Agglomeration Of Colloidal Particles Research Articles

Mechanisms of thixotropy in cement suspensions considering influences from shear history and hydration

AbstractThe rheological properties of fresh concrete are a direct function of the interaction behaviour of the granular inventory of the concrete (i.e., gravel, sand and cement) and especially of the colloidal fractions of cement. Under low shear stresses, agglomeration of colloidal particles is observed, while at high shear stresses, dispersion of these agglomerates occurs. Besides the agglomeration state, the formation of shear banding, zones with concentrated shear flow, is another controlling mechanism of the flow behaviour of cement suspensions. Rheological creep tests in this study are focused on investigating the influence of shear history and hydration process on thixotropy of cement suspension. In this paper, the meaning of the word thixotropy is slightly extended to additionally encompass rheological aging and hydration effects. Selected samples were analyzed by coupling a rheometer to synchrotron X‐ray tomography to gain insight into the shear‐induced microstructural changes during shear start‐up tests. The observations show heterogeneities in the velocity profile in the shear gap and the development of shear banding.

Resorcinol-Formaldehyde Carbon Gels Adsorption: A Commentary

Abstract This work is aimed at highlighting the recent progress of resorcinol-formaldehyde carbon gels adsorption of water pollutants. The synthesis strategies of the carbon gels were discussed to shed some light on the development of mesoporous matrix of carbon gel via the agglomeration of colloidal particles. The surface area of adsorbent can reach as high as 3000 m2/g by CO2 activation, while the surface functionalities are introduced through modification techniques for improving the removal performance. However, most of the recent studies are inclined at batch mode of adsorption with lack of information on the scale-up of the process in continuous mode. Carbon gel is a special class of porous material that can be moulded into desired size, hence a promising adsorbent candidate for monoliths and packings in column adsorption. Therefore, more dedicated works should be established to materialize the applications of carbon gel in column adsorption, particularly at industrial scale.

Bimetallic clustered thin films with variable electro-optical properties

The drop deposition of colloidal nanoparticles was performed from water-based colloidal solutions. The proposed procedure is based on the agglomeration of colloidal particles in laser-assisted evaporation processes. The evaporation process was resulted in the formation of clustered thin films on a glass substrate. In the experiments with bimetallic Au:Ag solutions, the clustered films are grown, the formation of the clustered films with the average height of 100 nm was achieved. Optical properties of the deposited structures were investigated experimentally. It is shown that the obtained films may become transparent and its properties are defined by its morphology.

Direct numerical simulations of agglomeration of circular colloidal particles in two-dimensional shear flow

Colloidal agglomeration of nanoparticles in shear flow is investigated by solving the fluid-particle and particle-particle interactions in a 2D system. We use an extended finite element method in which the dynamics of the particles is solved in a fully coupled manner with the flow, allowing an accurate description of the fluid-particle interfaces without the need of boundary-fitted meshes or of empirical correlations to account for the hydrodynamic interactions between the particles. Adaptive local mesh refinement using a grid deformation method is incorporated with the fluid-structure interaction algorithm, and the particle-particle interaction at the microscopic level is modeled using the Lennard-Jones potential. Motivated by the process used in fabricating fuel cell catalysts from a colloidal ink, the model is applied to investigate agglomeration of colloidal particles under external shear flow in a sliding bi-periodic Lees-Edwards frame with varying shear rates and particle fraction ratios. Both external shear and particle fraction are found to have a crucial impact on the structure formation of colloidal particles in a suspension. Segregation intensity and graph theory are used to analyze the underlying agglomeration patterns and structures, and three agglomeration regimes are identified.

Considerations on Improving Flocculation

As a whole, flocculation can be bettered by analyzing integral parts and promoting efficiency of each of these.