Interfacial Phenomena Flashcards
What is an interface?
A boundary between the two phases eg. oil and water
What is a surface?
A type of interface.
When one of the phases is gas/vapour eg. The surface of a cup of water.
What are symbols represent interfaces?
L/L - liquid/liquid
L/V - liquid/vapour
S/L - solid/liquid
S/V - solid/vapour
Explain surface tension?
At the surface, there is attraction from below but no attraction from above; due to there being no liquid molecules above.
So the molecules on the surface experience a net downward force.
They are pulled from below.
This creates a tendency for the surface to shrink and contract.
This results in a tension AKA surface tension.
Explain surface tension in terms of inward force?
At the surface, molecules experience new inward attraction forces.
The molecules at the surface tend to move inward and thus create surface tension or surface energy.’
When pulled downwards, it first moves horizontally. Horizontal tension is created.
Explain how the horizontal attraction is created and hence surface tension?
When one molecule moves down: A gap is formed between the adjacent molecules and the attraction between them pull them to each other to fill the gap.
This creates the horizontal attraction; creating surface tension.
Why is there always a tendency for a system to go towards a lower energy level?
Systems are more stable at lower energy levels.
What is the equation for Work, W?
W = E2 – E1
What is the equation for Surface tension?
γ = W/A
What is work equal to?
Work is equal to the surface energy, E
So W and E =
γ x A
This sis surface tension x Surface area
Explain how surface area and surface tension effects the surface energy?
The larger the surface area, the higher the surface energy.
The higher the surface tension, the higher the surface energy
What is surface energy for solids?
The work you do (energy used) to create a new surface
Explain surface tension in curved surfaces such as bubbles?
The surface tension of the curved film generates an inward pressure (it is trying to shrink to reduce its surface free energy).
So the pressure inside a bubble is higher than atmospheric pressure outside.
P int > P ext
