2.2 Flashcards
what is adhesion
is the attachment of 2 materials that resist the force of separation
different types of adhesion
mechanical
chemical
what is mechanical adhesion
it depends the mechanical interlocking of 2 phases and can include microscopic attachments
what is chemical adhesion
this is related to chemical bonding between 2 material
what is surface energy
atoms on the surface of a (s) or (l) have more energy than interior atoms
what is surface tension
surface energy for liquids
(atoms on the surface of a (L) has more energy than within the body of the (L)
can be mesured by (dynes per cm)
rules of surface energy
‘surface energy of metal or oxide (crystalline structure ) is higher than in (L)
the stronger the bond the greater the surface energy
increase surface area =increace energy
what is capillary penetration
surface tension creates pressure so that it drives the liquids into crevices (narrow spaces)
what does capillary penetration depend on
capillary rise (h)
h = 2 γ cos θ/rdg
the higher the surface tension- greater penetration coefficient
higher viscosity - lower penetration coefficient
what is wetting
ability of a (L) to maintain contact with a solid
rules of wetting and surface tension
presence of impurities causes
wetting to increase
surface tension to decrease
what is viscoelasticity
materials that have mechanical properties dependent on loading that exhibit both elastic and viscous behavior
what is elastic behaviour
materials that have mechanical properties independent of loading rate
what is a viscous response
when materials exhibit a lag in response to when a load is applied
e.g of dental materials in a fluid state that have a viscous response
cement and impressions are a fluid state
when set the viscosity increases making it more solidlike and less viscous
