Surface Tension and Surfactants Tutorial 6 PDF

Faculty of Pharmacy and Biotechnology Department of Pharmaceutical Technology Physical Chemistry and Physical Pharmacy [PHTCt 102] Tutorial 6: Surface Tension and Surfactants Presented by: Physical Chemistry and Physical Pharmacy Team Important Definitions: Interface:...

Faculty of Pharmacy and Biotechnology Department of Pharmaceutical Technology Physical Chemistry and Physical Pharmacy [PHTCt 102] Tutorial 6: Surface Tension and Surfactants Presented by: Physical Chemistry and Physical Pharmacy Team Important Definitions: Interface: It is the boundary between two phases when they exist together. Phase Types and interface examples Gas-liquid Liquid surface, water exposed to atmosphere Gas-Solid Solid surface, Table top Liquid-liquid Liquid-liquid interface, emulsion water drop Liquid-solid Liquid-solid interface, suspension Solid-solid Solid-solid interface, powder particles in contact Emulsion Powder particles Liquid A Liquid B Suspension 2 Physical Chemistry and Physical Pharmacy PHTC 102  Important Definitions: Therefore; Surface tension exists between liquid phase and gaseous phase while Interfacial tension exists between two immiscible liquid phases. 3 Physical Chemistry and Physical Pharmacy PHTC 102 Important Definitions: - Pharmaceutics: It is the science of dosage form design. - Dosage forms are the carriers through which drug molecules are delivered to different sites of action within the body - Dosage forms are combinations of the drug and different types of non drug component called excipients. - Different types of Dosage forms include: 4 Physical Chemistry and Physical Pharmacy PHTC 102 What is Surface Tension? - What is surface tension? Therefore; Surface tension exists as a result of the Cohesive forces Adhesive forces inward pulling force toward the bulk due to cohesive force present between water molecules which contracts between water molecules > between water and air molecules the surface. Unbalanced forces create a tension on the surface 5 Physical Chemistry and Physical Pharmacy PHTC 102 What is Interfacial Tension? -What is the interfacial tension? - Is there interfacial tension between two miscible liquids? No, because there is NO interface Interface “boundary” Two immiscible liquids Two miscible liquids 6 Physical Chemistry and Physical Pharmacy PHTC 102 Surface tension in Pharmaceutics Creams and other dosage forms are emulsions; mixtures of oily and aqueous phases But oil and water are immiscible Why? Polarity! Water molecule Oil molecule Interfacial tension N.B Polarity is related to the overall charge distribution in a molecule. 7 Physical Chemistry and Physical Pharmacy PHTC 102 Surface tension in pharmaceutics Suspensions High interfacial tension Low Wettability Low interfacial tension High Wettability 8 Physical Chemistry and Physical Pharmacy PHTC 102 How do surfactants reduce surface/interfacial tension? How do surfactants reduce interfacial tension? - Surfactants break/reduce surface tension by interrupting the intermolecular cohesive forces between water molecules Surfactant=surface active agent (SAA) How are they used in the preparation of suspensions and emulsion? 9 Physical Chemistry and Physical Pharmacy PHTC 102 What is an emulsion? 10 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions Can water and benzene naturally mix? Why? How can they be mixed to form an emulsion? Can water and acetic acid naturally mix? Water and CCl4 a) Are Miscible b) Are Immiscible c) Are Soluble d) Can form an emulsion by addition of surfactant e) a&d f) b&d 11 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions How to form an emulsion between water and any of the oils mentioned? Which of these oils is miscible with water? Why? 12 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions The resistance of a liquid to an increase in its surface area is a) Viscosity b) Surface tension c) Meniscus d) Impossible When there are no external forces, the shape of a liquid drop is determined by its a) Density b) Viscosity c) Temperature d) Surface tension 13 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions As the temperature of a liquid increases, its surface tension a) Decreases b) Increases c) Stays the same The boundary between two or more phases is called a) Surface b) interface c) Both d) Neither 14 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions If two liquid are completely miscible with each other, what is the interfacial tension? a) 24 dyne/cm b) 37 dyne/cm c) 72 dyne/cm d) Does not exist When a drop of liquid falls, which of the following regarding the forces acting on it is correct? a) The cohesive forces between the molecules exceeds the adhesive forces b) The adhesive forces exceed the cohesive forces c) Gravity exceeds the cohesive forces holding the molecules together d) Gravity exceeds the adhesive forces holding the molecules together 15 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions Interfacial tension will exist between all the following except a) Immiscible liquids b) miscible liquids c) solid- solid d) solid-liquid For the molecules in the bulk of a liquid which of the following statement is correct? a) They are surrounded in all directions by other molecules for which they have an equal attraction b) Only attractive cohesive forces with other liquid molecules which are situated below and adjacent to them c) They can develop adhesive forces of attraction with the molecules of the other phase in the interface d) The net effect is that the molecules at the surface of the liquid experience an inward force towards the bulk of the liquid and pull the molecules and contract the surface with a force F 16 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions Cohesive forces are the forces acting… a) Between molecules of different materials b) Between molecules of same material c) Between water and glass capillary tube d) Due to gravity For the molecules at the surface (at the liquid/air interface) which of the following statement is incorrect? a) They are surrounded in all directions by other molecules for which they have an equal attraction b) Only attractive cohesive forces with other liquid molecules which are situated below and adjacent to them c) They can develop adhesive forces of attraction with the molecules of the other phase in the interface d) The net effect is that the molecules at the surface of the liquid experience an inward force towards the bulk of the liquid and pull the molecules and contract the surface with a force F 17 Physical Chemistry and Physical Pharmacy PHTC 102 Practice questions What is the main result of adding surfactants into a liquid composed of two immiscible phases such as oil and water? a) Reduction in the interfacial tension between the phases b) Increase in the interfacial tension between the phases c) Catalysation of a chemical reaction between the phases d) Nothing happens Which of the following is an application of surface tension? a) Use of soaps and detergents as cleansing agents b) Surfactants are incorporated in preparations like toothpaste c) All of the mentioned 18 Physical Chemistry and Physical Pharmacy PHTC 102  Reference Book Sinko, P. J., & Martin, A. N. (2017). Martin's physical pharmacy and pharmaceutical sciences: Physical chemical and biopharmaceutical principles in the pharmaceutical sciences. Philadelphia: Lippincott Williams & Wilkins. 19 Physical Chemistry and Physical Pharmacy PHTC 102