Recent studies have turned scientists’ beliefs about the ability of bulk solids to withstand pressure
Scientists have found that the surface of a free-flowing mixture can withstand weight, which is largely dependent on the coordination number of each particle in the mixture.
Due to the presence of stable structures that are located inside each bulk substance, they can support the weight of other objects on their surface. These stable structures are made up of discrete parts called bridges. The results of the latest study by German scientists have shown that the limit of weight that such “bridges” can hold depends little on external forces, for example, on gravity or the interaction of individual particles with each other. Based on the analysis of the data obtained, it turns out that only the average number of neighbors of each particle has an effect on weight retention. To prove their assumptions, scientists had to create a three-dimensional structure of colloidal solutions, since their parameters tend to vary in a very wide range compared to dry mixtures.
At first glance, free-flowing substances, such as sand, seem to be homogeneous, but in reality, this is not at all the case. For example, the pressure of grain on the walls of the barn in different places will be different, and the “plugs” in the pipes or gutters through which the sand flows, have a direct effect, turning it into a solid body.
For a long period of time, scientists could not determine whether there was a connection between the arrangement of particles in space and the constituent parts of a free-flowing mixture. In order to understand this, it was necessary to study free-flowing substances, the surface of which can withstand a lot of weight.
If you follow elementary physical laws, then the weight of an object that is on top of a pile of sand cannot be divided equally among all the particles. In fact, the object is held only by those particles that are directly involved in the formation of the same “bridges” that carry out mutual stabilization among themselves in certain directions. The placement of “bridges” is carried out according to different principles. The most common mechanism for placing them is one that resembles the bricks in the vault of an arch.
In order to establish the similarity between these so-called “bridges”, a group of researchers from one of the German universities used spheres with a diameter of 2 microns. These spheres were placed in transparent liquids of different compositions. Thanks to the colloidal systems created in this way, scientists were able to observe the phenomena that occur when conditions change in a wide range using a microscope, that is, the type of liquid, the number of particles changed. Thus, the colloidal system turned into a free-flowing mixture, which acquired the ability to withstand some weight on its surface.
Some time ago, the same group of researchers developed an algorithm that helped identify the particles that make up three-dimensional “bridges”. After discovering the bridges, scientists began looking for different similarities in different kinds of systems with different characteristics.
Soon, research results led to the conclusion that “bridges” are formed under the influence of the coordination number, that is, the average number of neighbors of each particle. Such a result of the experiments carried out was a complete surprise to scientists. After all, it was previously believed that the retention of some weight on the surface of granular substances was influenced by the properties of the substance itself. Although, of course, it is worth noting that this opinion cannot be completely rejected.