The GRADFLEX experiment of ESA has shown that under microgravity conditions a stationary thermodiffusion process is accompanied by giant non-equilibrium fluctuations with size as large as the size of the sample. In the presence of small concentration gradients, the features of the non-equilibrium fluctuations can be described by means of linearized hydrodynamics. However, the linear models are not suitable to describe most cases of applicative interest, such as fluctuations induced by large gradients and under non-stationary conditions. Moreover, presently the investigation of non-equilibrium fluctuations has mainly involved single component fluids and binary mixtures, but recently transport processes in ternary mixtures have attracted increasing interest due to the experiments performed on the International Space Station in the framework of the DCMIX project of ESA. The Giant Fluctuations (NEUF-DIX) project of ESA will investigate non-equilibrium fluctuations during diffusive processes occurring in complex multi-component mixtures, where one of the components is a macromolecule, such as a polymer, a colloid or a protein. Important objectives will be the exploration of the features of the fluctuations under non-ideal conditions, such as large gradients, transient processes, and concentrated samples, and the understanding of how the fluctuations affect the interactions between macromolecules. The project involves the development of a dedicated facility, consisting of an array of shadowgraph optical instruments working in parallel, each one equipped with a thermal gradient cell. Here we outline the design concept of the facility and the results of performance tests performed on a breadboard to evaluate the suitability of the designed instrument to carry out scientific measurements of non-equilibrium concentration fluctuations in space.

ESA的GRADFLEX实验表明，在微重力条件下，固定的热扩散过程伴随着巨大的非平衡波动，其大小与样品的大小一样大。在浓度梯度小的情况下，可以通过线性流体动力学来描述非平衡波动的特征。但是，线性模型不适合描述大多数有实际应用意义的情况，例如，由大梯度引起的波动以及非平稳条件下的波动。此外，目前对非平衡波动的研究主要涉及单组分流体和二元混合物，但是最近，由于在国际空间站（ESA）DCMIX项目框架内在国际空间站上进行的实验，三元混合物的运输过程引起了越来越多的兴趣。ESA的巨型波动（NEUF-DIX）项目将研究复杂的多组分混合物（其中一种组分是大分子，例如聚合物，胶体或蛋白质）发生的扩散过程中的非平衡波动。重要的目标将是探索非理想条件下波动的特征，例如大梯度，瞬态过程和浓缩样品，以及了解波动如何影响大分子之间的相互作用。该项目涉及专用设施的开发，由一系列并行工作的阴影图光学仪器组成，每个仪器都配备一个热梯度传感器。在这里，我们概述了设施的设计概念以及在试验板上进行的性能测试的结果，以评估所设计仪器的适用性，以对空间中非平衡浓度波动进行科学测量。