Abstract

We performed ground-based experiments on the sample polystyrene–toluene–cyclohexane in order to complement the experimental activities in microgravity conditions related to the ESA projects DCMIX4 and Giant Fluctuations. After applying a stabilizing thermal gradient by heating from above a layer of the fluid mixture, we studied over many hours the density variations in the bidimensional horizontal field by means of a Shadowgraph optical setup. The resulting images evidence the appearance of convective instability after a diffusive time associated with the binary molecular solvent consisting of toluene and cyclohexane, confirming the negative sign of the Soret coefficient of this mixture. After a larger diffusive time related to mass diffusion of the polystyrene in the binary solvent, convection was suppressed by the increasing stabilizing density gradient originated by the Soret-induced concentration gradient of the polymer. This is compatible with a positive sign of the Soret coefficient of the polymer in the binary solvent.

Graphic Abstract

中文翻译：

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具有两个相反符号的 Soret 系数的三元混合物中的稳定对流

摘要

我们对样品聚苯乙烯-甲苯-环己烷进行了地面实验，以补充与 ESA 项目 DCMIX4 和巨幅波动相关的微重力条件下的实验活动。在通过从流体混合物层上方加热来施加稳定的热梯度后，我们通过 Shadowgraph 光学装置在数小时内研究了二维水平场中的密度变化。所得图像证明在与由甲苯和环己烷组成的二元分子溶剂相关的扩散时间后出现对流不稳定性，证实了该混合物的 Soret 系数的负号。在与聚苯乙烯在二元溶剂中的质量扩散相关的较长扩散时间之后，由 Soret 诱导的聚合物浓度梯度引起的稳定密度梯度的增加抑制了对流。这与聚合物在二元溶剂中的 Soret 系数的正号相符。

图形摘要