Small-Molecule Diffusion in Semicrystalline Polymers as Revealed by Experimental and Simulation Studies

• Diffusion of n-hexane in poly(ethylene-co-1-hexene)s with 15-75 wt.% crystallinity was studied by desorption experiments analyzing data using the Fickian equations with a concentration dependent diffusivity. The effect of the impenetrable crystalline phase on the penetrant diffusivity (D) is described by D = D-a/(tau beta), where D-a is the diffusivity of the amorphous polymer, tau is the geometrical impedance factor and beta is a factor describing the constraining effect of the crystals on the non-crystalline phase. For a polymer with 75 wt.% crystallinity, tau beta varied markedly with penetrant concentration (V-1a) in the penetrable phase: 1000 (V-1a = 0) and 10 (V-1a = 0.15). This penetrant-uptake had no effect on the gross crystal morphology, i.e. beta must be strongly dependent on V-1a. Samples saturated in n-hexane exhibited a penetrant-induced loosening of the interfacial structure, as revealed by an increase in crystal density that require an increased mobility in the interfacial component and by a decrease in the intensity of the asymmetric X-ray scattering associated with the interfacial component. The geometrical impedance factor has been modelled by mimicking spherulite growth and tau was obtained as the ratio of the diffusivities of the fully amorphous and semicrystalline systems. The maximum tau obtained from these simulations is ca. ten, which suggests that beta in the systems with V-1a = 0.15 takes values close to unity. The simulations showed that the geometrical impedance factor is insensitive to the ratio of the crystal width and the crystal thickness. A free path length scaling parameter characteristic of the amorphous phase correlated with tau.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Andra medicinska och farmaceutiska grundvetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Other Basic Medicine (hsv//eng)

Nyckelord

diffusion

morphology

polyethylene

simulation

Chemistry

Kemi

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