Transport Theory
Physical processes involving gas or vapor uptake by glassy polymers occur through two distinct mechanisms involving dissolution and hole filling. Scientists describe dual-mode sorption as the combination of Henry’s law behavior and Langmuir kinetics within a single material. These mechanisms account for the non-linear relationship between pressure and gas concentration inside a solid matrix.
Small molecules occupy pre-existing microvoids or dissolve into the polymer chains depending on the local energy state. This theory explains why gas permeability in glassy polymers differs from the behavior seen in rubbery materials.
Polymer Behavior
Equilibrium states depend heavily on the thermal history of the material. In dual-mode sorption, the dissolution component represents the mobile population of molecules moving through the dense regions of the polymer. The hole-filling component identifies molecules trapped in the unrelaxed free volume of the glassy state.
Measurement Precision
Pressure decay methods provide the data required to distinguish between the two populations. Researchers apply dual-mode sorption models to interpret how moisture or gases penetrate protective coatings.
Application Boundary
Predictive accuracy depends on the temperature staying below the glass transition point of the host material. When the temperature exceeds this threshold, the dual-mode sorption model collapses into a single-mode dissolution process. Testing identifies the specific pressure at which the hole-filling sites become saturated.
Verification involves long-term gravimetric analysis where samples are weighed until they reach a constant mass at multiple pressure setpoints.
