ppt SURFACE AND INTERFACIAL TENSION

SURFACE AND INTERFACIAL TENSION

1. SURFACE AND INTERFACIAL TENSION Presented by , RD

2. CONTENTS Introduction Detergency Foaming agents Anti Foaming agents Spreading coefficient Wetting References

3. INTRODUCTION Surface tension- The tension in the surface is the force per unit length that must be applied parallel to the surface so as to counter balance the net invert pull. This is called surface tension. Unit- N/m Interfacial tension- It is the force per unit length existing at the interface between two immiscible liquid phases and like surface tension has the unit N/m.

4. DETERGENCY Surfactants in aqueous solution are used to remove dirt from the substrate such as glass, fabric, skin etc. The HLB requirement of detergent is from 13-16. Some ex. of detergent of ionic type are- Cationic – cetrimide Anionic – sodium lauryl sulfate

5. Mechanism of Detergency The hydrocarbon tails of the detergents anions dissolve in the grease The grease spot gradually breaks up and becomes pin cutioned by the detergent anions. Small bit of grease are held in colloidal suspension by the detergent. The anionic bonds keep the greece from combining because the particles carries the same electric charge.

6. FOAMING AGENTS Any solution containing surface active material produces stable foams when mixed intimately with air. A foam is relatively stable structure consisting of air packets enclosed with in the films of liquid i.e. the gas in liquid dispersion being stabilized by foaming agents. ANTI FOAMING AGENTS Some surfactants can be used to break the foam and are known as Anti foaming agents. Ex alcohols, ether, castor oil

7. SPREADING COEFFICIENT When a substance such as oleic acid is placed on the surface of water , it will spread as the film if the force of adhesion between the oleic acid molecules is greater than cohesive force between the oleic acid molecules itself. It is the difference between work of adhesion and work of cohesion. The HLB of the spreading agents is 04-09.

8. Application of spreading coefficient Adsorption of medicaments from creams , lotions etc. Stabilization of emulsions. Coating of tablets.

9. WETTING AGENT Adsorption at solid liquid interface is involved in the phenomenon of wetting agents. Wetting agents also decreases the surface energy of the molecules as given in the formula- E=W/A Where, E= surface free energy of molecules W= work done to release the dirt. A = occupied surface area

10. CONTACT ANGLE The most important action of wetting agent is to lower the contact angle between surface and wetting liquid The contact angle is the angle between a liquid droplet and the surface over which it spreads.

11. Application of wetting agent Intimate contacts of solids or liquid with liquid is initial step towards the preparation of suspension and emulsion. Film coating required wetting & spreading of liquid over the tablet surface. Dissolution of the tablet or capsules necessities the penetration of liquid into pours of dosage forms.

12. REFERENCES Martin Alfred, “Physical pharmacy,” 4 th edition, B.I. Waverly private limited new Delhi, page no. 145-168. Darle D.V. , essentials of Physical pharmacy, Sai hanuman sagar boddu, 2th edition, new Delhi, page no. 240-253.