| 초록 |
We present an efficient and environmentally friendly method to produce aligned porous materials. Aligned porous structures could be produced by spreading a thin film of polymeric solution on a substrate, directional freezing and subsequent freeze-drying. While the solvent is freezing, the growth of solvent crystals expels the polymer molecules to grain boundary region (cryo-concentration). Under these conditions, the polymer chains are aligned between the growing ice crystals. In this approach, poly(vinylidene fluoride) (PVDF) and cellulose acetate were used to investigate the relations between structural properties and freezing conditions. We demonstrated that the free-standing films of 20-200 μm thickness and 50-80 vol% through-thickness porosity could be prepared from control of freezing rate and direction. It was discovered that PVDF crystallized into an oriented ferroelectric β phase by directional freezing, which could potentially enhance ferroelectricity and piezoelectricity. |
