|Arrhenius Law - Arrhenius Equation - Van't Hoff Law|
-Heat of Solution for small gases is usually positive, hence an increase of solubility with temperature. Heat of Solutions of large gases are negative, so a decrease of solubility with temperature. Helium and Hydrogen are per definition small gases. The solubility temperature dependence of larger chemicals, like Oxygen, Nitrogen, Carbon Monoxide, Argon and Carbon Dioxide depends on the polymer under consideration.
-Solubility of liquids increases as a function of temperature.
Read more on solubility of gases and liquids in polymers in the case stories section (check the case on Hildebrand solubility parameters).
5] Effect of crosslinking
Increasing the degree of crosslinking in thermosetting resins such as polyester, epoxy and vinyl ester or for example sulphur in natural rubber, increases the activation energy.
6] One may question what happens with permeability P as a function of temperature. In case of liquid and solvent permeation in polymer and composite materials this is obvious: permeability increases as a function of temperature. When dealing with a gas, usually the acitvation energy for diffusion is higher than the possible negative enthalpy of solution, hence the permeability also increases as a function of temperature.
We measured the diffusivity of carbon dioxide in high density polyethylene with a crystalline fraction of 0.77, at a temperature of 40 and 50 degrees Celsius (313 and 323 Kelvin). We want to know the diffusion coefficient at 60 degrees Celsius.
D (313 Kelvin) = 4.0 E-11 m2/s
D (323 Kelvin) = 6.1 E-11 m2/s
Applying the Arrhenius equation on the two data points we obtained an activation energy of:
37 Kilo Joule (37 KJ).
Then the diffusion coefficient at 60 degrees Celsius is:
D (333 Kelvin) = 9 E-11 m2/s
The diffusion coefficient is strongly dependent on temperature.
Go to the plastics, elastomer, coatings and polymers and composite material properties forum to learn more on diffusion, chemical resistance and mechanical properties of polymers & composites. Interested in watching molecules actually diffusing through a substance? click here for the movie on Brownian Movement.