Huo, Zijian
(2023)
Experimental and Computational Investigation of Mechanochemical Activation
in Triblock Copolymers.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Polymer mechanochemistry offers a unique approach to promote chemical reactions in polymeric materials by applying external force. In the past decade, significant effort has been focused on designing, developing, and engineering functional materials with targeted mechanochemical responses. However, in bulk materials, the efficiency of mechanochemical responses is limited by chain relaxation and the properties of the polymer network, and understanding what features control this efficiency is critical for designing functional mechanochemical materials. To address this challenge, this thesis uses block copolymers as a model system for investigating how polymer composition, conformation, and molecular weight distribution affect the physics of force transmission at the molecular level. In particular, a variety of systems based on poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) (MBM) containing spiropyran mechanophores are investigated via both experimental and computational approaches to provide fundamental insights into the mechanochemical activation process. Experimentally, the force-driven spiropyran conversion is monitored by observing a color change of a small-molecule mechanophore in the polymers under uniaxial tensile deformation. Computationally, the mechanophore is modeled by a double-well potential, and its conversion is quantified by monitoring the change in its bond length during extension in molecular dynamics simulations. Together, our results demonstrated that increasing the glassy content of the polymers not only increases the overall mechanophore conversion but also results in its earlier activation. In addition, our computational work revealed that such an activation process occurs primarily in the tie chains that connect different glassy domains. These findings indicate that polymer composition and chain conformation both play critical roles in controlling mechanochemical activation and significantly impact the efficiency of mechanochemical responses.
Finally, we showed that the overall mechanophore conversion is dominated by the short tie chains in triblock copolymer blends, suggesting that non-uniform force distributions in polymers with different strand lengths can greatly affect the resulting mechanochemical responses. In summary, this thesis provides new fundamental insights into how the molecular-scale properties of polymers and polymer networks control the efficiency of mechanochemical activation and offers guidance for the future design of functional materials with targeted mechanochemical responses.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
10 May 2023 |
| Date Type: |
Publication |
| Defense Date: |
9 February 2023 |
| Approval Date: |
10 May 2023 |
| Submission Date: |
1 March 2023 |
| Access Restriction: |
2 year -- Restrict access to University of Pittsburgh for a period of 2 years. |
| Number of Pages: |
214 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
mechanochemistry, triblock copolymers, force distribution, mechanochemical activation |
| Date Deposited: |
10 May 2023 18:49 |
| Last Modified: |
10 May 2023 18:49 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/44249 |
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