Questions and Answers
What is the characteristic of the hydrophilic part of a non-ionotropic/nonionic surfactant?
What is the primary factor in the formation of micelles in an aqueous system?
What is the characteristic of amphoteric/zwitter surfactants?
What is the minimum concentration of surfactant at which micelles first form in solution?
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What is the characteristic of cationic surfactants?
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What is the minimum concentration of surfactant required for micelles to form in solution?
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What is the primary driving force behind the formation of micelles in aqueous solutions?
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What is the relationship between the concentration of surfactant and the number of micelles formed?
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What is the term used to describe the temperature at which surfactants will form micelles?
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What is the thermodynamic driving force behind micelle formation?
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Study Notes
Non-Ionotropic/Nonionic Surfactant
- Hydrophilic part carries no charge
- Derive polarity from having an oxygen-rich portion of the molecule at one end and a large organic molecule at the other end
- Oxygen component is usually derived from short polymers of ethylene oxide or propylene oxides
Cationic Surfactant
- Positively charged molecules usually derived from nitrogen compounds
- Not commonly used as cleaning agents in hard surface cleaners
- Many cationic surfactants have sanitizing properties that are useful in creating disinfectants that leave a cationic disinfectant film on the surface
Amphoteric/Zwitter Surfactant
- Change their charge with pH
- Can be anionic, nonionic, or cationic depending on the pH
- Charge of the hydrophilic part is controlled by the pH of the solution
- Can act as anionic surfactants in an alkaline solution or cationic surfactant in an acidic solution
- Usually, any one amphoteric can be any two of the three charge states
Micelles
- Definition: Self-assembled little spheres formed when surfactants are added to water, with hydrophilic head facing out and hydrophobic tail pointing in
- Made out of amphipathic molecules
- Can form in polar or non-polar liquids
- Formed because only one end of the amphipathic molecules is compatible with the liquid
Formation of Micelle
- In aqueous systems, high interfacial energy between water molecules and hydrocarbon chains of the surfactant is the primary factor
- In non-polar systems, attractive interaction between polar parts serves as the force governing the association process
- Critical micellization concentration (CMC) is the concentration of surfactant at which micelles first form in solution or the concentration above which micelles will form spontaneously
- Higher the concentration, the more micelles there are
- Micelle formation is also dependent on the Krafft temperature, which is the temperature at which surfactants will form micelles
- The hydrophobic effect is also a driving force that needs to be taken into account
- Micelle formation can be summed up by thermodynamics, driven by entropy and enthalpy
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Description
Learn about the characteristics of non-ionotropic and cationic surfactants, including their structures and uses.
