Dispersions Flashcards
What is the IUPAC definition of a dispersion?
A material comprising more than one phase, where at least one phase consists of finely divided phase domains dispersed throughout a continuous phase.
How are dispersions sub-classified?
Based on the size of the discontinuous phase particles, whether precipitation occurs, and the presence of Brownian motion.
What are colloids?
Dispersions with small particles (5 nm to 0.5 µm) that do not sediment and are stabilized by Brownian motion.
What are suspensions?
Dispersions with larger particles (>0.5 µm) that will eventually sediment and are typically opaque.
What is the Tyndall effect?
The scattering of light by colloidal particles, which makes a light beam visible in a colloid but not in a true solution.
What is the significance of surface tension in dispersions?
Surface tension arises from unbalanced cohesive forces at the interface between incompatible phases, minimizing surface area and stabilizing droplets.
What is Laplace pressure?
The outward force exerted at the droplet interface, which affects the shape and stability of droplets in dispersions.
How are dispersions classified based on the state of continuous and discontinuous phases?
Examples include solid foams (solid continuous phase, gas dispersed), gels (liquid dispersed in solid), and emulsions (liquid dispersed in liquid).
What are some examples of foods that are classified as dispersions?
Bread (solid foam), milk (emulsion), and ice cream (suspension).
Types of Dispersions
vapors (gas-in-gas), fog (liquid-in-gas), and smoke (solid-in-gas).
How do cohesive forces influence the behavior of droplets in dispersions?
Cohesive forces can lead to the formation of stable droplets by minimizing surface area and creating surface tension at the interface.
How does temperature affect the stability and behavior of colloids?
Changes in temperature can affect particle motion, viscosity, and the stability of colloids, potentially leading to aggregation or sedimentation.
