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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Glass Transition and Molecular Dynamics in Core-Shell-Type Nanocomposites Based on Fumed Silica and Polysiloxanes: Comparison between Poly(dimethylsiloxane) and Poly(ethylhydrosiloxane)
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Glass Transition and Molecular Dynamics in Core-Shell-Type Nanocomposites Based on Fumed Silica and Polysiloxanes: Comparison between Poly(dimethylsiloxane) and Poly(ethylhydrosiloxane)

机译：基于气相二氧化硅和聚硅氧烷的核 - 壳型纳米复合材料中的玻璃转变与分子动力学：聚（二甲基硅氧烷）与聚（乙基氢硅氧烷）的比较

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The interfacial polymer in nanocomposites (PNCs) is widely believed to exhibit modified dynamics and structure, which are considered responsible for the improved PNC properties. Owing to its high resolving power, broadband dielectric spectroscopy (BDS) is one among the most suitable tools for studying polymer dynamics. Here, BDS combined with differential scanning calorimetry (DSC), microscopy, infrared spectroscopy, and thermally stimulated depolarization currents (TSDC) are employed to study low-molecular weight polydimethylsiloxane (PDMS) and a slightly modified siloxane, polyethylhydrosiloxane (PEHS), in bulk and in the form of silica-polymer "core-shell"-type PNCs. The dielectric/calorimetric mapping for the systems based on PEHS is demonstrated for the first time. Bulk-like dynamics (alpha relaxation, glass transition) is recorded faster and less cooperative in the PNCs, in agreement between the techniques, most probably due to spatial confinement between the neighboring nanoparticles. The constraints arising from the particle-polymer interactions resulted in the formation of an interfacial polymer fraction, being rigid and similar in amount for the two polymers in DSC, whereas a part of this latter amount (e.g. tails and loops) exhibits retarded dynamics in BDS and TSDC. The interfacial polymer dynamics is recorded individually via the alpha(int), relaxation next to a in the PNCs. For PEHS, alpha(int) is quite weak showing a non cooperative character (sparsely distributed short tails), while it is strong exhibiting low cooperativity for PDMS (loops and tails). Because both polymers consist of small chains and exhibit similar flexibility, it is concluded that the differences in alpha(int) arise from the type and the extent of interfacial interactions, for example, the additional covalent bonding in silica/PEHS leading to the formation of many immobile trains. Finally, the absolute differences in the relaxation times between the a and alpha(int) were found similar for PEHS and PDMS, which, interestingly, suggests a "coupling" between the polymer structure and its dynamics in the bulk (unconstrained) and interfacial (constrained) state.
机译：纳米复合材料（PNC）中的界面聚合物被广泛认为具有修饰的动力学和结构，其被认为是对改进的PNC性质负责。由于其高分辨率高，宽带介电光谱（BDS）是研究聚合物动力学的最合适的工具中的一种。这里，BDS与差分扫描量热法（DSC），显微镜，红外光谱和热刺激的去极化电流（TSDC）联合使用，研究低分子量的聚二甲基硅氧烷（PDMS）和略微改性的硅氧烷，聚乙基水硅氧烷（PEHS），散装以二氧化硅聚合物“核 - 壳” - 型PNC的形式。第一次证明了基于PEHS的系统的介质/量热映射。在技​​术之间的协议中，PNC在PNC中达成更快，更少的合作动态（α弛豫，玻璃转换），可能是由于邻近纳米颗粒之间的空间限制。由颗粒聚合物相互作用产生的约束导致界面聚合物级分的形成，其两种聚合物的刚性和类似的DSC的量，而后一种金属（例如尾部和循环）的一部分在BDS中表现出延迟动态和TSDC。界面聚合物动力学通过α（int）单独记录，在PNC中的A旁边放松。对于PEHS，α（int）非常弱，显示非合作性格（稀疏分布的短尾），而它表现出低于PDMS（环和尾部）的低合作性。因为两种聚合物包括小链子和表现出类似的灵活性，所以得出结论，α（int）的差异来自界面相互作用的类型和程度，例如，二氧化硅/ PEH中的额外共价键导致形成许多不动的火车。最后，发现A和α（int）之间的弛豫时间的绝对差异类似于PEHS和PDMS，有趣的是，有趣的是，在散装（无约束）和界面中的聚合物结构和其动力学之间的“耦合”建议“耦合”（约束）状态。

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