用超快红外光谱测量聚烯和聚甲酸中的自由体积元素大小和动态
Sebastian M Fica-Contreras1, David J Hoffman1, Junkun Pan1
1Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Journal of the American Chemical Society
|February 25, 2021
概括
研究人员使用超快的红外光谱来研究聚合物中的自由体积元素 (FVE). 聚乙烯 (PS) 比聚甲酸 (PMMA) 具有更大,更多样化的FVE,具有不同的动态和静电性质.
科学领域:
- 聚合物科学
- 光谱学
- 材料科学
背景情况:
- 自由体积元素 (FVE) 对于聚合物特性如扩散和机械行为至关重要.
- 了解FVE的大小,分布和动态对于聚合物设计至关重要.
- 之前的技术缺乏对FVE静电特性和动态的详细见解.
研究的目的:
- 研究聚乙烯 (PS) 和聚甲酸 (PMMA) 中的FVE的尺寸,尺寸分布,动态和静电特性.
- 在聚合物矩阵内描述振动探针的方向动态,以推断FVE特征.
- 通过使用振动Stark效应将FVE半径与电场强度进行相关联.
主要方法:
- 采用了限制定向异位法 (ROAM),一种超快的红外光谱技术.
- 使用振动探测器 (烯酸,PhSeCN) 分析了其整个吸收频谱的方向动态.
- 应用了第一阶段的振动史塔克效应, 将FVE射线与局部电场联系起来.
主要成果:
- 与PMMA (平均半径3.0 Å,近高斯分布) 相比,聚乙烯具有更大的FVE (平均半径3.4 Å) 和更广泛的非高斯尺寸分布.
- FVE 结构动态发生在 ~ 150 ps 的时间尺度上,涉及保持平均 FVE 尺寸的形状波动.
- 对于每个电场强度,PMMA显示出独特的FVE半径,而PS则显示出与强电场广泛分布相关的较小半径.
结论:
- ROAM提供了前所未有的FVE动态和聚合物的静电特性.
- 在PS和PMMA之间存在显著的FVE特性差异,影响了它们的材料特性.
- 这项研究揭示了FVE大小和PS的局部电场之间的复杂关系,这表明电荷载体具有独特的行为.
更多相关视频
11:27Studying Soft-matter and Biological Systems over a Wide Length-scale from Nanometer and Micrometer Sizes at the Small-angle Neutron Diffractometer KWS-2
Published on: December 8, 2016
12.6K
09:43Interfacial Molecular-level Structures of Polymers and Biomacromolecules Revealed via Sum Frequency Generation Vibrational Spectroscopy
Published on: August 13, 2019
9.6K
相关概念视频
01:16IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
2.3K
A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to...
According to Hooke's law, the vibrational frequency is directly proportional to...
2.3K
01:08Molecular Weight of Step-Growth Polymers
2.6K
Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
2.6K
01:10Polymers: Molecular Weight Distribution
4.2K
For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
4.2K