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Physical Pharmaceutics-I Unit-III Surface and Interfacial tension (Part-1)(Liquid interface, surface and interfacial tension )

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Physical Pharmaceutics-I Unit-III Surface and Interfacial tension (Part-1)(Liquid interface, surface and interfacial tension )

  1. 1. IIIrd Semesester B. pharmacy Physical Pharmaceutics-I Unit-III Surface and Interfacial tension (Part-1) (Liquid interface, surface and interfacial tension ) Miss. Pooja D. Bhandare (Assistant professor) Kandhar college of pharmacy
  2. 2.  LIQUID INTERFACE • When phases are in contact with each other, the boundary between them is know as interface. • If one of two phases is a gas or vapour, the term ‘surface’ is generally used instead of interface. • No interface can be observed between two gas phases because they are mutually miscible in all proportions. • The pharmacist encounter several types of interface, while handling dosage form.
  3. 3. • Solid- solid interface are important in pharmacy in the area of adhesion of granules to form a tablet, flow of granules through hopper during tableting. • In the liquid state, the cohesive forces between adjacent molecule are well developed. • Molecules in the bulk liquid are surrounded in all directions by other molecule for which they have an equal attraction. • But molecules at the surface (i.e., at the liquid-air interface) can only develop attractive cohesive forces with other liquid molecules that are situated below and adjacent to them.
  4. 4. • Table 1: Classification of Interfaces Phases Types of Interface Example of interface Gas - Gas No interface possible Gas - Liquid Liquid surface Body of water exposed to atmosphere. Gas - Solid Solid surface Table top Liquid - Liquid Liquid-Liquid interface Emulsion Liquid - Solid Liquid – Solid interface Suspension Solid - Solid Solid - Solid Powder particle
  5. 5.  SURFACE AND INTERFACIAL TENSION • Surface tension is defined as the force, in newtons, acting on the surface of the liquid at right angles to any line of the length surface, 1 metre. • Unit surface tension and interfacial tension:  CGS system : dyne/cm SI system : N/m • Surface tension of liquid can be explained by considering the intermolecular forces between the molecules in the neighbourhood
  6. 6. • In liquid, molecules experience greater attraction from the neighbouring molecules. • Such intermolecular attraction between like molecules are called cohesive forces while attraction between unlike molecules are called adhesive forces.
  7. 7. The phenomenon of surface tension is responsible for the following process:  Formation of spherical globules in emulsion.  Formation of nearly spherical shape of falling water droplet.  Formation of spherical shape of mercury particles on flat surface.  Rise of liquid in capillary tube
  8. 8. Molecule at the surface: • Cohesive (attraction) forces are not properly balanced. • Experienced an inward forces of attraction towards the bulk of liquid. • Surface of liquid gets contracted and molecules at the interface are pulled together. • Force exactly counterbalance the inward pull is surface tension. Molecules in bulk: • Surrounded by other molecules which have equal attraction in all directions. • Net attraction is zero
  9. 9. Interfacial tension is between two immiscible liquids arises as a result of imbalance forces. It is the per unit length existing at the interface between two immiscible liquid phases. Although, in the general sense, all tension may be referred to as interfacial tension, this term is most often used for the attractive forces between immiscible liquids. Generally interfacial tension are less than surface tension because the adhesive forces between two liquid phases forming an interface are greater than when a liquid and a gas phase exist together
  10. 10. • Surface Tension of Some Liquids Liquids Surface tension.mN/m (=dy/cm) Water 71.60 Glycerine 66.00 Ethanol 21.62 Paraffin 30.0 Mercury 480
  11. 11. Thank You!

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