Hydrogel is a kind of gel material formed by cross-linking water and polymer substances, which has been widely used in medical, cosmetic, petroleum and other fields because of its high water absorption, softness, plasticity and other characteristics. The properties of hydrogels are affected by their rheological properties, so it is necessary to study and explore the rheological properties of hydrogels. Rheology is the study of the deformation and flow laws of substances under the action of external forces.
In the field of hydrogel research, the application of rheology can reveal the deformation characteristics, mechanical properties, stability and other aspects of hydrogels, and provide a basis for their improvement and optimization in production and application. The following is a systematic introduction to the rheological properties of hydrogels.
1.Rheological properties of mesoscopic structures.
The Baosheng RH-30 rheometer can test the deformation behavior of hydrogels with different structures under the action of external forces. The mesoscopic structure of hydrogels determines the complexity and diversity of their rheological behavior. Common mesoscopic structures include reticular structure, staggered structure, chondrite structure, etc.
The reticular structure is the most common hydrogel structure and has significant self-assembly properties in hydrogels. Under the action of external force, the arrangement order between molecules and the distance between molecules will change, which will cause the change of their physical properties. When the external force is small, the network structure hydrogel shows high elastic modulus and high viscosity, showing the characteristics of solid, and when the external force is large, the structure of the hydrogel begins to break, showing the liquid properties of the fluid.
The particle diameter of staggered hydrogels is often between 1 and 10, and its deformation is affected by the staggered structure on its surface. When the external force is small, the staggered structure hydrogel shows high elastic modulus and high viscosity, but when the external force acts more than a certain extent, the staggered structure begins to break down, showing the characteristics of fluid.
Spheroidal hydrogels are composed of a large number of spherical polymer particles, and the dispersion cross-sections of the particles are widely spaced. When an external force acts on its surface, the structure of the interparticle void begins to change and leads to liquid penetration. This type of hydrogel has a smaller specific surface area, lower viscosity, and easier flow.
2.Rheological instability.
Rheological instability refers to the sudden uneven distribution and flow of initially stable hydrogels under the action of external forces. This phenomenon is usually under the action of external forces, some areas in the hydrogel are stressed more, and some areas are less stressed, which leads to the destruction of local structures and the transformation of system properties.
In hydrogels, rheological instability is caused by a combination of factors. For example, changes in the direction of external forces, mesoscopic structures, and particle structures may lead to rheological instability of hydrogels. An effective way to deal with rheological instability is to monitor the deformation behavior of hydrogels under the action of external forces and analyze their mesostructural changes. In terms of preventing the instability of hydrogels, it is also an effective method to reduce the change of external force and maintain the stability of the mesoscopic structure.