Physical properties and biocompatibility Flashcards
List the thermal properties
- Thermal conductivity
- Thermal diffusivity
- Specific Heat
- Coefficient of Linear Thermal Expansion
- Coefficient of Volume Thermal Expansion
Define ‘thermal conductivity’ (k)
Rate of heat (energy) flow through a material.
Define ‘thermal diffusivity (h)’
Rate of temperature change as heat passes through a material.
Define ‘specific heat (C)’
Energy needed to raise the temperature of one kilogram of a substance by 1 degrees Celsius (J/kg degrees Celsius)
Define ‘Coefficient of Linear Thermal Expansion’
Fractional change in length per degree increase in temperature.
Strain = e = change in length / original length = length per degree (alpha L) * change in temperature
Units = 1 / degrees Celsius
Define ‘coefficient of Volume Thermal Expansion’
Fractional change in volume per degree increase in temperature.
- Three times the coefficient of linear thermal expansion.
- alpha(v) = 3 alpha (L)
Define ‘adhesion’
Bonding unlike molecules
Define ‘ cohesion’
Bonding like molecules
Define ‘adhesive’
Materials that are capable of bonding two surfaces together.
Define ‘adherend’
Materials to which the adhesive is applied.
Describe ‘mechanical attachment’
- The adhesive engages in undercuts, irregularities or pores in the surface of the adherend.
- The mechanical attachment is the basic bond for many filling materials used in undercut cavities.
Describe ‘chemical attachment’
The adhesive has a chemical affinity for the surface of the adherend.
Describe ‘physical attachment’
The attachment takes place through van der Waals forces between adhesive and adherend atoms.
Regarding surface energy, atoms in bulk of substance have lower or higher energy than atoms at surface?
Lower energy
Describe ‘surface energy/tension’
Excess energy at surface of material compared to the bulk substance.
- Proportional to the intermolecular bonds of the material.
What gives superior attachment regarding surface energy?
Higher surface energy of adherend or lower surface tension of adhesive.
- Allows excellent “wetting” of surface.
- Low contact angle of adhesive.
What gives inferior attachment regarding surface energy?
Lower surface energy of adherend or higher surface tension of adhesive.
- Allows poor “wetting” of surface
- High contact angle of adhesive
Describe Snell’s Law
- Light is refracted as it passes from one medium to the next.
- n = speed of light in vacuum/speed of light in medium.
- n(initial) sin (initial) = n (refracted) sin (refracted angle)
- If sin (refractive angle) is greater than 90 degrees, then light is reflected.
In reflection, the angle in incidence = the angle of reflection.
Light can be transmitted and reflected in between two interfaces.
True
Describe ‘specular reflection’
No scattering at reflection or transmission.
Angle of incidence - angle of reflection.
Define ‘diffuse reflection’
Scattering at reflection or transmission.
- Angle of incidence different to angle of reflection.
- Many angles of reflection.
Define ‘hue’ as a quantitative description of colour
Dominant colour (circumference position)
Define ‘ value’ as a quantitative description of colour
Lightness or darkness (height on pole)
Define ‘chroma’ as a quantitative description of colour
Intensity of colour (Distance from centre)
Define ‘biocompatibility’
Appropriate biological response of a material in a given environment.
