Adhesion of SiO2-methyl vinyl silicone rubber molecular interface modified by silane coupling agents
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摘要: 纳米SiO2掺杂已经成为提升甲基乙烯基硅橡胶(MVSR)性能的有效方法，但是纳米SiO2容易发生团聚现象，将其直接掺到MVSR基体中时，纳米SiO2难以在MVSR基体中分散，从而造成SiO2-MVSR分子界面粘结效果不佳、分子界面存在缺陷等不利影响，进而无法实现提升MVSR性能的目的。为了提升SiO2-MVSR分子界面的粘结性，使纳米SiO2在MVSR基体中更易分散，本文构建了未修饰和KH550、KH560、KH570、KH792四种硅烷偶联剂修饰下的SiO2-MVSR分子界面模型，并对模型进行结构优化和分子动力学计算。通过比较不同模型中分子界面的结合能、粘结深度和粘结热稳定性的变化规律，从分子结构角度分析硅烷偶联剂修饰下SiO2-MVSR分子界面粘结性提升的原因。研究表明：提升SiO2-MVSR分子界面粘结性的关键在于优选硅烷偶联剂的非水解基团，当非水解基团中与MVSR分子链相同的化学键占比越大，包含电负性较强原子的数量越多时，修饰后SiO2-MVSR分子界面粘结性的提升效果就越好，同时，硅烷偶联剂较长的链长与较大的相对分子质量也会对粘结性的提升起到一定帮助。
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关键词:
- 硅烷偶联剂 /
- 修饰 /
- 二氧化硅-甲基乙烯基硅橡胶分子界面 /
- 粘结性 /
- 分子动力学模拟
Abstract: Nano-SiO2 doping has become an effective way to improve the performance of methyl vinyl silicone rubber (MVSR). However, nano-SiO2 is easy to agglomerate. When it is directly mixed into MVSR matrix, nano-SiO2 is difficult to disperse in MVSR matrix, resulting in poor adhesion effect of SiO2-MVSR molecular interface, defects in the molecular interface and other adverse effects, so that the purpose of improving MVSR performance cannot be achieved. In order to improve the adhesion of SiO2-MVSR molecular interface and make nano-SiO2 more easily dispersed in MVSR matrix, this paper constructed the SiO2-MVSR molecular interface models that unmodified and modified by KH550, KH560, KH570 and KH792, and carried out structural optimization and molecular dynamics calculation. By comparing the adhesion energies, adhesion depths and adhesion thermal stabilities of the molecular interface in different models, the reason for the improvement of the adhesion of SiO2-MVSR molecular interface modified by silane coupling agents was analyzed from the perspective of molecular structure. The results show that the key to improve the adhesion of SiO2-MVSR molecular interface is to select the non-hydrolytic group of the silane coupling agents. When the proportion of the same chemical bond between the non-hydrolytic group and MVSR molecular chain is larger, and the number of more electronegative atoms is more, the effect of improving the adhesion of SiO2-MVSR molecular interface is better. At the same time, the longer chain length and larger relative molecular weight of silane coupling agent will also help to improve the adhesion. -
图 1 硅烷偶联剂KH560修饰过程及四种常用硅烷偶联剂的分子模型
Figure 1. Modification process of silane coupling agent KH560 and four kinds of molecular models of silane coupling agent
图 2 甲基乙烯基硅橡胶(MVSR)的分子结构
Figure 2. Molecular structure of methyl vinyl silicone rubber (MVSR)
图 3 MVSR分子单链模型及温度为358 K时4种硅烷偶联剂修饰下SiO2-MVSR分子界面模型的构建过程
Figure 3. Single chain model of MVSR and the construction process of SiO2-MVSR molecular interface model modified by 4 kinds of silane coupling agents at 358 K
图 4 4种硅烷偶联剂修饰下SiO2-MVSR分子界面结合能随温度的变化曲线
Figure 4. Temperature dependence of the adhesion energy of SiO2-MVSR molecular interface modified by 4 kinds of silane coupling agents
图 5 4种硅烷偶联剂修饰下SiO2及MVSR沿Z轴方向分布的相对浓度曲线
Figure 5. Relative concentration curves of SiO2 and MVSR along Z-axis under the modification of 4 kinds of silane coupling agents
图 6 358~458 K温度下MVSR分子链的均方位移曲线
Figure 6. Mean square displacement curves of molecular chain of MVSR at 358~458 K
图 7 4种硅烷偶联剂修饰下SiO2-MVSR复合材料试样的变温FTIR图谱
Figure 7. Temperature dependent FTIR spectra of SiO2-MVSR composites modified by 4 kinds of silane coupling agents
表 1 不同分子界面模型中SiO2及MVSR沿Z轴方向分布的重叠区域及粘结深度
Table 1. Overlapping regions and adhesion depths of SiO2 and MVSR along Z-axis in different molecular interface models
Model category Overlapping area/nm Adhesion depth/nm Unmodified 1.402-2.203 0.801 Modified by KH550 1.522-2.971 1.449 Modified by KH560 1.605-3.283 1.678 Modified by KH570 1.634-3.345 1.711 Modified by KH792 1.358-3.016 1.658 
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表 2 4种硅烷偶联剂的链长与相对分子质量
Table 2. Chain lengths and relative molecular weights of 4 kinds of silane coupling agents
Category Chain length/nm Relative molecular weight KH550 0.5426 221 KH560 0.8965 236 KH570 0.9140 248 KH792 0.8639 222
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表 3 4种硅烷偶联剂的结构信息
Table 3. Structure information of 4 kinds of silane coupling agents
Category Non-hydrolytic group Central element Hydrolytic group Hetero group Same group KH550 NH2— CH2—CH2—CH2— Si —(OCH3)3 KH560 CH2—(O)CH—CH2—O— KH570 CH2=(CH3)C—(O)C—O— KH792 NH2—CH2—CH2—NH—
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表 4 358~458 K温度条件下SiO2-MVSR不同分子界面模型中形成的氢键数量
Table 4. Numbers of hydrogen bonds formed in different SiO2-MVSR molecular interface models at 358-458 K
Model category 358 K 378 K 398 K 418 K 438 K 458 K Unmodified 195 167 181 174 176 190 Modified by KH550 270 258 280 287 265 265 Modified by KH560 237 240 234 227 196 216 Modified by KH570 242 247 243 247 231 257 Modified by KH792 299 280 289 300 308 283
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表 5 甲基乙烯基硅橡胶分子单链结构信息
Table 5. Single chain structure information of methyl vinyl silicone rubber
Head/tail group Link formation Functional group Link trunk Different groups Same group —Si(CH3)3 Dimethylsiloxane chain link CH3— CH3— Si—O —OSi(CH3)3 Methyl vinyl siloxane chain link CH2=CH— CH3—
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表 6 各试样中硅烷偶联剂官能团与SiO2表面上的H—O峰位变化
Table 6. Peak position change of the functional group of silane coupling agent and H—O on the surface of silicon dioxide in each sample
Model category Δ1/cm−1 Δ2/cm−1 Modified by KH550 19 4 Modified by KH560 24 13 Modified by KH570 23 9 Modified by KH792 9 2 Notes: Δ1—Absolute value of the difference between the peak position of the stretching vibration peak of the silane coupling agent at 358 K and the peak position at 458 K; Δ2—Absolute value of the difference between the peak position of the bending vibration peak of H—O at 358 K and the peak position at 458 K on the surface of SiO2.
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