Life and death of colloidal bonds control the rate-dependent rheology of gels

AbstractColloidal gels exhibit rich rheological responses under flowing conditions. A clear understanding of the coupling between the kinetics of the formation/rupture of colloidal bonds and the rheological response of attractive gels is lacking. In particular, for gels under different flow regimes, the correlation between the complex rheological response, the bond kinetics, microscopic forces, and an overall micromechanistic view is missing in previous works. Here, we report the bond dynamics in short-range attractive particles, microscopically measured stresses on individual particles and the spatiotemporal evolution of the colloidal structures in different flow regimes. The interplay between interparticle attraction and hydrodynamic stresses is found to be the key to unraveling the physical underpinnings of colloidal gel rheology. Attractive stresses, mostly originating from older bonds dominate the response at low Mason number (the ratio of shearing to attractive forces) while hydrodynamic stresses tend to control the rheology at higher Mason numbers, mostly arising from short-lived bonds. Finally, we present visual mapping of particle bond numbers, their life times and their borne stresses under different flow regimes.

Download Full-text

Time–connectivity superposition and the gel/glass duality of weak colloidal gels

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2022339118 ◽

2021 ◽

Vol 118 (15) ◽

pp. e2022339118

Author(s):

Bavand Keshavarz ◽

Donatien Gomes Rodrigues ◽

Jean-Baptiste Champenois ◽

Matthew G. Frith ◽

Jan Ilavsky ◽

...

Keyword(s):

Superposition Principle ◽

Time Spectrum ◽

Gel Point ◽

Colloidal Gels ◽

Mechanical Spectroscopy ◽

Time Resolved ◽

Reduced Frequency ◽

Brownian Particles ◽

Colloidal Gel ◽

Dual Character

Colloidal gels result from the aggregation of Brownian particles suspended in a solvent. Gelation is induced by attractive interactions between individual particles that drive the formation of clusters, which in turn aggregate to form a space-spanning structure. We study this process in aluminosilicate colloidal gels through time-resolved structural and mechanical spectroscopy. Using the time–connectivity superposition principle a series of rapidly acquired linear viscoelastic spectra, measured throughout the gelation process by applying an exponential chirp protocol, are rescaled onto a universal master curve that spans over eight orders of magnitude in reduced frequency. This analysis reveals that the underlying relaxation time spectrum of the colloidal gel is symmetric in time with power-law tails characterized by a single exponent that is set at the gel point. The microstructural mechanical network has a dual character; at short length scales and fast times it appears glassy, whereas at longer times and larger scales it is gel-like. These results can be captured by a simple three-parameter constitutive model and demonstrate that the microstructure of a mature colloidal gel bears the residual skeleton of the original sample-spanning network that is created at the gel point. Our conclusions are confirmed by applying the same technique to another well-known colloidal gel system composed of attractive silica nanoparticles. The results illustrate the power of the time–connectivity superposition principle for this class of soft glassy materials and provide a compact description for the dichotomous viscoelastic nature of weak colloidal gels.

Download Full-text

Mechanical Properties of Colloidal Gels

MRS Proceedings ◽

10.1557/proc-155-83 ◽

1989 ◽

Vol 155 ◽

Cited By ~ 14

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.

Download Full-text

Embedding orthogonal memories in a colloidal gel through oscillatory shear

Soft Matter ◽

10.1039/c9sm02222h ◽

2020 ◽

Vol 16 (15) ◽

pp. 3746-3752

Author(s):

Eric M. Schwen ◽

Meera Ramaswamy ◽

Chieh-Min Cheng ◽

Linda Jan ◽

Itai Cohen

Keyword(s):

Network Structure ◽

Flow Direction ◽

Oscillatory Shear ◽

Attractive Interaction ◽

Colloidal Gels ◽

Colloidal Gel

We investigate shear training memories in colloidal gels, which include an attractive interaction and network structure, and discover that such systems can support memories both along and orthogonal to the training flow direction.

Download Full-text

Hydroxyapatite-Based Colloidal Gels Facilitate the Proliferation and Migration of Chondrocytes and the Adhesion of Umbilical Cord Mesenchymal Stem Cells

International Scholarly Research Notices ◽

10.1155/2014/935689 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7

Author(s):

Syed A. Jamal ◽

Qiang Ye

Keyword(s):

Stem Cells ◽

Mesenchymal Stem Cells ◽

Umbilical Cord ◽

Glycolic Acid ◽

Human Umbilical Cord ◽

Colloidal Gels ◽

Unidirectional Movement ◽

Colloidal Gel ◽

And Migration ◽

Proliferation And Migration

Collective movement of cells that have been delivered on biomaterials for transplantation purposes would be a desirable attribute that would promote wound healing, cell proliferation, and eventual growth and regeneration of damaged organs. We hypothesized that colloidal gels made from hydroxyapatite (HA) and poly(D,L-lactic-co-glycolic acid) (PLGA) particles will be conducive to the growth and migration of porcine chondrocytes, will allow the adhesion of human umbilical cord mesenchymal stem cells, and will have negligible effects on the cell cycle of these cells. Then, we performed experiments designed to assess the viability and migratory properties of porcine chondrocytes studded on nanosized HA/PLGA particles. Our experiments show that porcine chondrocytes migrated in and around a hydroxyapatite-based biomaterial that could be described as a colloidal gel. Cells in the colloidal gel demonstrated unidirectional movement. Cells were seen to be extending lamellae and were followed by other cells.

Download Full-text

Membrane Changes in Polymorphonuclear Leukocytes During Ionophore (A23187) - Induced Lysosomal Release

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007984x ◽

1977 ◽

Vol 35 ◽

pp. 482-483

Author(s):

P.L. Moore ◽

P.L. Sannes ◽

H.L. Bank ◽

S.S. Spicer

Keyword(s):

Structural Changes ◽

Calcium Release ◽

Clear Understanding ◽

Ionophore A23187 ◽

Enzyme Release ◽

Extracellular Medium ◽

Pmn Leukocytes ◽

Intracellular Ion Concentrations ◽

Membrane Changes ◽

Pmn Leukocyte

It is thought that calcium and/or magnesium may play important roles in polymorphonuclear (PMN) leukocyte functions such as chemotaxis, adhesion and phagocytosis. Yet, a clear understanding of the biological roles of these ions has awaited the development of techniques which permit a selective alteration of intracellular ion concentrations. Recently, treatment of cells with the ionophore A23187 has been used to alter intracellular divalent cation concentrations. This ionophore is a lipid soluble antibiotic produced by Streptomyces chartreusensis that complexes with both calcium and magnesium (3) and is believed to carry these ions across biological membranes (4). Biochemical investigations of human PMN leukocytes demonstrate that cells treated with A23187 and extracellular calcium release their lysosomal enzymes into the extracellular medium without rupturing and releasing their soluble cytoplasmic enzymes (5,6). The aim of the present study and and a companion report (7) was to investigate the structural changes that occur in leukocytes during ionophore-induced lysosomal enzyme release.

Download Full-text

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079176 ◽

1977 ◽

Vol 35 ◽

pp. 330-333

Author(s):

T. Gulik-Krzywicki ◽

M.J. Costello

Keyword(s):

Biological Materials ◽

Molecular Organization ◽

X Ray Diffraction ◽

Glass Capillary ◽

X Ray ◽

Rate Dependent ◽

Before And After ◽

Freeze Etching ◽

Diffraction Patterns ◽

Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

Download Full-text