In order to study the deformation caused by force, rheology has two ways to promote each other: experiment and theoretical simulation. In the experiment, capillary rheometer and other rheometers were used to measure the changes of fluid viscosity and flow rate under different shear stresses, and then analyzed them, from which important properties such as modulus and molecular weight of substances were obtained. The same is true of hemorheology commonly used in medical examination. Rheometer can also be used to simulate the stress and deformation of fluid during injection molding, making rheology a necessary content for studying polymer processing.
Theoretical simulation is to put forward the physical background of this kind of substance through experimental data and combine it with universal mathematical model. The goal is that fluid motion can be described by mathematical calculation. Its physical background is very complicated. For purely elastic objects, Hooke's law can be used to describe, that is, stress is proportional to strain. For Newtonian fluid, it can be described by stress = viscosity × strain rate. But in reality, solids have plastic deformation that does not conform to Hooke's law, and liquids are all non-Newtonian fluids. Especially for polymers, it has viscoelasticity and the situation is complicated. Its mathematical model mainly depends on continuum mechanics. At present, the theoretical simulation effect is good for the simple flow of general fluid, but for the complex flow channel, due to many complex boundary effects, the current calculation ability can not give good results, which has become an important direction of rheology research in recent years.
Rheology, as a subject to study the flow and deformation of substances, is closely related to chemistry, especially colloid chemistry and polymer chemistry. With the continuous development of the three major synthetic materials industries, rheological research has also developed rapidly in recent years. Rheological society has been established in various countries, especially in industrialized countries, such as Britain, Germany, France, Netherlands, Sweden, Japan, Mexico and Canada. As an interdisciplinary subject, rheology has a wide range of applications.
Application in petroleum and petrochemical industry
Because from crude oil exploitation technology, such as tertiary oil recovery and completion, to crude oil storage and transportation, short-distance transportation, acid fracturing, polymer fracturing and clean micelle fracturing fluid, it is all related to rheology. Therefore, rheology has been widely valued in this industry and has been well promoted.
The newly drilled enhanced oil well can maintain a certain pressure and spray some crude oil, but when the pressure of the well begins to drop, secondary oil recovery will soon begin. Viscous fingering is easy to occur at the oil-water interface during water injection, which is not conducive to oil production. At this time, 50% of the crude oil has not been mined. There is great potential to improve oil recovery or tertiary oil recovery. Polymer solution injection is one of the methods of tertiary oil recovery. The selected materials are relatively flexible polyacrylamide and relatively rigid xanthan gum. Although their behaviors in shear flow field are similar, they are quite different in tensile flow field, which must be clearly judged from the rheological point of view.
Generally, polymer processing can only be applied after reprocessing. Processing can be divided into injection molding, extrusion, calendering, blow molding, spinning and other processes. However, no matter what form of processing, it is full of rheological problems. There are experts specializing in polymer processing in developed countries such as Europe and America, and experts specializing in polymer processing rheology in developed countries, and annual meetings are held every year for academic exchanges. Because foreign countries have developed computer design application software based on rheology, it can manufacture large plastic automobile castings and large aircraft fuselage castings.
Agricultural films are usually made by blow molding. Blow molding is mainly carried out through the polymerization of melt, that is, the melt comes out of the extruder in the form of tubes or bubbles and is drawn into a film to achieve the final thickness and molecular orientation. At this time, the tensile viscosity of raw materials is obviously an important rheological parameter. Therefore, it is not surprising that the measurement of tensile viscosity in rheology is considered to be a research of industrial importance.
The purpose of adding polymer thickener to lubricating oil is to reduce the drastic change of viscosity with temperature, so that it can maintain good dynamic lubrication at high temperature and will not wear too much at low temperature. The viscosity of automobile oil is expressed by grades, and gasoline meeting the needs of various grades can be prepared by using rheological additives. Additives can increase the viscosity of base oil by more than 3 times. Viscoelastic effect can be measured in lubricating oil, but the rheology of lubricating oil thinks that the increase of viscoelasticity and viscosity is beneficial to supporting load.
Application in medical field
Biorheology If traditional rheology was developed to meet the needs of industry, it came into being with the development of life science. At present, the most extensive and in-depth research in biological rheology is blood and vascular rheology, which is an important frontier discipline between modern medicine and science and technology.
In addition, it is also used in clinical medicine, pharmacy and other fields.
Application in light industry
Rheological indexes must be used in quality control and formula adjustment of light industrial products such as toothpaste, cosmetics and detergents. Take toothpaste as an example. When people use toothpaste, it should be easy to squeeze out, and it should be hard after it is squeezed out. Don't sink into your toothbrush, and brush your teeth with ease. That is to say, the viscosity of toothpaste should drop rapidly when it is sheared, and there should be a certain yield stress when it is at rest to keep it firm.
The applied research of rheology in China started late, and there were only a few spontaneous studies in the 1960s. At present, there are few applied research fields, and even the polymer processing industry on which rheology depends is poorly understood. Taking plastic products as an example, imported polymer particles are eaten by molds imported from plastic factories, and the products are smooth and beautiful, which can be comparable to similar products abroad, but once they are replaced by domestic raw material particles, the quality of the products will decline. This is because the mold used is designed according to the rheological characteristics of foreign raw materials, while the rheological characteristics of domestic raw materials are not exactly the same as those of imported raw materials, so the quality of products declines. Although the manufacturer improved the mold, it only made mechanical changes based on experience, without considering the rheological characteristics of particles.
At present, the applied research of rheology is far from universal in China, let alone play its due role. In order to strengthen the research of rheology in China, it is suggested that relevant departments should give policy support to such interdisciplinary subjects as rheology, and at the same time, rheology courses, such as chemical engineering and polymer processing, should be offered in universities, especially key universities, especially for the training of senior researchers such as masters and doctors.