adhesion

Question 1

What is etching?

Answer 1

The act or process of making designs/imprints on a surface by the corrosive action of acid-based solutions

Question 2

What is adhesion?

Answer 2

The force that binds two dissimilar materials together when they are brought into intimate contact

Question 3

What are the criterias for adhesion?

Answer 3

Intimate contact molecularly
~viscosity of adhesive 
~surface roughness of substrate
Formation of attractive bonds
Wettability

Question 4

What is solid-liquid adhesion?

Answer 4

Complete intimate contact

Secondary bonds- London forces

Question 5

What is solid-solid adhesion?

Answer 5

Only specific places of contact due to surface roughness
Distance between interacting molecules should be <0.0007micrometers
Solved with intermediary

Question 6

What is an intermediary?

Answer 6

Solid-liquid-solid

Liquid adhesive like glue sticking two pieces of paper together

Question 7

What is wettability?

Answer 7

Ability of adhesive to contact substrate depends of wettability
Eg. Non-wetting, partial wetting, complete wetting

Question 8

What is surface energy?

Answer 8

Imbalance that grt surface energy of material
Eg. Surface tension in liquids
Measured in milliJoules per square meter

Question 9

How is perfect wetting achieved?

Answer 9

Critical surface energy of the solid is greater than surface tension of liquid
Liquid spreads more over the surface

Question 10

What is the contact angle?

Answer 10

The more the liquid spreads, the smaller the contact angle so the surface is more hydrophilic

Question 11

What are the mechanisms of adhesion?

Answer 11

Physical, chemical, micromechanical and molecular entanglement

Question 12

What is physical adhesion?

Answer 12

London forces, hydrogen bonding
Dipole interaction
Rapid and reversible but weak
Not suitable for permanent bonding but can be a precursor for chemical

Question 13

What is chemical adhesion?

Answer 13

Covalent and ionic bonding
Sharing electrons
Strong bonds
Eg. Dental adhesives

Question 14

What are dental adhesives?

Answer 14

Solution of resin monomers inc.
~curing initiators
~inhibitors
~solvents
~inorganic fillers
Some better systems inc.
~polymerisable vinyl double bonds
~reactive isocyanate groups
~acrylate groups

Question 15

What is micromechanical adhesion?

Answer 15

Microscopic undercuts
Resin flows in before setting 
Wettability is key
Clean surface
To break it must fracture

Question 16

What is molecular entanglement?

Answer 16

Highly porous surface
Add monomer
No clear border between materials
Leaves a hybrid layer and adhesive resin on top