Jiro Seta

Effects of pressure and solvent on the diffusion of aromatic compounds through polymers

The diffusion of six azo and five anthraquinone derivatives through nylon 6, poly(ethylene terephthalate) and secondary cellulose acetate films were studied under high hydrostatic pressures of up to 3000 bar and at temperatures 80–130 °C, by analyzing the diffusion profiles yielded in a stacked multiple film, placed in the solution of the diffusant. It was found that the diffusion coefficient,D, of the diffusant decreased with increasing pressure, giving a linear relationship between InD and the pressure, the slope of which gave the activation volume for the diffusion,ΔV≠. It was revealedΔV≠ increased linearly with increasing intrinsic molecular volume of the diffusant,Vw, the slopes being different between the azo and the anthraquinone derivatives. The ratio ofΔV≠ toVw (ΔV≠/Vw) ranged from 0.13 to 0.93, depending in a sensitive manner on the degree of swelling of the polymer matrix which in turn was varied by the solvent. The overall results could be explained in accordance with the formulation,Vf, local +ΔV≠=Vw, whereVf, local represents the free volume contribution. It was proposed thatVw is increased by solvation when the solvent is good for the diffusant.

Diffusion of linear aliphatic esters in polyethylene as a function of chain length of the esters, pressure and temperature

Diffusion of linear aliphatic mono- and diesters (CN) havingN main chain atoms (N=13–68) in bulk medium-density polyethylene (MDPE) has been studied under hydrostatic pressures up to 2500 bar at temperatures between 60°C and 125°C. Three triglycerides, phenyl stearate, and p-aminoazobenzene (pAAB, 80°C) as the diffusants and low-density (LDPE) and high-density (HDPE) polyethylenes as polyethylene substrate were used for comparison. Diffusion coefficientD was determined from concentration distribution of the diffusants through stacked PE sheets as substrate. Regarding the linear esters at 90°C, the relationshipD ∝Nα holds at constant pressures. Under the atmospheric pressure, α became −2.10 in accordance with de Genness proposal (1971)D ∝N−2 as well as with the experimental results reported by Klein and Briscoe (1979) forN larger than 30.Ds for the glycerides deviate from the relationshipD ∝N−2 toward the smaller values by comparison at the sameN. The exponent α is pressure-dependent. It decreases with increasing pressure according to α=−2.10−0.000942P, whereP is measured by the unit of bar. Plots of lnD vsP for all the diffusants show linear relationships with negative slopes, from which activation volume for the diffusion ΔV‡ was calculated. At 90°C, ΔV‡ increases slowly with increasingN and increasingVKi, the intrinsic molecular volume of the diffusant, from 39.3 cm3/mol for ethyl caprate (C13,VKi=136 cm3/mol) to 76.8 cm3/mol for behenyl behenate (C45,VKi=466 cm3/mol). Observed ΔV‡s are explainable on the basis of the reptation mode of the chain molecule diffusion. ΔV‡s for C25 and C45 are found to increase with increasing degree of crystallinity where MDPE, heat-treated MDPE, LDPE, and HDPE were used. The results obtained by varying temperature are as follows. ΔV‡ for C45 was always found to be larger than C25. Both decreased linearly with increasing temperature, giving two linear lines with different slopes whose extensions intersected at 132°C, the melting point of the MDPE, where the difference in ΔV‡ disappeared. The apparent activation energiesEDs for the diffusion of C25 and C45 increased linearly with increasing pressure, whose slopes are explainable according toED=E0+PΔV‡[1-(dln ΔV‡/dlnT)P].