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The Strathprints institutional repository is a digital archive of University of Strathclyde's Open Access research outputs. Strathprints provides access to thousands of Open Access research papers by University of Strathclyde researchers, including by researchers from the Department of Computer & Information Sciences involved in mathematically structured programming, similarity and metric search, computer security, software systems, combinatronics and digital health.

The Department also includes the iSchool Research Group, which performs leading research into socio-technical phenomena and topics such as information retrieval and information seeking behaviour.

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Positron annihilation lifetime spectroscopy and large molecule diffusion into a polyurethane matrix

Ward, S. A. and Pethrick, R. A. (2011) Positron annihilation lifetime spectroscopy and large molecule diffusion into a polyurethane matrix. Macromolecules, 44 (21). pp. 8479-8486. ISSN 0024-9297

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Abstract

Positron annihilation lifetime spectroscopy (PALS) measurements are reported on a three polyurethane (PU) materials created by the reaction of polymeric toluene diisocyanate with either ethylene glycol, 1,10-decanediol, or a silicone containing diol. Dynamical mechanical analysis indicated that the glass transition temperature of the PU’s were respectively 118, 95, and −40 °C. Whereas the ethylene glycol and 1,10-decanediol materials exhibited a glass–rubber transition, the silicone containing PU showed rubber characteristics over the temperature 0–180 °C. The PALS measurements on the silicone-based PU’s showed significantly larger voids dimensions than the other PU’s. Void collapse is observed to occur on the time scale of the oPs measurements. The permeation of dioctyl phthalate, 2-ethylhexylbenzyl phthalate, nonylphenol ethoxylate, isopropyl myristate, and oleic acid into a polyurethane matrix was measured gravimetrically. The silicone containing material at low temperatures exhibits relative simple permeation behavior however deviations from simple Fickian-type behavior are observed at higher temperature. Surprisingly, the ethylene glycol and 1,10-decanediol exhibited no significant absorption over a period of 5 months with the exception being nonylphenol ethoxylate. A comparison of the void sizes with the molecular dimensions for the lowest energy conformations of the permeants obtained using theoretical calculations indicate that for the silicone-based material the diffusion cross section for the permeants is larger than the available void size. The permeation process is considered to occur by a reptation type of motion of the permeants into channels created by the phase segregation of the flexible segments.