Influence of Chain Stiffness on the Segmental Dynamics and Mechanical Properties of Cross-Linked Polymers
Influence of Chain Stiffness on the Segmental Dynamics and Mechanical Properties of Cross-Linked Polymers
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DOI：
10.1021/acs.macromol.3c01077
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发表时间：
2023-09
期刊：
影响因子：
5.5
通讯作者：
Xiangrui Zheng;Wenjian Nie;Yafang Guo;Jack F. Douglas;Wenjie Xia
中科院分区：
文献类型：
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作者：
Xiangrui Zheng;Wenjian Nie;Yafang Guo;Jack F. Douglas;Wenjie Xia
我们扩展了以前对一类模型粗晶聚合物网络形成材料的系统研究，重点研究了不同的分子刚性对这类材料的基本构象性质(即回转半径Rg和持续长度lp)、链段动力学(结构松弛时间τα)和力学性质(剪切力G和体积Bmodi)的影响。我们发现，分子刚性的增加增加了网络链的回旋半径和持续长度，就像以前在聚合物溶液中观察到的那样。分子刚性的增加导致链段动力学显著减慢，特征温度(即起始温度TA、玻璃化转变温度Tg和伏格尔温度T0)和玻璃形成的脆性显著增加。我们还发现，结构松弛时间τα和GandB并不表现出先前对于具有可变的交联密度和内聚能但具有固定的链弯曲刚度的全柔性交联网络的温度降低的近普遍的标度T/Tgas。随着网络链在所研究的范围内变得更加坚硬，这两个模数的大小都变得越来越小。此外，τα和模数(G，B)都与德拜-沃勒参数⟨U2⟩有很强的相关性，该参数相应地被用来定义材料“刚度”的局部度量。基于这一刚性度量的颜色图表明，在相同的折合温度T/Tg下，随着链刚性的增加，局部刚性波动的平均值和方差都减小。我们的模拟观察提供了新的物理见解，即改变链的刚性如何影响交联网络的玻璃化形成，这将有助于交联热固性材料的设计。
We extend previous systematic investigations of a family of model coarse-grained polymer network-forming materials by focusing on the influence of varying molecular rigidity on basic conformational properties (i.e., radius of gyrationRgand persistence lengthlp), segmental dynamics (structural relaxation time τα), and mechanical properties (shearGand bulkBmoduli) of this broad class of materials. We find that increasing molecular rigidity increases the radius of gyrationRgand persistence lengthlpof the network chains, as observed before in polymer solutions. The increase in molecular rigidity leads to a significant slowing down in the segmental dynamics and a strong increase in the characteristic temperatures (i.e., onset temperatureTA, glass transition temperatureTg, and Vogel temperatureT0) and fragility of glass formation. We also find that the structural relaxation time τα, along withGandB, does not exhibit the near-universal scaling with reduced temperatureT/Tgas found previously for fully flexible cross-linked networks having variable cross-link density and cohesive energy, but a fixed chain bending stiffness. Both of these moduli become progressively smaller in magnitude as the network chains become stiffer over theTrange investigated. Moreover, ταand the moduli (G,B) all exhibit strong correlative relationships with the Debye–Waller parameter ⟨u2⟩, which is correspondingly utilized to define a local measure of material “stiffness”. Color maps based on this stiffness measure indicate that both the average value and variance of the local stiffness fluctuations decrease with an increasing chain stiffness at the same reduced temperature,T/Tg. Our simulation observations provide novel physical insights into how varying chain stiffness influences the glass formation of cross-linked networks, which should be helpful in the design of cross-linked thermoset materials.