The degree to which a polymer allows the passage of a gas or fluid.
Symbol:
Dk. Oxygen permeability (
Dk) of a material is a function of the
diffusivity (
D) (that is the speed at which oxygen molecules traverse the material) and the
solubility (
k) (or the amount of oxygen molecules absorbed, per volume, in the material). Values of oxygen permeability (
Dk) typically fall within the range 10-150 ✕ 10
−11 (cm
2 ml O
2)/(s ml mmHg). A semi-logarithmic relationship has been demonstrated between hydrogel water content and oxygen permeability.
Unit: Barrer.The
International Organization for Standardization (ISO) has specified the permeability of contact lenses using the SI unit hectopascal (hPa) for pressure. Hence
Dk = 10
−11 (cm
2 ml O
2) /(s ml hPa). The former unit can be converted to this new SI unit by multiplying it by the constant 0.75. The
ISO has established a classification of contact lens materials based on a range of values of oxygen permeability
Dk. Group 1: 1-15; group 2: 16-30; group 3: 31-60; group 4: 61-100; group 5: 101-150; group 6: 151-200; group 7: 201-250; higher codes can be added in bands of 50.
See Barrer;
oedema;
equivalent oxygen pressure;
critical oxygen requirement;
refractometer.