Sattar Mohammad Abdul, Patnaik Archita
Colloid and Interface Chemistry Laboratory, Department of Chemistry, Indian Institute of Technology Madras, Chennai600036, India.
R&D Centre, MRF Limited, MRF Road, Tiruvottiyur, Chennai 600019, India.
ACS Omega. 2020 Aug 13;5(33):21191-21202. doi: 10.1021/acsomega.0c02929. eCollection 2020 Aug 25.
Intermolecular interactions between the constituents of a polymer nanocomposite at the polymer-particle interface strongly affect the segmental mobility of polymer chains, correlated with their glass transition behavior, and are responsible for the improved dynamical viscoelastic properties. In this work, we emphasized on the evolution of characteristic interfaces and their dynamics in silica (SiO NP)-reinforced, solution-polymerized, styrene butadiene rubber (SSBR) composites, whose relative prevalence varied with the phosphonium ionic liquid (PIL) volume fraction, used as an interfacial modifier. The molecular origins of such interfaces were examined through systematic dielectric spectroscopy, molecular dynamics (MD) simulations, and dynamic-mechanical analyses. The PIL facilitated H-bonding, cation-π, surface-phenyl, and van der Waals interfacial interactions between SSBR and SiO NP, thereby regulating the polymer chain dynamics, orientation, and mean-square displacement. Specifically, the mass density profiles from MD simulations revealed the dynamic gradient of polymer chains in the interfacial region as a function of radial distance from the center of mass of the SiO NP surface. The results showed a structuring effect to result in well-resolved density peaks at specific radial distances with the tangential orientation of styrene monomers in the vicinity of the SiO NP surface. These domino effects highlighted strong interfacial interactions to have an indispensable effect on the viscoelastic performance and thermal motion of SSBR molecular chains, leading to a higher glass transition temperature ( ) by ∼15 K, validating the experimental data. More importantly, our results gave new insights into the fundamental understanding of the fact that the strength of intermolecular interactions induced by PIL at the polymer-particle interface is the key to control the α-relaxation dynamics and optimization, desired for specific applications.
聚合物纳米复合材料在聚合物 - 颗粒界面处的组分间分子相互作用，强烈影响聚合物链的链段流动性，这与它们的玻璃化转变行为相关，并决定了其动态粘弹性性能的改善。在这项工作中，我们着重研究了二氧化硅（SiO₂ 纳米颗粒）增强的、溶液聚合的丁苯橡胶（SSBR）复合材料中特征界面的演变及其动力学，其相对含量随用作界面改性剂的鏻离子液体（PIL）体积分数而变化。通过系统的介电谱、分子动力学（MD）模拟和动态力学分析，研究了此类界面的分子起源。PIL促进了SSBR与SiO₂ 纳米颗粒之间的氢键、阳离子 - π、表面 - 苯基和范德华界面相互作用，从而调节了聚合物链的动力学、取向和均方位移。具体而言，MD模拟得到的质量密度分布揭示了界面区域聚合物链的动态梯度是距SiO₂ 纳米颗粒表面质心径向距离的函数。结果表明存在一种结构化效应，导致在特定径向距离处出现分辨率良好的密度峰，且在SiO₂ 纳米颗粒表面附近苯乙烯单体呈切向取向。这些多米诺效应突出了强界面相互作用对SSBR分子链的粘弹性性能和热运动具有不可或缺的影响，使玻璃化转变温度（Tg）提高了约15 K，验证了实验数据。更重要的是，我们的结果为深入理解以下事实提供了新的见解：PIL在聚合物 - 颗粒界面处诱导的分子间相互作用强度是控制α - 弛豫动力学和特定应用所需的Tg优化的关键。
