Do you know! “What is viscosity in chemistry". To understand about viscosity, we take example of some liquids like Honey and Water. As we know honey is thicker than water. So, honey flow with very slow speed on floor than water, as water is very less thick, so it flows quickly.
Hence, we can say that liquids with high thickness (like honey) flow slowly and have high viscosity while a liquid with low thickness (like water) flows quickly and have low viscosity.
Example of Viscosity
To understand viscosity very well, just take few examples of viscosity in daily life.
Cooking Oil
Honey
Lubricant
Engine Oil
Brake Oil
Liquid Soap
These highly viscous liquids are some examples of viscosity in science. You know viscosity very well, even before listening this term viscosity in your physics & chemistry class.
Viscosity can be defined as the fluids resistance to flow.
What is Viscosity
In chemistry, Viscosity of a fluid is the measure of its resistance to gradual deformation by the tensile stress or shear stress. We can also say that viscosity is the internal resistance of the fluid. Fluids which have high viscosity resists to move as its molecular makeup gives this fluid a too much internal friction to motion, while fluids which have low viscosity resists less to move as its molecular makeup gives this fluid a less internal friction to motion.
So, we can say that molecular makeup decides internal friction between them, and which ultimately provides viscosity of fluid. Honey has high internal friction than water, so honey have high viscosity than water.
What is absolute viscosity?
Absolute viscosity is also known as dynamic viscosity. It is a fundamental property of a fluid that describes its resistance to shear or flow when subjected to an applied force.
It quantifies how easily a fluid deforms or flows when a shearing force is applied to it. The SI unit of absolute viscosity is the pascal-second (Pas), but other units like the poise (P) and the centipoise (cP) are also commonly used.
What is Meaning of Viscous
To understand viscosity. First, we learn what is the meaning of word “Viscous”. So, viscous is property of material i.e., material having a thick, sticky consistency between solid and liquid and also having a high viscosity.
Who Poses Viscosity
Along with liquids or fluids, gases also have viscosity, but it is very difficult to notice viscosity of gases at ordinary conditions.
We learn this chemistry topic under chemistry terminology category and Physical Chemistry Notes by Chemistry Notes Info ChemistryNotesInfo.com in simple way, we can say that “Viscosity is the resistance of a fluid to change in its shape”, viscosity is resistance to flow. Fluidity is the reciprocal of viscosity, so now we can say that honey has high viscosity and low fluidity while water has low viscosity and high fluidity.
Viscosity plays very important role in determining characteristics of fluids used in lubrication and transportation, spraying, surface coating, injection moulding etc.
Formula of Viscosity
Viscosity of any liquid can be calculated with viscosity formula. And viscosity formula is given below to calculate viscosity of any fluid or liquid.
Viscosity = Force×Time ∕Area
Newton’s Viscosity Law
According to the Newton’s viscosity law’, Shear stress between the two adjacent fluid layers is directly proportional to the velocity gradients between these two layers.
Unit of Viscosity
Unit of Viscosity is Newton second per square meter (Ns/m2)
SI unit of viscosity is Pascal second (Pas)
Relation of viscosity with temperature
Viscosity of the liquids decreases quickly with increase in the temperature, while viscosity of the gases increases with increase in the temperature.
Temperature ->
27 °C
77 °C
Viscosity of Water
0.85×10-3 pascal second
0.36×10-3 pascal second
Viscosity of Air
1.85×10-5 pascal second
2.08×10-5 pascal second
Types of Viscosity
Viscosity is classified in two types. which are as follows-
1. Dynamic Viscosity
Dynamic viscosity is defined as the measure of the ratio of 'shear stress to shear rate' of the fluid.
Formula of Dynamic Viscosity
2. Kinematic Viscosity
Kinematic viscosity is defined as the measure of ratio of 'viscous force to inertial force' on the fluid.
Formula of Kinematic Viscosity
Measurement of viscosity
Viscosity is measured by various types of Rheometers or Viscometers.
Viscometers and its uses
Viscometers are scientific instruments designed to measure the viscosity of a fluid. Viscosity is a measure of a fluid's resistance to flow. Viscosity is a critical property in various fields of science, chemistry and industry.
Viscometers are essential tools for determining the flow behaviour and consistency of liquids, and they have a wide range of uses across different applications.
Some of the primary uses of viscometers:
1. Quality Control in Manufacturing: Viscometers are commonly used in industries such as food and beverages, pharmaceuticals, cosmetics, oils and chemicals to ensure product quality and consistency. Manufacturers can use viscometers to check the viscosity of raw materials and finished products to meet specific quality standards.
I personally used viscometers in QC lab to test viscosity of engine oils in Savita Oil Technology Ltd.
2. Oil and Petroleum Industry: In the oil and petroleum industry, viscometers are crucial for measuring the viscosity of crude oil, lubricants, and fuel oils. This information is essential for product formulation, transportation, and ensuring proper lubrication in machinery and engines.
3. Paints and Coatings: Viscosity plays a significant role in the application and performance of paints and coatings. Viscometers help manufacturers control the viscosity of paint formulations to ensure they are suitable for spraying, brushing, or rolling onto surfaces.
4. Pharmaceuticals: Pharmaceutical companies use viscometers to measure the viscosity of drug formulations, including syrups, suspensions, and creams. Consistency in viscosity is crucial to ensure accurate dosing and drug delivery. Viscosity results plays important roles in stablishing the quality standards of many drugs.
Now I am working in pharma company, and we will always check that viscosity results are within range in drug analysis COA (Certificate of analysis) along with other quality parameters.
5. Food and Beverage Industry: In the food industry, viscometers are used to measure the viscosity of various products, including sauces, beverages, and dairy products. Proper viscosity ensures the desired texture and mouthfeel of food products.
6. Polymer and Plastics: The viscosity of polymer melts is vital in the manufacturing of plastics, rubber, and other polymer-based products. Viscometers help control the processing conditions and quality of these materials.
7. Environmental Testing: Viscometers are used in environmental studies and water quality analysis to measure the viscosity of water samples and other liquids. Changes in viscosity can provide insights into the presence of pollutants or contaminants.
8. Research and Development: Scientists and researchers use viscometers to investigate the rheological properties of fluids, conduct experiments, and develop new materials. Viscometry is essential in various scientific disciplines, including chemistry, physics, and materials science.
9. Cosmetics and Personal Care: In the cosmetics industry, viscometers are used to assess the consistency and texture of skincare products, shampoos, and lotions. This ensures that the products are easy to apply and provide the desired sensory experience.
10. Biotechnology and Pharmaceuticals: Viscometers are used in biotechnology and pharmaceutical research to measure the viscosity of biological fluids, such as blood or cell culture media. Understanding viscosity can aid in the development of drug delivery systems and medical devices.
Overall, viscometers are versatile instruments that play a crucial role in ensuring product quality, optimizing manufacturing processes, and advancing scientific research in a wide range of industries. They come in various types, including rotational viscometers, capillary viscometers, and vibrational viscometers, each suited to specific analysis, research, testing application and measurement requirements.
Newtonian and nonnewtonian fluids
Newtonian and non-Newtonian fluids are two categories of fluids that exhibit different behaviours in response to applied forces. These classifications are based on the relationship between shear stress (force per unit area) and shear rate (the rate of change of velocity with respect to distance) within the fluid.
Characteristics of Newtonian Fluids:
1. Linear Relationship: Newtonian fluids, such as water, air, and many simple liquids, exhibit a linear relationship between shear stress and shear rate. We can simply say that, as we increase the force applied to these fluids (shear stress), their rate of deformation (shear rate) also increases proportionally.
2. Constant Viscosity: The key characteristic of Newtonian fluids is that they have a constant viscosity, also known as dynamic viscosity or absolute viscosity. Viscosity is the ratio of shear stress to shear rate, and for Newtonian fluids, this ratio remains constant regardless of the shear rate. The SI unit for dynamic viscosity is pascal-seconds (Pas).
3. Example: Water is example of a Newtonian fluid. Its viscosity does not change as you vary the shear rate or applied force. When you stir water with a spoon, it responds predictably, and the force you apply is directly proportional to the resulting motion.
Characteristics of Non-Newtonian Fluids:
1. Non-Linear Relationship: Non-Newtonian fluids do not exhibit a linear relationship between shear stress and shear rate. These fluids show a variety of behaviours. Their viscosity can change with the applied shear rate.
2. Variable Viscosity: Non-Newtonian fluids can have variable viscosity. The viscosity may increase with shear rate (shear-thickening or dilatant behaviour) or decrease with shear rate (shear-thinning or pseudoplastic behaviour). Some non-Newtonian fluids may even exhibit time-dependent behaviour.
3. Examples: Some common examples of nonnewtonian fluids are ketchup (shear-thinning), whipped cream (thixotropic, meaning viscosity decreases with time under constant shear stress), and cornstarch mixed with water (a non-Newtonian fluid that can behave as a solid under high stress and a liquid under low stress).
What is the viscosity of water:
The viscosity of water (H2O) at the room temperature (that is at about 20 degrees Celsius or 68 degrees Fahrenheit) is approximately 1.002 millipascal-seconds (mPa·s) or 1.002 centipoise (cP).
This measurement value of 1.002 mPa·s (approx.) represents the resistance of water to flow and is used as a reference point for measuring the viscosity of other liquids. Viscosity can change with temperature; generally, water becomes less viscous as it is heated and more viscous as it cools.
Water is a chemical compound with chemical formula H2O. Water molecule contains two hydrogen and one oxygen atom. These atoms are connected by covalent bonds to form water molecule. This water molecule is essential for life on earth. Water molecules act as universal solvent for both living and non-living things. So, this chemical compound (water) is very essential for life on this planet earth.
Dynamic viscosity & kinematic viscosity of water
Dynamic viscosity & kinematic viscosity of water along with density at different temperatures from 20°C to 30°C.
Temp. [°C]
Dyn. Viscosity [mPa.s]
Kin. Viscosity [mm²/s]
Density [g/cm³]
20
1.002
1.003
0.998
21
0.978
0.980
0.998
22
0.954
0.957
0.998
23
0.932
0.934
0.998
24
0.911
0.913
0.997
25
0.890
0.893
0.997
26
0.870
0.873
0.997
27
0.851
0.854
0.997
28
0.832
0.836
0.996
29
0.815
0.818
0.996
30
0.797
0.801
0.996
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