Interfacial Phenomena 2 Flashcards
Interfacial Adsorption Outline
How particles are arranged at the interface
Positive Adsorption Def
Substance binds to water st interface. Decreasing surface tension and decreasing interfacial energy (eg surfactant). Makes more stable
Negative Adsorption Def
Substance binds to water in bulk (prevents water molecules reaching interface = increased contractility). Increasing surface tension and increasing interfacial free energy (eg increasing solutes = increasing no interfaces). Makes less stable
Surfactants Outline
Amphilic (hydrophilic and hydrophobic components). Hydrophilic attaches to water and hydrophobic attaches to air. Prevents water from contracting away from air = decreasing surface tension = decreasing surface free energy. There must be the correct hydro/lipophilic balance to allow interface
Surface Active Agents Outline
Molecules that absorb positively/negatively at interfaces. Forms a monomolecular film
Relationship between surfactant conc and emuslification
higher surfactant conc = more spontaneous emulsification
Relationship between interfacial tension and chances of surfactant absorbing
Higher interfacial tension = higher chance of surfactant absorption
Surface excess def
How much surfactant is in bulk vs at interface
What is the risk of high surfactant conc
Toxicity
Relationship between surfactant non-polar tail and efficacy
Longer tail = higher efficacy
Soluble Monolayers Outline
Surfactant can dissolve in continuous layer and saturate interface
Insoluble Monolayers Outline
Surfactants don’t dissolve in continuous layer. Creates bilayers to contain constituents inside of cells (creates lysosomes).
How is insoluble monolayers characterised
Langmuir troph. Substances in troph exert lateral pressure (surface pressure). Way of evaluating surface tension
Relationship between surface pressure and surface tension
increased surface pressure = decreased surface tension
Surface pressure Def
Surface tension of liquid without a monolayer - surface tension of liquid with a monolayer. Measure of surfactant at monolayer (more surfactant = lower surface tension = higher surface pressure)
Gaseous Film Def
Molecules in monolayer are spaced out and compressible. Low surface pressure
Expanded/liquid Film Def
Molecules in a monolayer are closely packed but still compressible. Moderate surface pressure
Condensed film
molecules in monolayer are tightly packed and not compressible. High surface pressure
How to change monolayer between 3 fil states
Increase molecule conc or increase surface pressure on layer (pushing them together)
When can monolayers act as enteric coating
When at low pH can form a more condensed film
Gibbs Adsorption Isotherm Outline
Equilibrium of surfactants at interface vs the bulk. Same level of surface access for surfactants at interface and bulk
Traube’s Rule Outline
Among substances of the same homologous series (have same hydrophilic head), for every additional C attached to hydrocarbon tail, the surfactant effiacy increases 3 fold. 3 fold reduction in surface tension for every extra C
Critical Micelle Concentration (CMC) Outline
The concentration of surfactant where micelles begin to form (interface already saturated). Beyond CMC there’s no decrease in surface
What happens when the interface is saturated with surfactants and more are added (CMC)
Surfactants in bulk arrange themselves into spheres where hydrophilic heads shield internal hydrocarbon tails
2 Factors of Micellisation Outline
Intermolecular attractions (induced dipoles) between hydrocarbon chains and hydrophobic effect of water-carbon head bonds.
Formation of micelles in water
Water is ordered = lower entropy = thermodynamically unstable
Another way of measuring surface tension
Equivalent conductance
Kraft Point/Critical Micelle Temp Outline
Narrow temp range where micelles start to form (surfactant solubility increases)
Mixed micelle outline
Micelle made up of 2 different types of surfactants. Fundamental in lipid digestion (fatty acids to emulsion droplets)
