The Exploration And Mechnism Research Of Bowl-like And Cage-like Microspheres In Large-scale Preparation Via High Temperature Pyrolysis

In recent years, as a new type of functional material, sub micrometer non-spherical colloidal microspheres attracted more and more attentions due to their special structure and properties. Bowl-like and cage-like microspheres are typical non-spherical colloidal particles. Bowl-like microspheres have many applications in a range of areas including catalysis, medicine slow release, molecular printing, optical, controlled release, super capacitor and so on, due to the unique structure such as openings, asymmetric structure, hollow structure and flat side. For Cage-like microspheres, they have pore structure which runs through the inside and outside and the internal cavity and could be widely applied in drug store and slow-release, catalyst carrier, micro reaction vessel, adsorption and so on. Although there are a lot of methods for the preparation bowl-like and cage-like microspheres, some chanllenges such as the nonuniform particle size, the difficult to tune the pore size and the large-scale preparation of these particles are still need to be overcome. In this thesis, we prepared bowl-like and cage-like microsphere via high temperature pyrolysis of the soft core/hard shell PS particles, which is simple and efficient and can be large-scale prepared. It has important significance for broadening the preparation and application of cage-like and bowl-like microspheres.In chapter two, we synthesized hexagon bowl-like hollow cross-linked polymer microspheres with ordered array and same tropism through direct high temperature pyrolysis of soft core/hard shell polystyrene(PS) particles in the air. In the process, we explored the impact of the calcination conditions and crosslinking degree on the bowl-like microspheres morphology. The study found that, we can get two kinds of microspheres with different morphology including hexagon microspheres and hexagon bowl-like microspheres through adjust calcination temperature in a wide range. We found that all the microspheres turned into bowl-like structure in 270℃~420℃.We also find that the wall thickness of the capsules is becoming thinner along with the temperature increment, but the size of cavities increases firstly, accompanying consequent reduction; with the time of heat preservation extending, the shell thickness decreases progressively and the changing rule of the cavity size is similar to the temperature increment; as heating rate increased, the wall of the capsule is becoming thicker and the cavity is turning smaller. The shell thickness and cavity size of capsules are increased with the augment of crosslinking degree. But there is a serious adhesion between microspheres, which is unable to form the monodisperse microspheres. Finally, we prepared PS microspheres which have a layer of silicon dioxide on their surface, solveing this problem well.Bowl-like microsphere with pore structure is one of the popular research topic in recent years due to that it has both unique bowl-shaped structure and pore structure, which will broaden its application. In chapter three, we synthesized monodisperse bowl-like microspheres with pore structure on their surface through high temperature pyrolysis of raspberry PS-Si O2 microspheres in the air, which is derived from the enlightenment of the chapter two. The mechanism of this is that high temperature calcination makes the the linear styrene decomposition and silica embedded in the expanding polystyrene shell layer. In the preparation process, we emphatically researched the calcination conditions on the effect of the monodisperse bowl-like microspheres morphology. We found that with the increase of calcination temperature, the morphology of bowl-like microspheres is transformed from double layer bowl to "single layer" bowl, and the indentation depth of the pit/pore on the surface is also increased; with increasing of calcination time, the morphology of microspheres is transformed from the coexistence of bowl-like microspheres and polyhedral microspheres to all of the bowl-like microspheres, following the wall thickness and the amount of pore increased; with increasing of heating rate, the morphology of monodisperse bowl-like microspheres is changed by single-layer bowl to double layer bowl to the coexistence of mushroom-head shape microspheres and polyhedral microspheres, and the surface topography is changed from large pore to a small pit to non pit.In chapter four, we synthesized cage-like microspheres via high temperature pyrolysis of raspberry PS-Si O2 microsphere in the nitrogen atmosphere. In the process of preparation, we studied preparation methods of the raspberry microsphere and carbonization conditions, founding that the composite microspheres by adding cationic surfactant STAB haveing a better coated degree and making it possible to be large prepared. And in the study of carbonization conditions and carbonization template, we found that we can get mesoporous cage-like carbon microsphere via selecting appropriate carbonization condition for 20 wt% PS microspheres crosslinked 4 h/6 h, which also provides a simple, convenient, green and large-scale preparation for mesoporous cage-like carbon microsphere. As a result of the mesoporous of these cage-like microspheres, we selected 30 wt% PS-STAB-Si O2 as the template to prepare macroporous cage-like microsphere, resuting in the macroporous cage-like microsphere from putting it in the appropriate carbonization condition.