Local conformations and heterogeneities in structures and dynamics of isotactic polypropylene adsorbed onto carbon fiber
Local conformations and heterogeneities in structures and dynamics of isotactic polypropylene adsorbed onto carbon fiber
复制标题
DOI：
10.1016/j.polymer.2022.125584
复制
发表时间：
2023-01
期刊：
影响因子：
4.6
通讯作者：
Zhixing Huang;Yashasvi Bajaj;J. Carrillo;Y. Nakanishi;Kiminori Uchida;Kazuki Mita;Takeshi Yamada;T. Miyazaki;B. Sumpter;M. Endoh;T. Koga
中科院分区：
文献类型：
--
作者：
Zhixing Huang;Yashasvi Bajaj;J. Carrillo;Y. Nakanishi;Kiminori Uchida;Kazuki Mita;Takeshi Yamada;T. Miyazaki;B. Sumpter;M. Endoh;T. Koga
碳纤维（CF）增强聚合物（CFRP）已经在各个行业中广泛使用。碳纤维增强复合材料的宏观性能主要取决于复合材料基体与碳纤维之间的界面。有越来越多的证据表明形成了结合聚合物层（BPL），即，物理吸附在填料表面上的聚合物链。然而，该界面总是与聚合物基体的较厚部分接触，使得对其的理解成为一项困难的任务。其中，我们使用碳纤维增强等规聚丙烯（iPP）作为一个合理的CFRP。为了表征CF表面上的BPL，我们使用对二甲苯溶剂冲洗从CFRP中提取它。采用差示扫描量热法和热重分析法对BPL的物理和热性能进行了表征，采用小角中子散射和准弹性中子散射（QENS）技术对其微观结构和动力学进行了研究。随后，我们采用原子分子动力学（MD）模拟，以补充QENS结果以上的散装熔融温度，并揭示实验无法访问的细节。我们观察到BPL的结晶度比本体低得多，而BPL的熔融温度保持与本体相同。在QENS和MD探测的给定长度和时间尺度内，我们还观察到大多数结合链是移动的，在CF表面附近形成高密度区域（厚度小于1 nm）。由QENS和MD探测的结合链的链段动力学也比自由链的链段动力学快得多，这可能是由于在BPL的最高表面处存在自由表面区域。分子动力学结果表明，主链和侧基在CF表面上几乎是平的，这是iPP BPL克服总自由能中构象熵损失的平坦化过程的驱动力.
Carbon fiber (CF) reinforced polymers (CFRPs) have experienced widespread use in various industries. One of the most important parameters that controls the macroscopic property of CFRPs is the interface between a polymer matrix and CF. There is growing evidence to suggest the formation of a bound polymer layer (BPL), i.e., polymer chains that physically adsorb on a filler surface. However, this interface is always in contact with the thicker part of a polymer matrix, rendering its understanding a difficult task. Therein, we use CF-reinforced isotactic polypropylene (iPP) as a rational CFRP. To characterize the BPL on the CF surface, we extracted it from the CFRP using solvent-rinsing with p-xylene. The physical and thermal properties of the BPL were characterized by differential scanning calorimetry and thermogravimetric analysis, while its microscopic structures and dynamics were probed by small-angle neutron scattering and quasi-elastic neutron scattering (QENS) techniques. Subsequently, we employed atomistic molecular dynamics (MD) simulations to complement the QENS results above the bulk melting temperature and reveal details that were experimentally inaccessible. We observed that the degree of crystallinity of the BPL was quite lower than the bulk, while the melting temperature of the BPL remained the same as the bulks. Within the given length and time scales probed by QENS and MD, we also observed that most of the bound chains were mobile, with the formation of a high-density region (less than 1 nm in thickness) near the CF surface. The segmental dynamics of the bound chains probed by both QENS and MD were also much faster than those of the free chains, possibly due to the presence of a free surface region at the topmost surface of the BPL. Furthermore, the MD results demonstrated that the backbone chains and side groups lie nearly flat on the CF surface, which is the driving force for the flattening process of the iPP BPL to overcome the conformational entropy loss in the total free energy.