Interfaces Flashcards
5 types of interface?
Solid/solid , solid/liquid , solid/gas , liquid/gas , liquid/liquid
Surface energy?
Energy needed to create a new surface by breaking bonds in substance
What is surface energy proportional to?
Strength of bonding between atoms and molecules
Surface tension?
Is the surface energy of a liquid.
Due to water molecules at surface receiving uneven attraction, they tend to be drawn to centre of liquid. Is in a state of tension that minimises it’s surface area
Inward pull of drop?
Surface tension
How do water droplets form on grease?
Water has a higher surface energy than greasy surface.
Droplet shape is caused by?
Higher surface tension of liquid = more spherical shape of droplet
What is wetting?
Contact between solid and liquid.
Depends on contact angle between droplet and surface.
Ability to wet depends on?
The attraction of liquid particles to bulk of liquid
AND
The attraction of liquid particles to surface of solid
Particles are strongly attracted toward centre of liquid in than solid in terms of wetting?
Liquid doesn’t wet, and a droplet forms
Particles in liquid are strongly attracted to solid surface than centre in terms of wetting?
Liquid spreads out across solid surface and wets
How will wetting occur?
If surface energy of solid is greater than surface tension of water
What are surfactants?
Surface active agents. Eg, detergent
Detergent molecules reduce hydrogen binding between water molecules and surface tension is reduced.
What is meniscus?
The curved surface of water, can be concave (wetting occurs) or convex.
Concave meniscus?
Water has a lower surface energy than container, and will wet to the container producing a concave meniscus.
Convex meniscus?
Surface tension of container is weaker than liquid (mercury). Wetting does not occur.
What is capillary action?
Water has lower surface energy than capillary tube and will continue to rise up tube. This will happen until attractive forces between water molecules and glass causing upward momentum are counterbalanced by downward force of water
What does capillary action depend on?
The diameter of the tube and the nature in bonding of water and capillary tube
What does hydrophilic mean?
LOVE water. Have polar sites and dissolve readily in water.
What is hydrophobic?
HATE water. Repel water and substances are non-polar.
What is oil-in-water emulsions?
Tiny droplets of oil suspended in water.
Will be cool because of water, electrically conductive, and mixes with polar substances.
What is water-in-oil emulsions?
Tiny drops of water suspended in oil.
Feel warm and greasy due to oil, low conductivity, and mixes with non-polar substances
What is an interface?
Boundary region between solids, liquids and gases
