Porous polymer films with tailored light scattering properties

在“蜂胶”项目中，我们将开发具有可定制光散射特性的多孔聚合物薄膜。这种多孔网络的灵感来自于在亮白色甲虫的鳞片中发现的网络，将使用超临界二氧化碳高度可扩展的发泡过程来制造。通过控制气孔的形核和生长来调节结构无序，从而得到可调的直径分布(从微米到纳米级)、密度和气孔在薄膜中的分布。我们在SPP 1839第一阶段获得的聚合物共混物自发相分离的专业知识将被用来控制多孔网络的3D形态，包括闭孔和开孔结构。了解所开发薄膜的光学性质之间的关系(光散射和传输平均自由程、散射各向异性、前向/后向散射的相对比例等)。而多孔网络形态是我们项目的一个关键方面。为此，我们利用光技术研究所(LTI)在光学表征方面的专业知识和微结构技术研究所(IMT)在仿生纳米结构制造方面的专业知识。为此，我们将开发基于光线跟踪(蒙特卡罗)模拟和T矩阵方法的专用数值方法来解释相干多次散射效应。形态表征将被用来模拟真实的构型模型，并结合光谱测量，通过反转过程得出主要的光学特性。我们将最终证明，多孔聚合物层为不同的能源相关应用提供了一种经济有效和灵活的解决方案。作为概念验证，我们将优化这类薄膜的光散射特性，以提高量子点发光二极管的光转换效率、被动辐射制冷系统的冷却功率和薄膜太阳能电池的集光能力。

In the "PROPOLIS" project, we will develop porous polymer films with tailorable light scattering properties. The porous network is inspired by that found in the scales of brilliant white beetles and will be fabricated using a highly scalable foaming process with supercritical CO2. Structural disorder will be tuned by controlling the pores nucleation and growth, resulting in adjustable diameter distributions (from micrometer to nanometer scale), density and distribution of the pores within the films. Our expertise of the spontaneous phase separation of polymer blends, which was acquired during the first period of the SPP 1839, will be exploited to control the 3D morphology of the porous network, covering both close-cell and open-cell configurations.Understanding the relationship between the optical properties of the developed films (light scattering and transport mean free path, scattering anisotropy, relative fraction of forward/backscattered, etc.) and the porous network morphology is a pivotal aspect of our project. For that, we use the expertise of the Light Technical Institute (LTI) on optical characterization and of the Institute of Microstructure Technology (IMT) on the fabrication of biomimetic nanostructures. To this end, we will develop dedicated numerical methods either based on ray-tracing (Monte Carlo) simulations as well as on the T-matrix method to account for coherent multiple scattering effects. Morphological characterization will be used to simulate realistic configurations models and, in combination with spectroscopic measurements, to derive the main optical characteristics via an inversion procedure.We will finally demonstrate that the porous polymer layers offer a cost-effective and flexible solution for different energy-related applications. As a proof-of-concept, we will optimize the light scattering properties of such films in order to improve the light conversion efficiency of quantum dots-based light emitting diodes, the cooling power of passive radiative cooling systems and light harvesting in thin film solar cells.