Dispersed Volume Fraction Research Articles

Silk Fibroin Acts as a Self-Emulsifier to Prepare Hierarchically Porous Silk Fibroin Scaffolds through Emulsion-Ice Dual Templates.

Silk fibroin (SF) has shown enormous potentials in various fields; however, application of SF in emulsion technology is quite limited. Here, we use SF as a self-emulsifier to form an oil-in-water (O/W) emulsion by emulsifying 1-butanol in SF aqueous solution. This showed that SF possessed strong surface activity to stabilize the O/W emulsion without the need for any other surface-active agent until its solidification because of 1-butanol-induced conformational transition of SF to β-sheet. After freezing the preformed emulsions at −20 °C, robust three-dimensional porous SF scaffolds were prepared without the need for any further post-treatment. The evolution from the O/W emulsion to porous scaffold formation under freezing was tracked, and an emulsion–ice dual template mechanism was proposed for scaffold formation, based on which SF scaffolds with controllable hierarchically porous structures were achieved by tuning the dispersed droplet volume fraction. Furthermore, SF scaffolds with hierarchical porosity showed significantly higher bioactivity toward L929 fibroblasts than that of SF scaffolds with mono macroporosity, highlighting the great asset of this hierarchically porous SF scaffold for broad applications in tissue engineering. Therefore, the strong surface-active characteristic of SF presented here, in addition to its distinct advantages, sheds a bright light on the application of SF in the vast range of emulsion technologies, especially in cosmetic-, food-, and biomedical-related areas.

Hybrid multi-objective optimization of microstructural and mechanical properties of B4C/A356 composites fabricated by FSP using TOPSIS and modified NSGA-II

Abstract A356 alloy was used as the base metal to produce boron carbide (B4C)/A356 composites using friction stir processing (FSP). The microstructural and mechanical properties of B4C/A356 composites were optimized using artificial neural network (ANN) and non-dominated sorting genetic algorithm-II (NSGA-II). Firstly, microstructural properties of the composites fabricated in different processing conditions were investigated. Results show that FSP parameters such as rotational speed, traverse speed and tool pin profile significantly affect the size of the primary silicon (Si) particles of the base metal, as well as the dispersion quality and volume fraction of reinforcing B4C particles in the composite layer. Higher rotational to traverse speeds ratio accompanied by threaded pin profile leads to better particles distribution, finer Si particles and smaller B4C agglomerations. Secondly, hardness and tensile tests were performed to study mechanical properties of the composites. FSP changes the fracture mechanism from brittle form in the as-received metal to very ductile form in the FSPed specimens. Then, a relation between the FSP parameters and microstructural and mechanical properties of the composites was established using ANN. A modified NSGA-II by incorporating diversity preserving mechanism called the ɛ elimination algorithm was employed to obtain the Pareto-optimal set of FSP parameters.

Multiscale modeling and analysis of graphene nanoplatelet/carbon fiber/epoxy hybrid composite

Abstract The elastic response of Graphene Nano Platelet/carbon fiber/epoxy hybrid composite was investigated using multiscale modeling and analysis. The importance of volume fraction of graphene, GNP dispersion, and strain rates on the mechanical behaviors was determined. The analysis entailed the building of computational molecular dynamic model, involving multilayer graphene nano-platelets in epoxy composite, and micromechanical modeling. The predicted results show that the elastic responses of the hybrid composite increase with increased GNP volume fraction, dispersion, and strain rates.

Effect of Nanoparticles and Surfactant on Phase Inversion of Two Phases

In the present study, a pressure drop technique was used to identify the phase inversion point of oil-in-water to water-in-oil flows through a horizontal pipe and to study the effect of additives (nanoparticles, cationic surfactant and blend nanoparticles-surfactant) on the critical dispersed volume fraction (phase inversion point). The measurements were carried for mixture velocity ranges from 0.8 m/sec to 2.3 m/sec. The results showed that at low mixture velocity 0.8 and 1 m/sec there is no effect of additives and velocity on phase inversion point, while at high mixture velocities the phase inversion point for nanoparticles and blend (nanoparticles/surfactant) systems was delayed (postponed) to a higher value of the dispersed phase volume fraction (oil volume fraction) compared to the system of surfactant where the phase inversion point was occurred at low dispersion phase volume fraction.
 For all systems the desperation volume fraction at the point of inversion decreases with increasing mixture velocity.
 Indeed, the results showed that surfactant was more effective on phase inversion point than solid nanoparticles.

Effect of local spatial location on chord length distribution in stirred tank

Measurement of dispersed modality at different spatial locations is performed in a 1000ml borosilicate beaker at various dispersed volume fractions in both W/O and O/W system. It is found that mean chord length at different spatial locations shows a similar distribution in both W/O and O/W dispersion that the closer to impeller the smaller the mean chord length. Further, in dilute W/O dispersion (3%), results show that both number counts and mean chord length of droplets at impeller region are smaller than other locations; however, it gradually turns to be larger at higher dispersed fraction (20%). For O/W dispersion, it is found that number counts of small droplets in region around impeller become smaller than other locations with the addition of dispersed oil phase (10%). Flow characteristic measured by 2D angle-resolved particle image velocimetry in pure oil/water phase is employed to further explain the deviation. Besides, the critical dispersed fraction affecting the dispersed modality at different spatial location is discussed.

Transient peristaltic transport of grains in a liquid

Pumping suspensions and pastes has always been a significant technological challenge in a number of industrial applications ranging from food processing to mining. Peristaltic pumps have become popular to pump and/or dose complex fluids, due to their robustness. During the transport of suspensions with peristaltic pumps, clogging issues may arise, particularly during transient operations. That is a matter of particular concern whenever the pumping device is used intermittently to generate flow only on demand. Further understanding of the transient dynamics of such systems and of the conditions that can lead to jamming would result in more robust peristaltic pump design. To achieve these goals, an experimental setup that simplifies the statorrotor assembly of a peristaltic hose pump was used. In this setup, a roller transfers momentum to a liquid suspension, upon application of a constant load. The evolution of the velocity of the roller was recorded for different concentrations of mono-dispersed spheres of different diameters. The flow is found not to be strongly dependent on the dispersed particle volume fraction, if the size of the suspended phase is comparable with the hose diameter. Conversely, the flow is strongly slowed down when their size is small and the particle concentration is increased. These findings could help improving the design of peristaltic pumps by a more appropriate sizing, given the diameter of the hose and that of the particles to be transported.

Modelling and experimental investigation of micromixing of single-feed semi-batch precipitation in a liquid–liquid stirred reactor

A finite-mode probability density function (FM-PDF) model is adopted to simulate the semi-batch precipitation process of barium sulfate from aqueous solutions of barium chloride and sodium sulfate in the presence of kerosene drops in a turbulent liquid–liquid stirred reactor driven by a Rushton turbine. The turbulent kerosene–water flow field is calculated with an anisotropic two-phase explicit algebraic stress model (EASM) and the standard k–ε model based on an Eulerian–Eulerian approach using in-house codes. The flow predictions are validated against macromixing homogenization curves measured from tracer mixing experiments. The particle size distribution has been calculated by solving five moments of the particle size distribution coupled with both nucleation and growth kinetics. The effects of impeller speed and inert dispersed oil volume fraction have been investigated. Agreement between micromixing model predictions and experimental data is satisfactory, which suggests that the time-dependent finite-mode probability density function model is a feasible approach for numerical prediction of the fast precipitation process in turbulent two-phase stirred reactors.

The surface tells it all: relationship between volume and surface fraction of liquid dispersions.

The properties of liquid dispersions, such as foams or emulsions, depend strongly on the volume fraction ϕ of the continuous phase. Concentrating on the example of foams, we show experimentally and theoretically that ϕ may be related to the fraction ϕs of the surface at a wall which is wetted by the continuous phase - given an expression for the interfacial energy or osmotic pressure of the bulk system. Since the surface fraction ϕs can be readily determined from optical measurement and since there are good general approximations available for interfacial energy and osmotic pressure we thus arrive at an advantageous method of estimating ϕ. The same relationship between ϕ and ϕs is also expected to provide a good approximation of the fraction of the bubble or drop surface which is wetted by the continuous phase. This is a parameter of great importance for the rheology and ageing of liquid dispersions.

The potential role of novel diffusion imaging techniques in the understanding and treatment of epilepsy.

Epilepsy is a common neurological disorder in which magnetic resonance imaging plays a key role. Diffusion imaging based on the molecular diffusion of water has been widely used clinically and in research for patients with epilepsy. Diffusion tensor imaging (DTI), the most common model, has been used for around two decades. Several parameters can be derived from DTI that are sensitive, but non-specific, to underlying structural changes. DTI assumes a single diffusion process following a Gaussian distribution within each voxel and is thus an overly simplistic representation of tissue microstructure. Several more advanced models of diffusion are now available that may have greater utility in the understanding of the effects of epilepsy on tissue microstructure. In this review, I summarise the principles, applications in epilepsy and future potential of three such techniques. Diffusion kurtosis imaging (DKI) characterises the degree to which diffusion deviates from Gaussian behaviour and gives an idea of the underlying tissue complexity. It has been used in both focal and generalised epilepsy and seems more sensitive than DTI. Multi-compartment models separate the signal from extra- and intra-axonal compartments in each voxel. The Composite Hindered and Restricted Model of Diffusion (CHARMED) can characterise axonal density but has not yet been applied in patients with epilepsy. The Neurite Orientation Dispersion and Density Imaging (NODDI) model can determine the intracellular volume fraction (ICVF) and degree of dispersion of neurite orientation. Preliminary data suggest it may more sensitive than conventional and diffusion imaging in localising focal epilepsy.

Tuning Cellulose Nanocrystal Gelation with Polysaccharides and Surfactants

Gelation of cellulose nanocrystal (CNC) dispersions was measured as a function of the presence of four nonionic polysaccharides. Addition of hydroxyethyl cellulose (HEC), hydroxypropyl guar (HPG), or locust bean gum (LBG) to CNC dispersions induced the gelation of dilute CNC dispersions, whereas dextran (DEX) did not. These behaviors correlated with adsorption tendencies; HEC, HPG, and LBG adsorbed onto CNC-coated quartz crystal microbalance sensors, whereas DEX did not adsorb. We propose that the adsorbing polysaccharides greatly increased the effective volume fraction of dilute CNC dispersions, driving more of the nanocrystals into anisotropic domains. SDS and Triton X-100 addition disrupted HEC-CNC gels whereas CTAB did not. Surface plasmon resonance measurements with CNC-coated sensors showed that SDS and Triton X-100 partially removed adsorbed HEC, whereas CTAB did not. These behaviors illustrate the complexities associated with including CNC dispersions in formulated products: low CNC contents can induce spectacular changes in rheology; however, surfactants and soluble polymers may promote gel formation or induce CNC coagulation.

Permeation of Dispersed Particles through a Pore and Transmembrane Pressure Behavior in Dead-End Constant-Flux Microfiltration by Two-Dimensional Direct Numerical Simulation

This paper presents numerical procedures for a coupled scheme that combines immersed boundary and discrete element methods to simulate two-dimensional fluid and particle motion. We simulated the dead-end, constant-flux microfiltration of dispersed particles and investigated the effect of hydrodynamic interactions between the fluid and particles on the transmembrane pressure. The permeation of a single particle through a pore was first simulated to obtain the fundamental characteristics of transmembrane pressure behavior. The effects of the particle dispersion volume fraction and the pore size on the transmembrane pressure were then investigated. The results show that the transmembrane pressure increases and fluctuates even in the absence of membrane fouling when a particle penetrates the pore. Transmembrane pressure behavior is also significantly affected by the number of particles within the pore and the location of particles around the pore.

Synthesis of Porous Emulsion-Templated Monoliths Using a Low-Energy Emulsification Batch Mixer

Emulsion-templated porous monoliths based on castor oil-in-black liquor emulsions have been prepared using a low-energy emulsification technique. Lignins from black liquor polymerize in the continuous phase of the high internal phase emulsion to obtain highly microcellular materials with interconnected open porous structures. A two-step emulsification operating mode was developed in order to increase the maximum value of the castor-oil dispersed volume fraction obtained with the one-step emulsification mode (limited to 53 % of the total emulsion volume due to the very high viscosities of the fluids). A rheological study of the black liquor and of the prepared Medium Internal Phase Emulsions, have been conducted. Depending on the emulsification operating mode used, the morphology of the porous monoliths will differ. A rather low mean droplet size (about 6 μm) is obtained with the one-step mode, the two-step technique leads to a broader void size distribution and a further increase of added castor oil (up to 69 %) do not favor the homogeneity of the material.

Extensional viscosity of o/w emulsion stabilized by polysaccharides measured on the opposed-nozzle device

The shear and extensional viscosities characteristics of mineral oil-in-water emulsions with dispersed volume fractions varying between 20 vol.% and 40 vol.% have been investigated and compared. The opposed-nozzles configuration was used to measure the extensional viscosity. Four kinds of hydrocolloids were used: xanthan gum (XG), guar gum (GG), hydroxypropylmethylcellulose (HPMC) and carboxymethylcellulose sodium salt (Na-CMC). Presented results of rheological measurements have shown that the extensional viscosity of the o/w emulsion with the addition of hydrocolloids determines the properties of the continuous phase and the structure of dispersed phase. The greatest relative increase between extensional viscosity of the emulsion and extensional viscosity of aqueous polymer solution was observed when the dispersed phase was strongly flocculated. At the same time, the value of the extensional viscosity of the weakly flocculated emulsion has been determined by the rheological properties of the continuous phase when viscoelastic liquid (emulsions with the addition of XG) was under concern.

Evolution of dispersed drops during the mixing of mineral oil and water phases in a stirringtank

In this paper, a focused beam reflectance method is used to investigate the evolution of dispersed droplets at various dispersed volume fractions for an Exxsol D80 mineral oil–water dispersion in a stirring tank. Two types of inversion experiments are compared, the direct and continuous mixing of the oil–water phases. The number density of the chord lengths and distributions are identified as the main parameters for comparison. The drop coalescence is dominant slightly before inversion, at which point the measured mean square weighted (Sqr-wt) chord length increases significantly. The way of mixing will also influence the effect of drop coalescence and result in different inversion processes.

The experimental measurement and modelling of sedimentation and creaming for glycerol/biodiesel droplet dispersions

This paper presents both experimental measurements and numerical modelling on the separation of glycerol from biodiesel. Glycerol is a natural by-product of biodiesel production and removal of glycerol droplets from biodiesel is required to attain fuel quality standards. Experimental observations on the separation kinetics for sedimentation and creaming of droplet dispersions as a function of time and dispersion volume fraction are presented using both optical techniques and magnetic resonance imaging (MRI). Optical contrast between the biodiesel and glycerol enabled droplet behaviour to be followed optically and it was noticed that because of a droplet size distribution, smaller drops often flowed counter-current to the main direction of droplet flow. Droplet size distributions were measured using droplet size apparatus, but instability in the droplet sizes due to break up and coalescence resulted in uncertainties in the data. A numerical model was developed extending earlier work of, Davis and Russel. Multiple population droplet sizes were found to be necessary in order to describe the experimentally observed concentration profile evolution. The model also included an axial dispersion coefficient which accounted for the experimentally observed counter-current flow of some droplets. In general the model predictions were able to match experimental data with reasonable accuracy.

Dynamical Arrest, Percolation, Gelation, and Glass Formation in Model Nanoparticle Dispersions with Thermoreversible Adhesive Interactions

We report an experimental study of the dynamical arrest transition for a model system consisting of octadecyl coated silica suspended in n-tetradecane from dilute to concentrated conditions spanning the state diagram. The dispersion's interparticle potential is tuned by temperature affecting the brush conformation leading to a thermoreversible model system. The critical temperature for dynamical arrest, T*, is determined as a function of dispersion volume fraction by small-amplitude dynamic oscillatory shear rheology. We corroborate this transition temperature by measuring a power-law decay of the autocorrelation function and a loss of ergodicity via fiber-optic quasi-elastic light scattering. The structure at T* is measured using small-angle neutron scattering. The scattering intensity is fit to extract the interparticle pair-potential using the Ornstein-Zernike equation with the Percus-Yevick closure approximation, assuming a square-well interaction potential with a short-range interaction (1% of particle diameter). (1) The strength of attraction is characterized using the Baxter temperature (2) and mapped onto the adhesive hard sphere state diagram. The experiments show a continuous dynamical arrest transition line that follows the predicted dynamical percolation line until ϕ ≈ 0.41 where it subtends the predictions toward the mode coupling theory attractive-driven glass line. An alternative analysis of the phase transition through the reduced second virial coefficient B(2)* shows a change in the functional dependence of B(2)* on particle concentration around ϕ ≈ 0.36. We propose this signifies the location of a gel-to-glass transition. The results presented herein differ from those observed for depletion flocculated dispersion of micrometer-sized particles in polymer solutions, where dynamical arrest is a consequence of multicomponent phase separation, suggesting dynamical arrest is sensitive to the physical mechanism of attraction.

In vitro digestion of emulsions: mechanistic and experimental models

Digestion is a complex combination of physical, chemical and biological processes. In order to investigate the impact of food structure on the digestion of lipids, we work on a controllable triglyceride-based system: emulsion. In this study, the emulsion was composed of a single triglyceride (tricaprylin or triolein), decanal as a model lipophilic micronutrient, and a single emulsifier (β-lactoglobulin or sodium oleate) at different concentrations. We investigated the effects of these parameters on an in vitro intestinal static digestion, which was monitored using classic physicochemical methods: fatty acid titration, lipids extraction/chromatography and sizing. To interpret the results, we developed several mechanistic models based on mass transfer kinetics, which enable a direct comparison and identification of the factors influencing the digestion. These factors are the molar mass of the lipids, the initial interfacial area (droplet size) and dispersed volume fraction, the interfacial tension and dilatational viscoelasticity. We also developed an experimental digestion model based on a single droplet using tensiometry. This technique was able to monitor the kinetics of lipolysis and micellar solubilization simultaneously. All methods confirmed the result from our previous study that the type of triglyceride is the major parameter influencing the digestion. Moreover, the mechanistic and experimental models proved that digestion was usually faster for β-lactoglobulin emulsions/droplets compared to the sodium oleate ones. There was no clear effect of the emulsifier concentration.

Oxygen Absorption into Stirred Emulsions of n-Alkanes

Absorption of pure oxygen into aqueous emulsions of n-heptane, n-dodecane, and n-hexadecane, respectively, has been studied at 0 to 100% oil volume fraction in a stirred tank at the stirring speed of 1000 min−1. The volumetric mass transfer coefficient, , was evaluated from the pressure decrease under isochoric and isothermal (298.2 K) conditions. The O/W emulsions of both n-dodecane and n-hexadecane show a maximum at 1-2% oil fraction as reported in several previous studies. Much stronger effects never reported before were observed at high oil fractions. Particularly, all n-heptane emulsions showed higher mass-transfer coefficients than both of the pure phases. The increase is by upto a factor of 38 as compared to pure water at 50% n-heptane. The effect is tentatively interpreted by oil spreading on the bubble surface enabled by a high spreading coefficient. In W/O emulsions of n-heptane and n-dodecane increases with the dispersed water volume fraction; the reason for this surprising trend is not clear.

Extensional Viscosity of w/o Emulsions

The opposed nozzles configuration was used to measure the extensional viscosities of water-in-oil emulsions of dispersed volume fractions varying between 5% and 30%. The two Newtonian type mineral oils with dynamic viscosities about = 0.2182 and 0.0443 [Pa s] were used. All emulsions were prepared with sorbitan monooleate (Span 80) as emulsifier. The results obtained for extensional viscosity of w/o emulsions show that only at very low concentrations of dispersed phase values of the Trouton ratio ( Tr = η E/ η ) are approximately constant (in range of 7-11) while for pure oil are slightly lower (3-6). Additionally, the Trouton ratio is independent of oil phase viscosity in the range of water phase concentration from 5 to 10%. For 20% and higher concentration of disperse phase the extensional viscosity rises with increase of a nozzle diameter. Presented experimental results indicate that the opposing nozzles rheometer used in this work is not a suitable device for measuring the extensional viscosity of viscoplastic fluids.

Electrokinetic and electrorheological properties of poly(vinyl chloride)/polyindole conducting composites

In this study, poly(vinyl chloride) (PVC), polyindole (PIN), and PVC/PIN conducting composites having five different compositions were used. Particle sizes, densities, dielectric constants, and sedimentation ratios of the materials were determined. The zeta‐potentials of the samples were measured in aqueous and nonaqueous (silicone oil [SO]) media. The dispersions prepared in SO were subjected to external electric field strength, and their electrorheological properties were investigated. Then the effects of dispersed particle volume fraction, shear rate, external electric field strength, frequency, and temperature onto electrorheological activities of the dispersions were examined. Further, creep and creep‐recovery tests were applied to the PIN/SO and PVC/PIN/SO dispersions, and reversible viscoelastic deformations were observed. Finally, the vibration damping capacity of PVC (66%)/PIN (34%)/SO dispersion system was tested by using an automobile shock absorber. Copyright © 2011 John Wiley & Sons, Ltd.