Ultrathin Shell Layers Dramatically Influence Polymer Nanoparticle Surface Mobility
Ultrathin Shell Layers Dramatically Influence Polymer Nanoparticle Surface Mobility
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DOI：
10.1021/acs.macromol.8b01804
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发表时间：
2018-11-13
期刊：
影响因子：
5.5
通讯作者：
Fytas, George
中科院分区：
文献类型：
--
作者：
Kang, Eunsoo;Kim, Hojin;Fytas, George
纳米粒子合成、自组装和表面涂层或图案化的进展使从光子晶体和声子晶体制造到药物输送载体的各种应用成为可能。限制其潜力的关键障碍之一是结构和热稳定性。玻璃化转变的存在可以促进纳米颗粒内部的变形，从而导致结构和性能的显著变化。最近，我们在单个聚苯乙烯纳米颗粒中检测到玻璃态转变，并将其起源与表面层的存在联系起来，与块体相比，表面层的动力学增强。这种可移动层的存在可能会对聚合物纳米颗粒的热稳定性产生重大影响。在这里，我们演示了如何在纳米颗粒上添加一个像单个聚合物链一样薄的壳层，从而完全消除聚苯乙烯纳米颗粒表面流动性增强的任何证据。超薄的聚合物壳层通过两种方式放置在纳米颗粒的表面：(I)共价键或(Ii)静电相互作用。通过布里渊光散射记录的粒子振动光谱的温度依赖性，用来探测有和没有壳层的纳米粒子的表面迁移率。除了对表面迁移率的抑制外，超薄聚合物壳层的存在对纳米颗粒的玻璃化转变温度和剪切模数也有影响，尽管影响程度较小。这项工作的含义是，核壳结构允许裁剪纳米颗粒的弹性、表面软化和玻璃化转变温度。
Advances in nanoparticle synthesis, self-assembly, and surface coating or patterning have enabled a diverse array of applications ranging from photonic and phononic crystal fabrication to drug delivery vehicles. One of the key obstacles restricting its potential is structural and thermal stability. The presence of a glass transition can facilitate deformation within nanoparticles, thus resulting in a significant alteration in structure and performance. Recently, we detected a glassy-state transition within individual polystyrene nanoparticles and related its origin to the presence of a surface layer with enhanced dynamics compared to the bulk. The presence of this mobile layer could have a dramatic impact on the thermal stability of polymer nanoparticles. Here, we demonstrate how the addition of a shell layer, as thin as a single polymer chain, atop the nanoparticles could completely eliminate any evidence of enhanced mobility at the surface of polystyrene nanoparticles. The ultrathin polymer shell layers were placed atop the nanoparticles via two approaches: (i) covalent bonding or (ii) electrostatic interactions. The temperature dependence of the particle vibrational spectrum, as recorded by Brillouin light scattering, was used to probe the surface mobility of nanoparticles with and without a shell layer. Beyond suppression of the surface mobility, the presence of the ultrathin polymer shell layers impacted the nanoparticle glass transition temperature and shear modulus, albeit to a lesser extent. The implication of this work is that the core shell architecture allows for tailoring of the nanoparticle elasticity, surface softening, and glass transition temperature.