surface tension part 1

Content:
Introduction of surface and interface
Significance of ST
Factors influencing surface tension

1. Khalifa M.Asif Yunus
M.Pharm (Pharmaceutics)
J I IU ’ S
Ali-Allana College of Pharmacy Akkalkuwa
NBA Accredited
Asst. Prof.
Pharmaceutics Department
Ali-Allana college of pharmacy Akkalkuwa
E-mail: [email protected]. No. [phone]

2. Watch this video for better understanding
https://www.youtube.com/watch?v=XvxZ4XLDkR8&t=162s
Introduction of Surface tension

3. Theboundarybetweentwophasesisgenerallydescribedasan
interface
Whenoneofthephaseisagasoravapor,thetermsurfaceis
frequentlyused.
Thesetermssurfaceandinterfacecanbeusedinterchangeably
insomecases.

4. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Solid Phase
Gas Phase (air)
Solid Surface

5. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Liquid Surface
Liquid Phase
Gas Phase

6. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Liquid Phase
Solid Phase
Solid-Liquid
interface

7. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Liquid-Liquid
interface
Liquid Phase
Liquid Phase

8. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa

9. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Surface Tension
Thesurfacetension(γ)isdefinedas:Theforceindynesactingalong
thesurfaceofaliquidatrightangletoanyline1cminlength.
Units of Surface Tension
InCGSsystemisdynespercentimeter(dynecm
–1
).
InSIsystem,theunitisNewtonpermeter(Nm
–1
).

10. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Surface molecules pulled
inward
Interior molecules pulled
equally in all direction

11. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Surfacetensioniscausedbythenetinwardpullonthesurface
molecules.
Atthebulkoftheliquid;
Moleculesintheinteriorexperienceanattractiveforcefrom
neighboringmoleculeswhichsurroundonallsides
Attheliquidsurface:
Moleculesonthesurfacehaveneighboringmoleculesonly
ononesideandthusexperienceanattractiveforcewhich
tendstopullthemintotheinterior

12. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Theneteffectisthatthemoleculesatthesurfaceoftheliquid
experienceaninwardforcetowardthebulkoftheliquid.
SuchforceresultsinwhatiscalledSurfaceTension.
Duetothisunbalancedforces,thesurfaceoftheliquid
behaveslikeastretchedelasticmembranecontainingthe
moleculesoftheliquidinside.

13. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
sincetheliquidtendstocontracttoaminimumarea,thesurface
oftheliquidappearstobeinastateoftension,soinorderto
increasetheareaofthesurfaceitisnecessarytodoworktobring
themoleculesfromthebulkoftheliquidtothesurfaceagainst
theinwardattractiveforce.

14. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Duetotheseunbalancedforcestheliquidtendstoadjustitselfto
giveaminimumsurfacearea,whichtakestheformofasphereand
forthisreason
Liquidrisesincapillarytubes
Dropletsacquiresphericalshape

15. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
1.Formationofsphericalglobulesinemulsions.
Thephenomenonofsurfacetensionisresponsibleforfollowing
processes.(Significance)

16. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
2.Formationofnearlysphericalshapeoffallingwaterdroplets.

17. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
3.Formationofsphericalshapeofmercury
particleonflatsurface.

18. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
4.Riseofliquidincapillarytube.

19. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
5.Formationofhemisphericalsurfacei.e.
lowermeniscus.

20. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Adhesional and Cohesional forces
Adhesionalforces:Areforceswhichactbetweenmoleculesof
differentphases.
Cohesionalforces:Areforceswhichactbetweenmoleculesofthe
samephase.
Cohesionalforcetendtokeepthephasesseparatewhile
adhesionalforcestendtoincreasetheaffinityoftwophases
Ifadhesiveforce>cohesiveforceresults;
•Wetting•Spreading•Risinginthetube

21. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Interfacial Tension
“Thetensionexistingattheinterfacebetweentwoimmiscible
liquids.“
“Theforceperunitlengthexistingattheinterfacebetweentwo
immiscibleliquid.”
Whentwoliquidarecompletelymiscible,theinterfacecannot
beobservedandhence,donotpossessinterfacialtension.E.g.
water&alcohol.

22. By: Khalifa M Asif Y Asst. ProfessorPharmaceutics Dept. AACOP Akkalkuwa
Factors influencing Surface and Interfacial tension
Internal
Factors
External
Factors
As temp increases the S.T of liquids
decreases due to enhance kinetic
energy that weakens cohesive force.
Water : 72.8
Benzene: 28.9
CCl
4 : 26.7
Electrolyte increase S.T
S.A. Agents decreases S.T
Intermolecular
attractive forces