Surface tension and viscosity

What is Viscosity?



A quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow.

or

Viscosity is a property of the fluid which opposes the relative motion between the two surfaces of the fluid that are moving at different velocities.
What is Surface Tension?

“Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. Surface tension is an important property that markedly influences the ecosystem.”
or
“Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area.”
or
“surface tension is often expressed as an amount of force exerted in the surface perpendicular to a line of unit length.”

1. Physical Chemistry Quaid - e - Azam University Islamabad

2. Group Members Umm -E- Kalsoom . Shazia Sultan. Muneebah Noor. Hira Sulaiman .

3. Topic “Surface Tension” & “Viscosity”

4. Viscosity: Introduction What is Viscosity? A quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow. or Viscosity is a property of the fluid which opposes the relative motion between the two surfaces of the fluid that are moving at different velocities. The word "viscosity" is derived from the  Latin  " viscum ", meaning  mistletoe

5. Types: About types Dynamic (or Absolute) Viscosity : The dynamic viscosity( η ) of a fluid is a measure of the resistance it offers to relative shearing motion. F=դ A ( դ : Pa-s) Kinematic Viscosity : It is defined as the ratio of absolute viscosity to the density of fluid. ν= η/ρ m ² /s ; ρ= density of fluid   Viscosity is a quantitative measure of a fluid’s resistance to flow.

6. Viscosity Measurements About measurements Viscosity is measure by following meters: Kinematic viscosity measurements: 1) Capillary Viscometer. 2) Bubble Viscometer. Dynamic viscosity measurements: 1) Rotational Viscometer. - Rotating Cylinder . - Cone-on-plate Viscometers. 2) Rheometer.

7. Exceptions: Inviscid fluid: A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. - Zero viscosity is observed only at very low temperatures in super fluids. - A liquid is said to be viscous if its viscosity is substantially greater than that of water. - A liquid is said to be mobile if the viscosity is noticeably less than water.

8. Dependence: It depends upon…. 1.Temperature: OF LIQUIDS : Their viscosity decreases with increase in temperature, Due to increase in average speed of molecules, that causes intermolecular forces to becomes weak so, decreases the viscosity. OF GASES : Their viscosity increases with increase in temperature , Because the motion of molecules become more disorganize due to increase in the intermolecular collisions of gas molecules , that causes the viscosity to increase.

9. Dependence: It depends upon…. 2.Intermolecular Forces: Stronger the intermolecular forces among the molecules, higher is the viscosity . For example water is more viscous than methanol mainly due to extensive hydrogen bonding. 3.Molecular size: Liquids whose molecules are small and compact have low viscosity . Whereas liquids having large and irregular shaped molecules tends to get tangled up with each other. This inhibits the flow of molecules and leads to high viscosity.

10. Dependence : 4.Pressure: Lubricants viscosity increases with pressure. For most lubricants this effect is considerably largest than the other effects when the pressure is significantly above atmospheric. The Barus equation : It depends upon….

11. Units: It’s units are…. S.I Units: Dynamic Viscosity: Kgm -1 s -1 Nm -2 s Pa-s Kinematic Viscosity: m 2 ·s −1 Non S.I Units are: Poise 10 poise= 1 pa-s Stokes 1 St = 1 cm 2 ·s −1 = 10 −4  m 2 ·s −1 .

12. Applications of Viscosity About applications Engineering: Selection of lubricants for various purpose. - we can choose an optimum range of viscosity for engine oil. - for high load and also for speed operation high viscous lubricants is required. In pumping operation - for high viscous fluid high power will require. - for low viscous fluid low power will require. In making of blend fuel - less viscous fuels easy to mix. In the operation of coating and printing .

13. Applications of Viscosity About applications Medical: To determine the viscosity of plasma - To prevent cardiovascular risk and other disease such as, obesity, hypertension ,and diabetes. - To determine the force required to inject a new drug formulation into a patient. - It helps in absorbing drugs into the human body. Used in pharmaceutical industries. - Accurate viscosity values of proteins are essential in understanding behavior, designing delivery systems, and accurately determining particle size of protein based drugs.

14. Applications of Viscosity About applications Industries: To determine the viscosity of chemical structure for ionic liquids to measure: - impurity of solution. - chemical structure of solution. - composition of solution. To determine the viscosity of polymer solution such as, polyamide, - T o control the quality of polyamide during production. - T o control the quality of the end product, molar mass and chain length of the polymer. To determine the viscosity of adhesive. - Low-viscosity adhesives will flow more readily than high-viscosity ones, so a high-viscosity adhesive is ideal. 

15. Applications of Viscosity About applications Industries: In food industries to check the viscosity of, - syrup, to ensure their use as a binders in the production of food, e. g. of chocolate cereal mixes or sauces. - a product so that it can travel efficiently through pipes and take less time to set or dry. - food such as a chewing gum, butter, margarine, bread, candy, chocolate, to find best composition ratios when producing them.

16. Lunch Break .. 30 seconds

17. Surface Tension: Introduction What is Surface Tension? “Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. Surface tension is an important property that markedly influences the ecosystem.” or “Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area.” or “surface tension is often expressed as an amount of force exerted in the surface perpendicular to a line of unit length.”

18. Surface Tension: Phenomena • The cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. •In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. •The molecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards. •This creates some internal pressure and forces liquid surfaces to contract to the minimal area. Surface tension is responsible for the shape of liquid droplets.

19. S URFACE TENSION

20. What’s going on at the surface of a liquid? Let’s take a look!

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36. Dependence: It depends upon……. 1.Intermolecular Forces: Stronger the intermolecular forces among the molecules of a liquids, greater is the surface tension and vice versa. e.g , the surface tension of water is higher than many liquids due to strong hydrogen bonding between water molecules. 2.Nature : It is different for different liquids due to the presence of different types of intermolecular forces.  

37. Dependence: It depends upon…. 3.Temperature: Surface tension of a liquids decreases with the increase of temperature , reaching a value of 0 at the  critical temperature . This is because increased kinetic energy of the molecules decrease the strength of intermolecular forces. 4.Solute Concentration: Solutes can have different effects on surface tension depending on the nature of the surface and the solute: A solute can exist in a different concentration at the surface of a solvent. This difference varies from one solute–solvent combination to another.

38. Physical Units: It’s units are….. Units: Surface tension, is usually represented by a symbol “ γ ”,is measured in force per unit length. γ = F /d S.I UNIT: γ = Nm -1 or Jm -2 CGS UNIT: γ = dyn cm -1 or erg cm -2

39. Applications: It’s use are…….. 1.Spherical Shape of Water Droplets: Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the   cohesive forces of the surface layer. The spherical shape minimizes the necessary "wall tension" of the surface layer according to  LaPlace's law. In the absence of other forces, including gravity, drops of virtually all liquids would be approximately spherical. a sphere has the smallest possible  surface area to volume ratio

40. Applications: It’s use are…….. 2.Walking on water: Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface. 3. Floating a needle: A small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then needle will quickly sink. 4. Soaps and detergents: Surface tension help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.

41. Applications: It’s uses are….. 5.Don't touch the tent: Common tent materials are somewhat rainproof in that the surface tension of water will bridge the pores in the finely woven material. But if you touch the tent material with your finger, you break the surface tension and the rain will drip through. 6. Clinical test for jaundice: Normal urine has a surface tension of about 66 dynes/cm but if bile is present (a test for jaundice), it drops to about 55. In the Hay test, powdered sulfur is sprinkled on the urine surface. It will float on normal urine, but sink if the S.T. is lowered by the bile.

42. Applications: It’s uses are….. 7.Washing with cold water: The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unnecessary. 8. Surface tension disinfectants: Disinfectants are usually solutions of low surface tension. This allow them to spread out on the cell walls of bacteria and disrupt them. One such disinfectant, S.T.37, has a name which points to its low surface tension compared to the 72 dynes/cm for water.

43. Applications: It’s uses are….. 9.Capillary Action: Capillary action is the result of adhesion and surface tension. Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the whole liquid surface is dragged upward. 10.Alveoli of the Lungs: The oxygen exchange in the lungs takes place across the membranes of small balloon-like structures called alveoli attached to the branches of the bronchial passages. These alveoli inflate and deflate with inhalation and exhalation. The behavior of the alveoli is largely dictated by  LaPlace's law and surface tension.

44. Applications: It’s uses are….. 11.Cell Maintenance: Water particles at the atomic level help keep the cell membrane from collapsing on itself. Water is a critical component in cytoplasm this means that the surface tension of water allows the cytoplasm to hold-up the cell membrane. If the pressure is too extreme, , then the water breaks down the cell membrane and the cell "drowns". 12.Transportation: The high surface tension of water is also essential for processes such as water and blood transport in plants and animals respectively. The concave motion of the surface of the water allows it to be "pulled up" by plants from the ground

45. QUESTIONS?

46. Reference: ‘Engineering Tribology’ by “ Gwidon W. stachowiak ” and “Andrew W. Batchelor ”. ‘Engineering Tribology’ by “J. A. Williams”. Petrucci, Ralph H., et al. General Chemistry: Principles and Modern Applications. Upper Saddle River, NJ: Prentice Hall, 2007. www.wikipedia.org www.google.com

47. thank you