Abstract
Self-healing poly (ethylene co-methacrylic acid) ionomers (EMAA) are thermoplastic materials that when punctured, cut, shot or damaged in a variety of ways, are capable of autonomously reorganizing their physical structure to heal and, in many instances, permanently seal the damaged location. However, a complete picture of the mechanisms responsible for their unusual behavior is not well understood. In this article we report the observation of time dependent acoustic and ultrasonic spectral evolution, measured using resonant acoustic and ultrasonic spectroscopy, for both pre and post-damage EMAA samples. The results provide a means to differentiate healing phases, quantify healing timescales, and potentially elucidate the composition parameters that most significantly impact healing behavior.
Highlights
(ethylene co-methacrylic acid) ionomers (EMAA) are thermoplastic materials that are capable of autonomously self-healing and have potential applications such as emergency containment, self-healing consumer products and others[1,2,3]
Efforts to improve characterization of these unique materials led to the use of Time Dependent Resonant Spectroscopy (TDRS) as a means to assess spectral variation in post-damage EMAA samples[11]
Resonant modes whose resonant frequencies change with time were discovered in both undamaged and damaged EMAA samples, indicative of persistent elastic evolution
Summary
Determination of the spectral evolution was accomplished by measuring the acoustic and ultrasonic spectra of both pre and post-damage EMAA samples. For the samples reported here the average rate was (1.9 ± 0.6) × 10−1 kHz/min, approximately two orders of magnitude larger than the undamaged sample rates After this secondary post-damage state, a transition is visible in all the spectral evolution plots. During the roughly 30 to 60 minutes, resonant frequency variation continued to occur during the tertiary healing phase, but at a reduced rate of (4 ± 2) × 10−2 kHz/min, approximately one order of magnitude larger than the undamaged sample rates. During this phase most, but not all (e.g. sample c of Fig. 4), transitions resulted in increased resonant frequency. Post-Damage Healing Phases Sample a (3.56 × 4.64 × 1.464 mm3) Sample c (4.23 × 4.11 × 1.33 mm3) Sample b (7.11 × 7.86 × 1.43 mm3)†
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