Moisture dependence of positron annihilation spectra in nylon-6

Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes

“…These trends have been reported by others for other polymers [22][23][24]. One of the polymers studied was nylon-6, which is somewhat similar to the aromatic polyamide investigated in this study.…”

“…Aromatic polyamides, having higher cross-linking and limited segmental mobility, would require a higher concentration of water to cause inter-and intra-chain weakening within the polymer matrix. This supposition is supported by the hole swelling effect occurring at a water activity above 0.6 which is much higher than that observed for nylon-6 [22] and other polymers [24]. This swelling at high water activity coincides with the clustering of water at high water activity shown in Fig.…”

“…One of the polymers studied was nylon-6, which is somewhat similar to the aromatic polyamide investigated in this study. Singh et al [22] attributed the initial decrease in the free volume cavity size for nylon-6 polymer to the disruption of the hydrogen bonds between C¼O and H-N by the hydrogen in H 2 O, which lowers the glass transition temperature to room temperature in the hydrated polyamide. They attribute the increase in the free volume at moisture contents above 25% to the association of water to other bonding sites once all the hydrogen bonds have been saturated.…”

“…Similarly, Kim et al [21] used PALS to probe the free volume of a dry MPD/TMC polymer and propose the existence of two types of cavities: network cavities with radii of 0.21-0.24 nm and aggregate cavities, which they describe as interspaces between clusters of network cavities, with radii of 0.35-0.45 nm. It has been reported for nylon 6 [22], an aliphatic polyamide, as well as other polymers [23,24], that as the dry polymer takes up water the free volume cavity size initially decreases at low water uptake, but increases at high water uptake. However, to the best of the authors' knowledge, the effect of moisture uptake by the aromatic polyamides on the free volume has not been reported.…”

Humidity‐induced plasticization and antiplasticization of polyamide 6: A positron lifetime study of the local free volume

“…From this comparison we hope to obtain information that will contribute to the understanding of the reasons and mechanism of humidity induced antiplasticization. A few positron studies on moisture sorption in polyamides were published in the past,21–24 most recently by Welander and Maurer23 in 1991, and by some of the authors of this article24 in 1998. To our best knowledge there is only one article, published in 1972 by Chuang et al,21 dealing with the temperature dependence of the free volume in PA6 in the limited temperature range from 25 to 100°C.…”