miscelles and sufficants Flashcards
(16 cards)
What is a surfactant?
A surface-active agent that reduces surface tension by accumulating at interfaces (e.g., air–liquid, oil–water).
How is surface tension measured?
Using methods like the Du Noüy ring or Wilhelmy plate, which measure the force needed to detach a probe from the liquid surface.
What is Traube’s rule?
States that for homologous series of surfactants, surface tension decreases with each added CH₂ group, roughly tripling the surface activity.
What does the Gibbs adsorption isotherm describe?
It relates surface tension change to the concentration of surfactant at the surface: Γ = −(1/RT)(dγ/dlnC)
Where Γ = surface excess concentration, γ = surface tension, C = concentration.
What is a monomolecular film?
A single layer of molecules (e.g., lipids) spread over a surface like water, often studied using Langmuir troughs.
What is a micelle?
A spherical aggregate of surfactant molecules formed above the Critical Micelle Concentration (CMC) in aqueous solution.
What is the critical micelle concentration (CMC)?
The minimum surfactant concentration at which micelles form. Below CMC, only monomers exist.
What lowers CMC?
- Longer hydrophobic chains
- Addition of electrolytes (ionic surfactants)
- Structure-making solutes like sugars
What raises CMC?
Structure-breakers like urea or formaldehyde.
What is the structure of a micelle?
Hydrophobic core (nonpolar tails) and hydrophilic shell (polar heads), allowing solubilization of hydrophobic drugs.
What are lyophilic colloids?
Colloids that are solvent-loving and form spontaneously (e.g., micelles, macromolecules in water).
What is the Tyndall effect?
Scattering of light by colloidal particles — a way to distinguish colloids from true solutions.
What are the two types of adsorption?
Physisorption: Physical, weak, reversible
Chemisorption: Chemical, strong, often irreversible.
What are Type I, II, and III isotherms?
Type I: Monolayer adsorption
Type II: Multilayer adsorption
Type III: Weak interaction, no monolayer saturation.
What affects non-covalent adsorption?
Surface area, polarity, pH, temperature, and surface energy of the adsorbent.
What is detergency?
The cleaning action of surfactants that remove dirt/oil by reducing interfacial tension and forming micelles to trap and wash away contaminants.
