Istituto Italiano di Tecnologia (IIT) , via Morego 30, IT-16163 Genova, Italy.
Dipartimento di Chimica e Chimica Industriale, Università di Genova , via Dodecaneso 31, IT-16146 Genova, Italy.
Nano Lett. 2016 Oct 12;16(10):6154-6163. doi: 10.1021/acs.nanolett.6b02371. Epub 2016 Sep 12.
Progress in the integration of nanocrystals with polymers has enabled the creation of materials for applications ranging from photovoltaics to biosensing. However, controlling the nanocrystal segregation and aggregation in the polymer phase remains a challenging task, especially because nanocrystals tend to form amorphous clusters inside the polymer matrix. Here, we present the ability of octapod-shaped particles to overcome their strong entropy-driven tendency to aggregate disorderly and form instead centipede-like linear arrays that are randomly oriented and fully embedded in polystyrene films upon controlled solvent evaporation. This behavior cannot be entirely described by short-range van der Waals interactions between the octapods in the polymer solution. An important role here is played by the increment of the viscosity of the medium during the evaporation of the solvent, which prevents disaggregation of the chains once they are formed. We show that increasing the octapod loading in the blends does not impact the length of the linear arrays beyond a critical length, while it favors instead chain demixing to form self-segregated regions of parallel interlocked chains. Our experiments evidence that softening of the polymer matrix by ex situ heating of the films induces a tail-to-tail coupling of the preformed chains and leads to the formation of longer linear structures of octapods, up to 2 μm long. The presence of 1D arrays of octapods in free-standing polystyrene films improves the creep response by a remarkable 37%, owing to an octapod pinning effect of the polymer matrix.
纳米晶体与聚合物的集成进展使得能够制造出从光伏到生物传感等应用的材料。然而，控制聚合物相中纳米晶体的隔离和聚集仍然是一个具有挑战性的任务，特别是因为纳米晶体在聚合物基质中往往形成非晶团簇。在这里，我们展示了八足形颗粒的能力，它们能够克服其强烈的无序聚集的熵驱动倾向，形成蜈蚣状的线性排列，这些排列在控制溶剂蒸发时随机取向并完全嵌入聚苯乙烯薄膜中。这种行为不能完全用聚合物溶液中八足之间的短程范德华相互作用来描述。在此过程中，溶剂蒸发过程中介质粘度的增加起着重要作用，一旦链形成，就可以防止它们的解聚集。我们表明，在共混物中增加八足的负载量不会影响线性排列的长度超过临界长度，而有利于链的分相以形成平行互锁链的自分离区域。我们的实验证明，通过对薄膜进行原位加热来软化聚合物基质，会导致预先形成的链的尾对尾耦合，并形成更长的八足线性结构，最长可达 2 μm。在独立的聚苯乙烯薄膜中存在一维八足排列会显著提高 37%的蠕变响应，这是由于聚合物基质的八足钉扎效应。
