Geometrical confinement can profoundly affect the dynamics of glass-forming polymers. In this context intense research has been mostly devoted to the understanding of how polymers subjected to 1-D confinement, that is, thin films, vitrify when cooled from the supercooled melt or recover equilibrium while in the glassy state. With the aim of extending our knowledge to other kinds of confinement, here we consider polystyrene (PS) nanospheres, that is, systems subjected to 3-D confinement. We investigate the physical aging following the enthalpy recovery in the glassy state employing fast scanning calorimetry, allowing heating/cooling rates as large as ∼1000 K/s. These systems have been previously shown to exhibit suppressed glass transition temperature in comparison to bulk PS. We find accelerated recovery toward equilibrium, in line with previous findings on other confined polymer glasses exhibiting weak interactions with the substrate. Furthermore, the time evolution of the enthalpy exhibits two mechanisms of equilibration. Apart from a slow one, normally observed in proximity of the glass transition, a fast, mildly activated mechanism of equilibration is observed. We emphasize the analogy with bulk glasses, also exhibiting this behavior though on considerably larger time scales.

中文翻译：

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聚苯乙烯纳米球结构恢复的双重机理

几何限制会深刻影响形成玻璃的聚合物的动力学。在这种情况下，大量的研究主要致力于理解聚合物如何经受一维约束，即薄膜如何在从过冷熔体中冷却时玻璃化或在玻璃态下恢复平衡。为了将我们的知识扩展到其他类型的限制，我们在这里考虑聚苯乙烯（PS）纳米球，即经受3-D限制的系统。我们使用快速扫描量热法研究了玻璃态焓恢复后的物理老化，其加热/冷却速率可高达〜1000 K / s。与块状PS相比，这些系统先前已显示出抑制的玻璃化转变温度。我们发现加速恢复至平衡，与先前关于在其他受限聚合物玻璃中表现出与基材的弱相互作用的发现相一致。此外，焓的时间演化表现出两种平衡机制。除了通常在玻璃化转变附近观察到的缓慢反应之外，还观察到了快速，轻度激活的平衡机制。我们强调与散装玻璃的类比，尽管在相当大的时间范围内也表现出这种行为。