Parametric Study for Dimeric Anthracene-Based Mechanophore-Embedded Thermoset Polymer Matrix Using Molecular Dynamics
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Parametric Study for Dimeric Anthracene-Based Mechanophore-Embedded Thermoset Polymer Matrix Using Molecular Dynamics Bonsung Koo1, Ryan Gunckel1, Aditi Chattopadhyay1, and Lenore Dai1 1 School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, U.S.A.
ABSTRACT This paper presents a parametric study to investigate the effect of relevant design variables on mechanochemical reaction and mechanical properties of a mechanophore-embedded thermoset polymer matrix. Mechanophores emit fluorescence when a specific covalent bond breaks due to external stress, and thus have attracted immense research interest as a damage sensor. Recently, a mechanophore named dimeric 9-anthracene carboxylic acid (Di-AC) was synthesized successfully and incorporated into epoxy-based thermoset polymer matrix to detect damage precursor. However, there is significant potential in modeling the complex mechanochemistry associated with the Di-AC to obtain a better understanding of this mechanophore and its interaction with the host thermoset material. In this study, a hybrid MD simulation methodology is employed to explore this complex mechanochemistry along with the investigation of the effect of design parameters on the mechanophore performance. The hybrid MD simulation method enables the simulation of Di-AC synthesis, epoxy curing, and mechanical loading test; therefore, the experimental process performed can be emulated accurately. Previously, the hybrid MD method showed the capability of capturing experimentally observed phenomena such as early signal detection and yield strength variation between neat epoxy system and epoxy with 5 wt% Di-AC thermoset polymer. In this paper, the effect of curing temperature on mechanophore activation and mechanical properties is investigated. A series of temperatures are used in the curing simulation, which are experimentally achievable. Results show that curing temperature below glass transition temperature maintains early signal detection and yield strength decreases when the curing temperature increases above the glass transition temperature. Good correlation is observed with experimental results. INTRODUCTION Fiber reinforced polymer composites (FRPC) provide numerous advantages such as light weight, specific strength, and tailorable mechanical properties. However, understandings of damage initiation and progression mechanisms have not been addressed clearly, which eventually restricts full implementation of FRPC. A significant amount of research has been reported on developing sensors for damage detection but very limited literature is available on understanding the precursors to damage in highly heterogeneous FRPC systems. Force-sensitive molecular units named mechanophore have attracted significant attention in recent years due to their nanoscale damage detection capability. The covalent bond breakage under external stress of mechanophores leads to a change of color in mechanophore system; this color change can be an indication of early damage or damage precursor.
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