Preparation Of Aligned Porous Materials By Crystal Phase Separation

Materials with aligned porous structures have broad potential in applications such as organic electronics, microfluidics, and tissue engineering. Directional freezing is a cheap, simple, and novel route to prepare aligned porous materials in the form of2D surface patterns or3D monolithic structures. In this paper, we used dimethyl sulfoxide (DMSO) as the solvent which is called the universal solvent. DMSO is frozen unidirectionally and the pore structure is templated from the aligned solvent crystals that are formed. These methods can produce complex composite materials with a range of aligned pore architectures.Honeycomb monolith structured porous poly(lactic acid)(PLA) was successfully fabricated by combining pseudo steady state unidirectional freezing and freeze-drying techniques. Using the crystalline structure as a template, the PLA was solidified and structured. The effects of polymer concentration, freezing temperature and leaching solvents on the aligned porous structure were thoroughly investigated. A honeycomb monolith structure with micro/nanoscale porous walls was successfully fabricated in PLA by integrating polymer-solvent and polymer-polymer phase separations induced during a pseudosteady-state unidirectional freezing process. A sea-and-island morphology, where PEG domains were dispersed in the PLA matrix, was developed, and pores were created in the channel walls of the honeycomb monolith structure by leaching out the PEG domain. The effects of the PEG molecular weight and the PLA/PEG weight ratio on the aligned honeycomb structure and the pores in the channel walls were investigated, and the formation mechanism of the pores in the channel walls are proposed. On the basis of directional freezing, the droplet-freezing process is introduced in this paper. The process of preparation of the spheres is simple, and the results show that the preparation parameters such as freezing temperature and polymer concentration can be used to adjust the morphology of porous beads, the average diamerer (2.3～3.5mm), the porosity (86～95%), and the pore structure.In this paper, the directional crystallization was combined with HIPE for the first time, and aligned structure of dispersed phase was prepared based on emulsion template method. The effects of polymer concentration of the dispersed phase and water/oil ratio on the morphology of the porous materials were investigated, and the results show that the polymer concentration of the diapersed phase can adjust the average pore diameter (23-821μm) and the alignied structure. This method overcomes the disadvantage of the short-range order structure prepared by the freezing crystallization, and this preparation method is expected to be used for the preparation of hierarchically ordered structure of the porous materials.