KEYWORDSDielectric spectroscopy; Epoxy networks of the diglycidyl ether of bisphenol A; 3,3 0 and 4,4 0 -diaminodiphenyl sulfone isomers; Chain motions; Vogel temperature; Kramers-Kro¨nig transformation Abstract Epoxy networks of the diglycidyl ether of bisphenol A (DGEBA) were prepared using 3,3 0 -and 4,4 0 -diaminodiphenyl sulfone isomer crosslinkers. Secondary relaxations and the glass transitions of resultant networks were probed using broadband dielectric spectroscopy (BDS). A sub-T g c relaxation peak for both networks shifts to higher frequencies (f) with increasing temperature in Arrhenius fashion, both processes having the same activation energy and being assigned to phenyl ring flipping in DGEBA chains. A b relaxation is assigned to local motions of dipoles that were created during crosslinking reactions. 4,4 0 -based networks exhibited higher T g relative to 3,3 0 -based networks as per dynamic mechanical as well as BDS analyses. The Vogel-Fulcher-Tam mann-Hesse equation fitted well to relaxation time vs. temperature data and comparison of Vogel temperatures suggests lower free volume per mass for the 3,3 0 -based network. The Kramers-Kro¨nig transformation was used to directly calculate dc-free e 00 vs. f data from experimental e 0 vs. f data. Distribution of relaxation times (DRT) curves are bi-modal for the 3,3 0 -crosslinked resin suggesting large-scale microstructural heterogeneity as opposed to homogeneity for the 4,4 0 -based network whose DRT consists of a single peak. Ó 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
In this study, we used broadband dielectric spectroscopy to analyze polymer nanofibers of poly(vinyl alcohol)/chitosan/silver nanoparticles. We also studied the effect of incorporating silver nanoparticles in the polymeric mat, on the chain motion dynamics and their interactions with chitosan nanofibers, and we calculated the activation energies of the sub-Tg relaxation processes. Results revealed the existence of two sub-Tg relaxations, the first gets activated at very low temperature (−90 °C) and accounts for motions of the side groups within the repeating unit such as –NH2, –OH, and –CH2OH in chitosan and poly(vinyl alcohol). The second process gets activated around −10 °C and it is thought to be related to the local main chain segments’ motions that are facilitated by fluctuations within the glycosidic bonds of chitosan. The activation energy for the chitosan/PVA/AgNPs nanocomposite nanofibers is much higher than that of the chitosan control film due to the presence of strong interactions between the amine groups and the silver nanoparticles. Kramers–Krönig integral transformation of the ε′′ vs. f spectra in the region of the chitosan Tg helped resolve this relaxation and displayed the progress of its maxima with increasing temperature in the regular manner.
We adapt a scalable layered intelligence technique from the game industry, for agent-based crowd simulation. We extend this approach for planned movements, pursuance of assignable goals, and avoidance of dynamically introduced obstacles/threats as well as congestions, while keeping the system scalable with the number of agents. We demonstrate the various behaviors in hall-evacuation scenarios, and experimentally establish the scalability of the frame rates with increasing numbers of agents.
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