Molecular dynamics of a catalysed epoxy resin (DGEBA) as a function of temperature

Epoxy resin polymers primarily consist of long chain hydrocarbons in a network, which exist in an
amorphous structure. These chains undergo relaxations at different temperatures, partly due to the change
in free volume and partly due to the change in kinetic energy. These relaxations necessarily cause a change
in the structure: notably at the glass transition temperature (Tg), where alpha-relaxation processes
dominate and the epoxy changes from a hard, brittle“glassy” form to a viscous, rubbery state. While existing
macroscopic measurements provide an overview of these process they do not address the underlying
physical mechanisms, and a microscopic probe allows observation of these process at a molecular level.
We have observed a change in the Muon response at temperatures that align with alpha, beta and gamma
relaxation regimes across a broad temperature range (50 K to 425 K) as well as changes in both the
diamagnetic and Muonium fractions in T20 and longitudinal field (T1) scans. We have determined estimates
for the Tg at several B fields and calculated activation energies from Arrhenius plots of ln (T1) vs 1 /T and
seen evidence for the gamma and beta relaxations (and determined a preliminary value for the gamma
activation enrgy). These are in good agreement with values obtained from macroscopic measurements,
However, in each case more data is necessary to reduce errors.

环氧树脂聚合物主要由呈网状结构的长链烃类构成，整体呈现无定形（amorphous）结构。这类长链会在不同温度下发生弛豫（relaxation）过程，其成因一部分源于自由体积的变化，另一部分则来自动能的改变。此类弛豫过程必然会引发结构变化：尤为显著的是在玻璃化转变温度（glass transition temperature, Tg）处，此时α弛豫（alpha-relaxation）过程占据主导，环氧树脂会从坚硬脆硬的“玻璃态”转变为粘稠的橡胶态。尽管现有的宏观测量手段能够对这类弛豫过程进行整体表征，却无法揭示其背后的物理机制；而微观探针技术则可在分子层面观测此类过程。我们在覆盖50 K至425 K的宽温区间内，于与α、β、γ弛豫区域对应的温度下观测到了μ子（Muon）响应的变化；同时在T20与纵向场（longitudinal field, T1）扫描实验中，也观测到了抗磁性（diamagnetic）组分与μ子素（Muonium）占比的变化。我们已在多个磁场（B fields）条件下估算得到了Tg的数值，并通过ln(T1)与1/T的阿伦尼乌斯（Arrhenius）作图法计算得到了活化能（activation energy），同时观测到了γ与β弛豫过程的相关证据（并初步确定了γ弛豫的活化能数值）。上述结果与宏观测量得到的数值吻合度良好，但在所有情形下，仍需补充更多实验数据以降低误差。