Porous polymer films with tailored light scattering properties

在“PROPOLIS”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。多孔网络的灵感来自于在明亮的白色甲虫的鳞片中发现的，并将使用超临界CO2的高度可扩展的发泡工艺制造。结构无序将通过控制孔的成核和生长来调节，从而导致可调节的直径分布（从微米到纳米尺度）、膜内孔的密度和分布。我们在SPP 1839第一阶段获得的聚合物共混物自发相分离方面的专业知识将用于控制多孔网络的3D形态，包括闭孔和开孔配置。了解所开发薄膜的光学性能之间的关系（光散射和传输平均自由程、散射各向异性、前向/后向散射的相对分数等）多孔网络形态是我们项目的关键方面。为此，我们利用光技术研究所（LTI）在光学特性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，我们将开发专门的数值方法，无论是基于射线跟踪（蒙特卡罗）模拟以及T矩阵方法来考虑相干多次散射效应。形态学表征将被用来模拟现实的配置模型，并结合光谱测量，通过反演程序推导出主要的光学特性。我们最终将证明多孔聚合物层为不同的能源相关应用提供了一个具有成本效益和灵活的解决方案。作为概念验证，我们将优化这种薄膜的光散射特性，以提高基于量子点的发光二极管的光转换效率，被动辐射冷却系统的冷却能力和薄膜太阳能电池的光收集。

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.