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Regiochemical Effects on Mechanophore Activation in Bulk Materials
Yangju Lin1, Meredith H Barbee1, Chia-Chih Chang1
1Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States.
Journal of the American Chemical Society
|November 8, 2018
Summary
Mechanochromic force probes, like spiropyran derivatives, visualize polymer stress. This study shows three spiropyran regioisomers respond differently to strain, but activate at the same high strain level.
Area of Science:
- Polymer Science
- Materials Science
- Mechanochemistry
Background:
- Mechanochromic force probes, particularly spiropyran derivatives, are valuable for mapping stress, strain, and fracture in polymers.
- Understanding the relationship between molecular structure and macroscopic mechanical response is crucial for designing advanced materials.
Purpose of the Study:
- To investigate the macroscopic mechanical response of silicone elastomers cross-linked with three distinct spiropyran regioisomers.
- To correlate the regioisomeric structure of spiropyran derivatives with their colorimetric response under uniaxial tensile loading.
- To compare experimental observations with predictions from molecular modeling regarding mechanical sensitivity and strain activation.
Main Methods:
- Synthesis of silicone elastomers incorporating three spiropyran (SP) regioisomers: SP(o), SP(m), and SP(p).
- Application of quasi-static uniaxial tensile load to the modified elastomers.
- Colorimetric analysis to quantify the response of the spiropyran derivatives.
- Molecular modeling to predict mechanical sensitivity.
Main Results:
- The relative colorimetric response under tensile load followed the order SP(o) > SP(m) > SP(p), aligning with predicted mechanical sensitivities.
- All three spiropyran regioisomers exhibited an indistinguishable strain onset for detectable activation at approximately 90% uniaxial strain.
- The ratiometric response of the isomers remained constant across the investigated strain range (90-135% uniaxial strain).
Conclusions:
- The study demonstrates that while spiropyran regioisomers exhibit varying sensitivities, their activation strain onset is uniform under significant uniaxial strain.
- The observed constant ratiometric response contradicts simulation expectations for strained polymer networks, suggesting complex network behavior.
- These findings offer insights into the design and application of mechanochromic probes for polymer analysis.
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