Adhesion Flashcards
(31 cards)
dental bonding
enamel and dentine bonding
etching
act or process of making designs/imprints on a surface (metal/glass) by the corrosive action of acid based solutions (surface treatment/removal)
adhesion
force that binds 2 dissimilar materials together when they are brought into intimate contact
criteara for adhesion
intimate contact at a molecular level
formation of attractive bonds
wettability
what affects the intimate contact at a molecular level
viscosity of the adhesive
surface roughness of the substrate
solid to liquid adhesion
complete intimate contact (liquid flows on the grooves of the solid) secondary bonds (van Der wals) - see pic for lec
solid to solid adhesion
If both solids are rough
- won’t fit together
- only specific places of intimate contact due to surface roughness
not easy to achieve contact at the microscopic level
distance needed for adhesion to occur
less than 0.0007um for adhesion to occur
Uses for fluid/semi fluid intermediaries
solid -liquid- solid adhesion
clean surface is key to intimate contact
wettabiltiy
ability of an adhesive to contact a substrate depends on the wet ability of the adhesive on that particular substrate
see lec for pic demonstration
Surface energy - surface
imbalance that gives raise to the surface energy of the material (surface tension in liquids)
surface energy - bulk
attractive forces in all directions
all molecules in the surface have an imbalance of energy
what is surface tension in liquids
where all liquids have an imbalance of energy
-attractive forces in all diresctions
what is required for perfect wetting
critical surface energy of the solid has to be greater than the surface tension of the liquid
- solid needs energy (higher surface energy ) to spread the liquid by pulling the molecules
surface tension measured in
Mj/m2( squared)
how do you measure wettability
contact angles
contact angle
smaller the contact angle
- more hydrophilic
i. e. more wetable
mechanisms of adhesion
physical
chemical
micromechnical
molecular entanglement
Physical adhesion
van der Waals and hydrogen binding and dipole interaction
- rapid but reversible and weak bonding
- not sutible for permanent bonding but can be a precursor for chemical
Permanent dipole ovement
molecules are pilar
- hydrogen bonds due to electromagnetic attraction between polar molecules
temporary induced dipole movemnt
non polar molecules do not normally have a dipole moment but can have a temporary dipole
temporary dipole cuase
distortion of electron cloud
- induced electrical interactions between 2 or more atoms or molecules that are close to each other
- atoms have a positive charge in the nucleus, electrons around the outside
chemical adhesion
covalent and ionic bonding
and metallic
metallic
share electrons
