Micelle and Critical Micelle Concentration

all aspects of micellization and cmc

1. Critical micelle concentration Presented By Guided By MS. KRUTIKA H. PARDESHI MRS.S.B.SANDHAN M.Pharm (Pharmaceutics ) ( Assistant professor) Sem -II , Roll no. 37 NDMVP SAMAJ’S COLLEGE OF PHARMACY, NASHIK M.Pharm Semester II -seminar

2. CONTENT Introduction Micelle - Micelle formation - Process of micellization - Structure of micelle - Mechanism of micelle formation - Types of micelle Critical micelle concentration (CMC) - Introduction - Determination of CMC - Factors affecting CMC C onclusion References 2

3. INTRODUCTION 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 aggregate into a structure. Structure called as micelle and Amphiphilic molecule is known as Surface Active Agent. 3

4. 4 1.Surfactants- : Surfactants are usually organic compounds that are amphiphilic , meaning they contain both hydrophobic groups (their tails) and hydrophilic groups (their heads ). 2.Micelle -: A micelle is an electrically charged particle formed by an aggregate of molecules, above a critical concentration and occurring in certain colloidal electrolyte solutions, especially those of soaps and detergents. 3.Critical Micelle Concentration-: Critical Micelle Concentration is the concentration at which the surface becomes completely loaded with surfactant and any further additions must arrange as micelles.

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-Oct-16 5

6. MICELLE FORMATION 1. The process of forming micelle is known as micellization . 2. Typical micelle is Spherical in structure which contain 50-100 monomers. 3. Number of monomers to form micelle is called as aggregation number. 6

7. Process of micellization 7 SAA bulk Concentration Surface excess Surface saturated with SAA Excess in the bulk Micelles( colloidal aggregates 30-100nm)

8. Structure of micelle 5-Oct-16 8

9. MICELLE FORMATION MECHANISM. 9

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11. Types of micelle 1. Oil in water type 2. Water in oil type 11

12. 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. 12

13. 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 13

14. The CMC is an important characteristic of a surfactant. Before reaching the CMC, the surface tension changes strongly with the concentration of the surfactant. The value of the CMC for a given dispersant in a given medium depends on temperature, pressure, and (sometimes strongly) on the presence and concentration of other surface active substances and electrolytes. Micelles only form above critical micelle temperature . For example, the value of CMC for sodium dodecyl sulfate in water (no other additives or salts) at 25 °C, atmospheric pressure, is 8x10 −3 mol /L. 14

15. Upon introduction of surfactants (or any surface active materials) into the system, they will initially partition into the interface , reducing the system free energy by: 1. lowering the energy of the interface (calculated as area times surface tension), and 2. removing the hydrophobic parts of the surfactant from contact with water . Subsequently, when the surface coverage by the surfactants increases, the surface free energy (surface tension) decreases and the surfactants start aggregating into micelles, thus again decreasing the system's free energy by decreasing the contact area of hydrophobic parts of the surfactant with water . Upon reaching CMC, any further addition of surfactants will just increase the number of micelles (in the ideal case). 15

16. 16 Increasing concentration of surfactant in water slowly forming a layer on the surface and eventually forming micelles at or above the CMC

17. 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 17

18. 1. SURFACE TENSION 18 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.

19. CONDUCTIVITY Below the CMC, the addition of surfactant to an aqueous solution causes an increase in the number of charge carriers and consequently, an increase in the conductivity. Above the CMC, further addition of surfactant increases the micelle concentration while the monomer concentration remains approximately constant (at the CMC level). Since a micelle is much larger than a monomer it diffuses more slowly through solution and so is a less efficient charge carrier. 5-Oct-16 19

20. TURBIDITY Turbidity surface activity observed by adding proper amount of hydrocarbon solution with surfactant concentration, the concentration of turbidity point mutation is the surface active agent CMC. 5-Oct-16 20

21. Factors Affecting CMC Structure of hydrophobic group – length of hydrocarbon chain Micelle size CMC Addition of Electrolyte Micelle Size CMC Effect of Temperature up to cloud point Micelle Size CMC 21

22. References Ana Domínguez , Aurora Fernández , et.al., "Determination of Critical Micelle Concentration of Some Surfactants by Three Techniques", Journal of Chemical Education,1997, 74(10):1227-1231 Hakiki , F., Maharsi , et.al., “Surfactant-Polymer Coreflood Simulation and Uncertainty Analysis Derived from Laboratory Study” Journal of Engineering and Technological Sciences. 2016, 47(6 ):706-724 . Mukerjee , P.; Mysels , K. J. “Critical Micelle Concentrations of Aqueous Surfactant Systems” NIST National Institute of Standards and Technology: Washington D.C. USA ,: 36 22

23. M.E . Aulton , “Pharmaceutics science of dosage form design”, 2 nd Edition, churchill livingstone publication, page no:88-89 Leon Lachman , H. A. Liberman , “The Theory and Practice of Industrial Pharmacy”, verghese publication house, 3 rd edition, page no:106 Sanjay K. Jain, Vandana Soni , “ Benley’s Text Book of Pharmaceutics”, 1 st edition, elesvier publication,page no:68-74 23

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