Introduction
Rheometer is an instrument which can measure the rheological properties of a polymer solution, using the principle of fluid rheology, in which the shear stresses can be measured by varying the shear rate. This is based on the terminology, called ‘Rheology. Whereas, “Rheology” is the ‘study of deformation and, the flow of matter’.
The rheological properties of a polymer solution is needed to understand the flow behavior of a fluid when it forced some shear stress, which is much needed for the engineering point, and for the study of complete rheological properties measurements of a polymeric solution. The rheological properties can play an important role in the synthesis, and in processing of polymer solutions at industrial level. There are numerous types of rheometers available in market, with different accessories, that can provide the proper rheological data analysis of different types of polymeric solutions.
Rheometer
Rheometer is a device that can characterize the rheological properties of polymer solutions.
Working Principle
The working principle of rheometer is based on rotational motion working principle, that is to attain the simple shearing flow, to control the strain rate, that is in the terms of applied control strain rate, which is rotation, and then measuring the resulting couple or torque.
Another way is that, called ‘control stress’, which can be done by applying the couple or torque, and measuring the strain rate. There would be two ways to apply rotation, and to measuring the resulting couple or torque; one way is that, drive-in first member, and measuring the couple or torque on the same one, other way is that, drive-in the first member, and measuring the resulting couple or torque on the other one. In modern rheometer instruments, like; ‘Deer’ constant stress rheometer, the electrical drag-cup motor is used to producing the couple or torque, with the rages of (10-6 Nm – 10-2 Nm), and the ranges of shear rates of (10-6 s-1 – 103 s-1).
Parameter studied on Rheometer
Viscosity
The viscosity is described as ‘Internal friction, or ‘resistance to flow.
Stress
Stress is defined as, Force per unit area.
Strain
The Deformation due to applied stress is called strain.
Newtonian Fluid
The liquid, in which components of stresses are linear, said to be Newtonian Liquid.
Non-Newtonian Fluid
The liquids, whose behavior can’t be described by the ‘Navier-Stokes equations’ are said to be non-Newtonian liquids.
Shear Thinning
When the viscosity decreases with the increase in the shear rate, that phenomenon is said to be shear thinning behavior.
Shear Thickening
When the viscosity increases with the increase in the shear rate, that phenomena is said to be shear thickening behavior.
Thixotropy
Time dependent shear thinning behavior is said to be thixotropy.
Viscoelasticity
The material heaving simultaneously existence of the ‘Viscous’ and ‘elastic’ behavior in it, or the behavior which falls in-between the extremes of ‘Newtonian liquid’ behavior, and ‘Hookean elastic’ behavior called viscoelasticity.
Applications of Rheometer
The Rheometer can provide the detail study of the rheological properties of polymer solutions.
- Study of the dynamic Modulus
- Storage modulus G`
- Loss modulus G“
- Study of the interacting forces in the suspended, and in the colloidal particles in polymer solution
- Measurement of the flow behavior of polymer solutions, under the applied stress or applied strain
- Emulsion stability of polymer solutions
- Suspension of polymer solutions
- Leveling of polymer solution
- Controlling the flow of polymer solution
- Study of thermal stability of polymer solution
- Extrusion ability of polymer solution
- Processing accessibility of polymer solution
The rheology information can also provide the data which concerns with the following:
- Fluids
- Foods
- Paints
- Adhesives
- Melts
- Coatings
- Cream
- Lotions
- Toilet bleaches,
- Medicines
- Inks
- Fuels
- Oils
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