DLVO theory-Stability of colloids ( lyophobic )

This theory is explain by Derjaguin , Landau , Verway , Overbeek So it is known as DLVO Theory.
According to this theory , The forces on colloidal particles in a dispersion medium are due to –
1. Electrostatic Repulsion
2. London type Vander Waals Attraction

1. Smt. B.N.B. Swaminarayan pharmacy college 1 Stability of Colloids (Lyophobic):DLVO THEORY Name : Pratik B. Gondaliya Utkarsh B. Kikani Sem : 6 th sem College : Smt. B.N.B Swaminarayan pharmacy college , Salvav.

2. Introduction Dispersion System: The dispersion system consist of particulate matter (particles) known as dispersed phase, distributed through out a continuous or dispersion medium . According to mean diameter of particles in dispersion , It classify as:- 1. True solution / Molecular dispersion :- - Size <0.01 μ m -Examples: Urea, Sucrose Solution,Oxygen gas 2. Colloidal dispersion :- - Size: 1m-1 μ m -Examples: Acacia, Albumin, Insulin, Silver sols 3. Coarse Dispersion :- - Size: 10-100 μ m -Examples: Calamine suspension, Magnesium oxide, RBCs Smt. B.N.B. Swaminarayan pharmacy college 2

3. Colloidal dispersion : colloidal system is define as those polyphesic system where dimension of dispersed phase measures between 1nm to 1 μ m. Characteristic of Dispersed phase:- 1. Particle size : -influences the colour of dispersion colloidal gold : red colour coarse dispersion of gold : blue colour 2. Particle shape : -Examples: sphericle particle of gold: red colour disc like particle : blue colour 3. Surface area : Has a higher surface area 4. Surface charge : -colloidal particle posses charge on their surface - Example: negative : acacia, sulphur, tragacanth positive : gelatin (pH<4.7),Bismuth, Aluminium Smt. B.N.B. Swaminarayan pharmacy college 3

4. Classification : 1. Lyophillic colloids: - Solvent loving 2. Lyophobic colloids: - solvent hating 3. Association colloids: -Amphiphilic in nature Smt. B.N.B. Swaminarayan pharmacy college 4

5. Stability of Colloids 1. Lyophilic colloids: 2. Lyophobic colloids: Thermodynamically stable Stabilize by Providing electric charge Providing protective sheath of solvent to each particle prevent adherence of particle Thermodynamically unstable Stabilize by only by providing electric charge The Stability of lyophobic colloids is explained by DLVO Theory . Smt. B.N.B. Swaminarayan pharmacy college 5

6. DLVO Theory This theory is explain by Derjaguin , Landau , Verway , Overbeek So it is known as DLVO Theory. According to this theory , The forces on colloidal particles in a dispersion medium are due to – 1. Electrostatic Repulsion 2. London type Vander Waals Attraction Smt. B.N.B. Swaminarayan pharmacy college 6

7. Zeta Potential The potential difference across an electric double layer usually between solid surface and liquid. It should be optimum, increase or decrease in zeta potential leads to instability in suspension Range : -30 to +30 mV. Smt. B.N.B. Swaminarayan pharmacy college 7

8. In this theory, When two particle close together according to following condition : Same charged particles – Repulsion Opposite charged particles – Attraction When two same charge particles are brought together forcefully ( explain deflocculated suspension ) Effect of electrolytes on particles ( explain flocculated suspension ) Smt. B.N.B. Swaminarayan pharmacy college 8 Describe instability

9. P otential Energy Curve Smt. B.N.B. Swaminarayan pharmacy college 9

10. Same charge particles: When two same charge particle present in suspension, initially positive energy (zeta potential) is low , As distance between particle decrease increase repulsive force increase zeta potential So increase +ve energy as shown in figure (repulsive curve V R ). This increase in energy leads to sedimentation , hence leads to instability in suspension. Smt. B.N.B. Swaminarayan pharmacy college 10

11. 2. Opposite charge particles: When two opposite charged particles present in suspension , initially energy (zeta potential) is low. As, Distance between particles decrease increase attractive force increase zeta potential (-ve energy) as shown in figure (Attraction curve V A ) . This increase in –ve zeta potential /energy leads to coagulation followed by sedimentation Smt. B.N.B. Swaminarayan pharmacy college 11

12. 3. Two same charge particle brought together forcefully: As we decrease distance between particle increase potential energy repulsion But as we decrease forcefully (<0.5-2 nm) The molecular orbital of each particle are bounded with each other The potential energy decrease as –ve energy leads to attraction and form hard cake Smt. B.N.B. Swaminarayan pharmacy college 12

13. This negative potential energy and attraction due merging of molecular orbital of particles is known as Primary Minimum. Example: Hard cake formation deflocculated suspension. Deflocculated suspension Undisturbed long time so increase force on particle due to gravity Particle may bound with each other as describe above Aggregates forms Leads to formation of hard cake Smt. B.N.B. Swaminarayan pharmacy college 13

14. 4. Effect of Electrolytes on particles: Electrolyte like NaCl is added into suspension The +ve charged (Na+) absorbed on the particles. The –ve charged ( Cl - ) helps to form a weal bond between in salt absorbed particles and form loosely arranged flocs. This causes slight decrease in negative potential energy , So weak attractive force between the particles . So on agitation weakly bonded flocs easily break and redispersed . Smt. B.N.B. Swaminarayan pharmacy college 14

15. This slight decrease in negative potential energy due to flocs formation is known as Secondary Minimum. Example: Flocs formation in Flocculated suspension Application: - since 1940s DLVO theory has been used to explain phenomena found in colloidal science, adsorption etc. - nanoparticle research: DLVO theory used to explain behaviour of both material nanoparticle (like fullerene particle) and micro organisms. Smt. B.N.B. Swaminarayan pharmacy college 15

16. References: “Physical Pharmacy - Physical Chemical Principles In The Pharmaceutical Science “ by Alfred Martin , James Swarbrick , Arthur Cammarata ,3 rd edition , Varghese Publishing House , Page no. 486 “Leon Lachman / Liberman’s – The Theory And Practice of Industrial Pharmacy “ By Roop K Khar , S.Vyas , 4 th Edition – 2013 , CBS Publisher And Disributors , Page no. 660 Smt. B.N.B. Swaminarayan pharmacy college 16

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