Abstract
An elegant and precise method to fabricate asymmetrical structures and/or gradient structures was developed based on a vapor-phase sublimation and deposition process. The fabricated materials exhibited versatility and had advantages such as well-controlled pore structures and functional properties ranging from an asymmetrical distribution to a gradient hierarchy; precisely addressed interface chemistries and properties for the constructed materials; and flexibility to produce the materials at multiple scales. By using a time-dependent customization parameter to control the bulk size and/or the dispersion of molecules, fabrication of the materials was demonstrated, producing particles with hierarchical pore structures and with bulk sizes ranging from >500 μm to submicrons, as well as gradients with both continuously varied porosity and chemical functionality that were demonstrated to be in a controlled direction and varied across multiple scales (centimeter, millimeter, and micrometer). By exploiting chemical vapor deposition to enable multicomponent copolymerization during the fabrication process, multifunctional poly-p-xylylenes formed building blocks for these hierarchical materials and provided the defined surface chemistries. The proposed functional hierarchical materials were constructed and assembled in the vapor phase and in one step, and prospective materials produced by this method are expected to have novel properties and unlimited applications..png)