Preparation Of Long-range Ordered Porous Materials Through Ice-templating Method

Directional freezing(DF)has received increasing attention as a processing method for fabricating long-range ordered microstructures since it is fast,scalable,and environmentally friendly.Furthermore,its reliance on oriented ice crystals as template can be applied towards a wide variety of materials including cryogels,ceramics,polymers,and composites.In this study,aligned porous hydrogels were fabricated by directional freezing,and a new principle for controlling microstructure was proposed.Wettability of the freezing surfaces is adjusted to control pore size within monolithic PEG cryogels synthesized by cryo-polymerization.More hydrophilic substrate can generate smaller pores.A numerical fitting between water contact angle of the substrates and pore size of the cryogels is obtained.Tubular pores as small as approximate 2μm can be created by freezing from a PVA coated copper sheet via liquid nitrogen freezing,which is nearly an order of magnitude smaller than using previous DF technique.Moreover,pores with locally varied size can form patterns duplicating wetting patterns of the freezing substrates.Graphene aerogels with hierarchical architectures mimicking plant stem were fabricated by bidirectional freezing.Such biomimetic architecture composed of lamellae with interconnected bridges endows the graphene aerogels with exceptional strength and resilience simultaneously,which are usually mutually exclusive and challenging to achieve.We systematically studied the effect of different architectures on the robustness of the biomimetic graphene aerogels and illustrated their potential in flexible electronics.Our study provides insights and paves a new way to mimic natural porous architectures in synthetic aerogels to improve their mechanical properties and functions.