Fickian Diffusion

Gradient Equilibrium

Polymer swelling rates match molecular penetration kinetics when penetrant activity remains constant at exterior boundaries. Concentration profiles establish steady state profiles across membrane thicknesses according to predictable mathematical functions. Temperature fluctuations alter kinetic energy levels and shift equilibrium points within polymeric membranes.

Crosslinking density reduces fractional free volume and slows down the rate at which concentration gradients achieve balance.

Partition Kinetics

Solubility parameters dictate the concentration ratio of penetrants between exterior fluid phases and interior polymer boundaries. Thermodynamic affinity determines whether molecules absorb readily into specific polymer matrix sites. Sorption isotherms measure mass uptake against vapor pressure values under controlled isothermal conditions.

Plasticizer migration accelerates local chain relaxation and invalidates standard partition calculations when solvent concentration exceeds critical thresholds.

Penetrant Mobility

Local activation energies control the jump frequency of diffusing molecules between microscopic voids inside polymer structures. Free volume theory quantifies the unoccupied space available for molecular relocation under specific stress states. Crystallinity introduces impenetrable barriers that force diffusing molecules along tortuous pathways.

Void size distribution variations cause localized diffusion anomalies that standard concentration gradient models fail to predict accurately.