Molecular Design Rules for Complex Viscoelastic Spectra in Vitrimers
Abstract
This project will address major challenges regarding the predictive molecular design of viscoelasticity in soft materials using dynamic covalent networks (vitrimers) as a model platform. Specifically, we will emphasize a fundamental understanding how mixed dynamic bonds, network architecture, proximity of bond exchange timescales to segmental dynamics, and copolymer sequence impact the relaxation spectrum. Our emphasis is on complex multimodal spectra and controlling breadth in extremely dynamically heterogeneous polymers. The interaction of multiple dynamic bonds is not yet even qualitatively understood in most cases, making it difficult to predict where relaxation modes will end up after mixing. Broad damping peaks can arise from many sources including the dynamic bonds or the polymer itself, and careful characterization and analysis are required to deconvolute these contributions. We will focus on three key areas associated with viscoelastic design beginning with the role of mixed dynamic bonds on networks with very low glass temperatures. First, we will probe how different exchange mechanisms in a single network lead to multiple relaxation modes depending on polymer architecture. Next, we will investigate how segmental dynamics (from the polymer) can impact bond exchange in glassy vitrimers. Mixing of segmental dynamics and bond exchange processes will lead to substantial broadening of the glass transition, and fast bond exchange can lead to dissipative processes deep into the glassy state. Our third objective is to design extremely broad relaxation spectra for impact and shock dissipation using gradient copolymers, where the composition of monomer along the backbone transitions from nearly pure monomer A to nearly pure monomer B, containing dynamic crosslinks. Continuous damping spectra spanning up to 15 orders of magnitude in breadth will be targeted.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 06, 2024
- Source ID
- FA95502310348
Entities
People
- Christopher M Evans
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Illinois Urbana–Champaign