Micelle and critical micelle concentration

micelle formation its types and cmc. how cmc can be determined
factors affecting on cmc

1. Micelle Formation and Critical Micelle Concentration Presented by- Meghnath Kalita M.Sc 2 nd semester Roll no. 06 1

2. Contents Introduction Concept of Micelle Micelle formation Critical micelle concentration (CMC) Determination of the CMC Factors affecting CMC Conclusion Reference 2

3. Introduction An Amphiphiles is a compound possessing both hydrophilic and lipophilic properties In dilute solution amphiphiles tend to reduce Surface tension As concentration molecules of amphiphiles goes on increasing they disturb hydrogen structure, to minimize the disturbance molecules tend to form to aggregate into a structure called as micelle and Amphiphilic molecule Surface Active Agent 3

4. Surfactants • A micelle is an aggregates of Surfactant molecules dispersed in liquid colloid • Surfactants (amphiphilic molecules) composed of a hydrophilic moiety known as head and a hydrophobic moiety known as tail. 4

5. Micelle • A micelle is an aggregate of monomer surfactant molecules dispersed in a liquid colloid . • Hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic tail regions in the micelle centre. (oil-in-water micelle ). • Inverse micelles have the head groups at the centre with the tails extending out (water-in-oil micelle). 5

6. Types of Micelles Following are three types of micelles Spherical micelle, Rod shaped micelle, Lamellar micelle. 6

7. Oil in Water Type Because of arrangement monomers micelle is capable to hold lipid nature drug at centre Water in oil type In Reversed micelle at middle able to hold relatively large amounts of water in their interior. In that way, a "pocket " is formed which is particularly suited for the dissolution and transportation of polar solutes through a non polar solvent. 7

8. Micelle Formation The process of forming micelle is known as micellization. In the aqueous system the high interfacial energy between the water molecules and the hydrocarbon chains of the surfactant is the primary factor in the process, while in a nonpolar system the attractive interaction between the polar parts serves as the force governing the association process. Number of monomers to form micelle is called as aggregation number The micellization in aqueous solutions may be perceived as a phase separation that is modified through geometrical restrictions, while the corresponding phenomenon in oils is a chemical equilibrium similar to that of alcohols in such media. The consequence of this difference is that the process in water is highly cooperative and the designation of a critical micellization concentration (cmc) is justified . Kraft Temperature is the min. temperature at which surfactants form micelle .Below Kraft temperature there is no value for CMC i.e micelle cannot form 8

9. SAA bulk Concentration Surface excess Surface saturated with SAA Excess in the bulk Micelles( colloidal aggregates) 9

10. 10 Fig: Micelle formation

11. Critical Micelle Concentration(CMC) The lowest concentration at which micelles first appear is called the critical concentration for micelle formation The critical micelle concentration is the point at which surfactant molecules aggregate together in the liquid to form groups known as micelles. 11

12. The critical micelle concentration of a surfactant indicates the point at which surface active properties are at an optimum and performance is maximised. The CMC is the concentration above surfactant when micelles will form spontaneously. Increase in concentration of surfactant beyond CMC change number size or shape but not provide increase in concentration of monomeric species 12

13. Determination of the CMC Micelles are formed at the critical micelle concentration (CMC), which is detected as an inflection point in physical properties which are plotted as a function of concentration. • surface tension, • Conductivity, • Turbidity, 13

14. Surface Tension Method Determine surface tension of solution towards several different concentrations, and then draw a graph of surface tension against log C the logarithm of concentration, and the turning points is the CMC. Technique Various technique available one of which is Will Helmy side method Principle Force is required to detach a thin microscopic slide of known thickness and width from the surface of liquid is measured. 14

15. Graph log of Concentration Vs Surface tension A graph of surface tension versus log concentration is produced. The CMC is found as the point at which two lines intersect; the baseline of minimal surface tension and the slope where surface tension shows linear decline. 15

16. 1. At very low concentrations of surfactant only slight change in surface tension is detected. 2. Additional surfactant decreases surface tension 3.Surface becomes fully loaded, no further change in surface tension. 16

17. Conductivity Method By the relationship between conductivity of ionic surfactant solution and concentration, draw curves of conductivity versus concentration or molar conductivity on which turning points is the CMC. Graph Molar Conductivity vs. concentration Precautions Clean electrode after each determination through ethanol and rise rapidly with demonized water and dry Limitation Can not used for non- ionic surfactant. 17

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19. Factors Affecting CMC Structure of hydrophobic group. – as the length of hydrocarbon chain is increases--- CMC decreases. Addition of Electrolyte – decreases due to decreases in thickness of ionic atmosphere surrounding the ionic head groups Effect of Temperature – first decreases to a minimum and then increases . Due to decreased in hydration of the hydrophilic group 19

20. solubilisation Solubilization is the preparation of a thermodynamically stable isotropic solution of a substance normally insoluble in a given solvent by the introduction of an additional amphiphilic components Micelle can be used to increase the solubility of material that are normally insoluble or poorly soluble in dispersed medium phenomenon called as solubilisation Importance Hydrophilic drugs can be adsorbed on the surface of the micelle. Completely insoluble hydrophobic drugs may be located in the Inner Core of the micelle. Drugs with intermediate Solubility should be located in intermediate positions within the micelle such as between the hydrophilic head group of Micelles 20

21. Conclusion 21 An Amphiphiles is a compound possessing both hydrophilic and lipophilic properties Amphiphiles aggregate into a structure called as micelle Surfactants composed of a hydrophilic moiety known as head and a hydrophobic moiety known as tail.--- lowers the surface tension CMC----The lowest concentration at which micelles first appear is called the critical concentration for micelle formation CMC is detected as an inflection point in physical properties

22. References “Principles of Physical Chemistry” –Puri , Sharma & Pathania -46 th Edition— Vishal Publishing co. D.S Pahari , “Physical Chemistry” ,2 nd Edition Paul C. Hiemenz , Raj Rajagopalan , “Principle of Colliods and Surface Chemistry” 22

23. THANK YOU 23