Innovative synthesis routes towards hierarchically organized nanostructured materials combined with in-situ SAXS characterization techniques

为了更好地理解纳米材料的形成过程，我们将通过原位小角X射线散射来研究纳米和微米尺度的溶胶-凝胶体系中的相分离现象。高孔氧化物，例如二氧化硅、二氧化钛、氧化铝等，或通过一种新的合成路线制备的二氧化硅-金属氧化物混合材料将作为模型体系。它不仅可以将氧化材料的范围从二氧化硅扩展到其他过渡金属氧化物，而且还可以通过机械剪切等方式在孔区诱导一定程度的各向异性。因此，拟议的研究包括来自化学和物理的三个相互关联的要素：1)通过量身定做的前体分子进行精心设计的网络；创新的制造方法和3.)对网络发展的详细描述，强调原位(小角)X射线散射和衍射。从化学的角度来看，我们将开发新的合成路线，通过应用金属二酸盐来实现高度多孔、层次化组织的过渡金属氧化物整体。金属二醇酸盐具有在纯水溶液中可加工的优点，因此与溶致液晶相相容，这些相将在合成中作为结构导向剂。作为起始化合物，相应的醇盐，例如二氧化钛，四异丙氧钛将被乙醇化，得到稳定的酸可溶的前驱体钛酸二(2-羟乙基)酯。这种前驱体将在预先形成的水溶致液晶相存在的情况下进行处理，以产生具有特意设计的孔结构的氧化物。我们将通过应用类似的(混合)金属前驱体来展示这种合成方法在具有多模孔尺寸分布的材料上的高潜力。从物理角度来看，一个重点是从糖基化前体分子获得的最终材料的结构研究。此外，先前的实验表明，与预期相反，溶致液晶相并不是直接模板化的，而是在添加乙醇化前体后发生重组过程。最终的网络结构受到形成机制的强烈影响。因此，第二个重点是原位SAXS测量，跟踪从溶胶到最终凝胶的混合物的结构演变，以允许更深入地了解潜在的相分离过程。由于搅拌速度、离心力、温度等外部参数对孔结构有很大影响，因此计划进行额外的测量，包括剪切诱导孔系统的取向和在不同外部实验参数下的测量。

Aiming at a better understanding of the formation process of nanostructured materials, we will investigate phase separation phenomena in sol-gel systems on the nano- and micrometer length scale via in-situ small angle X-ray scattering. Highly porous oxides, for example silica, titania, alumina, etc. or mixed silica-metal oxide materials prepared via a novel synthesis route applying metal diolates and comprising a porous network with different levels of hierarchy in the pore sizes will serve as model systems. It is envisioned not only to expand the range of oxidic materials from silica to other transition metal oxides, but also to induce a certain degree of anisotropy into the pore domains, e.g. by mechanical shearing of the sol. Thus, the proposed research comprises three inter-related elements from chemistry and physics: 1.) deliberate network design by tailor-made precursor molecules; 2.) innovative fabrication methods and 3.) detailed characterization of the network development emphazising on in-situ (small angle) X-ray scattering and diffraction. From a chemical point of view, we will develop novel synthetic routes towards highly porous, hierarchically organized transition metal oxide monoliths by applying metal diolates. Metal diolates have the advantage of being processable in purely aqueous solution and thus being compatible with lyotropic liquid crystal phases that will serve as structure-directing agents in the synthesis. As starting compounds the respective alkoxides, e.g. for titania, titanium tetraisopropoxide will be glycolated to give bis(2-hydroxyethyl)titanate as a stable and acid-soluble precursor. This precursor will be processed in the presence of a preformed aqueous lyotropic liquid crystalline phase to yield the oxide with a deliberately designed pore structure. We will demonstrate the high potential of this synthetic approach towards materials with a multimodal pore size distribution by the application of analogous (mixed) metal precursors. From a physical point of view, one focus lies on the structural investigation of the final materials obtained from the glycolated precursor molecules. In addition, previous experiments have shown that contrary to what was expected the lyotropic liquid crystalline phase is not directly templated, but that reorganisation processes occur upon addition of the glycolated precursor. The final network structure is strongly influenced by the mechanism of formation. Therefore, the second focus is on in-situ SAXS measurements, following the structural evolution in the mixture from the sol to the final gel to allow for a deeper understanding of the underlying phase separation processes. Since external parameters such as stirring speed, centrifugation, temperature, etc. have a strong influence on the pore structure, additional measurements are planned comprising shear-induced alignment of the pore system and measurements under different external experimental parameters.