Session: Government Agency Student Posters

Paper Number: 173175

Utilizing Mechanical Force to Reveal and Modulate Chemical Reaction Pathways 

Traditional chemical reactions are activated by specific energy inputs such as heat, light, and electricity. In recent years, mechanical force has received significant attention due to its ability to initiate chemical reactions that exhibit color change, NIR light emission, and drug release. Significant research in polymer mechanochemistry has been extensively explored and studied over the last few decades, showing significant advances in fundamental science and engineering applications, such as the development of next-generation smart materials, advanced ultrasound imaging, and ultra-sensitive biomechanical sensing. 

Mechanophores represent a unique class of reactive molecules that undergo chemical reactions when mechanical stress is applied. Spiropyran (SP), a classical photosensitive dye, is extensively used as a photoswitch and pH sensor. It undergoes a chemical transformation to generate another colored structure, merocyanine (MC), under various reaction conditions, including UV radiation and acids. The transition between SP and MC involves a complex pathway with several intermediates; however, detailed mechanisms remain unexplored experimentally due to rapid reaction rates and kinetics. Mechanical force can also induce the transition from SP to MC at a slower rate due to the slow relaxation time scale in the polymer matrix. The SP-MC transition is reversible and can be repeated for multiple cycles. Our study identified a molecular intermediate with a Z-configuration during the transition between MC and SP. This Z-configuration, not previously reported in experimental studies, is pivotal for understanding the reaction mechanisms. 

We used a poly(methyl acrylate)-based polymer film with spiropyran chemically crosslinked into the matrix through photopolymerization. The PMA film was subjected to uniaxial tensile experiments coupled with RGB analysis to monitor structural changes of SP. Three stages of the tensile tests have been performed, including stretching, holding, and releasing. Benchmark analysis of the PMA-SP film was obtained from its stress-strain profile. The RGB analysis revealed distinct profiles for stretching and relaxation, with the green channel indicating the presence of the metastable Z-configuration during relaxation, which was not previously reported experimentally. The identification of Z-merocyanine provides an opportunity to examine detailed internal structural changes, offering new insights into the mechanistic chemical pathways of molecular switches. 

Furthermore, this work also provides a new mechanical sensing platform for tracking force profiles and histories within soft materials on the microscale. The PMA-SP film has shown a correlation between the applied force and RGB profile, indicating that the force history can be observed and the loaded force can be quantified. The visual color change provides a facile way to track internal mechanical information, indicating whether it is close to the breaking point. Further in-depth evaluation will uncover how mechanical force stabilizes critical intermediates and provides detailed reaction mechanisms. This study could significantly broaden the applications of converting mechanical energy into various responses toward the development of future mechanically responsive materials and a nanoscale real-time mechanical sensing platform.  

Presenting Author: Robert Davis Clarkson University

Presenting Author Biography: Robert Davis is a Senior at Clarkson University majoring in mechanical engineering with a minor in business. Robert works as the lab manager for the Lu Research group. Robert has previously presented at the Research and Project showcase five times and at the Center for Advanced Materials Processing Annual Technical meeting twice. He has been applying the skills learned at school and in the lab during his internships at GE Aerospace. During his internships, Robert worked on a sensor to detect leaks in the engine and change its fuel source if a leak was detected, along with participating in kaizen and 5S events during the second rotation to improve the efficiency of the assembly of the T700 and T408 engines. Robert plans to pursue mechanical engineering or biomechanical engineering after graduation to align with his research motivation of finding more efficient ways to treat and help those in need.

Authors:

Robert Davis Clarkson University
Xiaocun Lu Clarkson University