Interfacial Science And Surfactants Flashcards
What are surfactants
Molecules which accumulate at the surface
What happens at the liquid/air interface
Adsorption
Hydrophobic part outside of water
What happens at the oil/water interface
Adsorption between aq and non aq
Hydrophobic group in non aq and hydrophilic group in aq
What happens at the liquid/hydrophobic solid interface
Surfactants adsorb onto the surface which reduces contact between hydrophobic groups and water
Minimum energy state
What happens to surface tension when a surfactant is added to a liquid
Surfactants adsorbed at solution/air interface
Some water molecules replaced by surfactants molecules
Forces of attraction between bulk water molecules and surfactant molecule is less than water water attraction
Contracting power of surface is reduced
Surface tension is reduced
What happens to the interfacial tension when a surfactant is added
Surfactant migrates to interfacial later
Tension is reduced
Less interactions
Factors affecting adsorption
Solubility of absorbate = high solubility means low adsorption
Ph= affects ionisation
Nature if adsorbent
Surface area= more sa means greater adsorption
Temperature= increase in temp means decrease in adsorption
What is critical micelle concentration
Concentration of surfactant molecules in a medium at which micelles start to form
Aggregation number
Number of surfactant molecules in a micelle
Why do ionic micelles have low aggregation number
Small, fewer molecules because they are repulsive
Why does non ionic micelles have larger aggregation numbers
Not charged
Less work
What factors affect cmc and micellar size
Structure of hydrophobic group (increase length = increase size and decreased cmc)
Nature of hydrophilic group (non ionic= lower cmc and higher aggregation number)
Nature of counterion (increase size= increase size and reduce cmc)
Electrolytes (lowers cmc and increased micellar size)
Why does increasing size mean increasing micellar size and reduced cmc
Increased size
Increase ionic radius
Reduce ionic field
Less solaveted (surrounded by solvent)
Readily adsorbed on the micellar surface
Solubilisation
Water insoluble substances are brought into solution by incorporation into micelles
