Interfaces and Interphases Flashcards
What are qualities of interface?
- Strong bond needed for good stress transfer.
- Enhances toughness
- Gives resistance to chemical attack.
- Surfaces of reinforcing particles or fibre often treated to improve interfacial bond.
What does oxidative plasma use?
Often used with carbon fibres.
How does oxidative plasma work?
Generates reactive ends to bond to matrix.
What does non oxidation plasma due?
Increase surface energy.
What does Ion implantation use?
Used with glass to alter surface chemistry.
What are coupling agents?
- Most common with glass.
- Provides a link between the
Non polar, hydrophobic
Polar. hydrophilic glass - Silanes most commonly used
What is the shrinkage effect?
- Many matrix materials shrink when curing / solidifying.
- This shrinkage compresses the matrix onto the reinforcements.
- Provides additional interfacial strength through friction.
What is Poisson’s Contraction?
- When stressed in tension, most material contract laterally.
- Amount is determined by Poisson’s ratio v.
Define as : v = - ez/ex
What is the effect of Poisson?
As Poisson’s ratio is higher for almost all matrix materials than fibres:
- Tensile stress makes matrix contract more.
- Pushes matrix onto fibre.
- Provides extra interfacial strength.
Why does interphase have different structure / properties?
Interphase (regions of matrix) that has different structure /properties.
- Higher crosslink density.
- Lower crosslink density.
- Higher crystallinity.
- Lower crystallinity.
What happens when the crosslink density is: Polar curing agents migrate to polar fibre surface?
- More crosslinking in interphase.
- Seen with amine curing agents in glass / epoxy composites.
What happens when the crosslink density is: Polar curing agents migrate to NON-polar fibre surface?
Less crosslinking interphase.
What happens to interphase during crystallinity?
- Longer chains can segregate to the fibres.
- Polymer crystals can nucleate on fibres.
