10 Questions
What is the primary requirement for amphiphiles to be concentrated at the interface?
To have a balanced ratio of water and oil soluble groups
What happens if an amphiphile is too hydrophilic?
It remains within the aqueous phase and exerts no effect at the interface
What is the HLB number scale used to quantify?
The relative efficiency of the hydrophilic portion of the surfactant molecule
What is the characteristic of surfactants with HLB > 10?
They are more hydrophilic
What is the range of HLB values for ionic surfactants?
0 to 50
What is the primary function of surfactant molecules at the surface or interface of a liquid?
To reduce the surface or interfacial tension
What is the term used to describe surfactants due to their ability to have affinity for both polar and non-polar solvents?
Amphiphiles
What type of group does a surfactant molecule have that exhibits high affinity for non-polar and organic solvents?
Lipophilic group
Why do surfactant molecules reduce the surface tension when they adsorb at the water surface?
Because they replace some of the water molecules at the surface
What is the term used to describe a surface active agent (SAA)?
Surfactant
Study Notes
Surfactants
- Surfactants are substances with molecules having both polar and non-polar groups, which are preferentially adsorbed at the surface or interface of a liquid and reduce the surface or interfacial tension.
- They are also known as surface active agents (SAA).
Structure of Surfactants
- Consist of two parts: a lipophilic (hydrophobic) group and a hydrophilic (lipophobic) group.
- Lipophilic group: non-polar group like long saturated hydrocarbon chain, aromatic ring, or heterocyclic group, which has high affinity for non-polar and organic solvents.
- Hydrophilic group: polar group such as hydroxyl, carboxylate, sulfonate, sulfate, ammonium, phosphate, which has high affinity for polar solvents and water.
Amphiphiles
- Surfactants are also termed amphiphiles due to their affinity for both polar and non-polar solvents.
- The word "amphiphile" comes from the Greek roots "amphi" meaning "double" or "from both sides", and "philos" meaning "friendship" or "affinity".
Classification of Amphiphiles
- Predominantly hydrophilic (water-loving)
- Predominantly lipophilic (oil-loving)
- Well-balanced between these two extremes
Importance of Balance
- Amphiphiles must be balanced with the proper amount or ratio of water and oil soluble groups to be concentrated at the interface.
- If the molecule is too hydrophilic, it will remain within the aqueous phase and exert no effect at the interface.
- If the molecule is too lipophilic, it will dissolve completely in the oil phase and little appears at the interface.
Hydrophilic-Lipophilic Balance (HLB)
- Definition: relative efficiency of the hydrophilic portion of the surfactant molecule to its lipophilic portion.
- Griffen's system of HLB numbers: an arbitrary scale between 0 and 20 that expresses numerically the size and strength of the polar portion relative to the non-polar portion of the molecule.
- HLB values for ionic surfactants are much higher (up to 50) based on the ionization properties.
- Higher surfactant HLB value indicates more hydrophilic properties, while lower surfactant HLB value indicates more lipophilic properties.
This quiz covers the concept of surfactants in pharmaceutical nanotechnology, their properties, and applications. It is part of the Physical Pharmacy course, PPH102, in the PharmD program.
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