CHEE2945 – Lecture 3
Frequency distributions:
- Frequency distribution of particles in a size range follows the following
equation:
ni ni
f n ( d av , i )= =
( di −d i−1) ∆ d i
- Similarly, a frequency distribution can also be defined using mass.
mi m
f m ( d av ,i )= = i
(d i−d i−1) ∆ d i
- When considering just one of these graphs, it is easy to overlook
contamination in the sample.
Colloids:
- A colloid is an object approximately 1 nm – 1 .
- They can be solid particles, hollow capsules, droplets, bubbles,
macromolecules, flocs, etc.
Interface interactions:
- Particle boundaries have an energy cost. Therefore, in nature, they are
minimised by making things circle.
- Some particles, such as water molecules, are polar, and hence will be
affected by charges, e.g., water being deflected by charged rod.
- Some particles, such as hexane, are non-polar.
- Consider a solid surface of silica, which is polar. If a drop of water (also polar)
is placed on it, it will spread out relatively flat, wetting the silica. Whereas, if a
drop of hexane was placed on the silica, it will not wet the silica and will
remain as a relatively spherical droplet.
- Polar liquids wet polar solids, and non-polar liquids do not wet polar solids.
Conversely, polar liquids do not wet non-polar solids.
- Consider a layer of oil on water. If it is shaken, and small droplets of oil get
dispersed in the water, the interfacial area is much larger. Hence, creating
these droplets costs energy in terms of Gibbs free energy. When these
droplets touch each other, they will coalesce and rise to the surface,
separating the oil and water again. The oil dispersed in water is known as an
unstable emulsion. The oil droplets in water will have a spherical geometry to
minimise the surface area.
- Interfacial tension is the energy per unit area to create an interface.
Frequency distributions:
- Frequency distribution of particles in a size range follows the following
equation:
ni ni
f n ( d av , i )= =
( di −d i−1) ∆ d i
- Similarly, a frequency distribution can also be defined using mass.
mi m
f m ( d av ,i )= = i
(d i−d i−1) ∆ d i
- When considering just one of these graphs, it is easy to overlook
contamination in the sample.
Colloids:
- A colloid is an object approximately 1 nm – 1 .
- They can be solid particles, hollow capsules, droplets, bubbles,
macromolecules, flocs, etc.
Interface interactions:
- Particle boundaries have an energy cost. Therefore, in nature, they are
minimised by making things circle.
- Some particles, such as water molecules, are polar, and hence will be
affected by charges, e.g., water being deflected by charged rod.
- Some particles, such as hexane, are non-polar.
- Consider a solid surface of silica, which is polar. If a drop of water (also polar)
is placed on it, it will spread out relatively flat, wetting the silica. Whereas, if a
drop of hexane was placed on the silica, it will not wet the silica and will
remain as a relatively spherical droplet.
- Polar liquids wet polar solids, and non-polar liquids do not wet polar solids.
Conversely, polar liquids do not wet non-polar solids.
- Consider a layer of oil on water. If it is shaken, and small droplets of oil get
dispersed in the water, the interfacial area is much larger. Hence, creating
these droplets costs energy in terms of Gibbs free energy. When these
droplets touch each other, they will coalesce and rise to the surface,
separating the oil and water again. The oil dispersed in water is known as an
unstable emulsion. The oil droplets in water will have a spherical geometry to
minimise the surface area.
- Interfacial tension is the energy per unit area to create an interface.
