Infuence of solidification dynamics on the component distribution and particle orientation in polymer particle composites with flaky particles

在聚合物基质中掺入纳米颗粒是一种改善材料性能的方法，如抗拉强度、生物兼容性或光学性能。这些复合材料的功能取决于材料的选择和组分的分布。后者受干燥过程中组分的分散稳定性和相互作用以及工艺条件的强烈影响。在先前的研究方案中，通过低温REM和拉曼光谱来评估干燥条件对组分分布的影响。发现了三种不同的颗粒分布：(I)颗粒在衬底上的浓缩，(Ii)颗粒和聚合物的均匀分布，以及(Iii)颗粒在薄膜自由表面的浓缩。此外，还模拟了干燥过程中的组分分布，考虑了所有组分的扩散、颗粒的干燥和沉淀。确定了薄膜厚度、干燥速度、初始溶剂含量、颗粒大小、密度和聚合物溶液粘度的比值作为关键参数。这些参数可以用无量纲数字来概括，通过这些数字可以映射不同的分布。这些地图通过所进行的实验得到了验证。建立的干燥制度图有助于浆料的设计以及干燥条件的选择，以调整干燥和最终薄膜中的组分分布。到目前为止，干燥状态图仅限于球形颗粒。然而，在许多应用中，使用的是片状颗粒。继续这项研究项目的假设是，也有可能为预测成分分布的片状颗粒建立干燥制度图。片状粒子的另一个自由度是粒子方向。颗粒取向对最终薄膜的功能性起着重要作用。初步研究表明，颗粒靠近基片时，其取向平行于基片和自由表面。因此，人们假设取向和颗粒分布之间存在显著的相关性。提出的研究项目的目的是建立片状颗粒的干燥状态图并进行实验验证。此外，还将系统地研究粒子的取向作为分布的函数。

Incorporation of nanoparticles into a polymeric matrix is a way to modify material properties such as tensile strength, biocompatibility or optical properties. The functionality of these composites depends on the material selection and on the component distribution. The latter is strongly affected by the dispersion stability and interactions of the components as well as the process conditions during drying.In the previous research proposal the influence of the drying conditions on the component distribution was evaluated via cryoREM and Raman spectroscopy. Three different particle distributions were found: (i) particle enrichment at the substrate, (ii) even distribution of particles and polymer and (iii) particle enrichment at the free surface of the film. Additionally the component distribution during drying was modeled, taking diffusion of all components, drying and sedimentation of particles into account. As pivotal parameters the ratio of film thickness, drying rate, initial solvent content, particle size, density and the viscosity of the polymer solution was identified. These parameters could be summarized by non-dimensional numbers, by which the different distributions were mapped. These maps were validated with the experiments that were carried out. The established drying regime maps facilitate the paste design as well as the choice of drying conditions to adjust the component distribution in the drying and final film. The drying regime maps are so far limited to spherical particles. In many applications, however, flaky particles are used. The hypothesis for continuing the research project is that it is possible to establish drying regime maps also for flaky particles that predict the component distribution. An additional degree of freedom for flaky particles is the particle orientation. The particle orientation can play an important role for the functionality of the final film. Preliminary investigations show that the particles orient parallel to the substrate and free surface if they come close to it. Therefore, one assumes that a significant correlation of orientation and particle distribution. Aim of the proposed research project is to establish drying regime maps for flaky particles and their experimental validation. Additionally the orientation of the particles as function of the distribution will systematically be investigated.