Using molecular dynamics simulations, we study the properties of liquid state polymer–nanoparticle composites confined between two parallel substrates, with an attractive polymer–substrate interaction. Polymers are in the semidilute regime at concentrations far above the overlap point, and nanoparticles are in good solvent and without enthalpic attraction to the substrates. An increase of temperature then triggers the crystallization of nanoparticles on one of the two substrate surfaces—a surprising phenomenon, which is explained in terms of scaling theory, such as through competing effects of adsorption—and correlation blobs. Moreover, we show that the first, closely packed layer of nanoparticles on the substrate increases the depletion attraction of additional nanoparticles from the bulk, thereby enhancing and stabilizing the formation of a crystalline phase on the substrate. Within the time frame accessible to our numerical simulations, the crystallization of nanoparticles was irreversible; that is, their crystalline phase, once created, remained undamaged after a decrease of the temperature. Our study leads to a class of thermoreactive nanomaterials, in which the transition between a homogeneous state with dissolved nanoparticles and a surface-crystallized state is triggered by a temperature jump.

中文翻译：

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聚合物在基底上诱导纳米颗粒的逆温结晶

使用分子动力学模拟，我们研究了液态聚合物-纳米粒子复合材料的性能，该复合材料被限制在两个平行的基材之间，并且具有很强的聚合物-基材相互作用。聚合物处于半稀释状态，其浓度远高于重叠点，纳米颗粒处于良好的溶剂中，没有焓吸引到基质上。然后，温度升高会触发纳米颗粒在两个基材表面之一上的结晶-一种令人惊讶的现象，这是通过缩放理论（例如通过吸附的竞争效应）和相关斑点来解释的。此外，我们显示出基材上第一层紧密堆积的纳米颗粒层会增加其他纳米颗粒从主体中的耗尽吸引力，从而增强并稳定了衬底上结晶相的形成。在我们的数值模拟可以达到的时间范围内，纳米粒子的结晶是不可逆的。也就是说，它们的结晶相一旦产生，在温度降低后就不会受损。我们的研究导致了一类热反应纳米材料，其中温度溶解触发了具有溶解的纳米颗粒的均质状态和表面结晶状态之间的过渡。