POLYMERS OF DIFFERENT VISCOSITIES

The mixing of viscous polymers of dissimilar viscosities undergoing an overall shear is considered. Data are presented to illustrate the effects of component viscosity ratio and relative volume fraction on the quality of mixing. Experiments and analysis are based upon the geometry suggested by a tumbled mixture of polyethylene pellets in the hopper of an extruder. For a system in which the viscosity of the initially disperse phase exceeds that of the major component, deformation is modelled as the elongation of circular cylinders resulting from heightened shear stresses and discontinuous normal stresses at the component interface. In fluids as viscous as the polymers considered, these stresses are strongly dependent upon the cross-sectional area of the mixing channel, and the interaction between elongating drops is modelled as a decreasing effective cross-sectional area. 1t is shown that the interaction between neighboring drops is sufficiently strong that at a certain drop length the disperse phase begins to behave as if it were present continuously across the mixing channel; in other words, the disperse phase and suspending medium behave at large strains like high-modulus reinforcing fibers in a lower-modulus solid matrix. This critical drop length is surprisingly small, ranging from 2 to 8 times the nominal linear dimension of the undeformed drop in the systems considered. For a system in which the major component is more viscous than the disperse drops, such a condition of substantially equal strain is shown to exist throughout the mixture.     

A review on emulsification via microfluidic processes

Emulsion is a disperse system with two immiscible liquids, which demonstrates wide applications in diverse industries. Emulsification technology has advanced well with the development of microfluidic process. Compared to conventional methods, the microfluidics-based process can produce controllable droplet size and distribution. The droplet formation or breakup is the result of combined effects resulting from interfacial tension, viscous, and inertial forces as well as the forces generated due to hydrodynamic pressure and external stimuli. In the current study, typical microfluidic systems, including microchannel array, T-shape, flow-focusing, co-flowing, and membrane systems, are reviewed and the corresponding mechanisms, flow regimes, and main parameters are compared and summarized.