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To understand, at a molecular scale, the effect of water on the structure of the amorphous region of polyamide 6,6 (PA6,6), atomistic molecular dynamics simulations have been carried out. Our results concerning the very local water organization relative to PA moieties agree qualitatively with a two-step sorption model. The first sorption mode seems to be saturated well below the lowest water concentration studied (5% relative to the amorphous phase). Moreover, above this saturation, the overall water organization displays at 300 K larger clusters than the 2−3 molecules usually assumed in the literature. The temperature dependence of free volume, hole size, and hydrogen bonding has also been investigated. It shows a transition between plasticized and antiplasticized behavior.

The binary blend compatibility of polyamide 6 (PA6) with poly(vinyl alcohol) (PVOH), poly(vinyl acetate) (PVAC), and partially hydrolyzed PVAC was studied for a wide range of compositions, by atomistic and mesoscopic modeling. The Flory−Huggins interaction parameter χ, calculated for these mixtures by atomistic modeling, showed that favorable interactions develop for PVAC with a low hydrolysis degree for a specific composition and also for compositions rich in either component. The effect of the PVAC hydrolysis degree on the mixture compatibility was explained in terms of the reduced ability of the acetylated chains to form hydrogen bonds, which in turn, may result in weaker intramolecular interactions. Such an effect may also be due to the more extended conformations assumed by these chains because of the bulky side groups. Calculations at high temperature gave small negative χ parameters, in good agreement with results reported by others. The χ and other structure-dependent parameters, derived from the ...