Mechanical Properties of Colloidal Gels

1989 ◽  
Vol 155 ◽  
Author(s):  
W.-H. Shih ◽  
J. Liu ◽  
W. Y. Shih ◽  
S. I. Kim ◽  
M. Sarikaya ◽  
...  
Keyword(s):  
Power Law ◽  
Particle Concentration ◽  
Colloidal Particles ◽  
Colloidal Suspension ◽  
The Other ◽  
Colloidal Gels ◽  
Yield Strain ◽  
Colloidal Gel ◽  
Type Of Behavior ◽  
Gel Network

A colloidal suspension can be either dispersed or flocculated depending on the interaction between the colloidal particles. If the interaction is repulsive, particles can relax to the minimum of the potential due to their neighboring particles, and the system can reach an equilibrium dispersed state. In the case of attractive interaction, particles form aggregates that settle to the bottom of the container. As the concentration of particles is increased, the overcrowding of the aggregates produces a continuous network throughout the suspension before they settle and a colloidal gel is formed. A major difference between a colloidal gel and a colloidal suspension is that the gel can sustain finite stress and is therefore viscoelastic. Previously we studied the storage modulus and the yield strain of boehmite gels and found that they are related to the particle concentration in a power-law fashion [1]. Similar scaling behavior of the shear modulus was found for other colloidal particulate networks by Buscall et al. [2]. We developed a scaling theory [1] which successfully explains the experimental results on boehmite gels. The theory further predicts that there can be two types of power-law behavior depending on the relative elastic strength of the clusters to that of the links between clusters within the gel network. Furthermore, there can be a crossover from one type of behavior to the other as the particle concentration is varied.

Mechanical Properties of Colloidal Gels Subject to Particle Rearrangement

1990 ◽  
Vol 195 ◽  
Author(s):  
Wan Y. Shih ◽  
Wei-Heng Shih ◽  
Ilhan A. Aksay
Keyword(s):  
Mechanical Properties ◽  
Fractal Dimension ◽  
Particle Concentration ◽  
Fine Particles ◽  
Volume Fraction ◽  
Weak Link ◽  
Colloidal Suspension ◽  
Colloidal Gels ◽  
Strong Link ◽  
Gel Network

In a colloidal suspension with attractive interaction, particles form aggregates that settle to the bottom of the container. As the concentration of particles is increased, the overlapping of the aggregates (flocs) produces a continuous network throughout the suspension before settling occurs and a colloidal gel is formed. Colloidal gels may be divided into hard gels and soft gels.1 Hard gels are those formed by fine particles such as silica or boehmite of about 0.01 µm in size with high interparticle attraction energies. Under small shear rates, there is little restructuring in the gel network. The flocs that pack to form the gel network still retain their fractal structure, which gives rise to the scaling behavior of various mechanical properties of a gel with respect to particle concentration. For example, the storage modulus G' of a hard gel remains constant at small strain and increases in a power-law fashion with particle concentration, (φ, as G' - φn. There can be two regimes, a strong-link regime and a weak-link regime. In both regimes, the exponent n can be expressed in terms of the fractal dimension of the flocs, D, and the fractal dimension of the backbone of the flocs, x, while the form of n depends on what regime the system is in. Furthermore, a gel may crossover from the strong-link regime to the weak-link regime as the particle volume fraction is increased2.

Spatiotemporal Control of Supramolecular Polymerization and Gelation of Metal-Organic Polyhedra

2020 ◽  
Author(s):  
alexandre legrand ◽  
Li-Hao Liu ◽  
Philipp Royla ◽  
Takuma Aoyama ◽  
Gavin Craig ◽  
...  
Keyword(s):  
Acid Concentration ◽  
Self Assembly ◽  
Colloidal Particles ◽  
Soft Materials ◽  
Supramolecular Materials ◽  
Time Resolved ◽  
Colloidal Gel ◽  
Metal Organic ◽  
Spatiotemporal Control ◽  
Gel Network

In coordination-based supramolecular materials such as metallogels, simultaneous temporal and spatial control of their assembly remains challenging. Here, we demonstrate that the combination of light with acids as stimuli allows for the spatiotemporal control over the architectures, mechanical properties, and shape of porous soft materials based on metal-organic polyhedra (MOPs). First, we show that the formation of a colloidal gel network from a preformed kinetically trapped MOP solution can be triggered upon addition of trifluoroacetic acid (TFA), and that acid concentration determines the reaction kinetics. As determined by time-resolved dynamic light scattering, UV-vis absorption and <sup>1</sup>H NMR spectroscopies and rheology measurements, the consequences of the increase in acid concentration are (i) an increase in the cross-linking between MOPs; (ii) a growth in the size of the colloidal particles forming the gel network; (iii) an increase in the density of the colloidal network; and (iv) a decrease in the ductility and stiffness of the resulting gel. We then demonstrate that irradiation of a dispersed photoacid generator, pyranine, allows the spatiotemporal control of the gel formation by locally triggering the self-assembly process. Using this methodology, we show that the gel can be patterned into a desired shape. Such precise positioning of the assembled structures, combined with the stable and permanent porosity of MOPs, could allow their integration into devices for applications such as sensing, separation, catalysis, or drug release.

Forced spreading of films and droplets of colloidal suspensions

2014 ◽  
Vol 742 ◽  
pp. 495-519 ◽  
Author(s):  
Leonardo Espín ◽  
Satish Kumar
Keyword(s):  
Particle Concentration ◽  
Colloidal Particles ◽  
Hard Spheres ◽  
Colloidal Suspension ◽  
Colloidal Suspensions ◽  
Concentration Gradients ◽  
Vertical Diffusion ◽  
Interface Evolution ◽  
Dependent Viscosity ◽  
Liquid Dynamics

AbstractWhen a thin film of a colloidal suspension flows over a substrate, uneven distribution of the suspended particles can lead to an uneven coating. Motivated by this phenomenon, we analyse the flow of perfectly wetting films and droplets of colloidal suspensions down an inclined plane. Lubrication theory and the rapid-vertical-diffusion approximation are used to derive a coupled pair of one-dimensional partial differential equations describing the evolution of the interface height and particle concentration. Precursor films are assumed to be present, the colloidal particles are taken to be hard spheres, and particle and liquid dynamics are coupled through a concentration- dependent viscosity and diffusivity. We find that for sufficiently high Péclet numbers, even small initial concentration inhomogeneities produce viscosity gradients that cause the film or droplet front to evolve continuously in time instead of travelling without changing shape as happens in the absence of colloidal particles. At high enough particle concentrations, particle diffusion can lead to the formation of long-lived secondary flow fronts in films. Our results suggest that particle concentration gradients can have a dramatic influence on interface evolution in flowing films and droplets, a finding which may be relevant for understanding the onset of patterns that are observed experimentally.

scholarly journals Spatiotemporal Control of Supramolecular Polymerization and Gelation of Metal-Organic Polyhedra

2020 ◽  
Author(s):  
alexandre legrand ◽  
Li-Hao Liu ◽  
Philipp Royla ◽  
Takuma Aoyama ◽  
Gavin Craig ◽  
...  
Keyword(s):  
Acid Concentration ◽  
Self Assembly ◽  
Colloidal Particles ◽  
Soft Materials ◽  
Supramolecular Materials ◽  
Time Resolved ◽  
Colloidal Gel ◽  
Metal Organic ◽  
Spatiotemporal Control ◽  
Gel Network

In coordination-based supramolecular materials such as metallogels, simultaneous temporal and spatial control of their assembly remains challenging. Here, we demonstrate that the combination of light with acids as stimuli allows for the spatiotemporal control over the architectures, mechanical properties, and shape of porous soft materials based on metal-organic polyhedra (MOPs). First, we show that the formation of a colloidal gel network from a preformed kinetically trapped MOP solution can be triggered upon addition of trifluoroacetic acid (TFA), and that acid concentration determines the reaction kinetics. As determined by time-resolved dynamic light scattering, UV-vis absorption and <sup>1</sup>H NMR spectroscopies and rheology measurements, the consequences of the increase in acid concentration are (i) an increase in the cross-linking between MOPs; (ii) a growth in the size of the colloidal particles forming the gel network; (iii) an increase in the density of the colloidal network; and (iv) a decrease in the ductility and stiffness of the resulting gel. We then demonstrate that irradiation of a dispersed photoacid generator, pyranine, allows the spatiotemporal control of the gel formation by locally triggering the self-assembly process. Using this methodology, we show that the gel can be patterned into a desired shape. Such precise positioning of the assembled structures, combined with the stable and permanent porosity of MOPs, could allow their integration into devices for applications such as sensing, separation, catalysis, or drug release.

scholarly journals Appearance of a Solitary Wave Particle Concentration in Nanofluids under a Light Field

Nanomaterials ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 1291
Author(s):  
Abram I. Livashvili ◽  
Victor V. Krishtop ◽  
Polina V. Vinogradova ◽  
Yuriy M. Karpets ◽  
Vyacheslav G. Efremenko ◽  
...  
Keyword(s):  
Solitary Wave ◽  
Wave Velocity ◽  
Light Field ◽  
Particle Concentration ◽  
Colloidal Suspension ◽  
Type Equation ◽  
Concentration Wave ◽  
Nanoparticle Concentration ◽  
Constant Intensity ◽  
Concentration Convection

In this study, the nonlinear dynamics of nanoparticle concentration in a colloidal suspension (nanofluid) were theoretically studied under the action of a light field with constant intensity by considering concentration convection. The heat and nanoparticle transfer processes that occur in this case are associated with the phenomenon of thermal diffusion, which is considered to be positive in our work. Two exact analytical solutions of a nonlinear Burgers-Huxley-type equation were derived and investigated, one of which was presented in the form of a solitary concentration wave. These solutions were derived considering the dependence of the coefficients of thermal conductivity, viscosity, and absorption of radiation on the nanoparticle concentration in the nanofluid. Furthermore, an expression was obtained for the solitary wave velocity, which depends on the absorption coefficient and intensity of the light wave. Numerical estimates of the concentration wave velocity for a specific nanofluid—water/silver—are given. The results of this study can be useful in the creation of next-generation solar collectors.

Stability of a Binary Colloidal Suspension and its effect on Colloidal Processing

1989 ◽  
Vol 155 ◽  
Author(s):  
Wan V. Shih ◽  
Wei-Heng Shih ◽  
Jun Liu ◽  
Ilhan A. Aksay
Keyword(s):  
Particle Size ◽  
Hard Sphere ◽  
Colloidal Particles ◽  
Colloidal Suspension ◽  
Fluid Phase ◽  
Ceramic Processing ◽  
Colloidal Processing ◽  
Interparticle Interactions ◽  
The Stability ◽  
Binary Suspension

The stability of a colloidal suspension plays an important role in colloidal processing of materials. The stability of the colloidal fluid phase is especially vital in achieving high green densities. By colloidal fluid phase, we refer to a phase in which colloidal particles are well separated and free to move about by Brownian motion, By controlling parameters such as pH, salt concentration, and surfactants, one can achieve high packing (green) densities in the repulsive regime where the suspension is well dispersed as a colloidal fluid, and low green densities in the attractive regime where the suspensions are flocculated [1,2]. While there is increasing interest in using bimodal suspensions to improve green densities, neither the stability of a binary suspension as a colloidal fluid nor the stability effects on the green densities have been studied in depth as yet. Traditionally, the effect of using bimodal-particle-size distribution has only been considered in terms of geometrical packing developed by Furnas and others [3,4]. This model is a simple packing concept and is used and useful for hard sphere-like repulsive interparticle interactions. With the advances in powder technology, smaller and smaller particles are available for ceramic processing. Thus, the traditional consideration of geometrial packing for the green densities of bimodal suspensions may not be enough. The interaction between particles must be taken into account.

Cross-Correlations in the Brownian Motion of Colloidal Nanoparticles

2020 ◽  
Vol 65 (1-2) ◽  
pp. 27-34
Author(s):  
Sz. Kelemen ◽  
◽  
L. Varga ◽  
Z. Néda ◽  
◽  
...  
Keyword(s):  
Brownian Motion ◽  
Power Law ◽  
Cross Correlation ◽  
Colloidal Particles ◽  
Pearson Correlation ◽  
Transverse Component ◽  
Collective Effects ◽  
Colloidal Nanoparticles ◽  
Diffusive Motion ◽  
Cross Correlations

"The two-body cross-correlation for the diffusive motion of colloidal nano-spheres is experimentally investigated. Polystyrene nano-spheres were used in a very low concentration suspension in order to minimize the three- or more body collective effects. Beside the generally used longitudinal and transverse component correlations we investigate also the Pearson correlation in the magnitude of the displacements. In agreement with previous studies we find that the longitudinal and transverse component correlations decay as a function of the inter-particle distance following a power-law trend with an exponent around -2. The Pearson correlation in the magnitude of the displacements decay also as a power-law with an exponent around -1. Keywords: colloidal particles, Brownian motion, cross-correlation. "

scholarly journals The Examination of the Tissues and Some Observations on the Blood Platelets of Rabbits at Intervals of Five Minutes, and Later, after Intravenous Inoculations of Staphylococcus aureus and Indian Ink

1931 ◽  
Vol 31 (2) ◽  
pp. 247-256 ◽  
Author(s):  
Leonard S. Dudgeon ◽  
H. K. Goadby
Keyword(s):  
Staphylococcus Aureus ◽  
Endothelial Cells ◽  
Colloidal Particles ◽  
Blood Platelets ◽  
The Other ◽  
Colloidal Silver ◽  
Intravenous Injections ◽  
Inert Particles ◽  
Tissue Reactions ◽  
Lung Capillaries

1. The tissue reactions in rabbits from intravenous injections of live and dead Staphylococcus aureus and massive doses of indian ink and colloidal silver have been studied.2. Any particles injected into the circulation cause the accumulation of polymorphs in the lung capillaries.3. Inert colloidal particles such as indian ink are clumped in the capillaries of the lungs, liver, spleen and kidneys, and are phagocytosed by the endothelial cells.4. Staphylococci (S. aureus), live or dead, are nearly all held up in the lungs, where they are actively phagocytosed by the polymorphs within 5 minutes of an intravenous injection.5. Subsequently the cocci are distributed to the other organs, where phagocytosis continues mainly by polymorphs, but in the liver also by the Kupfer cells.6. Special attention is drawn to the localisation of the cocci in certain areas in the kidneys.7. Platelet counting on animals injected with various substances showed that there is an agglomeration of the particles with the platelets, which are consequently removed from the circulation.8. In the case of the inert particles the platelets are then restored to the circulation. With organisms (S. aureus) some of the platelets appear to be completely removed from the blood together with the bacteria.

Statistics on Jupiter's Current Sheet with Juno Data: Geometry, Magnetic Fields and Energetic Particles

2021 ◽  
Author(s):  
Zhi-Yang Liu ◽  
Qiu-Gang Zong ◽  
Michel Blanc
Keyword(s):  
Magnetic Fields ◽  
Current Sheet ◽  
Power Law ◽  
Heavy Ions ◽  
Particle Interaction ◽  
The Other ◽  
Gaussian Functions ◽  
Fixed Energy ◽  
Thin Current Sheet ◽  
A Current

&lt;p&gt;Jupiter's magnetosphere contains a current sheet of huge size near its equator. The current sheet not only mediates the global mass and energy cycles of Jupiter's magnetosphere, but also provides an occurring place for many localized dynamic processes, such as reconnection and wave-particle interaction. To correctly evaluate its role in these processes, a statistical description of the current sheet is required. To this end, here we conduct statistics on Jupiter's current sheet, with four-year Juno data recorded in the 20-100 Jupiter radii, post-midnight magnetosphere. The results suggest a thin current sheet whose thickness is comparable with the gyro-radius of dominant ions. Magnetic fields in the current sheet decrease in power-law with increasing radial distances. At fixed energy, the flux of electrons and protons increases with decreasing radial distances. On the other hand, at fixed radial distances, the flux decreases in power-law with increasing energy. The flux also varies with the distances to the current sheet center. The corresponding relationship can be well described by Gaussian functions peaking at the current sheet center. In addition, the statistics show the flux of oxygen- and sulfur-group ions is comparable with the flux of protons at the same energy and radial distances, indicating the non-negligible effects of heavy ions on current sheet dynamics. From these results, a statistical model of Jupiter's current sheet is constructed, which provides us with a start point of understanding the dynamics of the whole Jupiter's magnetosphere.&lt;/p&gt;

scholarly journals Viscosity Estimation of a Suspension with Rigid Spheres in Circular Microchannels Using Particle Tracking Velocimetry

Micromachines ◽  
2019 ◽  
Vol 10 (10) ◽  
pp. 675 ◽  
Author(s):  
Kawaguchi ◽  
Fukui ◽  
Funamoto ◽  
Tanaka ◽  
Tanaka ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Power Law ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Colloidal Particles ◽  
Fluid Model ◽  
Relative Viscosity ◽  
Circular Cross Section ◽  
Rigid Spheres ◽  
Power Law Index

Suspension flows are ubiquitous in industry and nature. Therefore, it is important to understand the rheological properties of a suspension. The key to understanding the mechanism of suspension rheology is considering changes in its microstructure. It is difficult to evaluate the influence of change in the microstructure on the rheological properties affected by the macroscopic flow field for non-colloidal particles. In this study, we propose a new method to evaluate the changes in both the microstructure and rheological properties of a suspension using particle tracking velocimetry (PTV) and a power-law fluid model. Dilute suspension (0.38%) flows with fluorescent particles in a microchannel with a circular cross section were measured under low Reynolds number conditions (Re ≈ 10−4). Furthermore, the distribution of suspended particles in the radial direction was obtained from the measured images. Based on the power-law index and dependence of relative viscosity on the shear rate, we observed that the non-Newtonian properties of the suspension showed shear-thinning. This method will be useful in revealing the relationship between microstructural changes in a suspension and its rheology.

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